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International Journal of Minerals,Metallurgy and Materials 2023年第4期30卷 724-733页

作者： Guangming Xie Ruihai Duan Yuqian Wang Zong’an Luo Guodong Wang State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China

Fusion welding easily causes microstructural coarsening in the heat-affected zone(HAZ) of a thick-gauge pipeline steel joint. This is most significant in the inter-critically coarse-grained HAZ(ICCGHAZ), which considerably deteriorates the toughness of the joint. In the present work, 11-mm thick pipeline steel was joined by preheating and double-sided friction stir welding(FSW). A comparative study on the microstructure and toughness in the ICCGHAZs for FSW and gas metal arc welding(GMAW) was performed. The toughness in the ICCGHAZ for FSW was improved significantly than that in the ICCGHAZ for GMAW. Generally, the nugget zone(NZ) has a coarse microstructure in the FSW steel joint formed at the highest peak temperature. However, in the current study, the microstructure in the one-pass NZ was remarkably refined owing to the static recrystallization of ferrite. An excellent toughness was achieved in the NZ of the pipeline steel joint that employed FSW.

关键词： pipeline steel thick-gauge plate friction stir welding microstructure toughness

Microstructure and properties of Nb,V and N alloyed low magnetic hot rolled stainless steel plate

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Tungsten 2023年第4期5卷 512-521页

作者： Jing-Bo Dong Kun Li Li-Xiang Gao Chang-Sheng Li State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang110819China

It is a common technical difficulty to improve the strength of low magnetic stainless steel plates on the premise of ensuring ductility,corrosion resistance,and low magnetism.In this paper,the chemical composition of low magnetic stainless steels with excellent paramagnetic stabilities and corrosion resistances was formulated through composition design and calculation.Through the alloying of Nb,V,and N and the controlled hot rolling process,large numbers of uniformly distributed high-temperature second phase particles were formed in the steel plate,and low magnetic stainless steel 35 mm plate with yield strength,ultimate tensile strength and elongation of 407 MPa,739 MPa and 54%respectively were obtained.The main strengthening strategies of the steel were solid solution strengthening and precipitation strengthening.The precipitation law and types of the high-temperature second phase in the steel were explored.The micro structure of the steel plate was characterized by scanning electron microscope,electron probe microanalysis,and transmission electron microscope.The magnetic properties of the steel plate were tested by a vibrating sample magnetometer.The relative magnetic permeability of the hot rolled plate was 1.0063 which met the requirement of low magnetism.

关键词： Low magnetic stainless steel Steel plate Solution strengthening Second phase Precipitation strengthening

Application of distributed model predictive control based on neighborhood optimization in gauge-looper integrated system of tandem hot rolling

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Journal of Iron and Steel Research(International) 2023年第2期30卷 277-292页

作者： Jie Sun Fan Hou Yun-jian Hu Long-jun Wang Hao-yue Jin Wen Peng Xiao-jian Li Dian-hua Zhang State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang110819LiaoningChina

To solve the coupling relationship between the strip automatic gauge control and the looper control in traditional control strategy of tandem hot rolling,a distributed model predictive control(DMPC)strategy for the tandem hot rolling was explored,and a series of simulation experiments were carried out.Firstly,based on the state space analysis method,the multivariable dynamic transition process of hot strip rolling was studied,and the state space model of a gauge-looper integrated system in tandem hot rolling was established.Secondly,DMPC strategy based on neighborhood optimization was proposed,which fully considered the coupling relationship in this integrated system.Finally,a series of experiments simulating disturbances and emergency situations were completed with actual rolling data.The experimental results showed that the proposed DMPC control strategy had better performance compared with the traditional proportional-integral control and centralized model predictive control,which is applicable for the gauge-looper integrated system.

