Microstructure and precipitated phase changes of A710 copper precipitation strengthening steel under the action of welding thermal cycling

Objective This paper aims to explore influence of different thermal simulation processes on microstructure, properties and precipitated phase of A710 copper precipitation strengthening steel. Methods Through welding thermal simulation tests under different processes, effects of heating and cooling processes of welding on microstructure and precipitated phase of A710 copper precipitation strengthening steel were simulated. Hardness distribution of specimen was measured with a Vickers hardness tester, and low-temperature toughness under different parameters was measured with an impact testing machine. The changes in the matrix microstructure and precipitated phases of thermal simulation specimen were observed with equipments such as metallography and transmission electron microscopy. Results The results show that after welding thermal cycle, hardness of the matrix decreases with the increase of t_8/5 and the decrease of peak temperature. Metallographic structure changes from upper bainite and granular bainite to granular bainite and ferrite. After the action of welding thermal cycle, copper precipitation phase dissolves at the position of original precipitation phase and reprecipitates, and the number of precipitated phases varies with the change of peak temperature. Moreover, the size of reprecipitated nanophase decreases compared with precipitated phases in the base metal, and the morphology has changed. Conclusion Under the effect of welding thermal cycling in different processes, microstructure and properties of base metal and precipitated phases have different changes.