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RISS 인기검색어
- 검색키워드
- 저자 : Haijiang Hu (검색결과 5 건)
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Kinetics Model of Bainitic Transformation With Stress
Mingxing Zhou,Guang Xu,Haijiang Hu,Qing Yuan,Junyu Tian 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.1
Thermal simulations were conducted on a Gleeble 3800 simulator. The main purpose is to investigate the effects ofstress on the kinetics of bainitic transformation in a Fe-C-Mn-Si advanced high strength bainitic steel. Previousstudies on modeling the kinetics of stress affected bainitic transformation only considered the stress below theyield strength of prior austenite. In the present study, the stress above the yield strength of prior austenite is takeninto account. A new kinetics model of bainitic transformation dependent on the stress (including the stresses belowand above the yield strength of prior austenite) and the transformation temperature is proposed. The new modelpresents a good agreement with experimental results. In addition, it is found that the acceleration degree of stresson bainitic transformation increases with the stress whether its magnitude is below or above the yield strength ofaustenite, but the increasing rate gradually slows down when the stress is above the yield strength of austenite.
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Man Liu,Jun Wang,Qi Zhang,Haijiang Hu,Guang Xu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8
Five quenching temperatures were designed to investigate the relationship between volume fraction of retained austenite andmicrostructure, mechanical properties of a medium carbon quenching and partitioning (Q&P) steel. It is normally acceptedthat the optimal mechanical property of Q&P steels is obtained by quenching at optimum temperature, which corresponds tothe maximum amount of retained austenite. However, the present work clarified that maximum volume fraction of retainedaustenite in Q&P steels is indeed unrelated to the optimum mechanical property of steels. The microstructure consisting ofcoarse martensite laths, dispersive bainite and thin retained austenite films was obtained by quenching at fine martensite starttemperature (FMs), resulting in the optimum comprehensive mechanical property of Q&P steel with the better elongationat the expense of slightly smaller yield strength and tensile strength.
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In‑Situ Observation of Martensitic Transformation in a Fe–C–Mn–Si Bainitic Steel During Austempering
Junyu Tian,Guang Xu,Zhengyi Jiang,Haijiang Hu,Qing Yuan,Xiangliang Wan 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.7
The martensitic transformation in a Fe–C–Mn–Si bainitic steel was examined by in situ high-temperature laser scanningconfocal microscopy (LSCM) and dilatometry. The phenomenon of continuous martensitic transformation during austemperingwas firstly dynamically observed by LSCM. Differing from the commonly accepted viewpoint on martensite formationin bainitic steels, the martensitic transformation in the conventional medium-carbon bainitic steel was not instantaneous andproceeded gradually when the sample was austempered below martensite starting temperature (MS). It can be attributed tothe generation of internal stresses, thermal activation, stimulating nucleation, and the segregation of Mn. In addition, apartfrom the continuous martensitic transformation, the bainitic transformation was also directly observed by LSCM duringaustempering below MS. Moreover, it was clear from the results of dilatation during austempering that the inflection point inthe dilatation curve against time was not the demarcation point between martensitic and bainitic transformation, and in situobservations confirmed that martensite was still formed after the inflection point. Therefore, the obtained results could be anexcellent reference to further understand the mechanism of bainitic and martensitic transformations in Fe–C–Mn–Si bainiticsteel during austempering below MS.
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Junyu Tian,Guang Xu,Zhengyi Jiang,Haijiang Hu,Mingxing Zhou 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.6
The effects of Nickle (Ni) addition on bainitic transformation and property of ultrahigh strength bainitic steels are investigatedby three austempering processes. The results indicate that Ni addition hinders the isothermal bainite transformation kinetics,and decreases the volume fraction of bainite due to the decrease of chemical driving force for nucleation and growth ofbainite transformation. Moreover, the product of tensile strength and total elongation (PSE) of high carbon bainitic steelsdecreases with Ni addition at higher austempering temperatures (220 and 250 °C), while it shows no significant differenceat lower austempering temperature (200 °C). For the same steel (Ni-free or Ni-added steel), the amounts of bainite and RAfirstly increase and then decrease with the increase of the austempering temperature, resulting in the highest PSE in thesample austempered at temperature of 220 °C. In addition, the effects of austempering time on bainite amount and propertyof high carbon bainitic steels are also analyzed. It indicates that in a given transformation time range of 30 h, more volumeof bainite and better mechanical property in high carbon bainitic steels can be obtained by increasing the isothermal transformationtime.
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Combined Effect of the Prior Deformation and Applied Stress on the Bainite Transformation
Mingxing Zhou,Guang Xu,Li Wang,Haijiang Hu 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
There has been a continued interest over the past years in the effects of external stress or prior deformation onthe bainite transformation. In this study, the combined effect of prior deformation and stress on the bainitetransformation was investigated and the interaction between the effects of prior deformation and stress wasdiscussed in detail. The results show that although single deformation and single stress promote the bainitetransformation, their combination cannot promote the bainite transformation to a much larger degree. In addition, atthe early stage of transformation, the promotion effects of prior deformation and stress on the amount of the bainitetransformation are enhanced by each other. However, at the latter stage, the deformation weakens the promotioneffect of the stress. Moreover, prior deformation at a low temperature accelerates the kinetics of the bainite transformationwith stress, but it decreases the amount of the bainite transformation even if the deformation is small.
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