Microstructures and toughness in simulated coarse grain heat-affected zones of copper-bearing steel

Microstructures and toughness of simulated coarse grain heat-affected zone of hot continuously rolled copper-bearing steel were investigated using physical simulation. The results showed that brittlement is easy to happen in the region of CGHAZ with slower thermal cycles (t(8/5)>= 45s). Granular bainite transformed from austenite led to brittlement. The dimensions of granular martensite and austenite (M-A) constituents are main factors influencing the impact toughness. There is no visible effect on the toughness when the dimensions of M-A constituents are less than I p in. However, the toughness decreases greatly once the dimensions exceed I P in. Therefore, decreasing the dimensions of M-A constituents by controlling weld heat input will do good to improve the impact toughness of copper-bearing steel.