The use of color etching to study the microstructure of laser welded steel used in the automotive industry

Abstract

In the present article the results of a microstructure study of dual phase, multiphase (with transformation induced plasticity effect) and manganese-boron steel have been presented in the as-delivered state and after laser fusion by means of color metallography, which, up to now, has not been applied in those types of joints. In order to reveal the components of the microstructure of the steel types studied, five reagents were applied: nital, pikral, Klemm, LePera and sodium metabisulfite, in different combinations. Various phases were revealed in the material in the as-delivered state and after fusion, and this would not have been possible using standard procedures by means of a light microscope. In the as-delivered state all basic phases were observed. In the state after laser remelting, the observed microstructures were completely different than in the received state giving bainite and martensite an advantage. Measurements of the hardness of the as-received material and the welds of the tested steels were performed, showing a significant increase in weld hardness.