2800MPa级马氏体时效钢组织性能的研究

发布时间：2018-06-14 21:50

  本文选题：马氏体时效钢 + 显微组织　； 参考：《昆明理工大学》2017年硕士论文

【摘要】：马氏体时效钢早已经被广泛应用于航空航天等领域。尤其是在它进行过离子渗氮处理过后,其性能更加优越。作为超高强度钢的杰出代表,使用量呈现日益增加的趋势。但是目前研究者们探索的屈服强度高达2800 MPa的400级马氏体时效钢由于塑韧性太低,并且高含量的合金元素导致成本过高,且生产工艺较为复杂而并没有得到广泛的应用。因此探寻具有良好工艺性和力学性能的超高强度马氏体时效钢迫在眉睫。马氏体时效钢的强化机制有固溶强化、相变强化和析出强化,其中析出强化使强度的增加最具优势。强化元素主要有Ti、Al、Mo,对应析出相为Ni3Ti、NiAl、Ni3Mo、Fe2Mo,同等重量比的情况下,Ti和A1对强度贡献较大,但严重损害韧性。Co可以使得Mo元素在基体内易于形成过饱和固溶体,抑制位错回复,继而使析出相获得更多的形核位置,促进其细小均匀弥散析出,相对于Ti元素或A1元素的单独强化具有更好的强韧性配比。为了更好地了解马氏体时效钢的力学相关性能及合金元素特别是Co元素和Mo元素对2800MPa级马氏体时效钢力学性能的影响,本文设计制备了 9Co5Mo、14Co5Mo和14Co7Mo三种试验钢,研究了试验钢经不同热处理后的组织与力学性能,结果表明:(1)14Co5Mo再结晶温度也即是最佳固溶温度为820℃,在780℃以下固溶时,14Co5Mo试验钢遗留了部分锻态变形组织,未能完全再结晶,出现混晶。此外,试验钢14Co7Mo的再结晶完成温度则为840℃。(2)Co和Mo对试验钢的Ms点和Mf点有较大影响:相比9Co5Mo,较高的Co含量使14Co5Mo试验钢的Ms点和Mf点分别提高71℃和91℃;相比9Co5Mo,较高的Mo、Ti含量使14Co7Mo试验钢Ms点大幅降低192℃,导致其Mf点低于室温。(3)9Co5Mo试验钢和14Co5Mo试验钢峰时效温度为480℃,14Co7Mo试验钢峰时效温度为500℃,其中,在峰时效时,9Co5Mo试验钢抗拉强度和屈服强度分别为2103MPa和2052MPa,对应断后伸长率、断面收缩率和冲击功分别为9.0%、63%和41J而14Co5Mo试验钢抗拉强度和屈服强度分别为2190MPa和2121MPa,对应断后伸长率、断面收缩率和冲击功分别为10.5%、68%和44J;14Co7Mo试验钢抗拉强度和屈服强度分别为2765MPa和2677MPa,对应断后伸长率、断面收缩率和冲击功分别为6.0%、45%和15J。(4)试验钢14Co7Mo深冷后基体组织为板条马氏体;于500℃时效5h时,可见在基体上析出的短棒状金属间化合物,直径约为4nm,长度约为10nm,随着时效时间延长,金属间化合物进发生长大和粗化,时效时间达到100h后,直径约为20nm,长度约为35nm。(5)14Co7Mo的最佳热处理制度为14Co7Mo试验钢最佳热处理为840℃×1h油淬,-73℃×1h升温至室温,500℃×5h空冷,可在2800MPa强度级别获得较好的综合力学性能。
[Abstract]:Maraging steel has been widely used in aerospace and other fields. Especially after the ion nitriding treatment, its performance is more superior. As an outstanding representative of ultra-high strength steel, the usage is increasing day by day. However, the 400 grade maraging steel with yield strength up to 2800 MPA has not been widely used because of its low ductility and high content of alloying elements. Therefore, it is urgent to explore ultra-high strength maraging steel with good processing and mechanical properties. The strengthening mechanisms of maraging steel include solid solution strengthening, transformation strengthening and precipitation strengthening. The main strengthening elements are TiAL-AlN Mo.The corresponding precipitated phase is Ni3Ti-NiAl-Ni3Mo-Ni3Mo-Fe2Mo.When the same weight ratio, Ti and Al contribute greatly to the strength, but the severely damaged toughness. Co can make Mo easily form supersaturated solid solution in the base body and suppress dislocation recovery. Then more nucleation positions of precipitates are obtained, and the fine and uniform dispersion precipitates are promoted. Compared with the single strengthening of Ti or A1 elements, the ratio of strength and toughness is better. In order to better understand the mechanical properties of maraging steel and the effect of alloying elements, especially Co and Mo elements, on the mechanical properties of 2800MPa grade maraging steel, three kinds of test steels, 9Co5Mo-14Co5Mo and 14Co7Mo, were designed and fabricated. The microstructure and mechanical properties of the tested steel after different heat treatment were studied. The results showed that the recrystallization temperature of the steel was 820 鈩，

本文编号：2019068