A Physical Simulation of Heat Affected Zone of Creep Resistant Steel: Microstructure and Mechanical Properties Analysis

The structural integrity of ASTM P92 steel welded joints is of concern due to the Type IV cracking associated with the heat-affected zone (HAZ). Two HAZ treatments were done on P92 steel using a Gleeble® 3500 thermo-mechanical simulator at 900°C (intercritical HAZ) and 950°C (fine-grained HAZ). Followed by post-weld heat treatment (PWHT) of the samples in two sets:: a conventional PWHT at 760°C for 2 hours followed by air cooling; or re-austenitisation at 1050°C for 40 minutes then air cooling, followed PWHT. After conventional PWHT, the HAZ simulated at 950°C had the lowest toughness (108J) than the base metal (130J). After the heat treatments, samples that underwent a 900°C HAZ simulation had higher Charpy toughness (improved from 130-208 ± 6J) and lower hardness (decreased from 234.4-222.3HV0.5) than those at 950°C. The microstructures had lath martensite with differing precipitate densities depending on the thermal treatment. Keywords: P92 steel, heat affected zone, post-weld heat treatment, precipitates