Influence of die and temperature on microstructure and properties of 1 500 MPa thermoforming steel

This paper studies the effects of mould shape and heating temperature on microstructure and resilience of thermoforming steel of 1 500 MPa gradeutilizing optical microscope, scanning electron microscope, and unidirectional tensile test. Results show that the microstructure of the initial cold-rolled steel sheet is mainly composed of ferrite and pearlite. With the increase of heating temperature, the strength of the thermoforming steel sheet increases significantly at first and then decreases gradually. The optimal heating temperature is 860 ℃. Due to the deformation of the U-shaped part during thermal forming, the tensile strength of the sides is lower than that of the bottom part, which will cause the work piece rebound. According to experiments, U-shaped parts rebound most slightly at 860 ℃ with an average rebound angle of 16.6. In conclusion, thermoforming steel with optimum properties can be produced by adopting U-shaped mould when the material temperature reaches 860 ℃.