本文選題：稀土 + 氮碳共滲�。� 參考：《哈爾濱工業(yè)大學(xué)》2015年博士論文

【摘要】：M50Ni L鋼是新一代的高強(qiáng)軸承鋼,廣泛應(yīng)用于航空制造業(yè)等高端裝備制造業(yè)。對于軸承而言,其失效形式主要為接觸疲勞失效和磨損失效,因此要求其具有優(yōu)異的表面性能。然而目前對于M50Ni L鋼的表面改性技術(shù)卻鮮有報道。如何在軸承鋼表面獲得超細(xì)化的組織且較深的改性層一直以來是化學(xué)熱處理的研究熱點(diǎn)。本文針對M50Ni L鋼稀土氮碳共滲層的高強(qiáng)韌性的性能要求,將等離子體稀土氮碳共滲技術(shù)應(yīng)用于M50Ni L鋼的表面改性�；谘h(huán)相變超細(xì)化思想,設(shè)計了變溫循環(huán)稀土氮碳共滲工藝,以期實(shí)現(xiàn)共滲組織超細(xì)化;同時研究了不同鐵基合金低溫稀土共滲過程中的稀土元素催滲機(jī)制。在不同相區(qū)對M50Ni L鋼進(jìn)行稀土氮碳共滲,研究溫度、氮?dú)浔燃肮矟B時間對共滲層組織結(jié)構(gòu)的影響。結(jié)果表明:M50Ni L鋼a相區(qū)稀土氮碳共滲層無化合物層,共滲層微結(jié)構(gòu)為粗大的板條馬氏體。共滲層的相組成主要為a′N、g′-Fe4N及e-Fe2-3N,且相結(jié)構(gòu)隨溫度變化較大,隨氮?dú)浔茸兓幻黠@。g相區(qū)稀土氮碳共滲層組織同樣無化合物層,相結(jié)構(gòu)受溫度及氮?dú)浔扔绊戄^大。相同氮?dú)浔认?g′-Fe4N含量隨溫度升高而減少;當(dāng)?shù)獨(dú)浔葹?.3:0.1 L/min時,650°C下共滲1h后,開始形成g-Fe N0.076,說明奧氏體化開始。以不同相區(qū)M50Ni L鋼稀土氮碳共滲層相結(jié)構(gòu)演變規(guī)律為基礎(chǔ),通過熱力計算設(shè)計了變溫循環(huán)共滲工藝,在共滲層表面上獲得了納米級的超細(xì)組織,而在共滲層內(nèi)部30mm處局部得到了超細(xì)化的組織。其中,g?a相區(qū)(降溫)循環(huán)共滲表面超細(xì)化組織由a′N+g′-Fe4N或單一的g′-Fe4N組成,g相區(qū)(升溫)循環(huán)共滲表面超細(xì)化組織由a′N和非晶組成。M50Ni L鋼變溫循環(huán)稀土氮碳共滲超細(xì)化機(jī)制為:首先,g相區(qū)共滲過程中發(fā)生奧氏體化,形成g-Fe N0.076,其次在后續(xù)的降、升溫循環(huán)過程中反復(fù)發(fā)生g-Fe N0.076#174;a′N+g′-Fe4N轉(zhuǎn)變以及馬氏體相變(g#174;a′N)。與此同時合金元素導(dǎo)致e和g′氮化物的穩(wěn)定性下降,使其在共滲過程中不易長大,最終形成超細(xì)化共滲層組織。M50Ni L鋼經(jīng)不同相區(qū)稀土氮碳共滲后,硬度及耐磨性均大幅提高。磨損機(jī)制隨磨損速度由氧化疲勞磨損逐漸轉(zhuǎn)變?yōu)槟チＤp和粘著磨損。其中g(shù)?a相區(qū)(降溫)循環(huán)2次共滲層具有最優(yōu)的耐磨性。而稀土La的加入能夠抑制共滲層的脆性,提高共滲層的強(qiáng)韌性,增強(qiáng)共滲層的耐磨性。超細(xì)化共滲層耐磨性提高得益于其特殊的表面組織結(jié)構(gòu)。細(xì)小的含氮馬氏體+彌散析出的g′-Fe4N組織有利于提高共滲層的強(qiáng)韌性和耐磨性。稀土元素在化學(xué)熱處理中被證實(shí)具有明顯的催滲效果,然而其催滲機(jī)制尚未得到很好的揭示,尤其在等離子體低溫稀土共滲中。本文的實(shí)驗(yàn)和熱力學(xué)計算結(jié)果證實(shí):等離子體低溫稀土共滲過程中La與N之間的作用是相互吸引的。通過實(shí)驗(yàn)和理論計算提出等離子體低溫稀土共滲過程中稀土催化機(jī)制:首先,稀土共滲過程中,在La和La Fe O3的共同作用下,使共滲表面變得粗糙,比表面積增大,有利于N的吸附;其次La對N的吸引提高了表面N的活度,與此同時通過La Fe O3對O的吸附,使得共滲表面N原子與La分離而向內(nèi)深層擴(kuò)散�；趯辖鹪豅a Fe O3晶體氧空位形成能的計算,解釋了高合金鋼不催滲的原因,同時提出了深層滲氮鋼的設(shè)計思想,即:深層滲氮鋼的成分選擇上應(yīng)含有適量的Ni元素,同時應(yīng)盡量減少Cr、Mo、V等元素的含量。
[Abstract]:M50Ni L steel is a new generation of high strength bearing steel, which is widely used in high end equipment manufacturing industry such as aviation manufacturing. For bearings, its failure forms are mainly contact fatigue failure and wear failure, so it is required to have excellent surface properties. However, there are few reports on the surface modification technology of M50Ni L steel at present. In this paper, the plasma rare-earth nitrocarburizing technology is applied to the surface modification of the M50Ni L steel for the performance requirements of the high strength and toughness of the rare earth nitrogen carbon co permeable layer of M50Ni L steel. Based on the idea of cyclic phase transition superfine, this paper designs a variable temperature evidence-based process. The rare-earth nitrocarburizing process is expected to realize the superfining of the co permeable tissue. At the same time, the rare-earth element infiltration mechanism of different iron base alloys in the process of low temperature rare earth co permeation is studied. The effects of rare-earth Nitrocarburizing on M50Ni L steel in different phase regions, the influence of temperature, nitrogen and hydrogen ratio and the time of CO infiltration on the microstructure of the co permeable layer are studied. The results show that M50Ni L steel a There is no compound layer in the rare-earth nitrocarburizing layer, and the microstructure of the co impermeable layer is large lath martensite. The phase composition of the co impermeable layer is mainly a 'N, G' -Fe4N and e-Fe2-3N, and the phase structure changes with the temperature. The phase structure is affected by the temperature and the nitrogen hydrogen ratio with the change of the nitrogen and hydrogen ratio in the.G phase. With the same nitrogen and hydrogen ratio, the content of G '-Fe4N