Efeito da fração volumétrica de Martensita, formada no resfriamento após recozimento intercrítico no grau estriamento, propriedades mecânicas e estampabilidade de um aço tipo AISI 430

Abstract

The subject of this work was to develop an AISI 430 steel with a modified chemical composition, processed on intercritical annealing followed by a fast cooling, with the same mechanical properties and drawability of the standard AISI 430 steel, and also, with a ridging level below 0.7. The steel was industrially cast and hot rolled to 4.00 mm. In a lab, different cooling rate were used, after intercritical annealing, in order to get different martensite volumetric fractions and to determine the influence of this parameter on steel properties after cold rolling and annealing operations. The results related to ridging level showed that an increase of martensite volumetric fraction decreased a lot the ridging tendency after cold rolling. By visual analysis, the ridging level was zero for 34% and 43% martensite volumetric fraction, 0.7 and 1 for 21% and 0% martensite volumetric fraction, respectively. The mechanical properties were according to the specification range for standard AISI430 steel grade. The yield strength and tensile strength increased and elongation decreased as the martensite volumetric fraction was increasing. These results were explained in terms of the reduction of grain size and chromium carbide particles with the increase of martensite amount. The decrease on the ridging level for fractions of martensite in the 21 to 43% range was related to the reduction or elimination of grains colonies having the same crystallographic orientation. The lower values observed for the average strain ratio compared to standard AISI 430 steel grade was attributed to the martensite wich reduces of g fibre intensity