Hot Galvanizing Research Articles

Влияние предварительной плазменной обработки поверхности стали 09Г2С на формирование покрытия в результате горячего цинкования

In recent years, the range of silicon-containing steels subjected to hot galvanizing has been expanding. Alloying of steel with 0.5–1 % of silicon leads to the formation of a zinc coating of great thickness with a matte or multi-colored surface. This is associated with the changes in phase reactions between iron and zinc in the Fe–Zn–Si system. The development of ways to neutralize the negative influence of silicon on the formation of zinc coating is an urgent task. The purpose of the work is to study the influence of preliminary plasma cutting and plasma surface hardening of 09G2S (S355J2) steel on the thickness and structure of zinc coating formed on treated surfaces. It was found that after plasma cutting, the structure of the surface layer of steel is martensite, and after plasma surface hardening, it is martensite and ferrite. Analysis of the change in microhardness from the steel surface to the middle showed that the hardened layer depth is 400 μm. A zinc coating consisting of a δ-phase and a ζ-phase is formed on the surface of the steel without pretreatment. On the surface of the steel after plasma treatment, a zinc coating is formed characteristic of low-silicon steels and consisting of the δ-phase, ζ-phase, and η-phase. It was found that the thickness of the zinc coating on the surface after plasma cutting is two times less than on the untreated surface, and the reduction in the coating thickness occurs due to a decrease in the ζ-phase thickness. A hypothesis was suggested that the martensite formation on the steel surface leads to the disappearance of the ordered FeSi phase and changes the phase equilibrium in the Fe–Zn–Si system. Consequently, preliminary plasma treatment of the steel surface allows controlling the structure and thickness of the resulting zinc coating and is therefore recommended for introduction into the hot galvanizing process of silicon-containing steels.

Effect of Coating on Stress Corrosion Performance of Bridge Cable Steel Wire

Hot galvanization on steel surfaces can isolate the steel from corrosive environments and alleviate the stress corrosion cracking caused by the anodic dissolution mechanism. However, the cathodic protection potential of the coating is excessively negative, which may aggravate the hydrogen embrittlement problem. The effect of a coating on the stress corrosion performance of bridge cable wire was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), a thermal desorption analysis (TDA), an electrochemical workstation, and an FIP test. The results show that hot-dip ZnAl and ZnAlMg alloy coatings can significantly prolong the stress corrosion fracture time of steel wire substrates. From a macroscopic perspective, the stress corrosion cracking fracture is a brittle fracture caused by hydrogen embrittlement. Moreover, the coating type has little effect on the fracture morphology of bridge cable wire. In NH4SCN solution (50 °C, 20 wt.%), a corrosion product layer composed of ZnS and Al2O3 was formed on the surface of the coated steel wire. The electrochemical analysis showed that the corrosion resistance of the ZnAlMg coating was better than that of the ZnAl coating, which was the main reason for the improvement of the stress corrosion performance.

Experimental investigation on galvanized steel elements at elevated temperature

Recent studies showed that hot galvanization can reduce the surface emissivity with abeneficial effect on the steel temperature. Therefore, background documents for next generation of Eurocode suggest considering this effect through a temperature dependant surface emissivity relationship. This paper shows the results of high-temperature small-scale tests, aimed at investigating the galvanization effect on steel plates temperature with variable section factors (A m/V). For each Am/V, both galvanized and blank steel specimens were tested to directly compare the temperatures, by using an input curve with a slower heating rate than ISO834 fire curve. The test results show that the heating in galvanized specimens was slower than the one recorded in blank samples, confirming the galvanization beneficial effect. To quantify this effect and to calibrate the emissivity of galvanized steel, the analytical method to assess steel temperature development, was applied using the temperature recorded in the furnace and in the samples. The surface emissivity was confirmed to be temperature dependant. Some applications of temperature dependant emissivity law were carried out, by varying Am/V and the fire curves, to quantify the galvanization beneficial effect. In particular, the ISO834 fire curve and several parametric fire curves, obtained by varying the opening factor, were considered.

