Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, some of which are more quantitative. In comparison, gray cast iron is harder. This is a comparison table for some gray iron casting grades in these standards: Grey iron is usually quenched and tempered to increase its resistance to wear and abrasion by increasing hardness with a structure consisting of graphite embedded in hard martensite. Reasonable Cast Iron Hardness Range. Brinell hardness of malleable cast iron – ASTM A220 is approximately 250 MPa.. Brinell hardness of ductile cast Iron – ASTM A536 – 60-40-18 is approximately 150 – 180 MPa.. Hardness of Ductile Cast Iron – ASTM A536 – 60-40-18. Comparison Table for Some Gray Iron Casting Grades. Hardness of Malleable Cast Iron – ASTM A220. The differences are due to the microstructures of graphite within these iron alloys. Too low hardness will cause the low tensile strength, reduce the resistance to abrasion, so reduce the lifetime of iron castings.Too high hardness will cause the difficulty to machining, so enlarge the machining time, reduce the life time of cutters, and even can not be machined. Gray iron is also better at vibration damping. The hardness has large affect to the properties of cast iron. The Mohs scale of mineral hardness (/ m oʊ z /) is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Gray cast iron is 2.5–4% carbon and 1–3% silicon by weight. Cast iron in general are never water-quenched (except in surface-hardening) as it has relatively high hardenability to get martensite by oil-quenching, and without inducing large quenching stresses. Hardness of Malleable Cast Iron – ASTM A220. EN-GJL-250, CAST IRON GG25. In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. EN-GJL-250 is a high material grade of grey cast iron in European standard EN 1561, it is also named as cast iron GG25 in standard DIN 1691 by Germany and Austria. This hardness means that it manages surface wear well. ASTM A48, SAE J431, GM 274M and ASTM A126 are standards for gray cast iron.They have some grades which have some equal or similar mechanical properties, such as tensile strength and hardness. Brinell hardness of malleable cast iron – ASTM A220 is approximately 250 MPa. The followings are its equivalent grades, chemical composition, mechanical properties, and some photos of grey iron castings made by Dandong Foundry. In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching.