Estudio de la microsegregación en aceros colados de alto Silicio

NICOLÁS E. TENAGLIA; A. BASSO; J. MASSONE; R. BOERI

Santa Fe

Congreso; Congreso SAM-CONAMET-IBEROMAT; 2014

SAM

Carbide free bainitic steels are medium C and high Si steels that are austempered. This composition and heat treatment lead to a microstructure composed of acicular ferrite and high percentages of retained austenite enriched in carbon, that shows very high mechanical properties. Numerous studies on these steels were focused on determining the kinetics of phase transformations and mechanical properties, and the influence of the chemical composition of steel and heat treatment parameters applied. However, most of the studies were carried out using hot rolled materials. It the case of cast parts, the segregation during solidification will cause the metallic matrix to show variations in local chemical concentration, ordinarily called microsegregation, that are much larger than those found in hot rolled materials. This heterogeneity may influence the kinetics of solid state transformations, critically affecting the resulting microstructure.This paper focuses on the study of the segregation of a cast steel alloyed with Cr, Mo, Ni and high Si. Specimens were taken from U blocks cast specifically for this project. Metallographic color etching techniques and EDS were used together to observe a complete pattern of segregation. The specimens were examined in as cast state.The results allowed to calculate the partition coefficients of Si, Mn, Cr and Ni, obtaining in all cases direct segregation. Also, qualitative method for microsegregation determination (color etching) matches with quantitative method (EDS). However, the first one allows to observe bigger areas easily, constituting a very effective tool for microstructural analysis