Einfluß von Verformung und spannungsinduzierten Ausscheidungen auf die Korrosionsbeständigkeit von siliciumlegiertem,nichtrostendem Stahl X2CrNiSi 18 15 in Salpetersäure

Effect of deformation and stress-induced precipitations on the corrosion resistance of silicon alloyed stainless steel X2CrNiSi 18 15 in nitric acid The corrosion resistance of silicon alloyed X2 CrNiSi 18 15 stainless steel with about 4 wt.-% Si in nitric acid depends on both deformation degree of the material and number and distribution of precipitations in the microstructure. After cold deformation and subsequent heat-treatment at 700°C (1292°F), the corrosion rate in 5 M HNO₃ is higher than that of non-deformed material. This result was established with specimens isolated from each other but was particularly pronounced with specimens being in galvanic contact. By deformation and subsequent annealing at 700°C, precipitations are formed at the grain boundaries the number of which increases with increasing degree of deformation. With higher degree of deformation, the precipitations are preferably arranged at slip-lines. They were identified as chromium carbide, M₂₃C₆, and silicide of the Cr₅Ni₃FeSi₂ type. It is shown by electrochemical measurements that these precipitations stimulate the cathodic partial reaction, i.e., the reduction of nitric acid. Hence, the corrosion resistance of the silicon alloyed stainless steel is impaired by deformation and stress-induced precipitations formed during annealing at 700°C.