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Refinement of packet size in low carbon bainitic steel by special thermo-mechanical control process

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Journal of university of science and technology beijing 2004年第3期11卷 221-224页

作者： Chengjia Shang Xuemin Wang Shanwu Yang xinlai he materials science and Engineering school, university of science and technology beijing, beijing 100083, china Mat. Sci. and Eng. Sch. Univ. of Sci. and Technol. Beijing Beijing 100083 China

The packet size of bainitic steel can be refined by a specialrelaxation-precipitation-control phase transformation (RFC) technology. When processed by RPCprocess, the low carbon bainitic steel composes of two kinds of main intermediate transformationphases. One is ultra-fine lath-like bainitic ferrite and the lath is less than 1μm in width andabout 6 μm in length; the alignment of laths forms a refined packet, and the size of packets isabout 5-7 μm in length and about 3-4μm in width. The other is acicular structure. The morphologyand distribution of these acicular structures are influenced by relaxation process, the thin andshort acicular structures cut the prior austenite grain and refine the bainitic packet size. For theoptimum relaxation time, the packet size can be refined to the finest. The mechanical propertiesare influenced by relaxation time and the 800 MPa grade low carbon bainitic steel with excellenttoughness can be obtained by RPC process.

关键词： packet size refinement bainitic steel RPC process

Dissolving of Nb and Ti carbonitride precipitates in microalloyed steels

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Journal of university of science and technology beijing 2003年第5期10卷 78-80页

作者： Wenjin Nie, Shanwu Yang, Shaoqiang Yuan, and xinlai he{2. science and Engineering school, university of science and technology beijing, beijing 100083, china materials science and Engineering {2. University of Science and Technology Beijing Beijing 100083 China

The dissolving behaviour of Nb and Ti carbonitride precipitates inmicroalloyed steels during isothermal holding at 1300℃ was investigated by Transmission electronmicroscopy (TEM) and energy dispersion x-ray spectrum (EDX). It was found that all precipitates inNb-Ti microalloyed steel are (Nb, Ti)(C, N). With holding time increasing, the atomic ratio of Nb/Tiin precipitates decrease gradually. These precipitates still existe even after holding for 48 h at1300℃ while Nb(C, N) precipitates dissolve away in Nb microalloyed steel only after 4 h at the sametemperature. These results show that formation and thermostability of precipitates are considerablyinfluenced by interaction between Nb and Ti.

关键词： dissolving (Nb, Ti)(C, N) TEM EDX

Stability of Ultra-fine Microstructures during Tempering

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Journal of university of science and technology beijing 2001年第2期8卷 119-122页

作者： Shanwu Yang, Chengjia Shang,xinlai he, Xuemin Wang, Yi Yuan (Material science and Engineering school, university of science and technology beijing, beijing 100083, china) Univ Sci & Technol beijing Mat Sci & Engn Sch Beijing 100083 Peoples R China

The stability of ultra-fine microstructure during tempering at 650 degreesC was investigated on a Nb-containing steel. The steel had undergone 5 passes controlled rolling, then was relaxed lair cooled) to 730 degreesC: and cooled in water. The evolution of microstructure was that, in early stage of tempering, no obvious change was detected by means of optical microscopy while dislocation cells were formed inside bainitic laths. With further tempering, bainitic laths started to coalesce in some regions. Finally, polygonal ferrite was formed while hardness decreased dramatically. Some samples taken from the same primary plate were reheated at 930 degreesC for 0.5 h followed by quenching into water before tempering. Despite their lower original hardness, the reheated samples softened Faster during tempering. Ferrite was quickly formed in the reheated samples. These results indicate that the evolution of microstructures towards equilibrium during tempering of the steel is mainly determined by whether dislocations are pinned rather than the dislocation density.

关键词： microalloyed steel bainite tempering

Relaxation of Deformed Austenite and Refinement of Bainite in a Nb-Containing Microalloyed Steel

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Journal of university of science and technology beijing 2001年第3期8卷 214-217页

作者： Shanwu Yang, Xuemin Wang, Chengjia Shang, xinlai he, Yi Yuan Material science and Engineering school, university of science and technology beijing, beijing 100083, china Univ Sci & Technol beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China

By means of stress relaxation and strain-induced precipitation in deformed austenite, bainite with micron sheaves size was obtained in Nb-containing steel. Microstructures of deformed samples isothermally relaxed for various time followed by cooling in water were examined. Stress relaxation test and transmission electron microscopy (TEM) were employed to detect precipitation of microalloy elements, such as Nb, Ti, during isothermal holding after deformation. All the samples were constituted by lath-like bainite along with acicular ferrite, but the size of bainitic sheaves and the amount of acicular ferrite were changed with relaxation time. To achieve optimum refinement, relaxation should be confined in the stage when the precipitates have sufficiently grown and started to coarsen. The sample having not undergone relaxation does not exhibit obvious refinement despite of its higher dislocation density. These results indicate that relaxation promotes bainite to refine, which is because deformed austenitic grains are divided by dislocation walls formed during relaxation and acicular ferrite formed before bainitic transformation.

