Formation of Edge Crack in 1.4%Si Non-oriented Electrical Steel during Hot Rolling简

Microstructure evolution, dynamic recrystallization, high temperature oxidation and hot ductility of 1.4 % Si non-oriented electrical steel sheets were investigated to reduce edge cracking. The causes of cracking were found to be coarse as-cast microstructure, grain boundary oxidation in reheating furnace, lack of dynamic recrystallization during hot rolling and increase of temperature, resulting in reduced hot ductility in strip edge region. Countermeas- ures against the edge crack are proposed accordingly. Lowering reheating temperature and reducing holding time re- duced oxidation and decarburization. Hot charging temperature was increased to decrease reheating temperature. And using an edger can refine microstructure in strip edge region. Finally, edge heater can be added to increase edge re- gion formability by inducing dynamic reerystallization and ductility by increasing temperature.     

Characterizing the Structure Evolution of Tertiary Scale during Simulated Coiling by EBSD简

An oxide scale formed at 900 ℃ for 60 s in dry air was subjected to the simulated coiling processed with different coiling temperatures. The phase transformation behavior, especially the orientation distribution of the oxide scale, was analyzed using electron backseattered diffraction （EBSD） technique. When cooling from the coiling tem- perature of 650 ℃, the scale consists of FeaO4 layer, FeO layer and FeaO4 seam. The FeaO4 precipitates are ob served in the FeO grains of the scale formed with the coiling temperature of 550 and 450 ℃. With the cofling temperature of 350 ℃, the decomposition of FeO is suppressed due to the low temperature. The Fe3O4 grains, which are decomposed from FeO, has the same orientation as the parent FeO grains. Moreover, the FeO grains, of which the growth direction is parallel to 〈001〉, is easier to decompose into Fe3O4 than the grains with other orientations.     

Microstructures and Mechanical Properties of X100 Pipeline Steel Strip简

Dynamic CCT （continuous cooling transformation） curves and effects of microstructures and M/A islands of X100 hot rolled strip on mechanical properties were studied by means of a thermal simulator, a scanning electron mi- croscope （SEM）, a transmission electron microscope （TEM）, a digital micro-hardness tester and Image-Pro Plus analysis software. The results show that high contents of C and Mo can make transformation lines of acicular ferrite and bain- ite shift rightward. High Mo tested strip has higher strength and micro-hardness and lower toughness than the other one because lath bainite appears instead of quasi-polygonal ferrite. Tested strip with granular bainite, lath bainite and M/A islands has better mechanical properties and in the microstructures lath bainite content is around 36.50% and M/A islands are fine and disperse in the matrix.     

Hot Deformation Behavior of Ni3Al-based Alloy MX246A简

The hot deformation behavior of homogenized Nia Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1 150--1225 ℃ and strain rate range of 0. 001-0.1 s-1. Microstructural obser- vation revealed striped secondary γ＇ phase which was vertical to compression axis, and precipitation of fine ternary γ＂ phase. The amount of striped secondary γ＇ phase reduced and that of fine ternary γ＇ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controUed by dynamic recovery mechanism.     

Multi-class Classification Methods of Enhanced LS-TWSVM for Strip Steel Surface Defects简

Considering strip steel surface defect samples, a multi-class classification method was proposed based on enhanced least squares twin support vector machines （ELS-TWSVMs） and binary tree. Firstly, pruning region samples center method with adjustable pruning scale was used to prune data samples. This method could reduce classifierr s training time and testing time. Secondly, ELS-TWSVM was proposed to classify the data samples. By introducing error variable contribution parameter and weight parameter, ELS-TWSVM could restrain the impact of noise sam- ples and have better classification accuracy. Finally, multi-class classification algorithms of ELS-TWSVM were pro- posed by combining ELS-TWSVM and complete binary tree. Some experiments were made on two-dimensional data- sets and strip steel surface defect datasets. The experiments showed that the multi-class classification methods of ELS-TWSVM had higher classification speed and accuracy for the datasets with large-scale, unbalanced and noise samples.     

