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我们对40CrNiMo、20SiMn2MoV等几种中、低碳合金结构钢的不同热处理状态的断裂韧性K_(IC)及其与其它基本机械性能的关系进行了研究,得出:对于中碳合金结构钢40CrNiMo,随着强度的提高, 断裂韧性是降低的,符合一般的认为断裂韧性与强度是相互矛盾的看法;但对低碳合金结构钢20SiMn2MoV等,在低、中温回火范围内,K_(IC)值却是随强度的增加而增加,这类钢既具有较高的强度又具有较高的断裂韧性。我们对上述几种钢的断裂韧性试样断口进行了电子显微镜观察,研究了断裂韧性与电子断口特征的关系,对低碳合金结构钢具有高断裂韧性的原因,从电子断口特征方面进行了初步的分析与解释。研究表明:断裂韧性试样预制疲劳裂纹带之后有一个较平坦的延伸带,延伸带后紧接着是有一定宽度的韧窝带。它们的出现与否及宽窄,与材料的K_(IC)值有密切关系。延伸带W_s愈宽,材料K_(IC)值愈高。W_s与表明材料微区塑性的裂纹尖端曲率半径ρ或裂纹尖端张开量2V_c成正比,而K_(IC)~2≈4Eσ_s∈Eρ(=4Eσ_sV_C)。高强度低碳马氏体合金结构钢既具有高的σ_S,又有宽的延伸带W_s(即大的ρ和V_c),因而这种材料在具有高强度的同时,又具有高的断裂韧性。韧窝带W_D的宽度与计算的塑性区尺寸Y_P有相同的数量级,可以从W_D的大小来比较K_(IC)的高低。文中还描述了塑性稳定扩展和脆性失稳扩展的断口特征,并做了一些解释和说明。
We studied the fracture toughness K IC and its relationship with other basic mechanical properties of 40CrNiMo, 20SiMn2MoV and other medium and low carbon alloy structural steels under different heat treatment conditions. The results show that for medium carbon alloy structural steel 40CrNiMo, With the increase of strength, fracture toughness is reduced, in line with the general view that the fracture toughness and strength are contradictory; However, low-carbon alloy steel 20SiMn2MoV, in the low temperature tempering range, K IC value But increases with the increase of strength. Such steels not only have higher strength but also higher fracture toughness. We examined the fracture toughness of the above several kinds of steel by electron microscopy, studied the relationship between fracture toughness and electronic fracture characteristics, low fracture toughness of low carbon alloy structural steel, the characteristics of the electronic fracture preliminary Analysis and explanation. The results show that the fracture toughness specimen has a relatively flat extension zone after the prefabricated fatigue crack zone, and the extension zone is followed by a dimple zone with a certain width. Their presence or absence and width, and material K_ (IC) values are closely related. The wider the extension zone W_s, the higher the material K_ (IC) value. W_s is proportional to the radius of crack tip ρ or crack tip opening 2V_c, which indicates the plasticity of the material. K_ (IC) ~ 2≈4Eσ_s∈Eρ (= 4Eσ_sV_C). High-strength low-carbon martensitic alloy structural steels have both high σ_S and wide extensional zones W_s (ie, large ρ and V_c), so this material has high strength and high fracture toughness. The width of the dimple W_D is about the same order of magnitude as the calculated plastic zone size Y_P, and the level of K_ (IC) can be compared from the size of W_D. The article also describes the fracture characteristics of plastic stable expansion and brittle instability expansion, and gives some explanations and explanations.