Influência dos teores de carbono e manganês no grau de bandeamento microestrutural e na resistência a HIC de chapas de aço ASTM-A516 grau 70 normalizadas

Abstract

The present study evaluated the influence of the C and Mn content on the microstructural banding degree and on the HIC resistance on ASTM-A516-70 steel plate. Three heats were produced in pilot scale, varying the contents of Mn and C. The ingots obtained were hot-rolled and then normalized. The steel characterization was carried out through analysis of inclusion content, volume fraction of constituents, ferrite grain size, microstructural banding degree, HIC susceptibility, tensile and Charpy tests. It was verified that C content was more effective than Mn content on microestructural banding degree, and the microestructural banding degree increased according to C/Mn ratio. The steels with higher Mn contents showed lower ferrite grain sizes, due to lower AR3 transformation temperatures, allowing also the achievement of the best results of the notch toughness. The cracks observed after HIC test occurred in the mid thickness of plates, in the region with higher amount of hydrogen "traps", and emerged from the regions containing martensite and / or MA constituents. The HIC resistance decreased as the degree of banding decreased. The decrease of HIC resistance was more influenced by the microstructural constituents present than by its distribution, while the reducing of the microestructural banding degree was attributed mainly to the reduction of C content.