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Hard magnetization direction and its relation with magnetic permeability of highly grain-oriented electrical steel

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International Journal of Minerals,Metallurgy and Materials 2014年第11期21卷 1077-1082页

作者： Hao Wang Chang-sheng Li Tao Zhu state key laboratory of rolling and automation Northeastern University

The magnetic properties of highly grain-oriented electrical steel vary along different directions. In order to investigate these properties, standard Epstein samples were cut at different angles to the rolling direction. The hard magnetization direction was found at an angle of 60° to the rolling direction. To compare the measured and fitting curves, when the magnetic field intensity is higher than 7000 A/m, it is appropriate to simulate the relation of magnetic permeability and magnetization angle using the conventional elliptical model. When the magnetic field intensity is less than 3000 A/m, parabolic fitting models should be used; but when the magnetic field intensity is between 3000 and 7000 A/m, hybrid models with high accuracy, as proposed in this paper, should be applied. Piecewise relation models of magnetic permeability and magnetization angle are significant for improving the accuracy of electromagnetic engineering calculations of electrical steel, and these new models could be applied in further industrial applications.

关键词： electrical steel magnetization direction magnetic permeability mathematical models

Numerical analysis of heat transfer intensity from twin slot vertical jet impingement on strip surface after hot rolling

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Journal of Central South University 2015年第7期22卷 2816-2824页

作者：石建辉袁国江连运赵昆王国栋 state key laboratory of rolling and automation(Northeastern University)

The flow field and heat transfer of the strip surface due to the twin slot vertical jet impingement were investigated using the ANSYS *** RNG k-ε model was carried out in the turbulent *** parametric research was conducted by varying the jet velocity of nozzle exit(V=5 m/s,7.5 m/s,10 m/s),the temperature of cooling water(T_w=280 K,300 K),the normalized spacing from the nozzle to the strip surface(H=10,15,20,33),and the normalized spacing from the nozzle to nozzle centerline(W=0,15,30).The velocity streamline of the flow domain and the general trend of the distribution of the local Nusselt number on the impingement surface of strip were *** result indicate that,the average Nusselt number increases by about70%(90%) as the jet velocity is increased from 5 m/s to 7.5 m/s(from 7.5 m/s to 10 m/s),and T_w,Hand//have minimal effect on *** the valley Nusselt number decreases by about 10%-43%with the increase of H and *** functional relationship between the average Nusselt number and the systematic parameters is derived by the least square regression method.

关键词： ultra-fast cooling heat transfer flow field twin slot nozzle Nusselt number

Deformation Behavior of Fe-36Ni Steel during Cryogenic( 123-173 K) rolling

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Journal of Iron and Steel Research International 2016年第5期23卷 447-452页

作者： Jian-jun ZHENG Chang-sheng LI Shuai HE Ban CAI Yan-lei SONG state key laboratory of rolling and automation Northeastern University

Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature（ 123-173 K） with 20%- 90% rolling reduction in *** deformation process was accompanied by twinning at cryogenic temperature,and the mean thickness of deformation twins was about 200 nm with 20% rolling reduction. When the rolling reduction was above 40%,twinning was suppressed due to the stress concentration in the tested steel. Deformation microstructure of Fe-36Ni steel consisted of both twin boundaries and dislocations by cryogenic rolling（ CR）,while it only contained dislocations after rolling at room temperature（ RT）. The tensile strength of Fe-36Ni steel was improved to 930 MPa after 90% reduction at cryogenic temperature,while the tensile strength after 90% reduction at RT was only 760 MPa. More dislocations could be produced as the nucleation sites of recrystallization during CR process.

关键词： Fe-36Ni steel cryogenic rolling twinning dislocation slip room temperature deformation microstructure

Microstructure Evolution and Strain-Dependent Constitutive Modeling to Predict the Flow Behavior of 20Cr–24Ni–6Mo Super-Austenitic Stainless Steel During Hot Deformation

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Acta Metallurgica Sinica(English Letters) 2018年第4期31卷 401-414页

作者： Yan-Sen Hao Wan-Chun Liu Zhen-Yu Liu state key laboratory of rolling and automation Northeastern University

