摘要
Gleeble-1500D thermal simulator was used to simulate the thermal cycle of different welding processes in C-Mn steel. The toughness of steel matrix and heat-affected zone （HAZ） was investigated, and the microstructure and inclusion were characterized as well. The results showed that the welding process has a great influence on the microstructure in HAZ. When t8/5 （the cooling time from 800 to 500℃ ） value of the welding process is less than 111 s, the microstructure in HAZ is mainly bainite/Widmanstatten in spite of the addition of rare earth. However, when t8/5 value is more than 250 s, there are a lot of acicular ferrites in the steel containing rare earth, while the main microstructures are grain boundary ferrite and bainite/Widmanstatten in the steel without rare earth. The impact toughness of the HAZ at ambient temperature first decreases and then increases with the increase in t8/5 value. The impact toughness is the worst when t8/5 value is 111 s. Rare earth can improve the impact performance of HAZ at ambient temperature, especially when t8/5 value of the welding process is 445 s. After the rare earth treatment, the cooling rate of forming acicular ferrite is about 0.5-7.5 ℃/s. Acicular ferrite can form even during the welding process with larger t8/5 value up to 600 s in rare earth-treated steel.
Gleeble-1500D thermal simulator was used to simulate the thermal cycle of different welding processes in C-Mn steel. The toughness of steel matrix and heat-affected zone （HAZ） was investigated, and the microstructure and inclusion were characterized as well. The results showed that the welding process has a great influence on the microstructure in HAZ. When t8/5 （the cooling time from 800 to 500℃ ） value of the welding process is less than 111 s, the microstructure in HAZ is mainly bainite/Widmanstatten in spite of the addition of rare earth. However, when t8/5 value is more than 250 s, there are a lot of acicular ferrites in the steel containing rare earth, while the main microstructures are grain boundary ferrite and bainite/Widmanstatten in the steel without rare earth. The impact toughness of the HAZ at ambient temperature first decreases and then increases with the increase in t8/5 value. The impact toughness is the worst when t8/5 value is 111 s. Rare earth can improve the impact performance of HAZ at ambient temperature, especially when t8/5 value of the welding process is 445 s. After the rare earth treatment, the cooling rate of forming acicular ferrite is about 0.5-7.5 ℃/s. Acicular ferrite can form even during the welding process with larger t8/5 value up to 600 s in rare earth-treated steel.
基金
Acknowledgements The authors are grateful for the support of the National Natural Science Foundation of China （NSFC） （Grant Nos. 51804229, 51604198 and 51474163）, the Wuhan University of Science and Technology （WUST） Backbone Training Project of Scientific and Technological （Grant No. 2017xz001） and the Open Fund of Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education （Grant No. FMRUlab17-6）.
