Structure and Properties of Simulated HAZ Regions of T24 Steel

Abstract

This diploma thesis deals with thermal simulation of individual parts of the HAZ in T24 steel. Mechanical properties and microstructure of simulated parts of the HAZ were compared with real homogeneous T24 weldments in the as-welded state and after PWHT at 740 °C for 1 hour. The thermal simulation of the CG HAZ was accompanied by total dissolution of minor phases, which formed during the quality heat treatment, except for the primary TiX. This was followed by coarsening of austenite grains. Decomposition of austenite resulted in the formation of bainite/martensite. Hardness in the CG HAZ exceeded the value of HV 10 = 350 and impact energy was significantly lower than the minimum required value (40 J). PWHT at 740 °C was accompanied by intensive precipitation and recovery of the matrix. After PWHT both hardness and impact energy values complied with requirements. The results indicate that if we wish to prevent unacceptable hardening of the CG HAZ in homogeneous T24 welds the application of PWHT is necessary.