表面選擇性氧化行為對雙相鋼熱浸鍍鋅及熱浸鍍鋅合金化的影響

雙相鋼是現今廣泛應用於工業汽車用鋼的高強度鋼種之一，同時具備高強度及良好的成形性。其中乃藉由添加的合金元素，如錳，矽，鉻於其中，除了控制其相轉變，也會發生固溶強化及析出強化，以提高鋼材的機械性能。鋼材必須進行表面處理以達防蝕之用，熱浸鍍鋅是鋼材最常見的表面處理製程。熱浸鍍鋅時，雙相鋼與熔融鋅反應，於介面形成鐵鋅合金層，冷卻後即為熱浸鍍鋅（GI）鋼板。而後續合金化處理可增加Fe-Zn介金屬化合物，如FeZn13（ζ），FeZn10（δ），Fe5Zn21（或Γ1），Fe3Zn10（Γ），鐵鋅合金相可提供鋅層與鋼材間冶金上的接合，合金化處理後則稱為熱浸鍍鐵鋅(GA)鋼板。鋼材中添加的的合金元素，不僅影響鋼材機械性能，也在後續的GI和GA過程中扮演重要的角色。在本研究中使用微量合金元素添加成分高與低的雙相鋼材料，低合金成分鋼為HDA，而高合金成分鋼以HDB表示，並使用實驗室熱浸模擬器進行熱浸鍍鋅及後續合金化製程。研究結果顯示，在退火過程中，合金成分較高的HDB雙相鋼底材易在表面形成較多的選擇性氧化物，因此當GI製程結束後，雖有鋁熱還原反應發生，但仍有殘留氧化物於其上，可由橫截面TEM觀察，這使得其鐵鋅相生長較緩慢。另外，除了TEM顯微結構觀察外，本研究亦使用較簡易的開路電位法做為快速分析氧化層是否存在的方法，而將此電化學剝離後試片進行SEM觀察也可了解各鍍層結構及形貌。另外，經由GDOES及EPMA與TEM 成分線掃描分析，本研究認為鐵鋁障蔽層將由於鐵鋅的快速擴散於其中而轉變為鐵鋅相，鋁則均勻固溶於鐵鋅相中。

關鍵字

雙相鋼；熱浸鍍鋅；選擇性氧化；鐵鋅擴散；開路電位量測法； TEM結構分析

並列摘要

Dual Phase Steels (DP steels), which has high strength with an excellent formability, offer potential for weight savings in the automotive industry.Adding alloy elements, such as Mn, Mo, Si, and Cr ,can stabilize the austenite, coarsen the size of martensite and are expected to enhance the mechanical properties by solid solution hardening and precipitation hardening. In order to maintain the steels in the corrosive environment, surface treatment is becoming an extremely important issue in the studies. Due to effective barrier protection and galvanic protection on steels, Zinc coating is the most common type of steel surface treatment. Hot-dip galvanizing is an economic method to make a full coating on steels. In Hot-dip galvanizing process, the steel reacts with molten Zn to form a coating with an alloy layer at the Zn/steel interface. After being withdrawn from the Zn bath, the steel is cooled down to form hot-dip galvanized (GI) steel or heated up for growing more Fe-Zn intermetallic compounds (IMCs) like FeZn13 (ζ), FeZn10 (δ), Fe5Zn21 (Γ1), and Fe3Zn10 (Γ), which is known as galvannealed (GA) steel. However, the mechanism of the growth of Fe-Zn IMCs is not well understood yet. The alloy elements not only affect the mechanical properties of the steel substrate, but also play an important role in the following GI and GA process. In this research, the effects of those alloy elements on the interaction between the substrate and coating were studied using a laboratory simulated GI and GA on dual-phase steels. Two kinds of dual-phase steels were used and denoted as HDA and HDB. By OM observation, Fe-Zn IMCs growing between the substrate and the coating layer are fewer in HDB than HDA among GA for 0s process. This result shows the important fact that HDB specimen, with higher content of Mn, Cr, and Mo, have poor interaction between steels and zinc layer at GA for 0 sec. The selective oxidation at steel surface during the annealing process prior to hot dipping play a key role in retarding the growth of Fe-Zn IMCs. These results can be confirmed by TEM observation and OCP measurement. The OCP test is a simple and quick technique to analyze the complicated layered structure of the GI and GA coatings.. Otherwise, from GDOES and TEM analysis, it clearly revealed that those IMCs was formed by the transformation from the Fe-Al inhibition layer.

並列關鍵字

Dual Phase Steel ； Hot-Dipping galvanizing and galvannealing ； selective oxidation ； Fe-Zn inter-diffusion ； OCP ； TEM observation

參考文獻

[ 51 ] 柳彥志, “雙相鋼熱處理顯微組織之研究”, 碩士論文,(2004)

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[ 3 ] R. Bode, M. Meurer, T. W. Schaumann and W. Warnecke, “Selection and Use of Coated Advanced High-Strength Steels for Automotive Applications”, Galvatech’04 Conference Proceedings, U.S., pp.107-118, (2004)

[ 8 ] P.J. Gellings, G. Gierman ,D. Koster and J. Kuit, “Synthesis and Characterization of Homogeneous Intermetallic Fe-Zn Compounds”, Materials Research and Advanced Techniques, Vol. 71, pp.70-75, (1980)

[ 9 ] P. J. Brown , “The Structure of the δ-Phase in the Transition Metal-Zinc Alloy Systems”, Acta Crystall, Vol. 15, pp.608-612,(1962)

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表面選擇性氧化行為對雙相鋼熱浸鍍鋅及熱浸鍍鋅合金化的影響

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