INFLUENCE OF COLD ROLLING PROCESS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AISI 304 STEEL

The performed investigations concerned the influence of degree and temperature of deformation on the microstructure and mechanical properties of metastable austenite in 304 stainless steel after its strain-induced martensitic transformation. Samples of steel strip were cold-rolled within the degree of deformation from 20% to 70% and stretched at room and cryogenic temperature. The microstructure was observed by means of a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been found that in samples stretched at a temperature of -100C and -196C microstructure of the matrix displayed a considerable density of dislocations with lath areas of the martensite ’ and precipitations of carbides M23C6. Fractographic examinations permitted to determine the influence of the deformation temperature on the character of the fracture of investigated steel obtained during the decohesion of samples in a tensile test at room and cryogenic temperature. After cold rolling and tensile test at room temperature the samples have transcrystalline ductile fracture. However, after the plastic deformation at cryogenic temperature, ductile facture with characteristic smooth areas with traces of plastic deformation of the surface and numerous craters were observed.