【摘要】：軸承鋼的組織均勻性及組織配比等對軸承的疲勞壽命有顯著的影響,因此應保證軸承鋼熱加工和熱處理過程中組織的均勻性及熱穩(wěn)定性 本文以高碳鉻軸承鋼為研究對象,基于熱力學和動力學微觀組織調(diào)控理論和控制方法,以控軋控冷和熱處理關鍵工藝為核心,定性、定量分析碳化物演變過程,探討馬氏體/貝氏體相變行為,揭示不同工藝條件下碳化物的析出和溶解規(guī)律及其對馬氏體/貝氏體相變行為的影響。主要研究內(nèi)容和成果如下： 軋后冷卻過程先共析網(wǎng)狀碳化物的析出對GCr15軸承鋼的質(zhì)量存在不利的影響,形變工藝制度、冷卻速率和合金元素的添加均會影響其析出行為。在奧氏體單相區(qū)施加一定的壓縮變形后,冷卻過程中網(wǎng)狀碳化物析出溫度相比于靜態(tài)轉(zhuǎn)變有所提高,CCT曲線向左移動。Mo元素的添加及SU Mn元素含量的提高,均使得相轉(zhuǎn)變區(qū)間向右移動,提高了實驗鋼的淬透性,對網(wǎng)狀碳化物的析出有一定的抑制作用。 熱軋后的軸承鋼經(jīng)球化退火后室溫組織為鐵素體+球狀碳化物,該組織和加熱速率決定了后續(xù)加熱過程奧氏體化行為。鑒于JMAK模型中動力學參數(shù)k對溫度的敏感性,引入加熱速率對該參數(shù)的影響。運用疊加法則分別建立了連續(xù)加熱過程鐵素體-奧氏體和碳化物溶解動力學模型,并對模型進行了驗證。 基于界面局部平衡理論,運用Thermo-Calc熱力學軟件的TCFE7和DICTRA動力學軟件的MOBFE數(shù)據(jù)庫,對860℃保溫過程碳化物的溶解行為進行宏觀定量計算,分析元素微觀擴散機理。結(jié)果表明：碳化物的溶解過程分為兩個階段,第一階段為保溫10min前的快速溶解,C元素在奧氏體內(nèi)快速均勻分布,而Cr元素只是在界面處獲得了局部平衡；第二階段為隨后的緩慢溶解,Cr元素在奧氏體和碳化物內(nèi)發(fā)生再分配。從微觀尺度來看,碳化物的溶解依靠奧氏體/碳化物界面處平衡的破壞及兩相間元素的擴散。初期碳化物的溶解機制為C原子快速擴散控制的NPLE型；當奧氏體基體內(nèi)C活度與界面?zhèn)冗_到一致時,轉(zhuǎn)變?yōu)镃r原子緩慢擴散控制的PLE型。 通過分析淬火+回火熱處理和貝氏體等溫處理后的微觀組織形貌,發(fā)現(xiàn)馬氏體針之間互不平行,晶粒大小不均,內(nèi)部含有高密度的孿晶�；鼗疬^程中,針內(nèi)碳原子聚集到孿晶部位,以碳化物的形式析出。貝氏體等溫相變的鼻尖溫度在300～350℃,影響其轉(zhuǎn)變動力學的因素有合金元素的均勻性、過冷奧氏體的C/Cr含量、保溫溫度和保溫時間等。貝氏體的形成與碳化物的析出同時進行,貝氏體板條間呈一定的取向生長,低的相變溫度促使碳化物細小彌散的分布。貝氏體等溫處理后性能與回火馬氏體相比,具有更高的強度和塑性,耐磨性相當。 針對貝氏體等溫處理耗時長的特點,分別研究了預應變和預淬火處理對貝氏體相變動力學的影響。預應變形成的過冷奧氏體晶內(nèi)亞結(jié)構(gòu)和預淬火引起的組織變化,均提高了貝氏體相變初期的轉(zhuǎn)變速率。但隨相變進行,最終與常規(guī)工藝歸于一致,對整個貝氏體相變過程的加速作用不明顯。提出了一種兩步處理方法,在250℃等溫處理50min后升溫到270℃保溫5min。殘留奧氏體含量為6%,相變時間為傳統(tǒng)工藝的27%左右,顯著縮短貝氏體相變時間的同時并未明顯降低力學性能和磨損性能
[Abstract]:The microstructure uniformity and microstructure of bearing steel have significant influence on the fatigue life of the bearing , so the uniformity and thermal stability of the structure during hot working and heat treatment of bearing steel should be ensured .

In this paper , high carbon chromium bearing steel is used as the research object , based on the theory and control method of thermodynamic and dynamic microstructure regulation , the key technology of controlling rolling and cooling and heat treatment is adopted as the core , qualitative and quantitative analysis of the carbide evolution process , and the influence of the precipitation and dissolution of the carbide under different process conditions and its influence on the martensite / bainite transformation behavior are revealed . The main research contents and achievements are as follows :

After a certain compressive deformation is applied to the austenite single - phase region , the precipitation temperature of the net carbide in the cooling process is improved compared with the static transition , the CCT curve moves to the left . The addition of the Mo element and the increase of the content of the SU Mn element cause the phase transition region to move to the right , the hardenability of the experimental steel is improved , and the precipitation of the reticulated carbide is inhibited .

In view of the sensitivity of kinetic parameter k to temperature in the JMAK model , the influence of heating rate on the parameter is introduced . The dynamic model of ferrite - austenite and carbide dissolution in continuous heating process is established by superposition rule , and the model is verified .

Based on the local equilibrium theory of interface , using the MOBFE database of TCFE7 and DICTRA dynamic software of Thermo - Calc thermodynamic software , the dissolution behavior of carbides at 860 鈩，

本文編號：2132133