Heat-affected zone property diagrams for a grade 100 microalloyed steel

Abstract

The microhardness variations and microstructural alterations in the heat-affected zone (HAZ) of a grade 100 steel, microalloyed with titanium, niobium, and vanadium were examined for a range of heat inputs from 0.3 to 2.5 kJ/mm. The results of the precipitate dissolution analysis and weld thermal analysis were used to establish HAZ property diagrams and qualitatively explain grain size and microhardness profiles across the HAZ for different heat input values. The relative width of the coarse-grained HAZ (CGHAZ) increased and the grain coarsening temperature decreased with decreasing heat input, although the amount of grain growth decreased with decreasing heat input. Detailed microstructural examination using a transmission electron microscope (TEM) coupled with nanohardness measurements showed that the CGHAZ was not 100% martensite even at a low heat input of 0.5 kJ/mm, while the micro- and macrohardness values suggested a “fully martensitic” structure. Microhardness testing also revealed that the maximum HAZ hardness was in the CGHAZ at some distance from the fusion line, as opposed to being adjacent to the fusion line.