To improve the strength-toughness of traditional U-rib (TUR) and solve the problem of insufficient penetration between TUR and deckplate, a new local thickened U-rib (LTUR) has been proposed to improve the fatigue resistance of the weld joint under the premise of not increasing thickness and strength of the TUR material. And a hot/warm roll-forming process (RFP) adopting partially induction heating to 700—1000 °C was carried out to fabricate LTUR. The deformation behaviors in the forming process and microstructure of LTUR have been investigated. Mechanical properties and fracture mechanism of the LTUR after hot/warm RFP have been systematically discussed. Moreover, the results are compared with those obtained in cold RFP. Mechanical properties of the LTUR deformed above the critical transformation temperature (A c3) show high performance characteristics with marked fatigue resistance and superior toughness. Upon increasing the heating temperature from 700 to 900 °C, the initial coarse ferrite-pearlite structure transform into equiaxed ultrafine ferrite (1—3 μm) and precipitates such as (Nb, Ti)(C, N) are uniformly distributed in the matrix. The average dislocation density of the specimens after hot roll-forming at heating temperature of 900 °C decreases dramatically compared with those of the specimens subjected to the cold RFP. Furthermore, a typical characteristic of ductile fracture mechanism and the high impact energy are more convinced that the specimens deformed above 900 °C have obtained an optimal combination of strength and toughness.

Three types of titanium clad steel sheets were fabricated by a hot-roll bonding process at different rolling reductions (40%, 55%, and 65%). The specimens with stacking sequences of TA1/steel/TA1, TA1/T2/steel/T2/TA1 and TA1/BAg-8/steel/BAg-8/TA1, corresponding to Ti/steel clad composites bonded without a filler, with a red copper filler, and with a BAg-8 filler, are referred to here as Ti-steel, Ti-T2-steel, and Ti-Ag-steel, respectively. The Ti-steel specimen was prepared by direct hot-roll bonding with its four sides welded by arc welding, while the Ti-T2-steel and Ti-Ag-steel specimens were prepared by a combined brazing and hot-roll bonding process, named as a brazing-rolling process. These three types of as-roll bonded specimens were subjected to heat treatments, under 65% rolling reduction. The bonding quality, interface structure evolution, and mechanical properties of the clad composites were systemically studied. The results showed that the reduction in the shear strength of Ti-T2-steel under 65% rolling reduction was due to the poor interface components. The presence of brittle intermetallic compounds (IMCs) and the rapid increase of α-β Ti at the interface of Ti-T2-steel with increasing temperature were regarded as the key factors influencing interfacial failure. The formation of the TiFe2 phase at 800 °C for Ti-Ag-steel provided major sites for the nucleation and propagation of cracks during the tensile tests, leading to interfacial delamination. The experimental elongation values of these three types of clad composites were enhanced significantly at all heat-treatment temperatures compared with the calculated elongation values using the rule of mixture (ROM). In addition, the experimental values of yield strength (YS) decreased while those of the ultimate tensile strength (UTS) increased for Ti-Ag-steel, in contrast with the corresponding values by ROM, suggesting the favourable formability of the clad composite by lamination owing to low yield ratio.