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In this work, an evaluation method to calculate the austenite fraction during continuous heating and isothermal annealing from dilatometric data is proposed. By means of a single reference measurement to determine a scaling factor correcting for experimental errors, a framework is created to determine the austenite fraction as a function of time and temperature. In the evaluation of the dilatometric data the effect of the changing carbon concentration in austenite phase is taken into account. The method is applied to dilatometric data for a 0.16C-1.5Mn-0.4Si (wt%) low-silicon transformation induced plasticity (TRIP) multiphase steel. Three typical dilatometric data are obtained by heating the material to 750°C, 800°C or 900°C, which leads to three different microstructures consisting of (1) ferrite, cementite and austenite, (2) ferrite and austenite and (3) full austenite, respectively. The calculated results using the proposed new method are compared with the results from thermodynamic analysis and those from quantitative microscopic analysis. Significant inter-test discrepancies are observed. [ABSTRACT FROM AUTHOR]

The dependence of the transformation kinetics of an HSLA steel and related C-Mn steels on the austenitisation conditions have been investigated using calorimetry and dilatometry. It is observed that the ferrite-start temperature depends both on the manganese content and on the amount of niobium in solution. Calculations of the transformation kinetics based on an interface-mobility model applied in a tetrakaidecahedron austenite-grain geometry are used to investigate the background of the observed changes in transformation kinetics. [ABSTRACT FROM AUTHOR]

Dilatometry is a useful technique to obtain experimental data concerning transformation kinetics in ferrous alloys. This technique is commonly used in cooling experiments to study the austenite decomposition of hypo-eutectoid steel grades. In the standard analysis of the dilatation signal there are two factors that are normally neglected. During the pro-eutectoid ferrite formation the austenite enriches in carbon, resulting in a non-linear temperature dependence of the specific austenitic volume. Furthermore, the specific volume of the formed ferrite is considerably different from that of the formed pearlite. In total not taking into account these two effects can lead to an error in the determined fraction ferrite of up to 25%. A method is presented that takes into account the two above-mentioned factors. In order to determine both the fraction ferrite and the fraction pearlite, in the analysis the temperature range of the transformation is divided into a ferrite-formation range and a pearlite-formation range. Two possible criteria for this division are discussed, and it is shown that the choice does not have an essential influence on the results. [ABSTRACT FROM AUTHOR]