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.

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.

Allowable variation of cold-rolled strip transverse profiles in high tension

The formation mechanism of the cold-rolled strip shape with high tension was studied. An advanced method to calculate the allowable variation of strip transverse profiles was established by the strip buckling criterion, which can be more properly used in cold rolling. With this method, the aim allowable variation of the product strip transverse profile and the required transverse profile range of incoming strips can be reached. Besides, this method has been successfully applied in a domestic tandem cold mill, and the transverse profile range of incoming strips suggested with this method is more practicable and complete. Consequently, the good performance is acquired.

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.

四工作辊轧机轧制304不锈钢板件截面塑性变形分析

针对四工作辊轧机轧制304不锈钢板件存在变形量大、尺寸不稳定的问题,利用Solidworks软件建立四工作辊轧制系统有限元模型,采用Deform软件对304不锈钢板件在不同轧辊直径、轧辊转速和轧辊压下量下进行轧制仿真,分析其对轧件截面高度和等效应力分布的影响,根据轧制仿真分析结果设计制造了四工作辊轧机,并对不同压下量下仿真和生产的轧件截面高度进行对比分析。结果表明,轧件截面塑性变形可分为相互作用Ⅰ区、过渡Ⅱ区和变形Ⅲ区,等效应力、等效应变和截面高度在Ⅰ区最大,在Ⅲ区最小且变化平稳,Ⅱ区值位于两者之间并呈U型分布。

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。

轧制及退火对FeCoCrNiN_(0.07)高熵合金组织及力学性能的影响

采用粉末冶金热等静压法(HIP)制备了FeCoCrNiN_(0.07)高熵合金,研究了冷轧变形及后续750℃退火对FeCoCr-NiN_(0.07)高熵合金显微组织及力学性能的影响。结果表明;HIP态FeCoCrNiN_(0.07)高熵合金为简单的单相FCC结构,在经过轧制变形及后续750℃退火后无第二相产生。HIP态合金显微组织由大量的等轴晶粒和退火孪晶构成,经过轧制变形后显微组织中产生大量微观剪切带和一些变形孪晶,同时还存在大量的微观应变以及较高的位错密度。冷轧态合金经过750℃退火后发生完全再结晶形成大量细小的等轴再结晶晶粒和退火孪晶。HIP态合金表现出优异的塑性但强度较低,经过轧制后强度显著增大而塑性显著降低,这主要归因于位错强化。冷轧态合金在750℃退火后强度降低伸长率增加获得最佳的综合力学性能,强度的降低归因于再结晶软化作用,而强度优于HIP态归因于细晶强化的作用。

选区激光熔融制备FeCoCrNiMn-(N,Si)高熵合金在冷轧变形及500℃长时间退火后的析出行为

对选区激光熔融制备的FeCoCrNiMn-(N,Si)高熵合金先进行冷轧变形,然后在500℃进行长时间退火处理,研究长时间退火对其相稳定性及微观组织演变的影响。研究结果表明,在退火温度为500℃,退火时间为10~40 d时,合金基体内形成了3种类型的沉淀析出物(Cr_(2)N相、BCC-Cr相和L1_(0)-NiMn相),且氮原子的添加抑制了富FeCo相的形成;当退火时间从10 d增加到20 d时,沉淀物的尺寸显著增加。然而,当退火时间进一步增加到40 d时,沉淀物颗粒不长大,其尺寸保持不变。

Microstructure Recrystallization and Mechanical Properties of a Cold-Rolled TiNbZrTaHf Refractory High-Entropy Alloy

The equiatomic TiNbZrTaHf alloy was successfully rolled at room temperature with the reduction of ~ 85%. The microstructure and tensile properties were investigated after cold working and annealing. It was determined that the recrystallization temperature of the TiNbZrTaHf alloy between 850 and 900 ℃. Complete recrystallization and normal grain growth occurred, the high stability of single phase was maintained after annealing at 1000, 1200, and 1400 ℃. But the precipitated phase appeared after long term annealing, as seen after 500 h at 1000 ℃. After cold working, the tensile strength and the elongation of TiNbZrTaHf were 1137 MPa and 25.1%, respectively. The annealed alloy has a high tensile strength (σ_(b )= 863 MPa) and ductility (ε_(e )= 28.5%). Moreover, the oxidation of TiNbZrTaHf alloy at elevated temperatures has a significant impact on its mechanical properties. The poor oxidation resistance of TiNbZrTaHf can accelerate tensile failure by inducing fractures at grain boundaries.

