变速箱六档齿轮断裂分析及解决措施

对频繁出现轮齿早期断裂的变速箱六档齿轮进行了分析。通过对齿轮断裂特征、显微组织、硬度等方面的综合分析,确定了其断裂形式为低应力高周疲劳断裂。由裂纹扩展过程判断齿轮轮辐设计强度不足是导致其大批量早期疲劳失效的根本原因。据此通过改进齿形、油孔等设计措施,降低齿根部的设计应力水平,解决了这一问题。     

Rolling contact fatigue behavior of sintered and hardened steels

Powder-metal-processed bearings and gears are finding increasing application because of their economical and technical advantages. The residual pores from the sintering operatives act as lubricant pockets and dampen sound and vibration. However, porosity also decreases the mechanical strength and reduces the life of components fabricated by powder processing relative to similar wrought components. The rolling contact fatigue behavior of sintered and heat treated steel rollers was investigated using a fatigue test machine designed and fabricated for that purpose. The powder-metal-processed and the wrought steel rollers that were tested had similar composition and hardness and were mated against wrought steel rollers of high hardness. The contact stress versus number of cycles to failure data showed that the wrought steel had a very high endurance limit under rolling contact fatigue compared to the sintered steels investigated. Rolling contact fatigue behavior was found to depend on the porosity present in the material. Large surface peeling failures and pitting type fatigue failures were observed in the sintered and hardened steels, while only pitting type failures were observed in the wrought steels     

Festwalzen und Schwingfestigkeit

Deep Rolling and Fatigue Strength The fatigue properties of specimens and components are largely increased by deep rolling. Depending on geometrical shape of components and material strength the compressive residual stresses and the increased surface hardness made by deep rolling have a different effect on the improvement of fatigue strength. The fatigue properties of smooth specimens and components with a sufficient toughness can be raised by increase of surface hardness, whereas in case of notched parts the influence of permanent compressive residual stresses is dominant. The application of deep rolling in case of crankshafts shows a clear superiority of mechanical strengthening procedure to thermal surface strengthening. If there are some reasons to improve the wear behaviour beside the fatigue strength it is commendable to combine thermal and mechanical surface strengthening.     

Enhancing the lifetime and corrosion resistance of gears made of carbon steel

Gears for structural machines require high fatigue strength for high performance. Generally, gears made of carbon steel easily corrode, thus, shortening their fatigue life. The aim of this paper is to improve the fatigue strength of carbon steel gears by means of heat treatment method which was nitriding composed of 95 % nitrogen gas as well as 5 % hydrogen gas, and to investigate its properties after nitriding. Therefore, in order to find the optimum nitriding temperature to increase the hardness and corrosion resistance of gears, the gas nitriding process was conducted at two different tube furnace temperatures: low (550 °C) and high (1150 °C), both for four hours. Microstructural and mechanical property evaluation of the low and high temperature nitrided low-carbon steel BS970-080A15 were studied and the results were compared to identify which gear had better performance in terms of hardness as well as corrosion resistance. The results from Vickers hardness test and weight loss analysis proved that high temperature nitrided carbon steel is harder and more corrosion resistant than the low temperature one.     

5CrNiMo钢的强度水平和表面强化对冲击疲劳性能的影响

本文探讨了用冲击疫劳试验测定的疲劳寿命和疲劳裂纹扩展速率衡量热锤锻模材料疲劳抗力的合理性。研究了5CrNiMo钢在热锻模要求的硬度范围内,材料强度水平和表面强化对冲击疲劳性能的影响。试验结果表明,在相当小型锻模受载的低冲击能量作用下,适当提高材料强度可延长疲劳寿命;在相当大型锻模受载的高冲击能量作用下,提高材料塑性、韧性可提高疲劳寿命。软氮化并磨去脆性白层可显著提高低冲击能量下的冲击疲劳寿命。     

Effect of cryogenic treatment on tensile behavior of case carburized steel-815M17

