Estudo experimental da oxidação dos aços inoxidáveis ferríticos AISI 444 e AISI 439 a altas temperaturas em ar

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

It was carried on a comparative study of the response to oxidation, in high temperatures and dry air atmosphere, of the stainless steel AISI 444 and AISI 439, with the temperature range between 850C and 1.050C. Such steels differ in their chemical composition basically by containing molybdenum in the AISI 444 steel. It were used samples supplied by ArcelorMittal Inox Brasil, whose dimensions were 10mm x 10mm x 0.6mm. A hole of 0,8mm in diameter was drilled near an edge at the center of the samples with the purpose of sustainment by means of a platinum wire in a thermobalance. AISI 4 44 steel samples, after trimmed off utilizing water sandpaper, and having the two faces polished with diamond paste of 3?m and 1?m, were submitted to heat treatment of oxidation in a SETARAM thermobalance, whose sensitivity is equal to ?1? g, in the temperatures of 850C, 900C, 950C, 1000C and 1050C, with treatment time duration from 43h52min to 50h32min, into dry air atmosphere. Utilizing the same methodology, it was carried out the heat treatment of oxidation of the stainless steel AISI 439 at 1050C, into dry air atmosphere, during 47h41min. Besides, such steel samples mentioned before were submitted to oxidation treatment during 5, 10, 20 and 40min into dry atmosphere, in search of similarities to the conditions of the hot rolling utilized in industry. Thus, it was utilized a tube-furnace equipped with a temperature and atmosphere control. The films of oxide which were formed were microstructurally characterized by means of Scanning Electron Microscopy (SEM) and chemically by Energy Dispersive Spectroscopy (EDS). It was conducted the kinetic study of the film growth, measuring the mass gain per unit of area (?M/S) versus time of oxidation (t) and defining the constant of oxidation and its activation energy. The analysis of the oxidation at high temperature and dry air atmosphere showed that the film of oxide produced is more adhesive to the AISI 444 than to the AISI 439 steel, at the range of temperature from 850C to 950C. At this range, the AISI 444 steel is more resistant to oxidation than the AISI 439. At temperatures above 950C, the AISI 444 steel shows a decrease in its resistance to oxidation, what causes an intensification of the formed oxide layer detachment, turning its behavior similar to the one at 1050C. At all the temperatures, it was verified the parabolic increase of the films of oxide formed, containing a predominant content of chrome. It was detected a high content of iron in the regions in which the detachment occurred the most

ASSUNTO(S)

engenharia de materiais e metalurgica oxidação, aços ferríticos, aço inox aisi 444, aço inox aisi 439 oxidation, ferritic steels, aisi 444 stainless steel, aisi 439 stainless steel

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