Transformation kinetics
Transformation kinetics describes how the microstructure of steel changes during heating and cooling. It affects the strength and hardness of the weld.
Physico-Chemical Mechanism of Action
Transformation kinetics describes how the microstructure of metals changes over time and temperature, especially in iron-carbon alloys. During heating or cooling, different crystal forms (microstructural phases) can form or transform. These processes depend on the speed and the temperature profile.
Metallurgical Relevance & Welding Risks
Transformation kinetics has a big impact on the mechanical properties of the weld. Cooling too fast can lead to glass-hard martensite, which causes high stress buildup and cracks. Cooling too slow can result in a fine microstructure with higher toughness but possibly reduced strength characteristics.
Workshop Practice & Action Instructions
To get the transformation kinetics right, you have to precisely control welding parameters like temperature and cooling rate. For steels with high carbon content (e.g., HSS), a slow cooling after welding is needed to avoid glassy microstructures. For lower carbon content, fast cooling can be fine to boost hardness and strength.