压力对挤压铸造E级钢低温冲击韧性的影响

The grade E cast steel specimens under different pressures prepared by squeeze-casting were quenched and tempered. The Charpy impact test at low-temperature were carried out and the Brinell hardness were tested. The effect of pressures on the low-temperature impact toughness of grade E cast steel were investigated. The microstructure and impact fracture were observed by optical microscopy(OM) and scanning electron microscopy(SEM). The experimental results show that the low-temperature impact toughness at 40℃ of grade E cast steel increases first and then decreases when the pressures are in the range from 0 MPa to 150 MPa. The low-temperature impact energy exhibits their optimal values when the pressure is 38 MPa, which is 65.4% higher than that of metal gravity casting, and the hardness is only reduced by 6.17%. With the further increase of pressure, the Charpy impact energy decreases linearly and the hardness increases slightly. Microstructure analysis shows that with the increase of pressure, the grains of grade E cast steel are refined significantly and the content of ferrite increase. That is beneficial to the impact toughness of grade E cast steel. In addition, because of the increase of degree of super-cooling, the Widmanstatten is precipitated at the pressure of 60 MPa. This leads to the decrease of low-temperature impact toughness. Impact fracture analysis shows that the fracture of grade E cast steel produced by gravity casting in metal mould is quasi-cleavage morphology. The specimens prepared by squeeze-casting at the pressure of 38 MPa still has a large number of fine dimples even at 40℃, which belongs to ductile fracture.