Recent progress in third-generation low alloy steels developed under M^3 microstructure control

During the past thirty years, two generations of low alloy steels(ferrite/pearlite followed by bainite/martensite) have been developed and widely used in structural applications. The third-generation of low alloy steels is expected to achieve high strength and improved ductility and toughness, while satisfying the new demands for weight reduction, greenness, and safety. This paper reviews recent progress in the development of third-generation low alloy steels with an M^3 microstructure, namely, microstructures with multi-phase, meta-stable austenite, and multi-scale precipitates. The review summarizes the alloy designs and processing routes of microstructure control, and the mechanical properties of the alloys.The stabilization of retained austenite in low alloy steels is especially emphasized. Multi-scale nano-precipitates, including carbides of microalloying elements and Cu-rich precipitates obtained in third-generation low alloy steels, are then introduced. The structure–property relationships of third-generation alloys are also discussed. Finally, the promises and challenges to future applications are explored.

Application and failure evaluation of ferritic stainless steels for automotive exhaust systems

In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels （FSS） used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.

Research on the lack of alloying in the galvannealed coating of automotive sheet steel

Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed. X-ray diffraction （XRD） tests were carried out. The study discovers that the deficit of alloying was higher on both sides of the steel sheet when compared to the center and the thickness of the coating on the sides was also higher than the center. The results of the XRD tests demonstrate that the microstructure of the coating with a lack of alloy is mainly composed of zinc,ζ and δ. They also indicate that the lack of alloying is mainly due to a lower galvannealing temperature and thicker coating. It is shown by the optical micrographs of coating that the δ phase forms first in a discontinuous manner at the interface and then rapidly pushes towards the coating and enlarges.

Application of Electron Beam Surface Technologies in the Automotive Industry

Progress in the beam deflection technique opens up new possibilities for the application of electron beam (EB) surface and welding technologies in the automotive industry. This development is based on three-dimensional high-speed beam deflection and fully automatic online process control. So, in the EB surface treatment three-dimensional energy transfer fields can be realised which take into account the contour of a component, the conditions of heat conduction and the load conditions. High flexibility, precision and reproducibility are typical characteristics. High productivity is achieved by the simultaneous interaction of the EB in several processing areas or by carrying out several processes simultaneously. EB surface treatment is becoming more and more attractive and important especially in the automotive industry, and also in comparison to laser technologies. This paper deals with different EB surface technologies, for example hardening, remelting, surface alloying, dispersing or cladding of different materials such as steel, cast iron and different alloys of Al, Mg and Ti. Examples of applications in the automotive industry, especially engine components, will be discussed.

Recent progress in the development and application of the new Gen.AHSS at Baosteel

In recent years,despite the global economic recession and steel oversupply,the demand for high strength steel( HSS) and advanced high strength steel( AHSS) sheets has robustly increased. To supply the materials needed for automotive manufacturing,various AHSS products and application technologies have been developed by Baosteel,including the 1st,2nd,and 3rd Gen. AHSS,which makes Baosteel the world’s first steel maker to commercially provide all three generations of AHSS. Recently,the new Gen.( the 2nd and 3rd Gen. combined)AHSS products,which feature ultra-high strength and enhanced ductility,have drawn great attention from both steel makers and the automotive industry as these products can be used to produce auto parts with complicated shapes by cold forming and have great potential for manufacturing car bodies that are lighter in weight and have higher crash resistance. In this article,the concepts,properties,and applications of Baosteel’s new Gen. AHSS products,including quenching and partitioning( QP) steels,twinning-induced-plasticity( TWIP) steels,and Medium-Mn( Mn-TRIP)steels,are described and reviewed. Moreover,the progress of the Baosteel light-weight steel car body( BCB) was reported.

Recent development of UHSS and its hot-dip galvanizing processes in Baosteel

Baosteel has excelled in automotive steel sheets in the past three decades.It has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel products.Some milestones achieved by Baosteel automotive steel sheet were briefly reviewed.The current challenges in producing ultra-high strength steel(UHSS),especially hot-dip galvanized UHSS,were summarized.The most current advancements in UHSS and the corresponding hot-dip galvanizing processes were discussed.The galvanizability of Si-Mn-added QP steel and DP steel, Mn-added TWIP steel, and Al-added low-density steel has been improved by different techniques in Baosteel.

