Quenching

Quenching means: The hot component is quickly immersed in a cool medium such as water or oil. This suppresses the transformation into a soft structure and instead you get hard martensite. When welding, there is a risk that the weld and the heat-affected zone cool too quickly and thus crack. This often happens with hard or high-strength steels if you don't control the heat. In practice, this means: When working with such steels, you have to slow down the cooling, for example by preheating or allowing slow cooling. Simply quenching the weld with water is usually the wrong way – it causes stresses and cracks.