冷轧中Mn－TRIP钢的机理与研发进展

中Mn-TRIP钢作为第三代汽车用钢研发的重点,从21世纪初就得到越来越多国内外汽车及钢铁企业的关注。介绍了中Mn-TRIP钢种的最新机理研究与工业化进展。中Mn-TRIP钢主要由纳米级至微米级铁素体和亚稳奥氏体构成,有时也含有一定比例的马氏体,其组织特征和变形机理与其他先进高强钢有显著不同。众多科研院所做了大量工作,包括中Mn成分设计、相变精细结构表征、超细晶Lüders应变行为、相变诱导加工硬化、奥氏体不全位错滑移等,从而对中Mn-TRIP钢有了更为深入的认识。1 000~1 200 MPa级冷轧中MnTRIP钢和热镀锌中Mn-TRIP钢已经成功实现了工业化试制,其强塑积大于35 GPa·%,标志着冷轧中Mn-TRIP钢正逐步由基础研究向工业化生产推进。     

Friction in sheet forming with soft and hard tooling

Comparative studies were conducted with the drawbead-simulation (DBS) test on a bare steel, a galvannealed steel, three electrogalvanized steels, and a hot-dip galvanized steel as representatives of the major classes of steel sheets used in the automotive industry. Drawbeads of bare, plasma-nitrided and hard chromium-coated tool steels were prepared with various surface finishes. The zinc alloy Kirksite represented the soft tooling used in die tryout. A low-viscosity mineral oil, neat and compounded with oleic acid or a borate compound, served as lubricant. Correlation between friction on hard and soft surfaces was governed primarily by the extent and stability of a zinc transfer layer on the hard beads. Kirksite may be regarded as the equivalent of a very stable, more hard and less reactive transfer film. Correlation was generally better when the sheet surface was capable of entrapping the lubricant, when oleic acid (a boundary additive) was absent, borate (a parting compound) was present, and the plowing component of friction was low.     

热轧钢材免酸洗还原退火热镀锌技术进展

介绍了热轧钢材免酸洗还原退火热镀锌的主要技术进展，从钢材氧化铁皮的精细化控制技术入手，结合氧化铁皮退火还原和热浸镀锌过程中各个控制环节的研究成果，进行了氧化铁皮的精细化控制、氧化铁皮高效还原以及基于免酸洗还原退火的热镀锌等关键技术的开发，并进行试制生产。试制结果表明，采用免酸洗工艺生产的热浸镀锌板表面质量良好，锌层延展性优良，能够满足使用要求，同时大幅降低吨钢成本，能够创造更大的经济效益。     

双相钢中铝含量对表面氧化物及抑制层形貌的影响

 对3种不同铝含量的热镀锌双相钢进行连续退火镀锌模拟试验。研究表明：wAl=009%的双相钢表面的氧化物形貌为颗粒状和长条状的氧化物;XPS分析表明,这两种氧化物为MnO和Cr2O3。含铝wAl=012%的双相钢表面均匀分布扁平状的氧化物,氧化物平均直径为1262nm。含铝wAl=04%的双相钢表面为细小弥散分布的氧化物,平均直径为707nm。除了MnO和Cr2O3,这两种双相钢表面还生成了Al2O3。Fe-Al抑制层晶粒之间的空隙程度随着铝含量的增加逐渐变大,抑制层的致密度下降,其中含铝wAl=04%的双相钢表面的抑制层晶粒粗大。从表面氧化物与锌液有效铝之间反应的角度出发解释了抑制层形貌的变化。     

无机固体润滑处理热镀锌钢板的表面特性

为了改善汽车用热镀锌钢板的冲压成形性能,开发出了一种新型无机固体润滑处理热镀锌钢板。对该无机固体润滑处理热镀锌钢板的表面摩擦特性与涂装性能进行了分析,结果表明,新型无机固体润滑处理技术可以改善热镀锌钢板的表面摩擦特性,提高热镀锌钢板成形性,同时该润滑处理对热镀锌钢板的磷化性能、涂装后的耐腐蚀性能没有不良的影响,满足汽车行业常规涂装工艺生产要求。     

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.     

Surface Selective Oxide Reduction During the Intercritical Annealing of Medium Mn Steel

Third generation advanced high-strength steels achieve an excellent strength–ductility balance using a cost-effective alloy composition. During the continuous annealing of medium Mn steel, the formation of an external selective oxide layer of MnO has a negative impact on the coating quality after galvanizing. A procedure to reduce the selective oxide was therefore developed. It involves annealing in the temperature range of 1073 K to 1323 K (800 °C to 1050 °C) in a HN_x gas atmosphere. Annealing at higher temperatures and the use of larger H₂ volume fractions are shown to make the gas atmosphere reducing with respect to MnO. The reduction of the surface MnO layer was observed by SEM, GDOES, and cross-sectional TEM analysis.     

