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.

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.

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.

退火工艺对CSP供冷轧原料的SPCC板性能和织构的影响

在试验室条件下,模拟了CSP热轧带钢供冷轧原料的SPCC级低碳钢板的罩式炉退火过程,分析了不同退火工艺对CSP热轧带钢供冷轧原料的SPCC板的深冲性能和组织的影响,研究了织构随升温速度变化的演变规律。试验结果表明随升温速度的降低,r_m、Δr值都逐渐升高,r_m为1.68,Δr达到0.68:变形织构{112}〈110〉变弱,表明降低升温速度可以消除变形织构,但速度低于40℃/h时消除作用就不明显。降低升温速度也可以使{111}〈110〉织构和{111}〈112〉织构的强度差增大。钢板Δr值的变化受多重因素影响,{111}〈110〉织构和{111}〈112〉织构的强度差可能是导致Δr值升高的原因之一。

SPCC冷轧薄板退火工艺的优化与性能分析

分析了SPCC冷轧薄板成材率和性能合格率低的原因,确定退火过程产生的缺陷是造成废次品的主要原因;并通过采取优化退火工艺的措施,使退火缺陷明显下降,性能得到显著改善,从而有效提高了成材率和性能合格率。

唐钢SPCC冷轧板的工艺优化与性能分析

唐钢SPCC冷轧板原定位于建筑用板,为开发汽车用SPCC钢板,对其化学成分进行了优化设计,即在化学成分设计上提高了Als含量,降低了N含量,并采用高温加热、高温开轧、低温卷取、适宜的冷轧变形量(70%～75%)等优化的热轧,冷轧,退火工艺,使产品性能达到了汽车内板的使用要求。

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薄板冷轧及连续退火工艺研究

对SPCC薄板进行了冷轧及连续退火模拟试验。研究了冷轧及连续退火工艺对SPCC薄板再结晶组织的影响效果,以及再结晶晶粒尺寸对SPCC薄板力学性能的影响规律。研究发现,经工艺参数优化,可显著降低退火薄板的再结晶晶粒尺寸,同时提高薄板的屈强比性能指标。在晶粒尺寸最为细小的5.23μm SPCC薄板中得到市场上同类产品中最高的屈强比性能。

Surface Defects of Cold-Rolled Ti-IF Steel Sheets due to Non-Metallic Inclusions

Surface defects of the cold-rolled sheets of Ti-IF steel were studied and analyzed. After analyzing surface defects of cold-rolled sheets, such as shelling defects, holes and sliver defects by SEM/EDS, a variety of inclusions were found. In addition, the distribution of macro-inclusions in slabs was analyzed by MIDAS method. The results show the macroscopic inclusion bands of head slabs and normal slabs are in 1/8 slab thickness regions of both inner arc side and outer arc side. The formation process of the defects in the cold-rolled sheets was simulated with an experimental cold-rolling machine for comparison. The results show that there were three kinds of inclusions underneath the surface defects: Al2O3, SiO2 and particles from slag entrainment, which were the main reason for defect formation during cold rolling.

Causes of surface stripe cracks of Ti–4Al–2V alloy cold-rolled sheet

The stripe cracks which formed along rolling direction on the surface of Ti–4Al–2V alloy cold-rolled sheet were observed by stereoscope, scanning electron microscope（SEM）, and energy-dispersive spectrometer（EDS）. Morphology analysis indicates that cracks are dominantly in zigzag shape, with 10–30 mm in length and less than 10 lm in depth, and there is no evidence of crack tips. Chemical composition analysis shows that crack regions feather high oxygen concentration while smooth surface is at normal oxygen level. It is obvious that the occurrence of strip cracks is mainly related to residual oxide on the surface of Ti–4Al–2V alloy cold-rolled sheet.

CSP工艺不同冷轧压下率低碳钢板退火织构的演变

采用基于包钢CSP热轧工艺下2.75和4.5 mm现场冷轧至1.0 mm的SPCC钢板,冷轧压下率分别为64%和78%,实验室模拟了罩式退火工艺,并利用XRD测得了冷轧和退火过程中织构的演变.结果表明,两种不同冷轧压下率的钢板在冷轧和退火过程中织构演变规律相似,但是冷轧基料厚度为2.75 mm的钢板在整个过程变化幅度更大,而且成品的织构类型更有利.

退火工艺和稀土元素对SPCC冷轧板再结晶过程及织构的影响

研究了退火工艺和添加微量稀土元素对SPCC冷轧低碳钢板再结晶过程及织构的影响。结果表明,提高加热温度加快了SPCC冷轧板再结晶过程,促进晶粒长大;稀土元素的加入阻碍了再结晶过程,抑制了晶粒长大,明显提高了稀土SPCC冷轧板有利于深冲性能的{111}<011>织构、{111}<112>织构和{001}<100>立方织构的强度。

连续退火SPCC冷轧薄板性能的影响因素

研究了连续退火工艺、碳含量和热轧卷取温度对SPCC板性能的影响。结果表明,随着加热速率的减小或退火温度的升高,SPCC板的晶粒尺寸变大,屈服强度降低。试验钢的屈服强度和平均晶粒尺寸之间的关系可以用直线方程R eL=378.3d-1/2+142进行较好描述。降低碳含量或提高热轧卷取温度不仅能有效降低退火板的屈服强度,且可以增强{111}面织构,提高其深冲性能。

缓冷出口温度对连续退火SPCC冷轧薄板屈服强度的影响

研究了缓冷出口温度对连续退火SPCC冷轧薄板组织和屈服强度的影响。结果表明:连续退火SPCC冷轧薄板的组织由等轴的铁素体晶粒和晶界处的块状渗碳体及晶粒内的颗粒状渗碳体组成。随着缓冷出口温度从680℃提高至700℃,平均晶粒尺寸从10. 1μm增加至12. 5μm;此外,提高缓冷出口温度还能够抑制晶界处块状渗碳体的形成,促进晶粒内细小渗碳体更加细小弥散的析出。当缓冷出口温度从680℃提高至700℃时,冷轧薄板的屈服强度约降低了28 MPa。

冲压速度对车身钢板U型弯曲回弹的影响

为明确冲压速度对回弹的影响规律,采用试验及数值模拟方法研究了冲压速度为0.05～50 mm·s^-1时SPCC和DP780车身钢板U型弯曲回弹量的变化情况,并分析了冲压速度对回弹的影响机理。试验结果显示：DP780钢板的回弹量高于SPCC钢板;SPCC钢板的回弹量随着冲压速度的增加而减小,DP780钢板的回弹量随着冲压速度的增加而增大。为提高成形部件的尺寸精度,需要考虑冲压速度对不同材料回弹行为的影响。数值模拟结果显示：SPCC钢板的回弹行为对应变速率不敏感,因为受惯性影响在侧壁区的上侧和下侧切线应力有较大差异;而DP780钢板受应变速率强化的影响,对回弹行为很敏感。