Ein Verfahren zur Ermittlung der Rissentwicklung während des Feuerverzinkens

Hot‐dip galvanizing represents a very effective method to protect components against corrosion. During the hot‐dip galvanizing process, however, there is a risk that cracks form in the component. With an increase of the temperature of the zinc bath, the danger of crack formation also increases. This article describes a method to determine the start of the crack formation during hot‐dip galvanizing. With a few tests, this method allows to determine a stress‐strain limit (energy limit) below which no liquid metal assisted cracking (flüssigmetallinduzierte Rissbildung) can occur during the transient phase of hot‐dip galvanizing.     

Studies on the potential risk of liquid metal assisted cracking (LMAC) in normal‐temperature and high‐temperature hot‐dip galvanizing of high strength bolts of dimensions greater M24

Liquid metal assisted cracking (LMAC) mainly occurs due to an unfavorable interaction of three factors: a susceptible material condition, presence of a liquid metal and sufficient tensile stress. Hot‐dip galvanizing of high‐strength bolts induces high thermal loads in bolts made of tempered steel in the presence of a zinc melt and thus, provides the boundary conditions for the above mentioned critical factors to interact. The focus of this study is on investigating thermally‐induced stresses in large diameter bolts and their impact on the formation of liquid metal assisted cracking (LMAC). In order to calculate the thermal loads in hot‐dip galvanizing, simulations were carried out regarding the thermo‐mechanical behavior of bolts during the hot‐dip galvanizing process. The simulations illustrate that cracks are most likely to occur in the first thread turn. This prediction is confirmed by experimental observations.     

The origin of striations on the surface of iron–zinc coated steel sheet produced by hot-dip galvannealing

Dark striations are often observed on the surface of iron–zinc coated steel sheet annealed immediately after hot-dip galvanizing (galvanneal). The striations can be explained on the basis of the differential formation of an iron–aluminium barrier layer at the steel-bath interface during galvanizing. The contact of a submerged, grooved sink roll in the galvanizing bath with the steel sheet causes variations in the iron–aluminium barrier layer at the interface. A more coherent layer is formed in the areas where there is no contact i.e., the grooved areas on the sink roll. The growth of the iron–zinc coating under a higher local aluminium concentration during subsequent annealing leads to a pitted surface in those groove areas, and creates the appearance of dark striations on the surface of the coated sheet. The aluminium content of the galvanizing bath is a key factor in determining the extent of the non-uniformity imposed by the contact with the sink roll. Consequently the striations can be reduced by lowering the aluminium content of the galvanizing bath. This revised version was published online in November 2006 with corrections to the Cover Date.     

Enamel coating for protection of the 316 stainless steel against tribo-corrosion in molten zinc alloy at 460℃

Hot-dip galvanizing provides excellent corrosion and wear resistance for steels.However,the equipment itself,such as the steel roller,immerged in corrosive molten zinc suffers serious material loss during steel's production.Its protection has become the main technique problem in modern galvanizing line.In this study,an enamel coating was designed and prepared.Its tribo-corrosion in molten zinc alloy(Zn-0.2 wt%Al)at 460℃was investigated in comparison with the traditional WC-12 Co composite coating and the 316 stainless steel.Results indicate that the steel suffers serious material damage.Various corrosion products of Fe₂ Al₅ Znx form at the worn surface and the wear scar has reached 200μm deep after merely 5 h tribo-corrosion.Though the two coatings provide an improved tribo-corrosion resistance,for the WC-12 Co coating,its chemical reaction with the molten zinc increases brittleness and promotes cracking.The synergistic wear and corrosion cause its degradation.The enamel coating performs better during tribo-corrosion.It is chemically stable in molten zinc thus able to provide high corrosion resistance.In addition,the amorphous[Si04]network and the self-lubricating CaF₂ crystallite help it to build up an intact amorphous glaze layer readily at surface on sliding,leading to a reduced wear loss.During the whole tribo-corrosion process,the enamel coating is completely free of cracking,and the Zn penetration is inhibited.     

Das Verhalten von galvanisch verzinktem unlegiertem Vergütungsstahl bei schwingender und stoßartiger Beanspruchung

The Behaviour of Zinc Coated Unalloyed Quenched and Subsequently Tempered Steel with Cyclic and Impact Stress With many experiments was shown the influence of hydrogen embrittlement on zinc coated specimens of high strength quenched and subsequently tempered steel with cyclic and impact stress. The influence of hydrogen depends on the structure of the material and on the storing time between the end of zinc coating and the start of loading. Therefore zinc coated pieces of high strength quenched and subsequently tempered steel should be stored after galvanizing. Then there will be no hydrogen embrittlement in cyclic or impact stress.     

