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Failure analysis of 40CrNiMoA steel transmission shaft spline

Jin Yuliang, Liu Chunjiang, Wu Binlong, Zhang Hongliang

Heat Treatment of Metals 2022, 47 (8): 296-300. doi:10.13251/j.issn.0254-6051.2022.08.049

Abstract （94）

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Cracks were found in the spline part of 40CrNiMoA steel transmission shaft used in a aero engine during normal inspection. Macro analysis, scanning electron microscopy and energy spectrum analysis, metallographic analysis, hardness analysis and temperature and color contrast experimental analysis were carried out on the fracture site. The results show that the structure of spline crack zone of the 40CrNiMoA transmission shaft is consistent with that of the matrix, and no decarburization phenomenon is observed. The crack is intergranular fracture, and the oxidation of crack surface is obvious. Therefore, it can be inferred that the crack is generated during the heating stage of high-frequency quenching, which results from excessive heating current or uneven heating. It is suggested to reasonably control the high frequency quenching process of transmission shaft.

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Cause analysis on cold drawing fracture of ER70S-6 steel coil and process optimization measures

Fan Zhenxia, Zhang Yuming, Dong Qing, Zhao Haoqian, Li Yashuo , Wei Qiaoling

Heat Treatment of Metals 2023, 48 (8): 272-275. doi:10.13251/j.issn.0254-6051.2023.08.044

Abstract （88）

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ER70S-6 steel ø6.5 mm hot-rolled coil fractured during cold drawing, and the batch of coils was tested by means of chemical composition, mechanical properties, and microstructure inspection. The results show that the martensite in the core and bainite at the edge of the coil are the causes of drawing fracture. The production of martensite in the core and bainite at the edge can be effectively reduced by reducing the entering temperature of finishing rolling from 960 ℃ to 920 ℃ and increasing the length of insulation cover by 5 m.

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Low-temperature fracture failure analysis of 30CrMnSiA steel structural part

Guo Qiang, Chi Kegang

Heat Treatment of Metals 2023, 48 (8): 276-279. doi:10.13251/j.issn.0254-6051.2023.08.045

Abstract （88）

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Fracture of 30CrMnSiA steel structural part occurred under impact load in a low-temperature environment. The fracture morphology, microstructure and inclusions, chemical composition, hardness, tensile properties and impact properties were tested and analyzed by means of scanning electron microscope, metallurgical microscope, inductively coupled plasma spectrometer (ICP), hardness test, tensile test, and impact test. The results indicate that during quenching and tempering, the actual tempering temperature is lower than the required temperature, which results in the transformation of the metallographic structure into tempered martensite. The tempered martensite has low impact absorbed energy at -40 ℃, which is the main reason for brittle fracture under impact at -40 ℃. The grade of non-metallic inclusions such as sulfides and silicates exceeds the design requirements, and a large number of inclusions promote rapid crack initiation and propagation.

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Fracture causes analysis of front lifting lug of 30CrMnSiA alloy

Zheng Hong, Lin Wenqin, Yang Yuanxi, Xu Xinjie, Deng Feng, Wu Jiaxin, Jiang Hongjun

Heat Treatment of Metals 2022, 47 (8): 292-295. doi:10.13251/j.issn.0254-6051.2022.08.048

Abstract （86）

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A front lifting lug made of 30CrMnSiA alloy was broken and failed, whose fracture characteristics were analyzed and the hardness test was carried out. The results show that the fracture of the lifting lug is hydrogen embrittlement fracture and there is a phenomenon of excessive hardness. By combining the lug heat treatment and surface treatment process, it shows that incomplete hydrogen removal during surface treatment is the main cause of hydrogen embrittlement. Excessive hardness not only increases hydrogen embrittlement sensitivity, but also misleads the dehydrogenation process, so it is necessary for the lifting lugs to avoid excessive hardness. At the same time, the failure event reflects the lack of supplier quality control, and it is necessary to strengthen control and audit efforts in special processes and secondary outsourcing.

