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Anomalous residual austenite formation in root of welding layers of 9% Cr/CrMoV dissimilar welded joint

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Journal of Iron and Steel Research(International) 2018年第8期25卷 839-846页

作者： Kai Ding Hui-jun Ji Quan-liang Zhang Xia Liu Peng Wang Xiao-hong Li Ling Zhang Yu-lai Gao State Key Laboratory of Advanced Special Steel State Shanghai Key Laboratory of Advanced FerrometallurgySchool of Materials Science and Engineering Shanghai University Shanghai 200444 China Shanghai Turbine Plant Shanghai Electric Power Generation Equipment Co. Ltd. Shanghai 200240 China

The morphology and distribution of residual austenite in the welded zone of 9% Cr/CrMoV dissimilar welded joint were observed by color metallographic method. Moreover, the details of the distribution, shape, length, length-to-width ratio, and the content of residual austenite in each welding layer were systematically characterized using Image-Pro Plus image analysis software. Different from the techniques such as X-ray diffraction, vibrating sample magnetometer, and electron backscatter diffraction that only involve the content of residual austenite, color metallographic method can offer much more details of the residual austenite, including the location, shape, size, and content, helping evaluate the overall characteristics of the residual austenite produced in the weld. It is interesting that a large amount of block-like and film-like residual austenite was found in the root of each welding layer, while rare at the top. The area fraction of residual austenite located in this zone was approximately 7.5% compared with only 0.5% at the top. In addition, the average area, length, and length-to-width ratio of dispersed residual austenite were quantitatively evaluated to be （4.7 ± 0.6）μm2, （5.1 ±0.6） μm, and （1.1 ± 0.1） μm, respectively. This variety of residual austenite was resulted from the tempering effect by latter welding layer on the previous one and different cooling rates in these two regions during the welding process.

关键词： residual austenite Color metallographic method Dissimilar welded joint Narrow gap submerged arcwelding Multilayer and multi-pass welding

Hydrogen Embrittlement of Advanced High-Strength Steel for Automobile Application:A Review

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Acta Metallurgica Sinica(English Letters) 2023年第7期36卷 1144-1158页

作者： Ming-Tu Ma Ke-Jian Li Yu Si Peng-Jun Cao Hong-Zhou Lu Ai-Min Guo Guo-Dong Wang State Key Laboratory of Vehicle NVH and Safety Technology Chongqing 401122China China Automotive Engineering Research Institute Co. Ltd.Chongqing 401122China School of Metallurgy and Materials Engineering Chongqing University of Science&TechnologyChongqing 401331China CITIC Metal Co.Ltd Beijing 100004China RAL of Dongbei University Shenyang 110819China

The hydrogen embrittlement(HE)fracture of advanced high-strength steels used in lightweight automobiles has received increasing public attention.The source,transmission,and movement of hydrogen,characterization parameters,and test methods of HE,as well as the characteristics and path of HE fractures,are introduced.The mechanisms and modes of crack propagation of HE and hydrogen-induced delayed fracture are reviewed.The recent progress surrounding micro and macro typical fracture characteristics and the influencing factors of HE are discussed.Finally,methods for improving HE resistance can be summarized as follows:(1)reducing crystalline grain and inclusion sizes(oxides,sulfides,and titanium nitride),(2)controlling nano-precipitates(niobium carbide,titanium carbide,and composite precipitation),and(3)increasing residual austenite content under the reasonable tension strength of steel.

关键词： Hydrogen embrittlement High-strength steel Hydrogen-induced delayed cracking Hydrogen trapping residual austenite

Multi-dimensional controllability analysis of precision ball bearing integrity

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Advances in Manufacturing 2023年第4期11卷 682-693页

作者： Lai Hu Jun Zha Wei-Hua Zhao Xiao-Fei Peng Yao-Long Chen School of Mechanical Engineering Xi’an Jiaotong UniversityXi’an710049People’s Republic of China State Key Laboratory for Manufacturing Systems Engineering Xi’an Jiaotong UniversityXi’an710054People’s Republic of China Luoyang Bearing Science and Technology Co. Ltd.Luoyang471039HenanPeople’s Republic of China

Many factors affect the integrity of precision ball bearings.In this study,the multi-dimensional controllability of precision ball bearings produced in different company brands(bearing A and bearing B)were studied and compared.The geometric errors(flatness,parallelism,roundness and cylindricity of inner and outer rings,roundness,groove and roughness of inner and outer rings)and vibration errors of bearings were analyzed.Concurrently,the residual stress,residual austenite content,element content ratio,metamorphic layer and temperature-vibration displacement coupling test were also analyzed.Based on the above analysis conclusion,the bearing fatigue life test was carried out for 2150 h.The reliability of the conclusion is proved again as follows.When the residual austenite content in the raceway of precision ball bearing is 10%,the axial residual stress is 877.4 MPa;the tangential residual stress is 488.1 MPa;the carbon content is 6%;the test temperature of bearing is the lowest;and the service life is prolonged.

