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对30CrMnSiA,38Cr,30CrNi_2MoV,4Cr_9Si_2等四种合金钢进行了电子显微镜及普通金相方法的研究,研究结果表明这些钢种中的奥氏体晶粒长大过程应该分成四个阶段更为合理。其中在第二阶段发生的晶体学取向相近的晶粒团通过彼此间相邻的小角界的消失合并成大晶粒的过程是造成混晶长大的原因。这种混晶中的大晶粒和多边形化以后形成的奥氏体粗晶不同,它对常规力学性能没有明显不利影响,氮化铝也不能有效的控制它的形成。研究中发现在30CrMnSiA和38Cr这两种钢中,合金碳化物M_(23)C_6是奥氏体优先形核的非自发核心,它在珠光体中分布的取向择优和不均匀性是造成晶体学取向相近的小晶粒团形核长大并在随后合并成大晶粒,出现混晶的原因。控制混晶产生的关键是在于控制这些合金碳化物的分布。
Electron microscopy and ordinary metallographic methods were used to study the four alloy steels, 30CrMnSiA, 38Cr, 30CrNi_2MoV and 4Cr_9Si_2. The results show that the austenite grain growth in these steels should be divided into four stages. In the second stage, the crystal grains with similar crystallographic orientation are merged into large grains through the disappearance of the small boundary between adjacent small grains, which is the reason for the growth of mixed grains. The large grains in this mixed crystal are different from the coarse austenite formed after polygons, which has no significant adverse effect on the conventional mechanical properties and that aluminum nitride can not effectively control its formation. It is found that in the two steels 30CrMnSiA and 38Cr, the alloy carbide M 23 C 6 is a non-spontaneous nucleus preferentially nucleated by austenite. The preferential and inhomogeneous distribution of the carbides in the pearlite is the cause of crystallography Small grains with similar orientations grew into nuclei and then merged into large grains with mixed grains. The key to controlling mixed crystals is to control the distribution of these alloy carbides.