Strengthening of steels 30KhNMA and 30KhGSNA

Abstract

1. The strength of 20-mm medium-alloy construction steels can be improved 25 to 30% by decreasing the temperature and increasing the degree of deformation of quenched austenite to 60–70%, with subsequent transformation to martensite. The strengthing of steel probably takes place on account of a considerable breaking up of the structure, the occurrence of distortions and preferred orientation of the martensite. 2. Plastic deformation of over-chilled austenite starting from some degree of deformation (60–70%) increases the completeness of martensitic transformation during the hardening. 3. Deep chilling after TMT causes an additional strengthening of steel on account of the transformation of the residual austenite. 4. The use of intermediate hardening periods at deformation temperature and recrystallization of over-chilled austenite during TMT permits high-strength properties to be obtained at small intermittant deformations and considerably facilitates plastic deformation at lower temperatures. 5. Nonmartensitic products of isothermal austenitic transformation that occur during TMT have a negative Influence upon the mechanical properties of low-tempered steel, but to a lesser extent than upon the properties of steel which is heat-treated without deformation. Plastic deformation intensifies the isothermal transformation processes of austenite in the Ar' range.