Effect of post-weld heat treatment on the evolving properties of P355NL1

This paper reports the effects of Post-Weld Heat Treatment (PWHT) on the evolving properties of the fine-grain carbon alloy steel P355NL1. The plates used were welded using the Gas Metal Arc Welding (GMAW) method and PWHT was performed using a laboratory furnace. After PWHT, three dissimilar cooling media were used to cool the samples. The media used are air, water and the last sample was left in the furnace to cool down. There was a control sample wherein the plate did not undergo any PWHT. Different characterization techniques were employed to analyze and determine the properties of the samples. Optical microscope was used for microstructural analysis and to determine the grain size. The hardness profiling was done on a Vickers hardness tester and Intron Universal tensile testing was employed to determine the yield strength of the samples. The major findings from this study are highlighted as follows: The post weld heat treatment decreased the hardness properties of the samples that were cooled in the air and inside the furnace, but increased hardness value was noticed for the sample cooled in water. The ultimate tensile strength properties of the sample had shown some improvement for the water-cooled plate; the furnace and air-cooled samples however decreased in terms of their tensile strength. The yield strength properties of the samples revealed similar findings: where that of the water-cooled sample had increased; while those of the furnace- and air-cooled samples had decreased. Although the morphology of the sample structures revealed different concentrations of darker (pearlite) and lighter (ferrite) grains in the base metal, the overall study showed that there were no significant changes in the microstructure, however, the cooling media employed can be recommended as required for tailored applications.