表面凹坑缺陷對高速列車車軸鋼疲勞性能影響研究
發(fā)布時(shí)間：2018-11-03 10:36
【摘要】：運(yùn)行安全是高速動(dòng)車組關(guān)注的首要問題,高速動(dòng)車組車軸的疲勞壽命直接關(guān)系到高速動(dòng)車組的行車安全。本論文針對現(xiàn)役S38C表面感應(yīng)淬火高速動(dòng)車組車軸在異物高速?zèng)_擊下,其表面凹坑缺陷對疲勞壽命的影響開展細(xì)致研究,旨在為評價(jià)該類表面凹坑缺陷對車軸的疲勞壽命影響和提出該類表面凹坑缺陷的修復(fù)方法提供參考依據(jù)。高速動(dòng)車組車軸設(shè)計(jì)壽命一般為30年或者設(shè)計(jì)服役循環(huán)周次約為2×109。通常,造成車軸疲勞斷裂的主因是車軸表面損傷,這類表面損傷主要有:局部應(yīng)力腐蝕、冶金缺陷與夾雜、過盈配合壓裝表面微動(dòng)損傷等。隨著高速動(dòng)車組在中國客運(yùn)專線上的大量載客運(yùn)行和動(dòng)車所維修維護(hù)工作的跟進(jìn),發(fā)現(xiàn)高速運(yùn)行中的高速動(dòng)車組車軸由于異物沖擊,造成大量的車軸表面凹坑缺陷。目前,尚無針對此類缺陷對車軸疲勞壽命影響的系統(tǒng)研究。為系統(tǒng)評價(jià)車軸表面異物沖擊造成的凹坑缺陷對車軸疲勞性能的影響,本論文開展了如下研究工作:首先,根據(jù)形貌特征對S38C車軸表面的高速?zèng)_擊造成的凹坑缺陷進(jìn)行分類,采用硬度計(jì)、光鏡、透射電子顯微鏡和電火花直讀光譜儀分析車軸表面和心部的微觀組織和化學(xué)成分,在此基礎(chǔ)上設(shè)計(jì)實(shí)驗(yàn);其次,設(shè)計(jì)電火花加工缺口和人工壓痕兩種缺陷,結(jié)合疲勞試驗(yàn)機(jī)、硬度計(jì)、光鏡、透射電子顯微鏡、掃描電子顯微鏡和EDS、XRD等手段研究兩種缺陷對三種不同表面硬度梯度的車軸鋼標(biāo)準(zhǔn)疲勞試樣疲勞性能的影響;再者,截取S38C車軸上含有表面淬火層的四點(diǎn)彎曲疲勞試樣,研究電火花加工缺口和人工壓痕分別對其疲勞性能的影響,同時(shí),設(shè)計(jì)非標(biāo)的方法評價(jià)了 S38C車軸基體和表面感應(yīng)淬火層疲勞裂紋擴(kuò)展速率和門檻值。最后,對激光熔覆修復(fù)車軸表面電火花加工缺口和人工壓痕工藝進(jìn)行了探索性研究。本論文主要結(jié)論如下:1. S38C車軸表面異物沖擊凹坑缺陷分為垂直撞擊形成的溝槽和切向撞擊產(chǎn)生的擦痕兩類,車軸表面硬化層組織為高密度位錯(cuò)和晶格畸變的回火馬氏體,心部組織為純凈珠光體和鐵素體;2. S38C車軸鋼人工壓痕標(biāo)準(zhǔn)試樣和電火花加工缺口標(biāo)準(zhǔn)試樣疲勞極限均隨著缺陷投影面積的增加而降低,含有電火花加工缺口試樣的疲勞極限符合Murakami公式計(jì)算結(jié)果,人工壓痕試樣疲勞極限可用修正后的Murakami公式進(jìn)行描述;3.經(jīng)表面感應(yīng)淬火的S38C車軸鋼標(biāo)準(zhǔn)試樣疲勞極限均隨著人工壓痕尺寸的增大而降低,先淬火回火再引入人工壓痕標(biāo)準(zhǔn)疲勞試樣的疲勞極限降幅較大;4. S38C車軸鋼氮碳共滲標(biāo)準(zhǔn)試樣疲勞極限相對于未處理試樣提高了 12%,疲勞裂紋萌生于試樣表面疏松氧化層;人工壓痕造成化合物層破裂,疲勞極限隨著人工壓痕尺寸增大迅速降低,直至低于未處理人工壓痕試樣;拋光去除氮碳共滲化合物硬層可有效降低人工壓痕對試樣疲勞強(qiáng)度的影響。5.車軸表面淬火層的四點(diǎn)彎曲標(biāo)準(zhǔn)疲勞試樣的疲勞極限隨著電火花加工缺陷深度的增加而降低,人工鎢鋼球壓痕對試樣疲勞極限沒有影響。鎢鋼球破碎產(chǎn)生的二次壓痕底部具有微裂紋,試樣疲勞極限降低。表面回火馬氏體層的裂紋擴(kuò)展門檻值為1.43MPa√m,遠(yuǎn)低于基體的 5.66 MPa√m;6.激光熔覆修復(fù)車軸表面凹坑缺陷帶來的新缺陷導(dǎo)致試樣疲勞性能差異�；谝陨涎芯拷Y(jié)果可知,對于塑形較好的S38C車軸鋼標(biāo)準(zhǔn)疲勞試樣,局部材料在人工壓痕形成過程中產(chǎn)生大量的位錯(cuò)強(qiáng)化了缺陷處材料性能,可用引入強(qiáng)化常數(shù)Q修正后的Murakami公式預(yù)測含此種缺陷試樣的疲勞極限。對于表面感應(yīng)淬火回火形成的回火馬氏體,在受到塑形變形時(shí)晶粒納米化,塑形降低,受到?jīng)_擊時(shí)多方向剪切變形形成微裂紋。車軸表面淬火層裂紋擴(kuò)展門檻值低于基體材料,在循環(huán)應(yīng)力作用下微裂紋極易擴(kuò)展造成此類車軸失效。
[Abstract]:Operation safety is the primary concern of high-speed motor train unit, and the fatigue life of high-speed motor train unit is directly related to the driving safety of high-speed motor train unit. In this paper, the influence of surface pit defects on fatigue life of high-speed motor train EMUs at high speed under high-speed impact of foreign objects is studied in this paper. The purpose of this paper is to provide a reference basis for evaluating the effect of pit defects on the fatigue life of the axle and the method for repairing the defect of the surface pit. The design life of the axle of the high-speed motor train unit is generally 30 years or the design service cycle is about 2 mm109. In general, axle fatigue fracture is caused by the damage of axle surface, which mainly includes local stress corrosion, metallurgical defect and inclusion, over-interference fit pressing surface fretting damage and so on. With the follow-up of the operation and maintenance of the high-speed motor train unit in China's passenger dedicated line, it is found that the axle of the high-speed motor train unit in high-speed operation results in a large number of axle surface pit defects due to the impact of foreign matters. At present, there is no systematic study on the effect of such defects on the fatigue life of axles. In order to evaluate the effect of pit defects on axle fatigue performance caused by foreign body impact on axle surface, this paper carried out the following research work: Firstly, the pit defects caused by the high speed impact of S38C axle surface are classified according to the topographical features, and the hardness tester and light microscope are adopted. The microstructure and chemical composition of axle surface and core were analyzed by transmission electron microscope and electric spark direct reading spectrometer, and the experiment was designed on this basis; secondly, two defects of electric spark machining notch and artificial indentation were designed, combined with fatigue testing machine, hardness tester and light microscope. The effects of two kinds of defects on fatigue properties of axle steel standard fatigue specimens with different surface hardness gradient were studied by transmission electron microscope, scanning electron microscope and EDS, XRD, etc. The fatigue crack growth rate and threshold value of S38C axle matrix and surface induction hardening layer were evaluated by the design of non-target method. Finally, the notch and artificial indentation process of laser