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.

Development of top high-grade non-grain-oriented silicon steels at Baosteel

The development, production and application of top high-grade non-grain-oriented （NGO） silicon steels at Baosteel were introduced in this paper. Top high grades refer to the highest grades in the intemational silicon steel product standard and above. B35A230 and B50A250 were developed at Baosteel in 2009 and have been used in inverter compressors for air-conditioners, small transformers and big hydropower generators in the Three Gorges project. Small- batch production of B35A210 and B50A230, which exceed the highest grades listed in the intemational silicon steel product standard,began in 2010. That was a breakthrough in the silicon steel making history in China. Presently,Baosteel＇ s high- grade NGO products have passed the strict qualifications of the three major electric power equipment manufacturers in China and the leading international power equipment suppliers like ALSTOM, GE, SIEMENS, VESTAS, etc. These products are characterized by low iron loss, low anisotropy, good punchability and a high lamination factor. They have been used in the 770 MW hydropower generator at Xiluodu Power Station in the three gorges area, 1 000 MW thermal power generators and 2.5 MW wind power generators.

Analysis of formation causes for "oil-burn" defects and control measures during cold rolling of silicon steel

It has been found through analysis of defect components and micrographs that ＂oil-burn＂ defects on non- oriented silicon steel surf＇aces, which of ten occur after cold rolling, are composed of Fe, O, Si and C. This study analyzed the fomation mechanism of ＇toil-burn＂ defects and the strategies to prevent them,and proposed, according to the equipment and process status in the production fields ,some relevant optimized control measures and process adjustment schemes from two perspectives of reducing the residual emulsion trod avoiding the specific temperature range. The results demonstrate that the application of the proposed optimization meastu＇es effectively inhibits the formation of ＂oil-bum＂ defects.

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.

Transverse thickness difference control technology for non-oriented silicon steel

Transverse thickness difference is an important quality index of non-oriented silicon steel strips. In order to fulfill users＇ accuracy requirements on the transverse thickness of silicon steel and improve the production yield, the factors influencing transverse thickness difference were analyzed. Then the work roll shape, control strategy and incoming hot-rolled strips were optimized. Since the optimization measures were implemented in the actual production, the thickness difference of non-oriented silicon steel has been reduced greatly and fulfilled the requirements placed by users. These measures have achieved remarkable effects.

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。

Goss取向铁素体钢中形变孪晶的产生行为研究

采用电子背散射衍射(EBSD)技术,研究了Goss取向铁素体钢在不同冷轧压下率(10%~34%)下形变孪晶的演变行为。结果显示,在冷轧压下率为10%的样品中观察到了形变孪晶,孪生面为{112},孪生方向为〈111〉,孪晶晶界为Σ3晶界(〈111〉60°),形变孪晶在变形初始阶段的取向为{114}〈221〉。随着冷轧压下率从10%增大至17%,Goss晶粒逐渐向{221}〈114〉取向转变,形变孪晶逐渐向{001}〈110〉取向转变。当冷轧压下率从17%继续增大至34%时,形变孪晶的取向保持{001}〈110〉,孪晶与基体逐渐偏离理论取向差关系,即孪晶界取向差角逐渐偏离60°。

高牌号无取向硅钢生产流程中织构控制研究现状

在节能减排的背景之下,水电、风电和核电等清洁能源行业得到了快速发展。高牌号无取向硅钢是上述发电机组应用最普遍的铁芯材料。因此,开发低铁损和高磁感的高牌号无取向硅钢是清洁能源产业高质量发展的前提条件。织构是影响高牌号无取向硅钢磁感和铁损的主要因素之一,受到生产工艺的影响。然而,高牌号无取向硅钢工艺流程长,影响织构控制的工艺因素众多。为了满足高牌号无取向硅钢在低铁损时实现高磁感,在产品加工时应尽量避免对磁性能不利的{111}织构的形成,促进对其有利的{100}和{110}织构形成。本文首先介绍了高牌号无取向硅钢的工艺流程,对比了国内外钢铁企业产品的磁性能(P_(15/50)和B_(50))。其次,阐述了高牌号无取向硅钢在炼钢、热轧、常化、冷轧和成品退火过程中促进有利织构形成的影响因素。最后,归纳出能促进高牌号无取向硅钢有利织构形成的生产工艺,并对织构控制的发展方向提出了建议。

