Analysis of Microstructure and Mechanical Properties of Different Hot Stamped B‐bearing Steels

Hot stamping is a technique to produce ultra high strength automobile components. The common material used in hot stamping process is coated and/or uncoated 22MnB5 boron alloyed steel. Ferritic‐pearlitic microstructure in as‐delivered sheets is transformed to fully lath martensitic after hot stamping. In the present research, hot stamping under water or nitrogen cooling media was investigated using different boron alloyed steel grades. Microstructural analyses, linear and surface hardness profiling as well as tensile tests of hot stamped samples were performed. Various microstructures of fully bainitic and/or fully martensitic were produced. The resulting microstructures provided yield strengths of 650–1370 MPa and tensile strengths of 850–2000 MPa. There is an optimum carbon equivalent content for which the highest formability index value, UTS × A₂₅, is achieved. Using a nitrogen cooled punch resulted in higher yield strength without significant changes in ultimate tensile strength. It is concluded that a wide range of B‐bearing steels having an extended carbon equivalent range with an acceptable formability index value can be used by increasing the cooling rate in the die assembly.     

State‐of‐the‐Art of Friction Stir Processing

The aim of this study is to present an overall view of friction stir processing (FSP), including the method, the state‐of‐the‐art regarding current studies, and possible applications. FSP is a solid‐state thermo‐mechanical processing method. It can be used to produce defect‐free, recrystallized, homogeneous, fine grained microstructures. Structures can be processed at specific locations, through‐section or to a desired depth, or entirely. The benefits obtained with FSP include elimination of casting defects and refinement of microstructures resulting in improved strength, ductility, resistance to corrosion and fatigue, and formability (including high strain rate superplasticity). Alsosurface composites can be produced by FSP.     

热冲压钢镀层技术的研究现状

简要介绍了汽车用钢热冲压工艺技术的特点及其对镀层的性能要求,在此基础上着重描述了近年来国内外热冲压钢镀层技术的研究进展,详细列出了Al-10Si镀层的使用性能及GI(Galvanized)、GA (Galvanealed)镀层的研究状况.针对热冲压钢镀层产品的使用现状和未来需求方向,指出除了Al-10Si镀层外,发展GI/GA热冲压镀层技术是未来热冲钢发展的一个重要方向.     

热镀锌液中Al含量及工艺对TRIP钢表面质量的影响

通过对TRIP590钢进行不同Al含量锌液热镀锌对比试验,研究了锌液中不同Al含量及热镀锌工艺对TRIP钢镀层性能的影响。试验结果表明,镀锌液中加入5%Al,均热退火温度800℃,可明显提高TRIP钢的镀层质量,改善热镀TRIP钢的抗腐蚀性能。     

Effect of Mischmetal on Oxidation Resistance of 55Al－Zn Alloy Hot Dip Coating

ＥｆｆｅｃｔｏｆＭｉｓｃｈｍｅｔａｌｏｎＯｘｉｄａｔｉｏｎＲｅｓｉｓｔａｎｃｅｏｆ５５Ａｌ－ＺｎＡｌｌｏｙＨｏｔＤｉｐＣｏａｔｉｎｇＺｅｎｇｐｅｎｇ；（曾鹏）（ＧｕａｎｇｄｏｎｇＭｅｃｈａｎｉｃａｌＣｏｌｌｅｇｅ，Ｇｕａｎｇｚｈｏｕ５１０６４３，Ｃｈ...     

稀土元素对热镀铝锌镀层的影响研究

针对铝锌热镀板存在的问题,通过试验研究了添加稀土元素对热镀铝锌合金镀层的影响,结果表明:添加稀土后提高了铝锌镀板的总体性能,为该类镀板质量的改进和应用领域的延伸提供了途径。     

Determination of Thermal and Mechanical Material Properties of Ultra‐High Strength Steels for Hot Stamping

Direct and indirect hot stamping presently constitutes one of the most innovative forming technologies in the automotive industry through the combination of forming and hardening in one process step or line. Thus, structural components with strength up to 1600 MPa can be accomplished with the quench hardenable ultra‐high strength steel 22MnB5. With respect to the numerical investigation of the feasibility of different parts the knowledge of various thermal and mechanical material characteristics determined under process relevant conditions are required. Within the scope of this paper different experimental methods will be introduced for the determination of material properties according to the typical time‐temperature characteristics of the hot stamping process, as well as the modelling of it as input data for the FE analysis.     