关键词： Tandem hot rolling Gauge Looper integrated system state space model Distributed model predictive control Neighborhood optimization

Effect of grain size on the intrinsic mechanical stability of austenite in transformation-induced plasticity steels:The competition between martensite transformation and dislocation slip

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Journal of Materials Science & Technology 2023年第31期162卷 38-43页

作者： D.P.Yang T.Wang Z.T.Miao P.J.Du G.D.Wang H.L.Yi State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China

The deformation accompanied by austenite to martensite trans-formation was first studied in Fe-Ni alloys,high-Mn steels,and austenitic stainless steels with a full austenite microstructure.The plasticity of these steels can be improved by the trans-formation during deformation and hence they were named as transformation-induced plasticity(TRIP)steels[1].Over the past few decades,a series of TRIP steels with multiphase microstructure for automotive applications were developed.These steels contain-ing a certain amount of austenite were called TRIP-assisted steels,such as low-alloy TRIP steels[2],carbide-free bainitic steels[3],δ-TRIP steels[4],quenching and partitioning steels[5],and medium-Mn steels[6].The mechanical property of TRIP steels is largely determined by the mechanical stability of austenite[7]which de-pends on the chemical composition[8],grain size[9],orientation[10],and morphology[11]of austenite grains,as well as the nature of neighboring phases[12].In most cases of TRIP-assisted steels,larger austenite grains transform to martensite earlier or faster than smaller austenite grains with the increase of macrostrain[13-18],indicating lower mechanical stability.However,larger austen-ite grains usually contain less C and Mn[13,17-19]and suffer more strain than smaller grains during deformation[20],it doesn’t mean that grain refinement increases the mechanical stability of austen-ite.

关键词： austenite martensite transformation

On hot deformation behavior and workability characteristic of 42CrMo4 steel based on microstructure and processing map

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Journal of Iron and Steel Research(International) 2023年第3期30卷 537-547页

作者： Min Qi Hong-yan Wu Ying Dong Lin-xiu Du State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819LiaoningChina

In order to determine the safe region of 42CrMo4 steel during hot working and obtain excellent workability,the hot deformation behavior at the temperatures of 850-1150℃and the strain rates of 0.01-10 s^(-1)was investigated through single-pass compression test of thermo-simulation.Through observing and analyzing the true stress-strain curves,the conclusion may be drawn that the flow stress value increases with the decrease in deformation temperature and the increase in strain rate.Raising temperature and reducing strain rate are conductive to dynamic recrystallization(DRX)nucleating and growing,but adiabatic heating caused by higher strain rate can also promote it.Since the Zener-Hollomon(Z)value and dynamic recrystallized grain size(D_(DRX))have completely opposite trends with deformation condition parameters,the expression of Z value and DDRX can be determined as:D_(DRx)=15,567.645Z^(-02174).The processing map and instability map constructed at a strain of 0.9 show that the suitable window for hot working with a true strain of 0.9 is in the temperature range of 970-1150℃and strain rate range of 0.01-0.25 s^(-1),as well as at the temperature of 1150℃ and strain rate range of 0.25-10 s^(-1).The instability phenomenon appears in the process interval of 850-1096℃ and 0.22-10 s^(-1).

关键词： Hot deformation behavior Dynamic recrystallization Microstructure evolution Constitutive relationship Processing map

Effect of low-temperature ausforming on bainitic transformation and mechanical properties in ultrahigh-strength bainitic steel

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Journal of Iron and Steel Research(International) 2023年第9期30卷 1843-1853页

作者： Tian-yu Zhang Ling-yu Wang Yu Wang Jun Hu Hong-shuang Di Wei Xu State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819LiaoningChina

Low-temperature ausforming(LT-AF)prior to bainitic transformation leads to a noticeable acceleration of bainitic transformation kinetics;however,the effect of LT-AF on the retained austenite(RA)features and the resulting mechanical properties is still unclear.LT-AF was applied to ultrahigh-strength bainitic steel before austempering.The deformation behavior and the resulting dislocation substructures were investigated by thermomechanical simulator and transmission electron microscopy(TEM).The planar dislocation structures produced during deformation at 350℃ accelerate the bainitic transformation kinetics during isothermal holding.The effect of LT-AF on the bainitic transformation kinetics and the features of RA was elucidated via dilatometer measurement,TEM,scanning electron microscopy,and X-ray diffraction.It is observed that LT-AF not only retains more RA content but also facilitates improved RA stability.This trend is mainly due to the large amounts of planar dislocations in RA and bainitic laths inherited from undercooled austenite caused by LT-AF,the decrease in bainitic sheaves size,and the increase in filmy RA content compared to the sample without ausforming.A large fraction of filmy RA with high stability and the refinement of bainitic sheaves obtained by LT-AF remarkably enhance the strain hardening capacity and achieve significantly better ductility compared to the directly austempered sample.

