Failure analysis of an automobile differential pinion shaft
Abstract
Differential is used to decrease the speed and to provide moment increase for transmitting the movement coming from the engine to the wheels by turning it according to the suitable angle in vehicles and to provide that inner and outer wheels turn differently Pinion gear and shaft at the entrance are manufactured as a single part whereas they are in different forms according to automobile types Mirror gear which will work with this gear should become familiar before the assembly In case of any breakdown they should be changed as a pair Generally in these systems there are wear damages in gears The gear inspected in this study has damage as a form of shaft fracture
In this study failure analysis of the differential pinion shaft is carried out Mechanical characteristics of the material are obtained first Then the microstructure and chemical compositions are determined Some fractographic studies are 2005 Elsevier Ltd All rights reserved
Keywords Differential Fracture Power transfer Pinion shaft
1 Introduction
The finaldrive gears may be directly or indirectly driven from the output gearing of the gearbox Directly driven final drives are used when the engine and transmission units are combined together to form an integral construction Indirectly driven final drives are used at the rear of the vehicle being either sprung and attached to the body structure or unsprung and incorporated in the rearaxle casing The finaldrive gears are used in the transmission system for the following reasons [1]
(a) to redirect the drive from the gearbox or propeller shaft through 90°and
(b) to provide a permanent gear reduction between the engine and the driving roadwheels
In vehicles differential is the main part which transmits the movement coming from the engine to the wheels On a smooth road the movement comes to both wheels evenly The inner wheel should turn less and the outer wheel should turn more to do the turning without lateral slipping and being flung Differential which is generally placed in the middle part of the rear bridge consists of pinion gear mirror gear differential box two axle gear and two pinion spider gears
A schematic illustration of a differential is given in Fig 1 The technical drawing of pinion the fractured pinion shaft is also given in Fig 2 Fig 3 shows the photograph of the fractured pinion shaft and the fracture section is indicated
In differentials mirror and pinion gear are made to get used to each other during manufacturing and the same serial number is given Both of them are changed on condition that there are any
problems In these systems the common damage is the wear of gears [24] In this study the pinion shaft of the differential of a minibus has been inspected The minibus is a diesel vehicle driven at the rear axle and has a passenger capacity of 15 people Maximum engine power is 904000 HPrpm and maximum torque is 2051600 Nmrpm Its transmission box has manual system (5 forward 1 back) The damage was caused by stopping and starting the minibus at a traffic lights In this differential entrance shaft which carries the pinion gear was broken Various studies have been made to determine the type and possible reasons of the damage These are
• studies carried out to determine the material of the shaft
• studies carried out to determine the microstructure
• studies related to the fracture surface
There is a closer photograph of the fractured surfaces and fracture area in Fig 4 The fracture was caused by taking out circular mark gear seen in the middle of surfaces
2 Experimental procedure
Specimens extracted from the shaft were subjected to various tests including hardness tests and metallographic and scanning electron microscopy as well as the determination of chemical composition All tests were carried out at room temperature
