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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。
In order to reduce the deformation of 30Cr3SiNiMoVA ultra-high strength steel shell caused by heat treatment, a deformation heat treatment (tempering → forming → tempering) process was proposed. It is found that the tensile strength of the material increases first and then decreases with the increase of the secondary tempering temperature. It is necessary to analyze the reason from the microscopic scale. The structure, morphology, size and location of the microstructure and precipitated carbide of the material after tempering, deformation and tempering at medium temperature were studied by transmission electron microscopy. It was found that the tempered sorbite was tempered after fermenting, in which ferrite retained lath martensite and precipitated M23C6 carbides inside. Temperatures after tempering, ferrite slats began to grow and merge, M23C6 carbide rapid growth. Distortion and dislocation caused by large deformation to promote the temperature of ferritic matrix began to precipitate carbides M6C superalloy, precipitation increased with increasing the number of tempering temperature, resulting in dispersion strengthening effect. When the tempering temperature exceeds 400 ℃, the rapid growth of alloy carbides, the dispersion effect weakened lead to a sharp decline in material strength.