【摘要】 为减小热处理导致超高强度钢30Cr3SiNiMoVA壳体变形,提出了形变热处理(调质→成型→中温回火)工艺。发现材料抗拉强度随二次回火温度的升高出现先增加后减小的现象,有必要从微观尺度分析其原因。利用透射电子显微镜研究该材料在调质、变形、中温回火后的微观组织及析出碳化物的结构、形貌、尺寸、位置等。研究发现调质后的组织为回火索氏体,其中铁素体保持板条马氏体形貌,内部有M23C6合金碳化物析出。中温回火后,铁素体板条开始长大合并,M23C6型碳化物迅速长大。大变形产生的畸变及位错促使中温铁素体基体开始析出M6C型高温合金碳化物,随着升高回火温度析出数量增多,产生弥散强化作用。当回火温度超过400℃时,合金碳化物迅速长大,弥散效果减弱导致材料强度急剧下降。更多还原

【Abstract】 30Cr3SiNiMoVA( hereafter 30Cr3) was processed by an alternative technique named thermomechanical treatment including quenching and tempering,cold rolling and re-tempering at mid-temperature to avoid severe distortion. It is found that the tensile strength of the re-tempered 30Cr3 steel first increases and then decreases with the re-tempering temperatures increasing. The microstructure,morphology,precipitated carbide’s size and location in the steel were investigated by transmission electron microscope( TEM). The results show that the microstructure is tempered sorbite after the quenching and tempering,alloy carbide particle M23C6 with a size about100-200 nm is precipitated in the interior of lath ferrite in the tempered stage. During the re-tempering stage at mid-temperature,ferrite began to broader accompanied by M23C6 growth with the increasing tempering temperature. The observation of TEM shows the strength increasing is resulted from the precipitation of more stable M6C alloy carbide during the re-tempering below 400 ℃,whereas the strength decreasing is a consequence of the dramatic grown of M6C carbide size and quantity above 400 ℃.更多还原