發(fā)布時(shí)間：2018-03-07 05:36

  本文選題：噴丸強(qiáng)化　切入點(diǎn)：孔冷擠壓　出處：《燕山大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：隨著高強(qiáng)度鋼的應(yīng)用領(lǐng)域越加廣泛,由高強(qiáng)度鋼所制備的零部件因?yàn)殚L(zhǎng)時(shí)間承受交變載荷壓力,在表面上形成疲勞裂紋致使失效的情況逐漸增加。為此,采用噴丸、孔冷擠壓和滲碳等表面強(qiáng)化對(duì)這些承受交變載荷的高強(qiáng)鋼零部件進(jìn)行表面強(qiáng)化處理,采用實(shí)驗(yàn)研究與數(shù)值模擬相結(jié)合的方法,分析殘余應(yīng)力場(chǎng)的分布規(guī)律,以提高其使用壽命。本研究不僅具有重要的理論意義,更具有重要的工程意義。本文對(duì)不同噴丸與孔冷擠壓工藝基于高強(qiáng)度鋼試樣殘余應(yīng)力場(chǎng)的影響進(jìn)行了分析,并通過(guò)有限元法對(duì)噴丸與孔冷擠壓后形成的殘余應(yīng)力場(chǎng)開(kāi)展了數(shù)值模擬。研究了不同滲層深度及不同表面碳含量對(duì)20CrMn Ti鋼試樣殘余應(yīng)力場(chǎng)的影響,并采用有限元法對(duì)其進(jìn)行了數(shù)值模擬。通過(guò)X應(yīng)力儀測(cè)試噴丸、孔冷擠壓與滲碳后試樣的殘余應(yīng)力,再通過(guò)電解拋光法依次測(cè)試殘余應(yīng)力的范圍。此外,通過(guò)X射線衍射儀對(duì)噴丸、孔冷擠壓與滲碳前后試樣晶體結(jié)構(gòu)開(kāi)展了研究,測(cè)定試樣表面顯微硬度逐層變化情況,觀察試樣組織形貌。通過(guò)ANSYS軟件構(gòu)建有限元模型,對(duì)不同噴丸、孔冷擠壓和滲碳工藝條件下的殘余應(yīng)力場(chǎng)進(jìn)行了數(shù)值模擬。實(shí)驗(yàn)結(jié)果表明,伴隨噴丸時(shí)間的增長(zhǎng),不斷增大最大殘余應(yīng)力和強(qiáng)化深度,表面殘余應(yīng)力逐漸降低,相對(duì)于小直徑彈丸而言,通過(guò)大直徑彈丸形成的強(qiáng)化深度較大。如果噴丸強(qiáng)度不斷增加,最大殘余應(yīng)力、強(qiáng)度也不斷上升。通過(guò)玻璃丸與陶瓷丸開(kāi)展二次噴丸增強(qiáng)了試樣表面殘余應(yīng)力。噴丸后高強(qiáng)度鋼試樣表面位錯(cuò)數(shù)量有所上漲,試樣表面顯微硬度也增強(qiáng)�？桌鋽D壓后孔內(nèi)表面的晶粒發(fā)生變形并纖維化,在材料表面形成強(qiáng)化層,提高了材料表層的硬度,在距孔邊大約一個(gè)孔徑的范圍內(nèi)形成殘余壓應(yīng)力,最大殘余壓應(yīng)力出現(xiàn)在距孔邊大約1mm處。試樣經(jīng)過(guò)滲碳處理后,會(huì)在表層產(chǎn)生殘余壓應(yīng)力層,但壓應(yīng)力的最大值并不處在表層而是處在滲碳層的內(nèi)部。滲碳淬火后再進(jìn)行回火處理,明顯地降低了試樣的殘余壓應(yīng)力值;降低滲碳時(shí)間和表面碳含量都會(huì)使殘余壓應(yīng)力值降低,并使殘余壓應(yīng)力的最大值向表面移動(dòng)。模擬結(jié)果表明噴丸、孔冷擠壓和滲碳后試樣的殘余應(yīng)力場(chǎng)發(fā)展特點(diǎn)模擬結(jié)果和試驗(yàn)結(jié)果相同,表明模型的有效性可以運(yùn)用在各種工藝參數(shù)下噴丸、孔冷擠壓與滲碳過(guò)程中的數(shù)值模擬。噴丸工藝的模擬結(jié)果顯示,不斷增加彈丸速度,最大殘余壓應(yīng)力、最大殘余壓應(yīng)力深度、強(qiáng)化深度依次增長(zhǎng);彈丸彈性模量基于噴丸后殘余應(yīng)力場(chǎng)的影響較小。伴隨彈丸直徑的增大,最大殘余壓應(yīng)力、最大殘余壓應(yīng)力深度與強(qiáng)度也會(huì)隨之提高。隨著擠壓強(qiáng)度的增加,孔邊殘余壓應(yīng)力和外部的殘余拉應(yīng)力都隨之增大,同時(shí),殘余壓應(yīng)力的峰值點(diǎn)到孔邊的距離也隨著擠壓強(qiáng)度的增加而增加。隨著孔徑的增大,孔邊殘余壓應(yīng)力峰值的大小逐漸減小,但其分布寬度增加。當(dāng)孔邊距比e/d較小時(shí),孔邊殘余壓應(yīng)力較小,而外部的殘余拉應(yīng)力較大。伴隨e/d的增長(zhǎng),殘余壓應(yīng)力也會(huì)隨之提高,殘余拉應(yīng)力降低,殘余壓應(yīng)力的分布區(qū)域拓寬。用殘余應(yīng)力場(chǎng)模型對(duì)滲碳試樣在淬火冷卻過(guò)程中的瞬時(shí)應(yīng)力進(jìn)行模擬,試樣在冷卻到50秒時(shí),應(yīng)力分布為表面受拉,心部受壓;冷卻到260s時(shí)的應(yīng)力分布為表面受壓,心部受拉;冷卻到1300s時(shí)的應(yīng)力分布與260s時(shí)一樣,表面受壓,心部受拉,但壓應(yīng)力的數(shù)值明顯大于260s時(shí)的數(shù)值,在距表面大約0.7mm處,壓應(yīng)力達(dá)到最大值。
[Abstract]:With more and more application fields of high strength steel, high strength steel by the prepared parts because of long time alternating load pressure, resulting in the failure of the fatigue crack increases gradually formed on the surface. Therefore, the shot peening, strengthening the surface of the alternating load of high-strength steel reinforcement parts Kong Leng extrusion and carburizing and etc. the surface using the method of numerical simulation and experimental research of combining the analysis of the distribution law of residual stress field, to improve their life. This research not only has important theoretical significance, also has important engineering significance. In this paper, different shot peening and cold extrusion process of hole of high strength steel specimen based on the residual stress of the are analyzed, and through the finite element method of residual hole cold extrusion after shot peening and stress field numerical simulation was carried out. Effects of different depth and different surface of carbon The content of the stress field of the 20CrMn Ti steel specimens with residual, and by using the method of finite element numerical simulation is carried out. Through X test peening device, cold extrusion and hole after carburizing residual stress, followed by the test range of residual stress through the electrolytic polishing method. In addition, by means of X ray diffraction instrument for shot peening, hole cold extrusion and carburizing samples before and after the crystal structure was studied by determination