Heat-Affected Zone Softening
Heat-affected zone softening is the hardness drop in certain areas of the heat-affected zone due to softening processes in precipitation-hardened alloys. This can lead to a local decrease in tensile strength.
Physical-Chemical Mechanism of Action
Heat-affected zone softening occurs when precipitation-hardened alloys (such as steel) are softened during welding or cooling. This happens due to transformation of hardened martensite into a softer phase like austenite. Hardness drops because the metal becomes less glassy and its crystal structure changes.
Metallurgical Relevance & Risks in Welding
Softening can lead to a local decrease in tensile strength, affecting the mechanical properties of the weld. This increases the risk of cracking and fracture, especially if the HAZ is too large or cooling steps are irregular.
Workshop Practice & Action Guidelines
To minimize HAZ softening, ensure controlled cooling and avoid rapid temperature differences. Use suitable welding processes like gas welding or laser welding, which allow precise control of heat input. Be especially careful with steels with high carbon content (above 0.6 %), as they soften faster and may have a larger softening zone.