21 Chemical and metallurgical analysis
Chemical analysis of the fractured differential material was carried out using a spectrometer The chemical composition of the material is given in Table 1 Chemical composition shows that the material is a lowalloy carburizing steel of the AISI 8620 type
Hardenability of this steel is very low because of low carbon proportion Therefore surface area becomes hard and highly enduring and inner areas becomes tough by increasing carbon proportion on the surface area with cementation operation This is the kind of steel which is generally used in mechanical parts subjected do torsion and bending High resistance is obtained on the surface and high fatigue endurance value can be obtained with compressive residual stress by making the surface harder [57]
In which alloy elements distribute themselves in carbon steels depends primarily on the compound and carbide forming tendencies of each element Nickel dissolves in the α ferrite of the steel since it has less tendency to form carbides than iron Silicon combines to a limited extent with the oxygen present in the steel to form nonmetallic inclusions but otherwise dissolves in the ferrite Most of the manganese added to carbon steels dissolves in the ferrite Chromium which has a somewhat stronger carbideforming depends on the iron partitions between the ferrite and carbide phases The distribution of chromium depends on the amount of carbon present and if other stronger carbideforming elements such as titanium and columbium amount of carbon present and if other stronger carbideforming elements such as titanium and columbium are absent Tungsten and molybdenum combine with carbon to form carbides is there is sufficient carbon present and if other stronger carbideforming elements such da titanium and columbium are absent Manganese and nickel lower the eutectoid temperature [8]
Preliminary micro structural examination of the failed differential material is shown in Fig 5 It can be seen that the material has a mixed structure in which some ferrite exist probably as a result of slow cooling and high Si content High Si content in this type of steel improves the heat treatment susceptibility as well as
an improvement of yield strength and maximum stress without any reduction of ductility [9] If the microstructure cannot be inverted to martensite by quenching a reduction of fatigue limit is observed
There are areas with carbon phase in Fig 5(a) There is the transition boundary of carburization in Fig 5(b) and (c) shows the matrix region without carburization As far as it is seen in there photographs the piece was first carburized then the quenching operation was done than tempered This situation can be understood from blind martensite plates
22 Hardness tests
The hardness measurements are carried out by a MetTestHT type computer integrated hardness tester The load is 1471 N The medium hardness value of the interior regions is obtained as obtained as 43 HRC Micro hardness measurements have been made to determine the chance of hardness values along crosssection because of the hardening of surface area due to carburization The results of Vickers hardness measurement under a load of 4903 N are illustrated in Table 2
23 Inspection of the fracture
The direct observations of the piece with fractured surfaces and SEM analyses are given in this chapter The crack started because of a possible problem in the bottom of notch caused the shaft to be broken completely The crack started on the outer part after some time it continued beyond the centre and there was only a little part left And this part was broken statically during sudden starting of the vehicle at the traffic lights As a characteristic of the fatigue there are two regions in the fractured surface These are a smooth surface created by crack propagation and a rough surface created by sudden fracture These two regions can be seen clearly for the entire problem as in Fig 4 The fatigue crack propagation region covers more than 80 of the crosssection