decreases with the increase of temperature. When the ratio of nitrogen to hydrogen is 0.3:0.1 L/min, the g-Fe N0.076 is formed after the co infiltration of 1H at 650 degree C, indicating the beginning of austenitizing. The process of changing the phase structure of the rare-earth nitrocarburizing layer in the different phase region M50Ni L steel is based on the thermal calculation and design of the temperature variable circulation co infiltration process. The ultrafine microstructure of nanoscale layer was obtained on the surface of the co permeable layer, and the Superfine Microstructure was obtained in the 30mm part of the copermeable layer. In the G? A phase region (cooling) cycle, the superfine tissue was composed of a 'N+g' -Fe4N or single G '-Fe4N, and the ultrafine microstructure of the G phase region (Sheng Wen) circulated surface was composed of a' N and amorphous.M50Ni. The superfine mechanism of rare-earth nitrocarburizing in L steel temperature cycle is: first, austenitizing in the process of G phase co infiltration and forming g-Fe N0.076, followed by subsequent drop, and repeated g-Fe N0.076#174, a 'N+g' -Fe4N transformation and martensitic phase transition (g#174; a 'N). The qualitative decline makes it not easy to grow up in the process of CO permeation, and eventually forms the superfine copermeable layer of.M50Ni L steel. The hardness and wear resistance of the steel are greatly improved after different phases of rare-earth nitrocarburizing. The wear mechanism is gradually changed from oxidation fatigue wear to abrasive wear and adhesion wear with the wear rate. The 2 times co infiltration of G? A phase region (cooling) cycle The addition of rare earth La can inhibit the brittleness of the co permeable layer, improve the strength and toughness of the co permeable layer and enhance the wear resistance of the co permeable layer. The wear resistance of the ultra-fine co permeable layer is improved by its special surface structure. The microstructure of G '-Fe4N from the fine nitrogen martensite + diffusion precipitation is beneficial to the enhancement of the strength and toughness of the co permeable layer. The rare-earth element has been proved to have obvious effect in the chemical heat treatment, but its mechanism has not been well revealed, especially in the plasma low temperature rare earth co permeation. The experiment and thermodynamic calculation of this paper confirm that the effect of La and N in the process of plasma low temperature rare earth co permeation is mutually attractive. The rare-earth catalytic mechanism in the process of plasma low temperature rare earth co permeation is proposed by experiments and theoretical calculations. First, in the process of rare earth co osmotic, the co permeation surface becomes rough, the surface area is increased and the adsorption of N is increased under the joint action of La and La Fe O3. Secondly, the absorption of La to N improves the activity of the surface N, while La Fe O3 is used at the same time. The adsorption of O makes the N atoms of the co permeable surface separate from La and diffuse into the inner deep. Based on the calculation of the formation energy of the oxygen vacancy of the alloy element La Fe O3 crystal, the reason for the non urging of the high alloy steel is explained. At the same time, the design idea of the deep nitriding steel is put forward, that is, the composition of the deep nitriding steel should contain a proper amount of Ni elements, and at the same time, we should do the best. The content of Cr, Mo, V and other elements was reduced.

【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG156.82

【參考文獻(xiàn)】

相關(guān)期刊論文 前1條

1 羅文英;蔣靜;劉憲民;王春旭;;18Ni馬氏體時效鋼循環(huán)相變細(xì)晶工藝研究[J];熱加工工藝;2012年16期

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本文編號：1889660