Pearlite Transformation in a Deformed TRIP/TWIP Austenitic Steel
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rlite transformation has been widely studied in the last century and is one of the most well-known microstructures of steel.[1–3] According to the classical nucleation theory,[4] nucleation of pearlite starts with a nucleus of ferrite or cementite in a grain boundary or an inclusion,[5] and then a cementite or ferrite nucleus forms adjacent to the primary nucleus with a specific orientation relationship. Ferrite and cementite arrange themselves in a cooperative manner that results in alternate ferrite and carbide lamellae maintaining a crystallographic orientation relationship, which grow sidewise and edgewise to take over the austenite grain. Grain boundaries and inclusions act as nucleation sites due to the reduction of the energy necessary for nucleation by the destruction of the interface between these and the adjacent lattice. In the same way, other lattice defects such as twins or deformation bands
D. DE CASTRO, J. VIVAS, M.M. ARANDA, J.A. JIMENEZ, and C. CAPDEVILA are with the Centro Nacional de Investigaciones Metalu´rgicas (CENIM), Consejo Superior Investigaciones CientU´ficas (CSIC), Avda Gregorio del Amo, 8, 28040 Madrid, Spain. R. REMENTERIA is with the Centro Nacional de Investigaciones Metalu´rgicas (CENIM), Consejo Superior Investigaciones Cientı´ ficas (CSIC) and also with the Additive Manufacturing - New Frontier, ArcelorMittal Global R&D, Calle Marineros 4, 33490, Avile´s, Asturias, Spain. Contact e-mail: [email protected] Manuscript submitted January 8, 2018. Article published online October 30, 2018 METALLURGICAL AND MATERIALS TRANSACTIONS A
contribute to the reduction of the energy for nucleation by the removal their interface.[6] However, just a few studies focus on these nucleation sites and their effect on pearlite transformation. Furuhara et al.[7] studied the effect of slight warm deformation of austenite prior to pearlite transformation, concluding that deformation effectively accelerates the intragranular nucleation of pearlite even if intragranular pearlite is hardly formed without deformation. In addition, the authors observed that MnS particles activate as intragranular nucleation sites of pearlite. Umemoto et al.[8] studied the effect of warm rolling of austenite in pearlite transformation and concluded that deformation accelerates pearlite transformation. Besides the increase in the austenite grain surface area per unit volume by the elongation of grains, those authors suggested the possibility that twins or deformation bands generated during the warm rolling act as potential nucleation sites for pearlite. This last above-cited study was carried out in steels with chemical composition, which hinder austenite at room temperature, and hence the effects of stain in austenite reported correspond to indirect determination techniques. By contrast, the study presented here is carried out in a TRIP/TWIP steel (chemical composition is listed in Table I) austenite of which is stable at room temperature. The steel studied here is related with the so-called lightweight steels (Fe-Mn-Al-C system), which
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