Austenite
The face-centered cubic crystal structure of iron at high temperatures, which can dissolve a large amount of carbon. It is non-magnetic and serves as the foundation for stainless steels.
Austenite is a microstructural phase that forms at high temperatures and, in some steels, remains stable at room temperature due to alloying elements. When welding stainless steels, it's crucial that austenite doesn't transform into martensite – this happens with too rapid cooling and makes the material hard and prone to cracking. So weld with controlled heat input and don't let the part cool down suddenly. However, cooling too slowly is also not good, then the grain becomes coarse and the material loses toughness. Keep the interpass temperature in check and choose the heat input so that you stay in the austenitic range.