Effect of C Fraction on Corrosion Properties of High Interstitial Alloyed Stainless Steels
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As efforts to develop substituting materials for Nidependent austenitic stainless steels, high nitrogen stainless steel (HNS)[1–5] and high interstitial alloy (HIA)[6–14] have been proposed. The concept of combined addition of N and C to the low-Ni stainless steel has been embodied in HIA, which gives several advantages such as a cost-saving manufacturing process (i.e., excluding pressurizing process required for HNS) and excellent performance. Interstitial alloying elements of C and N effectively stabilize an austenite phase in a stainless steel, improve strength without much reduction in ductility,[1,6,7,9,10] and promote wear resistance. An in-depth investigation on an electronic structure and austenitic stability of various HIAs (Fe(13-18)Cr(16-20)Mn(0.250.88)N(0-0.49)C) was performed by Gavriljuk et al.[8–11] They clarified that the combined addition of N and C to the FeCrMn-based alloy changed the free electron density, short-range ordering, and austenitic stability; hence, the mechanical properties of the HIAs were varied. In addition, wear performance of commercial HIA (P558, Fe17Cr10Mn3Mo0.5N0.2C)[6] and precipitation behavior of Fe18Cr10Mn0.38N0.38C alloy were HEON-YOUNG HA, Senior Researcher, and TAE-HO LEE, Principal Researcher, are with the Advanced Metallic Materials Division, Korea Institute of Materials Science, Gyeongnam 642-831, South Korea. Contact e-mail: [email protected] SUNG-JOON KIM, Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science & Technology, Gyeongbuk 790-784, South Korea. Manuscript submitted March 28, 2012. Article published online June 30, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
examined.[14] As concerned with pitting corrosion behavior, it was reported that the alloyed C had similar beneficial effect to that of N,[1,13,15] which was strengthening a passive film of FeCrMn-based stainless steels.[13] Owing to the advantages, the development of HIA has become an important matter of concern. In HIA, a certain amount of N is required to enhance the performances and to form stable austenite at a given interstitial element content[9–11] because a stable region for austenitic phase cannot be obtained by adding C only due to an inevitable formation of M23C6. Considering the manufacturing cost, however, the N content should be controlled at an optimum level to exclude a pressurizing process. Consequently, on designing the HIA, it is important to control the N and C ratio, and hence, understanding the effects of the interstitial fraction on various properties is required. Particularly, the corrosion properties of stainless steels affected by the alloyed C have been rarely investigated so far. Thus, in this article, the change in various corrosion properties of Ni-free FeCrMn-based HIAs by adjusting an interstitial fraction of C ([C]/[C+N]) was examined. The alloys under investigation were Fe18Cr10Mnbased HNS and HIAs, whose chemical compositions and interstitial fraction of C ([C]/[C+N]) are presented in Table I. The alloys contained approximately 0
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