Grey iron
Grey iron is so called because of the colour of the fracture face. It contains 1.543% carbon and 0.3-5% silicon plus manganese, sulphur and phosphorus. It is brittle with low tensile strength, but is easy to cast.
Properties of some grey irons (BS 1452)
| Grade | Tensile strength (Nmm-2) | Compressive strength (Nmm-2) | Transverse strength (Nmm-2) | Hardness, BHN* | Modulus of elasticity (GN m-2) |
| 10 | 160 | 620 | 290-370 | 160-180 | 76-104 |
| 17 | 260 | 770 | 450-490 | 190-250 | 110-130 |
| 24 | 370 | 1240 | 620-700 | 240-300 | 124-145 |
Spheroidal graphite (SG) iron
This is also called nodular iron because the graphite is in the form of small spheres or nodules. These result in higher ductility which can be improved further by heat treatment. Mechanical properties approach those of steel combined with good castability.
Properties of some SG irons (BS 2789)
| Grade | Tensile strength (Nmm-2) | 0.5% permanent set stress (Nmm-2) | Hardness, BHN* | Minimum elongation (%) |
| SNG24/17 | 370 | 230 | 140-170 | 17 |
| SNG37/2 | 570 | 390 | 210-310 | 2 |
| SNG47/2 | 730 | 460 | 280-450 | 2 |
Malleable irons
These have excellent machining qualities with strength similar to grey irons but better ductility as a result of closely controlled heat treatment. There are three types: white heart with superior casting properties; black heart with superior machining properties; and pearlitic which is superior to the other two but difficult to produce.
Properties of some maUeabie irons
| Type | Grade | Minimum Tensile strength (Nmm-2) | Yield Point strength (Nmm-2) | Hardness, BHN* | elongation (%) |
| White heart, BS 309 | W22/24 | 310-340 | 180-200 | 248(max.) | 4 |
| White heart, BS 309 | W24/8 | 340-370 | 200-220 | 248(max) | 6 |
| Black heart, BS 310 | B18/6 | 280 | 170 | 150(max) | 6 |
| Black heart, BS 310 | B20/10 | 310 | 190 | 150(max) | 10 |
| Black heart, BS 310 | B22/14 | 340 | 200 | 150(max) | 14 |
| Pearlitic, BS 3333 | P28/6 | 430 | - | 143-187 | 6 |
| Pearlitic, BS 3333 | P33/4 | 460 | - | 170-229 | 4 |
* BHN : Brinell Hardness Number
Labels: engineering materials