Strength and ductility data for Q235B steel from 20 ℃ to 950 ℃ was obtained from tension tests with smooth cylindrical specimens (SCSs). The strain rate sensitivity was studied by conducting Split-Hopkinson Tension Bar (SHTB) test and uniaxial tension test on SCSs, while the influence of stress triaxiality on ductility was revealed by conducting upsetting tests on cylinder specimens, tension tests on pre-notched cylinder specimens and torsion tests on SCSs. Slightly modified versions of the two Johnson-Cook (J-C) models describing flow stress and fracture strain are presented to characterize the properties of Q235B steel as function of strain rate, temperature and stress triaxiality. Corresponding model parameters were calibrated based on the test data and with the help of finite element calculation. The validity of the model parameters was verified by Taylor test.