Hardness specification of structural steel used in the Republic of Kazakhstan B. Kulbayev, V. Lapin, T. Tuleyev, S. Aldakhov, Y. Aldakhov and A. Ali E3S Web of Conf., 389 (2023) 01002 Published online: 31 May 2023 DOI: 10.1051/e3sconf/202338901002