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grey cast iron GG25 property

grey cast iron GG25 property

Grey Cast Iron (Gray iron castings)(part) is so called because of the color of the fracture face. It contains 1.5-4.3% carbon and 0.3-5% silicon plus manganese, sulfur and phosphorus. It is brittle with low tensile strength, but is easy to cast.

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EN-GJL-250, GG25 Equivalent Grades

Besides GG25 in standard DIN 1691, this grade is also equivalent to the following grades:
ISO 185 - Class 250
GB 9439 - HT250 in China
ASTM A48 - Class 35 in USA
UNI 5007 - G25 in Italy
UNF - FG25 in Spain
AS 1830 - T250 in Australia
NS11 100 - SJG250 in Norway

The normal chemical composition should be C = 2.8-3.3, Si = 1.2-1.7, Mn = 0.8-1.2, P ≤ 0.15, S ≤ 0.12.

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Please notice, the chemical composition can not be taken as material quality inspection standard. In all standards, the chemical composition is just for reference. The grey iron foundries could adjust their composition according to their own production condition and experience, as long as they could guarantee to meet the mechanical properties, which is the only inspection standard.

However, if the iron castings need to meet special application, so will require the specific chemical composition, then the buyers should denote this requirement clearly, and the grey iron foundries should take it as the quality standard.

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EN-GJL-250, GG25 Mechanical Properties

Tensile Strength ≥ 250 Mpa
Yield Strength: No Requirement.
Hardness Range: 190 to 240 BH

Only the tensile strength is the quality inspection standard. Other mechanical properties are only for reference unless the buyers have particular requirements.

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This grade has comparatively high tensile strength, and will not need additional heat treatment, so its production cost is still kept low. However, its hardness is comparatively high, so as for the castings parts with thin wall thickness, the hardness for some positions will be very high, over 200 BH, therefore, will cause difficulty to machining, especially to drilling and milling. 

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