Effect of water quenching processing parameters on the mechanical properties of a cold-rolled C-Mn-containing steel sheet

Cold-rolled advanced high-strength steel sheets have become the material of choice for the automotive industry because of their unique attributes of high strength and balanced mechanical properties.High-hydrogen gas jet cooling and water quenching are the most commonly used ultrafast cooling technologies for producing martensite-containing high-strength steel sheets.The water quenching technology ensures the fastest industrial cooling rate of 1 000 K/s;therefore,it has the highest potential with respect to saving alloys.In this study,the water quenching of a C-Mn-containing steel sheet is simulated during continuous annealing to investigate the effect of water quenching and tempering parameters on its mechanical properties.The results reveal that at low quenching temperatures,the strength of the steel sheet decreases as the soaking temperature increases.However,at high quenching temperatures,a high soaking temperature corresponds to increased strength after quenching,regardless of whether the material was austenitized in the single austenite zone or the inter-critical zone.Therefore,a high quenching temperature always results in a high strength and a high yield ratio after quenching.Low-temperature overaging(tempering) considerably influences the yield strength and yield ratio,and the extent of this influence is correlated with the soaking temperature.

Effect of annealing parameters on mechanical properties of cold-rolled martensitic steel sheets

Cold-rolled martensitic steel sheets produced on continuous annealing lines with water quenching facility,have advantages of high strength and low alloying element contents.These are in good accordance with the trend of light-weighting and fuel saving for automotive steel.In this article,a cold-rolled martensitic steel is studied to investigate the effect of annealing parameters on its mechanical properties.It is found that the quenching temperature and the slow cooling speed as well as the overageing temperature have significant influence on the strength of the experimental steel.The temperature zone at which the austenite decomposition is slow or has not started may be chosen as the quenching temperature to ensure the steel’s strength stability.The slow cooling speed also influences the steel’s strength greatly.A high cooling rate will lead to significantly higher strength.Tempering would decrease the steel’s tensile strength but would increase its yield strength.

Development and application of Baosteel's cold-rolled martensitic steel sheets

Cold-rolled martensitic steel sheets are becoming widely applied in the automotive industry because of their ultra-high strength,which may result in satisfactory weight reduction. The grades of martensitic steel sheets are classified based on their tensile strength,which ranges from 980 to 1 700 MPa. The main applications include a series of structural parts of uniform cross-section or simple shape,such as bumper beams,door beams and door sills,etc. The study and development of cold-rolled martensitic steel sheets date back to 2007 in Baosteel,and some grades became commercially available in 2009. By 2015,Baosteel had commercially supplied thousands of tons of these steel sheets with tensile strength up to 1 400 MPa. Currently,1 500 MPa martensitic steel sheet is commercially available and 1 700 MPa martensitic steel sheet has been successfully produced. The process technology and application guides of Basoteel ＇s cold-rolled martensitic steels are summarized and analyzed in order to assist ongoing research and ensure correct applications of these ultra-high strength steel sheets.

Fatigue Response of Cold-Rolled Type-304 Stainless Steel Foil

This study presents the fatigue response of 304 stainless steel foil, cold-rolled to a thickness of 3.2 μm with 87 percent cold work at orientations of 0, 45, and 90 degrees to the direction of rolling. Fatigue specimens were fabricated by laminating a supportive layer of 20-μm polyimide film to one side of the foil and patterning 242 crack initiation features by photolithographic process. Progression of fatigue damage was determined through electrical resistance measurement. The fatigue response was demonstrated to be largely affected by anisotropy existing between the rolling direction and the off-axis orientations. Fatigue cracks that traveled in a direction parallel to the elongated grains (cyclic loads applied at 90-degree orientation to foil rolling direction) had the most fatigue response (undesirable characteristic). The construction of the specimens with thin foil supported by a film backing contributed to high fatigue threshold.

