CAST AUSTENITIC STAINLESS STEEL EXCELLENT IN NITRIC ACID RESISTANCE AND SURFACE TREATMENT THEREFOR

• Main Authors: UNO HIDEKI, ISHIGA JUNKO
• Format: Patent
• Language: English
• Published: 13.08.1996
• Edition: 6
• Subjects: ALLOYS; CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; FERROUS OR NON-FERROUS ALLOYS; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; METALLURGY; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PURPOSE: To produce a cast austenitic stainless steel for structural purposes, excellent in corrosion resistance under a nitric acid environment with a concentration not higher than azeotropic concentration and also having high strength and superior castability. CONSTITUTION: This steel is a cast high strength austenitic stainless steel having a steel composition which consists of, by weight, <=0.03% C, 0.3-1% Si, <=2% Mn, <=0.03% P, <=0.03% S, 19-21% Cr, 8.5-12% Ni, 0.05-0.2% N, 0.03-0.1% Nb+Ta, <=0.001% B, and the balance Fe with inevitable impurities and in which the ratio between Creq, represented by Creq=%Cr+1.5×%Si+1.4×%Mo+%Nb-4.99, and Nieq, represented by Nieq=%Ni+30×%C+0.5×%Mn+26×(%N-0.02)+2.77, is regulated to 0.9-1.2, also having superior castability, and excellent in nitric acid resistance under a nitric acid environment with a concentration not higher than azeotropic concentration. Surface treatment for this cast austenitic stainless steel excellent in nitric acid resistance can be performed by immersing this cast steel for >=30min in an aqueous solution having a temp. of 40-70 deg.C and 20-50wt.% nitric acid concentration.