SILICATE COATINGS FILLED WITH ZINC POWDER AND GRAPHENE NANOPLATES FOR STEEL CORROSION PROTECTION

The method is proposed to protect the carbon steel from corrosion by silicate coatings filled with powdered zinc and graphene nanoplates obtained by thermal splitting of graphite. The conditions for steel pre-treatment in an alkaline solution containing citrate ions and a nonionic surfactant, for the production of potassium liquid glass composition with the addition of zinc and graphene powders are selected. It is shown that coatings 70–80 µm thick, cured at room temperature for three days and containing 80–90 wt. % zinc, 7– 12 wt. % silicon dioxide and 0.2 wt. % carbon have the highest adhesion, water resistance and protective ability. The study of steel corrosion in 3.5% NaCl solution using methods of voltammetry and the dependence of open circuit potential on the test duration showed that silicate coatings filled with zinc and graphene provide cathodic polarization of steel and protect it from corrosion better than twice as thick coatings obtained by hot galvanizing. Graphene nanoplates enhance the contact of zinc particles with each other and with steel, promoting its cathodic polarization. Using scanning electron microscopy and X-ray spectral microanalysis, it has been shown that zinc corrosion products fill the pores of the near-surface layer of coatings, enhancing their protective ability.

Влияние времени выдержки в расплаве на морфологию цинкового покрытия на сталях с различным содержанием кремния

The formation of zinc coating on steels in the process of hot galvanizing is determined by such factors as the process temperature, holding time, the chemical composition of steel, and particularly, silicon content. In the 1940s of the XX century, R.W. Sandelin described the process of the significant acceleration of the reaction between ferrum and zinc at the silicon content in steel equal to 0.06–0.10 %. There are different methods of control of silicon reactance; however, the simplest method of control of coating thickness is the proper choice of time of product holding in the melt. The paper aims at the identifying the influence of time of holding in the melt on thickness and microstructure of the coating formed on steels with different content of silicon: S235 (Si=0.02 %), S235J0 (Si=0.04 %), S235JR (Si=0.17 %), 9MnSi5 (Si=0.6 %). To quantify silicon, the authors analyzed the chemical composition of steels using the spark spectrometry technique. The study identified that the coating thickens on steel with the course of time of holding in the melt according to the parabolic law. The most intensive growth of coating thickness with the course of time is observed on reactive steels with silicon content of 0.04 % and high-silicon steels with silicon content of 0.6 %. The reactive steel showed the significant growth of variations in thickness. The authors carried out the analysis of microstructure using the TESCAN Vega SB scanning electron microscope; the analysis showed that the growth of a coating is determined by the peculiarities of ζ-phase structure. The analysis of the Fe-Zn-Si triple diagram allowed concluding that with the silicon content of 0.04 % and 0.6 % in steel, the eutectic decomposition of fluid into ζ+η+FeSi phases’ mixture progresses in the system. This process leads to the direct contact of the melt and steel base and intensifies the interdiffusion of ferrum and zinc. As a result, the ζ-phase actively produces that leads to the rapid growth of the coating thickness.

Analysis of the internal stress in multicomponent zinc coatings

X-ray analysis provides information on the phase composition, macrostress, and texture of multi-component zinc coatings in which the basic alloying component is nickel. The coating is applied by hot galvanization. The coatings do not contain brittle γ phase, but a high level of type-I stress—close to the yield point of zinc-is formed on account of the heterophase structure and the solidification conditions. The coating is also characterized by axial solidification texture.

