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Causes analysis of induction hardening cracks in grey cast iron for high-end CNC machine tool guide rails

Yan Haoming, Yu Penghan, Yu Xingfu

Heat Treatment of Metals 2025, 50 (1): 282-286. doi:10.13251/j.issn.0254-6051.2025.01.043

Abstract （28）

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Effect of induction hardening on the microstructure, hardness, and hardened layer thickness was analyzed of a high-end CNC machine tool guide rail formed by HT300. The causes of cracks during the quenching process were also analyzed. The results show that after intermediate frequency induction hardening, the surface hardness of the machine tool integrated guide rail of cast iron HT300 can reach over 700 HV (60 HRC), and the depth of the harded layer can reach 5.5 mm. After induction hardening heat treatment, the surface layer of the cast iron guide rail mainly forms cryptocrystalline martensite, the transition layer mainly consists of martensite+pearlite structure, and the core is mainly composed of pearlite structure. Crack analysis shows that the graphite in cast iron is mainly E-type graphite, and the phosphorus eutectic structure present in the cast iron dissolves and precipitates during quenching, reducing the surface strength of the cast iron. After deep layer induction hardening, the tensile stress formed on the surface layer exceeds the strength of the cast iron, which is the main reason for the cracking of the cast iron during quenching. The cracking source is located on the surface, and the cracking location is mostly in the phosphorus eutectic region.

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Analysis of bare defects in alloyed hot dip galvanized DP980GA steel strip

Liu Xueliang, Zeng Songsheng, Long Xukai, Xiao Bing, Zeng Weimin, Cheng Yuqiang

Heat Treatment of Metals 2025, 50 (1): 287-291. doi:10.13251/j.issn.0254-6051.2025.01.044

Abstract （19）

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Causes of surface bare defects of alloyed galvanized DP980GA strip were analyzed by means of macro and micro morphology observation and composition analysis. The results show that a large number of manganese oxide and iron oxide particles are found inside the plating pit, and a small amount of alumina and chromium oxide are also found, which is due to the enrichment and selective oxidation of manganese on the surface of the steel strip in the continuous annealing furnace, and the aluminothermic replacement reaction in the zinc pot is incomplete, thus reducing the wettability of the strip surface and causing the bare defects. It is suggested that through moderately reducing the dew point temperature of the heating section in the continuous annealing furnace to reduce the manganese oxide film formed by selective oxidation on the surface and its thickness, and moderately increasing the Al content in the zinc pot to promote the aluminothermic replacement reaction, the manganese oxide on the surface of the strip can be fully replaced by alumina and sunk into the zinc pot, thereby the wettability of the strip surface can be improved and the problem of surface bare defects can be solved.

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Fracture failure analysis of 20CrMoH alloy steel reducer bevel gear shaft

Li Bing, Xu Feiyue, Zhang Peng, Xing junfeng, Tang Zhengqun

Heat Treatment of Metals 2025, 50 (1): 292-298. doi:10.13251/j.issn.0254-6051.2025.01.045

Abstract （31）

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In response to the problem of fracture of 20CrMoH alloy steel reducer bevel gear shaft during installation and tightening, the macroscopic morphology, microstructure, and hardness of the fracture specimen were tested and analyzed using optical microscopy, microhardness tester, scanning electron microscopy, and other detection methods to identify the cause of the fracture. The results show that the cracks in the 20CrMoH steel bevel gear shaft originate from poor machining of the thread start stop groove, with multiple points of fracture and severe wear in the source area. Subsequently, under the action of bending shear stress, the cracks propagate along the carburized transition layer and fracture, with the fracture morphology showing intergranular features. The chemical composition and hardness of the parts basically meet the requirements, but there is a significant variation in hardness at the core of the parts. Overall, the parts exhibit characteristics of high stress overload fracture, which is caused by stress concentration due to poor machining tool marks and material conditions, leading to the fracture. It is recommended to investigate the stress state during tightening and improve the heat treatment process conditions to reduce the depth of the induction annealing layer and narrow down the heat affected zone.

