Transformed austenite
The microstructure resulting from high-temperature austenite via thermal transformation processes during cooling. The exact phase distribution depends decisively on the respective cooling rate.
Austenite is a high-temperature phase in steel that, depending on the cooling rate, transforms into different microstructures such as ferrite, pearlite, or martensite. If you cool too quickly during welding, hard, crack-sensitive martensite can form, which robs the weld of its toughness. To ensure the austenite transforms cleanly and no hard microstructure forms, you need to control the cooling—so keep an eye on the heat input and don't let the weld cool too fast. For critical steels, it helps to let the weld cool slowly after welding, for example, with a heat treatment.