Heat treatment

1100 to 900°C 
Slow cooling in furnace or in thermo insulating material.

770 to 840°C 
Slow cooling in furnace. Hardness after annealing: max.280 Brinell

600 to 650°C 
Slow cooling in furnace. To relieve stresses set up by extensive machining or in tools of intricate shape. After through heating, hold in neutral atmosphere for 1 to 2 hours.

1150 to 1230°C 
Oil, salt bath (500-550°C), dry air blsast. Upper temperature range for parts of simple shape, lower for parts of complex shape. 
For cold working tools also lower temperatures are of important for higher toughness. Soaking time after heating up the whole section of a workpiece 80 seconds minimum is required for dissolving sufficient carbides. 
Maximum soaking time 150 seconds to avoid detriments by over soaking. In practice instead of soaking time the time of exposure from placing the workpiece into the salth bath after preheating until removing ( including the stages of heating to the specified surface temperature and of heating to the temperature throughout the whole section) is used. 
Vacuum hardening is also possible. The time in the vacuum furnace depends on the relevant workpiece size and furnace parameters. 

Slow heating to tempering temperature immediately after hardening/time in furnace: 1 hour for every 20mm of workpiece thickness, but not less than 2 hours/ air cooling( minimum holding time:1 hour) 
1 st tempering and 2 nd tempering to desired working hardness 
3 rd tempering for stress relieving. 
30-50°C below highest tempering temperature 
Obtainable hardness after tempreing:64-66HRC