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Fracture behavior of 06Cr25Ni20 austenitic heat-resistant steel at high tensile temperature

Wang Chu, Ai Fangfang, Pan Kaihua, Yan Bingyu, Hu Haiyang, Gao Tianyu, Wang Yong

Heat Treatment of Metals 2024, 49 (12): 289-294. doi:10.13251/j.issn.0254-6051.2024.12.046

Abstract （40）

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Static and dynamic microstructure evolution and fracture behavior of the 06Cr25Ni20 austenitic heat-resistant steel at different high temperature tensile temperatures were analyzed by means of optical microscope, scanning electron microscope, transmission electron microscope and high temperature laser confocal microscope. The results show that the yield strength of the tested steel decreases from 180 MPa to 40 MPa, the tensile strength decreases from 450 MPa to 50 MPa, and the elongation after fracture increases from 44% to 56% with the increase of tensile test temperature in the rang of 600-1000 ℃.The fracture is ductile. The number of dimples gradually decreases with the increase of temperature, and the size and depth gradually increase. The recrystallization phenomenon occurs in the microstructure, and the secondary phase black carbide and intragranular substructure decrease or even disappear with the temperature increasing. The formation of cracks and fracture are mainly generated at the interface between austenite and ferrite and high energy grain boundaries when the tested steel is stretched at high temperature.

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Reason analysis of color difference of 7075 aluminum alloy thick plate after sulfuric acid anodizing

Xun Jian, Yang Lei, Liu Meiling, Dong Xiaoyu, Ren Tianqi, Li Zhenghua, Cao Xiaorong, Zhou Liang

Heat Treatment of Metals 2024, 49 (12): 295-300. doi:10.13251/j.issn.0254-6051.2024.12.047

Abstract （34）

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In order to solve the problem of color difference caused by sulfuric acid anodizing of the 7075 aluminum alloy thick plate, optical microscope, scanning electron microscope, room temperature tensile testing and other methods were used to study the microstructure and properties of different color parts. The results show that the cooling rate is the main reason for the color difference of the sulfuric acid anodized film layer of the 7075 aluminum alloy thick plate. In the parts that can not reach the required cooling rate during solution treatment, a large number of micron-sized η phases are generated, and the film layer is formed unevenly during the sulfuric acid anodizing, resulting in a gray-black appearance. In the parts that can reach the required cooling rate during solution treatment, the microstructure is dominated by nano-scale η′ metastable precipitated phase, and the film layer is uniform during sulfuric acid anodizing, and the color is normally gray white. The gray-black part after sulfuric acid anodizing is re-heat-treated to regulate the microstructure, ant then the color of the film layer is returned to normal gray white.

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Fracture failure analysis and improvement of engine exhaust valve

Luo Changzeng, Zeng Xiaoxiao, Yao Yajun, Xu Deshi, Li Xucong, Ma Zongqiao

Heat Treatment of Metals 2024, 49 (12): 301-305. doi:10.13251/j.issn.0254-6051.2024.12.048

Abstract （35）

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During the reliability validation process of a specific natural gas engine, a fracture of the exhaust valve occurred. The fracture cause was analyzed by using methods such as morphology observation, chemical composition analysis and hardness testing, and improvement measures were proposed. The results indicate that the chemical composition and hardness of the exhaust valve material meet the requirements of GB/T 12773-2021. The hardness test shows that the maximum actual working temperature of the exhaust valve is 725-735 ℃. The oxide layer generated on the valve stem under high temperature extends to the substrate and forms microcracks on the surface of the valve stem. High temperature causes layered precipitates to precipitate along the grain boundary, further accelerating the propagation of microcracks along the grain boundary, and gradually developing into deeper cracks, ultimately leading to fatigue fracture of the valve stem. It is recommended that reducing the operating temperature of the exhaust valve through optimizing the combustion system parameters, or alternatively, selecting NCF 3015 or Inconel 751 materials with superior temperature resistance can ensure the exhaust valve meets the operational requirements.

