Co-reporter:Sha Liu, Yefei Zhou, Xiaolei Xing, Jibo Wang, Qingxiang Yang
Journal of Alloys and Compounds 2017 Volume 691() pp:239-249
Publication Date(Web):15 January 2017
DOI:10.1016/j.jallcom.2016.08.133
•In the hypereutectic FeCrC coatings with Ti additive, TiC precipitates firstly.•The primary M7C3 are refined by the preferentially precipitated TiC.•The interface between M7C3 and TiC is stable, and the interface is well jointed.•TiC is the heterogeneous nucleus of primary M7C3 and thereby refines it.Hypereutectic FeCrC coatings with and without Ti additive were developed by harden-surface welding. The equilibrium phase diagrams of the coatings were calculated by Thermal-calc software. The phase structures were determined by X-ray diffractometer (XRD). The microstructures were observed by optical microscopy (OM). The micro-morphologies of M7C3 and TiC were observed by field emission scanning electron microscopy (FESEM). The compositions of M7C3 and TiC were determined by energy dispersive spectrum (EDS). The crystal structure of primary M7C3 was determined by transmission electron microscopy (TEM). The phase diagrams indicate that TiC precipitates firstly in the coating with Ti additive. The subsequent phase transformation is the same as that in the coating without Ti additive, namely primary M7C3 precipitates and then eutectic reaction occurs. The XRD patterns are corresponding to the phase diagrams, which show that there exists TiC in the coating with Ti additive. By comparing their metallographic images, the primary M7C3 are obviously refined in the coating with Ti additive. From the micro-morphologies of M7C3 and TiC, it is found that TiC exists inside primary M7C3 and they are tightly combined. Therefore, TiC may be the heterogeneous nucleus of primary M7C3. On the basis of experimental research, the refining effect of TiC on primary M7C3 was investigated by first-principles calculation. The calculation results shows the work of adhesion of Fe3Cr4C3(0001)/TiC(111) interface is 3.48 J/m2 and the interfacial energy ranges from 0.921 J/m2 to 2.782 J/m2. The Fe3Cr4C3(0001)/TiC(111) interface is theoretically stable. The Fe3Cr4C3(0001)/TiC(111) interface is well jointed by TiC polar covalent/ionic bond and CrTi metallic bond. Therefore, the preferentially precipitated TiC in FeCrCTi alloy is the heterogeneous nucleus of primary M7C3 and thereby refines the primary M7C3.
Co-reporter:Jing Guo;Ligang Liu;Yunli Feng;Sha Liu;Xuejun Ren
Metals and Materials International 2017 Volume 23( Issue 2) pp:313-319
Publication Date(Web):2017 March
DOI:10.1007/s12540-017-6266-z
In this work, the morphology and structures of the eutectic and secondary carbides in a new high chromium Fe-12Cr-2.5Mo-1.5W-3V-1.25C designed for cold-rolling work roll were systematically studied. The precipitated carbides inside the grains and along the grain boundaries were investigated with optical microscope, scanning electron microscopy with energy dispersive spectroscopy, transmission electron microscopy and X-Ray diffraction. Selected area diffraction patterns have been successfully used to identify the crystal formation and lattice constants of the carbides with different alloying elements. The results show that the eutectic carbides precipitated contain MC and M2C distributed along the grain boundaries with dendrite feature. The composition and crystal structure analysis shows that the eutectic MC carbides contain VC and WC with a cubic and hexagonal crystal lattice structures respectively, while the eutectic M2C carbides predominantly contain V2C and Mo2C with orthorhombic and hexagonal crystal lattices respectively. The secondary carbides contain MC, M2C, M7C3 formed along the grain boundaries and their sizes are much larger than the eutectic carbides ones. The secondary M23C6 is much small (0.3-0.5μm) and is distributed dispersively inside the grain. Similar to the eutectic carbides, the secondary carbides also contain VC, WC, V2C, and Mo2C. M7C3 is hexagonal (Fe,Cr)7C3, while M23C6 is indexed to be in a cubic crystal form.
Co-reporter:Sha Liu, Jin Zhang, Zhijie Wang, Zhijun Shi, Yefei Zhou, Xuejun Ren, Qingxiang Yang
Materials Characterization 2017 Volume 132(Volume 132) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.matchar.2017.08.004
•Primary M7C3 carbide in hypereutectic Fe-Cr-C coating is refined and homogenized by adding nano-Y2O3 and Ti additive.•Nano-Y2O3 can act as the heterogeneous nucleus of TiC, which results in increased TiC particles and refining TiC size.•Nano-Y2O3 contributes to the refinement and homogenization of primary M7C3 carbide in a roundabout way.The microstructures of the hypereutectic Fe-Cr-C, Fe-Cr-C-Ti and Fe-Cr-C-Ti-Y2O3 coatings were observed by OM. The phase structures were characterized by XRD and XPS. The elemental distributions were analyzed by EDS. The interface relationship between TiC and nano-Y2O3 were observed by TEM and analyzed by lattice misfit theory. From the metallographic observations, the primary M7C3 carbide can be refined by Ti additive, while it is inhomogeneously distributed. However, the primary M7C3 carbide can also be refined further by adding Ti additive and nano-Y2O3 simultaneously, and it is homogeneously distributed. From the phase constituent analysis, TiC is formed by Ti additive, while TiC and Y2O3 are found by adding Ti additive and nano-Y2O3 simultaneously. From the elemental distribution mappings and TEM images, TiC nucleates upon nano-Y2O3 with orientation relationship {001}Y2O3//{001}TiC in the hypereutectic Fe-Cr-C-Ti-Y2O3 coating. By misfit computation, the lattice misfit between Y2O3 (001) plane and TiC (001) plane is 7.3%, which suggests that Y2O3 can act as the heterogeneous nucleus of TiC so that TiC particles are increased and dispersedly distributed. These numerous dispersed TiC particles can further act as the heterogeneous nucleus of the primary M7C3 carbide, which play a role in refining primary M7C3 carbide and promoting its homogenization.Download high-res image (297KB)Download full-size image
Co-reporter:Sha Liu, Zhijie Wang, Zhijun Shi, Yefei Zhou, Qingxiang Yang
Journal of Alloys and Compounds 2017 Volume 713(Volume 713) pp:
Publication Date(Web):5 August 2017
DOI:10.1016/j.jallcom.2017.04.167
•The previously precipitated NbC can refine the primary M7C3 carbide in hypereutectic Fe-Cr-C alloy.•The solid-liquid interfacial energy of M7C3 carbide is calculated as γSL=3.312Jm2.•The interfacial energy of M7C3/NbC interface is lower than the solid-liquid interfacial energy of M7C3 carbide somewhere.•The refining mechanism of NbC on primary M7C3 carbide is the heterogeneous nucleus theory.Two hypereutectic Fe-Cr-C hardfacing alloys were manufactured, whose Nb contents are 0 and 1.2 wt% respectively. Their phase precipitation curves were calculated by Thermal-calc software and their phase structures were detected by X-ray diffractometer, which indicate that NbC precipitates previously to the nucleation of primary M7C3 carbide. The alloys were observed by metallographic microscope, which finds that the primary M7C3 carbides in the alloy with 1.2 wt% Nb are obviously refined. The chemical compositions of carbides were further measured by energy diffraction spectrum, which finds that NbC particles are distributed in the primary M7C3 carbides. The melting process of M7C3 carbide was simulated by molecular dynamics method and the melting point of M7C3 carbide is identified to be 1625±5 K. The melting behaviors of M7C3 embryos with different radii were simulated, and the solid-liquid interfacial energy of M7C3 carbide was calculated to be 3.312 J/m2 based on the classical nucleation theory. Two kinds of M7C3(0001)/NbC(111) interface models with different atomic stacking modes were built. By means of first-principles calculations, M7C3(0001)/NbC(111) interface I is combined by polar covalent/ionic bonds and metallic bonds, while M7C3(0001)/NbC(111) interface II is combined by ionic bonds and metallic bonds. The works of adhesion are 1.23 J/m2 and 2.24 J/m2 respectively. There exists a region where the interfacial energy of interface II is lower than the solid-liquid interfacial energy of M7C3 carbide. The above experimental and calculation results demonstrate that NbC particle is the heterogeneous nucleus of primary M7C3 carbide and thereby refines it.