TiAl涂层对Ti3Al合金的热腐蚀防护

利用磁控溅射的方法在Ti3Al合金上溅射Ti-48Al-8Cr-2Ag涂层,研究涂层对Ti3Al合金热腐蚀行为的影响。热腐蚀采用浸盐法,在900℃25%Na2SO4+75%K2SO4熔盐中进行,利用带能谱的扫描电镜(SEM/EDX)对腐蚀膜进行观察分析。结果表明,在熔盐热腐蚀中,Ti3Al合金表面发生大面积脱落,而涂层试样表面腐蚀膜结合牢固。涂层对基体具有很好的防护作用。     

高发射率涂料应用于高炉热风炉的节能效果

应用数值模拟验证高发射率涂料在热风炉内的使用效果并比较涂料的不同使用区域对热风温度的影响,得出高发射率涂料在高炉热风炉内的最佳使用区域为高温区。应用这一结果在两座热风炉上进行工业对比试验,经过热诊断测试判定高发射率涂料的节能效果。热诊断结果表明,应用高发射率涂料可提高热风温度25℃,降低废气温度13℃,提高热效率5%。     

热风炉蓄热体高发射率节能涂层的制备及应用

采用超细化技术制备出微纳米涂料,并在高炉热风炉蓄热体表面成功制备出微纳米节能涂层,涂层的发射率达到0.93,涂层厚度约为300μm.该高发射率涂层强化了气-固相间的辐射传热和内部导热,使蓄热体蓄热速率和热量增加.在高炉热风炉上的应用效果表明,涂层能使热风温度分别提高57℃和28℃,同时减小送风温度的波动,降低废气排放温度,节约燃料消耗10%左右.     

Components with Optimised Properties due to Advanced Thermo‐mechanical Process Strategies in Hot Sheet Metal Forming

The increasing demand for car body structures with optimised energy absorption capacity and the ability to maintain their structural integrity even under the highest dynamic load has stimulated the development of new thermo‐mechanical process routes for the production of pressed and roll‐formed sheet metal parts in order to combine both extreme formability and a highest level of strength for the final product. These process routes offer a high potential for further improvements in the field of strength‐strain correlation and load adapted property distribution of the components, as well as an enhanced process productivity. A new type of thermo‐mechanical tailored processing of sheets and profiles is presented, based on the adequate application of differential heating and cooling strategies. By the control of local microstructural effects, the components develop a property distribution adapted to complex load situations. New tooling concepts complement these developments in order to ensure high process efficiency and reliability.     

溶剂法热轧镀锌板基体形貌对镀层表面质量的影响

由于溶剂法热轧板镀锌可生产出用于建筑的厚镀锌板,其成本较低,市场竞争力很强,目前深受广大企业的青睐,但是在生产中表面质量难以控制。介绍了采用溶剂法热镀锌的实际生产工艺,通过采用与冷轧板比较、人为制造划痕和凹坑把缺陷放大等手段,着重分析基体表面状态对镀层表面质量的影响,并从微观角度分析其形成原因。     

Corrosion Resistance of Different Metallic Coatings on Press‐Hardened Steels for Automotive

The corrosion resistance of laboratory press‐hardened components in aluminized, galvanized or galvannealed boron steels was evaluated through VDA 621‐415 cyclic test for the automotive industry. 22MnB5 uncoated steel for hot stamping and standard galvanized steel for cold forming were also included as references. Corrosion resistance after painting (cosmetic corrosion) was quantified by measuring the delamination of electro‐deposited paint from scribed panels. The rusting on their edges was used for determining the cut‐edge corrosion resistance. The corrosion resistance on unpainted deformed panels (perforating corrosion) was quantified by mass losses and pit depth measurements. Zinc‐coated boron steels were found to be more resistant to cosmetic corrosion than the other materials, and slightly more resistant to cut‐edge corrosion than the aluminized one. Red rust apparition could not be avoided due to the high iron content in all these hot‐stamped coatings. The three coated boron steels showed similar performances in terms of resistance to perforation. Aluminized boron steel presents the advantage of being less sensitive to hot‐stamping process deviation. Its robustness has been proved for many years on cars.     

