Effect of Mo Addition on the Transformation Stasis Phenomenon During the Isothermal Formation of Bainitic Ferrite
- PDF / 6,280,904 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 82 Downloads / 242 Views
ransformation has attracted significant attention from metallurgists due to its practical importance in steel design and production, and it has been widely studied in the literature.[1–6] Despite abundant effort, there are still many unresolved issues in the field of bainitic transformation, and transformation stasis (TS) (also called as incomplete bainite transformation) is one of them.[7–11] The TS phenomenon has been described as follows: the isothermal bainitic transformation reaches a temporary cessation at a bainite fraction which is lower than that allowed by paraequilibrium.[12,13] The transformation will resume till carbides start to precipitate, which reduces the carbon content and increases the chemical driving force for further formation of bainitic ferrite. There are two competing views about the origin of TS: (i) the CONGYU ZHANG, Ph.D. Student, HAO CHEN, Assistant Professor, CHI ZHANG, Associate Professor, and ZHIGANG YANG, Professor, are with the Key Laboratory of Advanced Materials of Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, People’s Republic of China. Contact e-mail: [email protected] KANGYING ZHU, Engineer, is with ArcelorMittal Research SA, Voie Romaine, 57280 Maizieres les Metz, France. Manuscript submitted May 17, 2016. Article published online October 11, 2016 5670—VOLUME 47A, DECEMBER 2016
diffusionless school considers bainitic transformation as a diffusionless process, and the transformation is expected to cease when the carbon concentration in austenite reaches T0 line.[8,14,15] In order to better fit with experiments, a constant strain energy of 400 J/mol is introduced into the calculation of T0, which leads to the T0¢ line;[9,16,17] (ii) the diffusional school argues that the bainitic transformation is diffusional, and its mechanism is essentially the same as that of ferrite formation.[18] Aaronson et al.[13] experimentally investigated TS phenomenon in a series of Fe-C-X alloys and found that the presence of TS phenomenon depends on the kind of X, composition, and temperature. TS was deduced to be due to the solute drag effect of alloying elements. In the past decades, substitutional alloying element effects on the migrating austenite-ferrite interfaces have been extensively investigated, and it is found that the interfacial alloying element partitioning plays a significant role in the kinetics of ferrite formation.[19–23] However, the effect of interfacial alloying elements partitioning on the bainitic transformation has been relatively less studied. Recently, a Gibbs energy balance approach (GEB) [24,25] based on solute drag theory has been used to explain the TS phenomenon in a series of ternary Fe-C-Mn and Fe-C-Mo alloys,[26,27] and it was deduced that the TS phenomenon is caused by Mn and Mo diffusion inside the interfaces. In the current study, the TS phenomenon during the isothermal bainitic transformation in a series of multicomponent alloys (Fe-0.2C-1.5Mn-1.5Si-xMo alloys, x = 0.2, 1.5, and 3 wt pct, hereafter deno
Data Loading...
