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Microstructural evolution of a steam-turbine rotor subjected to a water-quenching process: numerical simulation and experimental verification

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Advances in Manufacturing 2019年第1期7卷 84-104页

作者： Chuan Wu Qing-Ling Meng National-Local Joint Engineering Laboratory of Intelligent Manufacturing Oriented Automobile Die & Mould College of Mechanical Engineering Tianjin University of Technology and Education Tianjin 300222 People's Republic of China College of Civil Engineering Tianjin University Tianjin 300072 People's Republic of China

Cr-Ni-Mo-V steam-turbine rotors have been widely used as key components in power plants. In this study, a coupled thermomechano-metallurgical model was proposed to simulate the phase transformation and transformation-induced plasticity (TRIP) of a 30Cr2Ni4MoV steam-turbine rotor during a water-quenching process, which was solved using a user defined material mechanical behavior (UMAT) subroutine in ABAQUS. The thermal dilation, heat generation from plastic work, transformation latent heat, phase transformation kinetics, and TRIP were considered in the model. The thermomechanical portion of the model was used to predict the evolution of temperature, strain, and residual stress in the rotor. The phase transformation that occurred during the quenching process was considered. Constitutive models of phase transformations (austenite to pearlite, austenite to bainite, and austenite to martensite) and TRIP were developed. Experimental data were adopted and compared with the predicted results to verify the accuracy of the model. This demonstrates that the model is reliable and accurate. Then, the model was utilized to predict the temperature variation, dimensional change, minimum austenitization time, residual stress, TRIP, and volume fractions of each phase. It is concluded that this model can be a useful computational tool in the design of heat-treatment routines of steam-turbine rotors.

关键词： Thermomechano-metallurgical model user defined material mechanical behavior (UMAT) subroutine Microstructural evolution transformation-induced plasticity (TRIP)- Residual stress

Effect of Annealing on Microstructure and Mechanical Properties of Ultrafine-Grained Low-Carbon Medium-Manganese Steel Produced by Heavy Warm Rolling

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Acta Metallurgica Sinica(English Letters) 2019年第3期32卷 361-371页

作者： Sohail Ahmad Li-Feng Lv Li-Ming Fu Huan-Rong Wang Wei Wang Ai-Dang Shan School of Materials Science and Engineering Shanghai Jiao Tong University Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration(CISSE) Baosteel Research Institute

An ultrafine-grained(UFG) low-carbon medium-manganese steel was fabricated by the heavily warm rolling(HWR) and subsequent quenching, and the effects of annealing temperatures on microstructure and mechanical properties of the UFG HWRed steel were investigated. The results show that the HWRed steel exhibits simultaneous improvements in strength,uniform elongation and work hardening, which is mainly attributed to the refinement of martensitic microstructures. The HWRed steels comprise only a-phase when annealing at lower temperatures below to 550 °C and at higher temperatures above to 700 °C. Whereas, UFG c-austenite is formed by reverse transformation when the HWRed steel was annealed at intermediate temperatures from 550 to 700 °C and the volume fraction increases with increasing annealing temperatures,consequently resulting in a dramatic increase in ductility of the annealed HWRed steels. It was found that the transformed UFG austenite and ferrite remained ～500 nm and ～800 nm in size when the HWRed steel was annealed at 650 and700 °C for 1 h, respectively, showing an excellent thermal stability. Moreover, the HWRed steel annealed at 650 °C exhibits high strength-ductility combinations with a yield strength of 906 MPa, ultimate tensile strength(UTS) of1011 MPa, total elongation(TEL) of 51% and product of strength and elongation(PSE: UTS 9 TEL) of 52 GPa%. It is believed that these excellent comprehensive mechanical properties are closely associated with the UFG austenite formation by reverse transformation and principally attributed to the transformation-induced plasticity(TRIP) effect.

关键词： Ultrafine-grained medium-Mn steel Heavy warm rolling Annealing Microstructure and properties transformation-induced plasticity(TRIP) effect

Effects of quenching and partitioning process on mechanical properties of TRIP780 steel

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Journal of Iron and Steel Research(International) 2019年第9期26卷 991-999页

作者： Xian-hong Han Cheng-long Wang Yuan-yuan Li Gang Liu National Engineering Research Center of Die and Mold CAD School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai 200030China Shanghai Marine Equipment Research Institute Shanghai 200031China

A transformation-induced plasticity (TRIP) steel was applied to test its mechanical properties in quenching and partitioning (Q&P) process. A series of Q&P experiments followed by tensile tests, Charpy impact tests, fracture morphology analyses and microstructure observations were conducted. The experimental results showed that the Q&P treatment could increase the mechanical properties of TRIP steel evidently. The strength of tested TRIP780 after Q&P process reaches more than 1500 MPa with elongation of 17.8%, which is obviously greater than that of 22MnB5 after hot stamping. The microstructure observations indicate that the good combination of high strength and plasticity of TRIP steel after Q&P process is attributed to the multi-phase microstructure of hard martensite matrix and soft retained austenite.

