Bainitic microstructure formation

Bainite forms during cooling in the intermediate temperature range when the transformation of austenite to ferrite and cementite doesn't proceed properly. In welding, this indicates that the cooling time doesn't match the material. If you cool too fast, you get martensite with crack risk; if too slow, the structure becomes soft and tough. For practice: keep the interpass temperature within limits and adjust cooling to the steel, then the structure stays clean and you avoid hard, crack-prone spots.