Abstract: Taking 4 kinds of hot stamping steels with different strength grades as the object, the hot stamping quenching tests with different forming temperatures were carried out by using a Π-shaped molds in laboratory, and the influence of forming temperature on the microstructure, properties and dimensional accuracy of the hot stamping parts were studied. The results show that as the forming temperature decreases, the martensite content in the 600 MPa hot stamping parts decreases, and the martensite morphology transforms from blocky to granular, resulting in a gradual decrease in tensile strength. For the 1000 MPa and 1500 MPa hot stamping parts, ferrite appears in the microstructure when the forming temperature decreases to 700 ℃ and 650 ℃, respectively, and the mechanical properties undergo a significant reduction at 600 ℃. However, the microstructure of the 2000 MPa hot stamping parts maintains a fully martensitic under different forming temperatures, and the mechanical properties do not exhibit significant degradation. Comparing the springback data of the hot stamping parts with different strength grades at forming temperature of 700 ℃, it is found that the dimensional accuracy order of the parts is 1500 MPa>2000 MPa>600 MPa>1000 MPa. The variation pattern of phase transformation dilatometric amount is largely consistent with the springback pattern of the hot stamping parts.

Key words: hot stamping steel part, forming temperature, microstructure, properties, dimensional accuracy