镀锌DP780漏镀缺陷的成因分析与预防措施

为了解决热镀锌线生产高强度双相钢产品出现的表面漏镀问题,通过对缺陷的宏观与微观形貌以及成分进行分析,同时对漏镀的形成机理进行分析,确定影响表面漏镀的主要原因是双相钢中含有硅、锰等元素较多,容易发生选择性氧化,氧化物阻碍铁元素和锌液的铝热反应,形成漏镀。根据分析结果,采取提高炉区加热段露点和降低氢气含量的方法对漏镀进行预防。结果表明,同时提高炉区加热段露点和降低氢气含量能有效解决表面漏镀问题,取得了较好的实用效果,为进一步开发拓展更高级别镀锌双相钢提供了技术基础和理论依据。     

日本汽车用高强度合金化热镀锌钢板的开发

近年来,日本汽车向减轻自重和受冲击时确保安全性等方向发展,已经开发出具有良好成形性能590ＭＰａ级的高强度钢板,其中有以铁素体为基础的马氏体组织双相钢,这种双相钢的重要特点是低屈服比。汽车受高速冲击时吸收能量高,这样同时可以满足汽车对高强度和安全性方面的要求。从防锈蚀出发,汽车上正在使用的各种镀锌钢板,其中具有高腐蚀性能和廉价合金化热镀锌钢板的使用量逐渐增多。但是,这种高强度钢板在现行合金化热镀锌工艺中获得含有马氏体双相钢是困难的。低碳冷轧钢板为得到双相钢组织,在退火工序中的双相区采取快速冷却可获得以铁素体…     

汽车用冷轧超高强度双相钢的研发和生产

综述国内外汽车用冷轧超高强度双相钢的研究开发和生产工艺,包括冷轧超高强度双相、超高强度热镀锌双相钢的性能特点及成形性、高速冷却连退技术、锌淬技术等生产技术,提出汽车用冷轧超高强度双相钢的发展方向.     

双相钢表面山峰纹问题分析与控制

在生产过程中,热镀锌双相钢表面出现明显的山峰纹缺陷,严重影响热镀锌双相钢产品的表面质量。缺陷处有漏镀、锌层不均和抑制层形成不良等特征,基板表层有脱碳及微裂纹、表层毛刺突起等现象。通过分析认为,基板表层微裂纹是造成热镀锌双相钢表面山峰纹的根本原因。采用低温快烧的加热制度,适当降低轧制温度,合理控制除鳞及酸洗工艺,降低热卷厚度以降低冷轧压下率,可有效控制冷轧板浅表层微裂纹的形成,从而有效解决热镀锌双相钢表面山峰纹问题。     

点焊性良好的低碳当量型590～980MPa级合金化热镀锌钢板

以实现汽车车体轻量化、冲撞安全性和耐腐蚀为目的，川崎钢铁公司开发了高强度合金化热镀锌钢板(GA)。一般来说，GA钢板的高强度化是通过在钢中添加较多的合金化元素来实现的，但这种方法对合金化热镀锌性和点焊性有较大的影响。本文论述了新开发的590-980MPa级GA钢板的力学性能和钢板的点焊性。Mo、Ti、Nb等元素是连续热镀锌线热处理中最适宜的强化元素，在钢中加入这些元素可在不损失热镀锌性的情况下，使力学性能和冲撞安全性达到目前冷轧双相钢的水平。由于碳当量的降低，使点焊性能得到提高，特别是焊接区的延性比有显著的提高。     

超轻汽车车体用钢热镀锌的研究及应用现状

综述了超轻汽车车体用钢热镀锌的研究及应用现状,重点介绍了烘烤硬化钢、高强度IF钢、双相钢、相变诱导塑性钢等热镀锌的生产工艺和性能影响因素。     

退火温度和平整对冷轧热镀锌双相钢组织和性能的影响

本文在实验室试制了高强度冷轧热镀锌用双相钢,探讨了不同的退火温度和平整工艺对双相钢力学性能和组织的影响规律.研究表明:退火温度在800℃以上时,试制的低硅C-Mn-Cr系双相钢才能得到由铁素体和马氏体组成的性能优良的双相钢.平整工艺显著提高双相钢的屈服强度和屈强比,降低双相钢的延伸率,平整率小于1%时,有利于工业上得到综合性能良好的双相钢.     