Effect of strong shot peening cleaning and hot galvanizing on fatigue strength of steel welded joint

The soiling of the slag, spatter and the fume, etc., which come into contact with the steel sheet surface with welding, is cleaned making use of steel sphere shot material of large particle diameter, high projection pressure with strong peening processing (below, called strong peening cleaning). In this research, the cleaning state of the soiling with welding and improvement of fatigue strength of the hot galvanized welded joint was inspected, when the surface of a SM490A welded joint was cleaned with strong peening cleaning. The following experimental results were obtained: 1. The fatigue limit of smooth base metal which received strong peening cleaning at about 320 MPa was remarkably high in comparison with smooth base metal at about 245 MPa. 2. The fatigue limit of a welded joint which received strong peening cleaning at about 300 MPa was remarkably high in comparison with a welded joint at about 170 MPa. 3. The strong peening cleaning was highly efficient and the cleaning state was satisfactory. 4. The cause of the remarkable rise of the fatigue limit (300 MPa) of the welded joint which received strong peening cleaning was because the fatigue limit (about 170 MPa, 57%) of the welded joint was improved (about 130 MPa, 43%) with peening cleaning. It was considered that improvement effects were: a rise (about 68 MPa, 23%) of hardness of the weld toe; relief (about 43 MPa, 14%) of stress concentration; increase (about 136 MPa, 45%) of compressive residual stress; and the decrease (about − 96 MPa, − 32%) by increase of surface roughness. 5. The fatigue strength of the hot galvanized welded joint decreased remarkably. This was thought to be due to the decrease (about HV40) of hardness of the surface, the decrease (about 188 MPa) of the compressive residual stress and the influence of many factors which accompanied hot galvanizing.

Some Advances in the Application of Weathering and Cold-Formed Steel in Transmission Tower

Application of weathering and cold-formed steel in transmission lines can reduce steel consumption and environmental pollution. Some advances in the studies on the weathering and cold-formed steel in transmission tower are introduced. Firstly, corrosion-resistant tests of weathering steel samples under different simulating technical atmospheres were carried out separately for 240 hours. It shows that the corrosion degree of joint samples is higher than that of single chip samples, and the corrosion-resistant performance of weathering steel is superior to common carbon steel. The corrosion-resistance of weathering steel meets with the requirement of transmission tower. Secondly, experiments and finite element analysis for cold-formed angles and a 220kV prototype tower were completed, and the stability coeffi-cient fitting curves as well as the modification formulas of slenderness ratio for cold-formed members were determined. According to the structural characteristics of transmission towers, four sections of cold-formed angles with different sections and slenderness ratios were selected in this study. The finite element model well predicted the buckling behav-iour of the cold-formed members. Ultimate loads calculating by the fitting curve were well agreed to the experimental values, especially for the members with small slenderness ratios. Weight of the cold-formed steel tower can be reduced by more than 5 percent after considering the strength enhancement. Cost of the weathering and cold-formed steel transmission tower is nearly equivalent to that of hot-rolled steel tower with hot galvanizing.

Investigation on colourisation regularity of colouring hot dip galvanisation processing

The colouring hot dip galvanisation is a new hot galvanising processing. In this processing, a colour oxide film would be developed directly on the coating of the galvanised steel by the preferential oxidation of the additions in the hot dip galvanisation coating after hot dip operation. Due to their oxygen potentials and their oxide film properties, manganese and titanium were selected as additional elements in the colouring hot dip bath respectively. The influences of processing parameters on the colouring of coating were investigated systematically for the various binary Zn–Mn or Zn–Ti hot galvanising baths. The experimental results indicate that the colours on the coating of the galvanised steel would change continuously during its cooling period after hot dip operation. In the case of Zn–Mn bath, the possible colour tones of the oxide film are blue, yellow, purple and green, and their colour tones and the duration time varied with the manganese percentage composition and the hot dip temperature. In the case of Zn–Ti bath, the possible colour tones of the oxide film are blue, yellow and purple. However, titanium percentage composition in Zn–Ti bath has hardly effect on colouration regularity.

