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.

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.

Investigation of Surface Damage in Forming of High Strength and Galvanized Steel Sheets

Powdering/exfoliating of coatings and scratching galvanized steels and high strength steels （HSS）, are the main forms of surface damage in the forming of which result in increased die maintenance cost and scrap rate. In this study, a special rectangular box was developed to investigate the behavior and characteristics of surface damage in sheet metal forming （SMF） processes. U-channel forming tests were conducted to study the effect of tool hardness on surface damage in the forming of high strength steels and galvanized steels （hot-dip galvanized and galvannealed steels）. Experimental results indicate that sheet deformation mode influences the severity of surface damage in SMF and surface damage occurs easily at the regions where sheet specimen deforms under the action of compressive stress. Die corner is the position where surface damage initiates. For HSS sheet, surface damage is of major interest due to high forming pressure. The HSS and hot-dip galvanized steels show improved ability of damage-resistance with increased hardness of the forming tool. However, for galvannealed steel it is not the forming tool with the highest hardness value that performs best.

Effect of hot-dip galvanizing processes on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel

A C–Mn dual-phase steel was soaked at 800°C for 90 s and then either rapidly cooled to 450°C and held for 30 s(process A) or rapidly cooled to 350°C and then reheated to 450°C(process B) to simulate the hot-dip galvanizing process. The influence of the hot-dip galvanizing process on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel(DP600) was investigated using optical microscopy, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and tensile tests. The results showed that, in the case of process A, the microstructure of DP600 was composed of ferrite, martensite, and a small amount of bainite. The granular bainite was formed in the hot-dip galvanizing stage, and martensite islands were formed in the final cooling stage after hot-dip galvanizing. By contrast, in the case of process B, the microstructure of the DP600 was composed of ferrite, martensite, bainite, and cementite. In addition, compared with the yield strength(YS) of the DP600 annealed by process A, that for the DP600 annealed by process B increased by approximately 50 MPa because of the tempering of the martensite formed during rapid cooling. The work-hardening coefficient(n value) of the DP600 steel annealed by process B clearly decreased because the increase of the YS affected the computation result for the n value. However, the ultimate tensile strength(UTS) and elongation(A80) of the DP600 annealed by process B exhibited less variation compared with those of the DP600 annealed by process A. Therefore, DP600 with excellent comprehensive mechanical properties(YS = 362 MPa, UTS = 638 MPa, A_(80) = 24.3%, n = 0.17) was obtained via process A.

Laser brazing with filler wire for galvanized steel sheets

The process properties and interface behavior of CO_2 laser brazing with automatic wire feed for galvanized steel sheets were investigated, in which the brazing filler metal was CuSi3 and no flux was used. As to the appearance quality of the brazing seams, the roles of the processing parameters, such as brazing speed, wire feeding rate, inclination and feeding direction of the wire, laser power, spot diameter and heating position, were assessed. The further investigation indicates that the behavior of the active elements Si, Mn and Zn are significantly influenced by energy input. At the interface, the microstructure of the base metal was composed of columnar crystals and the acicular α solid solution was found on the filler metal side.

Hot-Dip Galvanized Sheet Production and Application

Hot-dip galvanized sheet is wildly used in construction,household appliances,ship,vehicle and vessel building and machinery,etc.In last ten years,with the development of automobile industry,the anti-eorrosion requirements for car body are increasingly strict,by which the rapid development in technology has been promoted.The application of hot-dip galvanized sheet,technological progress in production and some Chinese large units were introduced.

Effect of surface roughness on the surface lubrication performance of galvanized steel sheets with a self-lubricated coating

Four kinds of galvanized steel sheets having different surface roughness values were used to prepare the steel sheets with a self-lubricated coating. The effects of surface roughness on the surface lubrication performance of the steel sheets were examined using a friction coefficient tester. Results revealed large dynamic friction coefficients for the galvanized steel sheets, which increased remarkably with surface roughness. Once the self-lubricated coating was applied, significant drops in the dynamic friction coefficients were measured. After the first stage of the friction test,the coefficients were almost unchanged, which reflected a weak dependence on the surface roughness of the self-lubricated steel sheets. However, the dynamic friction coefficients gradually increased as the test progressed, where these increase clearly correlated with the surface roughness of the self-lubricated steel sheets.

