GMW GMW1 PDF

This material specification applies to malleable iron casting used in automotive and other allied industries.

This standard specifies mechanical properties from separately cast-to-shape test samples. Mechanical properties may also be specified from test bars excised from specific control locations in product castings. Microstructure features shall only be evaluated at specific control locations in the product castings. Criteria for separately cast test samples and/or control locations for mechanical property and metallographic criteria shall be agreed to by the purchaser and supplier and identified on the engineering drawing.

Material Description. Malleable iron is cast as a graphite free structure, i.e., the total carbon content is present in the combined form as cementite (Fe3C). Subsequent heat treatment precipitates out the graphite in the form of irregular nodules, known as temper carbon. The letter “W” indicates whiteheart malleable iron and the letter “B” indicates blackheart malleable iron. Whiteheart and blackheart denote the fracture appearance of the finished iron but also reflect the conditions under which the high temperature anneal (during which the temper carbon nodules are formed) are carried out. Whiteheart iron involves controlled decarburization of the iron in addition to the transformation of iron carbide into temper carbon nodules and matrix structure. Typically whiteheart iron is higher in sulphur and carbon and lower in silicon content than blackheart iron. Whiteheart irons are not made in North America, but are utilized in other countries for castings destined for welded assemblies. See Table 1 for GMW1 material identification.

Applicability. Malleable cast iron has a range of applications including wheel hubs, differential housings, differential carriers, connecting rods, diesel pistons and gears.