Hot compression tests were carried out with specimens of 20Cr-24Ni-6Mo super-austenitic stainless steel at strain rate from 0.01 to 10 s^-1 in the temperature range from 950 to 1150 ℃,and flow behavior was *** analysis indicated that dynamic recrystallization（DRX）behavior was more sensitive to the temperature than strain rate,and full DRX was obtained when the specimen deformed at 1150℃.When the temperature reduced to 1050 ℃,full DRX was completed at the highest strain rate 10 s-l rather than at the lowest strain rate 0.01 s-1 because the adiabatic heating was pronounced at higher strain *** addition,flow behavior reflected in flow curves was inconsistent with the actual microstructural evolution during hot deformation,especially at higher strain rates and lower ***,flow curves were revised in consideration of the effects of adiabatic heating and friction during hot *** results showed that adiabatic heating became greater with the increase of strain level,strain rate and the decrease of temperature,while the frictional effect cannot be neglected at high strain ***,based on the revised flow curves,strain-dependent constitutive modeling was developed and verified by comparing the predicted data with the experimental data and the modified *** result suggested that the developed constitutive modeling can more adequately predict the flow behavior reflected by corrected flow curves than that reflected by experimental flow curves,even though some difference existed at 950℃ and 0.01 s^-*** main reason was that plenty of precipitates generated at this deformation condition and affected the DRX behavior and deformation behavior,eventually resulted in dramatic increase of deformation resistance.

关键词： Super-austenitic stainless steel Hot compression Adiabatic heating Constitutive modeling Microstructure evolution

Microstructural Evolution and Toughness in the HAZ of Submerged Arc Welded Low Welding Crack Susceptibility Steel

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Acta Metallurgica Sinica(English Letters) 2013年第1期26卷 49-55页

作者： Chunlin QIU Liangyun LAN Dewen ZHAO Xiuhua GAO Linxiu DU state key laboratory of rolling and automation Northeastern University

Microstructural characteristics of different sub-regions of heat affected zone （HAZ） of low welding crack susceptibility steel weldment were investigated by using optical microscopy and scanning electron microscopy equipped with electron backscattered diffraction system. And the focus was put on the correlation between microstructural characteristics and HAZ toughness of the weldment. The results reveal that the toughness of fusion line zone （FLZ） specimens is much lower than that of fine grained HAZ （FGHAZ） specimens. The coarse inclusions in the weld metal and the large martensite-austenite constituents in the coarse grained HAZ （CGHAZ） have an obvious negative effect on the crack initiation energy of FLZ. Meanwhile, the coarse granular bainite with large effective grain decreases the crack propagation energy seriously. By contrast, fine crystallographic grains in the FGHAZ play a key role in increasing toughness, especially in improving crack propagation energy.

关键词： Steel Heat affected zone (HAZ) Submerged arc welding Effective grain size Toughness Microstructure

Identification and optimization for hydraulic roll gap control in strip rolling mill

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Journal of Central South University 2015年第6期22卷 2183-2191页

作者：孙杰陈树宗韩欢欢陈兴华陈秋捷张殿华 state key laboratory of rolling and automation (Northeastern University)

In order to improve the control performance of strip rolling mill, theoretical model of the hydraulic gap control(HGC) system was established. HGC system offline identification scheme was designed for a tandem cold strip mill, the system model parameters were identified by ARX model, and the identified model was verified. Taking the offline identified parameters as the initial values, online identification using recursive least square was carried out with model parameters changing. For the purpose of improving system robustness and decreasing the sensitivity due to model errors, the HGC system based on generalized predictive control(GPC) was designed, and simulation experiments for traditional controller and GPC controller were conducted. The results show that both controllers acquire good control effect with model matching. When the model mismatches, for the traditional controller, the overshot will increase to 76.7% and the rising time will increase to 165.7 ms, which cannot be accepted by HGC system; for the GPC controller, the overshot is less than 8.5%, and the rising time is less than 26 ms in any case.

