Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility.With the increase of the strain rate from 10^-4s^-1to 1 s^-1, the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress–strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions（n2and n1） and the transition strain（εL） decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress–strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.

Study on microstructure and properties of cold-rolled high strength steel for enameling

With its superior comprehensive properties, cold-rolled enameling steel is widely applied in many fields. However, its low yield stress greatly limits its application. This study aims to improve the yield stress of cold-rolled enameling steel under the premise of meeting formability and enameling properties by strengthening the ferrite matrix via solid strengthening of Mn. The grain size of ferrite before and after enameling,mechanical properties of annealed steel, and precipitation behavior of second-phase precipitates are obtained through studying the microstructure and properties of enameling steel at different stages. The microstructure of the steel investigated at room temperature is found to contain equiaxial ferrite and bunchy cementite particles;the ferrite grains have grown to some extent after enameling. The fine dispersed TiC particles and cementite particles contained in the annealed steel are the main factors improving the hydrogen storage capability. Finally, the result of a falling-ball impact test shows that the steel has achieved excellent adherence.

Research on the design of cold rolled ultra high strength sheet steel

This study researches cold rolled ultra high strength martensitic steel processed by water quenching. It is found that both the quenching and overageing temperatures greatly influence the mechanical properties of martensitic steel. A tensile strength of 1500 MPa can be obtained from 0.2% C-1.8% Mn steel by soaking at 840℃,quenching at 700℃ and overageing at 200℃ for several minutes. The continuous cooling transformation （CCT） diagram reveals that full martensite can be obtained at a cooling rate of 100℃/s or higher; and at a cooling rate of 3 - 10℃/s,austenite barely decomposes at 700℃. For steel with 0.2% carbon and less manganese, austenite decomposition occurs before it is cooled to 700℃ at a cooling rate of 3 - 10℃/s, which leads to lower tensile strength. It is possible to reduce the manganese content of the 1500 MPa martensitic steel by increasing the quenching temperature. To increase the quenching temperature,the control of flatness during water quenching becomes a major concern.

Effect of deformation twinning on the evolution of texture in TWIP steels during cold-rolling

Texture evolution of high-manganese twining-induced plasticity (TWIP) steels (Fe-16Mn-0.6C) during cold-rolling is studied by means of quantitative orientation distribution function (ODF)analysis.Thickness reductions of the specimens during cold-rolling are 10%,20%,30%,50% and 65%,respectively.Evolution of texture is of the Brass type,which is typical for low-stacking fault energy (SFE) materials.The contribution of deformation twinning to the development of texture is clearly illustrated by the monotonic increase of the twinned Cu component.In the present study,the deformation twinning was identified as significantly contributing to deformation up to the maximum reduction applied.These results are useful for the prediction and control of the texture in TWIP steels.

Investigation into microstructure of spray formed V4 cold working mould steel and its roiling and annealing

The material selected for this work was the spray formed Vanadis4 high alloy cold working mould steel （abbreviated to V4 steel）. Its microstructure, hot rolling process, and annealing treatment have been investigated. Observed from the optical and electron microscopes, the as-sprayed V4 steel had the finer microstructure of uniform and equiaxial grains ,while after hot rolling for densification and spheroidized annealing, the V4 steel obtained an excellent spheroidized structure that is favorable to subsequent quenching and tempering treatment. The spheroidized structure and level of annealed hardness of the V4 steel are almost the same as expensive imported powder metallurgy the V4 steel. It is difficult to produce V4 steel with the conventional ingot metallurgical technique, so the multi-step and high-cost powder metallurgy method is generally used at present. Compared to the powder metallurgy technique, using the spray forming technique to produce the V4 steel has obvious advantages and potential market competitiveness in reducing production costs, simplifying working process, and shortening the production cycle.