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Fracture analysis of automobile stabilizer bar

Liu Huadong, Shao Baiming, Li Junwan

Heat Treatment of Metals 2023, 48 (1): 253-256. doi:10.13251/j.issn.0254-6051.2023.01.044

Abstract （86）

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A stabilizer bar of automobile broke was failed in a short mileage during the durability test, then the fracture cause was analyzed by physical and chemical inspection, metallographic inspection and fracture analysis of the failed parts with direct reading spectrometer, hardness tester, metallographic microscope and scanning electron microscope, and in combination with the processing process of the stabilizer bar. The results show that the fracture morphology of the failed stabilizer bar is mainly intergranular, there are fatigue striations in the extended region, and the final fracture is dimpled. This is mainly due to the introduction of hydrogen through pickling treatment during the processing of the stabilizer bar, resulting in delayed cracking of the stabilizer bar first, and then fatigue and propagation in the durability test until the final fracture.

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Cracking analysis of 42CrMo steel hexagon head bolt by hot dip galvanizing

Zhao Quanyu, Liang Jiajun, Chen Xupeng, Tong Bo, Xia Guohua, Yan Qin, Ding Zhimin

Heat Treatment of Metals 2023, 48 (1): 257-260. doi:10.13251/j.issn.0254-6051.2023.01.045

Abstract （79）

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Cracks were found at the round corners of the 42CrMo steel hexagon head bolts after hot dip galvanizing through magnetic particle inspection. Fracture, microstructure and composition analysis of the cracked bolt were carried out by means of optical microscope, SEM and EDS. The results show that the fracture of the cracked bolts conforms to the characteristics of hydrogen embrittlement, and the mass fraction of hydrogen near the fracture is as high as 4×10^-6.The crack characteristics are consistent with the hydrogen embrittlement crack characteristics. The microstructure on both sides of the crack is normal quenched and tempered structure and zinc residue is found in the crack, which can exclude that the crack is caused by abnormal tissue or quenching. Therefore, it can be reasonably inferred that the crack of 42CrMo steel hexagonal bolt is hydrogen-induced cracking, which occurs in the process of hot dip galvanizing.

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Analysis of fatigue failure of automobile hollow gear shaft in bench test

Jin Guozhong, Wang Kaizhong, Hu Fangzhong, Yang Shaopeng, Yang Zhiqiang, Chen Shijie

Heat Treatment of Metals 2022, 47 (11): 266-270. doi:10.13251/j.issn.0254-6051.2022.11.045

Abstract （78）

PDF （612KB）（30）

The fatigue failure behavior of new type hollow gear shaft in bench test was analyzed by means of optical microscope, microhardness tester and scanning electron microscope. The results show that the transition arc position is the failure position of the hollow gear shaft. The chemical composition of part material, austenite grain size and non-metallic inclusions all meet the design requirements, while the effective carburized layer depth just approaches the lower limit of the design requirements. The calculation results show that the radius of the transition arc of the hollow gear shaft should be greater than 3.16 mm, and during the carburizing the smaller transition arc radius is prone to the "sharp angle effect", resulting in coarse carbides and stress concentration, which may be one of the reasons for the low fatigue life. The simulation results of CAE software show that there is obvious stress concentration at the transition arc, and the maximum stress on the surface exceeds allowable stress of the part, which may be another reason for failure of the hollow gear shaft. The maximum stress on surface of the part increases with the increase of hollow size. The maximum size of the hollow should be less than Ø17.1 mm.

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Cracking failure analysis of ultra-high strength martensite steel

Sun Lu, Li Jianying, Wei Huanjun, Li Zheng, Li Tao, Cheng Xiaoying

Heat Treatment of Metals 2023, 48 (1): 261-265. doi:10.13251/j.issn.0254-6051.2023.01.046

Abstract （68）

PDF （604KB）（53）

Cracked and uncracked ultra-high strength martensitic steel parts and the corresponding raw materials steels were analyzed due to phenomenon of cracking of the parts in their safe service period. The U-shaped bending beam experiment results in constant strain test show that both the raw materials of cracked and uncracked parts have good resistance to delayed cracking caused by hydrogen. Due to the difference of the production processes, the microstructure of the raw materials is plate martensite for the cracked part and lath martensite for the uncracked part, respectively. When machining into the same kind of parts, due to the structural difference of the martensite, the internal collaborative deformation uniformity is different in machining and forming processes, thus the residual stress in the cracked parts is larger. In addition, the stress concentration is caused by the formation of a large number of dislocation pile-ups in the structure of cracked parts, the local stress reaches the limit first, resulting in cracking.

