本文選題：高Cr-Co-Mo軸承鋼 + 多尺度��； 參考：《昆明理工大學》2015年博士論文

【摘要】：為滿足航空航天領域的特殊苛刻環(huán)境對軸承提出具備高強度、高硬度、耐腐蝕、韌性良好和優(yōu)異高溫性能的新要求,開發(fā)了滿足更高指標的新型高Cr-Co-Mo系軸承鋼。過去,對軸承鋼強-韌性能關系和強韌化機理的研究大多圍繞著相對簡單的結(jié)構(gòu)體系,其特征結(jié)構(gòu)單一并且尺度單一�；趶碗s“成分-結(jié)構(gòu)”而設計開發(fā)的高Cr-Co-Mo系軸承鋼具有多級的組織結(jié)構(gòu)要素和多尺度、多相、以及多層次耦合等特點,使高Cr-Co-Mo系軸承鋼在獲得高強度的同時仍保持充足韌性,并兼?zhèn)淦渌C合性能的改蓋。本論文運用多尺度的研究方法,并結(jié)合軸承鋼抗疲勞能力受多重因素影響的特點,通過系統(tǒng)地研究熱處理后各相、各尺度的組織以及各類機制對高Cr-Co-Mo馬氏體軸承鋼強韌性和疲勞性能的影響,采用SEM、EBSD及TEM等觀察手段,以定量表征的方式整合試驗鋼中精細組織結(jié)構(gòu)的演化規(guī)律。以揭示由多相、多尺度控制的組織所對應的本征力學性能及強韌化機制,闡明復雜結(jié)構(gòu)中調(diào)控強韌性能的組織控制單元,進而優(yōu)化其綜合性能。此外,根據(jù)項目指標要求設置強韌性能略有差異的對比試驗組,從表面狀態(tài)、應力及組織缺陷等方面揭示高Cr-Co-Mo軸承鋼疲勞破壞的決定因素及工藝可控的相應臨界指標范圍�；谏钊胂到y(tǒng)的理論分析研究與實際結(jié)果相結(jié)合,找出充分發(fā)揮試驗鋼應用潛能的組織調(diào)控方法,獲得了具有一定創(chuàng)新性和工程應用價值的研究成果。研究得出了高Cr-Co-Mo低碳馬氏體軸承鋼在不同熱處理工藝下的微觀組織變化規(guī)律。-82℃冷處理2h使得馬氏體晶格收縮導致間隙碳原子遷出并富集于M/A相界面附近,在隨后的回火過程中擴散進入并穩(wěn)定化殘余奧氏體,最終少量殘余奧氏體以薄膜狀穩(wěn)定存在于馬氏體板條間。對碳化物進行統(tǒng)計分析發(fā)現(xiàn),當固溶溫度升高至1060℃時,少量存在于大角度晶界處的未溶M6C碳化物,其平均尺寸約0.3μm,能一定程度釘扎晶界以抑制高溫階段奧氏體的粗化。淬火態(tài)析出的M2C碳化物面積百分數(shù)1%,尺寸集中分布于30-40nm之間；而冷處理后M2C碳化物的面積百分數(shù)增加至7%左右,尺寸集中分布于20nm的區(qū)間；回火使M2C面積百分數(shù)進一步提高至7.33%,尺寸集中分布于20-30nm之間,尺寸過小(10nm)的析出相略微長大以增加對位錯阻礙的有效位置。在馬氏體亞結(jié)構(gòu)中,板條領域尺寸由原奧尺寸決定：馬氏體板條束由大角晶界包圍,束間取向差約600而體現(xiàn)孿晶關系；通過晶體學分析發(fā)現(xiàn),板條領域內(nèi)包含三種變體群、6種變體,變體之間有特定結(jié)合模式。定量分析發(fā)現(xiàn),固溶溫度對M2C納米相的析出強化影響不顯著,但對細晶強化影響較大；淬火態(tài)試樣屈服強度受控于板條束寬度,控制板條束寬度在10μm以下并使M6C碳化物的體積分數(shù)低于0.5%,可獲得較好的強塑性配合。在冷處理-回火產(chǎn)生二次硬化以前M2C對屈服強度的貢獻僅7.6%；冷處理和回火階段析出尺寸40nm的M2C充分發(fā)揮了尺度效應,與位錯產(chǎn)生交互作用,使屈服強度的增加超過800MPa,其強度貢獻比例增至75%。經(jīng)二次冷處理-回火循環(huán)后,試驗鋼最終屈服強度達到1532MPa,沖擊吸收功保持在52J。與常規(guī)合金鋼相比,晶粒尺寸的細化未能有效改善沖擊韌性。根據(jù)Griffith脆斷理論分析M6C碳化物對試驗鋼韌性的影響發(fā)現(xiàn),大角晶界處的M6C降低韌性但不是決定因素,原因在于M6C的尺寸遠低于導致脆性解離裂紋萌生的臨界尺寸3μm。進而分析特征晶界的分布情況發(fā)現(xiàn),低能重位點陣(CSL)晶界所占比例直接決定試驗鋼的韌性,∑3晶界是所有CSL晶界中最主要的晶界；并且所有低能晶界所占比例之和與板條束寬度存在線性的數(shù)學關系,馬氏體板條束寬度的增加使束內(nèi)的馬氏體變體數(shù)量增加從而低能晶界比例隨之提高。通過研究解理裂紋的擴展路徑發(fā)現(xiàn),裂紋的傳播路徑單元是板條領域(Packet);定量統(tǒng)計表面,解理平臺尺寸與板條領域尺寸數(shù)值相互吻合。因此,板條領域尺寸是試驗鋼的韌性控制單元。根據(jù)項目指標要求,試驗測定高強-Q組和表面滲碳-ST組試樣通過107次應力循環(huán)的極限疲勞強度均超過600MPa。觀察疲勞斷口發(fā)現(xiàn),高韌-R組主要為表面缺陷導致疲勞斷裂,ST組經(jīng)表面滲碳處理既提高了加工表面的平整度,又提供了由外內(nèi)的壓應力以抑制裂紋的萌生和擴展,從而抗疲勞能力大幅提高。根據(jù)定量計算得出,試驗鋼加工精度的臨界粗糙度指標為0.53μm。而ST組主要由非金屬夾雜物導致疲勞斷裂,其臨界夾雜物尺寸為5.5μm。夾雜物所處位置和尺寸均影響疲勞壽命；并且疲勞強度還受制于夾雜物所處位置的基體硬度。夾雜物深度越深、尺寸越小且基體硬度值越高,抗疲勞能力可得到最優(yōu)化。對于試驗鋼而言,控制距離試樣自由表面100μm以內(nèi)的夾雜物尺寸將有效提高試驗鋼的抗疲勞能力。此外,Q組由于較大的晶粒尺寸易發(fā)生表面駐留滑移現(xiàn)象,由基體表層擠出微米級臺階,最終使疲勞裂紋源于擠出臺階兩側(cè)的高應力集中區(qū)域。
[Abstract]:In order to meet the needs of aerospace special harsh environment put forward with high strength, high hardness of bearing, corrosion resistance, good toughness and excellent new requirements of high temperature performance, developed to meet the new high Cr-Co-Mo bearing steel with higher index. In the past, the strong relationship between bearing steel toughness and strengthening and toughening mechanism of most of the studies focus on a relatively simple structure, the structure characteristics of single and single scale. Based on the complex "component structure and design of high Cr-Co-Mo bearing steel has developed organizational structure elements multi-level and multi-scale, multi phase characteristics and multi-layer coupling, high Cr-Co-Mo bearing steel still maintain adequate toughness in high the strength at the same time, to cover and combine with