Cr-C電鍍層在鍍鋅鋼板之抗高溫氧化研究

High-Temperature Oxidation Resistance of Electrodeposited Cr-C Coating on Galvanized Steel

陳陽(Yang Chen)

指導教授 ： 林招松

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202204141

摘要

先進高強度鋼通常使用熱沖壓製程來加工成型，熱浸鍍鋅層為一種工程上常用的保護鍍層系統，然而在沃斯田鐵化處理時，熱浸鍍鋅鋼板的鍍鋅層會發生高溫氧化及液態鋅脆化等問題，這些問題會大大影響鋼板的機械性質，進而限縮了應用範圍。
本實驗探討在熱浸鍍鋅鋼板上電鍍三價鉻膜層的抗高溫氧化能力。在三價鉻鍍浴中對熱浸鍍鋅鋼板進行了Cr-C膜層的電鍍，並研究了其在沃斯田鐵化過程中的抗高溫氧化能力。實驗總共使用4種不同電流密度電鍍，電鍍時間從1分鐘到8分鐘，並藉由使用掃描式電子顯微鏡(SEM)、X光射線能量散佈光譜儀(EDS)、X光射線繞射(XRD)分析了Cr-C膜層氧化前後的表面型態、組成成分分析和微結構，使用橫截面SEM比較了高溫熱處理前後膜層的微觀結構，並使用熱重量變化分析儀(TGA)評估膜層在升溫過程中的氧化增重行為。實驗結果顯示，在熱浸鍍鋅鋼板上電鍍Cr-C膜層時間需要至少4分鐘，若電鍍時間太短則會有大面積的裸露區不能被膜層覆蓋，如此會使抗高溫氧化效果低落。三價鉻電鍍膜層並不是膜層越厚抗高溫氧化效果越好，較厚的膜層因含有較多殘留應力，膜層表面會產生許多粗大裂紋，而粗大裂紋並不能有效抑制高溫氧化的進行。因此根據實驗結果，4分鐘的電鍍膜層具有足夠的膜層厚度，也能披覆大多數的面積，裂紋較細小，在高溫氧化實驗下具有最好的抗高溫氧化性能。

關鍵字

熱沖壓 ； 熱浸鍍鋅 ； 三價鉻電鍍 ； 微結構 ； 高溫氧化

並列摘要

The hot-dip galvanized layer is a common protective coating system for advanced high-strength steels, which are usually formed and processed by hot stamping process. However, the galvanizing layer of hot-dip galvanized steel sheets is subject to high-temperature oxidation and liquid zinc embrittlement during the austenitization treatment, and these problems greatly affect the mechanical properties of the steel sheets, thus limiting the applications.
This experiment investigates the resistance to high-temperature oxidation of trivalent chromium coating on hot-dip galvanized steel plates. The Cr-C coating of hot-dip galvanized steel plates was carried out in a trivalent chromium bath and the resistance to high-temperature oxidation was investigated during the austenitization treatment. The surface morphology, microstructure, and composition of the Cr-C layer before and after oxidation were analyzed by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray ray diffraction (XRD), and cross-sectional SEM to compare the surface morphology, microstructure and composition of the layer before and after high-temperature heat treatment. The cross-sectional SEM was used to compare the microstructure of the film layers before and after the high-temperature heat treatment. The experimental results showed that a minimum of 4 minutes is required to electroplate the Cr-C layer on the hot-dip galvanized steel plate. If the electroplating time is too short, there will be large exposed areas that cannot be covered by the coating, which will reduce the effect of high-temperature oxidation resistance. The relation of thicker the layer, the better the anti-high temperature oxidation effect does not exist. The thicker layer contains more residual stress, and the surface of the coating will produce many coarse cracks, and the coarse cracks cannot effectively inhibit high-temperature oxidation. Therefore, according to the experimental results, the 4 minutes electroplated layer has sufficient film thickness, can cover most of the area with smaller cracks, and has the best resistance to high-temperature oxidation after high-temperature oxidation.

並列關鍵字

Hot stamping steel ； Galvanized steel ； Trivalent chromium electroplating ； Microstructure ； High temperature oxidation

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