9Cr18 and 440C are both types of martensitic stainless steel, which means they are both hardened by heat treatment and are known for their high strength and corrosion resistance.
| Grade | C | Cr | Mn | Si | P | S | Ni | Mo |
| 9Cr18 | 0.95-1.2 | 17.0-19.0 | 1.0 | 1.0 | 0.035 | 0.030 | 0.60 | 0.75 |
| 440C | 0.95-1.2 | 16.0-18.0 | 1.0 | 1.0 | 0.040 | 0.030 | 0.60 | 0.75 |
In summary, 440C stainless steel typically offers higher hardness and slightly better corrosion resistance compared to 9Cr18, but both materials are suitable for a range of applications where high performance and durability are essential.