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Reasonable Cast Iron Hardness Range

The hardness has large affect to the properties of cast iron. 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.

However, what is the reasonable hardness range?

For example, for grey cast iron ASTM A48 NO.20, its 150-200 BH (Brinell hardness), NO.30 is 170-220 BH, NO.35 is 190-240 BH, NO.45 is 210-260 BH. For ductile cast iron ASTM A536 60-40-18, its 130-180 BH, 65-45-12 is 160-210 BH, 70-50-05 is 170-230 BH, 80-60-03 is190-270.

However, according to the experience of Dandong Foundry in China, the hardness of cast iron should be controlled under 220 BH. Upper 220 BH will cause the difficulty to machining.

What will affect cast iron hardness?

As for the sand molding castings, their hardness is mainly affected by the chemical components, cooling speed and inoculation.

1. The chemical components, such as carbon (C), silicon (Si) and Manganese (Mn) will have big affect to the hardness, moreover, the alloy elements such as Cr, Mo and Ni will have some affects too. Therefore, iron foundries should make the proper chemical components according to the material requirements. Adjusting chemical components are the common and easy way to adjust the hardness.

2. Changing the cooling speed is a difficult and dangerous way to adjust the hardness of cast iron.

3. The inoculation process is adding the inoculation agents, such as Si-Fe alloy. After inoculation, the hardness is more even, and the castings have better machining property, and improve the strength to cast iron. However, it will cause more costs to production too. So, normally, iron foundries will not use this way to adjust the hardness, but for the higher grade of grey iron, such as over A48 No.35 and almost all ductile iron grades, the inoculation will be necessary to improve the cast iron properties, but not just for hardness.

As for the buyers, you could stipulate the hardness range if your designer thought it was necessary, otherwise, you could just ask your suppliers to meet the material grade, as for the experienced iron foundry in China, they should be able to know the reasonable hardness range.

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