other comprehensive performance. This research method using multi scales, and combined with the characteristics of Bearing Steel Anti fatigue ability affected by multiple factors, through the systematic study of heat After each phase, the scale effect, the organization and all kinds of mechanism of high Cr-Co-Mo martensitic steel bearing strong toughness and fatigue performance of the SEM, EBSD and TEM in the observation methods, quantitative characterization of integration evolution of fine steel structure. As revealed by multiple phases, corresponding to multi scale control the organization of the intrinsic mechanical properties and toughening mechanism of complex structure, strength and toughness of the organization to clarify regulation control unit, and then optimize its comprehensive performance. In addition, according to the contrast test group project indicators requirements set slightly different from the properties of strength and toughness, surface state, corresponding critical index range of stress and tissue defects of determinants the fatigue failure of high Cr-Co-Mo bearing steel and process controllable. Systematic theoretical analysis and actual results based on the combination, give full play to find potential application organization adjustment test of steel Control method, obtained the innovative research achievements and application value. The research shows that the high Cr-Co-Mo low carbon martensite bearing steel under different heat treatment process of.-82 under the variation of microstructure at cold treatment 2H makes martensite lattice contraction leads to interstitial carbon atoms move out and enrichment near the M/A interface, diffusion into the and the stability of retained austenite during tempering, then in the final with a small amount of residual austenite film exist in lath martensite. The carbides for statistical analysis found that when the solid solution temperature to 1060 DEG C, undissolved M6C carbides exist in large angle grain boundaries less, the average size of about 0.3 m, can to some extent coarse grain boundary pinning to suppress the high temperature stage. The percentage of M2C 1% austenitic quenched carbide precipitation, concentrated in size between 30-40nm and M2C carbon after cold treatment; Area percentage of compounds increased to about 7%, the interval size mainly focus on 20nm M2C; tempering area percentage increased to 7.33%, concentrated in size between 20-30nm size (10nm) precipitates grow up slightly to increase the effective dislocation obstacle position. In the structure of the martensite lath. The field size is determined by the original Olympic size: martensite by grain boundary surrounded by beam orientation difference between about 600 and reflects the twin relationship; through crystallographic analysis found that in the field of slab contains three kinds of variant group, 6 variants have a specific binding mode between variants. Quantitative analysis showed that the temperature of solid solution precipitation M2C nano strengthening effect is not significant, but the influence of fine grain strengthening; quenching yield strength is controlled by the lath width, lath width control below 10 m and the M6C carbide volume fraction is less than 0.5% And can obtain better combination of strength and plasticity. Two tempering hardened in the