Influence of Microstructure Evolution on Reheat Cracking Behavior of T23 Steel Weld Joint

摘要

In this work, T23 steel was treated by two thermal cycles, to simulate the second heating process in coarse grained heated affected zone (CGHAZ) of weld. Meantime, the effect of microstructure evolution on reheat cracking sensitivity was investigated by using strain-to-fracture (STF) tests. It was found that the second thermal cycle procedure could alter the grain boundary network of prior austenite grain boundaries (PAGBs) of CGHAZ. The extent of boundary evolution was dependent on the peak temperatures of the applied thermal cycles. Kernel average misorientation (KAM) and fracture surface observation was applied to analyze plastic deformation and fracture mode after STF tests. The relevancy between the grain boundary character and reheat cracking sensitivity were analyzed quantitatively using fractal analysis. The results showed that the zigzag configuration of the PAGBs with larger fractal dimension could prevent the reheat crack from propagating and reduce reheat cracking susceptibility. The increase of the peak temperature of the second thermal cycle would lead to grains coarsening and straight grain boundaries, which improve the reheat cracking sensitivity for the reheated CGHAZ in T23 steel.