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4 马氏体及铁素体或碳化物组织这类组织对亚共析钢来说是马氏体及铁素体,对过共析钢来说是碳化物及马氏体组织.马氏体和铁素体组织.因铁素体的来源不同,其形态也不同.若淬火温度低于Ac_3/高温下有未溶铁素体,冷却时按图1中V_1;的速度冷却.奥氏体完全转变为马氏体,铁素体被保留下来成为组织组成物之一.若加热温度高于Ac_3,高温组织为单相奥氏体,冷却时以图1中V_4的速度冷却,也就是生产中有时采用的预冷淬火,即出炉后在空气中预冷一定时间,再淬入介质中快冷(相当于图1中V_5).但因在空气中预冷时间过长,使淬入介质之前已从奥氏体中析出铁素体,再淬入介质后剩余的奥氏体完全转变为马氏体.由于铁素体形态不同,所以这类组织可能有图4所示的三种形态.第一种是如图4a所示的块状铁素体加马氏体,铁素体是未溶的白色块状,其分布仍然保留淬火前沿轧向呈带状分布.第二种如图4b所示的条网状铁素体加马氏体.由于冷却不足,淬火时首先沿奥氏体晶界析出呈网状分布的铁素体,冷至M_s点时,过冷奥氏体发生马氏体转变,生成低碳马氏体.在b图中铁素体为白色网条状,明显可见沿奥氏体晶界分布的特点;图中还有极少量的针状铁素体.第三种是兼有前两种形态的铁素体,即既有未溶的块状铁素体,又有析出的条网状铁素体,如图4c 所示.图?
4. Martensite and Ferrite or Carbide Tissue These types of organizations are martensite and ferrite for hypo-eutectoid steels and carbide and martensite for hypereutectoid steels. Martensite And ferrite.For different ferrite source, its morphology is also different.If the quenching temperature is lower than Ac_3 / high temperature undissolved ferrite, cooling at the speed of V_1 in Figure 1. The rate of austenite Completely transformed into martensite, ferrite is retained to become one of the organizational composition.If the heating temperature is higher than Ac_3, the high-temperature structure of single-phase austenite, cooling time to V_4 in Figure 1 cooling rate, that is, production In the pre-cooling quenching sometimes used, that is, after pre-cooling the air in the oven for a certain period of time, and then quenched into the medium fast cooling (equivalent to V_5 in Figure 1) However, due to precooling time in the air is too long, so quenching medium Prior to precipitation of ferrite from austenite, and then quenched into the medium after the remaining austenite completely transformed into martensite. Due to the different ferrite morphology, so these organizations may have the three forms shown in Figure 4 The first is massive ferritic plus martensite as shown in Figure 4a, the ferrite being an undissolved white lump, the distribution of which still retains the quenching frontal rolling Ribbon distribution.The second kind of network as shown in Figure 4b martensite ferrite.As a result of insufficient cooling, quenching, the first along the austenite grain boundary precipitation was ferrite ferrite distribution, cooling to M_s Point, the martensite transformation of undercooled austenite, the formation of low-carbon martensite in Figure b ferrite is a white net, clearly visible along the austenite grain boundary distribution characteristics; A small amount of acicular ferrite.The third is both the first two forms of ferrite, that is, both undissolved massive ferrite, there are precipitated strip network ferrite, as shown in Figure 4c Show