The crown wheel and pinion represent the most highly stressed parts of a heavy vehicle; these are typically made of 815M17 steel. The reasons for the frequent failure of these components are due to tooth bending impact, wear and fatigue. The modern processes employed to produce these as high, durable components include cryogenic treatment as well as conventional heat treatment. It helps to convert retained austenite into martensite as well as promote carbide precipitation. This paper deals with the influence of cryogenic treatment on the tensile behavior of case carburized steel 815M17. The impetus for studying the tensile properties of gear steels is to ensure that steels used in gears have sufficient tensile strength to prevent failure when gears are subjected to tensile or fatigue loads, and to provide basic design information on the strength of 815M17 steel. A comparative study on the effects of deep cryogenic treatment (DCT), shallow cryogenic treatment (SCT) and conventional heat treatment (CHT) was made by means of tension testing. This test was conducted as per ASTM standard designation E 8M. The present results confirm that the tensile behavior is marginally reduced after cryogenic treatment (i.e. both shallow and deep cryogenic treatment) for 815M17 when compared with conventional heat treatment. Scanning electron microscopic (SEM) analysis of the fracture surface indicates the presence of dimples and flat fracture regions are more common in SCT specimens than for CHT and DCT-processed material.     

装甲车辆重载齿轮综合强化方法研究现状

机动性是装甲车辆的重要性能指标,对传动系统有着极高的要求。工况复杂、服役环境特殊的重载齿轮是装甲车辆传动系统的重要组成部分,如何有效对其进行强化一直是国内外的研究热点。材料的选择、优化及新材料开发是生产强化重载齿轮的基础,选用合理的热处理工艺可提升齿轮的综合性能,结合有效的表面强化技术能延长疲劳寿命。从以上3个方面出发,分析了重载齿轮生产流程中关键的强化阶段,阐述了重载齿轮综合强化方法的进展,讨论了具有应用前景的新方法,并就今后重载齿轮的发展提出了若干建议。     

Residual stress influence on fatigue lifetimes of electroplated AISI 4340 high strength steel

Residual stresses play an important role in the fatigue lives of structural engineering components. In the case of near surface tensile residual stresses, the initiation and propagation phases of fatigue process are accelerated; on the other hand, compressive residual stresses close to the surface may increase fatigue life. In both decorative and functional applications, chromium electroplating results in excellent wear and corrosion resistance. However, it is well known that it reduces the fatigue strength of a component. This is due to high tensile internal stresses and microcrack density. Efforts to improve hard chromium properties have increased in recent years. In this study, the effect of a nickel layer sulphamate process, as simple layer and interlayer, on fatigue strength of hard chromium electroplated AISI 4340 steel hardness – HRc 53, was analysed. The analysis was performed by rotating bending fatigue tests on AISI 4340 steel specimens with the following experimental groups: base material, hard chromium electroplated, sulphamate nickel electroplated, sulphamate nickel interlayer on hard chromium electroplated and electroless nickel interlayer on hard chromium electroplated. Results showed a decrease in fatigue strength in coated specimens and that both nickel plating interlayers were responsible for the increase in fatigue life of AISI 4340 chromium electroplated steel. The shot peening pre-treatment was efficient in reducing fatigue loss in the alternatives studied.     

基于内部失效机理预测评估渗碳Cr-Ni齿轮钢的超高周疲劳强度

对渗碳Cr-Ni齿轮钢进行应力比为0和0.3的室温超高周疲劳实验,观测试样中诱发裂纹萌生的夹杂和疲劳断口形貌,以全面评估渗碳Cr-Ni齿轮钢疲劳性能。将疲劳失效模式分为有细颗粒区(Fine granular area,FGA)的内部疲劳失效和有表面光滑区(Surface smooth area, SSA)的表面疲劳失效,并阐明了渗碳Cr-Ni齿轮钢的超高周内部疲劳破坏机制。基于累积损伤和位错能量法并结合细颗粒区形成机理和夹杂的最大评估尺寸,分别构建了两种渗碳Cr-Ni齿轮钢内部疲劳强度的预测模型。利用FGA尺寸与夹杂尺寸的比值和夹杂应力强度因子及应力比之间的关系,修正所提出的两种疲劳强度预测模型并给出了最大夹杂尺寸下的l_FGA-S-N曲线。结果表明,基于累积损伤法和位错能量法分别构建的疲劳强度预测模型都可用于预测评估渗碳Cr-Ni齿轮钢在多种应力比下的内部疲劳强度,基于位错能量法的强度预测模型精度较高。     

SKD61钢压铸模具开裂分析

通过化学成分分析、力学性能测试、金相检验以及断口分析等方法对SKD61钢压铸模具开裂原因进行分析。结果表明：由于该模具材料的钼和钒含量偏低,导致热处理后的硬度偏低,使得疲劳强度降低,从而在服役中以疲劳形式早期开裂失效。     

