本文選題：GCr15軸承鋼 + 滾道接觸疲勞��； 參考：《蘭州理工大學(xué)》2017年碩士論文

【摘要】：GCr15軸承鋼是一種廣泛應(yīng)用于制造軸承、齒輪等滾動零部件的高碳鉻鋼,通常情況下服役的軸承承受的是循環(huán)載荷,包括徑向壓縮應(yīng)力和周向摩擦力。在這種復(fù)雜工況下的軸承實際壽命往往低于設(shè)計壽命。雖然對軸承鋼的接觸疲勞性能研究已久,但是對其失效機制仍存在分歧。由于機械設(shè)備常常在高溫、高速、高載荷的條件下運行,因此接觸疲勞又成為眾多學(xué)者研究的熱點問題。本文用試驗?zāi)M軸承的工作環(huán)境,研究不同載荷和滾滑比下試樣接觸表面磨損形貌以及亞表面損傷機制,為追溯疲勞本源和延長軸承的服役壽命提供理論依據(jù)。本文以GCr15軸承鋼材料為試驗對象,采用MJP-20型滾動接觸疲勞試驗機進行線接觸滾動疲勞試驗,通過改變載荷、滾滑比等試驗參數(shù)研究材料接觸疲勞亞表面損傷機制。試驗前在同一熱處理狀態(tài)下獲得均勻的組織,對加工試樣材料的原始組織形貌以及成分含量進行了分析;試驗后利用光學(xué)顯微鏡(OM)和掃描電鏡(SEM)對接觸表面的磨損形貌、裂紋和亞表面組織形貌進行觀察,利用透射電鏡(TEM)觀察微區(qū)組織結(jié)構(gòu)變化,最后使用納米壓痕儀對白色蝕刻區(qū)(WEA)和附近基體材料的硬度進行測量對比。通過以上對接觸表面形貌、亞表面裂紋及微觀組織變化的分析。得到結(jié)論為:(1)GCr15軸承鋼試樣在不同的接觸壓力和滾滑比下表面磨損形貌存在很大區(qū)別,試驗表明載荷和滾滑比是影響表面磨損程度的共同因素。裂紋是導(dǎo)致軸承等工件剝落失效的直接原因。裂紋的不定向擴展會使材料產(chǎn)生多種失效模式,如點蝕、剝落和斷裂等。(2)滾動接觸疲勞是一個復(fù)雜的過程,在多個因素的影響下,疲勞裂紋的長大是連續(xù)或不連續(xù)擴展的一個過程,并且疲勞裂紋的擴展方向隨著工況的改變而改變。裂紋內(nèi)的磨屑是裂紋面相對運動及摩擦的結(jié)果。在裂紋內(nèi)部還出現(xiàn)了扭曲和旋轉(zhuǎn)的微觀結(jié)構(gòu),因此赫茲接觸是一個復(fù)雜的多軸應(yīng)力狀態(tài)。(3)WEA在接觸壓力和滾滑比的共同作用下形成且WEA在不同的接觸壓力產(chǎn)生。在WEA中已不存在碳化物且WEA和基體之間存在明顯的界面。在靠近WEA的基體中出現(xiàn)拉長的晶粒和大量的位錯簇。越靠近界面的位置,晶粒細化程度越高。由于晶粒細化,WEA的硬度比基體材料的硬度有明顯的升高。(4)滾動接觸疲勞引起微觀結(jié)構(gòu)變化有兩種方式:納米結(jié)晶和非晶化。于是,WEA可被分為變形WEA和轉(zhuǎn)化WEA。變形的WEA主要包含納米晶,而轉(zhuǎn)化WEA是非晶相和納米晶的共存體。這兩種類型的微觀結(jié)構(gòu)變化均由塑性變形的累積程度決定。
[Abstract]:GCr15 bearing steel is a kind of high carbon chromium steel which is widely used in manufacturing rolling parts such as bearings gears and so on. Usually the bearing in service is subjected to cyclic load including radial compression stress and circumferential friction. The actual life of bearing under this complex working condition is often lower than the design life. Although the contact fatigue properties of bearing steels have been studied for a long time, there are still differences on the failure mechanism of bearing steels. Contact fatigue has become a hot issue for many scholars because the mechanical equipment often runs under high temperature, high speed and high load. In this paper, the contact surface wear morphology and subsurface damage mechanism of the specimens under different load and rolling slip ratio are studied by simulating the working environment of the bearing, which provides a theoretical basis for tracing the fatigue source and prolonging the service life of the bearing. In this paper, GCr15 bearing steel is used as experimental object. Linear contact rolling fatigue test is carried out with MJP-20 rolling contact fatigue tester. The mechanism of contact fatigue subsurface damage is studied by changing load, rolling slip ratio and other test parameters. The uniform microstructure was obtained in the same heat treatment state before the test. The original microstructure and composition content of the processed samples were analyzed. After the test, the wear morphology of the contact surface was observed by optical microscope (OM) and scanning electron microscope (SEM). The microstructures were observed by TEM and TEM. Finally, the hardness of white etched area was measured and compared with that of the matrix material by nano-indentation. Based on the above analysis of the contact surface morphology, sub-surface cracks and microstructure changes. It is concluded that the wear morphology of GCr15 bearing steel under different contact pressure and rolling slip ratio is very different. The test results show that the load and the rolling slip ratio are the common factors affecting the wear degree of the bearing steel. Crack is the direct cause of spalling failure of bearing and other workpieces. The unorientated propagation of cracks will lead to a variety of failure modes, such as pitting, denudation and fracture. Rolling contact fatigue is a complicated process, and under the influence of many factors, Fatigue crack growth is a process of continuous or discontinuous growth, and the direction of fatigue crack growth changes with the change of working conditions. The wear debris in the crack is the result of the relative movement and friction of the crack surface. There are also twisting and rotating microstructures inside the crack, so Hertz contact is a complex multiaxial stress state. WEA is formed under the combined action of contact pressure and roll slip ratio, and WEA is produced at different contact pressure. There are no carbides in WEA and obvious interface between WEA and matrix. Elongated grains and a large number of dislocation clusters appear in the matrix near WEA. The closer the interface is, the higher the grain refinement degree is. Because the hardness of WEA is obviously higher than that of matrix material, there are two ways to change the microstructure of WEA: nanocrystalline and amorphous. Therefore, WEA can be divided into transformed WEA and transformed wea. The deformed WEA mainly contains nanocrystalline, while the transformed WEA is the coexistence of amorphous phase and nanocrystalline. Both types of microstructure change are determined by the cumulative degree of plastic deformation.
【學(xué)位授予單位】：蘭州理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG142.1

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