Estudo dos efeitos dos principais elementos de liga nos aços carbono, aços baixa liga e aços alta liga.

Abstract

Among the metallic alloys, the steel presents a combination of properties most useful to the engineering applications, therefore, a deep understanding of the microstructure of these materials is required, which is highly affected by the chemical composition, the manufacturing process and the thermal, chemical and/or mechanical treatments to which these steels were subjected. Together with the geometry of the manufactured component, the microstructure dictates the properties of these materials under certain working conditions. Since the microstructure and consequently the properties of the steels are altered with the chemical composition, the main objective of the study is to analyze and compare the influence of the main alloying elements of Ultra Low Carbon, AISI 1010, AISI 1040, AISI 1080, AISI 4340, E2(9Cr-7Mo) and ASTM 2205 in the microstructure of these steels using the technique of Optical Microscopy. It was observed that for the carbon steels Ultra Low Carbon, AISI 1010, AISI 1040 and AISI 1080 subjected to the normalization treatment, the carbon content is the main factor that changes the microstructure of these materials, which means, as the carbon content increases, the pro-eutectoid ferrite content decreases and the perlite content increases, ranging from an almost 100% ferritic matrix in Ultra Low Carbon to a 100% pearl matrix in AISI 1080. However, for the AISI 4340 normalized, it was possible to notice the addition of a low content of Ni, Cr and Mo did not affect considerably the microstructure in relation to the AISI 1040, but it was formed a small amount of a micro constituent that was not present in the AISI 1040, which could not be identified by the technique used in this study. Finally, it was verified the influence of a high content of Cr and Mo on the steel E2 (9Cr-7Mo) microstructure as received, which is composed by a ferritic matrix with small precipitates, since these chemical elements are ferrite stabilizer at room temperature. It was also observed the influence of a high content of Cr and Mo combined with a high Ni content, which stabilizes austenite at room temperature in the ASTM 2205 as received, generating a combination of ferrite and austenite in approximately equal fractions in this steel microstructure. In general, the present study presents the optical micrograph of the cited steels in order to demonstrate the effect of the alloying elements on the microstructure of these materials.