Surface topography evolvement of galvanized steels in sheet metal forming

U-channel forming tests were performed to investigate the surface topography evolvement of hot-dip galvanized(GI) and galvannealed(GA) steels and the effects of die hardness on sheet metal forming(SMF). Experimental results indicate that the surface roughness values of the two galvanized steels increase with the number of forming,i.e.,the surface topographies of galvanized steels are roughened in SMF. Moreover,GI steel has a better ability of damage-resistance than GA steel. The mechanisms of topography evolvement are different in the forming of GI and GA steels. Scratch is the main form of surface damage in the forming of GI steels. The severity of scratch can be decreased by increasing die hardness. GA steel results in exfoliating of the coating firstly and then severe scratching. The surface topography of galvannealed steels can be improved by increasing die hardness. However,the hardness should not be too high.

Effect of Variable Blank Holder Force on Rectangular Box Drawing Process of Hot-galvanized Sheet Steel

At first, a series of finite element method （FEM） simulation tests were used to find the critical forming conditions of hot-galvanized sheet steel during the rectangular box drawing processing when constant blank holder forces were applied. According the test results, the reasonable alteration scope of initial variable blank holder force （VBHF） was as 1.9-2.3 T. Then, based on the test productions of blank holder force, 12 typical VBHF curves were applied to perform the simulation tests by the simulation software of DYNAFORM. The simulation test results showed that VBHF had great effects on drawing formability of hot-galvanized sheet steel during the rectangular box drawing. However, the different VBHF curves were applied to control the whole drawing and it would get great different effects. At the same tine, the VBHF had great effects on the maximum thick thinning ratio, but had little effect on the maximum thick incrassation ratio. So, reasonable application of the VBHF would greatly decrease the fractures. When the VBHF profile is taken as curve L, the best effect of drawing formability could be obtained. When curve I is used, contrary effect could be gotten. The other types of curves would cause effects between above two types of VBHF curves. Finally, the actual tests were applied to check the validity of the FEM simulation tests. The results show that the FEM simulation tests are good ways for predicting and optimizing the VBHF.

Development of Cr-free anti-fingerprint hot-dip galvanized sheet for household appliances

China has become the maximum household appliances manufacturing base worldwide.It is a new challenge facing the steel industry to develop the low-cost and environment-friendly sheet for household appliance industry,so Cr-free anti-fingerprint hot-dip galvanized sheet for household appliances is the upgraded product which satisfies the requirement of China household appliance industry' s nuisanceless treatment.The paper discusses the technical key points of development on Cr-free anti-fingerprint galvanized sheet for household appliances,including the development of the Cr-free anti-fingerprint chemical and the production technology of Cr-free anti-fingerprint galvanized sheet for household appliances.The paper elaborates the main compositions,physical features and properties of the Cr-free anti-fingerprint chemical, surface quality control technology,anti-fingerprint coating quality control technology,influence of anti-fingerprint film weight on corrosion resistance,conductibility,high-temperature discolouration resistance,acid resistance,alkaline resistance and solvent resistance of Cr-free anti-fingerprint hot-dip galvanized sheet, influence of anti-fingerprint coating uniformity on paintability of the sheet,influence of strip surface roughness on corrosion resistance and conductivity of the sheet and influence of strip surface quality on corrosion resistance of the sheet.Adopting the suitable Cr-free anti-fingerprint chemical and the reasonable production process parameters,the properties of the Cr-free anti-fingerprint hot-dip galvanized sheet conform to the delivery technical norms and the Cr-free anti-fingerprint hot-dip galvanized sheet becomes the new material for household appliances such as computer case.

Properties of Baosteel inorganic-lubricant-coated galvanized steel sheet for automotive body panels

An inorganic lubrication treatment for a galvanized steel sheet was developed to improve the press formability of automotive body panels. The properties and application of Baosteel＇s inorganic-lubricant-coated galvanized steel sheet are demonstrated. Compared with galvanized steel sheets without the inorganic lubricant coating,the Baosteel inorganic-lubricant-coated galvanized steel sheet has a lower friction coefficient and excellent lubricating ability,more homogeneous tribological and stamping behaviors,lower sensitivity to stamping parameters,excellent spot weldability,good adhesivity,and perfect phosphate compatibility and paintability. These results verify that the Baosteel inorganic-lubricant-coated galvanized steel sheet has excellent press formability and a huge market application potential.