Properties of ultra-low carbon,cold-rolled sheet steels containing titanium or boron for use in enameling

Ultra-low carbon（ULC）,cold-rolled sheet steels for porcelain enameling containing alloys of titanium and boron are studied. The microstructure,mechanical properties,inclusions,and precipitates of the sheet steels are analyzed. The hydrogen permeation time of the sheet steels as-annealed and after skin-passed or cold-rolled at different reductions are measured. It is show n that the sheet steels possess different features of enameling properties in hydrogen permeability,fishscale resistance,and pinhole resistance.

Study on metallurgical properties and pellet proportioning technology of stainless steel cold-rolling sludge

With a complicated composition, large rolling sludge has been a focal point concerning neither at home nor abroad have any technologies suitable for bulk utilization of stainless steel cold- production and serious damage to the environment, stainless steel cold- environmental protection for stainless steel enterprises. Up to now, come into being that are not only proper, safe and economical but also rolling sludge. Based on the characteristics of the stainless steel cold- rolling sludge, orthogonal experiments were carried out on pellet proportioning and high-temperature roasting, and major metallurgical properties of sludge pellets were also tested. As the results show, pellets with 30% addition of cold-rolling sludge are qualified regarding their compressive strength, chemical composition and major metallurgical properties. No adverse impact happens to the blast furnace operation when sludge pellets account for 10% of the blast furnace raw materials. Therefore, the technical route applied in this paper is proved simple, feasible and environmentally friendly for cold-rolling sludge treatment.

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.

Research and application on the automatic measuring device for testing transverse thickness difference of cold-rolling steel sheet

Many advanced technologies have been applied in developing the automatic measuring device for testing transverse thickness difference of cold-rolling steel sheet,such as the technologies of automatic control,sensor measurement,marking identification,photographic location,computer application and information transmission.This measuring device can measure the transverse thickness difference of the steel plate accurately and quickly,with a high detection level of automation.It is an effective detection equipment for transverse thickness control of steel plate.Horizontal width of steel plate measuring 0.8-1.4 m, horizontal measurement point positioning accuracy±0.02 mm,thickness range 0.2-2.0 mm, measurement accuracy within±1μm.

Influence of heat treatment processing on the microstructure and properties in medium manganese steel

For the purpose of developing a 1 500 MPa grade steel sheet with excellent strength and ductility, a 0.15C-10Mn-1.5Al steel was employed to study austenite stability and microstructural evolution based on a novel double annealing processing.After a conventional intercritical annealing process, the sample was heated again to a temperature higher than A_(c3) for a very short time to generate austenite grains with different manganese content;thus, the microstructure of martensite plus austenite can be obtained at room temperature.The experimental results show that with increasing annealing temperature, the tensile strength and yield strength increase.When the annealing temperature was higher than 820 ℃,the microstructure consisted of martensite plus austenite, and the tensile strength almost remained invariant with the annealing temperature.A tensile strength of 1 537 MPa and an elong-ation of 25.1% were achieved for the 820 ℃ condition.The volume fractions of austenite and martensite were identified by X-ray diffraction.It was found that with increasing annealing temperature, the volume fraction of the retained austenite decreased, and the ductility also had a gradual downward trend.The related austenite stability was discussed here as well.

SPCC钢碱性无氰直接预镀铜工艺研究

目的提高LED支架的性价比,减少SPCC钢表面镀银预镀铜工艺的镀液污染,简化现有的预镀镍-镀铜施镀工艺,提高预镀层质量。方法采用HEDP碱性无氰直接预镀铜方法来简化工艺,用单因素实验法,系统研究了电流密度、镀液pH、电镀温度、HEDP/Cu^(2+)摩尔比、电镀时间等参数,对镀层镀速、孔隙率及镀层表面质量的影响,并表征镀层的微观组织及镀层结合力。结果在阴极电流密度为1.41 A/dm^2,pH值为9.5,温度为50℃,HEDP/Cu^(2+)摩尔比为3.75:1(Cu^(2+)为10 g/L),时间为11 min的条件下,可获得镀速约为1.7 mg/(cm^2·min)的预镀铜层,且镀层与基体的结合力良好,无孔隙,呈良好的光亮/半光亮状的细晶镀层。结论与钢铁表面氰化镀铜及镀银前预镀铜工艺相比,推荐的HEDP直接预镀铜工艺的镀层质量好,可满足直接镀铜和镀银前预镀铜工艺要求,可有效减少镀液污染和简化施镀工艺,对SPCC钢的镀铜工艺改善具有较好的推广价值。

