Effect of silicon on intergranular corrosion of stainless steel in nitric acid solutions

Corrosion mechanism of austenitic Fe-Cr-Ni alloys containing 0.06--3.76%Si in Highly oxidizing HNO{sub 3} solutions have been studied by exposure testing, electrochemical polarization, high resolution analytical electron microscopy (HRAEM), and Auger electron spectroscopy (AES) techniques. Results of these studies indicate that intergranular corrosion of {approximately} 1%Si alloy is caused by galvanic coupling effect between Si-rich grain boundaries and normal grain faces. Lower Si-content alloys have high corrosion resistance by an absence of the effect and forming Cr-rich oxide films. Corrosion tests using laser surface melted alloy and coupons simulating a galvanic couple support the identified mechanism.