轧制速度对二十辊轧机轧制硅钢薄带的影响分析

重点讨论了轧制速度在二十辊可逆冷轧机轧制生产硅钢薄带时对带钢表面质量和生产效率的影响:改变轧制速度可以在不改变预设压下率的情况下对带钢产品进行厚度微调,适宜的轧制速度可以使产品的厚度精度更高;适宜的轧制速度可以减少带材表面缺陷和不均匀性,提高硅钢带材的表面质量。在大量生产实验中,通过改变轧制速度,研究了轧后带材的厚度精度和表面质量。结果表明,通过选择合适的轧制速度可以在不影响成品带材质量的情况下有效提高硅钢薄带的生产效率。该研究针对森吉米尔二十辊可逆冷轧机的设备特点和轧制速度对硅钢生产的影响进行了深入探讨,为优化冷轧硅钢带材生产工艺提供了重要参考价值。

稀土处理对高牌号无取向硅钢中夹杂物的影响

通过工业试验研究了不同稀土含量对高牌号无取向硅钢中夹杂物的影响。研究结果表明,当稀土质量分数为0.0021%时,稀土元素主要形成(La,Ce)AlO_(3)夹杂物,从而进行脱氧、变质钢中Al_(2)O_(3)夹杂物;随着钢中稀土含量的增加,稀土主要形成以(La,Ce)AlO_(3)-(La,Ce)_(2)O_(2)S类和(La,Ce)_(2)O_(2)S类稀土夹杂物,主要降低了钢中硫化物的析出量,但是此时生成的稀土夹杂物对钢中大量温降过程析出和二次氧化产生的Al2O3类夹杂物的改性作用较弱,这导致稀土含量高时钢中Al_(2)O_(3)夹杂物的数密度明显增加。此外,夹杂物长宽比的统计结果表明,稀土处理使铸坯中夹杂物发生明显球化,但在随后的热轧工序中,常规处理与稀土处理的热轧板中夹杂物的平均长宽比差异较小。即在工业生产实际中,稀土处理对成品组织中的夹杂物的长宽比影响很小,影响夹杂物长宽比的主要因素主要是轧制过程的相关工艺参数。

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。

热轧板厚度对高牌号无取向硅钢磁性能的影响

基于高牌号无取向硅钢现场生产实验,将相同炉次的连铸板坯热轧至不同厚度(2.1,2.3,2.6 mm)的板卷,经常化均热工艺调控,获得晶粒较为均匀的常化板组织,再经85.7%~88.5%压下率冷轧,得到相同厚度(0.3 mm)的冷轧板,最终采用相同的退火工艺得到退火板;结合组织、织构和磁性能的相关检测分析,研究热轧板增厚对高牌号无取向硅钢产品磁性能的影响。结果表明:随高牌号无取向硅钢热轧板厚度的增加(在2.1~2.6 mm范围,即冷轧压下率降低),退火板组织中{111}晶粒占比提高,γ纤维织构强度逐渐增强,织构发生恶化;随热轧板厚度的增加,磁性能中铁损P_(1.0/400)线性增加,磁感强度B_(50)线性降低。热轧板厚度由2.1 mm增至2.3 mm时,P_(1.0/400)平均恶化0.20 W/kg,P_(1.5/50)平均恶化0.04 W/kg,B_(50)平均恶化0.005 T;热轧板厚度由2.3 mm增至2.6 mm时,P_(1.0/400)平均恶化0.24 W/kg,P_(1.5/50)平均恶化0.04 W/kg,B_(50)平均恶化0.009 T。

冷轧薄板激光切割热影响区的深度及性能

为确定激光切割热影响区深度和激光切割热影响区对不同厚度、不同强度冷轧薄板产品力学性能的影响,通过改变激光切割速率的方法,对冷轧薄板产品进行激光切割试验,并对激光切割后热影响区的组织、深度和板材的拉伸性能进行研究。结果表明:热影响区可分为两部分,第一部分为激光切缝边缘的熔化区,第二部分为非熔化区,熔化区主要为马氏体,非熔化区主要为马氏体+贝氏体,激光切割速率越快,冷轧薄板的热影响区深度越小,冷轧薄板的强度越高或厚度越厚,热影响区深度越大;激光切割加工试样比加工中心加工试样的屈服强度和抗拉强度高,断后伸长率低,且随着钢种等级的提高,两者间的差异不断增大。