Gas porosity defects in duplex stainless steer castings

Gas porosity defects are occasionally found in the production of duplex steel castings causing economic losses in the form of repair weldings. In order to determine the reasons for the porosity, a series of 17 test castings of cast duplex stainless steels ASTM A890 Grade 5A was made in this study. According to the results, several factors, like deoxidation, nitrogen content and solidification shrinkage of the steel, influence the porosity level. In order to study solidification and porosity formation, an FEM-based computer program, THETIS, has been developed. By applying it to one of the test castings it could be shown that, under certain conditions, the interaction of gases, inclusions and shrinkage make the casting susceptible to porosity formation.