Evolution of appearance profile of hot-dip galvanized car-body steel sheet during deformation process

In recent years, the waterborne free intermediate coating process has been widely used in the automotive industry. Because the baking times and coating thickness are decreased, the surface covering capability of the painting process is reduced, which directly affects the appearance quality（ long-and short-wave values） of the body paint. Thus, there are correspondingly higher requirements for the white body surface profile prior to painting. The surface profile of the white body is mainly affected by the plate material, the surface profile, and the deformation process. So,the change rule for the surface profile during deformation of the steel plate is a key factor in coating appearance optimization. In this paper, we first analyze the typical deformation of the outer cover of a car body. Then ,we examine the change tendency of the surface profile of steel plates with respect to different deformation rates, specifically for a steel plate comprising a hot-dip galvanized bake-hardened steel sheet. Based on our analysis of the influence of the deformation on the coating appearance,we selected 3% ,5% ,and 8% deformation rates in this research. We found the roughness （Ra） value in the typical deformation range （3% -8% ） of the car body to exhibit a decreasing trend at first and then an increasing trend. The Ra value of the 8% deformation is not more than the original plate test value. When the Pc value of the original plate is in the lower range （ about 60）, it exhibits a slight increasing trend in the deformation process （3 % -8 % ）. And when the Pc value of the original plate is in the higher range （ about 120 ）, it exhibits no increasing trend in the deformation process （ 3% -8% ）. In contrast,the waviness （WCA） value in the car body＇s typical deformation range （3%-8%） shows a significant growth trend.

The production and practice of cold-rolled steel sheets for automobile

Shougang Group has carried out a strategic structure adjustment in order to realize the promise of Chinese people to the Olympic Games.Automotive sheets are chosen as a type of strategic product and an engine to upgrade enterprise management,technology and operation to reach the top international level during the transition from long products to steel sheets in Shougang Group.Since 2006,Shougang Group has made an elaborate preparation on steel sheet culture,production line construction,technology import,pilot plant and talent reserve.It lays the foundation for the development of automotive sheets.The developing history of cold rolled automotive sheets is reviewed and the research and development of cold rolled automotive sheets, tackling key problem of defect on surface and the latest progress of automotive sheets construction are described in this paper.The main contents were given as follows:①The products of automotive sheets realize zero breakthrough in Shougang Group.Monthly output was 300 ton in January,2009 and it increased to 48 000 ton in June,2010.The ratio of IF steel sheets increases to 70%from 40%.The proportion of outside panel in automotive sheets occupys more than 15%.②A high emulational pilot plant is used as a product developing platform to develop successfully automotive sheets with 1 000 MPa and below.It guarantees that the industrial development of DP and TRIP sheets gets success at a time.It covers continuous annealing sheets with tensile strength≤780 MPa and galvanizing sheets with tensile strength≤590 MPa.③Individual design is used to meet special requirement of customer.Shougang owns 23 inner brands of LCAK and IF steels.It insures that the grades of yield strength cover whole range from 120 to 270 MPa.It keeps the stabilization of steel performance by means of chemical composition control and high accuracy rolling technology.For example,the strength of soft steel fluctuates within±15 MPa.④The steel sheets with surface grade O5 are produced steadily by solving forming striation of IF steel,grain coarse on surface,edge curling skin and mountains - and - waters painting defects.⑤The safeguard mechanism on quality of products is improved steadily and the output of automotive sheets and outside panel increases greatly by building consistency quality management system、information - system and customer service system.

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.

Feasibility of 0.02% Nb-Based Microalloyed Steel for the Application of One-Step Quenching and Partitioning Heat Treatment

