MARTENSITIC STAINLESS STEELS

To produce martensite in a stainless steel, the alloy must be transformed from the austenite phase field. According to the equilibrium phase diagram, this means that they have restricted chromium levels within the range required to form the gamma loop where austenite exists. The gamma loop is the region between 800 and 1400 C and 0 and 12.7% Cr in Fig. 11. Since austenite only exists in this restricted region, the steel must be heated within this temperature range and quenched to room temperature

to form martensite. Martensitic stainless steels contain added carbon, which expands the gamma loop to allow higher chromium contents to be used. Because they can be heat treated, the martensitic stainless steels generally have higher strength than the austenitic and ferritic stainless steels. The martensitic stainless steels are listed below:

403 Select quality for highly stressed parts

410 General-purpose martensitic stainless steel

414 Ni added for improved corrosion

416 Higher P and S for improved machinability

416Se Se added for improved machined surfaces

420 Higher C for increased strength

420F Free machining with higher P and S

422 Mo, V, and W added for increased strength and toughness

431 Higher Cr, Ni added for improved corrosion resistance

440A Highest Cr, C added for increased hardness

440B Highest Cr, more C added for increased hardness/toughness

440C Highest Cr, highest C for increased hardness/toughness

501 Low Cr, Mo added

502 Low C, Mo added

The compositional ranges for the martensitic stainless steels are shown in the aforementioned ASM table.

Bruce L. Bramfitt

International Steel Group, Inc.

Research Laboratories

Bethlehem, Pennsylvania

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