Fe-Cu-Ni-Al-Mn钢中强化相复合析出机制的研究

发布时间：2018-08-04 21:23

【摘要】：随着现代工业和科学技术的不断发展,提高钢铁材料的强度成为了备受关注的课题。析出强化是提高钢铁材料强度的一种重要的方式。Fe-Cu钢时效过程中析出了纳米级的富Cu相,具有明显的析出强化效果。当Fe-Cu钢中复合添加Ni、Al、Mn元素时,Fe-Cu-Ni-Al-Mn钢中含有多元强化相,析出强化更明显,研究复合析出强化,对发展高强度钢有重要意义。本文采用维氏显微硬度(VHN)、光学显微镜(OM)、高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等测试手段,结合析出动力学,分析了Fe-1.5 wt.%Cu、Fe-1.5 wt.%Cu-2 wt.%Mn、Fe-1.5 wt.%Cu-3 wt.%Ni-1wt.%Al和Fe-0.95 wt.%Cu-3.13 wt.%Ni-1.09 wt.%Al-1.87 wt.%Mn四种钢中强化相的析出过程,研究了钢中富Cu相和Ni(Al,Mn)相共存时,影响强度的规律和机理。主要研究结果和结论如下:(1)Mn影响钢中富Cu相析出的规律和机理。等温时效过程中,Fe-Cu-Mn钢比Fe-Cu钢先达到硬度峰值,过时效阶段Fe-Cu-Mn钢的硬度下降速率大于Fe-Cu钢,表明添加Mn元素加速了析出强化的进程;APT结果显示,时效初期,Fe-Cu-Mn钢比Fe-Cu钢中富Cu相的数量密度高,时效后期,Fe-Cu-Mn钢比Fe-Cu钢中富Cu相的尺寸大,数量密度低,表明Mn元素的添加加快了富Cu相的形核、长大和粗化速度。Mn降低了富Cu相与基体之间界面能,增加了形核的化学成分驱动力,因此提高了富Cu相的形核速率;Mn元素的添加改变了Cu的化学位,加速了Cu的扩散速率,从而加速了富Cu相的长大和粗化。随着时效时间的延长,富Cu相会由bcc结构向fcc结构转变,此转变过程中会产生缺陷,大量的Mn原子偏聚于缺陷处,富CuMn相会发生调幅分解,最终形成了片状富Cu相和片状富Mn相的交替排列的层状结构。(2)NiAl相影响钢中富Cu相析出的规律和机理。等温时效过程中,Fe-Cu-Ni-Al钢峰值硬度比Fe-Cu钢高,硬度峰值持续时间长,Ni、Al的加入增强了析出强化效果。相同的时效时间,Fe-Cu-Ni-Al钢中析出相的尺寸均小于Fe-Cu钢,数量密度均大于Fe-Cu钢。Ni、Al的加入提高了时效初期富Cu相形核率,富Cu相与α-Fe基体的界面为NiAl相的形核提供了质点和能量,形成了富Cu相在核心,NiAl相包裹在其外侧的核壳结构,这种结构使得析出相比较稳定,不易长大和粗化,从而保持良好的析出强化效果。随着时效时间的进一步延长,富Cu相和NiAl相发生了分离,显微硬度下降。(3)时效过程中,Fe-Cu-Ni-Al-Mn钢中首先析出了球形的富NiAlMnCu团簇,随着时效时间的延长,富NiAlMnCu团簇分解为富Cu相和Ni(Al,Mn)相,而且这两个析出相相互依存。Fe-Cu-Ni-Al-Mn钢时效过程中析出相的演化过程为:富NiAlMnCu团簇?Ni(Al,Mn)相和富Cu相。不论是Mn的加入,还是Ni,Al的加入都加速了富Cu相的形核,只是,Mn的加入促进了富Cu相的长大和粗化,Ni,Al的加入在一定程度上抑制了富Cu相的长大和粗化,因此四种钢形核速度依次为:Fe-Cu-Ni-Al-MnFe-Cu-Ni-AlFe-Cu-MnFe-Cu;长大速度依次为:Fe-Cu-MnFe-CuFe-Cu-Ni-AlFe-Cu-Ni-Al-Mn;粗化速度为:Fe-Cu-MnFe-CuFe-Cu-Ni-Al-MnFe-Cu-Ni-Al。(4)钢中两相区富Cu相和Ni(Al,Mn)相的析出特征。Fe-Cu-Ni-Al-Mn钢淬火后不可避免存在残余奥氏体,500℃时效1 h后,用APT观测到残余奥氏体中没有析出相,马氏体和马氏体/残余奥氏体界面处均有析出相的析出,马氏体中靠近界面处有一层析出贫化区。界面处析出相的等效半径和间距均大于马氏体中的析出相,界面处富Cu相和NiAl相中Cu,Ni和Al的含量均大于马氏体中的富Cu相和NiAl相,而且界面处富Cu相和NiAl相的分离趋势要大于马氏体,这是因为界面处存在大量缺陷,促进了析出相的长大,使得界面处和马氏体中的析出相处于长大的不同阶段。
[Abstract]:With the continuous development of modern industry and science and technology, improving the strength of steel materials has become a subject of great concern. The precipitation strengthening is an important way to improve the strength of steel materials..Fe-Cu steel has been precipitated in the process of aging of Cu and has obvious precipitation strengthening effect. When Fe-Cu steel is added, Ni, Al, Mn elements are added together Fe-Cu-Ni-Al-Mn steel contains multiple intensification phases and precipitation strengthening is more obvious. It is of great significance for developing high strength steel. In this paper, Vivtorinox microhardness (VHN), optical microscope (OM), high resolution transmission electron microscopy (HRTEM) and atomic probe chromatography (APT) are used to analyze Fe-1.5. The precipitation process of wt.%Cu, Fe-1.5 wt.%Cu-2 wt.%Mn, Fe-1.5 wt.%Cu-3 wt.%Ni-1wt.%Al and Fe-0.95 wt.%Cu-3.13 wt.%Ni-1.09 wt.%Al-1.87 wt.%Mn four kinds of steels is studied. The law and mechanism of the influence of the coexistence of the rich phase in the steel are studied. The main results and conclusions are as follows: (1) the precipitation of the rich phase in the steel is affected. In the process of isothermal aging, Fe-Cu-Mn steel reaches the peak of hardness first than that of Fe-Cu steel. The decrease rate of Fe-Cu-Mn steel in over aging stage is greater than that of Fe-Cu steel, which indicates that adding Mn element accelerates the process of precipitation strengthening. APT results show that the number density of Fe-Cu-Mn steel is higher than that of Cu phase in Fe-Cu steel at the early stage of aging, and the later period of aging, Fe-Cu-Mn, Fe-Cu-Mn. The size of Cu phase in steel is larger than that of Fe-Cu steel, and the number density is low. It shows that the addition of Mn elements accelerates the nucleation of the rich Cu phase. The growth and coarsening speed.Mn reduces the interfacial energy between the rich Cu phase and the matrix, increases the chemical