SAF 2205雙相不銹鋼利用反覆式固溶處理細化晶粒之研究

Grain Refinement of SAF 2205 Duplex Stainless Steel through Repeated Solution Treatments

2205 雙相不銹鋼經過熱滾軋加工而沿滾軋方向呈長條晶狀，可利用均質化處理的高溫作用使三軸向呈現一樣的等軸晶粒形狀。由於均質化熱處理會造成晶粒粗大且有σ相產生，若再採以固溶熱處理可使σ相消除，並同時達到晶粒細化的效果。本研究即針對反覆固溶處理對2205的晶粒細化程度加以探討，反覆固溶處理的條件為1050℃/持溫30分鐘後空冷。實驗結果顯示，均質化處理後的晶粒尺寸達到約50μm，但三軸向晶粒形貌會呈現一致性的島狀晶，然卻因σ相的產生而造成硬度上升。經一次反覆固溶處理結果發現，可以消除σ相；經二次反覆固溶處理結果可獲得到晶粒明顯細化，晶粒尺寸約縮小為22μm，縮減率達到56%的效果，且硬度值也比一次固溶處理來的高；經三、四次反覆固溶處理觀察發現，晶粒尺寸不再持續細化，顯微組織與硬度值也與二次反覆固溶處理者無太大差異。由本研究證實將均質化熱處理後之2205雙相不銹鋼再進行反覆固溶處理確實確可達到晶粒細化效果。

When 2205 duplex stainless steel undergoes hot rolling processing and is rolled in a direction to produce crystalline strips, the high temperatures of homogenization can be applied with a three-axis vector to present a form of crystalline grain that is identically equiaxed. Thus, homogenization heat treatment causes the grains to grow and produces precipitation phases. Repeated solution treatments can eliminate these phases and achieve crystallization simultaneously. This study investigated the effects of repeated solution treatments on the grain refinement of 2205 duplex stainless steel. The condition for the solution treatment was a maintained temperature of 1050 °C for 30 minutes through air cooling. The experimental results showed that the grains grew to approximately 50 μm after homogenization. However, the grains from the three-direction axis appeared to be unequiaxed. Moreover, the produced precipitation phases caused the hardness to increase. It was discovered that one round of solution treatment could remove the precipitation phases. Performing two rounds produced a noticeable thinning of the refinement grains of higher than 22 μm and a reduction rate of 56%. The hardness was also higher than that from one round of solution treatment. After three or four rounds of solution treatment, the refinement grains no longer continued to thin. In addition, the grain size and hardness exhibited little difference with those that underwent two rounds of solution treatment. The results of this study showed that repeated solution treatments on 2205 duplex stainless steel that has homogenization heat treatment substantially benefit grain refinement.