热镀锌TRIP钢还原铁/基板界面表征

预氧化还原工艺是改善热镀锌先进高强钢(AHSS)可镀性的有效手段之一。当它用于生产热镀锌先进高强钢时,有时也会出现镀层附着性不良的问题。为了明确还原铁/基板界面对热镀锌高强钢镀层附着性的影响,以预氧化还原工艺生产的、镀层附着性不同的热镀锌TRIP钢为研究对象,采用GDOES、SEM、FIB、TEM等手段研究了还原铁/基板界面位置的微观特征。结果表明,镀层附着性不良表现为150～300 nm厚的还原铁层与镀层一起从基板表面脱落,失效发生在还原铁/基板界面,而非镀层/还原铁界面,与常见的镀层/基板界面Fe₂Al₅抑制层缺失引起的镀层附着性不良明显不同。镀层附着性不同的试样在还原铁/基板界面位置均存在硅、锰元素富集,但硅、锰富集程度有差异,镀层附着性不良试样的界面硅、锰富集更高。还原铁/基板界面氧化物形态显著影响了还原铁/基板界面的结合力,当还原铁与基板之间形成连续的氧化膜时,界面结合力较差,易发生界面分离;当还原铁/基板界面形成细小的、不连续的氧化物颗粒时,界面结合力较好。在对热镀锌先进高强钢实施预氧化还原工艺时,为了获得良好的还原铁/基板界面结...     

Fe?Mn?Al?C系中锰钢的研究现状与发展前景

随着汽车保有量的提高,能源消耗和环境问题对汽车用钢提出了轻量化的要求。目前正在发展的第三代汽车用钢的研究思路是将加入轻量元素以“轻”和增强增塑以“薄”相结合。Fe?Mn?Al?C系中锰钢作为第三代汽车用钢的主要组成部分,是当今的研究热点之一。本文总结了近些年国内外Fe?Mn?Al?C系中锰钢的研究文献,从生产成本、力学性能等方面介绍了Fe?Mn?Al?C系中锰钢的优势。从成分设计、工艺设计、组织特征、变形及断裂机制等多个方面出发,对文献进行分析,总结出了合金成分、工艺路线和组织特征对性能的影响规律。阐述了奥氏体层错能及其稳定性对中锰钢变形机制,尤其是相变诱导塑性（TRIP效应）的影响规律。最后对目前Fe?Mn?Al?C系中锰钢研究过程中存在的争议问题进行了总结,展望了未来的发展趋势,以期为中锰钢的后续研究和实际生产提供参考。      

镀锌板光整过程表面粗糙度控制技术

 热镀锌带钢是高端汽车板的主要原料,用户对其表面质量控制提出了较高要求。首钢某热镀整机组的镀锌带钢出现了上下表面粗糙度分布不均匀,表现为带钢下表面粗糙度值高于上表面。针对此问题进行了大量的现场试验和理论研究。分析认为,光整过程的非对称因素是造成镀锌带钢表面缺陷的主要原因。以非线性有限元软件ABAQUS为仿真平台,建立二维平整轧制有限元模型,通过非对称仿真计算验证了镀锌带钢表面缺陷的产生原因,并且提出了优化光整轧制力 张力配比、辅助辊调整的改进措施,从而圆满地解决了镀锌带钢的表面质量问题,研究结果对生产实践具有借鉴意义。     

高Al低密度钢的高温氧化行为

为观察Fe-Mn-Al-C系高Al低密度钢在高温下的抗氧化性能,采用氧化增重法测定了4种合金在950~1 100℃下的氧化动力学曲线。通过SEM观察氧化层形貌特征,利用线扫描能谱分析氧化后合金元素的变化,分析了28Mn-10Al合金氧化膜发生膨胀破裂的原因。结果表明,Al元素提高钢的抗氧化性,而Mn元素则降低Al的抗氧化性。抗氧化性较好的28Mn-12Al、20Mn-10Al合金表层未发现Fe的氧化,而氧化严重的28Mn-8Al合金氧化层Fe元素含量较高。28Mn-12Al合金抗氧化性最好,氧化膜的连续性及致密性优于其他3种合金,氧化物连续且晶粒细小,在氧化过程中具有一定的防护作用。     

