Abstract

Nitrogen alloyed austenitic stainless steels (NAASS) exhibit attractive properties as high strength and ductility, good corrosion resistance and reduced tendency to grain boundary sensitisation. However, slabs produced by these steels with nitrogen content above about 0.2 mass% show the presence of small pores located just below the slab surface, with consequent downgrading of the product. The origin of the pores is to be attributed to the formation of gas bubbles due to segregation/supersaturation phenomena occurring during solidification of gas forming solutes. Thermodynamic methods and mathematical analysis of solidification have been used to predict the composition adjustments, still remaining in the NAASS grade, which permit to avoid the formation of bubbles. Predictions have been tested against results of laboratory scale solidification trials and found satisfactory.

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