C. García de Andrés

Application of dilatometric analysis to the study of solid–solid phase transformations in steels

Abstract This article outlines the use of dilatometry in solid–solid phase transformation research in steel. It describes how dilatometric data are interpreted, with an emphasis on continuous heating and cooling transformation diagrams. These diagrams show the microstructural constituents that result from given heating and cooling conditions, and are an invaluable tool for the metallurgist in characterizing steels with respect to their response to heat treatments. Several practical examples and applications of dilatometry in steel research are briefly described in this work.

Modelling of kinetics and dilatometric behavior of non-isothermal pearlite-to-austenite transformation in an eutectoid steel

European Coal and Steel Community (ECSC-7210. EC/939) and the Spanish Comisio´n Interministerial de Ciencia y Tecnologi´a (CICYTMAT95-1192-CE)

Metallographic techniques for the determination of the austenite grain size in medium-carbon microalloyed steels

Abstract Different techniques have been investigated to seek the best procedure to reveal the prior-austenite grain boundaries in three medium-carbon microalloyed steels. This study has been carried out over a wide range of temperatures (950–1250°C) and it has been found that thermal etching (TE) is the best technique to reveal the prior-austenite grain boundaries in these steels.

Revealing austenite grain boundaries by thermal etching: advantages and disadvantages

Abstract This article reviews the method of thermal etching for revealing the prior-austenite grain boundaries in steels. This method involves preferential transfer of material away from grain boundaries when the steel is exposed to a high temperature in an inert atmosphere. Thus, during austenitization of a prepolished sample, grooves are formed at the intersections of the austenite grain boundaries with the polished surface. These grooves remain intact after cooling and are clearly visible at room temperature outlining the austenite grain boundaries. However, at very high austenitization temperatures, those grooves might interfere with the advance of the austenite grain boundaries on the surface. In that case, this technique could lead to a wrong measurement of the austenite grain size. The aim of this work is to study the advantages and disadvantages of the technique to reveal the austenite grain boundaries in microalloyed steels.

Analysis of effect of alloying elements on martensite start temperature of steels

Abstract The stabilisation of austenite, a phenomenon that frequently occurs, renders the transformation from austenite to martensite difficult. The straightforward method of analysing the effect of a specific factor on the stabilisation of austenite is through its influence on the martensite start temperature M s. The present work outlines the use of an artificial neural network to model the M s of engineering steels based on their chemical composition and austenite grain size. The results are focused on elucidating the role in the stabilisation of austenite of alloying elements in steels, including less common elements such as vanadium and niobium, as well as the austenite grain size. Moreover, a physical interpretation of the results is presented.

Control of M23C6 carbides in 0.45C–13Cr martensitic stainless steel by means of three representative heat treatment parameters

Abstract Heat treatment parameters closely control the amount of carbides in steels. In this study, the influence of three parameters (heating temperature, heating rate and cooling rate) on the area percentage of M23C6-type carbides in the quenching microstructures of 0.45C–13Cr martensitic stainless steel has been studied. The experimental results obtained in this study demonstrate that the amount of carbides in the quenching microstructures of this steel can be severely modified through the heating and cooling conditions of the heat treatment.

Dilatometric characterization of pearlite dissolution in 0.1C-0.5Mn low carbon low manganese steel

The authors acknowledge financial support from the European Coal and Steel Community (ECSC- 7210. EC/939) and the Spanish Comisio´n Interministerial de Ciencia y Tecnologi´a (CICYT-MAT95-1192-CE)

Kinetics and dilatometric behaviour of non-isothermal ferrite-austenite transformation

Abstract A model that describes the ferrite–austenite transformation during continuous heating in Armco iron and three very low carbon, low manganese steels with a fully ferritic initial microstructure is presented. This model allows calculation of the volume fractions of austenite and ferrite during transformation as a function of temperature, and hence knowledge of the austenite formation kinetics under non-isothermal conditions in fully ferritic steels. Moreover, since dilatometric analysis is a technique very often used to study phase transformations in steels, a second model, which describes the dilatometric behaviour of the material and calculates the relative change in length that occurs during the ferrite–austenite transformation, has also been developed. Both kinetics and dilatometric models have been validated by comparison of theoretical and experimental dilatometric heating curves. Predicted and experimental results are in satisfactory agreement.

Characterization and morphological analysis of pearlite in a eutectoid steel

Three different morphologies of pearlite have been formed isothermally at three temperatures in a eutectoid steel. The interlamellar spacings of these morphologies have been measured by scanning and transmission electron microscopy. A comparison of these experimental results and the interlamellar spacing calculations using a theoretical model previously developed has allowed some standardization to be established for the morphological characterization of pearlite, in terms of sample preparation, examination conditions, and quantitative metallography procedures. It has been found that using scanning electron microscopy, the morphological characterization of pearlite with interlamellar spacing finer than 0.085 μm could lead to unreliable results, since the strain induced during metallographic preparation of very fine pearlite destroys the lamellar morphology of pearlite. In that case, it is advisable to measure the interlamellar spacing of pearlite using transmission electron microscopy.

Modelling of kinetics and dilatometric behaviour of austenite formation in a low-carbon steel with a ferrite plus pearlite initial microstructure

The compiled knowledge in literature regarding the isothermal formation of austenite from different initial microstructures (pure and mixed microstructures), has been used in this work to develop a model for non-isothermal austenite formation in low-carbon steels (C < 0.2 wt%) with a mixed initial microstructure consisting of ferrite and pearlite. Likewise, calculations of relative change in length have been made as a function of temperature, and the differences between theoretical and experimental results have been analysed in 0.1C–0.5Mn low-carbon low-manganese steel. Experimental kinetic transformation, critical temperatures as well as the magnitude of the overall contraction due to austenite formation are in good agreement with calculations.