Abstract: Microstructure and mechanical properties of the large size 1Cr17Ni2 steel under two processes of conventional quenching and stress controlled quenching were analyzed by means of optical microscope (OM) , scanning electron microscope (SEM) , X-ray diffractometer(XRD), electronic universal testing machine and metal pendulum impact testing machine. The results show that the microstructure of the 1Cr17Ni2 steel treated by the two processes is composed of tempered martensite, δ ferrite, fine carbide and trace retained austenite, and the microstructure of which under the stress controlled quenching process is finer, while the content of residual austenite is relatively more. Moreover, the mechanical properties of the 1Cr17Ni2 steel treated by the two processes are excellent as the tensile strength, elongation and impact absorbed energy exceeding 1200 MPa, 13.5% and 31.2 J, respectively. The comprehensive mechanical properties of the 1Cr17Ni2 steel after stress controlled quenching and tempering at 360 ℃ is the best, the impact absorbed energy can reach 96.4 J, which is 46.2% higher than that of the conventional quenching and tempering at 360 ℃. Both tensile and impact fracture morphologies of the 1Cr17Ni2 steel show ductile-brittle fracture, and there are more dimples under the stress controlled quenching process.

Key words: 1Cr17Ni2 steel, large size, heat treatment process, microstructure and properties