Numerical simulation of roll temperature field and analysis of influence factor during the single-stand reversing cold rolling process

Accurate calculation results of roll temperature are the key factors in rolling cooling and lubricating technology during the single-stand reversing cold rolling process. By combining the high-strength steel rolling experiments ,the numerical simulation of roll temperature, and the influence factors in reversing cold rolling were studied. The research results correspond with those of rolling experiments and show that the research method could provide effective instruction for roll cooling and emulsion flow rate control during the on-site rolling process.

航发轴承套圈电磁辅助轧制成形残余应力和组织演变

8Cr4Mo4V轴承钢被广泛应用于航空发动机主轴轴承,其热轧成形过程中易出现晶粒粗大等缺陷,导致强韧性不足。冷轧成形可实现晶粒细化,提高轴承钢的综合力学性能,具有巨大应用潜力,但8Cr4Mo4V轴承钢的碳含量和合金含量较高,冷轧过程中易产生微纳损伤和应力集中等缺陷。提出了电磁能场辅助轴承钢冷轧成形的创新技术思路,研究电磁辅助轧制对8Cr4Mo4V轴承钢残余应力和组织演变的影响。结果表明,电磁辅助轧制可调控轴承钢位错密度,减少碳化物与相界处的位错缠结,使残余应力均匀化并提高拉伸性能,实现8Cr4Mo4V轴承钢细晶低损伤成形。

冷轧压下率对高强无取向电工钢变形组织和磁性能的影响

借助场发射扫描电镜(SEM+EBSD)、快速升温管式炉和交流磁性能测量仪研究高强无取向电工钢冷轧变形组织和磁性能随冷轧压下率的变化规律。结果表明:冷轧高强无取向电工钢中形成含有大量亚结构的粗糙条带和变形量较小的光滑条带。粗糙条带具有γ取向,主要为{111}〈110〉,光滑条带具有{112}〈110〉和{001}〈110〉取向。粗糙条带中存在大量宽度约为2~3μm的剪切带,与轧向呈20°~35°夹角,且随压下率增大,数量逐渐增多。剪切带与基体间具有一定取向差,随压下率增大,剪切带逐渐从{111}〈110〉取向转向{223}〈110〉取向,与基体间取向差逐渐增大。退火后Goss和{111}面织构增多,{001}面织构减少;轧向磁感应强度增大,横向磁感应强度减小,各向异性显著,铁损下降。

1180 MPa级超高强钢冷连轧过程的厚度综合控制技术

针对超高强钢在冷轧过程中厚度波动大以及带头带尾厚度超差的问题,首先根据金属秒流量模型建立了厚度超差预测模型与辊缝调节量预估模型;随后开发了轧制过程中的厚度控制系统,并进行了辊缝调节量优化;最后建立了带钢头尾轧制过程中的轧制速度与张力优化模型。以国内某冷连轧机组的第1机架为技术应用对象,选择两种典型的超高强钢进行生产测试,测试结果表明:超高强钢AR4146E1与DU6220A1的厚度超差长度分别从70.3 m、36.89 m下降到了16.85 m、16.33 m。

MS1180方管连续辊弯成形角部开裂机理

方矩形管在辊弯成形中会产生角部开裂现象,这已成为严重制约方矩形管质量的关键问题,为解决其角部开裂缺陷展开深入研究,寻找控制开裂缺陷的方法。首先通过对MS1180进行单轴拉伸、缺口拉伸和平面应变实验得到了材料的力学特性,并分别利用3种拉伸试验将Ayada、Rice-Tracey和标准化Cockroft-Latham准则进行校准,得到了预测误差最小的一种断裂准则,并以此构建了方矩管辊弯开裂模型。其次利用辊弯成形COPRA RF设计软件和有限元MARC仿真专业软件,结合生产实际条件建立了方矩形管连续辊弯成形三维有限元模型,并进行辊弯实验验证模型的准确性。最后采用扫描电镜和金相显微镜对方矩形管开裂件以及断口进行微观观察,针对性的利用有限元模型探究了方矩形管连续辊弯成形时应力-应变分布规律,并分析了道次数量、角部成形半径和机架间距对方矩管角部应力-应变分布的影响。结果表明:发现材料起裂点位于角部近外层,对开裂断口进行分析,得到其开裂方式为准解理开裂,角部剪切面上所受的主应力过大导致其开裂;增加辊弯道次数量、方矩形管角部成形半径以及机架之间的间距能有效减少开裂问题的出现,为以后解决方矩形管角部开裂问题提供了理论基础。

