压力对挤压铸造E级钢低温冲击韧性的影响

Effect of Pressure on Low-temperature Impact Toughness of Grade E Cast Steel Prepared by Squeeze-casting

本工作采用挤压铸造工艺制备了不同压力下的E级钢调质态试样,并进行了低温夏比冲击试验和布氏硬度检测,研究了挤压压力对E级钢低温冲击韧性的影响规律,并用光学显微镜(OM)和扫描电镜(SEM)对显微组织和冲击断口进行了观察。研究结果表明,当挤压压力在0~150 MPa范围内,E级钢的40℃低温冲击韧性先增大后减小。在挤压压力为38 MPa时,E级钢低温冲击韧性最佳,比金属型重力铸造E级钢提高65.4%,硬度仅降低了6.17%。进一步提高压力,冲击吸收功呈线性下降,硬度小幅上升。显微组织分析表明,随着挤压压力的提高,E级钢晶粒明显细化,铁素体含量增多,有利于E级钢冲击韧性的提高。另一方面,由于过冷度的提高,E级钢在压力为60 MPa时析出了魏氏组织,导致低温冲击韧性显著下降。断口分析表明,金属型重力铸造E级钢低温冲击断口为准解理形貌,而采用38 MPa挤压铸造的E级钢即使在40℃低温下,断口仍存在大量细密的韧窝,属于韧性断裂。

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.