碳鋼中顯微組織對熱浸鍍鋁的作用

Effect of Microstructure on Hot-dip Aluminizing of Carbon Steel

本實驗使用1008低碳鋼、1045中碳鋼以及1085高碳鋼之商用鋼料做為底材，再利用正常化、退火、淬火與球化等熱處理方法使其得到不同種微結構後進行700℃的熱浸鍍純鋁，探討碳鋼微觀組織對熱浸鋁時，鋁化層及外部鋁層成長之作用。實驗結果顯示，熱浸鍍鋁後試片之塗層由外而內分別為外鋁層、鐵鋁介金屬層以及不同微結構組織之底材，其中鐵鋁介金屬層主要為Fe2Al5。碳鋼中的碳，無論是以固溶碳、球形雪明碳體或波來體的型式存在，均會阻礙Fe2Al5相的成長，因此鋼料之碳含量越低，Fe2Al5層之成長越多。Fe2Al5層之均勻性會被底材碳的分佈所影響，當碳的分佈越均勻，Fe2Al5層之厚度的變異量越小。影響外部鋁層厚度之最大因素為鋁層中碳化物的含量，外部鋁層之厚度隨鋼料內碳化物之增加而增厚，但其厚度變異量則不受鋼料內碳含量的影響，皆會隨熱浸時間的增加而縮小。

This experiment uses commercialized carbon steels, 1008 mild steel, 1045 medium-carbon steel and 1085 high-carbon steel as the substrate. The steels were underwent heat treatments, normalizing, annealing, quenching and spheroidizing, to obtain various kinds of microstructure. Hot-dip aluminizing was performed on the heat-treated steels in order to investigate the effect of the microstructure of the carbon steels on the growth of aluminum layer and external aluminum layer during hot-dipping. The experiment results show that the hot-dipped aluminide coatings were composed of an outer Al topcoat and an inner Fe-Al intermetallic layer (mainly Fe2Al5), respectively. The carbon in the carbon steels, whether it was in the forms of carbon solid solution, spherical cementite or pearlite, had the ability of impeding the growth of Fe2Al5. Therefore the lower the carbon content in the steels, the faster the Fe2Al5 layer grew. In addition, the uniformity of the Fe2Al5 layer was influenced by the distribution of carbon in the steels. The steels with the more uniform distribution of carbon possessed the smaller variance in Fe2Al5 layer thickness. Furthermore, the significant factor that affecting the thickness of the external aluminum layer was the amount of carbide in the aluminum layer. The external aluminum layer thicknesses increased as the amount of carbide in the aluminide layers increased, while the thicknesses variances were not subjected to the amount of carbon in the steels. The thicknesses variances of the external aluminum layers decreased as increasing the hot-dipping time.