Co-reporter:X.L. Xing, Y.F. Zhou, X.W. Qi, J.B. Wang, X. Lu, Y.L. Yang, Q.X. Yang
Materials Science and Engineering: A 2017 Volume 684() pp:249-253
Publication Date(Web):27 January 2017
DOI:10.1016/j.msea.2016.12.066
This study concerns that the high-silicon alloy steel treated by the laser hardening with an in-situ thermal treatment (LHITT) between Ms and Md temperature. The shear band, such as nano-twin and ε-martensite is expected to be obtained by the aid of thermal stress during laser hardening process to strengthen the steel. The in-situ thermal treatment temperature of the steel was confirmed by thermal mechanical simulator and thermodynamic model. The residual stress of the hardening layer was measured by X-ray stress analyzer. The phase structures were characterized by X-ray diffractometer (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Moreover, the nano-hardness was evaluated by the nano-mechanical tester. The experimental results demonstrate that the stacking faults were generated by the laser thermal stress which drives high density dislocations motion on {111}γ{111}γ planes. The shear band is formed by the overlapping of the stacking faults in austenite during the LHITT process. Besides, the high surface hardness (7.9 GPa) can be achieved by the LHITT. The hard points (9.5 GPa) in LHITT sample are related with the shear band as the analysis of the elastic modulus.
Co-reporter:X.L. Xing, X.M. Yuan, Y.F. Zhou, X.W. Qi, X. Lu, T.H. Xing, X.J. Ren, Q.X. Yang
Surface and Coatings Technology 2017 Volume 325(Volume 325) pp:
Publication Date(Web):25 September 2017
DOI:10.1016/j.surfcoat.2017.06.053
•Nanobainite layer with refined microstructure is investigated by laser surface melting.•Nanobanite layer is equipped with good wear resistance at 20 °C, 100 °C and 200 °C.•Formation of white-etching layer can improve the wear resistance.•Harder surface can provides higher mechanical support to the white-etching layer.In this work, bainite layer was prepared by Laser surface melting combined with isothermal treatment (LSMCIT) at 250 °C. The microstructures of the samples were analyzed by scanning electron microscopy (SEM), X-ray Diffraction (XRD) and transmission electron microscopy (TEM). Their wear resistances at 20 °C, 100 °C and 200 °C were measured using reciprocating tribometer. After the wear test, the confocal laser scanning microscope and SEM were used to characterize the topography of all abrasion surfaces, and the phase transformations occurred on the contact surfaces were analyzed by XRD. The results show that the microstructure of the LSMCIT sample has been refined to nanoscale. The wear volume reduction ratio of LSMCIT sample is 40.9% at 20 °C. The wear resistances of the samples are decreased with increasing of the temperature, however, the decrease in amplitude of the bainite is relatively small. The harder surface of the LSMCIT sample can provides higher mechanical support, and the white-etching layer on surface are difficult to remove by the reciprocating friction. The wear resistances of the LSMCIT samples at 20 °C, 100 °C and 200 °C are excellent, which shows the wide temperature ranges in wear applications.
Co-reporter:Jing Guo, Sha Liu, Yefei Zhou, Jibo Wang, Xiaolei Xing, Xuejun Ren, Qingxiang Yang
Materials Letters 2016 Volume 171() pp:216-219
Publication Date(Web):15 May 2016
DOI:10.1016/j.matlet.2016.02.054
•The carbide precipitation rule of the steel was calculated.•The types of the eutectic MC and eutectic M2C were determined.•The stability of the eutectic carbide in this steel during solidification was determined.The stability of the eutectic carbide in a self-designed Fe-Cr-Mo-W-V-C alloy during solidification was analyzed in this work. The carbide precipitation rule of the steel was calculated by Thermo-Calc. The typical microstructures at 1240 °C and 1200 °C were observed by optical microscope (OM), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The selected area diffraction patterns (SADPs) has been successfully used with TEM bright fields to identify the lattice structures of the carbides within a complex mixture of different types of carbides. The results show that the eutectic MC and M2C mix together along crystal grain boundary and exhibit the dendritic structure. The eutectic MC contains VC and WC, while the eutectic M2C contains V2C and Mo2C. The eutectic MC can exist stably and grows continuously, while the eutectic M2C disappears gradually.
Co-reporter:X.L. Xing, Y.F. Zhou, S.Y. Gao, J.B. Wang, Y.L. Yang, Q.X. Yang
Materials Letters 2016 Volume 165() pp:79-82
Publication Date(Web):15 February 2016
DOI:10.1016/j.matlet.2015.11.084
•A medium-carbon bainite was surface modified by LRFIT.•The austenite nano-twin has been detected in the surface modified bainite.•The surface modified bainite shows a satisfied mechanical properties.The medium-carbon bainite was surface modified by laser remelting and following isothermal transformation (LRFIT). The austenite nano-twin has been detected in the surface modified bainite by transmission electron microscopy (TEM). The austenite nano-twin films and blocks are embedded in bainitic ferrite with a thickness less than 10 nm, and the twinning occurred on the (1̅11) plane in the [1̅11] direction. The nano-hardness and the creep ratio of the nano-twin has been measured by nano-mechanical tester. The result suggests that, the surface modified bainite with nano-twin shows a satisfied mechanical properties. The nano-hardness and creep ratio of the nano-twin in surface modified bainite is 9.5±0.5 GPa and 7.5±0.3%, respectively.
Co-reporter:Sha Liu, Yefei Zhou, Xiaolei Xing, Jibo Wang, Yulin Yang, Qingxiang Yang
Materials Letters 2016 Volume 183() pp:272-276
Publication Date(Web):15 November 2016
DOI:10.1016/j.matlet.2016.07.135
•The microstructure, growth morphology and crystallographic characteristic of the primary (Fe,Cr)7C3 carbide in hypereutectic Fe-Cr-C alloy are investigated.•The hollows in the center and gaps on the edge of the primary (Fe,Cr)7C3 carbide are explained by the agglomeration model for the first time by observing the initial growth stage.•The low-angle boundary between the adjacent primary (Fe,Cr)7C3 carbides is firstly discovered by HRTEM and explained by the agglomeration model.The microstructure, growth morphology and crystallographic characteristic of the primary (Fe, Cr)7C3 carbide in hypereutectic Fe-Cr-C alloy are investigated. The primary (Fe, Cr)7C3 carbide is irregular polygonal shape with several hollows in the center and gaps on the edge. In the initial growth stage, the crystallographic orientations of neighboring (Fe, Cr)7C3 carbides are the same and some protrusions are emerged. The primary (Fe, Cr)7C3 carbide consists of several parts, which are divided by the low-angle boundaries. Analysis suggests that the primary (Fe, Cr)7C3 carbide exhibits agglomeration phenomenon which results in the low-angle boundary, as well as the hollows and gaps.
