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.

High performance nano-structured stainless steel sheet

High-strength steels have been attracting more and more attention of people,Unfortunately.deterioration of ductility limited their applications.To solve this problem,a nano-structured stainless steel sheet is developed to combine high strength and high ductility.Processing of the surface mechanical attrition treatment(SMAT) was introduced to obtain a nano-grain layer on the double surface of the stainless steel sheet.The microstructure of the nanostructured steel sheet is characterized by an alternate distribution of coarse grained layer and nanocrystalline layer.Then the dual surface nano-crystallized stainless steel sheets were co-warm rolled at 500℃.The experimental results reveal that the mechanical properties of the nanostructured steel exhibit high yield strength in the range of 700 -950 MPa and tensi le strength higher than 930 MPa.Moreover,elongation to fracture reaches to 15%-48%, together with a uniform elongation stabilized to 13%-45%.

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.

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.

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。

Influence of Mo on Dynamic Continuous Cooling Transformation of 1000 MPa Cold Rolled Dual Phase Steel

The expanding curves of two kinds of 1000 MPa ultra-high strength cold rolled dual phase steels,which were C-Si-Mn-Cr and C-Si-Mn-Cr-Mo steel respectively,were detected on Gleeble-1500 thermal-mechanical simulator at different cooling rates.Combined with metallographic and hardness methods,the continuous cooling transformation curves (CCT) of the two steels were obtained.The results showed that Mo could raise the A r3 temperature,and strongly restrain the pearlite and bainite transformation.The reason for this was the interaction that the addition of Mo could increase the chemical driving force of ferrite transformation and the activation energy for the diffusion of carbon in austenite,which could decelerate the ferrite transformation.The hardness of the two steels was similar in the cooling rates range of this experiment and got higher with the increase of the cooling rates.When the cooling rates were above 7 ℃/s,the hardness almost kept constant because the most part of the microstructure was martensite.

高延性混凝土加固薄壁方钢管短柱抗压承载力研究

针对薄壁方钢管短柱承载力较低的问题,提出了通过外包高延性混凝土的加固方式来提高构件的极限抗压承载力和延性。利用有限元分析软件ABAQUS建立了高延性混凝土加固薄壁方钢管短柱有限元模型,对现有材料进行了材性试验,将结果用于有限元建立本构关系中;采用环氧树脂作为黏结剂,分别考虑了在静力加载作用下不同宽厚比(40、48、67)、不同加固厚度(4、8、12 mm)对高延性混凝土加固薄壁方钢管短桩的极限抗压承载力和破坏模态的影响。有限元结果表明:采用高延性混凝土加固后,构件的极限抗压承载力提升效果可达到30%~50%左右,且加固效果随着宽厚比或加固厚度的增大而愈发明显。理论推导出了高延性混凝土加固薄壁方钢管短柱的承载力理论公式,理论公式与有限元误差可控制在10%以内。

河南省建筑用钢筋产品质量情况分析及建议

本文通过企业调研和风险监测,结合2023年国家监督抽查、地方监督抽查、质量安全委托检验、网络媒体舆情、消费者投诉等渠道收集产品质量状况;从产业政策、生产工艺、企业质量意识和人为因素四个方面进行质量问题分析,从技术帮扶与政策引导、抽查结果处理和专项整治三个方面对提升产品质量提出预期性建议。

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。

CVC六辊冷轧机轧制3102合金空调箔边紧肋松缺陷控制措施研究

对2300 mm CVC六辊冷轧机轧制3102合金空调箔边紧问题进行分析研究,主要因为轧辊边部散热大,热凸度不均,导致边紧肋松缺陷。通过调整输入宽度,增加板型辊测量环覆盖率,调整前后张力,增大C4和A16板形目标曲线系数,有效改善边紧肋松板形缺陷,并将裂变宽度由10 mm控制到5 mm以内,提高了空调箔坯料成品率。

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。

共析珠光体钢在冷轧过程中的组织变化

用SEM、TEM及XRD等方法研究了共析钢中珠光体经40％-90％的冷轧变形后所产生的显徽组织变化.按 渗碳体形态特点,变形珠光体组织可分为以下3种类型: (1)不规则弯曲片层型,即变形后的渗碳体与轧制面呈大角度偏离且不 规则弯曲的珠光体. (2)带有剪切带的粗大片层型,即被渗碳体剪切带分开且变形轻微的珠光体. (3)精细片层型,即与轧制方 向平行排列、片间距细小且渗碳体严重变形的珠光体.精细片层区域的比例随着轧制压下率的提高而增大.此外,重度冷轧变形还 引起渗碳体严重塑性变形和部分溶解.

冷轧高强IF钢再结晶温度的测定

采用盐浴退火处理,测定了两种冷轧高强IF钢定时条件下发生再结晶的温度和恒温条件下发生再结晶的时间。在所测盐浴处理升温时间的基础上,根据Arrhenius公式计算了两种钢的再结晶激活能,并由此确定了其在30 s、60 s、90 s退火时间条件下的再结晶温度。