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Fracture failure analysis of 20Cr1Mo1VTiB steel bolt

Liu Fei, Zhang Xuechao, Sun Changming, Dong Yunhe, Liu Yang, Zheng Jianjun

Heat Treatment of Metals 2024, 49 (12): 306-311. doi:10.13251/j.issn.0254-6051.2024.12.049

Abstract （44）

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A high-temperature fastening bolt (20Cr1Mo1VTiB steel) for the high-stress main steam valve of a steam turbine unit cracked after serving for 1.29×10⁵ h. The cracking failure cause of the high-temperature fastening bolt was analyzed by means of chemical composition examination, SEM and TEM microstructure observation, XRD detection, and mechanical property testing. The results show that the fracture of the bolt is primarily due to creep damage from long-term high-temperature and high-stress conditions of serving. Additionally, the accumulation of creep damage is mainly due to two types of creep voids forming in microcrack zones near coarse inclusions sharp corners and along the interface of Laves phase. With the increase of running time, the number of creep voids in the 20Cr1Mo1VTiB steel bolt matrix continuously rises and aggregates, eventually forming crack sources that lead to fatigue rupture.

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Fracture failure analysis of vehicle front stabilizer bar

Qin Xingzu, Zhang Bo, Zhou Renyu, Liu Xiang, Kuai Zhen, Zhang Wen

Heat Treatment of Metals 2024, 49 (12): 312-315. doi:10.13251/j.issn.0254-6051.2024.12.050

Abstract （34）

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Failure analysis of the fractured front stabilizer bar of a certain vehicle in strength endurance road test was carried out by using direct reading spectrometer, hardness tester, scanning electron microscope and metallographic microscope. The results show that chemical composition and Rockwell hardness of the front stabilizer bar can meet the requirement of material standard and part drawing. The fracture failure mode is fatigue fracture. Connection zone between the stabilizer bar and the stop ring, hard and brittle secondary quenching martensite and low hardness secondary tempered troostite exist in the crack source because of the heat input of the welding process in installation of the stop ring. Fatigue fracture occurs in the area of the test and extends till instantaneous overload fracture occurs. Failure phenomenon reproduced through rapid fatigue bench test. Such kind fracture failure can be avoided by controlling the welding parameters of the stop ring to make the microstructure of the stabilizer bar not be influenced.

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Fracture failure analysis of 60Si2MnA steel circlip

Chen Hehe, Liu Chunjiang, Jiang Tao, Guo Chen

Heat Treatment of Metals 2024, 49 (11): 302-307. doi:10.13251/j.issn.0254-6051.2024.11.047

Abstract （49）

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Circlip broke when installed in the hollow shaft of the rotor component. Macroscopic and microscopic morphologies on the fracture surface were observed, chemical composition of the raw material was tested, and the microstructure and hardness of the material were investigated in order to find out the failure mechanism of the circlip. The results show that the failure mode of the circlip is hydrogen embrittlement fracture. The circlip has a high sensitivity to hydrogen embrittlement due to its high hardness caused by low temperature tempering, and during electroplating, the accumulation of hydrogen inside the material increases, resulting in hydrogen embrittlement fracture during installation. Therefore, the heat treatment process of the circlip can be controlled to reduce the material hardness, meanwhile, the electroplating process can be controlled to reduce the thickness of the galvanized layer on the circlip.

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Formation reason analysis of spot segregation in 42CrMo steel forgings

Xu Quan, Chen Mintao, Dang Shue, Zhang Yingfan, Jiao Yongxing, Bai Hongliang

Heat Treatment of Metals 2024, 49 (11): 308-314. doi:10.13251/j.issn.0254-6051.2024.11.048

Abstract （42）

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Bright white spot segregation on the surface of 42CrMo steel forgings used in wind turbine gearbox was observed and analyzed by OM, SEM, EDS and other technologies. The results show that the bright white spots segregating on the surface of the forging are tempered bainite. This is due to the existence of composition segregation of the 42CrMo steel ingot, which shows strip and spot bainite segregation after forging. After conventional post-forging heat treatment (normalizing+high temperature tempering), the chemical composition is not homogenized, and the bainite segregation evolves into aggregated granular Cr and Mo carbide segregation. After further quenching and tempering treatment, the microstructure is tempered bainite with varying sizes and uneven distribution in the tempered sorbite matrix.

