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以扫描电镜为主,配合X-射线能谱仪,透射电镜及电子衍射,对40CrNiMo等五种低合金钢的过热过烧断口进行了观察分析。从中发现,钢的过热石状断口大多表现为沿高温奥氏体晶界发生的沿晶延性断裂。在40CrNiMo等三种钢中,这种石状断口是由小球状MnS造成的,在30CrNi2MoV钢中,则是由薄片状VC造成的。在40CrNiMo钢中,还发现由沿一定结晶学平面析出的更为细小的球状MnS造成的穿晶断裂小平面。45CrNiMoV钢的过烧断口表明,钢的过烧是以沿晶熔化为其本质特征的,同时,在熔化部分形成β—SiO_2和Mn_3O_4等氧化物相。
Scanning electron microscopy, with X-ray energy dispersive spectroscopy, transmission electron microscopy and electron diffraction, 40CrNiMo other low alloy steel overheating and overfire fracture were observed and analyzed. It was found that the steel overheated stone fractures are mostly along the ductile fracture along the grain boundaries of high temperature austenite. In 40CrNiMo other three kinds of steel, the stone-like fracture is caused by the small spherical MnS, in the 30CrNi2MoV steel, it is caused by the lamellar VC. In 40CrNiMo steels, transgranular fracture facets caused by the finer spherical MnS precipitated along certain crystallographic planes were also found. Overheating fracture of 45CrNiMoV steel shows that the overburning of steel is characterized by the intergranular melting and the formation of oxide phases such as β-SiO_2 and Mn_3O_4 in the melting part.