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Failure analysis on cracking of 7A09 aluminum alloy outer cylinder parts

Wang Hao, Fu Neng, Feng Kangtun

Heat Treatment of Metals 2023, 48 (5): 298-302. doi:10.13251/j.issn.0254-6051.2023.05.049

Abstract （65）

PDF （2278KB）（104）

Several 7A09 aluminum alloy outer cylinders of aircraft landing gear were found cracked during machining. The chemical composition, mechanical properties, fracture micromorphology, microstructure and microhardness of the aluminum alloy outer cylinder were analyzed to investigate the essence and causes of the cracks by means of ICP spectrometer, tensile testing machine, scanning electron microscope, optical microscope and energy dispersive spectrometer. The results show that the crack of the 7A09 aluminum alloy outer cylinder is developed from the initial crack source formed by forging at high temperature, and then the overburning microstructure along the parting surface is cracked into visible longitudinal cracks under the interaction of machining stress and thermal stress generated during the subsequent boring and heat treatment process. The main reason for the crack formation may be related to the overburning of the microstructure caused by the excessively high local temperature of the parting surface during the forging process, which belongs to the forging process defect.

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Fracture failure analysis of 35CrMo steel high strength bolt

Wang Pu, Tong Hui

Heat Treatment of Metals 2023, 48 (5): 294-297. doi:10.13251/j.issn.0254-6051.2023.05.048

Abstract （63）

PDF （2597KB）（132）

35CrMo steel high strength bolt of a heavy tractor broke after being tightened and placed for 2 days. The fractured bolt and the unused bolt of the same batch were studied by fracture analysis, metallographic examination, composition analysis, hardness analysis and mechanical testing. The results show that the harmful hydrogen introduced during the pickling and electroplating process is not effectively and timely removed, which results in the hydrogen accumulating towards the stress concentrated root of the bolt under the preload for tightening, so that the hydrogen induced delayed fracture phenomenon for the bolt occurs.

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Detection and analysis of grinding burns of 20Cr2Ni4 steel carburized and quenched spiral bevel gears

Xu Hongxiang, Wang Hongwei, Pu Jiangyong, Zhao Shaofu, Chen Shengchao, Rong Zeyu

Heat Treatment of Metals 2022, 47 (11): 271-275. doi:10.13251/j.issn.0254-6051.2022.11.046

Abstract （61）

PDF （611KB）（25）

Aiming at the cracks on the tooth surface of 20Cr2Ni4 steel spiral bevel gear after carburizing, quenching and grinding,the uncracked tooth surface(concave) and cracked tooth surface(convex) of the cutting tooth block were measured by using optical microscope and microhardness tester. The results show that the effective hardened layer depth and microstructure at the pitch circle of the uncracked tooth surface and cracked tooth surface away from the crack of the tooth block are normal, and there is no grinding burn characteristics. There are different degrees of grinding burn characteristics at the tooth root, especially in the cracks of the cracked tooth surface, the crescent-shaped white and black grinding burn morphology, the deepest part of the burn is about 0.9 mm, and the improved grinding process parameters are put forward to avoid grinding burn.

