Study on the reheat crack sensitivity in simulated coarse-grained heat-affected zone of 7CrMoVTiB10-10 steel

The simulated coarse grain heat-affected zone (CGHAZ) of 7CrMoVTiB10-10(T24) steel were prepared by thermal simulation method, and the reheat crack (RC) sensitivity of CGHAZ in the range of 500-750 degrees C was evaluated by isothermal slow strain rate tensile test. The microstructure, fracture mode and the evolution of inter-granular and intra-granular precipitates were characterized by OM, EBSD, SEM, and TEM-EDS to clarify the RC formation mechanism. The results show that T24 steel CGHAZ is sensitive to RC at 660-750 degrees C, and the microstructure of CGHAZ is still a mixture of martensite and bainite with slight recovery within the test tem- perature range, but the precipitation of M23C6 at grain boundary increases significantly with the increase of temperature. The formation mechanism of RC in T24 steel is due to the precipitation of M23C6 at grain boundary, which provides more locations for the nucleation of micro-voids and causes the depletion of alloying elements near the grain boundary, thus directly weakening the grain boundary. In addition, the RC sensitivity of T24 steel is lower than that of T23 steel, which may be because T24 steel contains more Ti.