Weld Metal Microstructure Hardness Prediction

The hardness of the weld metal mainly depends on the cooling rate and alloy composition. Rapid cooling can produce hard but brittle microstructures like martensite, while slow cooling gives softer material. In practice, if you know the cooling time (t8/5) and the base material, you can estimate the expected hardness well. You risk a too hard or too soft structure mainly if you don't control the heat input. So adjust preheating and interpass temperature to keep the microstructure in the desired range.