Effect of heat-input on austenite grain size in the heat-affected zone of HSLA-100 steel

The prior-austenite grain size in the heat-affected zones of single-pass butt welded joints in thick HSLA-100 steel plates was evaluated. The grain size was related with the temporal history of the location, which was obtained using an existing thermal model based on Gaussian heat source distribution for two different heat-input conditions. For a heat-input of 10 kJ/cm the grain size in the coarse grain heat-affected zone was 80 μm corresponding to a peak temperature of 1450 °C, but falls sharply to 40 μm within a distance of 0.5 mm from the fusion line. At a higher heat-input of 40 kJ/cm the grain size is 130 μm for the same peak temperature and the coarse grain heat-affected zone is 1.1 mm wide. The austenite grain size significantly influences the microstructure and properties of the heat-affected zone.