Martensite Start Temperature Calculation

Martensite forms when austenitic structure cools quickly. The temperature at which transformation starts depends heavily on steel composition, especially carbon content. The more carbon and alloying elements present, the lower this temperature drops. In welding, this means: if you cool the part too quickly, hard, brittle martensite forms, which tends to crack. Especially with higher-alloy steels, you must slow down cooling, e.g., by preheating or letting it cool slowly, to keep the structure tough.