摘要
采用冷却-凝固状态图可以预测铸铁是按白口、灰口或麻口凝固。影响铸铁碳原子析出形式的因素有:合金因素、冷却速度及熔液的核心状况。与其它合金一样,铸铁的偏析也分宏观偏析和微观偏析。合金元素和工艺因素都会影响微观偏析。
It is favorable for Fe3C formation when the temperature of molten iron is higher than some critical point; and when the temperature is lower than some critical point, Fe3C is unstable, and tends to be spontaneously decomposed into Fe and C. Its critical temperature is influenced by chemical composition and some other factors. The heredity of cast irons includes conservation of structure information, composition heredity effect and conservation of physical properties features. Changing charging materials, using the charge consisted of assorted materials for melting, conducting target-hitting treatment, melt superheating, and so on are the ways to eliminate harmful effect of the heredity. Under the condition of the same temperature, the solvability of graphite in the melt, austenite and ferrite is lower than that of cementite; both the austenite-graphite eutectic reaction temperature and eutectoid reaction temperature are higher than those of austenite-cementite. Silicon is favorable for the graphite to precipitate, and for the transition from Fe-Fe3C metastable system into Fe-C stable system. All graphitizing elements decrease the metastable eutectic temperature, increase the stable eutectic temperature and enlarge their distance. The solidification diagram demonstrates the temperature-composition-structure relationship under practical conditions, its characteristic boundaries can be shifted with the changes of melting process, melt treatment, cooling rate. Actually, all commercial cast irons solidify under the disequilibrium cooling conditions according to the solidification diagram and in accordance with the symbiotic region concept. Under the conditions of super cooling, it is possible that there is the hypo-eutectic dendrite (austenite) existing even in the structure of cast irons with eutectic or hyper-eutectic compositions.
出处
《现代铸铁》
CAS
2005年第3期25-32,共8页
Modern Cast Iron
关键词
铸铁
冷却-凝固状态图
偏析
cast irons
solidification
invisible factors
