In the present paper the influence of the temperature and strain rate on the stress strain behaviour of two different steels were investigated. Two microstructures were considered: pearlitic and austenitic. Tensile tests with the bearing steel 100Cr6 and the case hardening steel 20MnCr5 were accomplished at various temperatures. For this purpose the Ludwik equation was used to describe the stress-strain curve. The parameter of the constitutive equation was determined for each steel and microstructure. Especially for the austenitic state the parameters of the used material law were described as a function of the temperature.