Theoretical model of the interfacial reactions between solid iron and liquid zinc-aluminium alloy

Steel strip is often coated with a layer of zinc in order to protect it against corrosion. One of the most commonly used coating processes is continuous hot dip galvanizing. In this process, the steel strip is immersed in a molten zinc bath containing small amounts of aluminium (less than 1 wt%). A model has been developed describing the kinetics of the galvanizing reactions that occur at the steel/liquid zinc interface (dissolution of iron, heterogeneous nucleation and growth of the intermetallic phase designated Fe₂Al₅Zn _x ). The model has been validated using experimental data available in the literature for a classical galvanizing treatment that lasts three seconds.     

低碳钢丝焊网热镀锌工艺的改进

根据低碳钢热镀锌原理,分析了低碳钢钢丝焊网热镀锌工艺中存在的问题,包括工艺不完善、锌液成分不合理、镀后抹拭材料及方法不当等而导致的热镀锌层质量不稳定、锌耗高.针对上述问题,提出了相应的改进方法,包括采用复合除锈剂进行酸洗除锈,强化除锈效果;以氯化锌与氯化铵比例为1.2～1.6、总浓度为12%～15%的混合溶液代替单一的氯化铵作为助镀剂;增加助镀后的烘干工序;采用无机物和珍珠岩混合材料作为抹拭剂等改进措施.通过改进与完善工艺,所得镀锌层表面光滑,焊接点处无积锌,锌耗比工艺改进前降低2%.     

Zum Einfluss von Abkühlverlauf und Tauchdauer auf die Haftfestigkeit und das Bruchverhalten von Zinküberzügen nach DIN EN ISO 1461

The influence of cooling conditions and immersion time on the adhesive power and the nature of the break of zinc coatings in according to EN ISO 1461 Zinc coatings are exposed external and internal mechanical stresses The object of our investigation was to determine the influence on the adhesion test results of the parameters originally determining the structure and the properties of the zinc coatings, such as • chemical composition of steels (Si/P‐content) • galvanizing conditions (zinc melt composition, immersion time) • cooling conditions The results of the adhesion test by the modified pull‐off‐test in according to ISO 4624, metallographic, scanning electron microscope and EDX analytical investigations and also layer thickness measurements make it possible to state that the structure and constitution of zinc coatings are especialy depended on the immersion time and cooling conditions. The reasons for this would be found. The best results for adhesive power of zinc coatings were received by cooling in cold water immediately after the hot dip galvanizing process. Relevant informations for the galvanizing industry are given.     

熔融锌液腐蚀的研究现状

对热镀锌连续生产中受熔融金属腐蚀部件的防护现状进行了分析,目前的研究工作可分为两大类:选择整体材料和表面处理.由于采用整体材料生产成本太高,且其耐熔融锌液腐蚀性能提高有限,采用表面处理提高抗锌液腐蚀成为目前研究的重点.表面处理有扩散渗硼、热喷涂层以及表面涂覆、隔离等方法,这些方法各有其特点.最后,对材料在熔融金属的现有腐蚀机理进行了总结,并指出了今后的发展方向.     

Festigkeitsabfall in Stahldrähten beim Feuerverzinken

Hot dip galvanizing induced strength decrease in wire steels Wire steels C80D and C80D Nb obtained by hot dip galvanizing procedure were investigated by optical and electron microscopy as well as by X‐ray analysis. The investigations were carried out at different stages of production of wires. The results of the investigations were checked by micro‐hardness measurements. Arising of cracks in wires surface during hot dip galvanizing as a reason for decrease in tensile strength was established. Influences of technological parameter such as galvanizing velocity, type of cooling and residual stresses and strength of wires before galvanizing on cracking of wire was taken in consideration.     

活性钢热浸锌镍合金镀层工艺与性能

热浸锌镍合金镀层技术是解决活性钢热镀锌问题的有效方法。分析了在常规热镀锌浴中加镍后,镍在镀层形成过程中的作用,以及对镀层工艺、性能的影响。结果表明,热浸锌镍合金镀层具有良好的粘附性能和耐腐蚀性能,表面光亮、均匀,减少了超厚现象,硬度和耐磨性有所提高。     