冷轧变形量对热处理后CoCrFeMnNi高熵合金退火孪晶及力学性能的影响

经冷变形与热处理后的CoCrFeMnNi高熵合金性能会受到在退火过程中产生退火孪晶的影响,而孪晶形貌与种类的变化与冷变形量和热处理条件相关。探究了高温短时热处理下,冷变形量对退火孪晶及力学性能的影响。采用真空中频感应熔炼炉制备了FCC单相CoCrFeMnNi高熵合金,样品经均匀化退火后使用两辊轧机沿同一方向进行多次冷轧,得到不同变形量的样品。样品在900℃条件下退火1 h,采用金相显微镜、X射线衍射与透射电子显微镜对样品的微观组织形貌进行表征以观察样品中退火孪晶的变化,在室温下对样品进行了静态单轴拉伸试验,研究了不同变形量对于退火孪晶的影响以及退火前后力学性能的变化。结果表明,退火孪晶的种类和数量会随变形量变化:变形量30%的样品内部晶粒尺寸大,退火孪晶的种类和数量最少;变形量80%的样品晶粒尺寸与30%的样品相近,但退火孪晶数量、种类多;变形量50%的样品晶粒尺寸最小,退火孪晶数量与种类中等。未经热处理的样品其抗拉强度与变形程度呈正相关,抗拉强度最高可达到1333.44 MPa,经900℃×1 h退火处理后,其抗拉强度与变形程度呈负相关,抗拉强度最高为585.81 MPa。结果表明,CoCrFeMnNi高熵合金在高温短时间的热处理条件下具有良好的相稳定性,轧制和退火后均为FCC单相结构,没有析出相产生。冷变形后的样品在热处理后样品内部发生了再结晶,晶粒的尺寸大小与退火孪晶的数量和种类以及样品的力学性能会随着变形量的不同产生变化。同时,合金内部产生的小尺寸退火孪晶起到了存储位错的作用。

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。

冷变形对超低碳贝氏体钢中逆转变奥氏体的影响

采用硬度测试、拉伸试验、金相检验、X射线衍射测试、透射电镜检测、能谱分析等方法研究形变对超低碳贝氏体钢中逆转变奥氏体和力学性能的影响。结果表明:随着冷轧变形量的增大,超低碳贝氏体钢的硬度与强度呈显著增大趋势;超低碳贝氏体钢中的奥氏体体积分数从未变形时的0.4%逐渐增大到变形量为90%时的14.85%;钢中的逆转变奥氏体主要分布在晶界处,其形态由未变形时的薄膜状向块状转变;奥氏体中的Ni元素和Mn元素质量分数随变形量的增大而减小,Ni元素质量分数由未变形时的59%下降到变形量为90%时的11.64%,Mn元素质量分数由未变形时的16%下降到变形量为90%时的3.48%。

不锈钢冷轧高氮高盐废水处理集成技术的研究应用

不锈钢冷轧废水因总氮含量高、离子成分复杂、水质波动大,成为钢铁行业废水处理的技术难题。本文研制了“多段污泥+碳源互补A+多级曝气氧化O”的高效脱氮生化处理工艺,开发了柔性化智能精准调控模型,以构建一种高氮高盐废水脱氮降盐处理的集成技术,为行业废水处理提供一条新途径。同时,结合某冷轧废水脱氮处理的改造开展了应用,结果表明,总氮和盐分去除率分别可达98%和25%以上,与现有工艺对比,本技术脱氮处理效率达到最高,且吨氮处理占地面积、建筑面积和投资成本降至最低,具有良好的经济效益。

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。

六辊可逆冷轧机道次量综合优化技术的研究

在六辊单机架可逆轧机高速轧制过程中,轧制道次量的设定合理与否直接影响带钢的出口板形分布以及轧机轧制的稳定性,也对生产效率与机组能耗产生影响。高速轧制虽然速度快,但是高速轧制工况下,平均每个道次压下量受到限制,相对较小,要实现出口厚度一致要多出相应数量的道次。对于可逆轧机来说,道次的增加意味着整个机组能耗的较大增加。针对高速可逆轧制过程出现的板形和能耗较大问题,通过优化各道次的前后张力、轧制速度等参数,有效降低了后3道次的轧制压力和轧制功率。并建立了各道次的板形控制和功率控制目标函数,进行加权计算后,形成了一套以各道次轧制功率均匀为目标,同时兼顾板形控制、轧制稳定性以及表面缺陷防治等因素的轧制规程综合优化设定技术。将该优化技术应用到了国内某单机架可逆冷轧机组的带钢生产,带钢出口板形质量得到改善,滑伤率有效降低,生产效率得到提高。