Shaft works under the effect of bending torsion and axial forces which affect repeatedly depending on the usage place There is a sharp fillet at level on the fractured section For this reason stress concentration factors of the area have been determined Kt 24 value (for bending and tension) and Kt 19 value (for torsion) have been acquired according to calculations These are quite high values for areas exposed to combined loading
These observations and analysis show that the piece was broken under the influence of torsion with low nominal stresses electron microscopy shows that the fracture has taken place in a ductile manner (Fig6) There are some shear lips in the crack propagation region which is a glue of the plastic shear deformations Fig 7 shows the beach marks of the fatigue crack propagation The distance between any lines is nearly 133 nm
3 Conclusions
A failed differential pinion shaft is analysed in this study The pinion shaft is produced from AISI
8620 low carbon carburising steel which had a carbursing quenching and tempering heat treatment process Mechanical properties micro structural properties chemical compositions and fractographic analyses are carried out to determine the possible fracture reasons of the component As a conclusion the following statements can be drawn
• The fracture has taken place at a region having a high stress concentration by a fatigue procedure under a combined bending torsion and axial stresses having highly reversible nature
• The crack of the fracture is initiated probably at a material defect region at the critical location
• The fracture is taken place in a ductile manner
• Possible later failures may easily be prevented by reducing the stress concentration at the critical location
Acknowledgement
The author is very indebted to Prof S Tasgetiren for his advice and recommendations during the srudy
References
[1] Heisler H Vehicle and engine technology 2nd ed London SAE International 1999
[2] Makevet E Roman I Failure analysis of a final drive transmission in offroad vehicles Eng Failure Anal 2002957992
[3] Orhan S Aktu ¨rk N Determination of physical faults in gearbox through vibration analysis J Fac Eng Arch Gazi University 200318(3)97–106
[4] Tasgetiren S Aslantas K Ucun I Effect of pressfitting pressure on the fatigue damages of root in spur gears Technol Res EJMT 2004221–9
[5] Nanawarea GK Pableb MJ Failures of rear axle shafts of 575 DI tractors Eng Failure Anal 200310719–24
[6] Aslantas K Tasgetiren S A study of spur gear pitting formation and life prediction Wear 20042571167–75
[7] Savas V O ¨ zek C Investigation of the distribution of temperature on a shaft with respect to the deflection Technol Res EJMT 2005133–8
[8] Smith FW Principles of materials science and engineering 3rd ed USA McGrawHill Series 1996 p 517–18
[9] ASM metal handbook vol 1 Properties and selection irons steels and high performance alloys 1991
[10] Voort GFV Visual examination and light microscopy ASM handbook metallography and microstructures Materials Park (OH) ASM International 1991 p 100–65
汽车差速器齿轮轴失效分析
摘
差速器降低速度增加扭矩根合适角度两轮传递动力齿轮安装轴体装配前应熟悉齿轮结构发生障齿轮安装轴起更换般言系统中齿轮损坏形式磨损损坏项研究中检查齿轮损坏形式轴断裂项研究差速器齿轮轴障分析首先获材料机械特性然确定微观结构化学组合物
关键词：差速器断裂动力传递齿轮轴
1．简介
终驱动齿轮直接间接变速器输出齿轮驱动发动机传动装置结合起形成整体结构时需直接驱动终驱动齿轮间接驱动末级驱动器助辅助装置敷汽车方者纳入驱动桥传动系统中该齿轮原：
（1）传动轴变速器传动轴定90度
（2）发动机驱动轮间提供永久减速
车辆中差速器传递发动机车轮间运动部分滑路面运动两车轮均匀传动轮应转少外轮应转然转时会发生滑移差速器般放桥中间星形齿轮架差速器箱半轴齿轮星形齿轮组成
图1示意图图2图3显示齿轮轴技术图齿轮轴片指出断裂部分
差速器制造程中动轮齿轮相序列号出现问题二者需更换系统中常见损伤齿轮[24]磨损项研究中辆面包车差速器齿轮轴进行检查该面包车辆轮驱动柴油车
15载客力发动机功率90 4000马力转速扭矩205 1600纳米转分变速箱手动系统（5前1回）损害停交通灯启动面包车引起差速器中带齿轮入口轴破种样研究已确定类型损坏原：
•进行研究确定轴材料
•进行研究确定微结构
•断裂面相关研究
