Bainitic Substructure

Bainite forms when you don't fully cool the austenite but hold it in the intermediate stage. You get a fine structure of ferrite and carbides that is tough and hard. When welding, this means: if the cooling isn't right, the structure can form unevenly and you risk cracks in the weld metal. So make sure the heat input and cooling rate are right, then the structure stays clean and the weld joint holds.