宝钢率先开发出高强度热镀锌双相钢

目前,宝钢60公斤级别强度的热镀锌双相钢(包括纯锌和合金化产品)在国内研发成功,80公斤强度级别的热镀锌双相钢也将面世。这种钢在低变压区屈服强度提高很快,无屈服延伸和室温时效,弯曲性能良好,冲制成型时不易开裂。据国际超轻车身研究表明,未来车型设计中,钢材使用量的70%~80%会选用双相钢。宝钢生产的60公斤级别的热镀锌双相钢目前已供菲亚特轿车使用。宝钢率先开发出高强度热镀锌双相钢     

热镀锌双相钢表面粗糙问题分析与控制

 目前强度级别较高的双相钢产品已经可以普遍采用热镀锌工艺生产,热镀锌双相钢在生产过程中,表面出现明显的粗糙缺陷,形成边部与中部的色差,严重影响热镀锌双相钢产品表面质量。粗糙缺陷伴随粗糙度异常升高、锌层不均、抑制层形成不良、基板表面微裂纹等现象。分析认为,基板表面微裂纹是造成热镀锌双相钢表面粗糙的主要原因。热轧态组织和冷轧压下率是决定冷硬板浅表层微裂纹形成的关键因素。通过优化卷取温度及热轧卷厚度,改善热轧态组织及降低冷轧压下率,可有效控制冷轧板表面浅表层微裂纹的形成,从而良好解决热镀锌双相钢表面粗糙问题。     

冷轧热镀锌双相钢成分设计模型化的研究

文章对冷轧热镀锌双相钢主要合金成分对产品力学性能的影响进行了系统的研究，并在此基础上建立起力学性能与主要合金成分之间的数学关系式，从而实现了冷轧热镀锌双相钢合金成分设计的模型化，为今后优化冷轧热镀锌双相钢成分设计，克服现有成分设计的盲目性，节省开发成本和缩短开发周期提供了有效途径，同时也为今后开发不同级别的系列化冷轧热镀锌双相钢产品提供了有利工具。     

Hot-dip Galvanizing of Carbon Steel after Cold Rolling with Oxide Scale and Hydrogen Descaling简

A new processing method for producing hot dip galvanized steel is designed and tested, in which pickling is skipped. Hot-rolled low carbon steel sheets are roiled with oxide scale in an experimental mill at room temperature, prior to annealing under a 20% hydrogen reducing atmosphere and galvanizing on a hot-dip galvanizing simulator. Micro-cracks formed in the oxide scale during cold rolling roughen the steel surface and enlarge the specific surface. Through-thickness cracks provide transport channels for hydrogen, and hence the reduction of oxide scale is en- hanced. When the sheet is dipped in the zinc bath, cracks are submerged by liquated zinc and the defects are not dis- tinct after hot-dip galvanizing. The overlay coating occludes with rough surface of the sheet, whereby a superior coat- ing adherence is realized.     

Ti-IF钢基板晶粒对合金化热镀锌镀层的影响

利用合金化热镀锌模拟的方法,研究了Ti-IF钢基板晶粒对合金化热镀锌镀层的影响。首先利用不同的退火温度分别获得等轴晶和未再结晶基板,然后进行热镀锌并在不同温度下进行合金化处理,分别获得纯锌、欠合金化及合金化镀层。利用扫描电镜和光学显微镜观察镀层的表面、截面形貌以及镀层/基板界面上的Fe-Al阻挡层形貌。结果表明,等轴晶基板表面的GA镀层＂火山口＂形貌明显,微观上镀层厚度不均匀;未再结晶基板表面的GA镀层则表面较平,无＂火山口＂形貌,镀层厚度均匀。造成上述差异的原因是：等轴晶基板晶粒表面的Fe-Al阻挡层不均匀,而未再结晶基板晶粒表面的阻挡层均匀,从而导致合金化过程中合金化速度和程度的差异。     

国内外钢带连续热镀锌退火炉与合金化炉的技术发展

综述了近年来国内外在钢带连续热镀锌退火炉与合金化炉方面的最新技术进展,分析了国内外带钢热镀锌设备及工艺的技术特点、发展趋势,并介绍了集团公司自主研发的热镀锌退火炉的最新研究成果.     