关键词： stress relaxation strain induced precipitation refinement

Prediction of Enthalpies of Fusion for Divalent Rare Earth Halides Based on Modeling by Artificial Neural Networks and Pattern Recognition

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International Journal of Minerals,Metallurgy and materials 1999年第1期13卷 24-26页

作者： Yimin Sun Zhiyu Qiao Minghong he(Applied science {2., university of science & technology beijing, beijing 100083, china)(National Natural science Foundation of china, beijing 100083, china) Applied science school University of Science and Technology Beijing Beijing 100083 China National Natural science Foundation of china Beijing 100083 China

The artificial neural network (ANN) and the pattern recognition were applied to study the correlation of enthalpies of fusion for divalent rare earth halides with their microstructural parameters,such as ionic radius and electronegativity. The model,represented by a back-propagation netal network, was trained with a 12.set of published data for divalent rare earth halides and then was used to predict the unknown ones. Also the criterion equations were ptesented to determine the enthalpies of fuSion for divalent rare earth halides using pattern recognition in mis work. The results from the model in ANN and criterion equations are in very good agreement with reference data.

关键词： BP neural network pattern recognition enthalpy of fusion divalent rare earth halides microstructural parameters

A Special TMCP Used to Develop a 800MPa Grade HSLA Steel

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Journal of university of science and technology beijing 2001年第3期8卷 224-228页

作者： Chengjia Shang,Xuemin Wang, xinlai he, Shanwu Yang, Yi Yuan Material science and Engineering school, university of science and technology beijing, beijing, 100083, china Univ Sci & Technol beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China

The effect of relaxation after finished rolling on structures and properties of four microalloyed steel with different content of Nb and Ti was investigated. By alloy designing and control rolling + relaxation-precipitation-control phase trail storm ati on (RPC) process, a new 800 MPa grade HSLA plate steel could be obtained, the microstructure is composite ultra-fine lath bainite/martensite. The tempering process and mechanical properties of this kind of HSLA steel were investigated. The yield strength can achieve 800 MPa, and the ductility and impact toughness is satisfied.

关键词： HSLA steel microstructure and mechanical properties TMCP (thermomechanical control process) RPC

BEHAVIOUR OF VACANCY INFLUENCE DURING DIFFUSION IN METALS

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Acta Metallurgica Sinica(English Letters) 1992年第6期5卷 395-401页

作者： ZHANG Sanhong he xinlai CHU Youyi KE Jun (T.Ko){2.,china Doctor,Department of materials Physics,university of science and technology beijing,beijing 100083 beijing Univ of science and Technology Beijing China

The effects of vacancies on diffusion of interstitial and substitutional atoms as well as interaction between them in metals were *** the interstitial alloy,a coupling between interstitial atoms and vacancy is interrelated through the reaction of formation and dissociation of *** substitutional alloy with |E_b|he atom diffusion is of the vacancies exchange mechanism,the vacancies may considerably affect atom *** on the micromechanism of diffusion in these two alloys,their diffusion equations under general condition may be obtained,and the second Fick' s law is only an approximate form when neg- lecting vacancy influence.

关键词： vacancy diffusion Fick's law

Mechanical Method Determining Precipitation in an Ultra-Low Carbon Bainitic Steel

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International Journal of Minerals,Metallurgy and materials 1998年第3期12卷 115-118页

作者： Zijiu Dang Yan Thang Jun Ke xinlai he Shanwu Yang(State Key Laboratory for Advanced Metals and {2., university of science and technology beijing, beijing 100083, china)(Applied science school, university of science and technology beijing, Beijin State Key Laboratory for Advanced Metals and materials University of Science and Technology Beijing Beijing 100083 China Applied science school University of Science and Technology Beijing Beijing 100083 China

Stress relaxation was chosen as the best method for monitoring the precipitation process. Tests were carried out on an ultra-low carbon bainitic steel containing Mn, Nb and B over 800~950℃. Specimens were solu- tion treated at 12.0℃ for a certain holding period. A prestain of 2.% was applied at a strain rate of 0.1/s. The exper- imental results are displayed by a set of stress vs. 1g(time) curves different from the typical stress relaxation curves. There are two singularities forming a stress plateau on the stress vs.1g(time) curves when precipitates could be observed. Suppose the first one is the start of precipitation (Ps), and the second represcnts the fihish (Pf). As a result Precipitation-Time-Temperature relationship is described as C-shape curves based on two points. This mechanical method is suitable and precise for measuring precipitates in microalloyed steels during hot working.

关键词： stress relaxation precipitation ultra-low carbon bainitic steel (ULCB steel)

Change in dislocation configuration of deformed Fe-Ni-Nb-Ti-C-B alloy during stress relaxation

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Journal of university of science and technology beijing 2003年第3期10卷 76-78页

作者： Shaoqiang Yuan, Shanwu Yang, Wenjin Nie, and xinlai he Department of {2. Physics, university of science and technology beijing, beijing 100083, china Tangshan College, Tangshan 063000, china Dept. of Mat. Phys. Univ. of Sci. and Technol. Beijing Beijing 100083 China Tangshan Coll. Tangshan 063000 China

Transmission electron microscopy (TEM) was applied to investigate theevolution of dislocation configuration and strain induced precipitation behavior during relaxationprocess after deformation in Fe-Ni-Nb-Ti-C-B alloy. Experimental results indicate that thedislocation density is very high and distribute randornly before relaxation. As the relaxation timeincreasing, dislocation cells will form gradually by polygonization. The strain inducedprecipitation retards the progress. In the final relaxation stage, most dislocations get rid ofpinning of precipitates and the cells have developed into subgrains with large size.

关键词： relaxation dislocation cell strain induced precipitation