| LIU Shi-wen,MENG Xian-lu,ZHAO Yan,WU Guang-xin,ZHANG Jie-yu.Simulation of the Growth Process of Galvannealed Coatings at Different Zone Temperature in Fe-Zn Phase Diagram[J],52(10):403-410, 429 |
| Simulation of the Growth Process of Galvannealed Coatings at Different Zone Temperature in Fe-Zn Phase Diagram |
| Received:August 30, 2022 Revised:February 08, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.10.036 |
| KeyWord:galvannealed steel high strength steel mathematical model galvannealing process Fe-Zn alloy |
| Author | Institution |
| LIU Shi-wen |
School of Material Science and Engineering, State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
| MENG Xian-lu |
Baosteel Zhanjiang Iron & Steel Co., Ltd., Guangdong Zhanjiang , China |
| ZHAO Yan |
School of Material Science and Engineering, State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
| WU Guang-xin |
School of Material Science and Engineering, State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
| ZHANG Jie-yu |
School of Material Science and Engineering, State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai , China |
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| Abstract: |
| Galvannealed steel (GA) is widely used in the automotive industry, household appliances and construction for its good weldability, paintability, corrosion resistance and heat resistance. However, compared to GI coatings, GA coatings often fail in the press forming because the brittle and high hardness Fe-Zn phases can easily cause coating to undergo powdering and flaking, which results in severe decrease of its corrosion resistance and quality. Therefore, in order to improve the formability of GA coatings, the work aims to establish a GA coating phases growth model to control the coating phase composition, and obtain the best galvannealing process parameters to guide production. Based on the latest Fe-Zn phase diagram, the phase zone boundary concentration equation was formulated and combined with the phase zone boundary concentration equation, the phase boundary movement equation and the phase growth equation, GA coating phase growth model was constructed. The galvannealing model was constructed to simulate the growth process of phases η, ζ, δ and Γ in different phase zones of GA coating, the distribution of the phases along GA coating cross-section, and the change of GA coating Fe content during the galvannealing process. The established model could successfully simulate the phase growth process in different phase zones of the Fe-Zn phase diagram, and compare the growth differences of different phases in different phase zones. The phase transformation below the galvannealing temperature of 530 ℃ was η→ζ→δ→Γ, while the phase transformation above the galvannealing temperature of 530 ℃ was η→δ→Γ. The galvannealing temperature was set at 510 ℃ and 540 ℃. According to the simulation results at 510 ℃, η phase was gradually consumed by ζ phase and δ phase, and disappeared at 8.2 s. At the same time, ζ phase also grew to the surface of coating and stopped growing. Then the δ phase consumed the remaining ζ phase and grew rapidly to the coating surface at 9.7 s, Γ phase grew slowly by consuming δ phase and the thickness of Γ phase reached 1μm at 38 s. Simulation results at 540 ℃ indicated that η phase directly transformed to δ phase and disappeared at 6.8 s. δ phase stopped growing when reaching the surface of the coating at 6.8 s. With the extension of galvannealing time, Γ phase grew slowly by consuming δ phase from the steel substrate and the thickness of Γ phase reached 1 μm at 17 s. The galvannealing process to obtain the best coating phases was simulated:510 ℃ for 9.7 s and 540 ℃ for 6.8 s. The study shows that the change rule of Fe content in GA coating during the galvannealing process is that the increase rate of Fe content is faster at the initial stage of galvannealing, and the increase rate of Fe content slows down with the increase of galvannealing degree, because the phase diffusion coefficient of Fe-Zn phase diagram is ζ>δ>Γ. Therefore, as galvannealing time goes on, phases with high Fe content in GA coating increase, GA coating phase diffusion coefficient decreases with the increase of Fe content and the diffusion rate of Fe-Zn atoms decreases. GA coating phases growth model can simulate the best process parameters at different galvannealing temperature, and provide a process reference for the production of GA coatings. |
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