内氧化对热镀锌高强钢镀层/基板界面的影响

 由于高强钢中添加的Si、Mn等合金元素会在退火时会发生选择性氧化,从而影响镀液与带钢之间的润湿性,因此热镀锌高强钢生产存在可镀性的难题。为了提高热镀锌高强钢的镀层附着性,以不同镀层附着性的连续热镀锌0.2%C-1.8%Si-1.8%Mn高强钢为研究对象,采用GD-OES、SEM、FIB、TEM等研究了镀层/基板界面抑制层与基板次表层内氧化层的特征,同时采用模拟退火试验研究了退火气氛露点对内氧化层形成的影响,揭示了退火气氛露点、内氧化层厚度、抑制层覆盖率与镀层附着性之间的相关性。结果表明,该热镀锌高强钢镀层附着性优劣由镀层/基板界面位置抑制层决定,当抑制层覆盖率达到80%以上时,可获得良好的镀层附着性。内氧化层厚度对抑制层覆盖率的影响存在临界厚度,约为0.58 μm。当内氧化层厚度由0逐渐增加至0.58 μm时,抑制层覆盖率由约10%增加至约80%;当内氧化层厚度由0.58进一步增加至3.85 μm时,抑制层覆盖率略有增加,介于80%~90%之间。提高退火气氛露点可以促进基板次表层形成内氧化,在退火温度分别为800和870 ℃、保温时间为120 s、退火气氛为N₂-5% H₂(体积分数)的试验条件下,当退火气氛露点由-40 ℃提高到+10 ℃时,内氧化层厚度由基本为0提高至3~5 μm。为了获得合适的内氧化层厚度,建议将0.2%C-1.8%Si-1.8%Mn高强钢的退火气氛露点控制在-20~-10 ℃范围内。     

Behaviour Model of Austenitic Stainless Steels for Automotive Structural Parts

One of the most important preoccupation of car manufacturers is to reduce emissions and hence to reduce weight of cars. One of the outstanding materials able to reduce weight while at the same time keeping the same crash absorption and hence safety, is austenitic steel. Austenitic stainless steels are used in crash relevant parts of cars. Moreover, designers can use their very good corrosion resistance and their well known surface aspect for structural visible parts like wheels, cross members, roof panels or tailgates. In this paper, stainless steels for automotive use are presented in detail. First, their chemical composition and tensile properties are explained. Then, a model for forming and crash behaviour is described. Using this model, stainless steels can be engineered into automotive parts and thus stainless steel can be considered as a workable and predictable material for the automotive industry.     

Advanced HSLA Steels for Automotive Use

Characteristic HSLA steels for automotive use are introduced in which both of precipitation and microstructure is controlled to obtain suitable mechanical properties.For outer panels such as fender,the combination of low yield strength,high tensile strength and deep-drawability were realized by controlling the distribution of NbC and precipitation free zone.The other steel,developed for chassis parts such as lower arm,utilizes extremely fine interphase precipitation to obtain high yield strength and excellent hole expansionability.Both steels have contributed to the reduction of weight in car body.     

Surface Oxidation of the High-Strength Steels Electrodeposited with Cu or Fe and the Resultant Defect Formation in Their Coating during the Following Galvanizing and Galvannealing Processes

This study examined the surface oxidation of high-strength steels electrodeposited with Cu or Fe and the resultant defect formation in their coating during the following galvanizing and galvannealing processes. The high-strength steels were coated with an Cu or Fe layer by the electroplating method. Then, the coated steels were annealed in a reducing atmosphere, dipped in a molten zinc, and finally transformed into galvannealed steels through the galvannealing process. The formation of Si and Mn oxides on the surface of the high-strength steel was effectively suppressed, and the density of surface defects on the galvanized steel was significantly reduced by the pre-electrodeposition of Cu and Fe. This effect was more prominent for the steels electrodeposited at higher cathodic current densities. The finer electrodeposit layer formed at higher cathodic current density on the steels enabled the suppression of partial surface oxidation by Mn or Si and better wetting of Zn on the surface of the steels in the following galvanizing process. Furthermore, the pre-electrodeposited steels exhibited a smoother surface without surface cracks after the galvannealing process compared with the untreated steel. The diffusion of Fe and Zn in the Zn coating layer in the pre-electrodeposited steels appears to occur more uniformly during the galvannealing process due to the low density of surface defects induced by oxides.     

