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Influence of silicon on the microstructures, mechanical properties and stretch-flangeability of dual phase steels

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International Journal of Minerals,Metallurgy and Materials 2014年第8期21卷 755-765页

作者： Le-yu Zhou Dan Zhang ya-zheng liu School of Materials Science and Engineering University of Science and Technology Beijing

Uniaxial tension tests and hole-expansion tests were carried out to determine the influence of silicon on the microstructures, mechanical properties, and stretch-flangeability of conventional dual-phase steels. Compared to 0.03wt% silicon, the addition of 1.08wt% silicon induced the formation of finer ferrite grains （6.8μm ） and a higher carbon content of martensite （Cm≈ 0.32wt%）. AS the silicon level increased, the initial strain-hardening rate （n value） and the uniform elongation increased, whereas the yield strength, yield ratio, and stretch-flangeability decreased. The microstructures were observed after hole-expansion tests. The results showed that low carbon content martensite （Cm ≈ 0.19wt%） can easily deform in coordination with ferrite. The relationship between the mechanical properties and stretch-flangeability indicated that the steel with large post-uniform elongation has good stretch-flangeability due to a closer plastic incom- patibility of the ferrite and martensite phases, which can effectively delay the production and decohesion of microvoids.

关键词： dual-phase steel silicon content mechanical properties microstructure strain hardening

Surface decarburization characteristics and relation between decarburized types and heating temperature of spring steel 60Si2MnA

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International Journal of Minerals,Metallurgy and Materials 2013年第8期20卷 720-724页

作者： Chao-lei Zhang Le-yu Zhou ya-zheng liu School of Materials Science and Engineering University of Science and Technology Beijing

The characteristics of complete and partial decarburizations in spring steel 60Si2MnA were systematically investigated, including the microstructure, the hardness gradient, and the formation mechanism. The relation between decarburized types and heating temperature of the steel was comprehensively discussed. It is found that heating temper- ature has an important influence on the decarburized types. With the rise of heating temperature, the decarburized types change from no decarburization to complete decarburization, complete and partial decarburizations, partial decarburiza- tion, and no decarburization.

关键词： spring steel decarburization temperature microstructure hardness

Microstructure homogenization control of Nb-bearing X65 pipeline steel by the CSP process

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International Journal of Minerals,Metallurgy and Materials 2011年第1期18卷 35-41页

作者： Ming-yang Li ya-zheng liu Tao Zhu Ying Wang School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China Technology Center of Masteei Co. Ltd. Maanshan 243000 China

In order to get the controlled methods of microstructure homogenization and high strengthening-toughening combination by compact strip production （CSP） rolling,the dynamic recrystallization characteristics of each pass were obtained during CSP rolling using a Gleeble-1500 thermal mechanical ***,the CSP process was simulated by laboratory rolling *** thermal mechanical simulation experiment and laboratory rolling experiment,a design idea of Nb-bearing pipeline steel by CSP can be obtained as the following：the level of dynamic recrystallization behavior should be increased through the reasonable balance of high deformation temperature and deformation amount in F1 and F2 passes,and F3-F7 passes should be controlled in the austenite non-recrystallization ***,X65 pipeline steel with microstructure uniformity and good properties was produced by *** yield strength is up to 497 MPa,the tensile strength is up to 563 MPa,the elongation is 30% on average,and the toughness is very good whose Charpy impact value is 110 J on average and drop-weight tear test shearing areas are all 100% at -60,-40,-20,0,and 20℃.

