Abstract
In recent years, the price of alloys, such as Ni and Mo rises, so that it is difficult to use the stainless steel containing these elements. Therefore, Ni was reduced and Mn and N were added to the conventional stainless steels alternatively. 'Lean grade or Low grade1 duplex stainless steels have attracted industrial interest for substituting higher alloyed grades with the applications where strength is more important than corrosion resistance. In this research, studies were aimed at evaluating the corrosivity of low Ni high Mn-high N, namely duplex stainless steels S32101 and S32304 comparing with the conventional austenitic stainless steel SUS304. Vickers hardness test, Electrochemical Potentiokinetic Reactivation ratio (EPR) measurement, and microstructural observation were carried out using the steels subjected to 748K embrittlement of 748K, sensitization of 973K and sigma phase embrittlement of 1073K. The experimental results obtained in this study lead to the following conclusion. (1) The results of hardness test of the both duplex stainless steels showed the sign of 748K embrittlement, but did not show the sign of sigma phase embrittlement. (2) The hardness of the both duplex stainless steels were rather higher than SUS304 steel. (3) There may exist a correlation to the reactivation rate and the weight decrease rate of these stainless steels under freezing and thawing corrosive environment.