To attain an enhanced combination of mechanical properties for low alloyed steel, the current study has been made to fulfill that growing need in the industry. Its results are introduced within this paper. One step Quenching and Partitioning (Q&P) heat treatment has been applied on Niobium-based microalloyed steel alloy with 0.2 %C, in the form of 2 mm thickness sheets. The target of this study is to investigate the viability of applying that significantly recommended, results-wise, heat treatment on the highly well-suited alloy steel samples, to achieve the main target of enhanced properties. A single temperature of 275°C was used as quenching and Partitioning temperature. Four Partitioning periods (30, 200, 500, and 1000 Seconds) were used for soaking at the same temperature. The results were analyzed in the light of microstructural investigation and mechanical testing. All applied cycles did not enhance the strength but moderately improved the ductility and toughness, mainly caused by the slightly high soaking temperature used. Niobium impact of grain refining was apparent through all cycles. The cycle of 500 Seconds Partitioning time obtained optimum values at that particular temperature. The 1000 Seconds Cycle obtained the worst combination of properties. A set of recommendations are set. More research is required at this point, where a lower Partitioning temperature is advised. In the light of the applied combination of parameters, the Partitioning period at such temperature is advised to be between 500 and 1000 Seconds. A high probability that periods closer to 500 than 1000 Seconds will produce better results. More research is needed between those two values of Partitioning time to precisely determine the optimum time at that temperature on that specific alloy.

优化汽车大梁钢板形控制 提升产品质量

钢铁产业作为现代工业的支柱之一,随着技术的不断进步和市场的不断发展,钢铁产品不再是仅仅满足基本功能的产物,更加注重满足特定行业和客户的细分需求。汽车、航空航天和容器制造等领域对钢材的要求更为严苛,提出了更高的技术、质量和性能要求。从技术角度,深入钢铁企业下游单位,了解客户需求,解决产线产品的板形质量问题,如汽车大梁钢420L和700L的弓背、翘曲等重点板型问题。通过对下游大梁钢开平厂以及平整产线的走访驻点,深入了解客户的需求和关注点,着重解决客户提出的几项问题。根据客户提出的具体缺陷,回归产线,通过优化过程控制,提升产品质量。

汽车用高强度双相钢的化学成分和退火温度研究

实验室条件下设计了两种不同成分的汽车用高强度双相钢,通过微观组织和力学性能对比分析,确定适合现有退火生产线的成分,并采用奥钢联VAI退火热模拟试验机研究了退火温度对组织和性能的影响。试验结果表明:两种化学成分的试验钢均满足汽车用高强度双相钢的微观组织和力学性能要求,只添加Cr的试验钢可以代替复合添加Cr、Mo的试验钢;随着连续退火温度的升高,只加Cr试验钢的铁素体含量逐渐降低,马氏体含量呈先增加后降低的趋势,屈服强度逐渐上升,抗拉强度和断后伸长率先上升后降低;退火温度为820℃时,试验钢具有优良的综合力学性能,强塑积达到20.04GPa·%。

汽车用钢的发展与低熵化先进高强钢设计

介绍了汽车用钢的发展历史与推动汽车用钢发展的历史性事件,展望了未来汽车用钢在“双碳”背景下的发展方向。同时,介绍了汽车用先进高强钢的发展与分类,阐述汽车钢从软钢、低碳钢、高强钢到先进高强钢的发展过程,详细阐述第一代到第三代先进高强钢迭代升级过程中成本、合金、组态与性能等方面的设计思路。最后,提出创新性的低熵化设计理念,并介绍所设计的覆盖四类双相钢产品的低熵化产品,包含成分与工艺的设计思路。提出“组态异构”的低熵化设计,以用户切实的应用需求为导向,深入分析产品性能特征,结合钢铁材料的物理冶金机理与生产制造阶段装备及工艺特征,从设计端对产品进行减量化、单一化、归一化的梯度低熵化设计,实现产品低成本高性能生产制造思路。

低碳视野下无镀层热成形钢的激光拼焊研究

研究了低碳足迹的无镀层热成形钢激光拼焊及其与铝硅镀层热成形钢之间的激光拼焊,结果表明:无镀层热成形钢可在没有预剥离或填丝的条件下与自身或铝硅镀层热成形钢焊接获得高质量的激光拼焊焊缝,在单向拉伸试验中,拉伸断裂均发生在远离焊缝位置;在缺口冲击试验中,无镀层钢与铝硅镀层钢之间的焊缝冲击功维持在基材冲击功的86%。无镀层钢与铝硅镀层钢之间焊缝的微观组织主要为马氏体和少量因铝硅熔入焊缝形成的铁素体。焊缝硬度与铝硅镀层钢基材相当,未发现软区。最后,结合热力学及相转变动力学计算,分析了无镀层钢与铝硅镀层钢之间获得高质量激光拼焊焊缝的机理:无镀层热成形钢稀释了熔入焊缝中铝硅的浓度,避免因高温形成大量富铝硅的脆性铁素体;无镀层钢中添加的合金元素Cr可以提高焊缝的淬透性,在热冲压冷却过程中获得全马氏体微观组织,保证焊缝强度。

