带有马氏体渗碳体层的Fe-Nb合金中温内耗

通过对A_1点以下温度的氢-苯混合气流处理,使研究的Fe-Nb合金丝试样渗入0.5%C.淬火样品的金相观测表明,～40μm厚的样品表面渗碳层为马氏体,渗碳层下部为α-Fe相.用NHI-12型真空K(?)氏摆测量淬火试样的室温内耗和淬火-变形试样的室温-中温内耗发现:淬火样品有一高度达1×10~(-2)的45℃附近峰;而在变形样里则代之出现峰更高(1.7～2.0×10~(-2))的45～60℃内耗峰,还出现两个小内耗峰,即～300℃峰和～235℃峰.分析可知,它们分别是在实验(试样存在很强的宏观组织应力)条件下,马氏体bct晶格中C原子扩散运动峰、亚稳碳化物溶解过程SKK峰和变形α-Fe相的SK...     

Nb--Ti微合金化热冲压成形用钢的微观组织与力学性能

利用扫描电镜(SEM)、透射电镜(TEM)对Nb-Ti微合金化热成形钢的微观组织进行观察,采用Kahn撕裂试验对其韧性和撕裂性能进行了研究,并利用Thermo-Calc热力学软件对其析出行为和析出粒子成分进行分析计算.结果表明,含碳质量分数0.13%的热成形钢在Nb-Ti微合金化后的组织为马氏体,和传统热成形钢(22MnB5)相比其奥氏体晶粒、板条块和板条束都得到细化,并且其抗拉强度达到1500 MPa以上,撕裂强度和单位面积裂纹扩展能分别达到1878 MPa、436 kN·m-1.在950℃奥氏体化时,Nb-Ti合金元素几乎全部以析出粒子形式存在,能有效阻止奥氏体晶粒长大.另外在基体中主要存在两种析出物,一种是尺寸在100~200 nm的Ti(C,N);另一种是纳米级别的钛铌复合碳氮化物,能有效强化基体,提高强度.     

Reverse-transformation austenite structure control with micro/nanometer size

To control the reverse-transformation austenite structure through manipulation of the micro/nanometer grain structure, the influences of cold deformation and annealing parameters on the microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. The samples were first cold-rolled, and then samples deformed to different extents were annealed at different temperatures. The microstructure evolutions were analyzed by optical microscopy, scanning electron microscopy (SEM), magnetic measurements, and X-ray diffraction (XRD); the mechanical properties are also determined by tensile tests. The results showed that the fraction of stain-induced martensite was approximately 72% in the 90% cold-rolled steel. The micro/nanometric microstructure was obtained after reversion annealing at 820-870℃ for 60 s. Nearly 100% reversed austenite was obtained in samples annealed at 850℃, where grains with a diameter ≤ 500 nm accounted for 30% and those with a diameter >0.5 μm accounted for 70%. The micro/nanometer-grain steel exhibited not only a high strength level (approximately 959 MPa) but also a desirable elongation of approximately 45%.     

Stress-strain partitioning analysis of constituent phases in dual phase steel based on the modified law of mixture

A more accurate estimation of stress-strain relationships for martensite and ferrite was developed, and the modified law of mixture was used to investigate the stress-strain partitioning of constituent phases in dual phase (DP) steels with two different martensite volume fractions. The results show that there exist great differences in the stress-strain contribution of martensite and ferrite to DP steel. The stress-strain partitioning coefficient is not constant in the whole strain range, but decreases with increasing the true strain of DP steel. The softening effect caused by the dilution of carbon concentration in martensite with the increase of martensite volume fraction has great influence on the strain contribution of martensite. The strain ratio of ferrite to martensite almost linearly increases with increasing the true strain of DP steel when the martensite volume fraction is 22%, because martensite always keeps elastic. But the strain ratio of ferrite to martensite varies indistinctively with the further increase in true strain of DP steel above 0.034 when the martensite volume fraction is 50%, because plastic deformation happens in martensite. The stress ratio ofmartensite to ferrite decreases monotonously with increasing the true strain of DP steel whether the martensite volume fraction is 22% or 50%.     

多晶 CuZnAl 合金马氏体变体群结构及其生长过程研究

利用金相动态观察及Ｘ－射线衍射研究了多晶Ｃｕ－１８．５２Ｚｎ－６．３７Ａｌ合金Ｍ１８Ｒ马氏体变体群组态及其生长过程。多晶Ｃｕ－Ｚｎ－Ａｌ合金一个晶粒内多以一个变体群为主。每群由Ａ、Ｂ、Ｃ、Ｄ四个变体组成，形成ＡＣ型矛头状、ＡＢ平行及ＡＤ分叉型三种组态。变体群形成过程中，马氏体变体的消长及变体内小孪晶结构的形成等动力学特征反映了马氏体的热弹性及相变应力、应变自调节。在相变热循环中，变体群内形成大量非常稳定的残留马氏体。     

Cu-Zn-Al合金马氏体在稳定化过程中的反常浮凸

利用电阻温度曲线测量、记忆效应测量、金相观察、Ｘ射线衍射等方法研究了Ｃｕ－１４．５％Ｚｎ－７．１％Ａｌ合金热弹性马氏体稳定化过程．发现在马氏体稳定化过程中除马氏体晶格常数ａ与ｃ增大，ｂ减小，ａ／ｂ→０．８６６，β→９０°外，尚存在马氏体浮凸、逆向记忆效应及马氏体电阻增大等现象．根据马氏体相变晶体学对上述现象进行了分析，认为马氏体稳定化是一个类似于贝氏体转变的扩散型切变转变，它可看成是β１→Ｍ转变的继续．     

中碳铁基合金中马氏体的特征

应用电子及光学显微术对45钢及55钢中的马氏体形态、亚结构等特征进行了研究。结果表明,中碳铁基合金中马氏体的形貌是以板条状为主的混合马氏体形态,其典型的马氏体惯析面为{225}_y,随着奥氏体中碳浓度微区的波动,亦可发现{111}_y马氏体。{225}_y马氏体中的亚结构随马氏体的碳含量高低而变,有的以位错为主,有的则以孪晶为主。作者认为这种{225}_y马氏体是一种形态介于板条状和片状马氏体之间的一种特殊过渡形态马氏体。     

掺硼Ni_3Al-Fe合金中的马氏体转变

利用透射电子显微技术测定了掺硼加铁Ni_3Al合金中NiAl(β相)与Ni_3Al(γ′相)之间的取向关系,NiAl马氏体的晶体结构。分析了马氏体亚结构,其中孪晶马氏体的孪生关系为{111}〈112〉_(fct)或{101}〈101〉_(bct);另一类亚结构出现0(1/2)(1/2)超反射,说明加铁NiAl金属间化合物在淬火过程中所形成的马氏体可以进一步有序化。     

Fe-Mn-Si基合金中ε马氏体逆相变的内耗

利用音频内耗仪测试了Ｆｅ－Ｍｎ－Ｓｉ基形状记忆合金热诱发马氏体、一般应力诱发马氏体和热－机械训练后的应力诱发马氏体的逆相变过程．结果表明，热诱发马氏体的逆相变在４００～５００Ｋ完成；经训练后的应力诱发马氏体逆相变开始温度与热诱发马氏体逆相变开始温度相近，但高于一般应力诱发马氏体的逆相变开始温度；一般应力诱发马氏体的逆相变温度低于热马氏体的逆相变温度，随应变量的增加，Ａｓ降低