CCT diagram plotting based on the numerical analysisof dilatometric tests results

Abstract

This paper considers the issues related to plotting of continuous cooling transformation (CCT) phase diagram based on the dilatometric test results. The numerical data processing algorithm for uniformly analysis of the dilatometric curves is developed and implemented. Computing of the phase transformation ranges and coefficient of thermal expansion (CTE) were made in Microsoft Excel. Numerical algorithm contains determination of the critical points as the deviation dots from linear approximation function of the monotonous segment of experimental curve which is extrapolated to the start (or finish) of the phase transformation. Method of CCT diagram plotting based on the quantitative analysis of CTE during austenite continuous cooling is proposed. CTE quantitative evaluation of austenite and its decomposition products were accomplished by the analysis of linear approximation function of monotonous segment of dilatometric curve. Dependence of the CTE values on the range of cooling rates were used to define the phase transformation ranges on the CCT diagram. Obtained CTE dependence clearly defines critical cooling rate (ССR) as an intersection point of functions, describing austenite CTE changes with cooling rates and austenite- ferrite mixture. Point of intersection was found by solving the system of functions equations. Confirmation and clarification of results, based on the numerical analysis of the dilatometric curves, could be done as usual, using metallographic analysis and microhardness testing. The application of the developed numerical algorithm for dilatometric curves provides opportunity to unify dilatometric test analysis and to improve the accuracy of the CCT diagram plotting.