創新製程線上固溶化3XX不銹鋼產品開發

The Development of 3XX Stainless Steels with the On-line Solution Annealing Process

本研究開發線上固溶化之創新製程，生產3XX不銹鋼產品，並藉由與經傳統線外固溶熱處理之市售標竿材進行比對，探討以此省製程方式法生產之不銹鋼產品，於機械性質、耐水溶液腐蝕、耐高溫潛變等產品性質之差異程度，藉以確認此製程之可行性，並針對線上固溶製程及合金成分差異對其耐蝕性質之影響及其機理進行探討。試驗結果顯示：304 SS經較低線上固溶溫度+軟化回火熱處理後，會有明顯敏化現象發生，若使用低碳之304L SS即可避免。在含氯鹽環境下，3XX不銹鋼耐蝕性質差異主要取決於其抗孔蝕當量值（pitting resistance equivalent number, PREN）及其固溶熱處理條件。在沸騰、還原性酸環境中，3XX不銹鋼之耐蝕性主要取決於合金成分中之Cr、Mo及Cu的含量，且降低完軋溫度及施加後續正常化熱處理，導致其耐蝕能力大幅降低。耐高溫腐蝕之評估結果顯示：不銹鋼中之Cr23C6析出物為影響304（L） SS高溫潛變之主要因素，對304 SS而言，碳化物析出量越多、抗高溫潛變性越佳，然其耐水溶液腐蝕能力則越差。整體而言，若使用較低碳含量之線上固溶304不銹鋼，即使發生完軋溫度過低、需施以軟化退火熱處理之製程，於上述還原性酸環境下之耐蝕性，與傳統線外固溶製程或高完軋溫度之產品相去不大，均在可接受之範圍內。

Producing 3XX stainless steels with a new on-line solution annealing process is developed in this study. The mechanical properties, corrosion and creep behaviors of 3XX stainless steels with this new process are evaluated, and then the feasibility is assessed compared to those with traditional solution annealing process. Also, the mechanisms of process and chemical compositions on the corrosion behaviors are also discussed in this study. Sensitization for 304 stainless steel (SS) occurs after low-temperature on-line solution annealing + tempering process, but not for 304L SS. The resistance to the chloride-induced corrosion of 3XX SS is depended on its pitting resistance equivalent number (PREN) and parameters of solution annealing. The resistance to reducing acid-induced corrosion is determined by the contents of Cr, Mo, and Cu in SSs and annealing temperature. The creep behavior of 304(L) SSs is dominated by the amount of carbon precipitates. The higher content, the better performance in creep, however, the worse in aqueous corrosion. In general, the corrosion behaviors of 304L SS with online and traditional solution annealing processes are almost the same.