Austenitic Nickel- and Manganese-Free Fe-15Cr-1Mo-0.4N-0.3C Steel: Tensile Behavior and Deformation-Induced Processes be
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INTRODUCTION
DUE to their excellent combination of corrosion resistance and formability, the AISI 300 series austenitic stainless steels are of a high industrial importance.[1–3] Particularly for economic reasons, it is desirable to replace Ni by other austenite-stabilizing alloying elements. The replacement of Ni by Mn is one of the approaches towards making affordable austenitic stainless steels.[4–7] The increase in the Mn concentration is associated with an increase in the solubility of N in the liquid state and reduces the N2 pressure required to achieve a particular N content in the solid state.[5,8] For this reason, almost all Ni-free high N austenitic stainless steel developments also involve the addition of a high concentration of Mn.[4,9–12] The addition of C and N as strong austenite stabilizers effectively reduces the amount of Ni and Mn otherwise required to obtain an JAVAD MOLA, BUXIAO KUANG, REZA RAHIMI, and QIULIANG HUANG are with the Institute of Iron and Steel Technology, Technische Universita¨t Bergakademie Freiberg, 09599, Freiberg, Germany. Contact e-mail: [email protected] CHRISTIANE ULLRICH and DAVID RAFAJA are with the Institute of Materials Science, Technische Universita¨t Bergakademie Freiberg, 09599, Freiberg, Germany. ROMAN RITZENHOFF is with Benteler Steel/Tube GmbH, 46537, Dinslaken, Germany. Manuscript submitted February 12, 2016. Article published online January 13, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
austenitic microstructure at room temperature (RT). Furthermore, C and N have a pronounced solid solution strengthening effect.[4,13–18] Compared to C, N is a more effective solid solution strengthener[18,19] and imparts pitting corrosion resistance to steels.[20,21] Alloying with N increases the resistance of austenitic stainless steels to the formation of spontaneous and deformation-induced martensite; each mass percent of N decreases the highest temperature associated with the ) by strain-induced (a¢) martensite formation (Mcfia¢ d about 523 K (250 C).[22] This can be correlated with the effect of N on the stacking fault energy (SFE), since it is commonly known as an SFE-raising alloying element[12,23,24] although contrary reports exist too.[25] In contrast to discrepancies regarding the influence of certain alloying elements (e.g., N) on the SFE,[26] an increase in the temperature is unanimously known to increase the SFE.[19,27] Therefore, the variation of deformation temperature can be used as an effective way to alter the deformation mechanisms.[15,28–31] The high formability of high-Mn austenitic steels is often attributed to the twinning-induced plasticity (TWIP) effect.[32–34] For austenitic stainless steels too, maximum tensile elongations are achieved at deformation temperatures where pronounced deformation twinning but very limited martensite formation could be identified.[29,35–38] One of the reasons behind the high formability and the widespread use of austenitic stainless steels such as the VOLUME 48A, MARCH 2017—1033
AISI 304 grade is their ready twinning u
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