关键词： Precision ball bearing Controllability Geometric errors Carbon content residual austenite residual stress

Tempering Process to Improve Hardness Uniformity of Plastic Mould Steel

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Journal of Iron and Steel Research(International) 2012年第12期19卷 53-58页

作者： MIN Yong-an ZHOU Quan LUO Yi LI Dan WU Xiao-chun School of Materials Science and Engineering Shanghai University Shanghai 200072 China

A new design of copper-bearing non-quenched plastic mold steel is presented and explained. Two kinds of microstrueture can be obtained from this new type copper-bearing steel via cooling with different cooling rates, bain- ite and a mixed microstructure consisting of ferrite and bainite. It is found that, after proper tempering process, the hardness will be increased. Moreover, the hardness difference between different microstructures will be reduced. For further investigation, the samples tempered at different temperatures were examined by XRD and 3PAP （three di- mensional atom probe） analysis. Results show that the improvement is contributed mainly by the precipitation of Cu phase and transformation of residual austenite.

关键词： plastic mould steel tempering process Cu precipitation residual austenite

Embrittlement Mechanism due to Slow Cooling During Quenching for M152 Martensitic Heat Resistant Steel

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Journal of Iron and Steel Research(International) 2010年第6期17卷 60-66页

作者： YANG Gang WANG Chang LIU Xin-quan LIU Zheng-dong Central Iron and Steel Research Institute Beijing 100081 China

The mechanism of brittleness of M152 martensitic heat resistant steel due to slow cooling during quenching was experimentally investigated. The mechanical property tests and microstructure observation were conducted by TEM and XRD. The results showed that the presence of irreversible brittleness during slow cooling of quenching for M152 steel is attributed to the continuous M23C6 precipitation along prior austenite grain boundaries and M2C along prior residual austenite film. The residual austenite in the steel was unstable and decomposed after the precipitation of second phase during the process of slow cooling of quenching. The low cooling rate within the temperature range from 820 ℃ to 660 ℃ plays a key role in impact toughness, and the precipitation of second phase in the same temperature range results in irreversible brittleness.

关键词： M152 martensitic heat resistant steel brittleness carbides decomposition residual austenite

Test and application of 60 kg·m^(−1) bainite rails for heavy-haul railway

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Railway Sciences 2023年第2期2卷 170-178页

作者： Jiyong Jin Profile Product Research Institute Ansteel Group Iron and Steel Research InstituteAnShanChina

Purpose-In order to develop high-strength,high-toughness and high-wear-resistance rails suitable for the development and application of heavy-haul railways.Design/methodology/approach-Based on the trial production of 60 kg·m^(−1) bainite rails,the Zeiss inverted optical microscope,transmission electron microscope and static hydraulic universal tester were used to test the microstructure and property of rail base metal and welded joints.Meanwhile,a trial laying of rails,wing rails of frogs and switch rails for turnouts was performed to systematically analyze their strength,toughness and wear resistance.Findings-The results show that the base metal of 60 kg·m^(−1) bainite rail is of a uniform microstructure,with a carbide-free bainite matrix,a few of stable residual austenite and M/A islands,and it features high hardness,good wear resistance and good strength-toughness balance.The welded joint is of a uniform microstructure and has good properties.Originality/value-A bainite rail,laid in a curve section of heavy-haul railway is able to serve for 48 months with a gross traffic tonnage of nearly 600 million tons,whose service life is more than one time longer than that of pearlite rail;the service life of the wing rail of frog and the switch rail for turnout with 60 kg·m^(−1) bainite rails is 3-4 times longer than that with U75V rails,and no serious damage occurs.The bainite rails also have strong peeling and spalling resistance.

关键词： Heavy-haul railway 60 kg·m^(−1) Bainite rail residual austenite Base metal Welded joint