| FeNb70 | FeNb60A | FeNb60B | FeNb50 | ||
| Immpurites (% max) | Ta+Nb | 70-75 | 60-70 | 60-70 | 50-55 |
| Ta | 0.1 | 0.1 | 3.0 | 0.1 | |
| Al | 2.5 | 1.5 | 3.0 | 1.5 | |
| Si | 2.0 | 1.3 | 3.0 | 1.0 | |
| C | 0.04 | 0.01 | 0.3 | 0.01 | |
| S | 0.02 | 0.01 | 0.3 | 0.01 | |
| P | 0.04 | 0.03 | 0.30 | 0.02 | |
| W | 0.05 | 0.03 | 1.0 | 0.03 | |
| Mn | 0.5 | 0.3 | - | - | |
| Sn | 0.01 | 0.01 | - | - | |
| Pb | 0.01 | 0.01 | - | - | |
| As | 0.01 | - | - | - | |
| Sb | 0.01 | - | - | - | |
| Bi | 0.01 | - | - | - | |
| Ti | 0.2 | - | - | - | |