Influence of chemical composition on structural transformations in carbon steels and their welded joints

Abstract

In this paper, based on the analysis of the dependence of temperature critical points of structural transformations on the chemical composition of steel, it is shown that carbon can be considered a determining factor influencing the kinetics of structure formation in carbon steels and their welded joints. With the carbon content increases, the period of inertia of diffusion (perlite) and intermediate (beinite) transformation of subcooled austenite increases, while the course of transformation accelerates. This creates preconditions for solving the task of development of diffusion and intermediate transformation of subcooled austenite in metal of welded joints prone to hardenability and prevents martensitic (non diffusion) transformations. However, for the purposeful beginning of the indicated forms of transformations, an efficient method or a way of shortening the period of inertness of its decomposition within the predicted limits is necessary. Carbideforming alloying elements increase the positive effect of carbon on γ→α transformation in the diffusion region and weak in the intermediate region. All other alloying elements under conditions of continuous cooling slow down the decomposition of subcooled austenite in the diffusion and intermediate region and increase the period of inertia, necessary for its onset.