4Cr5MoSiV1，8407钢的热疲劳性能

采用自约束热疲劳试验方法,对比研究了相同热处理条件的4Cr5MoSiV1,8407钢的热疲劳特性,观察分析了疲劳裂纹形貌和深度,采用热疲劳损伤因子定量研究了二种钢的热疲劳过程。结果表明：两种钢的热疲劳裂纹萌生发生在100－200次之间。8407钢热疲劳裂纹的萌生较4Cr5MoSiV1钢均匀,细小;在1600次冷热循环前,二者的热疲劳损伤程度无明显差别,在1600次热循环后,前者的热疲劳损伤程度低于后者;在较低的回火温度条件下,8407钢的热疲劳抗力稍优于4Cr5MoSiV1;而在高温回火时,8407钢的热疲劳抗力属于4Cr5MoSiV1钢。分析了这二种钢的热疲劳机制,指出决定材料热疲劳裂纹抗力的是钢的热稳定性和钢的强度或硬度。     

Improvement in the fatigue strength of chromium electroplated AISI 4340 steel by shot peening

In landing gear, an important mechanical component for high responsible applications, wear and corrosion control is currently accomplished by chrome plating or hard anodising. However, some problems are associated with these operations. Experimental results have also shown that chrome‐plated specimens have fatigue strength lower than those of uncoated parts, attributed to high residual tensile stress and microcracks density contained into the coating. Under fatigue conditions these microcracks propagate and will cross the interface coating‐substrate and penetrate base metal without impediment. Shot peening is a surface process used to improve fatigue strength of metal components due to compressive residual stresses induced in the surface layers of the material, making the nucleation and propagation of fatigue cracks difficult. This investigation is concerned with analysis of the shot peening influence on the rotating bending fatigue strength of hard chromium electroplated AISI 4340 steel. Specimens were submitted to shot peening treatment with steel and ceramic shots and, in both cases, experimental results show increase in the fatigue life of AISI 4340 steel hard chromium electroplated, up to level of base metal without chromium. Peening using ceramic shot resulted in lower scatter in rotating bending fatigue data than steel shots.     

分动箱齿轮断裂原因

某分动箱的20CrMnTi钢齿轮在工作过程中发生断裂.采用宏观分析、微观分析、化学成分分析、硬度测试、硬化层深度测量、非金属夹杂物分析、金相检验等方法对齿轮的断裂原因进行了分析.结果表明:齿面上残留的加工刀痕导致应力集中,在周期载荷的作用下,疲劳裂纹源首先在残留的加工刀痕较深处形成,随后裂纹逐渐扩展,最终齿轮发生疲劳断...     

Cavitation peening to improve the fatigue strength of nitrocarburized steel

Shot peening is a commonly employed technique used to improve the fatigue strength of nitrocarburized components. However, the compound layer of the component can be broken by this technique. Cavitation peening (CP) is an alternative shotless technique, which can increase the fatigue strength of the component without separation of the compound layer. To evaluate the potential of CP as a means for improving fatigue strength, nitrocarburized carbon steel (JIS S50C) has been analyzed in the non‐peened and CP conditions. The fatigue strength of CP specimens was increased by 15% in comparison with that of non‐peened specimens. This increase in the fatigue strength of CP specimen was achieved by the increase in the maximum hardness and compressive residual stress within the diffusion zone.     

HXD1机车牵引电机转轴组件断裂失效分析

HXD1型电力机车的牵引电机转轴和小齿轮轴采用圆锥过盈配合传动结构(下称转轴组件),使用中该组件出现了早期断裂失效.本文通过理化检测、断口和配合面宏/微观形貌观察等失效分析技术对失效组件进行了分析.结果表明,材料成分、组织和显微硬度正常,小齿轮轴和电机转轴的失效形式分别为高周疲劳断裂和微动疲劳断裂.造成组件失效的原因和过程是,小齿轮轴近齿端油槽-油孔交界线处有较大的结构应力集中,油槽底部周向加工刀痕造成附加应力集中,在应力集中和旋转弯曲疲劳载荷作用下油孔边两个应力集中点萌生了疲劳裂纹并扩展;随小齿轮轴裂纹的不断扩展转轴组件结构刚度减小,继而诱发了与小齿轮轴匹配的电机轴配合面的微动疲劳,电机轴疲劳裂纹萌生于微动区的边缘处;电机转轴先于小齿轮轴完全断裂.基于本文的分析结果提出了提高组件抗疲劳断裂的技术措施.     