Co-reporter:J.B. Wang, Y.F. Zhou, X.L. Xing, S. Liu, C.C. Zhao, Y.L. Yang, Q.X. Yang
Surface and Coatings Technology 2016 Volume 294() pp:115-121
Publication Date(Web):25 May 2016
DOI:10.1016/j.surfcoat.2016.03.076
•Prior austenite grain size and the martensitic lath can be effectively refined by nitrogen additive;•Mechanical properties of the hardfacing are improved, and the fracture mode is changed to ductile transgranular fracture;•Martensitic lath width of the hardfacing is effectively equal to grain diameter D in the modified Hall-Petch Equation.The effect of nitrogen additive on the microstructure and mechanical properties of martensitic stainless steel hardfacing was investigated in this work. The phase structure of the hardfacing was analyzed by X-ray diffraction (XRD). The microstructures with and without nitrogen additive were observed by field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The mechanical properties of the hardfacing were measured, and the fracture surfaces were observed by FESEM. The equilibrium phase diagram and phase precipitation rule were calculated by ThermoCalc software. The results show that, by replacing carbon with nitrogen in hardfacing, the martensitic lath is refined, and the segregation and precipitation on prior austenite grain boundary cannot be found. In addition, the mechanical properties of the hardfacing can be improved obviously after composition optimization, in which, the yield strength and tensile strength are increased from 884 MPa and 996 MPa to 1078 MPa and 1554 MPa respectively. Meanwhile, the ductile of the hardfacing is significantly increased. The fracture surface is transformed from brittle intergranular fracture into ductile transgranular one.
Co-reporter:Cai-xia WANG, Jian YANG, Sha LIU, Xiao-lei XING, Ji-bo WANG, Xue-jun REN, Qing-xiang YANG
Journal of Iron and Steel Research, International 2016 Volume 23(Issue 11) pp:1213-1218
Publication Date(Web):November 2016
DOI:10.1016/S1006-706X(16)30178-9
The structure stability, elastic property and electronic structure of α-FT supercell with La atom were investigated by first-principles, in which, generalized gradient approximation (GGA) with the Perdew Burke Ernzerhof (PBE) was used as exchange-correlation functional. α-Fe supercells with La atom include α-Fe supercell with La atom in octahedral interstitial solid solute (La-OISS), that with La atom in tetrahedral interstitial solid solute (La-TISS) and that with La atom in substitutional solid solute (La-SSS). The results show that the La-SSS α-Fe supercell is more stable than La-OISS one. The resistance to volume change, reversible deformation and stiffness of La-OISS α-Fe supercell are stronger than those of La-SSS one. Moreover, the degrees of anisotropy and ionization in La-SSS α-Fe supercell are both stronger than those in La-OISS one. The bonding strength between La atom and Fe atom in La-SSS α-FT supercell is larger than that in La-OISS one.
Co-reporter:Xuebing Zhao, Yuguo Zhuo, Sha Liu, Yefei Zhou, Changchun Zhao, Caixia Wang, Qingxiang Yang
Surface and Coatings Technology 2016 Volume 305() pp:200-207
Publication Date(Web):15 November 2016
DOI:10.1016/j.surfcoat.2016.08.025
•The interfacial properties including adhesion strength and interface stability of WC/TiC coating were investigated by first principles at the first time.•The HCP stacking interface exhibits the larger work of adhesion (Wad) than the Hole, OT stacking interfaces.•The W-HCP-C interface exhibits the largest adhesion strength, and the C-HCP-Ti interface is followed. The W-HCP-C interface and C-HCP-Ti interface are more stable than the W-HCP-Ti interface.The adhesion strength between WC and TiC, materials commonly employed in wear resistant coatings, is determined by their interfacial properties. In this work, the adhesion energy, interfacial energy, electronic structure and bonding of WC/TiC interface were calculated by using first-principles method. The results show that the work of adhesion (Wad) of the HCP (interfacial Ti(C) atom located on top of C(W) atom in second layer of WC) stacking interface is larger than those of the Hole (interfacial Ti(C) atom located on top of vacancy of WC), OT (interfacial Ti(C) atom located on top of C(W) atom in surface of WC) stacking interfaces for all the terminations. For the three HCP stacking interfaces, the W-HCP-C interface exhibits the largest Wad, which is 10.16 J/m2. The C-HCP-Ti interface is followed, which is 7.75 J/m2. While the W-HCP-Ti interface exhibits the smallest Wad, which is 2.64 J/m2. The interfacial separation d0 exhibits an opposite trend. Over the entire range of C chemical potential (ΔμC), the interfacial energy of W-HCP-C interface is in the range of 1.03–1.43 J/m2, and the interfacial energy of C-HCP-Ti interface is 1.06–1.46 J/m2. While that of W-HCP-Ti interface is 3.78–4.18 J/m2. It is obvious that the W-HCP-C interface and C-HCP-Ti interface exhibit smaller interfacial energy, which are more stable than the W-HCP-Ti interface. The W-HCP-C interfacial bonding is a mixture of strong covalent bond and partially ionic bond. The bonding of C-HCP-Ti interface is covalent. While the W-HCP-Ti interfacial bonding is mainly metallic.
Co-reporter:Jian Yang, Xiaoru Hou, Peng Zhang, Yefei Zhou, Yulin Yang, Xuejun Ren, Qingxiang Yang
Materials Science and Engineering: A 2016 Volume 655() pp:346-354
Publication Date(Web):8 February 2016
DOI:10.1016/j.msea.2015.12.087
The hypereutectoid Fe–Cr–C hardfacing (harden-surface-welding) coatings with four nano-Y2O3 additives were developed. The effect of nano-Y2O3 additive on the mechanical properties of the hardfacing coating was researched systematically, and the influence mechanism was analyzed using first-principle calculations. The results indicate that, with the increase of the nano-Y2O3 additive, the dimension of the primary austenite grain decreases gradually, and the mechanical properties of the coating improve obviously. When the nano-Y2O3 additive is 0.76 wt%, the primary austenite grain is the smallest (average diameter is 17 μm), and all the mechanical properties are the most excellent, in which, the hardness is HRC 62.9, the tensile strength and yield strength are 1209 MPa and 989 MPa respectively, the impact energy is 26 J/cm2, the weight loss rate is 0.12 g/h, the numbers of thermal fatigue crack are 0, 0, 4 and 6 after 100, 200, 300 and 400 thermal fatigue cycles. In all the Y inclusions, the free energy of YAlO3 is the smallest (−755,103.18 J/mol), which indicates that it is formed most preferentially. For the YAlO3(001)/austenite(100) interface with O-terminated structure, when ΔμYΔμY is in the range of −11.46 eV to −11.04 eV, the interfacial energy is in the range of 0–0.204 J/m2, which meets the energy requirements as the heterogeneous nucleation interface. Therefore, the effectiveness of YAlO3 as the heterogeneous nucleus of austenite can be confirmed.
