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.     

Influence of annealing conditions on the galvanizability and galvannealing properties of TiNb interstitial-free steels, strengthened with phosphorous and manganese

A high-strength interstitial-free (HS IF) steel, solution strengthened with P and Mn, was hot-dip galvanized and galvannealed in a laboratory hot-dip simulator. The dew point of the N₂-H₂ annealing atmosphere during recrystallization was varied, and the effect of the dew-point changes on the galvannealing kinetics was studied. Annealing in a high-dew-point N₂-H₂ atmosphere improved the wettability by the zinc and the galvannealing reactivity of the Mn-P-added IF steels considerably. Scanning electron microscopy (SEM) analysis and glow discharge optical emission spectroscopy (GDOES) depth profiles of the surface of the steel sheet and the subsurface region revealed clear differences in oxidation mode after recrystallization annealing. Plane-view SEM and transmission electron microscopy (TEM) analyses were done on the inhibition layer of the as-galvanized samples. Differences in the Mn and P contents were found. By analyzing the Mn and P contents in the coatings during galvannealing, a mechanism was proposed to explain the higher galvannealing reactivity which is observed when the dew point during recrystallization annealing is increased.     

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。     

汽车用合金化热镀锌板镀层缺陷及其防止措施

合金化热镀锌钢板已广泛地用于汽车行业,如何消除汽车用合金化热镀锌钢板镀层粉化等缺陷是钢铁生产厂家和用户极为关注的热点问题。本文主要介绍汽车用合金化热镀锌钢板镀层粉化、亮点、波纹和条纹等缺陷的产生原因及其消除措施,同时还侧重介绍汽车用合金化热镀锌钢板今后需要研究的抗粉化课题。     

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。     

On-line control of surface quality for an axially moving steel strip partially immersed in fluid under tension

An on-line control method of surface quality for continuous hot-dip galvanized steel strip after cooling is presented,which combines analytical dynamics theory of a thin plate with the finite element method. The inherent characteristics of the non-immersed and partially immersed strip in liquid zinc were calculated on the basis of theoretical analysis and numerical simulation,respectively. Multi-parameter fitting of the deviation between results using different methods was performed. To optimize the strip excitation frequency away from the resonance region,on-line vibration control of the strip near the air knife under full product conditions was achieved by changing the field production parameters based on the field test results. The results indicate that although the axial velocity has little effect on the inherent characteristics of the strip compared with other manufacturing parameters such as the steel specifications and tension,it induces external excitations,including moving the aerodynamic load and bearing vibration. To some degree,the vibration near the air knife can be reduced by strengthening the support stiffness of the contact rolls. A total on-line control program of surface quality for continuous hot-dip galvanized pure Zn and galvannealed steel sheet in the cooling section is proposed.     

Production and application of Baosteel inorganic-lubricant-coated galvannealed automobile steel sheet

The inorganic-lubricant-coated galvannealed automobile steel sheet is a new product that improves the press formability of automobile body panels.In this paper,the production process,physical and chemical properties, press formability,and corrosion resistance of this new automobile steel sheet were discussed.Test results show that this inorganic solid-lubricant galvannealed automobile steel sheet has good surface friction characteristics and press formability.This product also meets the automobile industry's requirements for press formability,phosphate pro-perties,and corrosion resistance after coating.     

冷轧和镀锌汽车板的发展

冷轧汽车板应具备精确的尺寸，优良的板形、成型性能、抗凹陷性能、表面质量、涂装和焊接性能。介绍了冷轧汽车板和以冷轧板为基板生产的镀锌汽车板，包括热镀纯锌汽车板、合金化热镀锌汽车板和电镀锌汽车板的性能和发展情况，及我国冷轧、镀锌汽车板的发展展望。     

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.     

河钢集团汽车板产品研发与技术创新

 为了应对汽车行业对安全性、轻量化及节能环保的要求,河钢集团构建了汽车板生产、研发与EVI的创新体系,在此基础上实现了超深冲、高强钢系列品种的全覆盖,运用轻量化材料技术实现抗拉强度980 MPa 级的DP钢、780 MPa级的TRIP钢、1 500 MPa级的马氏体钢和热成形钢的批量供货,创新并实现了1 180 MPa级的DP钢、镀层热成形钢以及Q&P钢生产工艺。此外,介绍了河钢集团典型的轻量化钢种DP钢、马氏体钢、镀层热成形钢、Q&P钢的产品技术特点,指出汽车板材料轻量化和提升应用技术服务等是今后河钢集团汽车板产品结构调整与技术创新的发展方向。     

Galvannealing of (High‐)Manganese‐Alloyed TRIP‐ and X‐IP®‐Steel

In this study the influence of Mn on galvannealed coatings of 1.7% Mn‐1.5% Al TRIP‐ and 23% Mn X‐IP®‐steels was investigated. It is shown that the external selective oxides like Mn, Al and Si of the TRIP steel which occur after annealing at 800 °C for 60 s at a dew point (DP) of ‐25 °C (5% H₂) hamper the Fe/Zn‐reaction during subsequent galvannealing. Preoxidation was beneficially utilized to increase the surface‐reactivity of the TRIP steel under the same dew point conditions. The influence of Mn on the steel alloy was investigated by using a 23% Mn containing X‐IP®‐steel which was bright annealed at 1100 °C for 60 s at DP ‐50 °C (5% H₂) to obtain a mainly oxide free surface prior to hot dip galvanizing (hdg) and subsequent galvannealing. As well known from the literature Mn alloyed to the liquid zinc melt stabilizes δ‐phase at lower temperatures by participating in the Fe‐Zn‐phase reactions, it was expected that the metallic Mn of the X‐IP®‐steel increases the Fe/Zn‐reactivity in the same manner. The approximation of the effective diffusion coefficient (D_eff(Fe)) during galvannealing was found to be higher than compared to a low alloyed steel reference. Contrary to the expectation no increased Fe/Zn‐reaction was found by microscopic investigations. Residual η‐ and ζ‐phase fractions prove a hampered Fe/Zn‐reaction. As explanation for the observed hampered Fe/Zn‐reaction the lower Fe‐content of the high‐Mn‐alloyed X‐IP®‐steel was suggested as the dominating factor for galvannealing.     