Material behaviour of a dual hardening steel under thermomechanical loading

Dual hardening steels are a group of metals, which reach their material properties through a combination of strengthening via carbides and intermetallic precipitates. Because of their combination of mechanical properties, dual hardening steels are a promising alloying concept for hot‐work applications. The applied materials for hot‐work applications have to meet certain requirements, such as high hardness, high thermal strength, thermal stability, and fracture toughness. In this paper, a dual hardening steel in different heat treatment conditions was tested under out‐of‐phase thermomechanical loading conditions. All tests were done under full reverse strain control and the minimum temperature was kept constant. In the thermomechanical fatigue tests, solution annealed samples reached higher lifetimes compared with aged specimens. The hardness measurements show that the starting procedure of the thermomechanical fatigue leads to an increase of the hardness approximate to the values of the specimens with the ageing heat treatment. Cyclic softening can be observed in the test with the highest maximum temperature of 600°C. An increase of the maximum temperature also causes a decrease of the lifetime.     

Influence of laser shock peening on fatigue performance of LZ50 axle steel for railway wheel set

Laser shock peening (LSP) is a surface treatment technique that forms a strengthened layer on the metal surfaces. In this study, the LSP was applied on the locomotive LZ50 axle steel surface which was interference fitted with the wheel. The microstructures, fracture morphologies and fatigue performances of LSP‐treated and untreated axle steels were explored. The results indicated that after the LSP treatment, a strengthened layer was generated on the axle steel surface. The surface hardness was increased by 25%, that is, from around 204 to around 255 HV_0.3. The residual compressive stresses were improved from 260 to 345 MPa along the axial direction and from 165 to 225 MPa along the radial direction. The fatigue limit was increased by 30%, that is, from around 130 to around 170 MPa. The fracture surfaces could be divided into three regions: crack initiation, crack propagation, and short‐break regions. In the crack initiation region, the fatigue striation of the LSP‐treated steel was denser than the untreated steel. In the crack propagation and short‐break regions, the fracture morphologies of the LSP‐treated and the untreated axle steels were similar.     

A comparative study of the fretting fatigue behavior of 4340 steel and PH 13-8 Mo stainless steel

The fretting fatigue behavior of two high strength structural steels, PH 13-8 Mo stainless steel and quenched and tempered 4340 steel, is investigated. Both were heat treated to a similar hardness (43-44 HRC), comparable to the condition used in structural components. Both materials experienced significant reductions in fatigue strength due to fretting, with PH 13-8 Mo stainless steel exhibiting a greater susceptibility to fretting than 4340 steel, when operating in the mixed fretting regime. The use of fretting pads with different surface profiles showed that contact geometry did not significantly influence the fretting fatigue behavior of either steel for the range of loading conditions considered. The fretting fatigue lives are discussed in light of the low cycle fatigue and crack growth rate behavior of these steels. The life trends in fretting fatigue correlate more closely to the low cycle fatigue behavior.     

Enhancing torsion fatigue behaviour of a martensitic stainless steel by generating gradient nanograined layer via surface mechanical grinding treatment

Abstract

A gradient nanograined (GNG) surface layer was formed on a martensitic stainless steel bar sample by means of the surface mechanical grinding treatment (SMGT). The average grain size is ～25 nm on the topmost surface layer and increases gradually with increasing depth. The torsion fatigue strength is elevated by 38% with the GNG surface layer compared with the original material. An additional 8% increment in fatigue strength is achieved after a post-annealing treatment of the SMGT sample. By analysing the microstructure, hardness, surface roughness and residual stress distribution in the SMGT samples, we believe that the enhanced fatigue resistances originate from the GNG structure with a hard surface layer and a high structural homogeneity.     

The effect of contact pad hardness on the fretting fatigue behaviour of AZ61 magnesium alloy

In the present study, the effect of hardness of contact material on fretting fatigue strength was experimentally investigated as a function of stress ratio. AZ61 magnesium alloy used in defense and transportation industries was used as the material for both the specimen and the contact pad. Two levels of hardness of contact material, 55.3 Vickers Hardness (HV) and 83.3 HV, were prepared by heat treatments. According to the results, with increasing hardness, the fretting fatigue strength decreased. The relative slip amplitude increased with increasing hardness, while the tangential force amplitude was not influenced by the hardness. It was speculated that because the local tangential stress at the contact edge increases with increasing hardness, the fretting fatigue strength decreases with increasing hardness.