Co-reporter:Jing Guo, Yunli Feng, Ligang Liu, Xiaolei Xing, Xuejun Ren, Qingxiang Yang
Wear 2016 Volumes 358–359() pp:137-147
Publication Date(Web):15 July 2016
DOI:10.1016/j.wear.2016.03.033
•Wear behavior of carbide itself with/without protection of matrix was investigated.•Wear mechanism of carbide is related with its morphology, orientation and type.•Microcracks within the carbide are classified into inter- and transgranular crack.•During the wear process, matrix and eutectic carbide are interacted with each other.The characteristics of abrasive wear damage to the carbides and eutectic phases in a Fe–Cr–W–Mo–V–C alloy were systematically investigated using point scratch testing on heat-treated specimens with preserved eutectic structures from a characteristic eutectic carbide formation temperature of 1240 °C. A deep-etching method is applied to study the detailed morphologies of the eutectic carbides by optical microscopy (OM) and field emission scanning electron microscopy (FESEM). The types of the eutectic carbides were identified by X-ray diffraction (XRD) as V-rich eutectic MC and Mo-rich eutectic M2C. Single-pass scratch tests were carried out on polished and deep-etched surfaces of the specimens to investigate the micro-scale wear behavior of the eutectic carbides with and without protection by the matrix phase. It was found that, when a surrounding matrix is present, the micro-cracks initiate from the eutectic region during the scratch tests and slip-lines appear in scratched edges of the matrix phase. Without matrix protection as revealed in the deep-etched specimens, the main failure form is carbide dendrites break-off forming wear debris. The detailed differences in response and deformation mode of carbide microstructures with/without matrix support to single-point abrasion behavior are schematically depicted for main eutectic MC and M2C carbides under different loading conditions. Potential improvement on wear performance through the composition design is also discussed based on the different fracture and wear behavior of V-rich eutectic MC and Mo-rich eutectic M2C identified.
Co-reporter:X.L. Xing, Y.F. Zhou, Y.L. Yang, S.Y. Gao, X.J. Ren, Q.X. Yang
Applied Surface Science 2015 Volume 353() pp:184-188
Publication Date(Web):30 October 2015
DOI:10.1016/j.apsusc.2015.06.109
Highlights
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A low-carbon carbide-free bainite has been surface modified by laser remelting and following isothermal transformation.
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The martensite star temperature of the surface modification layer decreased by laser remelting and following isothermal transformation.
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The distribution interval of hardness of the specimens has an obvious improvement after the laser remelting and following isothermal transformation treatment.
Co-reporter:Xiao YUN, Yefei ZHOU, Jian YANG, Xiaolei XING, Xuejun REN, Yulin YANG, Qingxiang YANG
Journal of Rare Earths 2015 Volume 33(Issue 6) pp:671-678
Publication Date(Web):June 2015
DOI:10.1016/S1002-0721(14)60469-5
The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y2O3 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy dispersive spectrometer. The effectiveness of Y2O3 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The experiment results showed that, the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, γ-Fe and α-Fe phases. With the increase of nano-Y2O3 additives, primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 μm, when nano-Y2O3 additive was 2.54 wt.%. The calculated results showed that, the two-dimensional lattice misfit between the face (001) of Y2O3 and face (100) of orthorhombic M7C3 was 4.911%, which indicated that Y2O3 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3.TEM images of the M7C3 carbides (a), (b) The primary M7C3; (c), (d) The eutectic M7C3
Co-reporter:Jigang Chen;Xiaolei Xing;Yajun Wang
Journal of Materials Engineering and Performance 2015 Volume 24( Issue 3) pp:1157-1164
Publication Date(Web):2015 March
DOI:10.1007/s11665-014-1363-3
New hardfacing coatings with different vanadium (V) additions were prepared by surfacing technology. The microstructures of the hardfacing coatings were analyzed by field emission scanning electron microscope equipped with energy dispersive X-ray spectrometry and examined by transmission electron microscope. The hardness and wear resistances of the hardfacing coatings were measured. Worn debris were collected at the end of wear test and analyzed. The precipitation temperature of the phases in the hardfacing coatings and the mass fraction of MC carbide were calculated by Jmatpro software. The experimental results show that, the hardfacing coating mainly consists of granular bainite. No significant change in the size of linear martensite-austenite (M-A) islands is observed with the increase of V addition, while the size of massive M-A islands is decreased. The wear resistance of the hardfacing coating reaches a maximum level with V content of 0.14 wt.%. The calculated results show that, the mass fraction of MC carbide is increased with the increase of V content. Based on calculation following two-dimensional mismatch theory, MC carbide is a heterogeneous nucleus of the ferrite resulting refined ferrite in the hardfacing coating.
Co-reporter:Jian Yang, Jianjun Tian, Feifei Hao, Ting Dan, Xuejun Ren, Yulin Yang, Qingxiang Yang
Applied Surface Science 2014 Volume 289() pp:437-444
Publication Date(Web):15 January 2014
DOI:10.1016/j.apsusc.2013.10.186
Highlights
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Hardfacing metal of the hypereutectic Fe–Cr–C alloy with different La2O3 additives was developed.
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The dimension of the primary M7C3 carbide decreases with the increase of the La2O3 additives.
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Austenite precipitated in the liquid phase can improve the precipitation rate of M7C3 carbide.
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γ-Fe transforms into α-Fe can promote the growth of the M7C3 carbide in short period.
Co-reporter:Xiaoru Hou, Bin Zhao, Jian Yang, Xiaolei Xing, Yefei Zhou, Yulin Yang, Qingxiang Yang
Applied Surface Science 2014 Volume 317() pp:312-318
Publication Date(Web):30 October 2014
DOI:10.1016/j.apsusc.2014.08.118
Highlights
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Fe–0.4 wt.%C–6.5 wt.%Cr hardfacing coatings with different La2O3 additives were developed.
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The grain size of the hardfacing coating decreases with the increase of the La2O3 additives.
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The unidirectional wear resistance of the hardfacing coating is increased with the increase of the La2O3 additives.
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The friction coefficient is decreased and the reciprocating wear resistance is increased with the increase of the La2O3 additives.