关键词： pipeline steel hot rolling dynamic recrystallization precipitation microstructure mechanical properties

Effect of titanium microalloying on microstructure and mechanical properties of vanadium microalloyed steels for hot forging

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Journal of Iron and Steel Research International 2022年第2期29卷 295-306页

作者： Fan Zhao Guo-ning He ya-zheng liu Zhi-hao Zhang Jian-xin Xie Beijing Laboratory of Metallic Materials and Processing for Modern Transportation Institute for Advanced Materials and TechnologyUniversity of Science and Technology BeijingBeijing100083China State Key Laboratory of Materials Processing and Die&Mould Technology Huazhong University of Science and TechnologyWuhan430074HubeiChina School of Materials Science and Engineering University of Science and Technology BeijingBeijing100083China

Effect of titanium microalloying on the microstructure and mechanical properties of vanadium microalloyed steels for hot forging was *** microalloying improves the mechanical properties mainly through refining the austenite *** the heating temperature is in the range of 1050–1300℃,the austenite grain diameter is decreased from 77–133 to 26–68μm by titanium *** the decrease in austenite grain diameter,the final microstructure is refined significantly,and the high misorientation boundaries are *** the steel is heated at 1200℃(the common hot forging temperature)and cooled slowly,titanium microalloying decreases the yield strength from 548.4 to 519.4 MPa,and the tensile strength decreases from 842.7 to 808.7 ***,the elongation increases from 19.0%to 21.4%,and the impact energy increases from 9.8 to 38.2 J.V–Ti steel has a better combination of strength,plasticity and toughness than V *** addition,the nucleation of intragranular ferrite idiomorphs is promoted by titanium microalloying,which may have a beneficial effect on the property of steels with coarse microstructure caused by the critical deformation in hot die forging.

关键词： Titanium microalloying Microalloyed steel Microstructure Mechanical property Intragranular ferrite

Failure analysis of 18CrNi3MoA drilling tails

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International Journal of Minerals,Metallurgy and Materials 2012年第5期19卷 421-427页

作者： Hong-wu Zhu ya-zheng liu Le-yu lhobl Lei-ying Wang Bin Huang School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China Xining Special Steel Co. Ltd. Xining 810005 China

The fracture of a drilling tail made of 18CrNi3MoA steel in the exchanging water hole was analyzed in terms of inclusions, prior austenite grain size, carburized layers, and fatigue fracture morphology by means of optical microscopy, quantitative metallography, and scanning electron microscopy （SEM）. Fatigue crack initiation and propagation on the drilling tail were also studied. The results showed that the fracture on the drilling tail was not induced by inclusions and the distribution inhomogeneity of prior austenite grain size. Instead, be- cause the outside surface of the exchanging water hole was not continuously geometric, there was a great deal of stress concentration in those areas under continuous twisting, axial impact, and corrosion of mineral water. Thus three crack sources emerged in these areas. Initial cracks centered on these sources spread from the outside surface to the inside surface, and eventually the drilling tail ruptured. Furthermore, the fractograph of the region around the crack sources exhibited a typical ductile dimple fracture pattern, and cracks initiated on the outside sur- face of the carburized layers of the exchanging water hole. Three crack sources could be the sources of fatigue crack propagation. Based on the analysis of fatigue crack propagation, it was further demonstrated that fatigue damage originated from the outside surface of the ex- changing water hole.

关键词： drilling tools failure analysis crack initiation crack propagation

Austenite grain growth and its effect on splitting fracture property of a V-N microalloyed medium carbon steel connecting rod

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Journal of Iron and Steel Research International 2019年第8期26卷 875-881页

作者： Chao-lei Zhang Wen Fang Bao-run Cai Xiao-hang Sun ya-zheng liu School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China Xining Special Steel Co. Ltd. Xining 810005 Qinghai China

The growth behaviour of austenite grain in a V-N microalloyed medium carbon steel and its effect on splitting fracture property were investigated by mechanical tests, fracture morphology and microstructure analysis. When the heating temperature is 800℃, the austenite grain size is 7.6 μm, and the fracture surface is uneven with the impact energy of 235.9 J. When the heating temperature increases to 1100 ℃, the austenite grain size grows up to 65.5 μm and the impact fracture surface is much more even with the impact energy of 13.6 J. It is believed that the coarse austenite grain size of 65.5 μm is beneficial for the splitting fracture property of V-N microalloyed medium carbon steel connecting rod. In addition, austenite grain sizes of V-N microalloyed medium carbon steel increase with the increasing in heating tem-perature and holding time. Then, a grain growth model is established to predict austenite grain growth behaviour.

