本文選題：馬氏體時(shí)效鋼 + 顯微組織　； 參考：《昆明理工大學(xué)》2017年碩士論文

【摘要】：馬氏體時(shí)效鋼早已經(jīng)被廣泛應(yīng)用于航空航天等領(lǐng)域。尤其是在它進(jìn)行過(guò)離子滲氮處理過(guò)后,其性能更加優(yōu)越。作為超高強(qiáng)度鋼的杰出代表,使用量呈現(xiàn)日益增加的趨勢(shì)。但是目前研究者們探索的屈服強(qiáng)度高達(dá)2800 MPa的400級(jí)馬氏體時(shí)效鋼由于塑韌性太低,并且高含量的合金元素導(dǎo)致成本過(guò)高,且生產(chǎn)工藝較為復(fù)雜而并沒(méi)有得到廣泛的應(yīng)用。因此探尋具有良好工藝性和力學(xué)性能的超高強(qiáng)度馬氏體時(shí)效鋼迫在眉睫。馬氏體時(shí)效鋼的強(qiáng)化機(jī)制有固溶強(qiáng)化、相變強(qiáng)化和析出強(qiáng)化,其中析出強(qiáng)化使強(qiáng)度的增加最具優(yōu)勢(shì)。強(qiáng)化元素主要有Ti、Al、Mo,對(duì)應(yīng)析出相為Ni3Ti、NiAl、Ni3Mo、Fe2Mo,同等重量比的情況下,Ti和A1對(duì)強(qiáng)度貢獻(xiàn)較大,但嚴(yán)重?fù)p害韌性。Co可以使得Mo元素在基體內(nèi)易于形成過(guò)飽和固溶體,抑制位錯(cuò)回復(fù),繼而使析出相獲得更多的形核位置,促進(jìn)其細(xì)小均勻彌散析出,相對(duì)于Ti元素或A1元素的單獨(dú)強(qiáng)化具有更好的強(qiáng)韌性配比。為了更好地了解馬氏體時(shí)效鋼的力學(xué)相關(guān)性能及合金元素特別是Co元素和Mo元素對(duì)2800MPa級(jí)馬氏體時(shí)效鋼力學(xué)性能的影響,本文設(shè)計(jì)制備了 9Co5Mo、14Co5Mo和14Co7Mo三種試驗(yàn)鋼,研究了試驗(yàn)鋼經(jīng)不同熱處理后的組織與力學(xué)性能,結(jié)果表明:(1)14Co5Mo再結(jié)晶溫度也即是最佳固溶溫度為820℃,在780℃以下固溶時(shí),14Co5Mo試驗(yàn)鋼遺留了部分鍛態(tài)變形組織,未能完全再結(jié)晶,出現(xiàn)混晶。此外,試驗(yàn)鋼14Co7Mo的再結(jié)晶完成溫度則為840℃。(2)Co和Mo對(duì)試驗(yàn)鋼的Ms點(diǎn)和Mf點(diǎn)有較大影響:相比9Co5Mo,較高的Co含量使14Co5Mo試驗(yàn)鋼的Ms點(diǎn)和Mf點(diǎn)分別提高71℃和91℃;相比9Co5Mo,較高的Mo、Ti含量使14Co7Mo試驗(yàn)鋼Ms點(diǎn)大幅降低192℃,導(dǎo)致其Mf點(diǎn)低于室溫。(3)9Co5Mo試驗(yàn)鋼和14Co5Mo試驗(yàn)鋼峰時(shí)效溫度為480℃,14Co7Mo試驗(yàn)鋼峰時(shí)效溫度為500℃,其中,在峰時(shí)效時(shí),9Co5Mo試驗(yàn)鋼抗拉強(qiáng)度和屈服強(qiáng)度分別為2103MPa和2052MPa,對(duì)應(yīng)斷后伸長(zhǎng)率、斷面收縮率和沖擊功分別為9.0%、63%和41J而14Co5Mo試驗(yàn)鋼抗拉強(qiáng)度和屈服強(qiáng)度分別為2190MPa和2121MPa,對(duì)應(yīng)斷后伸長(zhǎng)率、斷面收縮率和沖擊功分別為10.5%、68%和44J;14Co7Mo試驗(yàn)鋼抗拉強(qiáng)度和屈服強(qiáng)度分別為2765MPa和2677MPa,對(duì)應(yīng)斷后伸長(zhǎng)率、斷面收縮率和沖擊功分別為6.0%、45%和15J。(4)試驗(yàn)鋼14Co7Mo深冷后基體組織為板條馬氏體;于500℃時(shí)效5h時(shí),可見(jiàn)在基體上析出的短棒狀金屬間化合物,直徑約為4nm,長(zhǎng)度約為10nm,隨著時(shí)效時(shí)間延長(zhǎng),金屬間化合物進(jìn)發(fā)生長(zhǎng)大和粗化,時(shí)效時(shí)間達(dá)到100h后,直徑約為20nm,長(zhǎng)度約為35nm。(5)14Co7Mo的最佳熱處理制度為14Co7Mo試驗(yàn)鋼最佳熱處理為840℃×1h油淬,-73℃×1h升溫至室溫,500℃×5h空冷,可在2800MPa強(qiáng)度級(jí)別獲得較好的綜合力學(xué)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，

本文編號(hào)：2019068