Abstract: HSLA-100 is a precipitate strengthened low alloy steel that is often used for its good combination of high yield strength and impact toughness. During initial fabrication and service, multipass welds and weld repairs often need to be made. Much work has been done to determine the properties in the heat affected zone (HAZ) for HSLA-100 but less results are available to understand microstructural evolution and resultant properties of the HAZ under multi-pass welding conditions. Variations in the HAZ hardness were observed and were shown to be associated with compositional banding. These differences between the enriched solute and depleted solute bands lead to differences in hardenability. Dictra simulations of the bands demonstrated that carbon preferentially segregates to the regions of higher concentrations of substitutional elements increasing the hardness. This difference in composition also leads to changes in the transformation temperatures, leading to significant differences in the microstructure. HAZ simulations showed that the hardness increases from the base metal (260 HV) to the fine grained HAZ (340 HV). The impact toughness was equal or higher than the BM, except for the coarse grained HAZ (CGHAZ), which was slightly below the acceptable minimum for the BM. However, the CGHAZ does not degrade in toughness after multiple thermal cycles. There is progressive phase transformation in the intercritical region, as seen with multiple weld passes, which increases the hardness and decreases the toughness. However, the fully transformed samples still maintained excellent impact toughness and high hardness.
Authors: Jonah E. Duch and John N. DuPont
Keywords: Welding, Multipass Welding, Diffusion Simulation