关键词： Ultrahigh-strength bainitic steel Bainitic transformation Low-temperature ausforming Retained austenite Strain hardening rate

Roles of nanoscale precipitates and metastable austenite in determining strength and toughness of high-strength Nb-bearing steel

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Journal of Iron and Steel Research(International) 2022年第10期29卷 1646-1658页

作者： Qi-bin Ye Cheng Zhou Jun Hu Xiao-lan Gong Yong Tian Xiu-hua Gao Zhao-dong Wang State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang110819LiaoningChina

The effects of tempering temperature on the microstructure and mechanical properties of high-strength structural steel containing niobium were investigated to examine the roles of nanoscale precipitates and metastable austenite in determining the yield strength and toughness.After hot-rolling and quenching,three experimental steels were tempered at 590,630,and 670℃.During tempering,nanoscale Nb(C,N)precipitates were formed with the recovery of quenched martensite.The average diameters of Nb(C,N)precipitates increased from 5.4 to 8.2 nm as the tempering temperature was increased.Notably,reversed austenite with a volume fraction of 9%was formed at tempering temperatures up to 670℃.The yield strengths of steel containing tempered martensite tempered at 590 and 630℃ were 965 and 831 MPa,and the tensile strengths were 998 and 879 MPa,respectively.However,the steel comprising reversed austenite and tempered martensite tempered at 670℃ showed continuous yielding behavior,affording yield and tensile strengths of 610 and 889 MPa,respectively.The impact energy increased from 105 to 260 J at−60℃ with increasing tempering temperature.Reversed austenite improves low-temperature toughness by significantly increasing the crack propagation energy.

关键词： High-strength structural steel Tempering Nanoscale precipitate Metastable austenite Mechanical property

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 analyzed.Microstructure 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 rate.In addition,flow behavior reflected in flow curves was inconsistent with the actual microstructural evolution during hot deformation,especially at higher strain rates and lower temperatures.Therefore,flow curves were revised in consideration of the effects of adiabatic heating and friction during hot deformation.The 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 level.Moreover,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 data.The 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^-1.The 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

Research and application of the angular rolling technology for plate mill

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Advances in Manufacturing 2023年第3期11卷 462-476页

作者： Zhi-Jie Jiao Jun-Yi Luo Zhi-Qiang Wang Zhi-Peng Xu Chun-Yu He Zhong Zhao State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819People's Republic of China

Angular rolling technology can overcome the size limitation of plate mill equipment and product heavy steel plate with large unit weight or improve the production efficiency of small width spreading ratio product.With the DEFORM software,the numerical simulation study of the angular rolling process was carried out,and the relation laws of the width,rolling force and strain of the rolled piece under different angular rolling process conditions were obtained.The simulation results show that with the rotation angle increasing,the width of the rolled piece increases.Comparing with the conventional rolling process,the rolling force changes gradually during the biting and throwing stage of the angular rolling pass.With the rotation angle increasing,both the equivalent strains in the thickness direction and in the width direction gradually increase.According to the pattern and dimension's changing formula in the double-pass angular rolling process,the prediction model of angle,reduction and width spreading is built.The opening value of side guide is set for the rotation angle controlling.For one 5000 mm heavy plate mill,the automation control system was modified,and the angular rolling technology was applied online.The absolute deviation of target width does not exceed±20 mm and the relative deviation does not exceed 1%.The large unit weight plate that cannot be rolled with traditional process,can be produced now,and the annual output increases by 10000 t.

关键词： Plate mill Angular rolling Numerical simulation Width spreading Prediction model Online application

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 thickness.The 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