Tempering Reactions and Elemental Redistribution During Tempering of Martensitic Stainless Steels
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TRODUCTION
DUE to the brittle nature of as-quenched martensite, the mechanical properties of martensitic steels are often modified by thermal treatment. The processes induced by the thermal treatment of martensite often involve C diffusion and redistribution and are collectively known
QIULIANG HUANG and OLENA VOLKOVA are with the Institute of Iron and Steel Technology, Technische Universita¨t Bergakademie Freiberg, Leipziger St. 34, 09599 Freiberg, Germany. MENGJI YAO is with the Max-Planck-Institut fu¨r Eisenforschung GmbH, Max-Planck-St. 1, 40237 Du¨sseldorf, Germany. ILANA TIMOKHINA is with the Institute for Frontier Materials, Deakin University, Locked Bag 20000, Geelong, VIC 3220, Australia. CHRISTIAN SCHIMPF is with the Institute of Materials Science, Technische Universita¨t Bergakademie Freiberg, Gustav-Zeuner-Straße 5, 09599 Freiberg, Germany. HORST BIERMANN is with the Institute of Materials Engineering, Technische Universita¨t Bergakademie Freiberg, Gustav-Zeuner-Straße 5, 09599 Freiberg, Germany. BRUNO C. DE COOMAN is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, South Korea. JAVAD MOLA is with Institute of Iron and Steel Technology, Technische Universita¨t Bergakademie Freiberg and Material Design and Structural Integrity Lab, Faculty of Engineering and Computer Sciences, Osnabru¨ck University of Applied Sciences, Albrecht St. 30, 49076 Osnabru¨ck, Germany. Contact e-mail: [email protected] Manuscript submitted December 24, 2018. Bruno C. De Cooman deceased on August 29, 2018. Article published online May 20, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
as tempering reactions.[1] In general, five distinct but often overlapping tempering stages can take place at successively higher temperatures. Stage 0 involves the segregation of solute C to defects and the formation of C clusters.[2] In stage I, transition carbides, such as e-carbides with hexagonal closed-packed structure and g-carbides with orthorhombic structure, are formed.[3,4] Subsequently, retained austenite (RA) decomposes into bainite, which is often referred to as stage II. It occurs in carbon and low-alloy steels containing RA[5] and frequently overlaps the stage III, namely, the replacement of transition carbides by cementite (M3C with M denoting Fe and substitutional alloying elements).[6] At higher temperatures (stage IV), cementite is replaced by the more stable alloy carbides.[7] Tempering reactions have often been studied by means of microstructural examinations,[8] X-ray diffraction (XRD),[9] differential scanning calorimetry (DSC),[10] and dilatometry.[11] Due to the differences in the magnetic properties of phases involved in tempering reactions,[12] such reactions can also be studied by magnetic measurements. With the knowledge of the mass magnetization of all phases in a steel consisting of n microstructural phases, the overall mass magnetization (r) can be obtained from the rule of mixtures as follows[13]: r¼
n X
ri fi ;
½1
i¼1
VOLUME 50A, AUGU
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