热输入量对890MPa臂架管焊接热影响区组织性能的影响

依据等强匹配原则,选用BHG-5焊丝对起重机臂架用890 MPa无缝钢管进行了斜Y型坡口焊接裂纹试验和不同热输入量的多层多道手动焊接试验,探究了材料的冷裂纹敏感性,以及不同热输入量对焊接接头组织和力学性能的影响。结果表明,预热温度为150℃时,可完全避免焊接冷裂纹的产生;随着热输入量的增加,焊缝金属接头强度变化不大,但焊接接头热影响区冲击韧性明显下降,选择小于20 kJ/cm热输入量焊接时可保证焊接接头具有较好的强韧性。

轧制退火工艺对高碳含量孪晶诱发塑性钢拉伸变形行为的影响

以Fe-18Mn-1.0C高碳含量TWIP钢为研究对象,利用单向拉伸试验、光学显微镜和扫描电子显微镜研究了冷轧压下量和退火温度对高碳TWIP钢拉伸变形行为的影响。结果表明,随着压下量的增加,试验钢中产生大量变形组织,在轧制变形组织作用下,Fe-18Mn-1.0C钢的屈服强度及抗拉强度显著提高但塑性降低;冷轧高碳TWIP钢拉伸过程中产生动态应变时效(DSA)现象,随着压下量的增加,锯齿幅度减弱,锯齿数量减少,DSA现象减弱;对冷轧40%试样进行不同温度的退火处理,发现随退火温度的升高,试样屈服强度降低,当退火温度超过400℃时,抗拉强度明显下降,伸长率出现先增加后降低的现象;对于高碳TWIP钢,当退火温度超过400℃时,碳化物快速析出是其抗拉强度及伸长率降低的主要原因。

高牌号硅钢冷轧中间辊服役损伤机理分析

轧制高牌号硅钢的连轧机,轧制难度提升,轧制事故率增加,导致服役下机的冷轧工作辊和中间辊辊面损伤概率增加。在磨削维护后进行检测,经常存在涡流检测不合格,对磨辊间的运维和轧辊检测处置造成很大困难。通过对受伤下机的冷轧中间辊辊面进行理化检测分析,发现导致其涡流检测不合格的原因为局部应力变化。通过常温时效处置或去应力回火可以有效恢复中间辊辊面状态,常温时效时间为60~80 d,去应力回火工艺为300℃×12 h,经过处置后的损伤中间辊,应力降低40%以上。再次磨削后,检测合格率大大提升,降低了冷轧中间辊再次上机的使用风险。

取向硅钢高温退火工艺研究进展

高温退火是冷轧取向硅钢生产过程中的重要工序,几十年来,许多从业者在这一领域进行了大量的研究工作,并取得诸多进展。本文根据取向硅钢高温退火工艺的特征,结合国内外研究,对取向硅钢高温退火设备、工艺和组织生长机理等方面进行了总结,并提出高温退火今后有待进一步研究的部分方向。