Co-reporter:Yajun WANG, Jigang CHEN, Jian YANG, Feifei HAO, Ting DAN, Yulin YANG, Qingxiang YANG
Journal of Rare Earths 2014 Volume 32(Issue 1) pp:83-89
Publication Date(Web):January 2014
DOI:10.1016/S1002-0721(14)60036-3
The purpose of this work was to investigate the effect of La2O3 on the granular bainite microstructure and wear resistance of hardfacing layer metal. The hardfacing layer metals with different contents of La2O3 were prepared. The microstructures of the hardfacing layer metals were observed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The hardness and wear resistance of the hardfacing layer metals were measured respectively. The results indicated that with the increasing content of La2O3, the amount of granular bainite increased, while that of martensite decreased and that of retained austenite did not change obviously. When the content of La2O3 was 2.55 wt.%, the volume fraction of the granular bainite in the hardfacing layer metal was 73.2%. Meanwhile, the wear resistance of the hardfacing layer metal was the largest, which was 12100 min/g. The mismatch between the face (100) of LaAlO3 and the face (100) of δ-Fe was 7.1%. Therefore, LaAlO3 could act as moderate effective heterogeneous nuclei of δ-Fe and the granular bainite could be refined.TEM of hardfacing layer metals with different contents of La2O3 (a) 0 wt.%; (b) 2.55 wt.%
Co-reporter:Jian Yang, Xiaoru Hou, Pengfei Zhang, Yefei Zhou, Xiaolei Xing, Xuejun Ren, Qingxiang Yang
Computational and Theoretical Chemistry 2014 Volume 1029() pp:48-56
Publication Date(Web):1 February 2014
DOI:10.1016/j.comptc.2013.12.023
•The effectiveness of LaAlO3 as the heterogeneous nucleus of austenite was analyzed.•There are four binding modes of LaAlO3 (1 0 0)/austenite (1 0 0) interface.•AlO2 terminated interface meets the energy requirements as heterogeneous nucleation one, when ΔμLa is low.•LaO terminated interface meets the energy requirements as heterogeneous nucleation one, when ΔμLa is high.In this work, the interface atomic structure, bonding character, adhesion work and interfacial energy of LaAlO3 (1 0 0)/austenite (1 0 0) interface were studied and the effectiveness of the LaAlO3 as the heterogeneous nucleus of austenite was analyzed by first-principles calculations. The results indicate that, in LaAlO3 bulk, the charge transfer and sp2 orbital hybridization not only appear between La atom and O atom, but also between Al atom and O atom, which indicate that the chemical bond in LaAlO3 bulk is a mixed one with both covalent and ionic characteristics. For LaAlO3 (1 0 0) surface, when La chemical potential (ΔμLa) is low, AlO2 terminated structure is stable than LaO terminated one. However, when La chemical potential (ΔμLa) is high, LaO terminated structure is stable than AlO2 terminated one. For austenite (1 0 0) surface, doped C terminated structure is stable than lack C terminated one all along. In the four LaAlO3 (1 0 0)/austenite (1 0 0) interfaces, the LaO-doped C terminated structure has the largest adhesion work and the smallest interface distance, which indicate that it is the most stable. The effectiveness of LaAlO3 as the heterogeneous nucleus of austenite is related with ΔμLa and ΔμC. When ΔμLa is low, the LaAlO3 (1 0 0)/austenite (1 0 0) interface with AlO2 terminated structure meets the energy requirements as the heterogeneous nucleation interface. With the increase of ΔμLa, the LaAlO3 (1 0 0)/austenite (1 0 0) interface with AlO2 terminated structure cannot be the LaAlO3/austenite heterogeneous nucleation interface any longer, while that with LaO terminated structure, especially with LaO-doped C terminated structure, meets the energy requirements as the heterogeneous nucleation interface greatly.Graphical abstract
Co-reporter:Lianlian Liu;Bo Liao;Jing Guo;Ligang Liu
Journal of Materials Engineering and Performance 2014 Volume 23( Issue 1) pp:39-48
Publication Date(Web):2014 January
DOI:10.1007/s11665-013-0749-y
The surface crack and lateral crack of the AISI 304 stainless steel thin strip produced by twin-roll casting were observed. The temperature at the center of outlet during twin-roll-casting process was determined by infrared thermometer. In order to avoid the surface cracks of the casting strip, the thermal flow coupling field of AISI 304 stainless steel during twin-roll-casting process was simulated by a 3D fluid-structure coupling model. According to the simulation result, the effect of the casting speed on thermal flow field was analyzed and the process parameters were optimized. Moreover, by studying heat flux curves, the heat transfer mechanism between molten pool and roll was analyzed. The results show that, with the increase of the casting speed, the temperature of the molten pool increases and the solidification point moves toward the outlet. Meanwhile, the whirlpool above gets larger. Based on the solidification front position, the optimized process parameters are 1500 °C and 0.37 m/s. The heat transfer mechanism between molten pool and roll contains direct contacting heat transfer and air gap heat transfer.
Co-reporter:Jian Yang, Xiaoru Hou, Xiaolei Xing, Xiao Yun, Yulin Yang, Xuejun Ren, Qingxiang Yang
Journal of Molecular Structure 2014 1076() pp: 63-68
Publication Date(Web):5 November 2014
DOI:10.1016/j.molstruc.2014.07.044
Co-reporter:S. Liu, S.Y. Gao, Y.F. Zhou, X.L. Xing, X.R. Hou, Y.L. Yang, Q.X. Yang
Materials Science and Engineering: A 2014 617() pp: 127-138
Publication Date(Web):
DOI:10.1016/j.msea.2014.08.049
Co-reporter:Jing Guo;Yuan-yuan Liu;Li-gang Liu
International Journal of Minerals, Metallurgy, and Materials 2014 Volume 21( Issue 7) pp:666-673
Publication Date(Web):2014 July
DOI:10.1007/s12613-014-0956-z
This study first investigated cracks on the surface of an actual steel strip. Formulating the Anand model in ANSYS software, we then simulated the stress field in the molten pool of type 304 stainless steel during the twin-roll casting process. Parameters affecting the stress distribution in the molten pool were analyzed in detail and optimized. After twin-roll casting, a large number of transgranular and intergranular cracks resided on the surface of the thin steel strip, and followed a tortuous path. In the molten pool, stress was enhanced at the exit and at the roller contact positions. The stress at the exit decreased with increasing casting speed and pouring temperature. To ensure high quality of the fabricated strips, the casting speed and pouring temperature should be controlled above 0.7 m/s and 1520°C, respectively.
Co-reporter:Jian Yang, Pengfei Zhang, Yefei Zhou, Xiaolei Xing, Xuejun Ren, Yulin Yang, Qingxiang Yang
Materials Science and Engineering: A 2014 Volume 591() pp:82-89
Publication Date(Web):3 January 2014
DOI:10.1016/j.msea.2013.10.079
The harden-surface-welding (hardfacing) alloys with different La2O3 additives were developed. The microstructure was observed and the phase structure was determined. Meanwhile, the hardness and wear resistance were measured, respectively. Moreover, the tensile strength, yield strength and impact toughness were measured too. In addition, the fractograph of the hardfacing alloy was observed. On this basis, the LaO-doped C terminated interface was taken, in which, the interfacial energy of LaAlO3 (100)/austenite (100) interface was calculated and the effectiveness of the LaAlO3 as the heterogeneous nucleus of austenite was analyzed by first-principles calculations. The experimental results indicate that, with the increase of the La2O3 additive, the primary austenite grain dimension of the hardfacing alloy decreases obviously. Meanwhile, the hardness, strength, toughness and wear resistance of the hardfacing alloy increase simultaneously. When the La2O3 additive is 3.32 wt%, all of the mechanical properties are the largest, the hardness is HRC 50, the tensile strength and yield strength are 1502 MPa and 1334 MPa respectively, the impact toughness is 7.1 J/cm2 and the wear resistance is 1.29 mg/min. The calculated results show that, for the LaAlO3 (100)/austenite (100) interface with LaO-doped C terminated structure, the interfacial energy is high when the La chemical potential ΔμLa and C chemical potential ΔμC are low. However, with the increase of the ΔμLa and ΔμC, the interfacial energy decreases gradually. When the ΔμLa and ΔμC meet the condition of −3.792 eV≤0.543ΔμLa+0.311ΔμC≤−3.588 eV, the interfacial energy of LaAlO3 (100)/austenite (100) interface is in the range of 0–0.204 J, which meets the requirements of the heterogeneous nucleation interfacial energy. Therefore, LaAlO3 can be the heterogeneous nucleus of austenite.