Lead and Cadmium Distribution in Tubes of Galvanized Steel by Hot-Dip Used for Drinking Water Supply

The main objective of this work was to evaluate the presence of lead and cadmium in galvanized steel tubes by hot-dip used exclusively for drinking water supply.In this research,samples of galvanized tubes were removed from walls of residential buildings with 30 years of use.In the process of hot galvanizing,the manufacturing standards allow or for low cost conveniences,and the use of primary zinc ingot with 1.6%metallic impurities,such as lead and cadmium,is allowed,enabling the incorporation of these metals into the zinc coating deposited on the carbon steel.The associated corrosion of these tubes can release these toxic metals,contaminating the drinking water used by residents.The samples taken from the tubes were evaluated by a square-wave anodic stripping voltammetry technique,and the results for lead and cadmium suggested randomly distributed levels,indicating that the contents of these contaminants depend mainly on the quality of the added primary zinc and the operational conditions of the immersion bath.The metallographic evaluations performed on the samples of the galvanized tubes showed irregularities in thickness and even a lack of the zinc layer deposited on the carbon steel surface.These facts suggest that galvanized tubes should not be used for drinking water.

The development of advanced Cr-free organic composite coated electrogalvanized steel sheet with excellent grounding property

In recent years,the concern about environmental protection is increasing on a world scale.Major manufacturers of home appliances and OA equipment have introduced so-called 'green procurement schemes' for reducing environmentally harmful substances in manufacturing process and end products. Under such background,a new type of chromate-free organic composite coated electro-galvanized steel sheet with high conductivity was developed by Baosteel,which meets the EU RoHS Directive(Restriction of the Hazardous Substances) and other related laws and regulations on environmental safety.It also provides excellent surface electrical conductivity,corrosion resistance,fingerprint resistance,solvent resistance,coating adhesion, heat resistance,formability and other special properties to meet the demand of manufacture's process of OA machine. Compared with previously developed anti-fingerprinting coated electro-galvanized steel sheet,this newly developed product has a good balance between high corrosion resistance(time to 5%white rust in salt spray test is 120 h for flat panel and 72 h for worked potion) and conductivity(surface electro-resistivity in accordance with LOREAST is less than 0.1 milliohm ) due to the special design of coating's structure.Besides,It also provides the properties of grounding and shielding against electromagnetic waves.The evaluation of surface performances of new product showed that it is comparable or even better than the similar products. Currently,the newly developed product has been commercialized. In this paper,the major properties are discussed,such as corrosion resistance,surface electrical conductivity, fingerprint resistance,solvent resistance,coating adhesion(ink/melamine alkyd paint),heat resistance and formability.Furthermore,the application is also briefly described.

Analysis of causes and influence factors of small black spot defects in hot-dip galvanized pure Zn products

In this study,the factors affecting the formation of small black spot defects on the surface of a hot-dip galvanized pure zinc strip are analyzed. These defects are primarily formed w hen the iron-aluminum inhibition layer is incompletely formed or fails to form or when foreign matter adheres to the surface or embeds in the zinc layer.The defects can be reduced by controlling the cleanliness and activity of the strip base before coating,regulating the zinc pot process parameters,and ensuring the cleanliness of the passline and workshop.

Influence of Ni-electrodeposited Pretreatment on Galvanized Coatings of Reactive Steels

Four types of steel sheets containing 0.04%, 0.09%, 0. 14% and 0.36% Si, respectively, were electrodeposited with a nickel layer of 3 tam in thickness and then galvanized in molten Zn at 450℃ for various periods of time. The formation and growth of intermetallic compound layers on the surface of the samples were investigated by SEM and EDS. The experimental results show that the method of Ni-electrodeposited pretreatment can distinctively restrain the over-growth of the galvanized coatings of reactive steels and get eligible coatings with a proper thickness, bright appearance and strong adherence. EDS results indicate that a series of Ni-Zn intermetallic compounds γ′, γ and δ, are first formed on the surface of the samples. With a prolonged immersion time, the F2-Fe-Zn-Ni and δ-Fe-Zn are formed accompanied by the gradual disappearance of γ′, γ and δ2 layer. After a longer immersion time, the lumpy ζ- Fe-Zn occurs between δ and liquid Zn and the F-Fe-Zn does between steel substrate and δ. Subsequently, ζ is in the form of a continuous and compact layer. The method of Ni-electrodeposited pretreatment changes the formation of Fe-Zn intermetallic compounds, which delay the growth of lumpy （and promote the growth of compact δ. Consequently, the abnormal growth of reactive steels is eliminated.

