Preheat/Post heat
When welding high hardenability steels control of the thermal cycle can prevent martensite formation
It is usual to preheat to temperatures between 100 and 150oC in a region up to 80mm either side of the weld
- helps to control cooling rate of material
- reduce this sufficiently to avoid martensite formation
Alternatively use a post weld heat treatment at higher temperature to temper the martensite (590-760oC)