Co-reporter:Jian Yang, Pengfei Zhang, Yefei Zhou, Jing Guo, Xuejun Ren, Yulin Yang, Qingxiang Yang
Journal of Alloys and Compounds 2013 Volume 556() pp:160-166
Publication Date(Web):15 April 2013
DOI:10.1016/j.jallcom.2012.12.099
Interface atomic structure, bonding character, cohesive energy and interfacial energy of ferrite (1 0 0)/TiC (1 0 0) were studied using a first-principles density functional plane-wave ultrasoft pseudopotential method. Meanwhile, the effectiveness of TiC as the heterogeneous nuclei of ferrite was analyzed. The results indicated that, TiC bonding is dominated by the C-2p, C-2s and Ti-3d electrons, which exhibits high covalency. With increase of the atomic layers, the interfacial energies of ferrite and TiC are both declined rapidly and stabilized gradually. There are two binding modes for TiC as the heterogeneous nuclei of ferrite, which are Fe atoms above the Ti atoms (Ti-termination) and Fe atoms above the C atoms (C-termination). Interfacial energy of the Ti-termination is larger than that of the C-termination, which means that for Fe atoms above the C atoms, the ability of TiC promotes ferrite heterogeneous nucleation on its surface is larger than that for Fe atoms above the Ti atoms.Graphical abstractHighlights► Interface stability of ferrite (1 0 0)/TiC (1 0 0) was studied. ► The effectiveness of TiC as the heterogeneous nuclei of ferrite was analyzed. ► Ti-termination and C-termination are the two binding modes for ferrite/TiC interface. ► Interfacial energy of the Ti-termination is larger than that of the C-termination. ► On C-termination, ability of TiC promotes ferrite heterogeneous nucleation is strong.
Co-reporter:J. Guo, L.G. Liu, Q. Li, Y.L. Sun, Y.K. Gao, X.J. Ren, Q.X. Yang
Materials Characterization 2013 Volume 79() pp:100-109
Publication Date(Web):May 2013
DOI:10.1016/j.matchar.2013.02.011
•The solidification process was analyzed by Thermo-Calc, DSC, XRD and SEM observation.•Primary and secondary carbides precipitated during solidification were determined.•The three dimensional morphologies of all carbides was observed.•The eutectic MC exhibits the dendritical structure which was not observed before.A novel steel for cold work roll was developed in this work. Its phase structures were determined by X-ray diffraction, and phase transformation temperatures during the cooling process were measured by Differential Scanning Calorimeter. The Fe–C isopleths of the steel were calculated by Thermo-Calc to preliminarily determine the characteristic temperatures of the different phases. Then the specimens were quenched at these characteristic temperatures. The typical microstructures were observed by Optical Microscopy and Field Emission Scanning Electron Microscopy with Energy Disperse Spectroscopy. The results show that α-Fe, MC, M2C and M7C3 precipitate when the specimen is cooled slowly to room temperature. According to the DSC curve and the Fe–C isopleths, the characteristic temperatures of the phase transformation and carbide precipitation are chosen as 1380 °C, 1240 °C, 1200 °C and 1150 °C respectively. Primary austenite precipitates at 1380 °C, then eutectic reaction occurs in residual liquid after quenching and the eutectic microstructures distribute along the crystal grain boundary. The eutectic MC is leaf-like and eutectic M2C is fibrous-like. Both of them precipitate in ternary eutectic reaction simultaneously at 1240 °C, grow together in the form of dendrite along the crystal grain boundary. Secondary MC precipitates from the austenitic matrix at 1200 °C and nucleates at the position where eutectic MC located accompanied by the dissolving of eutectic carbides. The mixed secondary M2C and M7C3 precipitate at 1150 °C. The secondary M2C is strip-like and honeycomb-like, while the M7C3 is chrysanthemum-like and maze-like.
Co-reporter:Chunmei Zhao, Hongyan Hu, Yefei Zhou, Yukui Gao, Xunjun Ren, Qingxiang Yang
Materials & Design 2013 50() pp: 78-84
Publication Date(Web):
DOI:10.1016/j.matdes.2013.02.073
Co-reporter:Jing Guo;Hong-wei Qu;Li-gang Liu
International Journal of Minerals, Metallurgy, and Materials 2013 Volume 20( Issue 2) pp:146-151
Publication Date(Web):2013 February
DOI:10.1007/s12613-013-0706-7
A high speed steel (HSS) was studied for rollers in this work. The steel was quenched at 1150°C and tempered at 520°C. The phase structures of the steel were determined by X-ray diffraction (XRD), and the hardness of specimens was measured. The volume fraction of carbides was counted by Image-Pro Plus software. The typical microstructures were observed by field emission scanning electron microscope (FESEM). Stable and meta-stable carbides were deduced by removing the existing phases one by one in the Fe-C equilibrium calculation. It is found that the precipitated carbides are bulk-like MC, long stripe-like M2C, fishbone-like M6C, and daisy-like M7C3 during the tempering process. The stable carbides are MC and M6C, but the meta-stable ones are M2C, M7C3, and M3C.
Co-reporter:Jian Yang, Yulin Yang, Yefei Zhou, Xiaowen Qi, Xuejun Ren, Qingxiang Yang
Surface and Coatings Technology 2013 Volume 219() pp:69-74
Publication Date(Web):25 March 2013
DOI:10.1016/j.surfcoat.2013.01.006
Flux-cored wire for surfacing hot-rolling supporting roller was developed and the specimens of surfacing layers were tempered at different temperatures. In order to characterize the high-alloy martensite in the surfacing layer during the tempering process, the microstructure and phase structure of the surfacing layer were analyzed, respectively. The nanoindentation hardness and phase transformation temperature of the high-alloy martensite were measured. The crystal structure of each phase was analyzed. The results show that the microstructure of the as-welded surfacing layer consists of martensite and retained austenite. Meanwhile, the high-alloy martensite with white reticular morphology is distributed on the crystal boundary. With increase of the tempering temperature, the high-alloy martensite disappears gradually, and the black reticular microstructure finally appears when the tempering temperature is 650 °C. The high-alloy martensite, whose average nanoindentation is 14.33 GPa, shows bulk morphology in field emission scanning electron microscope and starts to dissolve in the matrix at 420 °C. The contents of the alloy elements in the high-alloy martensite are higher than those in the normal one. However, the former decrease rapidly after tempering at 650 °C. The high-alloy martensite shows the body-centered tetragonal crystal structure, and the c-axis of the high-alloy martensite is longer than that of the normal one.Highlights► Hardfacing metal with high-alloy martensite was prepared. ► The content of alloy element in high-alloy martensite is higher than that in normal one. ► The c-axis of high-alloy martensite is longer than that of the normal one.
Co-reporter:Yefei Zhou, Yulin Yang, Jian Yang, Feifei Hao, Da Li, Xuejun Ren, Qingxiang Yang
Applied Surface Science 2012 Volume 258(Issue 17) pp:6653-6659
Publication Date(Web):15 June 2012
DOI:10.1016/j.apsusc.2012.03.101
Abstract
Arc surfacing layer of hypoeutectic high chromium cast iron (HCCI) expects refiner carbides in the microstructure to improve its mechanical properties. In this paper, Ti additive as a strong carbide forming element was added in the hypoeutectic HCCI arc surfacing layer. Microstructure of titaniferous hypoeutectic HCCI was studied by optical microscopy, X-ray diffraction and field emission scanning electronic microscopy with energy dispersive spectrometer. Furthermore, the M(M = Cr, Fe)7C3 carbide refinement mechanism was explained by the phase diagram calculation and lattice misfit theory. The results show that, the M7C3 carbide in arc surfacing microstructure of hypoeutectic HCCI has been refined with 2 wt.% Ti additive, and TiC carbide can be observed in/around the M7C3 carbide. With Ti addictive increasing, the micro-hardness along the depth in profile section of layer becomes more uniform, and the wear resistance has been improved. According to the phase diagram calculation, MC carbide precipitates prior to M7C3 carbide in Fe–Cr–C–Ti alloy. In addition, the lattice misfit between (1 1 0)TiC and (0 1 0)Cr7C3 is 9.257%, which indicates that the TiC as heterogeneous nuclei of the M7C3 is medium effective. Therefore, the M7C3 carbide can be refined.
