Determination of Hardness of High-Strength Steels by the Brinell Method. Part 1. Improvement of Measurement Accuracy

Based on the experimental studies and the corresponding analysis of regulatory documents governing the hardness measurements by the Brinell method, the methodology for determining the hardness of high-strength sheet steels was developed. It allows one to obtain more accurate values of some characteristic cases that led in practice to issues of the inconsistency of metal quality with the stated characteristics. In addition to compliance with the requirements of DSTU ISO 6506, the methodology contains additional requirements to take into account several factors specific to this class of materials, the choice of ball indentation, the load level, the friction force during ball indentation, heterogeneity of structures, surface preparation purity, etc. In developing the methodology, a cycle of studies was carried out to determine reliable Brinell hardness measurements according to DSTU ISO EN 6506 on the example of Armox 500T and Hardox 450 sheet steel, which made it possible to determine the hardness distribution pattern over the sample thickness, to establish the thickness of the decarburized layer, to determine the purity of the base metal surface sufficient to obtain reliable hardness measurements, that is without decarburized layer and to decide the indenter choice and the load level on it. It is recommended that the direction of the line along which the measured hardness is measured be placed along the sheet rolling axis with subsequent determination of the average hardness value. Increasing the number of prints significantly reduces measurement errors due to the ambiguity of the contour of the print caused by the metal sliding.