关键词： hydraulic roll gap control modeling system identification generalized predictive control

Case-Based Reasoning(CBR) Model for Ultra-Fast Cooling in Plate Mill

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Chinese Journal of Mechanical Engineering 2014年第6期27卷 1264-1271页

作者： HU Xiao WANG Zhaodong WANG Guodong state key laboratory of rolling and automation Northeastern University

New generation thermo-mechanical control process（TMCP） based on ultra-fast cooling is being widely adopted in plate mill to product high-performance steel material at low cost. Ultra-fast cooling system is complex because of optimizing the temperature control error generated by heat transfer mathematical model and process parameters. In order to simplify the system and improve the temperature control precision in ultra-fast cooling process, several existing models of case-based reasoning（CBR） model are reviewed. Combining with ultra-fast cooling process, a developed R5 CBR model is proposed, which mainly improves the case representation, similarity relation and retrieval module. Certainty factor is defined in semantics memory unit of plate case which provides not only internal data reliability but also product performance reliability. Similarity relation is improved by defined power index similarity membership function. Retrieval process is simplified and retrieval efficiency is improved apparently by windmill retrieval algorithm. The proposed CBR model is used for predicting the case of cooling strategy and its capability is superior to traditional process model. In order to perform comprehensive investigations on ultra-fast cooling process, different steel plates are considered for the experiment. The validation experiment and industrial production of proposed CBR model are carried out, which demonstrated that finish cooling temperature（FCT） error is controlled within±25℃ and quality rate of product is more than 97%. The proposed CBR model can simplify ultra-fast cooling system and give quality performance for steel product.

关键词： ultra-fast cooling plate mill case-based reasoning case representation similarity relation retrieval module

Some Aspects of High Manganese Twinning-Induced Plasticity (TWIP) Steel, A Review

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Acta Metallurgica Sinica(English Letters) 2013年第1期26卷 1-15页

作者： Liqing CHEN Yang ZHAO Xiaomei QIN state key laboratory of rolling and automation Northeastern University

High manganese twinning-induced plasticity （TWIP） steel is a new kind of structural material and possesses both high strength and superior plasticity and can meet the weight-lightening requirement for manufacturing vehicle body. The excellent formability of the TWIP steel comes from the extraordinary strain hardening effect during plastic deformation. The reduction of specific weight by aluminum alloying and strain hardening effect can lead to an effective weight reduction of the steel components, and provide a better choice for materials in vehicle body design. The TWIP effect in high Mn steels is generally associated with the successive work- hardening generated by twins and influenced by some factors, such as Mn content, AI addition revealed by stacking fault energy （SFE）, grain size, deformation temperature and strain rate. The present review introduces some aspects of the TWIP steels relating to their physical metallurgy, influencing factors associated with their deformation mechanisms, and a prospect for the future investigation is also described. Moreover, as a potential candidate for replacing Ni-Cr austenitic stainless steel, researches on the oxidation behavior and corrosion resistance of Fe-Mn-AI-C system steels are also reviewed.

关键词： Twinning-induced plasticity (TWIP) steel Physical metallurgy Stacking faultenergy Mechanical properties Oxidation behavior Corrosion resistance

Static Recrystallization and Precipitation Behavior of a Weathering Steel Microalloyed with Vanadium

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Journal of Materials Science & Technology 2013年第12期29卷 1197-1203页

作者： Hongyan Wu Linxiu Du Zhengrong Ai Xianghua Liu state key laboratory of rolling and automation Northeastern University

The static recrystallization （SRX） and precipitation behavior of a weathering steel microalloyed with vanadium were investigated through double-pass compression tests under controfled conditions using the MMS-300 thermal-mechanical simulator. The deformation temperatures ranged from 800 °C to 1000 °C, and the inter- pass time from 1 s to 500 s. The simulation results showed that SRX occurred after 5-10 s at the first compression deformation. The softening fraction of SRX was found to increase with increasing the deformation temperature and the pre-strain. However, the softening fraction scarcely changed during the process of strain-induced precipitation. In addition, the kinetics of SRX was described by the Avrami equation, and the Avrami exponent appeared to be closely associated with the deformation temperature. The microstructure evolution was investigated at the initiation and completion of recrystallization. The amount and distribution of the precipitates were analyzed. The relationship between the driving force of SRX and the pinning force of precipitation was discussed. Besides, the recrystallization inhibition was detected at the early stage of precipitation, and the pinning forces were found to be of a magnitude comparable to the driving force. Moreover, the pinning forces were found to increase with the degree of precipitation and reach a peak at the intermediate stage of precipitation, and finally reduce as the particles coarsened.

关键词： Vanadium-microalloyed weathering steel Static recrystallization Kinetics of SRX Microstructural evolution Precipitation