cold treatment before the M2C contribution to the yield strength of only 7.6%; cold treatment and tempering stage precipitation size 40nm M2C give full play to the scale effect, interact with dislocation, increase the yield strength of more than 800MPa, its contribution ratio increased to strength 75%. after two times of cold treatment tempering cycles, the final test of steel yield strength up to 1532MPa, keep the impact absorbing energy in the 52J. compared with the conventional alloy steel, grain size refinement could not effectively improve the impact toughness of Griffith. According to the theory of brittle fracture analysis of the influence of M6C carbides on the steel toughness test found that the angle grain boundaries of M6C decrease toughness but it is not the determining factor, because that distribution of the size of M6C is far lower than the critical size of brittle crack initiation leads to dissociation of 3 m. and the analysis of the characteristics of the grain boundary, low CSL (CS L) grain boundary proportion directly determines the steel toughness test, 3 Sigma is the main grain boundaries in the grain boundaries of all CSL; and all the proportion of low energy grain boundary and lath width linear mathematical relations of the martensite beam in martensite increases the width of the body so as to increase the number of low energy variable the proportion of grain boundaries increased. By extending the path of the cleavage cracks found crack propagation path unit is lath field (Packet); quantitative statistics of surface, the size of the platform and the numerical solutions agree with each other. Therefore the field size of lath lath, field size is the steel toughness test control unit. According to the project requirements, test of high strength -Q group and surface carburizing of -ST groups of samples by 107 times should limit the fatigue strength of stress cycles were more than 600MPa. observation of fatigue fracture finds that high toughness -R group mainly for surface defects and fatigue fracture of ST. After carburizing treatment can improve the smoothness of the surface, and provides the initiation and propagation by internal and external compressive stress to prevent crack, and anti fatigue ability has been greatly improved. According to the quantitative calculation, the critical processing precision of test steel roughness index is 0.53 M. and the ST group is mainly composed of non metals inclusion and fatigue fracture, the critical inclusion size of 5.5 mu m. inclusion location and size effect and fatigue life; fatigue strength is also subject to the inclusion of the location of hardness. The inclusion of the deep, the smaller the size and matrix hardness value is higher, the ability of anti fatigue test for steel can be optimized. In terms of control size of inclusion free surface within the sample distance of 100 m will effectively improve the ability of anti fatigue test of steel. In addition, the Q group due to surface persistslip prone to the phenomenon of large grain size, from the base The surface layer extruded the microscale step, and finally the fatigue crack originated from the high stress concentration area on both sides of the extrusion step.

【學位授予單位】：昆明理工大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG142.1

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