硫化物形貌对非调质钢力学性能各向异性的影响

为了明确硫化物变性处理前后材料力学性能各向异性的变化规律，利用金相显微镜、SEM、拉伸及冲击试验机研究了工业生产的具有不同硫化物形貌特征(硫化物变性与未变性处理)的35MnVS非调质钢锻态力学性能的各向异性。结果表明，经变性处理后硫化物由未经变性处理的细长条状向短棒状或纺锤状转变，硫化物长宽比在1～8范围内的个数比例由未经变性处理的不到40%提高到变性处理后的90%以上，且分布更加均匀，组织有所细化。硫化物变性处理能够明显地降低试验钢塑性和韧性的各向异性，断面收缩率和冲击功的各向异性分别减小了约10%和34%，横向断口形貌由脆性的朽木分层状向韧窝韧性断裂转变。     

Artificial Neural Networks for Hardness Prediction of HAZ with Chemical Composition and Tensile Test of X70 Pipeline Steels

A neural network with feed-forward topology and back propagation algorithm was used to predict the effects of chemical composition and tensile test parameters on hardness of heat affected zone(HAZ)in X70 pipeline steels.The mass percent of chemical compositions(i.e.carbon equivalent based upon the International Institute of Welding equation(CEIIW),the carbon equivalent based upon the chemical portion of the Ito-Bessyo carbon equivalent equation(CEPcm),the sum of the niobium,vanadium and titanium concentrations(CVTiNb),the sum of the niobium and vanadium concentrations(CNbV),the sum of the chromium,molybdenum,nickel and copper concentrations(CCrMoNiCu)),yield strength(YS)at 0.005 offset,ultimate tensile strength(UTS)and percent elongation(El)were considered as input parameters to the network,while Vickers microhardness with 10 Nload was considered as its output.For the purpose of constructing this model,104 different data were gathered from the experimental results.Scatter diagrams and two statistical criteria,i.e.absolute fraction of variance(R2)and mean relative error(MRE),were used to evaluate the prediction performance of the developed model.The developed model can be further used in practical applications of alloy and thermo-mechanical schedule design in manufacturing process of pipeline steels.     

Kinetics of Precipitation Behavior of Second Phase Particles in Ferritic Ti-Mo Microalloyed Steel

 Two types of stress relaxation tests were carried out to investigate the incubation time for incipient precipitation of Ti(C,N) in deformed austenite and (Ti,Mo)C in ferrite of ferritic Ti-Mo microalloyed steel. The size distribution, amount and chemical composition of precipitates were obtained by using physicochemical phase analysis, and calculated according to thermodynamics and kinetics. The experimental results demonstrated that the incubation time was reduced with increasing Ti content, and prolonged with the addition of Mo. After 30% deformation at 850 ℃, the nucleation of strain-induced Ti(C,N) was a relatively slow process. On the other hand, the temperature where the nucleation rate of (Ti,Mo)C in ferrite was the highest descended first and then ascended with increasing Ti content, and so did the temperature where the incubation time was the shortest. The key point is that the temperature of steel containing about 0. 09% Ti is the lowest. The mass fraction of MC-type particles with size smaller than 10 nm in steel containing 0. 09% Ti and 0. 2% Mo reached 73. 7%. The size distributions of precipitates in steel containing 0. 09% Ti were relatively concentrated compared with that in steel containing 0. 07% Ti.     

Hot flow behavior of boron microalloyed steels

This research work studies the effect of boron contents on the hot flow behavior of boron microalloyed steels. For this purpose, uniaxial hot-compression tests were carried out in a low carbon steel microalloyed with four different amounts of boron over a wide range of temperatures (950, 1000, 1050 and 1100 °C) and constant true strain rates (10⁻³, 10⁻² and 10⁻¹ s⁻¹). Experimental results revealed that both peak stress and peak strain tend to decrease as boron content increases, which indicates that boron additions have a solid solution softening effect. Likewise, the flow curves show a delaying effect on the kinetics of dynamic recrystallization (DRX) when increasing boron content. Deformed microstructures show a finer austenitic grain size in the steel with higher boron content (grain refinement effect). Results are discussed in terms of boron segregation towards austenitic grain boundaries during plastic deformation, which increases the movement of dislocations, enhances the grain boundary cohesion and modificates the grain boundary structure.     