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Analysis and improvement of unqualified magnetic properties of vacuum annealed DT4E electromagnetic pure iron

Xu Feng, Wu Xiaowei

Heat Treatment of Metals 2023, 48 (1): 249-252. doi:10.13251/j.issn.0254-6051.2023.01.043

Abstract （60）

PDF （616KB）（44）

Coercivity of a DT4E electromagnetic pure iron part after vacuum annealing exceeds the design requirements. In order to solve this problem, the DT4E electromagnetic pure iron was vacuum annealed at 860-1150 ℃ for 4 h to analyze the effects of annealing temperature, magnetic test ring size and impurity compositions in raw materials on the magnetic properties. The results show that with the increase of annealing temperature, the magnetic induction intensity B₂₅₀₀ changes as “M” type, the coercivity H_c changes as “V” type, and the change trend of maximum permeability μ_m is opposite to that of the coercivity. The optimum vacuum annealing temperature is 900 ℃,at which the magnetic induction intensity B₂₅₀₀ is 1.63 T, the coercivity H_c is 25.19 A/m, and the maximum permeability μ_m is 23.64 mH/m, all meeting the design requirements.Moreover, the size of the magnetic test ring has no significant effect on the measurement results of the magnetic properties of the DT4E electromagnetic pure iron. The content of impurity elements in raw materials has a great influence on magnetic properties. When the C content is higher, the permeability decreases and the coercivity increases, which easily leads to unqualified magnetic properties.

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Failure analysis of superalloy bolts for reducer cover plate

Jing Dong

Heat Treatment of Metals 2023, 48 (8): 291-294. doi:10.13251/j.issn.0254-6051.2023.08.048

Abstract （57）

PDF （3071KB）（38）

During the abnormal life cycle of the butterfly valve equipped in the dehydrogenation unit of a company, the nickel-base alloy bolts of the blind flange were broken. Through dimension measurement and stress deformation analysis, the fracture sequence of bolts was confirmed. Further physical and chemical analysis on the first broken piece confirms that the bolt fracture is brittle type, which is related to improper heat treatment in the manufacturing process, thus a large number of fibre structures without complete recovery and recrystallization are resulted.

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Fracture cause analysis of a 50CrVA spring steel part

Cui Jingbo, Wang Lingbo, Guo Fei, Lu Zhenguo

Heat Treatment of Metals 2024, 49 (4): 296-299. doi:10.13251/j.issn.0254-6051.2024.04.048

Abstract （56）

PDF （3209KB）（25）

Fracture cause of a 50CrVA spring steel part was analyzed by means of metallographic microscope, scanning electron microscope and analyzer of oxygen, nitrogen and hydrogen. The results show that the fracture of the 50CrVA spring steel occurs at the stress concentration position in the right corner in type of hydrogen embrittlement produced due to incomplete hydrogen removal treatment after galvanizing. Finally, the improvement measures are proposed, i.e., the blunted blanking die should be timely replaced, and the time of the hydrogen removal treatment should be increased.

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Analysis on crack causes of 30CrMnSiA steel ring support

Dong Na, Xu Zhoujue, Li Xiangjun, Zhou Wufeng, Chen Qifang, Tan Ruiqi, Yang Xiyang

Heat Treatment of Metals 2024, 49 (4): 293-296. doi:10.13251/j.issn.0254-6051.2024.04.047

Abstract （55）

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After quenched-tempered heat treatment, cracks were found in the ear pieces of an aircraft part of frame ring made of 30CrMnSiA steel plate. Comprehensive analysis of the cracked frame ring and raw material were carried out through macro and micro morphology examination, spectrum chemical composition analysis and mechanical properties test. The results show that the crack cause of the frame ring is a problem of raw material quality, due to insufficient annealing of raw materials, there is serious segregation, resulting in high local hardness and eventually quenching cracks.

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Fracture failure analysis of cover plate bolt of aircraft

Yin Xiaojian, Xu Yongchun, Zhang Bing, Feng Derong, Sun Xiaojun, Zhang Qinying

Heat Treatment of Metals 2023, 48 (10): 297-301. doi:10.13251/j.issn.0254-6051.2023.10.046

Abstract （52）

PDF （3410KB）（58）

A bolt for the wing cover plate of an aircraft fractured after service for some time. In order to find out the fracture mode and cause of the bolt, observation on appearance and fracture surface, metallographic structure examination, hardness testing, energy dispersive X-ray spectroscopy (EDS) analysis, hydrogen content testing and hydrogen embrittlement test were carried out. The results show that the fracture mode of the bolt belongs to delayed brittle cracking induced by hydrogen embrittlement. High material strength of the bolt leads to high sensitivity to hydrogen embrittlement, which is the internal cause for the hydrogen embrittlement fracture. Local surface corrosion leads to hydrogen absorption, which is the direct cause for the hydrogen embrittlement fracture. Such failure can be effectively prevented by adjusting the heat treatment process of the bolts so as to properly reduce their strength under the premise of meeting the design requirements as well as strengthening the corrosion protection for the bolts.

