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Journal of Iron and Steel Research International 2011年第3期18卷 59-64页

作者： ZHOU Min du lin-xiu LIU Xiang-hua State Key Laboratory of Rolling Technology and Automation Northeastern UniversityShenyang 110004LiaoningChina

The variation of heat treatments including directed quenching and tempering off-line after controlled rolling（DQT） and quenching off-line and tempering off-line after controlled rolling（RQT） with microstructure and mechanical properties of a low-carbon microalloyed steel was compared and *** DQT,the quenched steel was obviously banded microstructure,with increasing tempering temperature,lath martensite coarsened,the cusp carbide precipitated at grain boundaries,the yield strength fluctuated slightly,and the fracture-separation was *** impact toughness was better in the steel tempered at 500 ℃ for 1 *** RQT,with increasing tempering temperature,lath martensite degenerated,intragranular and intergranular finer precipitations with smaller than 30 nm precipitated and grew up and were distributed dispersedly,the stripe-like carbides were distributed at grain boundaries,and the yield strength and tensile strengthen decreased *** impact toughness of RQT process was much better than that of DQT process,and the comprehensive mechanical properties were better for the steel tempered at 500 ℃ for 1 h of RQT process.

关键词： X120 pipeline steel heat treatment microstructure mechanical property fracture-separation

Dynamic and Static Recrystallization Behavior of Low Carbon High Niobium Microalloyed Steel

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Journal of Iron and Steel Research International 2011年第1期18卷 55-60页

作者： LAN Liang yun QIU Chun lin ZHAO De-wen GAO xiu hua du lin-xiu State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China

The recrystallization behavior of a low carbon high niobium microalloyed steel was investigated using continuous and interrupted hot compression tests. The results showed that the initiation of dynamic recrystallization （DRX） could be detected from inflection in the plot of the strain hardening rate against stress regardless of the stress peak appearance. According to the Zener-Hollomon parameter equation, the activity energy of DRX （Qad） was ob tained and a new modified expression calculating Qdef was proposed in consideration of the chemical composition of experimental steel. Applying the 2% offset method, the static softening fraction was determined. The graphic representation of the softening fraction vs interruption time gave the information about the non-static reerystallization temperature （about 1 000℃ ） and the relationship of precipitation time temperature. Static recrystallization kinetics followed the Avrami＇s law at high deformation temperature, and different values of the exponent m were given to illustrate the effect of niobium element on static recrystallization at different deformation temperatures.

关键词： dynamic recrystallization static recrystallization high niobium microalloyed steel activity energy

Fatigue Property of Low Cost and High Strength Wheel Steel for Commercial Vehicle

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Journal of Iron and Steel Research International 2009年第4期16卷 44-48,77页

作者： WANG Ning LI Yi du lin-xiu WU Di LIU Xiang-hua The State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China

The fatigue properties of the newly developed wheel steel used for commercial vehicles were studied using push-pull axial loading fatigue tests with stress ratio R=-1. Q235B steel, which is conventionally applied to commercial vehicle wheels, was also analyzed for comparison. Although the chemical composition and microstructure （ferrite and pearlite） of newly developed wheel steel were similar to those of Q235B, the 107 cycles fatigue limit of the new wheel steel was 260 MPa, which is 24% higher than that of Q235B （210 MPa）. The improvement of the fatigue strength of the new wheel steel can be attributed to grain refinement. In order to investigate the effect of the decrease in thickness of the wheel steel on the fatigue property of the wheel, dynamic cornering fatigue tests were conducted on full scale wheels with the model of 8.25 × 22.5. The results indicated that the newly developed wheel steel had outstanding fatigue life even if the mass loss was 10% in comparison with Q235B.

关键词： high strength wheel steel fatigue strength grain refinement dynamic cornering fatigue test

Development of Nb-V-Ti Hot-Rolled High Strength Steel With Fine Ferrite and Precipitation Strengthening

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Journal of Iron and Steel Research International 2009年第4期16卷 72-77页

作者： YI Hai-long du lin-xiu WANG Guo-dong LIU Xiang-hua State Key Laboratory of Rolling Technology and Automation Northeastern University Shenyang 110004 Liaoning China

A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.

关键词： high strength steel precipitation hardening ductile-brittle transition temperature fine grain strengthening

linear Integral Analysis of Bar Rough Rolling by Strain Rate Vector

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Journal of Iron and Steel Research International 2010年第3期17卷 28-33页

作者： DENG Wei ZHAO De-wen QIN Xiao-mei GAO xiu-hua du lin-xiu LIU Xiang-hua State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China

A new linear integral method for bar hot rolling on roughing train was obtained. First, for plastic deformation energy rate, equivalent strain rate about Kobayashi＇s three-dimensional velocity field was expressed by two-dimensional strain rate vector; then, the two-dimensional strain rate vector was inverted into inner product and was integrated term by term. during those processes, boundary equation and mean value theorem were introduced; for friction and shear energy dissipation rate, definite integral was applied to the solution process. Sequentially, the total upper bound power was minimized, and the analytical expressions of rolling torque, separating force, and stress state factor were obtained. The calculated results by these expressions were compared with those of experimental values. The results show that the new linear integral method is available for bar rough rolling analysis and the calculated results by this method are a little higher than those of experimental ones. However, the maximum error between them is less than 10%.

