Corrosion behaviour of hot-pressed austenitic stainless steel in H₂SO₄ solutions at room temperature

The corrosion behavior of hot-pressed stainless steel (HPSS) of Type 316 was investigated. Samples of HPSS with porosity of 10-30% were prepared. The influence of the porosity factor on corrosion behaviour was investigated by potentiodynamic polarization, open circuit potential, identification of corrosion products by EDAX and SEM observation. It was found that porosity of the HPSS is the main factor affecting corrosion resistance. High porosity results in low corrosion resistance. The open circuit potential of the HPSS is about - 200 mV (VSCE) as compared to 200 mV for the wrought 316 stainless steel. The potentiodynamic measurements indicate that cathodic concentration polarization is achieved at a relatively low current density and secondary active-passive transition is observed at a relatively high current density in HPSS as compared to wrought 316 stainless steel. It is suggested that the main mechanism affecting the low corrosion resistance of HPSS in H₂SO₄ is the evolution of hydrogen concentration cells due to electrolytic stagnation in the interconnected open pores. As a result the surfaces of the interconnected open pores act as an active anode and the engineering sample surface acts as an active cathode.