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本文应用电镜薄膜技术,观察30CrMnSiNi2A超高强度钢在淬火与回火过程中马氏体的精细结构,发现此钢淬火后存在位错型和孪晶型两类马氏体。低温回火的断裂韧性值,主要取决于马氏体的分解产物的性质和形态,而与挛晶马氏体是否存在无关。均匀分布的χ-Fe_2C的消失以及脆性的Fe_3C相的择优偏析,导致400℃退火钢的严重脆化。550℃回火后出现高温回火脆性,除了合金元素和合金碳化物在晶界富集外,晶内的微细沉淀相对滑动位错的钉扎,都对它的断裂韧性下降有贡献。回火温度进一步升高,沉淀相球化,基体回复,使断裂韧性再次上升。
In this paper, the microstructure of 30CrMnSiNi2A ultra-high strength steel during quenching and tempering was observed by using the electron microscope film technique. It was found that there were two types of martensite such as dislocation and twin after quenching. The fracture toughness value of low-temperature tempering depends mainly on the nature and morphology of the martensite decomposition product, but not on the presence of tetrapotous martensite. The disappearance of homogeneously distributed χ-Fe 2 C and the preferential segregation of brittle Fe 3 C phase lead to severe embrittlement of annealed steel at 400 ℃. After tempering at 550 ℃, high temperature temper brittleness occurs. In addition to the enrichment of alloying elements and alloy carbides in the grain boundaries, the pinning of the fine precipitates in the crystal relative to sliding dislocations all contribute to the decrease of fracture toughness. Tempering temperature is further increased, precipitation phase of the ball, the matrix recovery, the fracture toughness rise again.