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有一些粉末冶金(Cr,Mo)合金钢是由大量生产的Astaloy CrM粉末(3%Cr,0.5%Mo)制造的,并且烧结件具有不同的含氧量。对这些材料的显微组织与断口形态进行了分析。发现,氧一般是以Cr_2O_3颗粒析出,聚集在沿以前颗粒边界的平面上。这种空间形相(spatial configuration)控制着烧结颈塑性变形时的晶核形成与微小孔隙的间距,因此,含氧量增高时,韧性与疲劳强度都会大大减低。最后表明,用高温烧结可制成兼具高强度与韧性好的粉末冶金(Cr,Mo)合金钢。这是因为高温烧结可将这些材料的含氧量(质量分数)减小到<0.05%。
Some powder metallurgy (Cr, Mo) alloy steels are made from the mass produced Astaloy CrM powder (3% Cr, 0.5% Mo) and the sintered parts have different oxygen contents. The microstructure and fracture morphology of these materials were analyzed. It is found that oxygen is generally precipitated as Cr 2 O 3 particles and accumulates on the plane along the boundary of the former particles. This spatial configuration controls the formation of nuclei and the spacing of fine pores during plastic deformation of the sintered neck, so that as the oxygen content increases, the toughness and fatigue strength are greatly reduced. Finally, it has been shown that a powder metallurgy (Cr, Mo) alloy steel having both high strength and good toughness can be made by sintering at a high temperature. This is because high temperature sintering reduces the oxygen content (mass fraction) of these materials to <0.05%.