Tear grid / Delta-ferrite network
A network-like residual delta-ferrite microstructure forming during solidification in high-alloy chromium-nickel steels, intended to prevent hot cracking during welding as a primary ferrite phase.
Tear grid / Delta-ferrite network is the fine ferrite network that forms during solidification of high-alloy chromium-nickel steels. It ensures that the material doesn't become too brittle during cooling and thus prevents hot cracking in the weld. If you don't get the structure right, it's usually due to the cooling or the composition of the filler material. Make sure the heat input is correct and the base material doesn't cool too quickly. When welding such steels, you have to ensure that enough ferrite remains in the structure, otherwise you'll have problems with cracks.