of microhardness change layer, microstructure morphology observation. Through the ANSYS software to build the finite element model of different shot peening, residual stress hole cold extrusion and carburizing process under the condition of field simulation experiment results. That, along with the peening time growth, increasing the maximum residual stress and hardening depth, surface residual stress decreased gradually, compared to the small diameter of the projectile, the projectile formation of large diameter reinforcement is relatively large in depth. If Shot peening intensity increasing, the maximum residual stress, strength is also rising. Through the glass and ceramic pill pill to carry out the two shot peening enhances the surface residual stress in specimen after shot peening. High strength steel surface dislocation number of samples increases, the surface microhardness of sample is enhanced. Coldworked hole hole surface after grain deformation and fibrosis, reinforced layer is formed on the surface of the material, improve the surface hardness, formed in the range of about an aperture from the edge of the hole in the residual stress, the residual stress in the distance of hole edge about 1mm. The sample after carburizing, will produce compressive residual stress in the surface layer, maximum but the value of compressive stress in the surface but not in internal. The carburized layer after carburizing and quenching tempering treatment, significantly reduce the residual compressive stress value; reduce carburizing time and surface carbon content will cause the residual The compressive stress decreases, and the maximum value to the mobile surface residual stress. The simulation results show that the shot peening, residual Kong Leng extrusion and carburizing were the stress field characteristics of the development of the simulation results and experimental results show that the same, the validity of the model can be used in all kinds of shot peening parameters, numerical simulation of cold extrusion and hole in the process of carburization. The simulation results show that the shot peening process, increasing the projectile velocity, the maximum compressive residual stress, the residual stress depth, strengthening depth increase in projectile; elastic modulus based on compressive residual stress field of influence is small. With increasing projectile diameter, the maximum compressive residual stress, the maximum residual the compressive stress depth and strength will be increased. With the increase of compressive strength, hole compressive residual stress and residual external tensile stress increases, at the same time, the peak residual stress to the edge of the hole distance Also increased with the increase of compressive strength. When the diameter increases, the hole compressive residual stress peak value decreases, but its distribution width increases. When the hole margin ratio e/d is smaller, the hole compressive residual stress is smaller, while the external residual tensile stress is larger. With the growth of e/d, residual pressure stress also increases, the residual tensile stress is reduced, the regional distribution of residual compressive stress. With the widening of residual stress field model to simulate the instantaneous carburized specimens during quenching process of the stress, the specimen in the cooling to 50 seconds, the stress distribution of surface tension, heart compression; cooling the stress distribution of surface compression to 260s, pulled by heart; cooling to 1300s the stress distribution and 260s, surface pressure, pull by heart, but the values of compressive stress was significantly higher than that of 260s when the distance from the surface, at about 0.7mm, the compressive stress reaches the maximum value.

【學(xué)位授予單位】：燕山大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG668

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