Effect of the Charging Temperature on the Hot Ductility of Nb‐Containing Steel in the Simulated Hot Charge Process

In order to develop a comprehensive understanding of the effect of hot charging temperature on the hot ductility of a Nb‐containing steel, direct hot charging process was simulated by using a Gleeble thermo stress/strain machine. Three kinds of thermal histories were introduced to assess the hot ductility of the steel during continuously cast, hot charging, and cold charging process by means of hot tensile test in relation to surface cracking of hot charging processed steel slabs. The ductility of the specimens charged at the temperature within the range of ferrite/austenite two‐phase region and charged at the temperature just below the A_r1 of the steel is largely reduced. These results can be ascribed to the retained ferrite films at the boundaries of austenite encouraging voiding at the boundaries and these voids gradually link up to give failure around 750°C, and the combination of inhogeneous austenite grain size and precipitations aggravating the ductility trough by encouraging grain boundary sliding at 950°C. The steel via the conventional cold charge process experienced a complete phase transformation from austenite to ferrite and pearlite structure during the cooling to the ambient temperature. This steel can be charged into a reheating furnace and rolled without experiencing hot embrittlement due to the recrystallization and the precipitates are trapped inside a newly formed grain of austenite. In comparison with the hot ductility results, the hot tensile strength is only slight influenced by the charging temperature.     

钢丝镀锌层防锌锈渗Cr工艺研究

Zn是一种较活泼的两性金属,在酸、碱性环境中很容易被腐蚀而产生锌锈,将热镀锌层进行渗Cr处理,在其表面形成一层致密的Zn、Cr合金氧化物膜层,能有效地防止镀层产生锌锈,使镀锌钢丝使用寿命提高40倍。     

Influence of Strain Rate on Hot Ductility of a V‐Microalloyed Steel Slab

The hot ductility and malleability of a vanadium‐microalloyed steel is investigated by means of tensile and compression tests at temperatures ranging from 700 to 850°C and strain rates of 3 × 10^?4 to 0.3 s^?1. The deformation tests are performed after austenitization and cooling to test temperature. The so‐called second ductility minimum is located around 750°C for all strain rates except for the highest one, where no ductility trough is observed. Ductility steadily increases with strain rate at a given temperature, and the fracture mode progressively changes from intergranular to transgranular. In the region of minimum ductility, intergranular cracking occurs at low strain rates by void nucleation, growth and coalescence within thin layers of deformation induced ferrite covering the austenite grain boundaries. Cracking is favoured by V(C,N) precipitation associated with the γ/α phase transformation. Ductility remains low above the temperature of minimum ductility, where no apparent ferrite formation is observed (790 °C). Void formation takes place as a result of grain boundary sliding in combination with matrix and grain boundary precipitation. These voids are able to grow and link up forming intergranular cracks. Ductility increases with strain rate mainly due to the short time available for precipitation as well as for intergranular void growth and coalescence.     

A Newly Developed Upper‐Bound Approach for Calculating the Width Flow in Hot Rolling

This paper presents an investigation of the 3D metal‐forming process during hot flat rolling by an upper‐bound approach. The general aspects of this limit analysis refer to the volume deformation taking into account a polynomial propagation of the free side surfaces. In this approach the deformation region is limited by the roll‐gap entrance and exit with parallel planes. It is characterized by a non‐linear velocity field. A mathematical model of an upper‐bound calculation for the symmetrical flat rolling is developed in order to examine the influence of the most relevant functions, namely the velocity field together with the boundary conditions. A comparison of reasonable onsets is proposed. Therefore, the study can offer useful knowledge for better prediction of lateral flow.