关键词： bar rough rolling linear integration strain rate vector roll separating force

Effect of Prestrain on Microstructures and Properties of Si-Al-Mn TRIP Steel Sheet With Niobium

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Journal of Iron and Steel Research International 2010年第4期17卷 59-65页

作者： TANG Zheng-you DING Hua DING Hao CAI Ming-hui du lin-xiu College of Materials and Metallurgy Northeastern University Shenyang 110004 Liaoning China State KeyLaboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China

Paint baking treatment was carried out in a silicon oil bath at 170℃ for 20 min for Si-Al-Mn TRIP Steel sheet with different prestrains, and effect of prestrain on microstructures and properties was studied before and after baking. The results show that with the increasing of prestrain amount during prestraining and baking, the volume fraction of retained austenite decreases, and the volume fraction of martensite and bainite increases as well as yield strength increases; as prestrain ranges from 0 to 4%, the baking-hardening （BH） value increases; while the prestrain ranges from 4% to 16%, the BH value decreases; when the prestrain amount is 4%, the highest BH value is about 70 MPa for Si-Al-Mn TRIP steel sheet with niobium, which displays excellent baking-hardening behavior.

关键词： TRIP steel sheet prestrain retained austenite baking-hardening

Effect of Ti(C,N)Precipitation on Texture Evolution and Fish-Scale Resistance of Ultra-Low Carbon Ti-Bearing Enamel Steel

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Journal of Iron and Steel Research International 2013年第4期20卷 39-45页

作者： DONG Fu-tao du lin-xiu LIU Xiang-hua HU Jun XUE Fei State Key Laboratory of Rolling and Automation Northeastern University College of Electrical Engineering Hebei United University

The Ti（C,N）precipitation and texture evolution in ultra-low carbon Ti-bearing enamel steel were studied to discover their *** different cooling paths of simulative coiling were adopted to gain different morphologies of Ti（C,N）precipitate in hot *** is found that the Ti（C,N）precipitate in hot strip using Path 2（put into asbestos box and air cooled）are finer and much more in quantity than that in hot strip using Path 1（held at 730℃ for 30min and furnace cooled）.The morphology of Ti（C,N）precipitate in hot strip has great effect on recrystallization texture in the subsequent cold-rolled annealed sheet.γ-fiber texture of strong recrystallization is gained in coldrolled and annealed sheet came from Path *** the contrary,in the one came from Path 2,theγ-fiber texture is *** may be due to the pinning force of numerous fine Ti（C,N）precipitate which retard the growth of preferential nucleated{111}orientated *** steel sheets in the test came from both paths have excellent fishscale resistance.

关键词： Ti(C N)precipitate texture fish-scale resistance ultra-low carbon enamel steel hydrogen diffusion coefficient

Effect of Warm-Rolled Pearlite Microstructural Features on Austenitic Transformation

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Journal of Iron and Steel Research International 2009年第4期16卷 55-59页

作者： YAO Sheng-jie du lin-xiu LIU Xiang-hua WANG Guo-dong State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China

The austenite transformation characteristics for various warm-rolled pearlite during rapid heating were investigated. The results indicate that the start temperature （Ts） is sensitive to the microstructural feature of pearlite, whereas the dislocation plays an important role in the transformation rate; at the same time, the uniformity of austenite grains is more or less affected by the amount of spheroidized pearlite. A critical effect on the state of austenite grain is created through the influence of initial microstructures on the start temperature of transformation.

关键词： warm rolling pearlite dislocation austenite transformation

Influence of Holding Time After Deformation on Bainite Transformation in Niobium Microalloyed Steel

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Journal of Iron and Steel Research International 2007年第5期14卷 62-65页

作者： YI Hai-long du lin-xiu WANG Guo-dong LIU Xiang-hua State Key Laboratory of Rolling Technology and Automation Northeastern University Shenyang 110004 Liaoning China

Using Gleeble-1500 system, the influence of holding time on bainite transformation in deformed niobium microalloyed steel during continuous cooling was analyzed, and the carbides in upper bainite were also systematically researched. The results show that the occurrence of the static recrystallization decreases the amount of bainite with an increase in the holding time and the emergence of retained austenite （RA） with the longer holding time. Two types of carbides were observed in upper bainite with regard to their precipitation sites. They either existed between the bainite ferrite laths or co-existed with RA. The formation mechanism of two kinds of carbides was analyzed by combining TEM micrographs with the model.

关键词： niobium microalloyed steel bainite carbide static recrystallization retained austenite

Strengthening Mechanism of a New 700 MPa Hot Rolled High Strength Steel

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Journal of Iron and Steel Research International 2008年第2期15卷 76-80页

作者： YI Hai-long du lin-xiu WANG Guo-dong LIU Xiang-hua State Key Laboratory of Rolling Technology and Automation Northeastern University Shenyang 110004 Liaoning China

The microstructural evolution in a 700 MPa hot rolled high strength steel was analyzed in terms of strengthening *** results show that the hot rolled sheet steel has yield strength of 710 MPa with good elongation and *** strength of the developed 700 MPa hot rolled high strength steel is derived from the cumulative contribution of fine grain size,dislocation hardening and precipitation *** fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength,and the amount of precipitation hardening is two or four times higher than that of conventional microalloyed hot rolled sheet steels reported in the *** toughness is due to refinement of ferrite grain size.

关键词： high strength steel strengthening mechanism dislocation hardening precipitation hardening