Roll Shape Setting Technology of Hot Galvanizing and Planishing Mill

A roll shape setting model was built for the hot galvanizing and planishing mill. The uniform transversal distributions of the front tension in the exit and the unit pressure were considered as the objective function. At the same time, the quality of the products, the stability of zinc layer, and the homogeneity of spangles were of considerable significance in the planishing process. The model was applied to the roll shape setting of the 1800 cold rolling 3# CGL hot galvanizing and planishing mill of Baosteel Co Ltd. After being planished, the flatness of a strip that was less than 6 I was more than 97%, and the flatness of others were less than 10 I; the pass percentage of the zinc layers reached 100%.

非鉄金属製錬プロセスと操業 彦島製錬（株）の亜鉛製錬

Hikoshima Smelting Co., Ltd. is located at the western end of Honsyu. The plant switched from a horizontal retort process to an electrolytic zinc process in 1970. Hikoshima Co., Ltd. had made various improvements to reduce the operating costs about roasting, leaching, purification, electrolysis, casting, labor-saving and so on. In addition, the annual capacity extended from 55,000 tons to 74,000 tons during several expansion stages.Main products are zinc alloys for hot galvanizing and zinc anodes for plating.This paper describes these recent improvements and operations.

Characteristics of electrode wear in resistance spot welding dual-phase steels

Hot galvanization dual-phase steel is a newly developed steel to be used in auto body to meet automobile light weight and safety requirement, which has high strength and good corrosion resistance. But welding of galvanization steels led to serious and uncertain electrode wear, which resulted in short electrode life and inconsistent weld quality. Experiment was carried out to study characteristics of electrode wear in welding 0.8 mm thickness galvanization dual-phase steels with 600 MPa strength (DP600) by servo weld gun. The characteristics of electrode radial wear and axial wear were compared with between DP600 and uncoated steels. The results showed that when welding DP600, more alloy products and electrode deformation were produced to make electrode diameter increase at earlier wear stage, which took higher electrode wear rate at this stage. Growth of pitting on electrode-tip face accelerated electrode invalidation. Undersized nugget was formed because of electrodes wearing out.

Development of new preservatives

Preservative-stamping oil Volgol-131 has been developed on the basis of a mixture of high-purity mineral oil and a group of additives that impart the desired service properties to the given product. The oil can be used in stamping operations and to provide long-term corrosion protection to cold-rolled products that have undergone electrolytic or hot galvanizing. The oil can be applied to the surface of the metal by dipping, rubbing, or spraying (including electrostatic spraying). One of the newest products of the company Volgokhimneft’ is water-soluble preservative Volgol-500, which was developed to preserve sized rolled products at any stage of the production process, as well as to preserve metal parts and finished products during storage, transport, and use.

Reduction of Metallurgical Wastes in an RF Thermal Plasma Reactor

Recovery of metals from iron and zinc oxides, as well as from zinc-containing metallurgical wastes, such as flue dust from the Siemens–Martin process and sludge from hot galvanizing, has been studied in an rf thermal plasma reactor under reducing conditions. The product composition was estimated by thermodynamic calculations based on the minimization of the Gibbs free enthalpy. Effects of the plate power of rf generator and the feed rate of powder on the chemical and phase composition of products have been investigated in detail. It has been proved that the rf thermal plasma treatment makes possible to produce unstable species in thermodynamic terms: metallic zinc was gained in the reaction of ZnO and hydrogen. The gradient cooling along the plasma reactor led to the segregation of the iron and zinc compounds. Valuable products were made from the particular wastes by a single step thermal plasma processing.

亜鉛めっき橋梁の溶融亜鉛めっきぜい化割れ発生に関する熱弾塑性解析

The aim of the present study is to clarify the mechanical behavlor of a bridge girder during hot galvanizing. The mechanical behavior is analyzed using finite element method (FEM) analysis in which the constitutive equation is given by Bodner's viscoplastic model. The mechanism of zinc induced cracking is also discussed in detall. A shape and size parameter, Rσmax. is proposed and discussed. Rσmax is the ratio of the maximum compressive thermal stress to the elastic buckling stress of the panel and is related to zinc induced cracking. The parameter Rσmax correlates well with the final tensile strain calculated by FEM analysis. Critical strain for crack initiation, εc, was obtained from bending tests and from FEM analysis for several steels. Each value of Rσmax at crack initiation was estimated from comparison with the final tensile strain and εc. The estimated critical value of Rσmax is nearly the same as the critical value of Rσmaxobtained by calculation of the transition from non-cracking to cracking behavior of bridge girders.

