Study on Microstructure and Mechanical Properties of 600 and 1500 MPa Boron Steels toward Process Regulation for Hot Stamping
摘要
This paper conducts U-shaped hot-stamping forming experiments using two differential strength grades of hot-stamping boron steels, 600 MPa and 1500 MPa, under the same process parameters within an integrated laser-welded tailored hot-stamping door ring. The comprehensive mechanical properties of the formed components using the same 1.5 mm thickness of steel sheet are comparatively studied through tensile tests, scanning electron microscopy (SEM), and EBSD. The differences are revealed through the analysis of microstructural evolution and fracture morphology to derive the optimized process parameters that can simultaneously meet the strength and plasticity standards for 600- and 1500 MPa-grade hot-forming components. The results show that with the content and size of martensite, comprehensive mechanical properties of 1500 MPa U-shaped hot-stamping component are increased with the increase in austenitization heating temperature and holding time. However, there is no clear pattern for 600 MPa U-shaped hot-stamping component. Within all the testing scenarios between austenitization heating temperature and holding time, optimal comprehensive mechanical properties are found under 930 °C austenitization heating temperature and 5-min holding time for 600 MPa U-shaped hot-stamped component. The thermal processing conditions of 930 °C/5 min, 950 °C/4 min, and 950 °C/5 min were demonstrated to be optimal parameters that concurrently meet the specified mechanical performance criteria for both grades of hot-stamping boron steels.