What are the characteristics of the materials used for the friction pairs in mechanical seals, namely cast iron and carbon steel? What medium is suitable?

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The earliest material combination for mechanical seal friction pairs in China’s refining industry was cast iron against graphite. Cast iron has the advantages of low cost and ease of processing. Although its hardness is not high, its wear resistance is comparable to that of cemented carbide, and cracks or similar issues do not occur during use. The reason is its high thermal conductivity, which is 3-4 times that of cemented carbide. The cast iron structure is relatively porous, allowing it to absorb trace amounts of liquid and form an oil-containing friction surface, thereby improving the lubrication conditions. Its disadvantage is poor corrosion resistance, so it can only be used in neutral media and in situations where the PV value is not high. To improve its corrosion resistance, alloyed cast iron is used; by adding appropriate elements such as aluminum, nickel, and chromium, its service life can be significantly extended at a very low cost. British company Crane Sealing has used alloy cast iron for the stationary ring, with good results. Commonly used carbon steels include grades 45 and 50; after quenching, their hardness and wear resistance are increased, making them suitable for use as sealing rings in neutral media.