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用金相、萃取相电子衍射、电子显微镜薄膜透射及选区电子衍射等方法研究了 Cr_(12)Mn_5Ni_4Mo_3Al 沉淀硬化不锈钢的时效强化机制。确定在400～600℃温度范围时效,马氏体和δ—铁素体都产生沉淀硬化。沉淀相有三种:体心立方α′相(a_0=2.91 )、六方结构 J 相(a_0=5.22 、C_0=10.8 )和 M_(23)C_6型碳化物。α′相据文献资料和化学分析推测,估计是(NiMn)Al 金属间化合物。J 相据初步化学分析,是富 Mo 含 Mn、Cr、Ni 等元素的金属间化合物,这可能是本合金中出现的一种新相。α′相在马氏体中析出是球形粒子,在δ—铁素体中析出是片状。J 相的形貌是片状。这两种相是主要强化相,但α′相的数量比 J 相多。合金强度与α′相粒度有明显的对应关系。当α′相的粒度一般在80～90 时马氏体的显微硬度最高;大于100(?)时,显微硬度明显下降。M_(23)C_6型碳化物的数量较少,对强度贡献不明显,但是其分布对冲击韧性影响很大。采用固溶—冷处理—时效三级工艺热处理,它主要在马氏体中析出,这时合金的韧性很好;若用固溶—调整处理—冷处理—时效四级工艺热处理,在调整处理时它沿奥氏体晶界析出,严重的成连续网状分布,使合金的韧性下降。在530℃以上温度时效过程中也发生马氏体向奥氏体逆转变。逆转变奥氏体的显微结构与残留奥氏体不同,前者遗留了马氏体的复杂位错网络结构.后者的位错通常是简单的线条。逆转变奥氏体的出现使宏观硬度 Rc 下降,但适量的奥氏体能改善合金的韧性,从而获得良好的综合机械性能。文中也讨论了α′相的沉淀机制,以及有待研究的问题。
The mechanism of aging strengthening of Cr 12 Mn 5 Ni 4 Mo 3 Al precipitation hardening stainless steel was studied by means of metallography, extraction phase electron diffraction, transmission electron microscopy and selected area electron diffraction. It is confirmed that the martensite and δ-ferrite both produce precipitation hardening at the temperature range of 400 to 600 ° C. There are three kinds of precipitated phases: body-centered cubic α ’phase (a_0 = 2.91), hexagonal phase J (a_0 = 5.22, C_0 = 10.8) and M_ (23) C_6 carbides. α ’phase According to the literature and chemical analysis speculated that the estimated (NiMn) Al intermetallic compounds. According to the preliminary chemical analysis of J phase, it is an intermetallic compound rich in Mo with Mn, Cr, Ni and other elements, which may be a new phase appearing in this alloy. The α ’phase precipitates in the martensite as spherical particles, and precipitates in the δ-ferrite as flakes. The shape of J phase is flaky. These two phases are the major strengthening phases, but the number of α ’phases is greater than that of J phase. There is a clear correspondence between the alloy strength and α ’phase size. When the α ’phase particle size is generally 80 ~ 90 when the martensitic microhardness highest; greater than 100 (?), The microhardness decreased significantly. The amount of M_ (23) C_6 carbides is small, which does not contribute significantly to the strength, but its distribution has a great influence on the impact toughness. Using solution-cooling treatment - aging three-stage heat treatment process, which is mainly precipitated in the martensite, then the toughness of the alloy is very good; if the solution treatment - conditioning - cold treatment - aging four-stage process heat treatment in the adjustment process Precipitation along the austenite grain boundaries, a serious continuous network distribution, the toughness of the alloy decreased. In 530 ℃ above the temperature aging process also occurred martensite reverse austenite. The microstructure of retrograded austenite is different from that of retained austenite, the former has a complex dislocation network structure of martensite, the latter usually has simple dislocations. The occurrence of retrograde austenite decreases the macroscopic hardness Rc, but the proper amount of austenite can improve the toughness of the alloy to obtain good comprehensive mechanical properties. The paper also discusses the precipitation mechanism of α ’phase, as well as the problems to be studied.