Análise da variação típica da composição química de placas de lingotamento contínuo

Abstract

A statistical dispersion study of elements C, Mn, S, Nb, P, Al, Si in steel plates APIX70 and IF-BH180, manufactured in continuous cast, and the results had been compared to liquid steel sample results. Plates analyzed using the technique of Baumann with results whithin the limits of the Usiminas´s standards. These plates had been cut in ten parts in relation to thickness and five parts in relation to width. Each sample, was analyzed five times in the same equipment of optic emission spectrometry spark, for the same operator, in the same day and with the same calibration, the analysis have been followed by tests in standardsamples; to eliminate the influence of the equipment on analysis. The analysis results have been presented in a schematic formconcerning the position the plate: average and standard desviation. A total of 500 chemical analysis, were analyzed by F test (one way ANOVA). The averages of the chemical analysis in samples of the plates were compared to liquid steel samples using the uncertainty of the laboratory as parameter of exclusion of representation. By use of this methodology it was possible to identify the representative points of the plate with reference to liquid steel and recomend those relative to lowest costs and best representation. The understanding of chemical composition profile in the plate, sampling and technique of analysis is the way to continuous improvement in the quality of chemical analysis results, without which it is impossible to follow more and more rigorous steel specifications.