Cryogenic Sub-Zero Treatment

Cryogenic deep freezing is a process to stabilize steel after hardening or welding. The workpiece is cooled to very low temperatures so the structure settles and retained austenite transforms into martensite. This makes the material harder and more wear-resistant, but it can also introduce stresses if you don't do it cleanly. When doing this, let the part slowly come back to room temperature, otherwise you risk cracks. For everyday workshop practice: only do it if the job really requires it, and then work with feel and patience.