Cryogenic treatment

Deep freezing converts residual austenite into martensite, making the steel harder and more wear-resistant. However, the material also becomes more brittle, and if you deep-freeze after welding, stresses can build up that lead to cracks—especially if the part wasn't stress-relieved before. It's important to bring the workpiece slowly back to room temperature, otherwise you risk damage. For welding itself, the treatment does nothing directly; it's more a matter for post-processing of tools.