鐵素體不銹鋼在高溫尿素環境中的腐蝕行為研究
2021-05-07 05:28:52
hualin
摘要
對三種商用車排氣系統用鐵素體不銹鋼（436L、439M、441）進行了尿素結晶腐蝕試驗，以模擬鐵素體不銹鋼在商用車排氣系統內選擇性催化還原器（SCR）中的滲氮腐蝕行為。探究了合金成分及夾雜物對不銹鋼耐高溫尿素腐蝕的影響，并依據EDS表征結果闡釋了材料內部腐蝕的滲氮機理。研究表明，在高溫熱震疲勞和氧化的協同作用下，高溫高氮的環境導致鐵素體不銹鋼晶界及晶內局部區域快速析出氮化鉻顆粒，造成晶界及基體局部區域貧鉻。由于436L和441不銹鋼含有較高的Mo和Nb，其耐高溫尿素腐蝕能力顯著優于439M。此外，由于436L和441不銹鋼中夾雜物細小彌散，也降低了氮化鉻在夾雜物的形核析出幾率，成為提高抗高溫尿素腐蝕的另一個因素。
關鍵詞： 材料失效與保護 ; 高溫尿素腐蝕 ; 晶間腐蝕 ; X射線能譜分析 ; 鐵素體不銹鋼 ; 滲氮機理 ; 夾雜物
Abstract
In order to simulate the nitriding corrosion behavior of ferritic stainless steels in selective catalytic reduction （SCR） system of commercial vehicle, urea corrosion tests were carried out on three ferritic stainless steels （436L, 439M and 441） used in exhaust system of commercial vehicles. The influences of alloy composition and inclusions on high temperature urea corrosion resistance of ferritic stainless steels were investigated. The results show that under the synergistic effect of high temperature fatigue and oxidation, the high temperature and high nitrogen environment results in the rapid precipitation of chromium nitride particles at grain boundaris and in the local area of the ferritic stainless steels, resulting in chromium depletion. As 436L and 441 ferritic stainless steels contain higher Nb and Mo, thy present significantly higher resistance to high temperature urea corrosion rather than 439M. Moreover, due to the fine dispersion of inclusions in 436L and 441 stainless steels, the probability of nucleation and precipitation of chromium nitride on inclusions is also reduced, which is another cause for improving the resistance to high temperature urea corrosion of the relevant steels.
Keywords： materials failure and protection ; high temperature urea corrosion ; intergranular corrosion ; EDS ; ferritic stainless steels ; nitriding mechanism ; inclusion