Zum Einfluß von Si und P auf das Verzinkungsverhalten Von Baustählen

The influence of Si and P contents in steels on the galvanizing behavior The galvanizing behavior of 40 structural steels in current use was investigated in relation to the complex influence of the Si/P content under conditions that are usual in the hot dip galvanizing industry (440/450/460 °C,5/10/15 min immersion time). The effect of P on the increase of coating thickness on steels with 0,01 to 0,40 % Si begins to be perceptible at > 0,020 % P. The influence of P increases with decreasing Si content of the steels and decreasing temperature of the melt. In steels with ≤ 0,12 % Si, an increased P content causes a shift of the thickness maxima in the temperature range from 440 to 450 °C, such as is otherwise typical of steels of 0,12 % to 0,28 % Si with < 0,020 % P. Zinc coatings on steels with the critical P/Si content (0 to 0,20 % Si/> 0,020 % P) as a rule are more unstable. With increased immersion time at the temperature stated above, floating away of the ξ phase into the zinc melt may occur. This could also be observed with Sandelin steels in the most critical Si range (0,07 to 0,10 %) with < 0,020 % P, with an immersion time of 15 min. It is possible to reduce the thickness of zinc coatings by adding small amounts of Al to the zinc melt (< 0,03 %). This effect of Al at a concentration that is below what is required for the known inhibitory action by the formation of an thin Fe₂Al₅-or Al-containing δ₁ film on the steel surface is attributed to the instability of the ξ phase, a proportion of which floats away into the zinc melt.     

热镀锌钢材的电偶腐蚀行为-划痕型缺陷

使用锌-碳钢异材质丝柬电极技术,模拟并研究了锌/钢电偶腐蚀不同阶段的电位和电流密度的空间分布.结果表明,在锌丝与钢丝面积比为10:1的情况下,锌丝能给钢丝提供足够的阴极保护,且锌丝之间存在明显的电位、电流分布不均现象;钢丝之间也存在电化学参数分布不均现象,而且在受到保护的同时钢丝表面有氢析出.     

Bindefestigkeit der Gleitlagerlegierung Sn‐12Sb‐6Cu‐1,8Bi

Blei‐ und Zinnbasislagermetalle für Gleitlager brauchen einen im Wesentlichen ferritischen Stahlstützkörper, um die Betriebslasten tragen zu können. Das Lagermetall wird auf dem Stützkörper als eine dünne Schicht von wenigen mm Dicke, z. B. bei Radiallagern im Schleudergussverfahren, aufgebraucht. Für beste Tragfähigkeiten bedarf es einer hohen Bindefestigkeit zwischen Stahl und Lagermetall, was man durch eine Tauchbeschichtung des Stahlstützkörpers in einem Bad aus reinem Zinn erreicht. Dabei bildet sich eine dünne FeSn₂‐Zwischenschicht, die sich beim Ausgießen auflöst und gute Benetzung und direkten Kontakt zwischen Stahl und Lagermetall sicherstellt. Bei einem neuen Hochleistungslagermetall mit 1,8 Gew.‐% Wismut als Mischkristallverfestiger ließen sich mit der FeSn₂‐Zwischenschicht ausreichende Bindefestigkeiten nicht reproduzierbar erzielen. Deshalb wurde ein Zink‐modifiziertes Tauchbad entwickelt, mit dem sich eine FeZn₉‐Zwischenschicht bildet. Mit dieser Beschichtung wurden bei allen untersuchten Zinnbasislagermetallen sehr gute Bindefestigkeiten erreicht. Lead‐ and tin‐base babbit materials for sliding bearings require a more or less ferritic steel backing to support the service loads. The babbit material is bonded to the steel as a thin layer of only a few mm thickness, e. g. in the case of radial bearings by centrifugal casting. For best load bearing capacity the bonding strength between steel and babbit must be high which is achieved by hot‐dip coating of the steel backing in a pure tin bath, thus forming a thin FeSn₂ interlayer dissolving during pouring and warranting a good wetting and direct contact between steel and babbit melt. With a new high performance babbit containing 1.8 wt.‐% bismuth as a solid solution strengthener, the FeSn₂ interlayer failed to provide reproducibly sufficient bonding strength. Therefore, a zinc‐modified hot‐dip coating bath was developed forming an FeZn₉ interlayer which produced very good bonding strengths to all investigated tin‐base babbit materials.     

非晶陶瓷涂层对耐高温液锌涂层耐腐蚀性能的影响

热镀锌技术是钢铁材料表层最为有效的防腐蚀手段。为进一步提高耐锌蚀涂层的使用寿命,采用等离子喷涂技术在熔锌装备表面制备了多级耐锌蚀复合涂层及非晶陶瓷涂层,并利用XRD和SEM对其物相组成、结构及形貌进行了研究。结果表明,非晶陶瓷涂层与熔融锌液存在着不浸润,但耐锌蚀涂层仍然会被腐蚀,镀锌装备内部由于存在温度差使得熔融锌液会进行上下、左右的流动,对非晶层会产生冲刷作用,长时间的冲刷会使非晶层变薄,直至消失。非晶陶瓷涂层的制备在一定程度上降低了加热管的导热性,但可以通过加大功率来进行弥补,封孔后的耐锌蚀涂层的热震性能提高了6倍,使用寿命是原来的2.2倍,延长寿命效果显著。     

Anwendung wissenschaftlicher Methoden zur Erklärung der Pustelbildung bei der Duplexbeschichtung

The occurrence of defects like pustules in varnish finishings results in economic problems in the industrial practice of powder coating of galvanized steel parts. The mechanism for the formation of pustules was investigated in a set of scientific integrating methods and a general theory was developed. Metallographic microscopy with its analytic tools as well as wet chemistry research were applied, further glow discharge spectroscopy (GDOS) and mass spectrometry. With mass spectrometry the outgassings from a hot dip zinc probe were identified: it is mainly water with 82% by volume, followed by carbon dioxide (10%) and hydrogen (8%), which together are responsible for the formation of the pustules.     