冷连轧机组吉帕级高强钢专用中间辊CVC辊形的优化

在吉帕级高强钢的生产过程中,现有的弯辊及窜辊达到最大值时仍无法补偿轧辊的弹性变形。即在原cvC轧辊配型制度下,中间辊窜辊量达到200mm时,等效凸度仅为0.8mm,轧机的辊缝凸度调控域不能满足超高强钢板形的控制要求。只有辊缝凸度调控域能够覆盖超高强钢的板形控制需求时,才能解决超高强钢板形不良的问题。本文对超高强钢生产专用中间辊辊形进行技术探索,当窜辊量达到120mm时,等效凸度就达到了0.8mm,最大等效凸度为1.075mm,其凸度调节范围高于国内同类型冷轧厂CVC辊形板形控制能力。通过改进轧辊辊形配置,拓宽了辊缝凸度调控域,凸度调节能力同比提升34.75%,且板形调节响应较快,能较好地弥补常见中间辊辊形在冷轧超高强钢生产过程中板形控制能力不足的问题。超高强钢生产专用中间辊辊形应用后,带钢平直度值由20IU降低到4IU以内,板形改善幅度达80%以上。

某核电厂发电机定子冷却水系统不锈钢管座开裂原因分析

某核电厂在功率运行期间,发电机定子冷却水系统不锈钢管座发生泄漏。为查明原因,采用宏观及显微组织分析、成分分析等方法对开裂的管座进行失效分析,结果表明不锈钢管座发生了高周疲劳开裂失效。为此提出相应改进措施,有效地解决了功率运行期间发电机定子冷却水系统不锈钢管座泄漏问题,也为其他机组解决类似问题提供借鉴。

Finite Element Simulation of Cold-Rolling Process of Shaped Steel Tube for Driving Shaft

Based on the deformation characteristics of Y-type mill,a finite element model for simulating the formation process of shaped steel tube for driving shaft is proposed.The distributions of stress and strain were obtained from the simulation.The outer diameter and transverse wall thickness were also analyzed quantitatively.Experiment was done on Y-type mill.A comparison between simulation results and experiment results shows that the simulated results of shaped steel tube are in good agreement with the on-site data.The model could provide the basis for theoretical research and engineering applications of shaped steel tube rolling process.

基于梯度提升决策树的冷轧高强钢卷力学性能预测

基于1180 MPa级超高强度冷轧双相(DP)钢卷生产数据,研究了基于主成分分析的化学主成分提取方法、网格搜索和交叉验证相结合的超参数寻优方法,建立了DP钢力学性能梯度提升决策树(GBDT)预测模型,并将预测结果与BP神经网络模型和广义可加模型的预测结果进行了比较。为了提高断后伸长率预测精度,以预测精度较高的GBDT预测模型为基础,通过模型预测误差分类模型和考虑误差补偿的模型预测修正方法,建立了考虑误差补偿的断后伸长率预测校正模型,该模型使断后伸长率在绝对误差±0.9%下的预测准确率达到了94.63%。DP钢性能预测模型在线运行时的实际预测精度较高,达到生产要求,有助于力学性能在线质量监控。

冷轧先进高强钢表面色差缺陷综合控制技术研究

针对C-Si-Mn系冷轧先进高强钢成品表面色差无法满足下游客户涂装的问题,采用扫描电镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)及激光共聚焦显微镜(LSCM)等手段分析缺陷产生原因。结果表明,成品表面色差缺陷为热轧、酸洗等多道工序综合作用的结果。通过优化板坯加热工艺、增强除鳞效果及酸洗能力,制定表面色差综合控制技术,表面色差缺陷得到了有效控制,满足客户使用要求。

700 MPa级热轧薄规格高强钢加工开裂行为分析

薄规格高强钢以其强度高、轻量化的优势一直受到了汽车市场的广泛关注,但其加工过程易受载荷、环境温度的影响而发生断裂失效。针对热轧700 MPa级别薄规格高强钢材料在制管剪切过程中出现的开裂问题进行了全流程系统剖析。对其冶金缺陷、晶粒及晶界缺陷、夹杂物控制、金相组织缺陷、元素偏析、零件加工缺陷、冷加工缺陷及脆性显微组织缺陷等可能的成因进行了逐项分析,最终认为材料在冷加工中产生的端部毛刺是高强钢开裂的根本原因。建议用户定期更换剪刃,尤其在钢管端部出现毛刺等缺陷时需尽快更换。