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Failure analysis for grinding delayed cracking of 300M steel components

Yue Haiyan, Jia Min, Zeng Zhiqiang, Sun Xinming, Cheng Sheng

Heat Treatment of Metals 2024, 49 (11): 315-319. doi:10.13251/j.issn.0254-6051.2024.11.049

Abstract （44）

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A large number of micro-cracks were found after the finishing of 300M steel components. The cracking reasons and mechanisms of this batch of components were analyzed from the aspects of appearance, material chemical composition, microstructure and crack characteristics and hardness. The results show that these are grinding micro-cracks, which initiate in the near-surface layer, mainly exhibiting intergranular and quasi cleavage cracking characteristics. The reason for the cracking is that after chrome plating, the surface material undergoes plastic flow during the grinding process and residual tensile stress is generated under rapid cooling conditions. The surface and near-surface material are burned and the phase transition stress is formed. Meanwhile, the hardness of burned material decreases. After a long time, hydrogen atoms from chrome plating diffuse to near-surface and gather at the dislocations and grain boundaries, that induces the grinding crack to have delayed forming in near-surface under the action of residual tensile stress and microstructure tensile stress.

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Failure analysis of gear cracking of containment isolation valve for a nuclear power plant

Tang Heng, Li Guoqiang, Xu Yangyang, Deng Jiangyong

Heat Treatment of Metals 2024, 49 (11): 320-324. doi:10.13251/j.issn.0254-6051.2024.11.050

Abstract （37）

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During the commissioning period of a nuclear power plant unit, the containment isolation valve did not close as expected. Upon disassembling the valve and inspecting it, it was found that there were cracks on the surface of gear shaft gear. The causes of valve gear cracking were analyzed by means of macroscopic inspection, chemical composition analysis, metallographic examination and hardness testing. The results show that the cracks are quenching cracks, which occur at the transition point between the tooth root and the outer edge of the gear shaft, and there are obvious rough machining tool marks at the transition point of the tooth root fillet. Due to the overall high hardness of the gear area and the hardening of all teeth, it does not meet the requirements of JB/T 6395-2010. The analysis suggests that the occurrence of cracks is mainly related to the incorrect selection of heat treatment methods and improper control of heat treatment processes. The obvious rough machining tool marks at the transition of the tooth root fillet are the contributing factors to the occurrence of cracks.

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Analysis on surface pitting defects of hot-rolled galvanized steel sheet

Li Shiming, Zhang Jie, Liu Xin, Zhang Ziyue, Chen Binkai, Zhang Qifu

Heat Treatment of Metals 2024, 49 (10): 278-283. doi:10.13251/j.issn.0254-6051.2024.10.045

Abstract （52）

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Causes of pitting defects on hot-rolled galvanized steel sheet were studied by means of systematic surface examination, detailed microstructure analysis and precise chemical composition testing. The results show that aberrant dew point conditions within the annealing furnace lead to an insufficiently reducing atmosphere, which induces the oxidation and formation of iron oxide on the surface of the steel sheet, so that the surface wettability of hot-rolled substrate is insufficient during galvanizing, thereby impeding the formation of the Fe-Al inhibition layer and leading to pinhole leakage in the zinc coating. These pinhole leakages disrupt the flow of the zinc liquid after the steel sheet is discharged the zinc pot, eventually manifesting as visible pitting defects on a macroscopic scale.

