Delta Ferrite

The high-temperature cubic body-centered phase of iron that forms directly from the melt prior to transforming into austenite.

Delta ferrite is a microstructural constituent that can form during solidification of high-alloy steels. It is basically ferrite that forms at high temperatures before austenite forms. If you don't control it during welding, it can cause problems. Make sure cooling is not too slow, otherwise you get too much of it in the heat-affected zone. That makes the material brittle and crack-sensitive. Best to use filler material with low carbon content, then you'll have less trouble with the structure.

MetallurgieSchweißtechnik