【摘要】：隨著現(xiàn)代工業(yè)和科學技術的不斷發(fā)展,提高鋼鐵材料的強度成為了備受關注的課題。析出強化是提高鋼鐵材料強度的一種重要的方式。Fe-Cu鋼時效過程中析出了納米級的富Cu相,具有明顯的析出強化效果。當Fe-Cu鋼中復合添加Ni、Al、Mn元素時,Fe-Cu-Ni-Al-Mn鋼中含有多元強化相,析出強化更明顯,研究復合析出強化,對發(fā)展高強度鋼有重要意義。本文采用維氏顯微硬度(VHN)、光學顯微鏡(OM)、高分辨透射電鏡(HRTEM)和原子探針層析技術(APT)等測試手段,結(jié)合析出動力學,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四種鋼中強化相的析出過程,研究了鋼中富Cu相和Ni(Al,Mn)相共存時,影響強度的規(guī)律和機理。主要研究結(jié)果和結(jié)論如下:(1)Mn影響鋼中富Cu相析出的規(guī)律和機理。等溫時效過程中,Fe-Cu-Mn鋼比Fe-Cu鋼先達到硬度峰值,過時效階段Fe-Cu-Mn鋼的硬度下降速率大于Fe-Cu鋼,表明添加Mn元素加速了析出強化的進程;APT結(jié)果顯示,時效初期,Fe-Cu-Mn鋼比Fe-Cu鋼中富Cu相的數(shù)量密度高,時效后期,Fe-Cu-Mn鋼比Fe-Cu鋼中富Cu相的尺寸大,數(shù)量密度低,表明Mn元素的添加加快了富Cu相的形核、長大和粗化速度。Mn降低了富Cu相與基體之間界面能,增加了形核的化學成分驅(qū)動力,因此提高了富Cu相的形核速率;Mn元素的添加改變了Cu的化學位,加速了Cu的擴散速率,從而加速了富Cu相的長大和粗化。隨著時效時間的延長,富Cu相會由bcc結(jié)構向fcc結(jié)構轉(zhuǎn)變,此轉(zhuǎn)變過程中會產(chǎn)生缺陷,大量的Mn原子偏聚于缺陷處,富CuMn相會發(fā)生調(diào)幅分解,最終形成了片狀富Cu相和片狀富Mn相的交替排列的層狀結(jié)構。(2)NiAl相影響鋼中富Cu相析出的規(guī)律和機理。等溫時效過程中,Fe-Cu-Ni-Al鋼峰值硬度比Fe-Cu鋼高,硬度峰值持續(xù)時間長,Ni、Al的加入增強了析出強化效果。相同的時效時間,Fe-Cu-Ni-Al鋼中析出相的尺寸均小于Fe-Cu鋼,數(shù)量密度均大于Fe-Cu鋼。Ni、Al的加入提高了時效初期富Cu相形核率,富Cu相與α-Fe基體的界面為NiAl相的形核提供了質(zhì)點和能量,形成了富Cu相在核心,NiAl相包裹在其外側(cè)的核殼結(jié)構,這種結(jié)構使得析出相比較穩(wěn)定,不易長大和粗化,從而保持良好的析出強化效果。隨著時效時間的進一步延長,富Cu相和NiAl相發(fā)生了分離,顯微硬度下降。(3)時效過程中,Fe-Cu-Ni-Al-Mn鋼中首先析出了球形的富NiAlMnCu團簇,隨著時效時間的延長,富NiAlMnCu團簇分解為富Cu相和Ni(Al,Mn)相,而且這兩個析出相相互依存。Fe-Cu-Ni-Al-Mn鋼時效過程中析出相的演化過程為:富NiAlMnCu團簇?Ni(Al,Mn)相和富Cu相。不論是Mn的加入,還是Ni,Al的加入都加速了富Cu相的形核,只是,Mn的加入促進了富Cu相的長大和粗化,Ni,Al的加入在一定程度上抑制了富Cu相的長大和粗化,因此四種鋼形核速度依次為:Fe-Cu-Ni-Al-MnFe-Cu-Ni-AlFe-Cu-MnFe-Cu;長大速度依次為:Fe-Cu-MnFe-CuFe-Cu-Ni-AlFe-Cu-Ni-Al-Mn;粗化速度為:Fe-Cu-MnFe-CuFe-Cu-Ni-Al-MnFe-Cu-Ni-Al。(4)鋼中兩相區(qū)富Cu相和Ni(Al,Mn)相的析出特征。Fe-Cu-Ni-Al-Mn鋼淬火后不可避免存在殘余奧氏體,500℃時效1 h后,用APT觀測到殘余奧氏體中沒有析出相,馬氏體和馬氏體/殘余奧氏體界面處均有析出相的析出,馬氏體中靠近界面處有一層析出貧化區(qū)。界面處析出相的等效半徑和間距均大于馬氏體中的析出相,界面處富Cu相和NiAl相中Cu,Ni和Al的含量均大于馬氏體中的富Cu相和NiAl相,而且界面處富Cu相和NiAl相的分離趨勢要大于馬氏體,這是因為界面處存在大量缺陷,促進了析出相的長大,使得界面處和馬氏體中的析出相處于長大的不同階段。
[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.
【學位授予單位】：上海大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG142.1

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