图4 裂隙面断裂面积距离片该断裂表面中间圆形标志齿轮造成
2实验程序
轴提取试样进行种测试包括硬度测试金相扫描电子显微镜化学成分测定测试室温进行
21化学冶金分析
光谱仪进行断裂材料化学分析材料化学成分表1中出化学成分表明该材料种低合金渗碳钢AISI 8620型低碳例钢淬透性低表面增加碳例胶结操作表面变坚硬持久耐部变强硬种常钢结构受扭弯机械零件中通残余压应力加强硬度获高疲劳强度高性表面
碳钢中合金元素分布取决元素化合物碳化物形成倾镍钢中铁素体中溶解没铁形成碳化物倾更硅刚中少部分氧反应形成非金属化合物然分解铁素体铁相铬更易碳反应掺入铬取决碳含量
失效差速器材料初步微结构检查示图5出该材料具混合结构中存某铁素体种钢高硅含量提高热处理敏感性
屈服强度提高应力减少塑性[ 9 ]果微观结构法通淬火马氏体转变观察疲劳极限降低
图5（1）碳相区图5渗碳渡边界（b）（c）显示矩阵区域渗碳里片件作品第渗碳淬火然回火操作种情况理解观察马氏体板
22硬度试验
开展mettest HT型计算机集成硬度计硬度测量负载1471中等硬度值部区43 HRC显微硬度测量已确定硬度值截面加渗碳4903 n示表2负荷维氏硬度测量结果
23 断裂处检查
章中出直接观测结果断裂面扫描电镜分析裂纹开始底部裂缝导致轴断裂裂缝开始外部分段时间继续超越中心部分断裂部分等交通灯车辆突然启动时破作疲劳特征断裂面2区域光滑表面裂纹扩展粗糙表面创建突然断裂2区域清楚整问题图4疲劳裂纹区覆盖80横截面
轴弯曲扭转轴力作受影响方反复锋利薄面水裂缝性剖面原该区应力集中系数确定KT 24价值（弯曲张力）KT 19价值（扭转）根计算获 相高数值区域暴露联合载荷观察分析显示扭转应力作轴断裂延展状态（fig6）裂纹扩展区定剪切裂痕塑性剪切变形图7显示疲劳裂纹扩展海滩纹线间距离133纳米
3结
项研究中失效差速器齿轮轴进行分析齿轮轴产生AISI 8620低碳渗碳钢渗碳淬火回火热处理工艺力学性微观结构特性化学成分断口分析确定断裂原：
•具高应力集中受弯曲扭转轴应力作具高度逆性区域发生断裂
•关键部位材料缺陷区域会引发断裂
•种韧性方式中发生断裂
•关键位置减少应力集中防止出现障发生
参考
[1] Heisler H Vehicle and engine technology 2nd ed London SAE International 1999
[2] Makevet E Roman I Failure analysis of a final drive transmission in offroad vehicles Eng Failure Anal 2002957992
[3] Orhan S Aktu ¨rk N Determination of physical faults in gearbox through vibration analysis J Fac Eng Arch Gazi University 200318(3)97–106
[4] Tasgetiren S Aslantas K Ucun I Effect of pressfitting pressure on the fatigue damages of root in spur gears Technol Res EJMT 2004221–9
[5] Nanawarea GK Pableb MJ Failures of rear axle shafts of 575 DI tractors Eng Failure Anal 200310719–24
[6] Aslantas K Tasgetiren S A study of spur gear pitting formation and life prediction Wear 20042571167–75
[7] Savas V O ¨ zek C Investigation of the distribution of temperature on a shaft with respect to the deflection Technol Res EJMT 2005133–8
[8] Smith FW Principles of materials science and engineering 3rd ed USA McGrawHill Series 1996 p 517–18
[9] ASM metal handbook vol 1 Properties and selection irons steels and high performance alloys 1991
[10] Voort GFV Visual examination and light microscopy ASM handbook metallography and microstructures Materials Park (OH) ASM International 1991 p 100–65
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Abstract
Differential is used to decrease the speed and to provide moment increase for transmitting the movement coming from the engine to the wheels by turning it according to the suitable angle in vehicles and to provide that inner and outer wheels turn differently Pinion gear and shaft at the entrance are manufactured as a single part whereas they are in different forms according to automobile types Mirror gear which will work with this gear should become familiar before the assembly In case of any breakdown they should be changed as a pair Generally in these systems there are wear damages in gears The gear inspected in this study has damage as a form of shaft fracture
In this study failure analysis of the differential pinion shaft is carried out Mechanical characteristics of the material are obtained first Then the microstructure and chemical compositions are determined Some fractographic studies are 2005 Elsevier Ltd All rights reserved
Keywords Differential Fracture Power transfer Pinion shaft
1 Introduction
The finaldrive gears may be directly or indirectly driven from the output gearing of the gearbox Directly driven final drives are used when the engine and transmission units are combined together to form an integral construction Indirectly driven final drives are used at the rear of the vehicle being either sprung and attached to the body structure or unsprung and incorporated in the rearaxle casing The finaldrive gears are used in the transmission system for the following reasons [1]
(a) to redirect the drive from the gearbox or propeller shaft through 90°and
(b) to provide a permanent gear reduction between the engine and the driving roadwheels