不锈钢汽车零部件涂装前处理工艺设计及应用

不锈钢汽车零部件因其良好的耐蚀性,逐渐被更多的汽车零部件制造商采用。本文对不锈钢零部件涂装前处理工艺进行研究,通过采用脱脂、酸洗,以及钝化等化学处理方式设计出一套适用于不锈钢材质汽车零部件的涂装前处理工艺,并应用于日常生产。

2250热轧产线800 MPa级汽车厢体钢的开发

介绍了某钢厂2250热轧产线800 MPa级汽车厢体钢的开发过程及关键技术。通过优化合金设计、调整热轧工艺参数及特殊的两段冷却控制,成功研制出满足汽车厢体结构强度要求的800MPa级高强度钢。详细阐述了合金元素的选择依据及其对钢材性能的影响,分析了热轧过程中温度、冷却模式及冷却速度对组织演变和力学性能的作用机制。研究结果表明,所开发的高强度钢具有良好的强度、韧性及成型性,能够满足汽车轻量化与安全性的双重需求。

Influence of Oxide Morphologies on Galvanizability of Third Generation Automotive Steel

Focusing on improving the galvanizability of the third generation automotive steel, the effect of surface ox ide morphologies on the galvanizability was studied. The results show that the surface oxide types of sample steels by X ray photoelectron spectroscopy （XPS） analysis after annealing in different conditions are the same. Only MnO, MnO2 and Cr2O3 were detected and no complex oxide exists on the surface. Morphologies of surface oxides can greatly influence the galvanizability of the third generation automotive steel. Nodule-like oxide surface can contribute to better wettability and inhibition layer than vitreous film like oxide surface. Galvanized panels of nodule-like oxide surface steels only show pinhole sized bare spots, while panels galvanized from vitreous film-like oxide surface steels reveal larger areas of bare spots and uncoated areas. Inhibition layer observed in galvanized panels of nodule-like oxide surface steels is compact but not homogeneous; some inhibition layer grains are fine, and others are coarse, while the inhibition layer grains of panels galvanized from vitreous film-like oxide surface steels have a non-compact morphology with some particularly fine equiaxed crystals which developed deficiently.

热成形工艺研究进展

综述了热成形工艺在汽车轻量化领域中的研究与应用进展。热成形工艺通过将高强钢板加热至奥氏体状态后快速冲压成形,并迅速冷却以形成高强马氏体结构,有效提高零件强度并减少材料使用量。研究探讨了热成形钢种的力学性能、工艺特点、模具设计、生产效率及成形后回弹等问题,探讨了铝合金在热成形过程中的塑性流动行为,晶粒异常长大(AGG)现象的成因及其控制方法。通过精确控制化学成分和优化热成形工艺,显著提升了汽车安全性能和轻量化水平。随着技术的不断进步,热成形工艺在铝合金材料的应用上展现出巨大的潜力,有望为汽车工业的可持续发展做出更大贡献。

Preface for Special Column on Automotive Steel

It is believed that steels are still the most important materials for automobile in the foreseeable future because of the advantages in performance, cost, tolerance, fabrication, and recycling, etc. Over decades, a variety of steels are developed and widely used in the car body, from low carbon steel to IF steel, BH steel,

冷轧CP980辊压梯形管焊缝开裂原因分析与工艺优化

针对冷轧高强复相钢CP980在辊压钢管的焊缝开裂问题,通过分析组织、显微硬度和受力情况以及焊缝处组织及硬度,结果表明:冷轧CP980辊压梯形管焊缝开裂的主要原因为焊接速度、焊接电流参数选择不当,焊缝的淬硬组织在焊接内应力的作用下产生微裂纹,而焊缝受力不均加剧了裂纹的进一步扩展;通过降低焊接速度,提高焊接电流,改善焊缝的质量,同时减小梯形钢管成形过程中的约束力,梯形钢管的焊缝开裂问题得到有效解决。