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 |