Effects of surface treatments of galvanized steels on projection welding procedure

A group of projection welding experiments and joints tension-shear tests are carried out for cold-rolled steel sheets, galvanized steel sheets (GSS) without treatment, GSS with phosphating and GSS with surface greasing, respectively. The experimental results are regressively analyzed on the computers, then the projection welded joint tension-shear strength curve and the perfect welding currents range of each material are obtained. The results show that surface treatments of galvanized steels have effects on their spot weldabilities. Among the four kinds of materials, GSS with surface greasing have the worst spot weldability, for they need higher welding current and have a narrow welding current range.

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.

A sandwich-like structure hybrid coating of cold galvanizing coating/polydopamine on hot-dip galvanized steel with enhanced adhesion and corrosion resistance

This study aims to enhance the adhesion strength and anti-corrosion performance of the cold galvanizing coating(CGC)applied on the hot-dip galvanized steel(HDG).Polydopamine(PDA)is deposited on the HDG surface with different time ranges and as an interlayer between CGC and HDG through covalent immobilization.The surface morphology and the covalent interaction between PDA/HDG are exhibited by scanning electron microscope(SEM),atomic force microscopy(AFM)and X-ray photoelectron spectroscopy(XPS).The pull-off adhesion tests before and after neutral slat spry tests show an enhanced dry adhesion strength and less adhesion loss of the hybrid CGC/PDA coated HDG compared with the direct CGC coated HDG.In addition,open circuit potential(OCP)reveals that the corrosion protection performance of the hybrid CGC/PDA coated HDG increases by 200%(up to 201 d)and the corrosion density icorrattaining about 4.45×10^(-7)A/cm^(2).Electrochemical impedance spectroscopy(EIS)measurements and X-ray diffraction(XRD)analysis confirm that the precipitate of the stable chelation formed by PDA and Zn^(2+)between CGC and HDG substrate can also improve the corrosion protection performance.Such a strategy of strengthening adhesion and forming the chelate compound at the HDG surface promises a new route to corrosion protection of CGC on HDG.

热镀锌钢板烘烤硬化值检测的影响因素

为了研究热镀锌钢板烘烤硬化值检测的影响因素,主要介绍了HC180BD+Z钢板烘烤硬化值的检测方法与检测结果,分析并探讨了试验温度、保温时间、加热装置、拉伸预应变等烘烤条件对烘烤硬化值检测的影响因素。结果表明:采用相同加热装置时,将保温时间控制为20 min,试验温度由160℃上升至180℃,烘烤硬化值一直保持上升趋势,但当试验温度为160~170℃时,烘烤硬化值的上升趋势要比试验温度为170~180℃的变化明显;采用相同加热装置时,控制试验温度为170℃,当保温时间由16 min延长至20 min时,烘烤硬化值随保温时间的延长而上升,但当保温时间由20 min延长至30 min时,烘烤硬化值无明显变化;采用相同的试验温度和保温时间,不同的加热装置时,烘烤硬化值的检测结果无明显差异;当拉伸预应变由1%增大至2%时,烘烤硬化值的变化趋势与拉伸预应变同步,均有上升趋势,当拉伸预应变由2%增大至3%时,烘烤硬化值却随着拉伸预应变的增大呈下降趋势。

冷轧厂薄带钢高效生产的问题及解决方案分析

热镀锌板具有抗腐蚀强、易于深加工、使用寿命长、成本低以及表面美观等特点,主要用于家用电器、汽车等产品的内部构件和面板应用。随着家电板、汽车板工业的发展,家电和汽车所用的镀锌板占全国钢产量的比例逐步提升。随着国内外家电板、汽车板轻质化和高质量的要求,客户对产品表面质量要求越来越严格。针对生产线在提速增产过程中出现的入口跑偏、工艺段带钢表面质量缺陷和薄带钢薄锌层产速受限问题,提出了相应的改进措施。优化后,不仅提高了产量,而且提高了产品质量。