新型等温淬火工艺对球墨铸铁弯曲性能的影响

Bending property of ductile cast iron by a novel austempering treatment

采用光学显微镜以及扫描电镜研究了球墨铸铁经新型等温淬火工艺热处理后(890℃奥氏体化15 min,快冷到100~200℃左右,然后快速升温到220℃保温5、15、30、60、240、600 min不同时间,随后空冷)的显微组织对硬度和弯曲性能的影响。结果表明:随着等温时间的延长,硬度增加,弯曲强度增加,在220℃保温240 min处理的球墨铸铁具有最佳的显微组织以及弯曲性能;弯曲强度和挠度的提高与所获得的针状贝氏体和残留奥氏体数量,以及残留奥氏体的TRIP效应有关。

A novel concept for the austempering of ductile cast iron is developed. This includes austenizing at 890 ℃ for 15 min,then rapidly quenched range from 100 ℃ to 200 ℃,and austempering at 220 ℃ for 5,10,30,60,240 and 600 min,respectively. The effects of microstructure on hardness and bending properties during austempering are investigated by OM and SEM. It is shown that both hardness and bending strength were increased with increasing austempering time. The maximum bending strength with maximum bending deflection can be obtained after austempering at 220 ℃ for 240 min,which is attributed to formation of bainitic ferrite and retained austenite with TRIP effect.