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Comprehensive evaluation of strength and toughness of hot stamping steel

Wang Qiuyu, Xu Kuan, Li Liming, Liu Shuying, Zhang Saijuan

Heat Treatment of Metals 2024, 49 (10): 284-289. doi:10.13251/j.issn.0254-6051.2024.10.046

Abstract （45）

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Taking the properties of 1.5 GPa grade hot stamping steel as the benchmark, the strength and toughness of 2 GPa grade hot stamping steel were accurately evaluated from multiple perspectives as elongation, strength, ultimate cold bending angle and crack nucleation work by means of uniaxial tensile test, three-point bending test and notch tensile test, and the strength and toughness were characterized by the method of weighted calculation of comprehensive score. The results show that after baking, the yield strength, elongation, ultimate cold bending angle, crack nucleation work which characterize the fracture toughness of the 1.5 GPa, 2 GPa and 2 GPa+AS hot stamping steel specimens are improved. Compared with the 1.5 GPa steel, the 2 GPa and 2 GPa+AS steels have higher safety performance within their tensile strength range, however, once holes or microcracks are formed in the specimen, the microcracks will rapidly expand to crack. Through weighted calculation of the comprehensive score, it is concluded that the comprehensive evaluation results of the strength and toughness of the tested hot stamping steels from high to low are 2 GPa>1.5 GPa>2 GPa+AS.

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Forming mechanism of water marks on cold-rolled nickel-saving stainless steel

Lu Fei, Liu Qu, Guo Yongliang, Li Xiaolei, He Liu

Heat Treatment of Metals 2024, 49 (10): 290-294. doi:10.13251/j.issn.0254-6051.2024.10.047

Abstract （32）

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Water marks occurred on the surface of cold-rolled nickel-saving stainless steel strip after continuous annealing, which would evolve into corrosion and cause serious loss. The surface morphology, composition, microstructure and corrosion resistance of the stainless steel strip specimens with and without water marks were compared and analyzed by means of metallographic microscopy, scanning electron microscopy and EDS analysis, and the forming mechanism of water marks was studied in combination with rolling process. The results indicate that during the cold rolling process of stainless steel, the middle part of the cold-rolled nickel-saving stainless steel where the water marks forms is in a high speed rolling state and is at a higher plastic deformation rate than the head and end without water marks. The high speed rolling results in numerous deformation bands within the microstructure of the strip which compromise the corrosion resistance of cold-rolled stainless steel, ultimately leading to the formation of numerous micro-pitting water marks.

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Plate shape prediction method in two stage based on CNN-LSTM for quenching process with roller-hearth quenching machine

Liu Ai, Zhang Tinghu, Wang Zhongliang

Heat Treatment of Metals 2024, 49 (10): 295-300. doi:10.13251/j.issn.0254-6051.2024.10.048

Abstract （43）

PDF （1776KB）（12）

Shape of the steel plate is a key quality indicator during the quenching process. In order to solve the problem of plate shape prediction of steel plates during the quenching process, a two-stage shape prediction method for steel plates in roller-hearth machine quenching process based on convolutional neural network and long short-term memory network (CNN-LSTM) was proposed. This method was divided into two stages. Firstly, the CNN was used to extract the plate shape features and capture the spatial information of the plate shape. Secondly, using quenching process parameters and historical plate shape characteristics as inputs, a plate shape prediction model was established through LSTM. Finally, by concatenating these two stages, both spatial and temporal information of the plate shape could be considered simultaneously. Based on the experiments with actual production data, the results show that the proposed method reduces the root mean squared error of the prediction is reduced from 0.0471 to 0.0264, which represents a 43.9% reduction in prediction error, achieving the goal of improving the plate shape prediction accuracy.