Dynamic and Static Recrystallization Behaviour of Coarse-grained Austenite in a Nb-V-Ti Microalloyed Steel简

The dynamic recrystallization （DRX） and static recrystallization （SRX） behaviour of coarse-grained aus- tenite in a Nb-V-Ti microalloyed steel were studied by using a Gleeble thermomechanical simulator. Continuous and interrupted compression tests of coarse-grained austenite were performed in the temperature range of 1000-1 150 ℃ at a strain rate of 0. 1- 5 s 1. The peak and critical strains for the onset of DRX were identified with strain hardening rate analysis, and the ratio of critical strain to peak strain was found to be consistent with the one reported for fine- grained austenite. An equation of the time for 50% softening was proposed by considering the activation energy of steel without microalloying elements and the solute drag effect of microalloying elements. Strain-induced precipitation may not take place at the deformation temperature above 1000 ℃, which indicates that SRX of coarse-grained aus- tenite is mainly retarded by coarse grain size and Nb in solution during rough rolling.     

Characteristics of Deoxidation and Desulfurization during LF Refining Al-killed Steel by Highly Basic and Low Oxidizing Slag简

Steel and slag samples were taken at the start and the end of LF refining for steel plate cold common （SPCC）, in the compact strip production （CSP） process, and at the same time, the temperature and oxygen activity a[o] were measured by using an oxygen sensor. Furthermore, inclusions in steel samples were monitored by scanning electron microscopy （SEM） combined with energy dispersive spectroscopy （EDS）. It was confirmed that a [o] in liq- uid steel was in equilibrium with inclusion rather than with top slag during LF refining. Desulfurization was related to deoxidation since a[o] at slag-steel interface was clarified to be very close to that in liquid steel under the specific con- dition in LF with intense stirring by argon blowing and refined by highly basic low oxidizing slag for Al-killed steel. Sulfur partition ratio （Ls） was very sensitive to a[o]. Since a[o] increased rapidly with temperature rise, it not only offset promotion to desulfurization reaction with temperature rise but decreased Ls. For Al-killed steel, the.modifica- tion of Al2O3 for lowering the activity of Al2O3 in inclusion was believed to be favorable for both deoxidation and desulfurization during LF refining.     

大变形X80管线钢的应变时效简

 大变形管线钢是一种管道在通过地质复杂地区(滑坡、地震、冻土等)时,为了降低地层移动对管道可能造成的变形损伤而开发出来的新型管道结构用材料。采用材料显微分析方法和力学性能测试等手段,对一种大变形X80管线钢在应变时效中的脆化规律进行了研究。结果表明,应变时效使试验钢产生脆化。随着应变时效温度的升高,强度和硬度增加,塑性和韧性下降。应变时效脆化形成的机制是管线钢间隙原子与位错的交互作用。与普通X80钢相比,大变形X80钢的应变时效倾向较小,这是因为双相组织中铁素体固溶的碳、氮原子少,位错密度低。     

高炉烘炉质量的研究简

 高炉烘炉质量直接影响高炉长寿,通过建立炉缸炉底砖衬传热模型,以1080m3高炉烘炉阶段炉缸炉底温度数据加以验证。分析了烘炉时间、烘炉温度、冷却强度等因素对冷却壁与炭砖间填料温度的影响。结果表明在0. 5m/s冷却水作用下,对于目前普遍采用的最高烘炉温度(600℃),填料最高温度仅为44℃,远低于要求的烘干温度,不能实现较好的烘炉效果。烘炉过程中需要减弱炉缸冷却甚至停水烘炉,适当提高烘炉温度,延长烘炉保温时间;停水烘炉时冷却壁最高温度仅为158℃,远低于铸铁冷却壁的安全工作温度。考虑到烘炉时热风的氧化性气氛,保证陶瓷质耐火材料严密覆盖在炉缸炉底炭砖表面,防止开炉前炭砖氧化烧损。通过插入冷却壁与填料交界面的热电偶温度分析炉缸砖衬的升温及保温,进而判断烘炉效果;并根据高炉固有的砖衬结构及设备参数,制定与高炉相匹配的烘炉制度。     

Hot-dip Galvanizing of Carbon Steel after Cold Rolling with Oxide Scale and Hydrogen Descaling简

A new processing method for producing hot dip galvanized steel is designed and tested, in which pickling is skipped. Hot-rolled low carbon steel sheets are roiled with oxide scale in an experimental mill at room temperature, prior to annealing under a 20% hydrogen reducing atmosphere and galvanizing on a hot-dip galvanizing simulator. Micro-cracks formed in the oxide scale during cold rolling roughen the steel surface and enlarge the specific surface. Through-thickness cracks provide transport channels for hydrogen, and hence the reduction of oxide scale is en- hanced. When the sheet is dipped in the zinc bath, cracks are submerged by liquated zinc and the defects are not dis- tinct after hot-dip galvanizing. The overlay coating occludes with rough surface of the sheet, whereby a superior coat- ing adherence is realized.     

