| PWHT---Post Weld Heat Treatment is aimed at reducing the residual stresses resulting from manufacturing and welding. This treatment also exerts metallurgical changes influencing the properties of the base metal, weld metal and the heat-affected zone (HAZ).; The thermal cycle of the heat treatment after welding is governed in the codes by the heating rate, the holding temperature, the holding time and the cooling rate. There is a relatively good agreement among Codes and Standards about the maximum tempering temperature from 600°C to 680°C, while there is discordance about the holding time at the same tempering temperature. For medium carbon and low alloy steels, there is little information about PWHT below 600°C.; PWHTs at 550°C and 500°C with different holding times were performed for medium carbon 1043 and low alloy 4140 steels welded with the SMAW process. Hardness measurements of the base metal (BM), heat-affected zone (HAZ) and weld metal (WM) and microstructural examinations were done to correlate the steel properties with different PWHT parameters.; Both steels can be post weld heat treated at temperatures under 600°C. PWHTs at 550°C/4.0 hours and 500°C/15.0 hours produced similar results to these of recommended PWHTs at 600°C and 600°C. Tempering parameters based on diffusion coefficients are slightly conservative while those based on the Hollomon-Jaffe parameter are overly conservative. |