关键词： transformation-induced plasticity steel Quenching and partitioning process Hot stamping Mechanical property

Effect of intercritical deformation on tensile performance of a low-carbon Si-Mn steel processed by quenching and bainitic partitioning

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Journal of Iron and Steel Research(International) 2020年第2期27卷 208-216页

作者： Ya-qiang Tian Zhong-qian Cao Wang Li Hong-bo Pan Xiao-ping Zheng Jin-ying Song Ying-li Wei Lian-sheng Chen Key Laboratory of the Ministry of Education for Modern Metallurgy Technology North China University of Science and TechnologyTangshan 063210HebeiChina Key Laboratory of Metallurgical Emission Reduction and Resources Recycling of Ministry of Education Anhui University of TechnologyMa'anshan 243002AnhuiChina

The effect of intercritical deformation on retained austenite and tensile performance of a low-carbon Si-Mn steel in modified quenching and bainitic partitioning processes was evaluated.The results showed that the intercritical deformation can play a positive role in stabilizing and refining the retained austenite,and possessed promising potential in balancing tensile strength and ductility of multiphase high-strength steels.The experimental low-carbon Si-Mn steel exhibited multiphase configuration comprising polygonal ferrite,granular bainite and granular structure after two different modified quenching and bainitic partitioning processes,and the bainitic ferrite laths got refined by intercritical deformation.The volume fraction of retained austenite in film-like and blocky morphology was increased from 11.5%to 13.9%due to applied intercritical deformation,and the larger amount of retained austenite provided the sufficient transformation-induced plasticity effect and resulted in enhanced work hardening degree;in response,enhanced ultimate tensile strength 1260 MPa and fracture elongation 22.1%were obtained,leading to increased product of strength and elongation in value of 27.7 GPa% compared to 20.8 GPa% of undeformed structure.

关键词： Bainitic steel Intercritical deformation Retained austenite Instantaneous work hardening index transformation-induced plasticity effect

Effect of Microstructure on Tensile Behavior and Mechanical Stability of Retained Austenite in a Cold-Rolled Al-Containing TRIP Steel

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Acta Metallurgica Sinica(English Letters) 2019年第10期32卷 1237-1243页

作者： Yang Zhao Wen-Ting Zhu Shu Yan Li-Qing Chen School of Materials Science and Engineering Northeastern University Shenyang 110819 China State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 China

In the present study, a quenching treatment prior to two-stage heat treatment was conducted on a Fe-0.28C-1.55Mn-2.06Al transformation-induced plasticity steel to tailor the final microstructure. Compared with the microstructure of the ferrite, bainite and blocky retained austenite obtained by conventional two-stage heat treatment, the microstructure subjected to quenching plus two-stage heat treatment was composed of the ferrite, lath bainite and film-like retained austenite. The corresponding tensile behavior and mechanical stability of retained austenite were investigated by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the mechanical stability of blocky retained austenite grains is lower and most of them transform to martensite during the tensile deformation, which leads to higher ultimate tensile strength and instantaneous work hardening exponent. Film-like retained austenite has relatively higher stability, which could cause sustained work hardening and high ductility as well as product of strength and elongation.

关键词： transformation-induced plasticity (TRIP) steel Retained austenite stability Microstructure Mechanical properties Work hardening behavior

Effect of retained austenite and nonmetallic inclusions on the thermal/electrical properties and resistance spot welding nuggets of Si-containing TRIP steels

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International Journal of Minerals,Metallurgy and Materials 2019年第1期26卷 52-63页

作者： V.H.Vargas I.Mejía V.H.Baltazar-Hernández C.Maldonado Metallurgy and Materials Research Institute Universidad Michoacana de San Nicolás de Hidalgo Edificio "U" Ciudad Universitaria Materials Science and Engineering Program Autonomous University of Zacatecas

Five advanced high-strength transformation-induced plasticity(TRIP) steels with different chemical compositions were studied to correlate the retained austenite and nonmetallic inclusion content with their physical properties and the characteristics of the resistance spot welding nuggets. Electrical and thermal properties and equilibrium phases of TRIP steels were predicted using the JMatPro? software. Retained austenite and nonmetallic inclusions were quantified by X-ray diffraction and saturation magnetization techniques. The nonmetallic inclusions were characterized by scanning electron microscopy. The results show that the contents of Si, C, Al, and Mn in TRIP steels increase both the retained austenite and the nonmetallic inclusion contents. We found that nonmetallic inclusions affect the thermal and electrical properties of the TRIP steels and that the differences between these properties tend to result in different cooling rates during the welding process. The results are discussed in terms of the electrical and thermal properties determined from the chemical composition and their impact on the resistance spot welding nuggets.

关键词： transformation-induced plasticity steel retained austenite non-metallic inclusions magnetic saturation electrical properties thermal properties resistance spot welding nugget

Microstructure,mechanical properties,and wear resistance of VCp-reinforced Fe-matrix composites treated by Q&P process

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International Journal of Minerals,Metallurgy and Materials 2018年第9期25卷 1060-1069页

作者： Ping-hu Chen Yi-bo Li Rui-qing Li Ri-peng Jiang Song-sheng Zeng Xiao-qian Li College of Mechanical and Electrical Engineering Central South UniversityChangsha 410083China State Key Laboratory of High Performance Complex Manufacturing Changsha 410083China Light Alloy Research Institutes Central South UniversityChangsha 410083China Valin ArcelorMittal Automotive Steel Co. Ltd.Loudi 417000China

A quenching and partitioning(Q&P) process was applied to vanadium carbide particle(VCp)-reinforced Fe-matrix composites(VC-Fe-MCs) to obtain a multiphase microstructure comprising VC, V8 C7, M3 C, α-Fe, and γ-Fe. The effects of the austenitizing temperature and the quenching temperature on the microstructure, mechanical properties, and wear resistance of the VC-Fe-MCs were studied. The results show that the size of the carbide became coarse and that the shape of some particles began to transform from diffused graininess into a chrysanthemum-shaped structure with increasing austenitizing temperature. The microhardness decreased with increasing austenitizing temperature but substantially increased after wear testing compared with the microhardness before wear testing; the microhardness values improved by 20.0% ± 2.5%. Retained austenite enhanced the impact toughness and promoted the transformation-induced plasticity(TRIP) effect to improve wear resistance under certain load conditions.

关键词： vanadium carbide Fe-matrix composites quenching and partitioning process transformation-induced plasticity effect microhardness impact toughness wear resistance