Co-reporter:Peng Zhang, Yunkun Zhang, Ligang Liu, Xuejun Ren, Yue Zhang, Yuan Fang, Qingxiang Yang
Computational Materials Science 2012 Volume 52(Issue 1) pp:61-67
Publication Date(Web):February 2012
DOI:10.1016/j.commatsci.2011.03.039
The specimens were taken from the 304 austenite stainless steel. Based on the measured results of the phase transformation temperature and phase structure curves of the 304 stainless steel, the finite element model was established. According to the simulated temperature field of 304 stainless steel during twin-roll strip casting process and the mechanical properties of 304 stainless steel determined, the stress field of the 304 stainless steel during twin-roll strip casting process was simulated. Meanwhile, the effect of different technologic parameters, such as casting speed, casting temperature, roller radius and strip thickness at the exit, on the stress field of the 304 stainless steel during twin-roll strip casting process was simulated too in this work. The results show that the largest tensile stress appears on the contact interface between strip and roller located 5–10° away from exit. The tensile stress appears on the surface and the compressive one in the center of the strip. The larger roller radius and strip thickness at the exit are, the larger the tensile stress on the surface of 304 stainless steel during twin-roll strip casting process is. However, the larger the casting speed and the casting temperature are, the smaller the tensile stress on the surface of 304 stainless steel is.HighlightsThe thermal elastic-plasticity model of the stress field above the exit was established. Near the exit, the maximum tensile stress occurs at the contacted surface position about 5–10°. The stress fields of 304 stainless steel with different technologic parameters were simulated.
Co-reporter:Hongwei Qu, Bo Liao, Ligang Liu, Da Li, Jing Guo, Xuejun Ren, Qingxiang Yang
Calphad 2012 Volume 36() pp:144-150
Publication Date(Web):March 2012
DOI:10.1016/j.calphad.2011.06.006
The continuous cooling transformation (CCT) curve of a new type of high speed steel (HSS) for rollers was determined along with its typical microstructures. The CCT curve established shows that the Ac1 of the steel is 770∼830 °C, the Acm is 920 °C and the starting temperature of martensite transformation is 190 °C. The Fe–C isopleths, mass fractions of all the phases and mole fractions of the alloying elements in austenite with different tungsten (W) content have been calculated using Thermo-Calc. The isopleths analysis show that MCI, M6C, M7C3, M23C6 and MCII carbides exist in the HSS with 1–5 wt% of tungsten (W) element, whilst only MCI, M7C3 and M23C6 are present without W. Studies on HSS with different W content show that both the starting precipitation temperature of austenite and its maximum mass fraction decrease with increasing W content. The starting precipitation temperature of MCI remains almost invariant (1380–1390 °C), with its maximum mass fraction decreasing slightly with increase of the W content. Similarly, the starting precipitation temperatures of M7C3 and M23C6 remain almost unchanged at the high temperature region, while that of M7C3 decreases at the lower temperature region, and the maximum mass fraction of both carbide groups decreases with the W content. The effect of W content on the starting precipitation temperature and the maximum mass fraction of M6C and MCII were found to be different from that of other carbide groups, both increase significantly. With the W content changed from 0 to 5%, the maximum mole fraction of element Cr in austenite increases from 5.0 to 5.1 mol% while that of element Mo decreases from 1.7 to 1.3 mol%. The results show that MCI carbide contains elements V and Nb, and dissolves elements Mo, Cr, W and Fe; M6C carbide contains elements Fe, W and Mo; M7C3 and M23C6 carbides contain elements Fe and Cr; MCII carbide only contains elements W and Mo in addition to carbon.Highlights► The CCT curve of a new high speed steel for rollers was determined. ► Thermo-Calc calculation is applied on a new high speed steel for rollers. ► The results calculated by Thermo-Calc are compared with the experimental ones.
Co-reporter:Y.F. Zhou, Y.L. Yang, Y.W. Jiang, J. Yang, X.J. Ren, Q.X. Yang
Materials Characterization 2012 Volume 72() pp:77-86
Publication Date(Web):October 2012
DOI:10.1016/j.matchar.2012.07.004
The microstructure and carbide refinement mechanisms of Fe–24 wt.%Cr–4.1 wt.%C hardfacing alloys with 0 wt.%, 0.5 wt.%, 1.0 wt.%, 2 wt.%, and 4 wt.% ceria additives have been systematically investigated in this work. Optical microscopy, field emission scanning electron microscopy with energy dispersive spectrometer, and X-ray diffraction were collectively used to study the microstructure, the phase components, and the chemical formation of inclusion formed in the welding process. Wear-resistance of the alloys was comparatively studied using an abrasive wear testing machine. The structure analysis results show that the Fe–Cr–C hardfacing alloy mainly consists of martensite, retained austenite, MC carbide and M7C3 carbide. With increasing ceria additive contents, the average size of the primary M7C3 carbide decreases and reaches a most refined state in the alloy with 2 wt.% ceria additives. Comparative wear tests data shows that the wear resistance of the hardfacing alloys with ceria additives is better than that without ceria additive. In a good agreement with the carbide refinement results, the wear resistance of the alloy reaches an optimum level in the sample with 2 wt.% ceria additive. The main RE inclusion type identified with in-situ XRD analysis is RE inclusion Ce2O2S. Thermodynamics calculation confirms that this type of RE inclusion could precipitate prior to M7C3 carbides, and act as a heterogeneous nucleus for M7C3 in the welding process, which effectively provides a mechanism for significant refinement of the M7C3 carbide and improves its wear resistance.Rare Earth inclusion (Ce2O2S) distributes in the primary M7C3 carbide. Moreover, Ce2O2S, which acts as heterogeneous nuclei of the primary M7C3 carbide, is medium effective. Therefore, the primary M7C3 carbide has been refined.Highlights► Micro-hardness of primary M7C3 carbide in Fe–Cr–C hardfacing alloy is 1594 HV. ► RE inclusion Ce2O2S can be observed in the primary M7C3 carbide. ► Ce2O2S as heterogeneous nuclei of the Cr7C3 is medium effective. ► Primary carbide is most refined with 2 wt.% ceria additive.
Co-reporter:Yefei ZHOU, Yulin YANG, Xiaowen QI, Yongwen JIANG, Jian YANG, Xuejun REN, Qingxiang YANG
Journal of Rare Earths 2012 Volume 30(Issue 10) pp:1069-1074
Publication Date(Web):October 2012
DOI:10.1016/S1002-0721(12)60180-X
The Fe-Cr-C claddings formed by arc surface welding with different La2O3 additions were investigated. The microstructures were observed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The phase structures were measured by X-ray diffraction (XRD). The wear resistances of the claddings were tested by friction and wear experiment. On this basis, the carbide refinement mechanism by inclusion enriched with La was discussed theoretically. The results showed that, the microstructure of the Fe-Cr-C cladding consisted of primary (Cr,Fe)7C3 carbides and eutectic (γ-Fe+(Cr,Fe)7C3) structure. With La2O3 addition increasing, the primary carbides were refined, and the mass loss of the cladding decreased gradually. The Fe-Cr-C cladding with 4 wt.% La2O3 addition had a best wear resistance behaviour. The RE inclusion LaAlO3 as heterogeneous nuclei of the primary M7C3 was medium effective, and could refine the M7C3 carbides. Besides, the wear resistance could be improved by adding La2O3 in the claddings.
