Interpretation of the role of silicon on the galvanizing reaction based on kinetics, morphology and thermodynamics

Foct, J.; Perrot, Pierre; Reumont, G.

doi:10.1016/0956-716x(93)90453-y

Cited by 86 publications

(53 citation statements)

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“…Due to a Si concentration gradient in liquid zinc from strip surface to the bulk and low solubility of Si, the z (zeta) crystals start forming away from the steel surface, and the formation of zinc pockets between z (zeta) crystallites takes place. 1,12,17) Similar coating structure with the presence of overly thick z (zeta) crystals embedded in zinc, a thin d (delta) layer and no G (gamma) layer in a 0.37 % Si steel was observed by Jintang et al18) for higher immersion time. In rephosphorized interstitial free steel (S 3 ), the coating consists of mainly z (zeta) phase and a thin d (delta) layer near the interface (Fig.…”

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“…47 (2007) by the presence of 0.36 % Si. Because the steel reactivity and therefore iron solubility in molten zinc varies with silicon content in steel, 12,13) and the consequent high coating growth rate is commonly known as the Sandelin effect.The rephosphorized interstitial free steel (S 3 ) showed low iron dissolution in molten zinc bath. The lower Fe-Zn reaction kinetics shown by rephosphorized steel is well known.…”

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Effect of Steel Composition on Iron Dissolution in Molten Zinc and Development of Fe–Zn Phases on Steel Surface

Mishra

Dutta

2007

ISIJ Int.

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The effect of steel composition on iron solubility in molten zinc and coating microstructure was studied by immersing test coupons of four different steel grades in zinc bath for 20 min at 470°C. The amount of iron dissolved in the molten zinc depends upon the steel composition. The coating was characterized by energy dispersive spectroscopy, X-ray diffraction and galvanostatic methods. The coating consists of mainly z (zeta) and d (delta) phases along with zinc layer at the top, irrespective of the steel composition. The presence of a thin layer of gamma phase has also been confirmed by XRD and galvanostatic analysis. However, the proportion and distribution of the coating phases varies with the steel chemistry.KEY WORDS: iron dissolution; hot-dip galvanizing; iron zinc alloys. ExperimentalThe iron dissolution and galvanizing experiments were carried out in an alumina crucible. Four different steel compositions (namely S 1 , S 2 , S 3 and S 4 ) were selected so that the effect of different interstitial and substitutional alloying elements like C, Si, P etc. could be examined. The details of cold rolled and annealed steel strips used in the experiments are listed in Table 1.Commercially pure zinc (800 g. of 99.99 % purity) was melted in the alumina crucible and held at 470°C for 15 min prior to each experiment to avoid any thermal gradient within the bath. Small test coupons (45ϫ40 mm 2 ) of 1 mm thick steel strips were pickled in hot HCl (15 %) for about 1 min and immediately dipped in the molten zinc for 20 min. The liquid zinc bath was stirred by the immersed sample after every 5 min (i.e. after 5, 10 and 15 min). For the entire experiment, the liquid zinc was maintained at 470°C (Ϯ5°C) in a closed chamber furnace. The dipping time was decided based on the iron saturation limit in zinc and the time required to attain that. The saturation limit of iron in molten zinc can be calculated from the following equation where [Fe] is in wt% and T is in Kelvin.The saturation limit comes to be 0.053 wt% at 470°C. The time required for saturation of molten zinc is in hours.5) The dipping time was therefore chosen such that significant iron dissolution takes place without attaining saturation in order to reveal the effects of different steel compositions. At the end of dipping i.e. after 20 min, the zinc bath was again stirred, the top dross was removed and steel test coupon was taken out of the bath quickly and air cooled. The molten zinc was cast in a sand mould. Chemical analysis of the cast zinc was carried out. This analysis has given the amount of Fe dissolved during 20 min of dipping in the molten zinc for each sample, which has been discussed in Sec. 3.1. A mixture consisting of 1 % picric acid in amyl alcohol and 1% nitric acid in amyl alcohol was used as the etchant. The micro structural and energy dispersive spectroscopy (EDS) characterization of the transverse section was carried out under scanning electron microscope (SEM) for coated samples to examine the elemental distribution across the coating. The coati...

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Effect of Steel Composition on Iron Dissolution in Molten Zinc and Development of Fe–Zn Phases on Steel Surface

Mishra

Dutta

2007

ISIJ Int.

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“…7,10,12,24) According to the nucleation mechanism, there are two possible routes to nucleate the ζ phase in the coating. First, the ζ phase can nucleate and grow at the area without or with lower Si contents.…”

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confidence: 99%

“…When the Si content exceeds 0.07 wt% (so called hyper-Sandelin steel), the ζ phase is disparted with FeSi and δ phases. [8][9][10] Moreover, Yasui et al employed a laboratory hot-dip galvanizing simulator to study the effect of remnant oxides on the rate of galvannealing (GA) reaction on Si-containing steel sheets, and found that the factor of delayed GA reaction cannot be concluded only by the remnant oxides. 11) They proposed that the Si may occupy the vacancies in the Fe-Al compounds or be dissolved in the δ phase, which, in turn, suppressed the diffusion of Al in Fe2Al5 and hindered the diffusion of Fe and Zn in the δ phase, respectively.…”

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confidence: 99%

Effect of Silicon in Dual Phase Steel on the Alloy Reaction in Continuous Hot-dip Galvanizing and Galvannealing

Lin

2014

ISIJ Int.

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The mechanical properties of steels can be significantly improved by alloying with Si. However, Si in dual phase steel retarded the alloy reaction in hot-dip galvanizing and galvannealing; specifically, a continuous Fe-Zn alloy layer was absent on the steel containing 0.44 wt% Si after 25 s of galvannealing at 500°C. This retardation may be due to the Si-rich molten Zn layer, in which the Si resulted from the aluminothermic reduction of Si oxide and the dissolution from the steel substrate.

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“…Previous experimental data and thermodynamic It is worth noticing that the c-phase cannot lead to any binary equilibrium with FeSi. The excess of silicon in the bath is likely to be reduced in two ways: (i) precipitation of FeSi particules; (ii) nucleation and growth of 61 [9]. In these cases, the presence of a third metal introduces a supplementary degree of freedom in the morphologies of the coating which then corresponds to other kinetics of growth.…”

Section: Morphologies and Kineticsmentioning

confidence: 99%

How does silicon lead the kinetics of the galvanizing reaction to lose its solid-solid character

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Interpretation of the role of silicon on the galvanizing reaction based on kinetics, morphology and thermodynamics

Cited by 86 publications

References 3 publications

Effect of Steel Composition on Iron Dissolution in Molten Zinc and Development of Fe–Zn Phases on Steel Surface

Effect of Steel Composition on Iron Dissolution in Molten Zinc and Development of Fe–Zn Phases on Steel Surface

Effect of Silicon in Dual Phase Steel on the Alloy Reaction in Continuous Hot-dip Galvanizing and Galvannealing

How does silicon lead the kinetics of the galvanizing reaction to lose its solid-solid character

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