Galvanizing and Galvannealing Behavior of CMnSiCr Dual-Phase Steels

Alloying elements, such as Mn, Mo, Si, and Cr, are commonly used to enhance the strength of advanced high-strength steels. Those elements also play an important role in the hot-dip galvanizing (GI) and galvannealing (GA) process. In this study, two kinds of CMnSiCr dual-phase steels were galvanized and galvannealed using a hot-dip simulator to investigate the effect of the alloying elements on the microstructure of the GI and GA coatings. The results showed that the dual-phase steels had good galvanizability because no bare spots were observed and the Fe-Zn phases were readily formed at the interface. However, the alloying reaction during the GA process was significantly hindered. XPS analysis showed that external oxidation occurred under an extremely low dew point [213 K to 203 K (?60 °C to ?70 °C)] atmosphere during the annealing prior to hot dipping. However, most of the oxides were reduced during the GI process. After the GI process, the Al was present as solid solutes in the Fe-Zn phase, suggesting that the Fe-Zn phase was formed from the transformation of the Fe-Al inhibition alloy. Meanwhile, the solubility of Si in the ζ phase was extremely low. With continued GA reaction, the ζ phase transformed into the δ phase, which contained approximately 1.0 at.pct Si. The Si also diffused into the Zn layer during the GA reaction. Hence, the ζ phase did not homogeneously nucleate at the steel substrate/Zn coating interface, but was found at the area away from the interface. Therefore, the Fe-Zn phases on the CMnSiCr dual-phase steels were relatively non-uniform compared to those on interstitial-free steel.     

Analysis of the influence of the hot-rolling material on galvanized product

Hot-rolled galvanized steel sheet is made from hot-rolled pickled sheet by continuous hot-dip galvanizing process.Without the cold-rolling process,it greatly reduces the operating costs and saves investment for shorter process and lower energy consumption.The economic advantage is obvious.The characteristics of high-yield and low cost will greatly enhance the competitiveness of enterprises in the market.There are big differences between the substrates of hot-rolled galvanized steel sheet and cold-rolled galvanized steel sheet in surface roughness,chemical elements,and surface defects.These factors directly affect on the quality of galvanized sheet.Pickling process is used to remove the oxide layer which is formed on the surfaces of hot-rolled steel sheet.The surfaces must be thoroughly cleaned for the oxide layer will seriously affect the adhesion of galvanized coating.Residual impurities,Carbon concentrating and other problems must not be caused during pickling as well.Therefore,the quality of galvanizing depends on the quality of pickled sheet surfaces.Experimental methods such as AES,XPS,SEM,OM are employed during the research for detailed analysis on the effects of hot-rolled plates and hot pickling plates on the quality of hot-rolled galvanized products.     

Selective Oxidation of TWIP Steel During Continuous Annealing

The selective oxidation of Al‐free and Al‐added TWIP steel after full austenitic annealing at 800°C in a N₂ + 10%H₂ gas atmosphere with a dew point of ?17°C was investigated by means of transmission electron microscopy. A thick MnO layer was formed at the surface of Al‐free TWIP steel after the recrystallization annealing. Small crystalline c‐xMnO · SiO₂ (x > 2) particles and amorphous a‐xMnO · SiO₂ (x < 0.9) particles were found at the MnO/steel interface. In the subsurface, the Mn depletion resulted in the formation of a narrow ferrite layer. The annealing of the Al‐added TWIP steel also resulted in the formation of a thick MnO surface layer. At the MnO/steel interface, Kirkendall voids were formed between the amorphous a‐xMnO · SiO₂ (x < 0.9) oxide and crystalline c‐xMnO · Al₂O₃ oxide in the case of Al‐added TWIP steel. In the subsurface, a thin layer was depleted of Mn and the original austenite had transformed into ferrite. Internal oxidation of Al to Al₂O₃ and the formation of crystalline c‐xMnO · Al₂O₃ (x > 1) compound oxide particles were found to occur at the grain boundaries of the Mn‐depleted ferritic zone. The present contribution highlights the implications of the selective oxidation of TWIP steels for their processing in continuous annealing and continuous hot dip galvanizing lines.     

IF钢合金化热镀锌钢带表面缺陷的研究

采用扫描电镜、能谱分析、X射线衍射和辉光放电光谱等技术对IF钢合金化热镀锌镀层表面缺陷形成的原因进行了分析.研究结果表明,黑斑缺陷是由悬浮渣和面渣与硅氧化物夹杂形成的;灰斑缺陷是由底渣形成的;深色波纹缺陷是由合金化工艺不当造成锌铁合金层局部生长到镀层表面形成的.