SPCC产品的连退工艺研究

在简单介绍宝钢冷轧薄板厂的连退设备及基本退火工艺的基础上,通过现场生产实践与实验室试验相结合,确定了SPCC产品的再结晶温度,同时定量分析出化学成分、热轧卷取温度、退火工艺等关键因素对产品性能的影响,给出了SPCC产品的最佳退火工艺,并将其应用到生产实践,取得了良好的使用效果,具有进一步推广应用的价值。

SPCC钢滑动摩擦与拉伸声发射信号比较分析

为了将声发射技术应用在金属塑性加工中的摩擦监测中,以SPCC钢在拉伸过程与相对运动速度为100mm/min、正压力为7.5kg的摩擦过程产生的声发射信号特征为研究对象,分别用数据统计、平均值等方法对比分析了两种声发射信号的能量、振铃计数、幅度等参数。实验结果表明:SPCC钢拉伸的声发射能量值要远小于摩擦声发射能量值;拉伸的声发射振铃计数分布范围要略大于摩擦声发射振铃计数分布范围;拉伸的声发射幅度要小于摩擦声发射的幅度。最后对出现该现象的原因进行了探讨。

SPCC钢锅缺陷原因分析

SPCC钢锅内表面出现无规则白亮串状缺陷。利用金相显微镜、扫描电镜及能谱仪等对产生原因进行了分析。结果表明:白亮串状缺陷实际上是鼓泡,是热轧基板上链状三次渗碳体沿晶析出,冷轧后出现沿晶微裂纹,渗氮后氮加剧裂纹扩展,并使裂纹处压力升高引起的。为了防止缺陷产生,应控制好热轧板卷曲温度,但在钢板中有少量的三次渗碳体析出并且弥散分布是比较好的。

SPCC钢塑性变形中动态再结晶的数学模型与模拟分析

利用热模拟设备Gleeble-1500D,对SPCC钢在不同变形量下的真应力-应变曲线进行了测定,并结合微观组织观察,确定了SPCC钢动态再结晶的数学模型,研究并分析了变形参数对动态再结晶晶粒的影响.通过DEFORM有限元软件对SPCC钢的热压缩过程进行模拟计算.分析了不同变形条件对晶粒尺寸的影响.模拟计算结果很好地与实验结果相吻合,为进一步研究这种钢的动态再结晶提供了一定的参考依据.

基于田口法的DP980/SPCC电阻点焊工艺优化及接头组织和性能分析

文中以冷轧DP980高强钢板与SPCC低碳钢板作为研究对象,基于田口法优化电阻焊接参数,并对最优参数的焊接接头进行组织性能分析。结果表明,在焊接电流10.5 kA、焊接时间30 cycles、电极压力3 kN、维持时间10 cycles的条件下,接头力学性能最优;且接头实现熔核剥离断裂,为韧性断裂,熔核剥离断裂起始位置位于熔核边缘处SPCC母材,最大拉伸力为11.78 kN;点焊接头主要为熔核区、热影响区、母材区3个区域;熔核区的显微组织主要为马氏体,DP980高强钢一侧热影响区的显微组织组织主要为马氏体和铁素体,SPCC低碳钢一侧热影响区的显微组织主要为马氏体、铁素体和珠光体。DP980高强钢热影响区硬度最高,其次为熔核区、SPCC热影响区,SPCC母材硬度最低。

SPCC钢精炼渣与夹杂物相关性研究

针对SPCC钢的生产工艺情况,研究精炼渣与夹杂物相关性,分析精炼渣化学成分、w(CaO)/w(Al2O3)等对钢中夹杂物大小、形貌、类别等的影响。研究表明,精炼渣w(CaO)/w(Al2O3)为1.38~1.66时,钢中夹杂物分布较好,即大颗粒夹杂物比率较小,小颗粒夹杂物比率较大。