cladding repairing axle surface were studied. The main conclusions of this thesis are as follows: 1. S38C axle surface foreign matter impact crater defects are divided into two types of grooves formed by vertical impact and scratches generated by tangential impact, the hardened layer of axle surface is tempered martensite with high density dislocation and lattice distortion, and the core part is pure pearlite and ferrite; 2. The fatigue limit of the S38C axle steel artificial indentation standard test specimen and the electric spark machining notch standard specimen decreases with the increase of the defect projection area, and the fatigue limit of the sample containing the electric spark machining notch conforms to the calculation result of Murakami formula. The fatigue limit of the artificial indentation test specimen can be described with the modified Murakami formula; 3. The fatigue limit of S38C axle steel subjected to surface induction hardening is reduced with the increase of the size of the artificial indentation. the fatigue limit of the S38C axle steel nitrocarburizing standard sample is improved by 12% relative to the untreated sample, the fatigue crack is formed on the loose oxide layer on the surface of the sample, the artificial indentation causes the compound layer to crack, the fatigue limit decreases rapidly with the increase of the size of the artificial indentation, The effect of the artificial indentation on the fatigue strength of the specimen can be effectively reduced by polishing the hard layer of the nitrogen-carbon co-infiltration compound until it is lower than that of the untreated artificial indentation sample. The fatigue limit of the four-point bending standard fatigue test specimen of the axle surface quenching layer decreases with the increase of the depth of the electric spark machining defect, and the indentation of the artificial tungsten steel ball has no influence on the fatigue limit of the sample. The bottom of the secondary indentation produced by crushing the tungsten steel ball has micro-cracks, and the fatigue limit of the specimen is reduced. The crack propagation threshold value of the surface tempered martensite layer is 1. 43MPa/ m, which is much lower than that of the matrix. A new defect in the surface pit defects of the laser cladding repairing axle leads to a difference in fatigue performance of the specimen. Based on the above results, it can be seen from the above research results that, for the S38C axle steel standard fatigue test specimens with better shape, a large number of dislocations are generated during the process of artificial indentation formation, The fatigue limit of the sample containing such defects can be predicted using the Murakami formula after correction of the reinforcement constant Q. For the tempered martensite formed by quenching and tempering on the surface, the grain is nano-shaped when subjected to shaping deformation, the shaping is reduced, and the micro-cracks are formed by the multi-directional shear deformation at the time of impact. The crack propagation threshold value of the surface quenching layer of the axle is lower than that of the matrix material, and the micro crack is easy to expand under the action of cyclic stress to cause such axle failure.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：U270.33;TG142.12
本文編號：2307539
[Abstract]:Operation safety is the primary concern of high-speed motor train unit, and the fatigue life of high-speed motor train unit is directly related to the driving safety of high-speed motor train unit. In this paper, the influence of surface pit defects on fatigue life of high-speed motor train EMUs at high speed under high-speed impact of foreign objects is studied in this paper. The purpose of this paper is to provide a reference basis for evaluating the effect of pit defects on the fatigue life of the axle and the method for repairing the defect of the surface pit. The design life of the axle of the high-speed motor train unit is generally 30 years or the design service cycle is about 2 mm109. In general, axle fatigue fracture is caused by the damage of axle surface, which mainly includes local stress corrosion, metallurgical defect and inclusion, over-interference fit pressing surface fretting damage and so on. With the follow-up of the operation and maintenance of the high-speed motor train unit in China's passenger dedicated line, it is found that the axle of the high-speed motor train unit in high-speed operation results in a large number of axle surface pit defects due to the impact of foreign matters. At present, there is no systematic study on the effect of