ALLOY BREAKDOWN: DUCTILE & GRAY IRON
A side-by-side comparison of the two most commonly cast ferrous alloys can help purchasers and designers choose correctly between gray and ductile iron.
B
Gray Iron
Ductile Iron
AN MCDP STAFF REPORT
ecause of their combination of properties, castabil- ity and cost eff ectiveness, gray and ductile iron are the dominant metals (based on weight) produced in metalcasting facilities today. In 2012, the U.S. produced 4.48 million metric tons of ductile iron castings and 4.3 million tons of gray iron castings.
When sourcing, designing and purchasing ductile and gray iron castings, a number of variables must be considered when choosing between the two. T is
Table 1. Standard Specifi cations, Characteristics and Applications Standard Specifi cations
ASTM A48: gray iron castings ASTM A74: cast iron soil & pipe fi ttings ASTM A126: gray iron castings for valves, fl anges & pipe fi ttings ASTM 159: automotive gray iron castings SAE J431: automotive gray iron castings ASTM A278 & ASME SA278: gray iron castings for pressure-containing parts for temperatures up to 650F (343C) ASTM A319: gray iron castings for elevated temperatures for non-pressure-containing parts ASTM A823: statically cast permanent mold castings ASTM A834: common requirements for iron castings for general industrial use
ASTM A395 & ASME SA395: ferritic ductile iron pressure-retaining castings for use at elevated temperatures ASTM A439: austenitic ductile iron castings ASTM A476 & ASME SA476: ductile iron castings for paper mill dryer rolls ASTM A536 & SAE J434: ductile iron castings ASTM A571 & ASME SA571: austenitic ductile iron castings for pressurecontaining parts suitable for low-temperature service ASTM A874: ferritic ductile iron castings suitable for low-temperature service ASTM A897: austempered ductile iron castings
Characteristics
Several strength grades; vibration damping; low rate of thermal expansion & resistance to thermal fatigue; lubrication retention; and good machinability.
comparison of gray and ductile iron will help designers and purchasers decide which alloy is suitable for a specifi c cast component. Gray iron is the preferred
material when seeking low-cost, complex geometries with strength and high density. Gray iron can be
Applications
Automobile engine blocks & heads; manifolds for internal combustion engines; gas burners; machine tool bases; dimensionally stable tooling subjectedto temperature variations,such as gear blanks & forming die covers; cylinder liners for internal combustion engines; intake manifolds; soil pipes; counterweights; and enclosures & housings.
Several grades for both strength & ductility; high strength, ductility & wear resistance; contact fatigue resistance; ability to withstand thermal cycling; and production of fracturecritical components.
Steering knuckles; plow shares; gears; automotive & truck suspension components; brake components; valves; pumps; linkages; hydraulic components; and wind turbine housings.
Sept/Oct 2014 | METAL CASTING DESIGN & PURCHASING | 39
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