Microstructures and Properties in Simulated Heat-Affected Zones of 685 MPa Grade Copper-Bearing Steel

The experiments were carried out upon the determination of SH-CCT diagrams and the characteristic of microstructures and properties in simulated coarse grain heat-affected zone of hot continuously rolled copper-bearing steel under single and double welding thermal cycle using physical simulation. The results show that with the help of SH-CCT diagram of copper-bearing steel, it is proposed to choose t8/5 ranging from 7s to 35s during welding. The copper-bearing steel has a narrow range of heat-input and brittlement is easy to happen in the region of CGHAZ with higher heat-input. Granular bainite transformed from austenite leads to brittlement. Softening starts when t8/5 is more than 7s. The dissolution of ɛ-Cu and coarse lath bainite and more ferrite cause softening. Moreover, the impact toughness decreases dramatically and obvious brittlement happens in the intercritical region of CGHAZ. The reason is pearlite formed on the interface of original austenite and coarse granular bainite, which can reduce the impact toughness.