Co-reporter:Q. Li;Y. K. Zhang;L. G. Liu;P. Zhang;Y. Zhang;Y. Fang
Journal of Materials Science 2012 Volume 47( Issue 9) pp:3953-3960
Publication Date(Web):2012 May
DOI:10.1007/s10853-012-6246-0
This study focuses on the numerical simulation of the temperature fields of the 304 stainless steel during twin-roll strip casting process. The cracks and fratographs of the 304 stainless steel strip with the practical casting parameters were observed by Scanning Electron Microscopy. The exit temperature of the 304 stainless steel during twin-roll strip casting process was measured. Meanwhile, it was simulated by means of finite element model. The observed results show that the strip from outside to inside are composed of refined crystal zone, columnar crystal one, and equated axis crystal one. The cracks occur on the strip surface, extended to interior along the columnar crystal boundary, and then, ended at the juncture between the columnar crystal zone and equated axis crystal one. The simulated result was compared to the measured temperature, which showed a good agreement, thus indicating that this model is valid and accurate. Then, by employing this model, the effects of the casting parameters, such as casting speed and casting temperature, on the freezing point position of the 304 stainless steel during twin-roll strip casting process were simulated too. The simulated results show that, the freezing point position is decreased with the increasing casting speed and casting temperature. For producing high-quality strip of 304 stainless steel during twin-roll strip casting, the limits of casting speed and casting temperature are 1.1 m·s−1 and 1,570 °C, respectively.
Co-reporter:Da Li 李 达;Zhan-quan Cui 崔占全
Journal of Shanghai Jiaotong University (Science) 2012 Volume 17( Issue 6) pp:679-683
Publication Date(Web):2012 December
DOI:10.1007/s12204-012-1345-2
Microstructure and forming quality of friction stir welding joints of 7075Al and AZ31BMg with different welding parameters were analyzed. The results show that, good welded joint is obtained when the rotating frequency is 13 r/s and the welding speed is 30 mm/min. An irregular area is formed in the welding center. Meanwhile, the river pattern and eddy-like distribution are found in the weld nugget zone. Besides, brittle intermetallic compounds Al12Mg17 and Al3Mg2 are found in the welded joint. They cause the increase of microhardness of welded joint. The maximum tension stress of welded joint is 112MPa.
Co-reporter:Peng Zhang, Hongyan Hu, Yuanyuan Liu, Yue Zhang, Yuan Fang, Xuejun Ren, Bo Liao, Qingxiang Yang
Materials Science and Engineering: A 2011 528(3) pp: 1201-1204
Publication Date(Web):
DOI:10.1016/j.msea.2010.09.093
Co-reporter:Hai-feng Dong;Jing Li;Yue Zhang
International Journal of Minerals, Metallurgy, and Materials 2010 Volume 17( Issue 2) pp:173-178
Publication Date(Web):2010 April
DOI:10.1007/s12613-010-0209-8
According to the stress-strain curves of single-phase martensite and single-phase ferrite steels, whose compositions are similar to those of martensite and ferrite in low Si-Mn-Nb dual-phase steel, the stress-strain curve of the low Si-Mn-Nb dual-phase steel was simulated using the finite element method (FEM). The simulated result was compared with the measured one and they fit closely with each other, which proves that the FE model is correct. Based on the FE model, the microstress and microstrain of the dual-phase steel were analyzed. Meanwhile, the effective factors such as the volume fraction of martensite and the yield stress ratio between martensite and ferrite phases on the stress-strain curves of the dual-phase steel were simulated, too. The simulated results indicate that for the low Si-Mn-Nb dual-phase steel, the maximum stress occurs in the martensite region, while the maximum strain occurs in the ferrite one. The effect of the volume fraction of martensite (fM) and the yield stress ratio on the stress-strain curve of the dual-phase steel is small in the elastic part, while it is obvious in the plastic part. In the plastic part of this curve, the strain decreases with the increase of fM, while it decreases with the decrease of the yield stress ratio.
Co-reporter:Da Li, Ligang Liu, Yunkun Zhang, Chunlei Ye, Xuejun Ren, Yulin Yang, Qingxiang Yang
Materials & Design (1980-2015) 2009 Volume 30(Issue 2) pp:340-345
Publication Date(Web):February 2009
DOI:10.1016/j.matdes.2008.04.061
The phase transformation and the carbide precipitation temperatures of the high chromium cast iron with Cr content of 15% were measured by using differential scanning calorimetry (DSC). The matrix and the type of carbides of the specimen after quenching were determined by using X-ray diffraction (XRD) in this work. Meanwhile, the shape and the number of carbides in the different specimens were detected by using optical microscope, scanning electron microscope (SEM) & energy dispersive spectrometer (EDS). The equilibrium phase of this high chromium cast iron was calculated by using Thermo-Calc software based on above experiments. The calculation results obtained from Thermo-Calc software is agreed with the ones from experiments. The work provides a practical method for engineers and researchers in related areas.
Co-reporter:Da Li, Yulin Yang, Ligang Liu, Jiazhen Zhang, Qingxiang Yang
Materials Science and Engineering: A 2009 Volume 509(1–2) pp:94-97
Publication Date(Web):25 May 2009
DOI:10.1016/j.msea.2009.02.018
Co-reporter:Da Li, Bo Liao, Ligang Liu, Chunmei Zhao, Xiqing Zhao, Xuejun Ren, Qingxiang Yang
Computational Materials Science 2008 Volume 44(Issue 2) pp:280-285
Publication Date(Web):December 2008
DOI:10.1016/j.commatsci.2008.03.034
This study focuses on the simulation of process stress of medium-high carbon steel during martensite transformation after hard-face-welding (hardfacing). Based on the measured results of temperature, residual stress field and the thermo-physical, mechanical parameters of the medium-high carbon steel, the finite element (FE) model of the stress fields were established. According to this model, the process stress of medium-high carbon steel during martensite transformation after hardfacing was analyzed in this work. The simulation results show that, the compressive stress appears on the surface of the specimen during hardfacing cooling process when martensite transformation occurs, while the large tensile stress will be appeared on the surface of the specimen and hold to room temperature with the increasing of the time.
Co-reporter:Ligang Liu, Qiang Li, Xiaohei Liu, Yukui Gao, Xuejun Ren, Bo Liao, Qingxiang Yang
Materials Letters 2007 Volume 61(4–5) pp:1251-1255
Publication Date(Web):February 2007
DOI:10.1016/j.matlet.2006.07.024
This study focuses on the numerical model simulation of stress and temperature fields of carburized specimens with different carbon content during the quenching process. In the models the coupling between thermal field, phase transformation field and stress field was considered. The changes of the thermomechanical parameters of the material, as a function of carbon content and thermal field, were considered in the stress simulations. The residual stress fields of 20CrMnTi specimens with different carbon content of 0.8% and 1.0% were measured using an X-ray stress analyzer. Finite element model (FEM) was built for simulating the residual stress field after quenching. Meanwhile, the temperature and stress fields during quenching were simulated. The measured and simulated results are in good agreement.
