Grey Iron Casting

What is Grey iron?

Grey iron, or grey cast iron, is a material type of cast iron with graphitic microstructure. We call this kind of material grey iron because of the gray color of the fracture. For the graphite lubricating the cut and breaking up the chips, grey iron is a common cast alloy due to its relatively low cost and good machinability. Besides, because the graphite flakes self lubricate, it also has good galling and wear resistance.

Grey iron also has less solidification shrinkage than other cast irons because of the graphite microstructure. Whe casting, the silicon element can promote good corrosion resistance and increase fluidity when casting. Gray iron is generally considered easy to weld. Compared to other iron castings, gray iron has a low tensile strength and ductility; that is why the impact and shock resistance of this kind of material is almost non-existent.

Frequently Used Grey Iron Grades

Gray Iron Wall thickness/mm C Si Mn P≤ S≤
HT150 <30 3.3-3.5 2.0-2.4 0.5-0.8 0.2 0.12
30-50 3.2-3.5 1.9-2.3 0.5-0.8 0.2 0.12
>50 3.2-3.5 1.8-2.2 0.6-0.9 0.2 0.12
HT200 <30 3.2-3.5 1.6-2.0 0.7-0.9 0.15 0.12
30-50 3.1-3.4 1.5-1.8 0.8-1.0 0.15 0.12
>50 3.0-3.3 1.4-1.6 0.8-1.0 0.15 0.12
HT250 <30 3.0-3.3 1.4-1.7 0.8-1.0 0.15 0.12
30-50 2.9-3.2 1.3-1.6 0.9-1.1 0.15 0.12
>50 2.8-3.1 1.2-1.5 1.0-1.2 0.15 0.12

Processes of Grey Iron Castings

grey iron casting

gray iron casting

Commonly used process for grey iron castings in the market is produced by sand casting. The processes using sand as the mold media have a somewhat similar effect on the rate of solidification of the casting, while the permanent mold process has a very marked effect on structure and properties.

In our foundry, we can make grey iron castings in below two types:

Lost Foam casting: The only investment casting process for cast iron components, which has lots of advantages to produce small gray iron invesmtent castings, such as saved mould cost, shorten production cycle and improve production efficiency. With lost foam casting process, we can help our customers to obtain high accuracy products with excellent surface finish, and less machining operations will be done.

Resin Sand casting: Main sand casting process for small and medium castings. Compare with other sand casting processes, resin sand casting is relatively precise casting method close to investment casting. As good rigidity of resin sand and high strength of sand mould when early casting,then we could effectively eliminate the shrinkage cavity, shrinkage defects of gray iron castings.

Heat Treatment of Grey Iron Castings

Most of the time, grey iron castings are supplied to our customers in the as-cast condition directly. But For some purposes, gray iron castings can also be heat treated, such as to relieve residual stresses, improve machinability, increase the hardness of the surface either through induction or flame hardening, or harden the entire section through an oil quench and draw treatment. Such heat treatment will not change the graphite structure. Although the graphite may increase in volume if a pearlitic iron is completely ferritized, in which case, the graphite is usually deposited on the flakes originally present. The matrix however is quite responsive to heat treatment just as in the case of steel.

Machining Capability of Grey Iron Castings

Grey iron supply a hardness level that is machinable. With machining facilities in house, we can do machining also after casting. Once our customers have machining requirement on grey iron castings, it will be best to supply us both casting and finished drawings. Our engineering team will strictly machine products referring to the machining drawings. Our machining capability can greatly reduce additional cost for our customers.

Grey iron casting is used in many market segments, including automotive, agricultural, machinery building, electronics, irrigation, ventilation, architecture, construction and transportation industries. In CFS foundry, we can make custom grey iron casting for any industries. Pls contact us if you have any demand of such products.