Calcium is used to improve the machinability of many stainless steel grades without significantly affecting corrosion resistance.
These grades combine the following characteristics:
- Improved machinability compared to normal grade. 10-50% improvement in productivity depending on grade and component
- Can be applied to austenitic, martensitic and PH grades, for example 304, 316, 420, 431, 17-4 PH
- No significant effect on corrosion resistance (unlike conventional free-cutting, high sulphur grades)
One of the major disadvantages for all stainless steels compared to carbon and alloy steels is their machinability. This is particularly true for the austenitic type where the high work hardening rate leads to difficulty in producing chips during machining. Machining rates are lower and tool wear is higher than for carbon and alloy steels. High levels of sulphur can be used to improve machinability in grades like 303 and 416. However, this reduces the corrosion resistance and weldability. Calcium treated steels contain a sulphur level at the higher end of the range for the normal grade, typically 0.015/0.030%. Calcium at very low levels < 0.001% produces modified non-metallic inclusions in the steel matrix which make it easier to produce chips in machining and lowers tool wear. The treatment is mostly applied to bar products but can also be applied to plate. Stainless steel mills typically use brand names to promote the improved machinability, for example IMCO, MAXIVAL, ROLDAMAX, PRODEC and UGIMA,
All sectors where machined components are used.