表面鋁化改質對T91鍋爐用鋼提升抗高溫氧化性能研究

Study the Surface-aluminizing Coating to Enhance High-temperature Oxidation Resistance of T91 Boiler-used Steel

本研究主要探討T91鍋爐用鋼經表面滲鋁改質後（T91-A）在600 ~ 900℃空氣下之高溫氧化行為，研究中表面鋁化參數是選用7%的AlF3於800℃通入200 cc/min氬氣，且持溫4小時之參數組合。研究結果顯示，T91-A在600-750℃下的氧化動力學遵守單段式拋物線律，而在800 ~ 900℃則呈現兩段式拋物線律，且穩定階段的氧化速率大幅降低，相對於T91原材而言，T91-A在850℃之氧化速率可減緩6.2個數量級，說明表面改質滲鋁能有效提升T91鍋爐用鋼之高溫抗氧化性能。整體而言，滲鋁改質合金的表面皆僅生成α-與θ-Al2O3，在低溫時以θ-Al2O3為主，α-Al2O3較少；而在850 ~ 900℃時則以α-Al2O3為主，而θ-Al2O3的繞射峰相對強度較低，此現象隨著時間增長更加明顯，因此可知氧化溫度與時間是影響α-Al2O3生成的主要因素，而它的生成是T91-A合金氧化速率降低的主因。

The oxidation behavior of surface aluminizing T91 boiler-used steel (T91-A) was investigated over the temperature range of 600 ~ 900 ℃ in dry air. The surface-aluminizing parameters for T91-A were to heat the T91 samples at 800 ℃ for 4 hr in 7% AlF3 at a 200 cc/min flow rate of Ar. The results showed that the oxidation kinetics of T91-A followed a single-stage parabolic-rate law at 600 ~ 750 ℃, while a two-stage parabolic-rate law was observed at 800 ~ 900 ℃. The steady-state oxidation rates at 850 ~ 900 ℃ were significantly slowly than those at lower temperatures. The oxidation rates of the aluminizing alloy were significantly lower than those of the T91 substrate by 6.2 orders of magnitude at 850 ℃. Both α- and θ-Al2O3 formed on top of T91-A surface after the oxidation. The amount of θ-Al2O3 gradually reduced and the amount of α-Al2O3 gradually increased with increasing temperature. It was found that the growth of α- Al2O3 is strongly dependant on the oxidation temperature and duration of time. The formation of α-Al2O3 is responsible for the lower oxidation rates of the T91-A alloy at 850 ~ 900 ℃.