RECENT TRENDS IN THE PRODUCTION AND USE OF HIGH-STRENGTH STAINLESS-STEELS

The strengthening mechanisms of steels have been well studied widely, and are the same of the mechanisms in high strength stainless steel, e.g., grain refinement by the thermomechanical treatment, solid solution strengthening by lattice distortion through the addition of alloying element, transformation strengthening by martensite transformation, work hardening by the formation of strain induced martensite through rolling, strain aging hardening by the tempering or aging of martensite, and precipitation strengthening of intermetallic compounds which are coherent with the matrix. These strengthening mechanisms relate to the thermomechanical treatment of the steel as well as the chemical composition. Various high strength stainless steels are produced by a combination of these mechanisms, and have peculiar mechanical properties depending on the final microstructure. Recently, the need for various other properties than high strength, e.g., ductility, toughness and weldability has been recognized. Work-hardened stainless steel, for example, has greater strength than SUS301 and is used for ID blades (inner diameter blade for cutting Si single crystal), etc. The additional strength of the steel results from solid solution hardening and strain aged hardening. Martensite stainless steel and ultra microduplex stainless steel were also developed and are now in use fitting a variety of needs. The former steel has high toughness with more than 1 700 N/mm2 tensile strength, and the latter has good strength and ductility but is not softened on welding.