In vehicles differential is the main part which transmits the movement coming from the engine to the wheels On a smooth road the movement comes to both wheels evenly The inner wheel should turn less and the outer wheel should turn more to do the turning without lateral slipping and being flung Differential which is generally placed in the middle part of the rear bridge consists of pinion gear mirror gear differential box two axle gear and two pinion spider gears
A schematic illustration of a differential is given in Fig 1 The technical drawing of pinion the fractured pinion shaft is also given in Fig 2 Fig 3 shows the photograph of the fractured pinion shaft and the fracture section is indicated
In differentials mirror and pinion gear are made to get used to each other during manufacturing and the same serial number is given Both of them are changed on condition that there are any
problems In these systems the common damage is the wear of gears [24] In this study the pinion shaft of the differential of a minibus has been inspected The minibus is a diesel vehicle driven at the rear axle and has a passenger capacity of 15 people Maximum engine power is 904000 HPrpm and maximum torque is 2051600 Nmrpm Its transmission box has manual system (5 forward 1 back) The damage was caused by stopping and starting the minibus at a traffic lights In this differential entrance shaft which carries the pinion gear was broken Various studies have been made to determine the type and possible reasons of the damage These are
• studies carried out to determine the material of the shaft
• studies carried out to determine the microstructure
• studies related to the fracture surface
There is a closer photograph of the fractured surfaces and fracture area in Fig 4 The fracture was caused by taking out circular mark gear seen in the middle of surfaces
2 Experimental procedure
Specimens extracted from the shaft were subjected to various tests including hardness tests and metallographic and scanning electron microscopy as well as the determination of chemical composition All tests were carried out at room temperature
21 Chemical and metallurgical analysis
Chemical analysis of the fractured differential material was carried out using a spectrometer The chemical composition of the material is given in Table 1 Chemical composition shows that the material is a lowalloy carburizing steel of the AISI 8620 type
Hardenability of this steel is very low because of low carbon proportion Therefore surface area becomes hard and highly enduring and inner areas becomes tough by increasing carbon proportion on the surface area with cementation operation This is the kind of steel which is generally used in mechanical parts subjected do torsion and bending High resistance is obtained on the surface and high fatigue endurance value can be obtained with compressive residual stress by making the surface harder [57]
In which alloy elements distribute themselves in carbon steels depends primarily on the compound and carbide forming tendencies of each element Nickel dissolves in the α ferrite of the steel since it has less tendency to form carbides than iron Silicon combines to a limited extent with the oxygen present in the steel to form nonmetallic inclusions but otherwise dissolves in the ferrite Most of the manganese added to carbon steels dissolves in the ferrite Chromium which has a somewhat stronger carbideforming depends on the iron partitions between the ferrite and carbide phases The distribution of chromium depends on the amount of carbon present and if other stronger carbideforming elements such as titanium and columbium amount of carbon present and if other stronger carbideforming elements such as titanium and columbium are absent Tungsten and molybdenum combine with carbon to form carbides is there is sufficient carbon present and if other stronger carbideforming elements such da titanium and columbium are absent Manganese and nickel lower the eutectoid temperature [8]
