Drill Rod Hardness and Machinability
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The rods are manufactured of annealed tool steel (O-1, A-2, D-2, H-13, S-7, M-2, or W-1). Then they are cold drawn and (usually) polished. The drill rod hardness is affected by the cold drawing manufacturing process. The hardness is greater for the small diameters as show by the table below. The table shows the hardness before any heat treatment is applied. The hardness after heat treatment is determined by the heating treating process that you use after receiving the rods from the manufacturer.
Drill Rod Hardness Table
| Material Type | Precision Diameter |
Brinell Hardness |
Rockwell Hardness |
| Tool Steel (Annealed) |
0.000 – 0.124″ | 341 | 110 Rb |
| 0.125″ – 0.249″ | 275 | 104 Rb | |
| 0.250″ – 0.875″ | 241 | 101 Rb | |
| 0.876″ + | 207 | 96 Rb |
The table below shows that machinability of drill rod as it depends on the grade of tool steel. To use this table, find your steel type in the second column. Read the machinability in the other column of the same row.
Drill Rod Machinability Table
| Material Type | Grade | Machinability * |
| Tool Steel (Annealed) |
O-1 | 95% |
| A-2 | 65% | |
| D-2 | 50% | |
| H-13 | 75% | |
| S-7 | 95% | |
| W-1 | 100% | |
| M-2 | 65% |
* Compared to 1.0% carbon steel.