铁素体不锈钢在高温尿素环境中的腐蚀行为研究

Corrosion Behavior of Ferritic Stainless Steel in High Temperature Urea Environment

对三种商用车排气系统用铁素体不锈钢(436L、439M、441)进行了尿素结晶腐蚀试验,以模拟铁素体不锈钢在商用车排气系统内选择性催化还原器(SCR)中的渗氮腐蚀行为。探究了合金成分及夹杂物对不锈钢耐高温尿素腐蚀的影响,并依据EDS表征结果阐释了材料内部腐蚀的渗氮机理。研究表明,在高温热震疲劳和氧化的协同作用下,高温高氮的环境导致铁素体不锈钢晶界及晶内局部区域快速析出氮化铬颗粒,造成晶界及基体局部区域贫铬。由于436L和441不锈钢含有较高的Mo和Nb,其耐高温尿素腐蚀能力显著优于439M。此外,由于436L和441不锈钢中夹杂物细小弥散,也降低了氮化铬在夹杂物的形核析出几率,成为提高抗高温尿素腐蚀的另一个因素。

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(436 L, 439 M 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 436 L and 441 ferritic stainless steels contain higher Nb and Mo, thy present significantly higher resistance to high temperature urea corrosion rather than 439 M. Moreover, due to the fine dispersion of inclusions in 436 L 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.