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Mechanism analysis and numerical simulation of transverse quenching crack in forgings for marine gear box input shaft

Zhang Wei, Li Peihai, Duan Yixian, Zheng Wei, Liang Zhexiao, Zhao Wencai

Heat Treatment of Metals 2024, 49 (10): 301-305. doi:10.13251/j.issn.0254-6051.2024.10.049

Abstract （36）

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By analyzing the macrostructure of 42CrMoA marine gear box input shaft forging and the microstructure of its crack region, the causes of quenching cracks were studied with the combination of numerical simulation of quenching process. The results show that the shape of the marine gear box input shaft forging is complex and with sharp changes in its cross section, thus the stress concentration occurs easily at the step shaft transition position and results in transverse quenching cracks during quenching.

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Cause analysis on crack of bolt thread tooth

Fan Kailun, Song Wenjun, Liu Wencheng, Pei Lieyong, Dai Aili, Zhang Renyin, Liu Hongyan, Li Aiping, Zhang Yongxiang

Heat Treatment of Metals 2024, 49 (10): 306-310. doi:10.13251/j.issn.0254-6051.2024.10.050

Abstract （111）

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Longitudinal cracks were found on the 1-2 teeth of the tail end of the 30CrMnSiNi2 bolt thread through magnetic particle testing. Combining with the bolt production process, the causes of microcrack formation were analyzed by means of macro and micro morphology observation of the microcracks and microstructure and hardness examination of the bolt. The results show that due to improper cooling during grinding, secondary quenching occurred at the 1-2 teeth of the thread end tail tooth, resulting in fine needle-like martensite appears, causing grinding burns and quenching cracks under secondary quenching stress. In order to avoid such problems recurrence, it is recommended reinforcing the grinding cooling detection and related personnel training and improving the equipment maintenance system.

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Brittle fracture characteristics and fracture behavior of hot rolled 60Si2Mn strip steel

Tian Yaqiang, Yao Zhiqiang, Nian Baoguo, Zhang Xiaolei, Xue Qihe, Song Jinying, Zhang Mingshan, Chen Liansheng

Heat Treatment of Metals 2024, 49 (8): 281-288. doi:10.13251/j.issn.0254-6051.2024.08.047

Abstract （37）

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Decarburization, inclusions, segregation and brittle fracture of hot rolled 60Si2Mn steel strip were analyzed by means of optical microscope, scanning electron microscope and electronic tensile testing machine. Microstructure and mechanical properties of the specimens near the brittle fracture and away from the fracture were characterized, and the brittle fracture characteristics and fracture behavior of hot rolled 60Si2Mn steel strip were investigated. The results show that there is no obvious decarburization, inclusion and segregation at the brittle fracture, and the fracture presents brittle fracture. The content of proeutectoid ferrite in the specimens near the brittle fracture and away from the fracture is 12.45% and 0.66%, respectively, and the pearlite lamellar spacing is 578 nm and 236 nm, respectively. The main cause of brittle fracture of hot rolled 60Si2Mn steel strip is that the content of proeutectoid ferrite in the brittle fracture is higher than that in the position away from the fracture, and the pearlite lamellar spacing is larger, which leads to poor resistance to deformation and is prone to uneven deformation during the rolling process. Additionally, the stress difference between the coarse ferrite and cementite layers can easily lead to brittle fracture, and the cracks propagate along the two-phase interface. However, the plastic deformation of fine pearlite is relatively uniform, and cracks propagate through the layers of pearlite.

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Cause analysis and solution of crack of hydraulic support column cylinder

Cui Leilei, Ma Ke, Lan Zhiyu, Wang Piaoyang, Deng Xiangtao

Heat Treatment of Metals 2024, 49 (8): 289-294. doi:10.13251/j.issn.0254-6051.2024.08.048

Abstract （42）

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Cracks in cylinder of a large hydraulic support column during service were analyzed by means of mechanical property detection, microstructure analysis and crack morphology characterization. The results show that the cracking of the cylinder of hydraulic support column is not directly related to the microstructure and properties of the matrix material, but is caused by the cladding defects. The cracks occur at the interface of the stainless steel clad layer and the matrix, and then expand to the matrix side and the clad layer side under the action of long-term load, finally, resulting in cracking failure. By improving laser cladding parameters, laser cladding defects can be effectively avoided.

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