Retained Austenite

After quenching, some austenite remains in the weld that didn't transform to martensite. It's softer than martensite and can cause dimensional changes because it behaves differently under heat than the rest of the structure. It also lowers the wear resistance of the weld. To avoid too much retained austenite, you need to cool in a controlled and rapid manner. Keep the cooling time in the critical range short, so no long insulation or slow cooling. This reduces the austenite content and makes the weld harder and more stable.