Computational and Experimental Analysis of Carbo‐Nitride Precipitation in Tempered Martensite

The present work describes the analysis of carbo‐nitride precipitation kinetics in tempered martensite of Nb–Ti‐microalloyed steel with a carbon content of 0.3 wt%. Based on the information obtained from transmission electron microscopy and scanning electron microscopy, a computational simulation procedure is developed within the software package MatCalc, which is capable of describing the experimental results in terms of the number density, composition, and type of precipitate phases. No explicit fitting parameters are used in the computer simulation. The input data is entirely based on independent physical or microstructural parameters. To determine the chemical composition and type of precipitates, energy dispersive X‐ray spectroscopy and selected area electron diffraction are utilized. The simulation results and the experimentally obtained information are in good agreement.     

1 800 MPa级微合金化热冲压钢的弯曲性能

通过力学性能3点弯曲试验和微观分析,研究了不同奥氏体化温度对1 800 MPa级微合金化热冲压钢弯曲性能的影响。结果表明,当奥氏体化温度为830～890 ℃时,试验钢的弯曲角度大于55°;当奥氏体化温度达到920 ℃时,试验钢的能量吸收能力和最大承载力明显降低。由于KAM升高引起的抗拉强度升高与由奥氏体晶粒尺寸增大和板条马氏体粗化引起的抗拉强度弱化相互作用,最终导致在不同奥氏体化温度和测试方向下试验钢的力学性能没有明显变化。     

中碳微合金非调质钢涨断连杆的开发

为提高发动机连杆性能,用中碳微合金非调质钢36MnVS4试制了发动机连杆,并对试制连杆的性能进行了检测。结果表明,试制的36MnVS4连杆的化学成分、显微组织、力学性能、疲劳性能、台架耐久性能和道路试验性能等性能不仅满足技术要求,且比高碳微合金非调质钢C70S6连杆的性能优异,可代替C70S6生产连杆,提高连杆性能。     

电解质等离子抛光在高碳微合金钢上的应用研究

目的提高金属针布产品(高碳微合金钢)的表面质量,降低针布产品的表面粗糙度值,有效提升产品的使用效果。方法采用电解质等离子抛光工艺在针布产品上展开工艺研究,探索了不同电解质浓度(无机盐质量分数)、不同生产速度和不同电解质等离子抛光单元组数对针布表面粗糙度的影响。利用非接触式粗糙度扫描仪测试粗糙度Ra,以此对针布表面的抛光质量进行表征。结果采用电解质等离子抛光工艺可以实现钢铁材料的表面抛光,抛光后不仅有效地去除了针布表面的氧化皮,并且表面平整且达到镜面效果。最佳工艺参数(电解质无机盐质量分数2.75%,走线速度40 m/min,电解质等离子抛光单元4组)下,表面粗糙度Ra值达到了0.11μm。结论电解质等离子抛光工艺成功地应用于钢铁材料上,且实现了非接触式连续抛光工艺,既不损伤工件,又实现了表面的光亮平整,还具有环境友好、节能和生产效率高等特点。     

连续镀锌线试验设备加工的含钒DP980钢组织与性能

利用连续镀锌模拟设备,研究了微合金化元素Nb、V和V-N加入到低碳高强(980级)双相钢后组织与性能的变化。在基本成分基础上,设计了不同含量的V或Nb、采用高N或正常N含量的钢,经过不同的热浸镀锌(GI)、合金化镀锌(GA)和超快冷处理。此外,还利用石英管炉对模拟镀锌后的钢板进行热处理。结果表明,马氏体—贝氏体—铁素体各相比例受到不同微合金化元素加入量的强烈影响,但是各相强度影响较小。在小于0.1%C~1.75%Mn钢中实测抗拉强度达到1 100 MPa、同时具有良好的塑性和加工硬化性能。