Hot galvanizing of parts hardened by surface plastic deformation

Hot galvanizing of parts hardened by surface plastic deformation

Hot galvanizing of tubes in an alloyed zinc melt

Hot galvanizing of tubes in an alloyed zinc melt

Hot galvanizing of spiral tubes for irrigation farming

The Yakubovskii Pipe Plant in Voroshilovgrad has mastered the production of hot-galvanized spiral pipes for irrigation farming 180, 250, and 350 mm in diameter, 1.2-1.8 nun in wall thickness, and 5 m in length. The pipes are made from low-carbon cold-rolled steel strip by spiral forming. The ends of the strip are welded with high-frequency currents. The welding of a bell mouth and sphere onto the ends of the pipes ensures their rapid assembly in the field.

鋼材溶接継手の亜鉛浴加熱急冷による疲れ強さの改善(第4報)

It was shown in previous reports that fatigue strength of steel welded joint was improved by hot galvanizing and that this effect was due to the heat treatment in hot galvanizing process, that is, this effect came from heating in zinc bath and rapid cooling in water. Rapid heating and cooling induce residual stress and aging effect on steel, even if the heating temperature is under A1 point. Therefore in this report the influence of the residual stress and aging of steel welded joint cooled in water after heating at various temperatures or after hot galvanizing on the fatigue strength is investigated.The results are summarized as follows:(1) When the steel welded joint is rapidly cooled in water after heating at various temperatures from 400°C to A1 point, the residual stress on the surface of the welded joint is converted from tension of as welded joint into compression. Rapid cooling in water after hot galvanizing has the same effect.(2) The larger the compressive residual stress of the surface of the welded joint, the more improved is the fatigue strength of the joint.(3) The higher the heating temperature up to A1 point and the cooling rate, the greater becomes the aging effect of steel and its welded joint.(4) Steel welded joint increases in the fatigue strength with age hardening.(5) The improvement of fatigue strength of steel welded joint by hot galvanizing is attributed to the compressive residual stress and aging of steel welded joint.

鋼材溶接継手の亜鉛浴加熱急冷による疲れ強さの改善(第3報)

It was shown in previous report that the fatigue strength of welded joint with reinforcement is remarkably improved by hot galvanizing treatment in comparison with that of non-treated joint. However, the reason why the fatigue strength of joint is improved by the treatment has not yet been made clear. Therefore, each step in hot galvanizing process is analysed and the effects of steps on the fatigue strength of welded joint are experimentaly investigated in this report.Generally, hot galvanizing process contains five steps, that is, pickling, rinsing, flux coating, dipping in zinc bath and cooling. At first hydrogen absorption in steel during pickling, rinsing and cooling in water are investigated. Hydrogen in steel during galvanizing process is released with time, but galvanized zinc layer retards the releasing rate of hydrogen. The fatigue strength of hot-galvanized steel decreases owing to the hydrogen, but it recovers if the hydrogen is released. Dipping of the joint for long time in rinse bath containing a little acid has no good effect on the fatigue strength. The higher is the temperature of zinc bath, the more effective is hot galvanizing for improving the fatigue strength of steel welded joint. The iron-zinc alloying phase formed at higher than 495°C is a ductile δ1 phase. When the joint is cooled in water bath immediately after dipping in zinc bath, the fatigue strength of it increases, but decreases by air cooling. The alloying layer formed during air cooling is harmful for the fatigue strength of welded joint. The iron-zinc alloying layer by hot galvanizing has hardly any influence on the fatigue strength of steel welded joint.