Study of phase transformations during tempering of AISI L6 low alloy tool steel by means of dilatometry and high temperature X-ray diffraction.
Douglas I. Quiñones-Salinas1*, Rafael D. Mercado-Solís1, Luis A. Leduc-Lezama1,
Florentino Fernandez-Guzman2, Rene Cerda-Rojas2.
1Universidad Autonoma de Nuevo León, México
2Frisa Forjados S.A. de C.V., México
The purpose of this work was to establish the influence of heating rate on the reaction kinetics during the double tempering of AISI L6 tool steel by means of dilatometry and high temperature X-ray diffraction (HTXRD). Phase transformations during tempering of the samples were analyzed heating from as-quenched condition to 700 °C at different heating rates 5, 50 and 150 °C/sec. The high temperature X-ray diffraction was used to confirm the presence of carbide precipitate and retained austenite existing in the material during the heating into the tempering temperatures. SEM was used to determine the phases present for as-quenched and tempered conditions. Dilatometry and HTXRD techniques allowed the identification of clustering of carbon particles, the full transformation of retained austenite and the cementite precipitation remaining to room temperature. These techniques showed that the first tempering mainly leads the retained austenitic transformation and the precipitation of cementite. The reactions of growing and distribution of carbides also was possible to measure only by dilatometry at the second tempering. Dilatometry and high temperature X-ray diffraction are powerful techniques for analyze the phase transformations during the tempering.
Keywords: tempering heat treatment, low alloy tool steel, precipitation, phase transformations, dilatometry, high temperature X-ray diffraction.