船用钛/钢混合结构二次焊接过程中，爆炸焊接头经历多次热循环后其界面微观组织和结合性能势必发生转变，直接影响混合结构的结合强度及船舶航行安全。本工作采用模拟瞬态热处理(STHT)实验研究二次焊接过程中温度与钛/钢界面微观组织及结合性能之间的关系。结果表明，当STHT温度低于600 ℃时，界面微观结构保持稳定；当温度达到并超过700 ℃时，钛/钢接头发生回复再结晶，界面附近晶粒明显粗化，由FeTi和TiC组成的界面金属间化合物层的厚度快速增加。随温度升高，与铝/钢接头的界面结合强度呈现单调下降不同，钛/钢接头的黏结强度和剪切强度先增加后下降，峰值分别在500和600 ℃处出现。中、低温热作用促进原子扩散和应力释放，从而提高界面结合强度；而高温下晶粒粗化和金属间化合物生长则导致接头结合强度下降。综合确定钛/钢接头界面的临界阈值温度为600 ℃。

During the secondary welding process of titanium–steel hybrid structures for ships, repeated thermal cycles inevitably change the interfacial microstructure and mechanical properties of explosive-welded transit joints. These changes directly affect the bonding strength of hybrid structures and navigational safety of ships. Herein, simulated transient heat treatment (STHT) was adopted to study the relationship among temperature, interfacial microstructure, and bonding properties of a titanium–steel hybrid structures during the secondary welding process. Results showed that when the STHT temperature was <600 °C, the interfacial microstructure remained stable. Meanwhile, at ≥700 °C, recrystallization occurred, causing grains near the interface to become coarse. Furthermore, the thickness of the intermetallic compound layer comprising FeTi and TiC increased rapidly. Unlike aluminum–steel hybrid structures, in which the interfacial bonding strength monotonically decreases with increasing temperature, the bonding and shear strengths of the titanium–steel hybrid structures initially increased and then decreased, with peaks appearing at 500 and 600 °C. The thermal effect at medium and low temperatures promoted atomic diffusion and stress release, thereby improving the interfacial bonding strength. At high temperatures, grain coarsening and intermetallic compound growth decreased the bonding strength of the transit joint. Overall, the critical threshold temperature at the interface of the titanium–steel hybrid structures is 600 °C.