Simulation of Phase Transformations upon Welding of Alloyed Steels

Abstract

A computer-oriented mathematical model of the austenite decomposition in alloyed steel in conditions of welding thermal cycle is presented. It is shown that each diffusion phase transformation can be described using four parameters: two limits of the temperature range of transformation and two parameters of the Avraami equation. Martensitic transformation can be described using three parameters. A procedure for determination of all required time-temperature parameters of the model obtaining from the chemical composition of steel is described. Regression models of the temperature intervals and kinetic parameters of ferrite-pearlite, bainite and martensite transformations are obtained on the basis of literature data. It is shown that shortcomings of existing visual methods of analysis of the final phase composition of steels are the reasons for inaccuracy and inconsistency of published transformation diagrams. The hardness of the sample which correlates with a number of other mechanical properties of the material is thus chosen as the most objective and reproducible criterion of final phase composition. To check the developed model we compare experimental data and the results of hardness calculation for 140 alloyed steels after their cooling at different values of the cooling rate.