SPCC钢CCT曲线测定与分析

结合膨胀法和金相-硬度法,利用Gleeble-1500D热模拟试验机测定了SPCC钢的临界点Ac_1、Ac_3,测得该钢在不同冷速连续冷却时的膨胀曲线﹑相转变点;分析了连续冷却过程中相转变及组织转变的规律;测定了不同冷速下相转变后的硬度,获得了SPCC钢连续冷却相转变曲线(CCT曲线)。结果表明:SPCC钢在连续冷却过程中发生了奥氏体向铁素体和珠光体的转变,且室温金相组织基本为铁素体,而珠光体量比较少;随冷却速率的增加,相变温度降低,晶粒尺寸从24μm减小到12μm,硬度变化不显著。

SPCC冷轧钢等温退火的微观组织和力学性能

在Gleeble-1500D热模拟机上,对SPCC冷轧钢进行等温退火试验和力学性能测试。分析了不同退火温度和保温时间对SPCC冷轧钢组织和性能的影响,建立了等温退火工艺参数与SPCC冷轧钢板力学性能间的数学模型。研究结果表明：退火温度低于550℃时,只发生铁素体回复;650~850℃时,发生铁素体的再结晶及晶粒长大。屈服强度和抗拉强度随退火温度升高而降低,在650℃时大幅度下降,850℃时达到最低。同样退火温度下,屈服强度和抗拉强度随保温时间增加先下降后趋于稳定。采用加权平均法建立SPCC冷轧钢力学性能模型,并对模型进行了验证。屈服强度、抗拉强度和伸长率的平均绝对误差分别为20.2 MPa、23.2 MPa和1.4%,平均相对误差分别为3.9%、4.3%和10.7%,证明模型具有较高的精度。

循环盐雾环境下SPCC钢腐蚀行为研究

为了研究商用冷轧钢板(SPCC)在循环盐雾腐蚀环境中的腐蚀行为并探究其腐蚀机理,通过GMW14872循环盐雾试验、腐蚀形貌观测及腐蚀失重法考察了SPCC钢的耐蚀性能,并采用光学3D表面轮廓仪对盐雾腐蚀后试样表面的腐蚀深度进行了表征。通过实验结果,对SPCC在盐雾腐蚀环境中的的腐蚀机理进行讨论,并分析腐蚀过程中SPCC钢的腐蚀产物转化对其腐蚀过程的影响作用。结果表明:SPCC钢经过24个循环盐雾过程,宏观腐蚀形貌由腐蚀初期的黑色、橙褐色逐渐转变为土黄色,耐腐蚀性呈现逐渐提升的趋势,腐蚀速率由1.13 mm/a下降到0.62 mm/a;随着腐蚀时间的增加,SPCC钢的腐蚀形态逐渐由点蚀发展为均匀腐蚀,表面腐蚀深度值由36μm增加到108μm;SPCC钢在腐蚀过程中,由于铁素体和渗碳体电位差的驱动引发了局部电偶腐蚀,腐蚀产物由腐蚀前期稳定性较差的Fe(OH)_(3)、γ-FeOOH、β-FeOOH逐渐转化为较为稳定的α-FeOOH,提高了耐蚀性。

再结晶退火对SPCC钢板组织和深冲性能的影响

通过实验室模拟工业罩式炉再结晶退火工艺,研究了退火温度和保温时间对SPCC钢板组织和深冲性能的影响,分析了退火后铁素体晶粒饼形度与深冲性能的关系。结果表明:随退火温度升高和保温时间延长,铁素体晶粒尺寸逐渐增大,同时深冲性能明显改善;700℃、保温4 h后晶粒尺寸和深冲性能再无明显变化。再结晶退火后铁素体晶粒饼形度与深冲性能有良好的对应关系,晶粒饼形度可以作为钢板深冲性能的判据之一。