关键词： Connecting rod Splitting fracture property Microstructure Austenite grain

Forming condition and control strategy of ferrite decarburization in 60Si2MnA spring steel wires for automotive suspensions

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International Journal of Minerals,Metallurgy and Materials 2012年第2期19卷 116-121页

作者： Chao-lei Zhang ya-zheng liu Le-yu Zhou Chao Jiang Jin-fu Xiao School of Materials Science and Engineering University of Science and Technology BeijingBeijing 10083China

The ferrite decarburization behavior of 60Si2MnA spring steel wires for automotive suspensions, including the forming condition and the influence of heating time and cooling rate after hot rolling, was investigated comprehensively. Also, a control strategy during the reheating process and cooling process after rolling was put forward to protect against ferrite decarburization. The results show that ferrite decarburization, which has the strong temperature dependence due to phase transformation, is produced between 675 and 875°C. The maximum depth is found at 750°C. Heating time and cooling rate after rolling have an important influence on decarburization. Reasonable preheating temperature in the billet reheating process and austenitizing temperature in the heat-treatment process are suggested to protect against ferrite decarburization.

关键词： spring steel decarburization phase transformations controlled cooling

Microstructure and texture evolution of cold-rolled deep-drawing steel sheet during annealing

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International Journal of Minerals,Metallurgy and Materials 2013年第6期20卷 541-548页

作者： Le-yu Zhou Lei Wu ya-zheng liu Xiao-jie Cheng Jin-hong Sun School of Materials Science and Engineering University of Science and Technology Beijing

In accordance with experimental results about the annealing microstructure and texture of cold-rolled deep- drawing sheet based on the compact strip production （CSP） process, a two-dimensional cellular automation simulation model, considering real space and time scale, was established to simulate recrystallization and grain growth during the actual batch annealing process. The simulation results show that pancaked grains form during recrystallization. （111} advantageous texture components become the main parts of the recrystallization texture. After grain growth, the pancaked grains coarsen gradually. The content of （111} advantageous texture components in the annealing texture increases from 55vo1% to 65vo1%; meanwhile, the contents of {112}〈110〉 and {100}〈110〉 texture components decrease by 4% and 8%, respectively, compared with the recrystallization texture. The simulation results of microstructure and texture evolution are also consistent with the experimental ones, proving the accuracy and usefulness of the model.

关键词： cold rolling deep drawing steel sheet cellular automata, recrystallization annealing

Dynamic Recrystallization Behavior of GCr15SiMn Bearing Steel during Hot Deformation

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Journal of Iron and Steel Research International 2014年第11期21卷 1042-1048页

作者： Dan ZHANG ya-zheng liu Le-yu ZHOU Qiang HAN Bo JIANG Zhong-zhi LI School of Material Science and Engineering University of Science and Technology Beijing Dongbei Special Steel Group Corporation Limited

The hot deformation behavior of GCr15SiMn steel was studied through high temperature compression tests on the Gleeble-1500 thermal-mechanical simulator. The initiation and evolution of dynamic recrystallization （DRX） were investigated with microstructural analysis and then the process variables were derived from flow curves. In the present deformation conditions, the curves of strain hardening exponent （n） and the true strain （e） at the deformation temperature of 1423 K and strain rates of 0.1, 1 and 10 s^-1 exhibit single peak and single valley. According to Zener-Hollomon and Ludwik equation, the experimental data have been regressed by using linear method. An expression of Z parameter and hot deformation equation of the tested steel were established. Moreover, the Q values of GCrlSSiMn and GCr15 steels were compared. In order to determine the recrystallization fraction under different con ditions, the volume fraction of DRX as a function of process variables, such as strain rate （ε）, temperature （T）, and strain （ε）, was established. Itwas found that the calculated results agreed with the mierostructure of the steel at any deformation conditions.

关键词： GCr15SiMn strain hardening exponent dynamic recrystallization critical strain kinetic model