composition driving force of the nucleation, thus increases the nucleation rate of the rich Cu phase, and the addition of Mn elements changes the chemical bit of Cu and accelerates the addition of Mn elements. The diffusion rate of Cu accelerates the growth and coarsening of the rich Cu phase. With the prolongation of the aging time, the rich Cu phase will change from the bcc structure to the fcc structure. The transition process will produce defects, a large number of Mn atoms are segregated at the defects, and the rich CuMn phase occurs in amplitude decomposition, and eventually forms the alternating layers of lamellar rich Cu and flaky Mn phase. (2) the law and mechanism of NiAl phase affecting the precipitation of rich Cu phase in steel. During isothermal aging, the peak hardness of Fe-Cu-Ni-Al steel is higher than that of Fe-Cu steel, the peak hardness duration is longer, the addition of Ni and Al strengthens the precipitation strengthening effect. The same aging time, the size of the precipitated phase in Fe-Cu-Ni-Al steel is less than that of Fe-Cu steel, and the quantity density is greater than Fe-Cu. The addition of.Ni and Al increases the nucleation rate of the rich Cu phase in the early aging period. The interface between the rich Cu phase and the matrix of the alpha -Fe provides the particle and energy for the nucleation of the NiAl phase, forming the core shell structure of the rich Cu phase in the core and the NiAl phase in its outer side. This structure makes the precipitate relatively stable, not easy to grow and coarsening, thus maintaining good precipitation enhancement effect. With the further prolongation of the aging time, the rich Cu phase and NiAl phase were separated and the microhardness decreased. (3) in the aging process, the rich NiAlMnCu clusters were first precipitated in Fe-Cu-Ni-Al-Mn steel. With the prolongation of the aging time, the rich NiAlMnCu clusters were decomposed into rich Cu phase and Ni (Al, Mn) phase, and the two precipitates were interdependent on.Fe-Cu-Ni-. The evolution of the precipitated phase in the aging process of Al-Mn steel is: the rich NiAlMnCu cluster? Ni (Al, Mn) Xiang Hefu Cu phase. Whether the addition of Mn, Ni, and Al accelerates the nucleation of the rich Cu phase, but the addition of Mn promotes the growth and coarsening of the rich Cu phase, and therefore, to a certain extent, inhibits the growth and coarsening of rich Cu. Therefore, four kinds of additives have been suppressed to some extent. The velocity of steel nucleation is Fe-Cu-Ni-Al-MnFe-Cu-Ni-AlFe-Cu-MnFe-Cu, and the growth rate is Fe-Cu-MnFe-CuFe-Cu-Ni-AlFe-Cu-Ni-Al-Mn in turn, and the coarsening speed is: the precipitating characteristic of Cu phase and Ni (Al, Mn) phase in Fe-Cu-MnFe-CuFe-Cu-Ni-Al-MnFe-Cu-Ni-Al. (4) steel will inevitably have retained austenite after the quenching of.Fe-Cu-Ni-Al-Mn steel. 50 After 1 h aging at 0 C, there are no precipitates in the retained austenite with APT. The precipitation of martensite and martensite / retained austenite is precipitated, and there is a layer of precipitation and dilution in martensite near the interface. The equivalent radius and spacing of the precipitated phase at the interface are all larger than the precipitates in martensite, and the interface is rich in Cu and Cu, N in the NiAl phase. The content of I and Al is greater than that of the rich Cu and NiAl phases in martensite, and the separation trend of Cu and NiAl phases at the interface is greater than that of martensite. This is due to the existence of a large number of defects at the interface, which promotes the growth of the precipitate phase and makes the precipitation in the interface and martensite get along with the different stages of growth.
【学位授予单位】：上海大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.1

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