Yaroslavl State Technical University, Yaroslavl, Russia.

V. A. Ivanova, Dr. Eng., Associate Prof., Director of the Institute of Engineering and Machinery Manufacturing, e-mail: ivanovava@ystu.ru

Naberezhnye Chelny Institute, Kazan (Volga Region) Federal University, Naberezhnye Chelny, Russia
A. G. Panov, Dr. Eng., Prof., e-mail: panov.ag@mail.ru

The paper concerns with the assessment of hardness measurements accuracy provided by standard methods. We performed hardness measurement by the Brinell method (GOST 9012-59), by the Rockwell method on the C scale (GOST 9013-59), and by the Vickers method (GOST 2999-75). The measurement by the Brinell method included a load of 250 kgf, a ball diameter of 5 mm, and an exposure time of 10 seconds. We used samples of alloyed cast iron with vermicular graphite with a uniform distribution and a high proportion of vermicular graphite after isothermal quenching. We provided the isothermal quenching at a temperature of 900 °C for 30 minutes under a layer of birch charcoal and cast iron chips, followed by quenching in a salt melt at a temperature of 290 °C with exposure for 30 minutes. The processing of the hardness measurement results was performed in accordance with GOST R 8.736-2011 “State system for ensuring the uniformity of measurements. Multiple direct measurements. Methods of measurement results processing. Main principles”. According to the assessment results, the Brinell hardness measurement method has the highest accuracy in measuring the hardness of cast iron with vermicular graphite. The Rockwell and Vickers hardness measurement methods have lower accuracy (test load 50 g). The Vickers measurement method has the lowest accuracy of hardness measurement of cast iron with vermicular graphite (test load 15 g). The larger phase inhomogeneity in the area of the print obtained by the Rockwell and Vickers hardness measurement methods compared to the Brinell method might explain the results.

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