Martensite start temperature
The martensite start temperature is the point at which austenite transforms into martensite when cooling. It varies with carbon content and alloying elements. Temperatures too low result in glass-hard martensite susceptible to hot cracking.
Physicochemical Mechanism of Action
The martensite start temperature is the temperature at which austenite (a soft, soluble phase) spontaneously transforms into martensite (a hard, glassy phase) during cooling. This process is influenced by rapid cooling and the set carbon content of the alloy.
Metallurgical Relevance & Welding Risks
If cooling is too rapid (t8/5 < 5 s), glass-hard martensite forms, causing hot cracks and poor toughness. This can lead to fractures and failure of the weld.
Workshop Practice & Action Instructions
To minimize risks, cooling should be controlled. For high-carbon steels (e.g., HSS), slow cooling is necessary (t8/5 > 25 s). Use a suitable cooling medium or fan to regulate the temperature in the critical range.