The Effect of Pre-Deformation at Elevated Temperatures on the Microstructure and Hardness of Boron Steel 22MnB5

To investigate the effects of the pre-deformation and deformation temperature on the microstructure and hardness of boron steel 22MnB5,isothermal tensile tests were carried out on the Gleeble 3800 system when the temperatures are 700℃,750℃,800℃,respectively.Three specimens were employed to obtain different deformation levels at each temperature.The cooling rate before and after deformation was 30℃/s.Then the microstructures of the specimens were observed and the harness of each specimen was measured.The results show the martensitic fraction decreases and the ferrite fraction increases with decreasing the deformation temperature or increasing the deformation level.The specimens deformed at higher temperature have greater hardness.The hot plastic deformation of austenite shortens the incubation period of ferrite transformation and accelerates the transformation rate.In addition,the isothermally holding time is longer in the case of a larger deformation amount,more austenite will transform to ferrite.Especially,the specimen deformed at 700℃ and with large deformation has almost full massive ferrite microstructure with larger size.     

预合金化时间对热成形钢锌基镀层组织和成分的影响

 利用扫描电子显微镜及附属EDS能谱仪研究了不同预合金化时间对热成形钢22MnB5锌基镀层组织形貌及成分分布的影响规律。结果表明,试样在加热之后,镀层表面氧化物主要为ZnO和Al2O3;在550 ℃预合金化时,随着时间的延长,基体中的铁逐渐向镀层中扩散,镀层组成由η相、ζ相、δ相和Γ相逐渐转变为只有Γ相;奥氏体化之后,镀层中的组织几乎全部为α-Fe（Zn）,只在表面有极少的Г相;预合金化保温时间为30 min时,在900 ℃保温5 min奥氏体化后能得到质量较好的镀层。     

Investigation on the Failure Mechanism of DP590-22MnB5 (Quenched) and DP590-DP590 Spot-Welding Joints

The failure mechanism of DP590-22MnB5(quenched) and DP590-DP590 spot-welding joints is studied through lap-shearing experiments,metallographic observation and three-dimensional finite element simulation.Both joints cracked on the DP590 steel,but the tensile shear strength of the DP590-22MnB5(quenched) joint is greater than that of the DP590-DP590 joint.A finite element model for the lap-shearing experiment is established according to the mechanical properties of DP590 and 22MnB5(quenched) steels and the metallographic analysis of welding spots.The simulation results show that the difference in the axis rotation of the two welding spots causes different distributions of stress and strain,which shifts shear loading condition to opening loading condition.Due to larger axis rotation angle of the DP590-DP590 joint,the stress concentration occurs at the middle of the nugget circumference,and it results in lower tensile shear strength of the DP590-DP590 joint.     

22MnB5钢溶质分配系数及TiN析出对微观偏析的影响

为了提高凝固过程中溶质微观偏析模型计算的准确性,基于溶质分配系数及夹杂物析出对溶质偏析的重要影响,定量分析了溶质分配系数以及TiN析出对凝固过程溶质元素含量的影响,为微合金高强钢凝固过程研究提供理论参考.针对22MnB5钢建立了耦合TiN析出热力学模型的溶质微观偏析模型,并探究了温度及钢液凝固路径对溶质分配系数的影响规...     

B1500HS硼钢热冲裁过程的相变和冲裁精度

为了研究热冲裁零件微观组织及尺寸精度的变化规律,采用不同的冲裁温度和模具间隙比对B1500HS钢板进行了热冲裁试验.根据冷却曲线,研究了冲裁温度对硼钢组织转变和零件力学性能的影响;根据落料件的尺寸,分析了冲裁温度和模具间隙比对尺寸精度的影响;通过观察零件的断口形貌,分析了冲裁温度对断口质量的影响.结果表明：当冲裁温度一定时,落料件的尺寸随着模具间隙比的减小而增大;当模具间隙比一定时,落料件的尺寸误差随着冲裁温度的降低出现“正—负—正”的增长波动趋势;当冲裁温度为600~650℃或750~800℃时,落料件具有较高的冲裁精度;落料件的硬度随着冲裁温度的升高而增大,当冲裁温度为650~800℃时,落料件的组织为马氏体,硬度值HV约为550;冲裁断面光亮带的宽度随着冲裁温度升高而增大.