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本文通过光学显微镜、X射线衍射、电子显微镜(透射和扫描电镜)、紧凑拉伸等试验方法研究了55SiMnMo钢在正火状态下的上贝氏体形态,回火转变以及对其机械性能的影响。该钢经900℃,0.5h奥氏体化后空冷所出现的上贝氏体形态由铁素体和30—35%富碳奥氏体片层相间组成。未发现有碳化物存在。这种形态的上贝氏体会发生回火转变,析出碳化物的回火转变温度约为400℃,此时金相组织变为由铁素体、碳化物和3—5%奥氏体组成,作者暂称这种组织为回火贝氏体。在发生回火转变时,裂纹扩展速率(da/dN)随回火温度增加而增加,在400℃时达最大值;断口的扫描电子金相从准解理型过渡到解理型。
In this paper, the microstructure, tempering transformation and mechanical properties of 55SiMnMo steel in normalizing condition were studied by means of optical microscope, X-ray diffraction, electron microscope (transmission and scanning electron microscope) and compact tensile test . The steel after 900 ℃, 0.5h austenitizing the upper bainite morphology appears by the ferrite and 30-35% carbon-rich austenite sheet phase composition. No carbides were found. This form of upper bainite tempering transformation occurs, the precipitation of carbide tempering temperature is about 400 ℃, then the microstructure becomes ferrite, carbide and 3-5% austenite, The authors tentatively call this organization tempered bainite. The crack growth rate (da / dN) increases with the increase of tempering temperature and reaches the maximum at 400 ℃. The scanning electron microstructure of the fracture transitions from quasi-cleavage to cleavage.