such defects on the fatigue life of axles. In order to evaluate the effect of pit defects on axle fatigue performance caused by foreign body impact on axle surface, this paper carried out the following research work: Firstly, the pit defects caused by the high speed impact of S38C axle surface are classified according to the topographical features, and the hardness tester and light microscope are adopted. The microstructure and chemical composition of axle surface and core were analyzed by transmission electron microscope and electric spark direct reading spectrometer, and the experiment was designed on this basis; secondly, two defects of electric spark machining notch and artificial indentation were designed, combined with fatigue testing machine, hardness tester and light microscope. The effects of two kinds of defects on fatigue properties of axle steel standard fatigue specimens with different surface hardness gradient were studied by transmission electron microscope, scanning electron microscope and EDS, XRD, etc. The fatigue crack growth rate and threshold value of S38C axle matrix and surface induction hardening layer were evaluated by the design of non-target method. Finally, the notch and artificial indentation process of laser cladding repairing axle surface were studied. The main conclusions of this thesis are as follows: 1. S38C axle surface foreign matter impact crater defects are divided into two types of grooves formed by vertical impact and scratches generated by tangential impact, the hardened layer of axle surface is tempered martensite with high density dislocation and lattice distortion, and the core part is pure pearlite and ferrite; 2. The fatigue limit of the S38C axle steel artificial indentation standard test specimen and the electric spark machining notch standard specimen decreases with the increase of the defect projection area, and the fatigue limit of the sample containing the electric spark machining notch conforms to the calculation result of Murakami formula. The fatigue limit of the artificial indentation test specimen can be described with the modified Murakami formula; 3. The fatigue limit of S38C axle steel subjected to surface induction hardening is reduced with the increase of the size of the artificial indentation. the fatigue limit of the S38C axle steel nitrocarburizing standard sample is improved by 12% relative to the untreated sample, the fatigue crack is formed on the loose oxide layer on the surface of the sample, the artificial indentation causes the compound layer to crack, the fatigue limit decreases rapidly with the increase of the size of the artificial indentation, The effect of the artificial indentation on the fatigue strength of the specimen can be effectively reduced by polishing the hard layer of the nitrogen-carbon co-infiltration compound until it is lower than that of the untreated artificial indentation sample. The fatigue limit of the four-point bending standard fatigue test specimen of the axle surface quenching layer decreases with the increase of the depth of the electric spark machining defect, and the indentation of the artificial tungsten steel ball has no influence on the fatigue limit of the sample. The bottom of the secondary indentation produced by crushing the tungsten steel ball has micro-cracks, and the fatigue limit of the specimen is reduced. The crack propagation threshold value of the surface tempered martensite layer is 1. 43MPa/ m, which is much lower than that of the matrix. A new defect in the surface pit defects of the laser cladding repairing axle leads to a difference in fatigue performance of the specimen. Based on the above results, it can be seen from the above research results that, for the S38C axle steel standard fatigue test specimens with better shape, a large number of dislocations are generated during the process of artificial indentation formation, The fatigue limit of the sample containing such defects can be predicted using the Murakami formula after correction of the reinforcement constant Q. For the tempered martensite formed by quenching and tempering on the surface, the grain is nano-shaped when subjected to shaping deformation, the shaping is reduced, and the micro-cracks are formed by the multi-directional shear deformation at the time of impact. The crack propagation threshold value of the surface quenching layer of the axle is lower than that of the matrix material, and the micro crack is easy to expand under the action of cyclic stress to cause such axle failure.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：U270.33;TG142.12
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