Preliminary micro structural examination of the failed differential material is shown in Fig 5 It can be seen that the material has a mixed structure in which some ferrite exist probably as a result of slow cooling and high Si content High Si content in this type of steel improves the heat treatment susceptibility as well as
an improvement of yield strength and maximum stress without any reduction of ductility [9] If the microstructure cannot be inverted to martensite by quenching a reduction of fatigue limit is observed
There are areas with carbon phase in Fig 5(a) There is the transition boundary of carburization in Fig 5(b) and (c) shows the matrix region without carburization As far as it is seen in there photographs the piece was first carburized then the quenching operation was done than tempered This situation can be understood from blind martensite plates
22 Hardness tests
The hardness measurements are carried out by a MetTestHT type computer integrated hardness tester The load is 1471 N The medium hardness value of the interior regions is obtained as obtained as 43 HRC Micro hardness measurements have been made to determine the chance of hardness values along crosssection because of the hardening of surface area due to carburization The results of Vickers hardness measurement under a load of 4903 N are illustrated in Table 2
23 Inspection of the fracture
The direct observations of the piece with fractured surfaces and SEM analyses are given in this chapter The crack started because of a possible problem in the bottom of notch caused the shaft to be broken completely The crack started on the outer part after some time it continued beyond the centre and there was only a little part left And this part was broken statically during sudden starting of the vehicle at the traffic lights As a characteristic of the fatigue there are two regions in the fractured surface These are a smooth surface created by crack propagation and a rough surface created by sudden fracture These two regions can be seen clearly for the entire problem as in Fig 4 The fatigue crack propagation region covers more than 80 of the crosssection
Shaft works under the effect of bending torsion and axial forces which affect repeatedly depending on the usage place There is a sharp fillet at level on the fractured section For this reason stress concentration factors of the area have been determined Kt 24 value (for bending and tension) and Kt 19 value (for torsion) have been acquired according to calculations These are quite high values for areas exposed to combined loading
These observations and analysis show that the piece was broken under the influence of torsion with low nominal stresses electron microscopy shows that the fracture has taken place in a ductile manner (Fig6) There are some shear lips in the crack propagation region which is a glue of the plastic shear deformations Fig 7 shows the beach marks of the fatigue crack propagation The distance between any lines is nearly 133 nm
3 Conclusions
A failed differential pinion shaft is analysed in this study The pinion shaft is produced from AISI
8620 low carbon carburising steel which had a carbursing quenching and tempering heat treatment process Mechanical properties micro structural properties chemical compositions and fractographic analyses are carried out to determine the possible fracture reasons of the component As a conclusion the following statements can be drawn
• The fracture has taken place at a region having a high stress concentration by a fatigue procedure under a combined bending torsion and axial stresses having highly reversible nature
