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采用透射电子显微镜详细观察了中碳铬镍钼钒钢大型锻件层状断口上呈条带状无光泽棱面的微观特征,对断面上萃取的各种第二相进行选区电子衍射和电子探针分析。发现这种棱面上有微细圆球α-MnS、薄膜或树枝状VC沉淀,还分布着沿热加工方向排列,以SiO_2为主体的片状Si、Mn复合氧化物,以及第Ⅰ类MnS夹杂。层状断口认为是由于钢的初始奥氏体晶界上的元素严重偏析,导致各种第二相晶间沉淀,从而引起晶界脆化。提出这种断口本质上类似“石状-冰糖”断口。层状断口能够显著降低钢的横向拉伸塑性,并稍许减低其冲击韧性。
Transmission electron microscopy was used to observe the microscopic features of banded matte facets on the layered fracture of medium-carbon chromium-nickel-molybdenum-vanadium steel forgings in detail. The selected second phases extracted from the sections were subjected to electron diffraction and electron probe analysis. It is found that there are microspheres α-MnS, thin films or dendritic VC precipitates on this facets, and also flake Si, Mn complex oxides mainly composed of SiO 2 and inclusions of type I MnS are arranged along the direction of thermal processing. . The lamellar fracture is believed to be due to the severe segregation of elements on the initial austenite grain boundaries of the steel, resulting in the precipitation of various second phase grains, causing grain boundary embrittlement. Proposed this fracture is essentially similar to “stone - rock sugar” fracture. Layered fractures can significantly reduce the transverse ductility of steel and slightly reduce its impact toughness.