新型超高强TRIP钢组织性能研究

采用增大冷轧压下量以及合理的连续退火工艺,得到了含有大量稳定残余奥氏体的一种新型适合于热镀锌的超高强贝氏体基体TRIP钢。该钢将硅含量降低到0.28%,加入0.08%的磷,弥补了由于硅含量降低而引起的强度损失,同时有效阻止渗碳体的析出,使室温组织中含有17.6%块状或片层状残余奥氏体。添加钒进一步提高了基体强度。贝氏体基体的TRIP钢具有优良的综合力学性能:抗拉强度1030MPa,强塑积达到22660MPa·%。     

Galvanizability of Complex Phase High Strength Steel

Complex phase (CP) steels have very high ultimate tensile strengths, resulting from the use of specific alloying elements, which improve the hardenability but cause difficulties when applying a zinc coating by means of continuous hot‐dip galvanizing. The galvanizability of a cold rolled 1000MPa complex phase steel was investigated by monitoring the surface chemistry before dipping and evaluating the quality of the zinc coatings applied by a laboratory hot‐dipping simulator. Two steel compositions with different Cr levels were used. The influence of the most important production parameters, the annealing temperature and the dew point of the annealing atmosphere, was investigated. Both steel compositions were galvanizable, but both the surface appearance and zinc coating adhesion were improved when low Cr contents were used. At a low dew point of ‐30°C, Cr, Mn and Si segregated to the surface and the presence of Mn₂SiO₄ could be demonstrated. At high dew point of +10°C, less oxides were present at the steel surface. There was no effect of the annealing temperature on the coatability.     

带钢热镀锌镀层单位面积质量神经网络预测模型

 为了解决带钢连续热镀锌镀层单位面积质量偏差大、调节时间长、锌原料浪费等问题,利用生产过程历史数据建立了气刀压力预设定模型和镀层单位面积质量预测模型。根据带钢热镀锌生产实践,分析了镀层单位面积质量的影响因素和控制策略。收集系统稳态样本数据并进行多变量偏相关分析,证明镀层单位面积质量与气刀压力、气刀距离、带钢速度相关。根据样本数据,以镀层单位面积质量、气刀距离、带钢速度为输入变量,采用BP神经网络建立气刀压力预设定模型,预设定精度达到3 000 Pa。收集热镀锌过程时间序列样本数据,采用NARX动态神经网络建立镀层单位面积质量预测模型,预测精度达到6 g/m2,为实现带钢热镀锌镀层单位面积质量闭环控制奠定了基础。     

镀锌和退火两用热镀锌机组

热镀锌和连续退火两用生产机组是一种新的机组型式,可以更好地适应市场对于热镀锌产品和连续退火产品的不同需求。针对不同的现有热镀锌机组,给出了实现热镀锌和连续退火两用生产的合理、完善的工艺方案和设备配置,这不仅完全保留了现有热镀锌产品的生产,而且能够生产出全工艺的连续退火产品。通过工程实践证明,在现有热镀锌机组上实现镀锌和连续退火两用生产是可行的,是提高现有热镀锌机组适应市场能力的快捷有效的途径。     

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/基板界面结合力,可以通过提高退火气氛露点促进合金元素内氧化,从而减少和细化还原铁/基板界面氧化物的数量和尺寸,避免形成连续的界面氧化膜。     

Effect of Chromium on Microstructure and Mechanical Properties of Cold Rolled Hot-dip Galvanizing DP450 Steel

Two cold rolled hot-dip galvanizing dual phase(DP) 450 steels with different amounts of chromium were designed and the effects of the chromium concentration and galvanizing processes on the microstructure and mechanical properties were also investigated. The results show that the experimental steels exhibit typical dual phase microstructure character. However, the ferrite phase of steel with higher chromium is more regular and its boundaries are clearer. Meanwhile, martensite austenite(MA) island in steel No. 2 is diffused and no longer distributes along the grain boundary as net or chain shape. More MA islands enriched with Cr element can be found in the ferrite grains, and the increment of Cr element improves the stablity of the austenite so that the austenite has been reserved in MA islands. In addition, the experimental steel with higher chromium exhibits better elongation, lower yield ratio and better formability. The mean hole expanding ratio of steels No. 1 and No. 2 is 161.70% and 192.70%, respectively.     

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.