Abstract: By adjusting the quenching transfer time, the mechanical properties and the microstructure changes of 16CrSiNi steel after tempering were studied by using the universal test machine, metallographic microscope and scanning electron microscope. The results show that as the quenching transfer time increases from 10 s to 100 s, the tensile strength of the 16CrSiNi steel after tempering decreases from 1154 MPa to 676 MPa, the elongation increases from 16% to 28%, and the percentage reduction of area decreases from 68% to 52% and then to 70%. The microstructure experiences transformation from lath martensite to equiaxed blocky ferrite, then to coexistence of ferrite and tempered martensite, and further to pearlite, finally the microstructure is mainly composed of ferrite, tempered martensite and pearlite. The quenching transfer time has a significant effect on the tensile macroscopic fracture of the 16CrSiNi steel. With the increase of quenching transfer time, the fibrous area of the fracture gradually decreases, the radiation area and shear lip area increase, the fracture morphology changes from brittle fracture to ductile fracture. The microscopic fractures are mainly characterized by dimples. When the quenching transfer time is less than 30 s, the dimples are small and dense, while when over 30 s, the dimple size increases significantly. For the 16CrSiNi steel rods with a diameter of ϕ10.5 mm, the quenching transfer time shall be controlled within 30 s to ensure that the microstructure and properties are basically not affected.

Key words: 16CrSiNi steel, quenching transfer time, mechanical properties, microstructure