采用淬火变形膨胀仪测量高铬铸铁在不同冷却速度下的膨胀曲线,研究了加热温度和冷却速度对高铬铸铁热处理冷却过程中其微观组织转变的影响规律。结果表明,在较低冷速下微观组织为典型的亚共晶白口铸铁组织形态,由初生奥氏体的低温转变组织和共晶体组成;在冷却速度为3℃/s时开始出现马氏体组织,并优先在共晶奥氏体区域大量形成;随着冷却速度的增加,马氏体量逐步增多,在10℃/s冷速下为连续的马氏体基体组织和共晶碳化物。二次碳化物在初生奥氏体区大量弥散析出,而在共晶奥氏体区近共晶碳化物周边位置没有二次碳化物生成,远离共晶碳化物的区域有少量二次碳化物的析出。随着加热温度的升高和冷却速度的增加,初生奥氏体和共晶奥氏体区的珠光体片层间距均逐渐减小。
Expansion curves of high chromium cast iron were measured at different cooling rates on an instrumented thermal simulator DIL805A and effeets of heating temperature and cooling rate on microstructure of the high chromium cast iron was researched.The results show that cooling rate is the key factor which determines structural transformation of high chromium cast iron during cooling process while the effect of heating temperature is relatively mild.The microstructure of the cast iron shows typical microstructure of hypoeutectic white cast iron at lower cooling rates,which consists of structure transformed by primary austenite at lower temperature and eutectic.At continuous cooling rate of 3℃/s martensite begins to appear,a large amount of which is formed earlier in the eutectic austenite.The amount of martensite increases gradually with the increasing of continuous cooling rate,the microstructure is composed of martensite and eutectic carbides at continuous cooling rate of 10 ℃/s.A large number of secondary carbides are precipitated in the primary austenite region while no one is observed around eutectic carbides and some is precipitated away from eutectic carbides in the eutectic austenite region.With the increasing of heating temperature and continuous cooling rate,the interlamellar spacing of pearlite decreases gradually in the primary austenite region and eutectic austenite region.
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