By Maruti Casting, Rajkot · Updated
What is grey cast iron?
Grey cast iron is iron with about 2.5 to 4% carbon and 1 to 3% silicon, in which most of the carbon forms thin flakes of graphite. The flakes make a freshly broken surface look grey, which gives the material its name. It is the most widely used casting metal because it melts and flows easily, machines well, absorbs vibration and resists wear, all at a low cost.
In India, grey cast iron is specified under IS 210. Most castings we make at Maruti Casting, from V-belt pulleys to pump casings and brake drums, are made to this standard.
How IS 210 grades are named
Each grade is written as FG followed by a number. FG stands for flake graphite. The number is the minimum tensile strength in N/mm² (MPa), measured on a separately cast test bar. So FG 200 must reach at least 200 MPa, and FG 260 at least 260 MPa. Higher grades are stronger and harder, but cost more to make and are slower to machine.
IS 210 grade comparison table
| IS 210 grade | Min. tensile strength (MPa) | Approx. ASTM A48 | Approx. EN 1561 | Typical uses |
|---|---|---|---|---|
| FG 150 | 150 | Class 20 to 25 | EN-GJL-150 | Covers, counterweights, light non-pressure parts |
| FG 200 | 200 | Class 30 | EN-GJL-200 | V-belt and flat pulleys, pump and motor housings, general machine parts |
| FG 220 | 220 | Class 30 to 35 | Between GJL-200 and GJL-250 | General engineering parts needing a little more strength |
| FG 260 | 260 | Class 35 to 40 | EN-GJL-250 | Valve bodies, brake drums, machine beds, gear blanks |
| FG 300 | 300 | Class 45 | EN-GJL-300 | Heavily loaded machine parts, cylinder blocks |
| FG 350 | 350 | Class 50 | EN-GJL-350 | High-strength castings, heavy-duty gears |
| FG 400 | 400 | Class 55 to 60 | No direct equivalent | Special high-strength applications |
Equivalents are the nearest grades, not exact matches, because each standard tests differently. Always state the standard and grade on your drawing.
How to choose the right grade
- Start with the load. Lightly loaded parts such as covers and counterweights work in FG 150 or FG 200. Parts under higher stress or pressure, such as valve bodies, usually need FG 260 or above.
- Think about wall thickness. Thick sections cool slowly and end up weaker than the test bar, while thin sections cool fast and can become hard. Tell your foundry the main wall thickness so the grade can be matched to it.
- Consider machining. Lower grades machine faster and give longer tool life. If a part needs a lot of machining and does not carry heavy load, FG 200 is often the economical choice.
- Check wear and heat. Brake drums and sliding surfaces benefit from the wear resistance and heat conduction of FG 220 to FG 260.
- Do not over-specify. Choosing a higher grade than needed raises cost without improving the part. If in doubt, share the application with us and we will suggest a grade.
Grey iron or SG iron?
SG (spheroidal graphite) iron, also called ductile iron and covered by IS 1865, has its graphite in tiny spheres instead of flakes. This makes it much stronger and tougher, so it is used for parts that face shock or impact, such as crankshafts and heavy-duty gears.
Grey iron remains the better choice where vibration damping, machinability, wear resistance and cost matter more than toughness, which covers most pulleys, housings, pump casings, valve bodies and machine bases.