FORMABILITY OF STAINLESS-STEEL

The forming behavior of austenitic stainless steels (types 201, 301, a nd 304) and ferritic stainless steels (types 437, 439, 444, and 468) w as investigated. The tensile behavior and the forming-limit diagrams ( FLDs) for these grades were determined. The ferritic alloys behave sim ilarly to plain carbon steels and are relatively insensitive to small variations of strain rate and temperature. The formability of the aust enitic alloys is influenced greatly by martensitic transformation duri ng straining. The fraction of martensite transformed as a function of strain was found to be very sensitive to temperature, which, in turn, depends on the strain rate at typical testing rates (10(-3) to 10(-1)/ s), At low rates (when the specimen remains near room temperature), th e formability of the austenitic alloys is markedly improved by transfo rmation strengthening. The enhancement of formability is largest on th e biaxial side of the FLD, because the fraction martensite transformed was found to depend on the absolute thickness strain, which is maximi zed in the balanced biaxial strain state.