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Analysis and improvement on quenching stripe of thin gauge wear resistant steel

Huang Peng, Zhen Fan, Du Ping, Qu Jinbo

Heat Treatment of Metals 2023, 48 (1): 266-269. doi:10.13251/j.issn.0254-6051.2023.01.047

Abstract （52）

PDF （607KB）（45）

Quenching stripe with hardness difference problem of thin gauge wear resistant steel plates was studied by means of microstructure and hardness examination combined with equipment and process analysis. The results show that the main reasons for the problem are the different water flows and cooling rates between the groove and collar regions of spiral rollers of the quenching machine. By optimization of the quenching temperature, water flow, roller speed and roll gap, the quenching stripe problem is solved and good plate flatness is obtained.

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Analysis of cracking cause of acid gas post-cooler head

Liu Min, Lu Meipeng, Liu Jiachen, Gu Baolan, Guo Jing, Sun Yuejun, Song Ming

Heat Treatment of Metals 2023, 48 (8): 265-271. doi:10.13251/j.issn.0254-6051.2023.08.043

Abstract （49）

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Bulges and cracks appeared in the inner wall of floating head of acid gas post-cooler in a natural gas purification plant. The causes of bulges and cracks were analyzed by means of macroscopic examination, chemical composition analysis, hardness test, metallographic examination, energy spectrum analysis, fracture analysis and EBSD test. The results show that the bulge and cracking of the inner wall of the head are hydrogen bulge (HB) and hydrogen-induced cracking (HIC). Since the microstructure of the head material (20g steel) is banded ferrite+pearlite along the rolling direction, with bainite and more MnS inclusions appearing at the position of 1/2 plate thickness caused by element segregation, and the service environment of the head contains wet H₂S medium which generates hydrogen after electrochemical reaction with the steel, then the hydrogen accumulates at the defects of 1/2 plate thickness, leading to bulge and cracking of the inner wall of the head.

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Failure analysis of high temperature fastening bolt of 20Cr1Mo1VNbTiB steel

Huang Jiang, Mou Shenzhou, Wang Jing, Tao Liang, Huang Qiaosheng, Wang Xue

Heat Treatment of Metals 2023, 48 (8): 286-290. doi:10.13251/j.issn.0254-6051.2023.08.047

Abstract （46）

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A high-temperature bolt made of 20Cr1Mo1VNbTiB steel for a certain supercritical unit was early fractured. The macroscopic and microscopic characteristics of the fracture were observed, the aging condition of the bolt was analyzed, and the failure reasons were discussed. The results show that after running at high temperature, the aggregate growth of carbides in the bolt is not obvious, the decrease of tensile strength and hardness is not significant, but the decrease of impact absorbed energy is obvious, which means that the bolt fracture failure is not related to the aging. Excessive preload during the bolt assembly accelerates its creep damage. According to the fracture morphology, it is determined that the fracture belongs to high temperature creep rupture.

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Fracture analysis on IN718 alloy bolt

Zhang Haifeng

Heat Treatment of Metals 2023, 48 (10): 302-306. doi:10.13251/j.issn.0254-6051.2023.10.047

Abstract （45）

PDF （3735KB）（51）

Early breaking failure occurred during the use of diesel engine exhaust bolts made of IN718 alloy. The causes of the bolt fracture were investigated by means of chemical composition testing, tensile testing, metallographic analysis, observation of fracture morphology, and transmission electron microscope observation of precipitates from two aspects of material microstructure and manufacturing process. The results show that the main reason for the bolt fracture is that the surface of the rolled thread is in a high-energy state, and a large amount of nano phases precipitate at the root of the thread during subsequent aging treatment, resulting in embrittlement of the surface layer at the root of the thread.

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