Avaliação de métodos analíticos para determinação de propriedades mecânicas de aços via ensaio de macroindentação instrumentada

Abstract

In situ instrumented indentation tests (IIT) can be used to determine tensile properties as a non-destructive alternative to the destructive tension test, especially when the removal of large amounts of test material from in-service structures implies high cost due to the interruption of operations. The ability of the analytical methods proposed by Haggag et al. and by Ahn and Kwon for determination of yield strength and ultimate tensile strength was assessed by instrumented indentation tests performed on steels for the oil and gas industry. For the analytical method proposed by Haggag et al. , the use of the material parameters Bm= 0.2285 and Xm= 1.200, employed for steels in several studies, proved unable to determine the tensile properties of steels analyzed in the present work. It was found that the indentation results were not in agreement with the tensile data (error up to 35%). Statistical analysis indicated that the empirical parameters Bm and Xm depend on both the indenter diameter and the maximum indentation load. An alternative for determining the tensile properties of steels using Haggag s Model is presented, based on the incorporation of the yield offset parameter, bm, and new values for the parameters Bm, bm and Xm. Use of different empirical correlations for estimating the yield strength and tensile strength from indentation hardness measurements was also investigated. The methodology here proposed validated the instrumented indentation test for determination of tensile properties of steels within a range of error of 10%. Furthermore, tests performed on ABNT 8550 steel specimens, exposed to a high hydrogen pressure, suggest that the instrumented indentation test may be applicable for hydrogen embrittlement detection in steels.