钢基热浸镀锌的研究

简要介绍了热浸镀锌的工艺，分析了热浸镀锌时镀层的形成以及浸镀温度对镀层厚度的影响，分析了锌池合金元素对热浸镀锌的影响及硅的反应性问题。     

Nitridische und oxinitridische HPPMS‐Beschichtungen für den Einsatz in der Kunststoffverarbeitung (Teil 1)

Nitride and oxy‐nitride HPPMS coatings for the application in the plastics processing (Part 1) In plastics processing adhesive and abrasive wear are some of the main damage mechanisms. For the wear protection and in order to increase the tool life time as well as to improve the quality of the plastic products, binary or ternary chrome‐based coatings like CrN and (Cr,Al)N deposited by physical vapor deposition (PVD) are used. As the chemical composition of the coating has a significant impact on the surface oxide layer formed after deposition and therefore on the wetting behavior of the plastic melt on the tool surface, the aim on this work was to synthesize different coatings from the system Cr‐Al‐O‐N. Therefore, a nitride coating (Cr,Al)N and two quaternary oxy‐nitride coatings (Cr,Al)ON were deposited by using a dcMS/HPPMS (direct current magnetron sputtering/high power pulse magnetron sputtering) hybrid process by varying the oxygen flux. This articles emphasis is on explaining the influence of varying the oxygen flux during the coating process on the coating properties as well as the composite properties towards the plastic mould steel. On this basis a follow up article in the next issue will concentrated on the more application oriented system properties of the three coating systems towards a polycarbonate melt.     

锌浴温度对0.49%Si活性钢热浸镀锌层组织的影响

研究了高硅钢(0.49%Si,质量分数)在不同浸镀温度(440,480,520,560,600℃)和不同浸镀时间(1,3,5,10min)下的热镀锌试样镀层组织,探讨了浸镀温度和浸锌时间对镀层组织的影响。SEM/EDS结果表明:440℃和480℃热镀锌,镀层由薄而连续δ层和破碎的块状ζ相组成,无Γ相。ζ相生长过快,镀层过厚、灰暗、黏附性差,镀层生长主要由界面反应机制控制;520℃热镀锌时,镀层由极薄的Γ层、致密δk层和疏松的δp层组成,镀层生长主要受扩散机制控制;560℃和600℃镀锌时,镀层为Γ层和致密的δ相层,部分δ粒子弥散分布在η层中,镀层生长为扩散机制控制并伴随有显著的δ溶解过程。最佳高温镀锌温度应在520~560℃。     

Korrosionsuntersuchungen an mittels PVD mit Zn und Zn/Mn beschichteten Stählen

Corrosion Studies of Steels Coated by means of PVD with Zn and Zn/Mn Alternative methods for hot dip‐ or electrogalvanic deposition of zinc coatings on steel are gas phase depositions (PVD). They posess high flexibility with respect to alloy composition, and are environmentally harmless. However, a PVD‐coated steel must have at least the same corrosion resistance than steels with “classical” surface finishing. Therefore, the corrosion behaviour of Zn‐coatings and Zn/Mn/system‐coatings deposited by electron beam evaporation without and with ion beam assistance (IBAD) on low alloy steel, was determined by means of salt spray test and electrochemical potential/time measurements. At first the influence of chemical and irradiation pre‐treatment and ion bombardment during deposition on the corrosion resistance of the coatings was investigated. Than the effect of the Zn‐layer thickness was determined in comparison with an 8μm thick electrogalvanized reference coating. Finally Zn/Mn‐alloys, Zn/Mn‐multilayers and Zn‐coatings with Mn‐ or Zn/Mn‐surface layers (top layers) were investigated. By means of optimised pre‐treatment and ion bombardment conditions one obtains, considering the layer thickness, PVD‐Zn coatings with corrosion resistance comparable with the reference layer. The best Mn‐containing coatings are Zn‐coatings with Mn‐toplayer. They surpass the corrosion resistance of the reference layer considerably. Additionally it could be shown that in tendency the potential/time measurements agree very well with the results of the salt spray test.