• The crack of the fracture is initiated probably at a material defect region at the critical location
• The fracture is taken place in a ductile manner
• Possible later failures may easily be prevented by reducing the stress concentration at the critical location
Acknowledgement
The author is very indebted to Prof S Tasgetiren for his advice and recommendations during the srudy
References
[1] Heisler H Vehicle and engine technology 2nd ed London SAE International 1999
[2] Makevet E Roman I Failure analysis of a final drive transmission in offroad vehicles Eng Failure Anal 2002957992
[3] Orhan S Aktu ¨rk N Determination of physical faults in gearbox through vibration analysis J Fac Eng Arch Gazi University 200318(3)97–106
[4] Tasgetiren S Aslantas K Ucun I Effect of pressfitting pressure on the fatigue damages of root in spur gears Technol Res EJMT 2004221–9
[5] Nanawarea GK Pableb MJ Failures of rear axle shafts of 575 DI tractors Eng Failure Anal 200310719–24
[6] Aslantas K Tasgetiren S A study of spur gear pitting formation and life prediction Wear 20042571167–75
[7] Savas V O ¨ zek C Investigation of the distribution of temperature on a shaft with respect to the deflection Technol Res EJMT 2005133–8
[8] Smith FW Principles of materials science and engineering 3rd ed USA McGrawHill Series 1996 p 517–18
[9] ASM metal handbook vol 1 Properties and selection irons steels and high performance alloys 1991
[10] Voort GFV Visual examination and light microscopy ASM handbook metallography and microstructures Materials Park (OH) ASM International 1991 p 100–65
汽车差速器齿轮轴失效分析
摘
差速器降低速度增加扭矩根合适角度两轮传递动力齿轮安装轴体装配前应熟悉齿轮结构发生障齿轮安装轴起更换般言系统中齿轮损坏形式磨损损坏项研究中检查齿轮损坏形式轴断裂项研究差速器齿轮轴障分析首先获材料机械特性然确定微观结构化学组合物
关键词：差速器断裂动力传递齿轮轴
1．简介
终驱动齿轮直接间接变速器输出齿轮驱动发动机传动装置结合起形成整体结构时需直接驱动终驱动齿轮间接驱动末级驱动器助辅助装置敷汽车方者纳入驱动桥传动系统中该齿轮原：
（1）传动轴变速器传动轴定90度
（2）发动机驱动轮间提供永久减速
车辆中差速器传递发动机车轮间运动部分滑路面运动两车轮均匀传动轮应转少外轮应转然转时会发生滑移差速器般放桥中间星形齿轮架差速器箱半轴齿轮星形齿轮组成
图1示意图图2图3显示齿轮轴技术图齿轮轴片指出断裂部分
差速器制造程中动轮齿轮相序列号出现问题二者需更换系统中常见损伤齿轮[24]磨损项研究中辆面包车差速器齿轮轴进行检查该面包车辆轮驱动柴油车
15载客力发动机功率90 4000马力转速扭矩205 1600纳米转分变速箱手动系统（5前1回）损害停交通灯启动面包车引起差速器中带齿轮入口轴破种样研究已确定类型损坏原：
•进行研究确定轴材料
•进行研究确定微结构
•断裂面相关研究
图4 裂隙面断裂面积距离片该断裂表面中间圆形标志齿轮造成
2实验程序
轴提取试样进行种测试包括硬度测试金相扫描电子显微镜化学成分测定测试室温进行
21化学冶金分析
光谱仪进行断裂材料化学分析材料化学成分表1中出化学成分表明该材料种低合金渗碳钢AISI 8620型低碳例钢淬透性低表面增加碳例胶结操作表面变坚硬持久耐部变强硬种常钢结构受扭弯机械零件中通残余压应力加强硬度获高疲劳强度高性表面
碳钢中合金元素分布取决元素化合物碳化物形成倾镍钢中铁素体中溶解没铁形成碳化物倾更硅刚中少部分氧反应形成非金属化合物然分解铁素体铁相铬更易碳反应掺入铬取决碳含量
失效差速器材料初步微结构检查示图5出该材料具混合结构中存某铁素体种钢高硅含量提高热处理敏感性
屈服强度提高应力减少塑性[ 9 ]果微观结构法通淬火马氏体转变观察疲劳极限降低
图5（1）碳相区图5渗碳渡边界（b）（c）显示矩阵区域渗碳里片件作品第渗碳淬火然回火操作种情况理解观察马氏体板
22硬度试验
开展mettest HT型计算机集成硬度计硬度测量负载1471中等硬度值部区43 HRC显微硬度测量已确定硬度值截面加渗碳4903 n示表2负荷维氏硬度测量结果
23 断裂处检查
章中出直接观测结果断裂面扫描电镜分析裂纹开始底部裂缝导致轴断裂裂缝开始外部分段时间继续超越中心部分断裂部分等交通灯车辆突然启动时破作疲劳特征断裂面2区域光滑表面裂纹扩展粗糙表面创建突然断裂2区域清楚整问题图4疲劳裂纹区覆盖80横截面
轴弯曲扭转轴力作受影响方反复锋利薄面水裂缝性剖面原该区应力集中系数确定KT 24价值（弯曲张力）KT 19价值（扭转）根计算获 相高数值区域暴露联合载荷观察分析显示扭转应力作轴断裂延展状态（fig6）裂纹扩展区定剪切裂痕塑性剪切变形图7显示疲劳裂纹扩展海滩纹线间距离133纳米
3结
项研究中失效差速器齿轮轴进行分析齿轮轴产生AISI 8620低碳渗碳钢渗碳淬火回火热处理工艺力学性微观结构特性化学成分断口分析确定断裂原：
•具高应力集中受弯曲扭转轴应力作具高度逆性区域发生断裂
•关键部位材料缺陷区域会引发断裂
•种韧性方式中发生断裂
•关键位置减少应力集中防止出现障发生
参考
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[5] Nanawarea GK Pableb MJ Failures of rear axle shafts of 575 DI tractors Eng Failure Anal 200310719–24
[6] Aslantas K Tasgetiren S A study of spur gear pitting formation and life prediction Wear 20042571167–75
[7] Savas V O ¨ zek C Investigation of the distribution of temperature on a shaft with respect to the deflection Technol Res EJMT 2005133–8
[8] Smith FW Principles of materials science and engineering 3rd ed USA McGrawHill Series 1996 p 517–18
[9] ASM metal handbook vol 1 Properties and selection irons steels and high performance alloys 1991
[10] Voort GFV Visual examination and light microscopy ASM handbook metallography and microstructures Materials Park (OH) ASM International 1991 p 100–65
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