Isothermal transformation diagram
A diagram that shows how the metal changes at constant temperature over time. It helps in selecting proper welding parameters.
Physical-Chemical Mechanism of Action
The isothermal time-temperature-transformation (TTT) diagram shows the phase transformations of a metal at constant temperature. It illustrates how the metal transforms from austenite into other structures, e.g., ferrite or martensite.
Metallurgical Relevance & Risks in Welding
The TTT diagram is crucial for selecting proper welding parameters, such as temperature and time. Incorrect settings can lead to unwanted microstructures, such as excessive martensite, which makes the metal hard and crack-prone. Too little martensite can reduce toughness.
Workshop Practice & Instructions
To use a TTT diagram correctly, you must set the specific temperature of the welding process and observe how the metal transforms over time. This requires a precisely calibrated welding machine and knowledge of the material being welded. For high-carbon steel, a TTT diagram can help find the right balance between hardness and toughness.