Hardened and tempered to 340HB hardness at room temperature and slightly higher temperature the physical properties of temperature 20 ℃ 20 200 400 Density kg / m3 7800 7750 7700 thermal expansion coefficient of from 1 / ° C - 12.7 * 10-6 13.6 * 10 - 6 Thermal conductivity W / m ℃ 29.0 29.5 31.0 coefficient of elasticity N / mm 2 205,000 200,000 185,000 460 ---- 718H tensile strength: Approximate values ??than the heat J / kg ° C. The specimen drawn by a 25.4 mm diameter round bar. Hardness 340HB test temperature of 20 ℃ to 200 ℃ 400 ℃ tensile strength Rm N/mm2, 1100 1 045 870 yield strength Rp0.2 N/mm2, 985 920 775 section shrinkage Z% 50 53 54 Elongation% 13 14 16 718H impact strength approximation value. The specimen drawn by a 25.4 mm diameter round bar. Hardness 340HB test temperature of 20 ° C to 200 ° C to 400 ℃