Manganese Austenite Stabilization

Manganese stabilizes the austenitic structure in the weld. If you have too little manganese, the structure transforms to martensite at low temperatures, becoming hard and brittle and can crack. So make sure the filler material brings enough manganese, then the weld stays tough and won't crack. When cooling, you don't have to rush, but the exact values depend on the alloy, so you need to check the material data sheet.