Ductile cast iron, which has other names such as nodular cast iron, spheroidal graphite cast iron or SG cast iron, is usually used to produce castings. Nodular cast iron obtains nodular graphite through spheroidization and inoculation treatment, which effectively improves the mechanical properties of the cast iron, especially the plasticity and toughness, so as to obtain higher strength than carbon steel. Nodular cast iron is a high-strength cast iron material developed in the 1950s. Its comprehensive properties are close to steel. Based on its excellent properties, the ductile iron has been successfully used for casting components of complex forces, strength, toughness and wear resistance. Nodular cast iron has rapidly developed into a cast iron material second only to gray cast iron and widely used. The so-called "substituting iron for steel" mainly refers to ductile iron. Ductile iron is often used to produce parts for crankshafts and camshafts for automobiles, tractors, and internal combustion engines, as well as medium-pressure valves for general machinery.

Ductile iron is not a single material but is part of a group of materials which can be produced to have a wide range of properties through control of the microstructure. The common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, the graphite is in the form of nodules rather than flakes as it is in grey iron. The sharp shape of the flakes of graphite create stress concentration points within the metal matrix and the rounded shape of the nodules less so, thus inhibiting the creation of cracks and providing the enhanced ductility that gives the alloy its name. The formation of nodules is achieved by the addition of nodulizing elements, most commonly magnesium (note magnesium boils at 1100°C and iron melts at 1500°C) and, less often now, cerium (usually in the form of Mischmetal). Tellurium has also been used. Yttrium, often a component of Misch metal, has also been studied as a possible nodulizer.

Ductile (Nodular) Cast Iron Mechanical Properties

Item according to DIN EN 1563 Measure Unit EN-GJS-350-22-LT EN-GJS-400-18-LT EN-GJS-400-18 EN-GJS-500-7 EN-GJS-600-3 EN-GJS-700-2 EN-GJS-800-2
EN-JS 1015 EN-JS 1025 EN-JS 1020 EN-JS 1050 EN-JS 1060 EN-JS 1070 EN-JS 1080
Tensile Strength Rm min.MPA 350 400 400 500 600 700 800
2% Yield Strength Rp0.2 min.MPA 220 240 250 320 370 420 480
Elongation A % 22,0 18,0 18,0 7,0 3,0 2,0 2,0
Hardness HB 110-150 120-160 140-190 170-220 200-250 230-280 250-330
Structures mainly ferritic mainly ferritic mainly ferritic ferritic + pearlite ferritic + pearlite mainly pearlite all pearlite
Shear Stress σaB MPa 315 360 360 450 540 630 720
Torsion TtB MPa 315 360 360 450 540 630 720
Modules of elasticity E GPa 170 170 170 175 175 175 175
Poisson number v – 0,280 0,280 0,280 0,280 0,280 0,280 0,280
Compressive Strength σdB MPa 700 700 800 870 1000 1150
Frature Toughness Klc MPa·√m 31 30 30 25 20 15 14
Density g/cm3 7,1 7,1 7,1 7,1 7,2 7,2 7,2

Ductile cast iron castings are the casting components made of ductile cast iron. At RMC Foundry, the ductile iron could be cast and poured by many casting processes including sand casting, shell casting, investment casting, lost foam casting and vacuum casting, depending the exact usage or if special requirements of the desired castings.

In the design stage of castings, a special project team should be set up to conduct "Design Failure Mode and Effects Analysis" (DFMEA). The project team generally consists of product designers, casting process designers, and environmental protection professionals. The main content of the DFMEA analysis should include whether the requirements of the casting quality for the part structure, the casting process for the casting structure, and the casting process for environmental protection requirements are all met.

Performance Characteristics of Ductile Iron Castings
• Fluidity and line shrinkage of ductile iron are very close to those of gray cast iron
• The tendency of volume shrinkage and internal stress formation is greater than that of gray cast iron, which is prone to shrinkage and cracks
• The strength, plasticity, and elastic modulus of ductile iron are larger than those of gray cast iron, with good abrasion resistance
• Shock absorption is worse than gray cast iron

Structural Characteristics of Ductile Iron Castings
• Generally designed to be uniform wall thickness, and try thick section should be avoid if possible
• For certain thick and large section castings, hollow structure or structure with reinforced ribs should be adopted

Ductile (Nodular) Cast Iron

GB/T 1348-1988

ISO 1083:1987(E)

ASTM A536-84(2004)

EN 1563:-1997

JIS G5502-2001


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