GMW GMW7 PDF

This material specification applies to grades of compacted graphite iron castings used in automotive and allied industries. Compacted graphite iron (CGI) is also known as vermicular graphite iron. This specification specifies mechanical properties from test bars machined from separately cast test samples. Mechanical properties may also be specified from test bars machined 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.

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Material Description. Compacted graphite iron is similar to nodular cast iron in chemistry except for a lower magnesium or cerium content. Unlike nodular iron, compacted graphite iron exhibits an as-cast structure containing graphite predominantly in the form of short thick flakes with rounded extremities and undulating surfaces. The development of graphite during solidification is sensitive to chemistry, inoculation and solidification rate. Thin sections may contain greater amounts of nodular graphite and be more susceptible to shrink than thick sections. Susceptibility to flake graphite also increases as time elapses after the final chemistry adjustment or final inoculation. Hence, chemistry, inoculation and pouring practice shall be balanced to meet required properties and microstructures. A thin skin of flake graphite can be expected at the as-cast surfaces, but elsewhere flake graphite is unacceptable in CGI components. The matrix can be made predominantly pearlitic or ferritic or a combination as required. Increasing the pearlite content of the matrix is typically achieved by alloying with a combination of manganese, copper, and tin. Mechanical properties of CGI are intermediate to gray iron and nodular iron, notably, modulus of elasticity, tensile and fatigue strengths, thermal conductivity, damping capacity and machinability.

Symbols. Not applicable.

Typical Applications. Compacted graphite irons with a predominately pearlitic matrix are applicable to flywheels (CG400) and engine cylinder blocks and heads (CG450). CGI with a predominantly ferritic matrix (CG300) is applicable to exhaust manifolds.