Manufacturing and metrological characterization of reference charpy specimens: first evaluations

Abstract

The first evaluations of the manufacture and metrological characterization of reference specimens for indirect calibration of Charpy impact testing machines by the Institute for Technological Research (IPT) are presented, seeking through the laboratory resources and expertise of the Institute, the accreditation of the laboratory as a producer of this reference material. The specimens are manufactured with 300 M steel by conventional machining. Heat treatments of normalizing, quenching, and tempering were used to control the mechanical properties. To obtain greater homogeneity in the specimens, it was decided to use tubular laboratory ovens and manufacture small batches with 32 specimens each. Initially, 2 batches were manufactured, one target at a nominal Charpy energy of 30 J and another 54 J. The pilot batches of 30 J and 54 J showed, respectively, standard deviations of 0.89 HRC and 0.96 HRC between samples and mean hardness with errors of −0.22 HRC and 0.83 HRC. The microstructures obtained after the heat treatments are tempered martensite and in the second batch, it is possible to observe that the microstructure is a little more spheroidized due to the higher tempering temperature.