基板划痕对热镀锌及合金化镀层组织结构的影响

研究了IF钢表面划痕深度对热镀锌镀层及合金化镀层表面缺陷的影响、划痕部位镀层的生长过程、组织结构及合金化行为.试验及分析结果表明,热镀锌时锌液能够有效填充划痕凹陷,从而降低基板表面的划痕缺陷,但划痕缺陷可以遗传到合金化镀层表面;在镀层合金化过程中,与正常部位相比缺陷部位的合金化速度快;随着镀层合金化的进行,缺陷部位的Z...     

含铌冷轧DP780钢的连退工艺对组织及性能的影响

 通过成分工艺优化,在传统冷轧铁素体和马氏体双相钢DP780的显微组织上引入了一定体积分数的残余奥氏体,研究了冷轧退火工艺参数对双相钢DP780的显微组织和力学性能的影响。通过调整连续退火工艺来控制显微组织中一次铁素体、二次铁素体、马氏体、残余奥氏体的比例、尺寸、形貌、分布,同时获得了连退工艺参数-显微组织-力学性能的本质关系。结果表明,通过在传统冷轧铁素体和马氏体双相钢的组织上引入了体积分数为5%～7%的残余奥氏体,不仅可以获得[ReL/Rm≤0.5]的超低屈强比型冷轧DP780,也改善了成型性能。     

逆相变退火中锰钢的组织性能与成形极限

摘要：分别通过SEM、XRD、单轴拉伸试验和FLD等方法对比研究了中锰钢（MMnS780钢）与DP780钢的微观组织、力学性能及成形极限。结果表明，DP780钢获得铁素体和马氏体双相组织，具有连续屈服及较大的加工硬化能力，而MMnS780钢由细小的铁素体和奥氏体构成，具有明显屈服、相对较小的加工硬化能力和较大的均匀伸长率；不同应变状态下MMnS780钢较DP780钢具有更高的极限应变。退火组织以及细小的晶粒尺寸使MMnS780钢产生明显的屈服现象，细小组织以及亚稳奥氏体的TRIP效应使其具有较高的塑性和成形性能。     

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...     

烘烤硬化钢热镀锌镀层450℃合金化退火模拟

 在实验室条件下模拟了烘烤硬化钢450℃下热镀锌镀层的合金化退火过程,研究镀层锌铁合金相的形成和?涔獭⒍撇阆嘟峁购投撇愕目狗刍阅埽⒏隽怂玫难芯糠椒ê椭饕芯拷峁Ｑ芯勘砻鳎憾撇阍?50℃合金化退火,当保温时间延长到60~120s时,镀层内的δ相将会分为δ1k相和δ1p相两层,而且随时间延长,δ1k相增厚、δ1p相减薄,同时镀层表面柱状ζ相也有所减少,镀层抗粉化性能相应变差。     

Application of WC cermet sprayed composite coating in hot-dip galvanizing lines

With the rapid development of the automobile industry,the use of galvannealed and galvanized steel sheets in automobiles is on the rise. These sheets must meet very high surface quality requirements. The surface treatment of line rolls is known to have a great impact on strip quality. To prevent dusts such as zinc ash from pressing into the strip surface,we used a composite thermal spray surface treatment technique to treat rolls. The successfully developed tungsten carbide( WC) + Ni-P composite plating technology improved the quality of the tungsten carbide thermally sprayed WC roll surface. This technique is also helpful to control defects such as adhered foreign materials in hot-dip galvanized automobile outer panel surfaces.     

双相钢激光焊管的焊缝组织演变及扩口性能研究

介绍了马氏体含量不同的双相钢(DP590和DP780)激光焊管的焊缝组织演变,研究了焊缝硬度分布特征及其对扩口性能的影响。结果表明:激光焊缝的熔合区存在明显硬化,组织为单一的马氏体,DP780钢热影响区出现了显著的软化,DP590钢无软化区存在,造成这一差别的原因在于两者马氏体含量不同;软化区的存在导致DP780钢激光焊管的扩口率急剧下降,仅为DP590钢的10%左右;建立了焊管扩口的数值模型,模拟结果与试验结果相吻合。     

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。     

780 MPa双相钢炼钢工艺控制实践

针对DP780炼钢工艺中对[P]、[S]、[H]的要求,对转炉脱磷及挡渣方式进行了优化,保证中间包[P]≤0.015%;通过铁水预处理与LF共同脱硫,保证中间包[S]≤0.003%;采用RH脱气处理,控制钢水中[H]≤4×10-6。对比了不同过热度及拉速下的铸坯质量,提出了过热度20~30℃及拉速≥1.2m/min的控制要求。优化后的炼钢工艺保证了780 M Pa双相钢的产品质量。