Hardness Conversion Table (Non-Austenitic Steels)
Per ASTM E140-12B(2019)e1. HRC = Rockwell C, HB = Brinell 3000 kg, HV = Vickers, HS = Shore Scleroscope. Approximate tensile strength (Rm) is estimated from hardness per ISO 18265.
| HRC | HB | HV | HS | Approx. Rm (MPa) | Typical Material |
|---|---|---|---|---|---|
| 68 | — | 940 | 106 | — | Carbide |
| 65 | — | 880 | 100 | — | Carbide tooling |
| 63 | — | 820 | 96 | — | Hardened D2, H13 |
| 60 | — | 750 | 91 | — | Hardened tool steel |
| 58 | — | 700 | 87 | — | H13 at max hardness |
| 55 | 560 | 600 | 80 | 2,100 | Hardened H13, A2 |
| 52 | 510 | 550 | 75 | 1,900 | Pre-hardened tool steel |
| 50 | 480 | 510 | 72 | 1,770 | Medium-hard tool steel |
| 48 | 460 | 480 | 69 | 1,680 | |
| 45 | 430 | 440 | 65 | 1,550 | H13 (typical hardened) |
| 42 | 400 | 410 | 61 | 1,420 | |
| 40 | 370 | 380 | 58 | 1,320 | Harder alloy steel |
| 38 | 350 | 360 | 55 | 1,240 | |
| 35 | 330 | 340 | 52 | 1,150 | |
| 33 | 315 | 320 | 50 | 1,090 | Ti-6Al-4V annealed |
| 32 | 300 | 310 | 48 | 1,050 | |
| 30 | 285 | 290 | 46 | 990 | P20 pre-hardened |
| 28 | 270 | 275 | 44 | 950 | |
| 25 | 255 | 260 | 41 | 890 | 4140 Q&T |
| 22 | 235 | 240 | 38 | 820 | 4140 annealed |
| 20 | 220 | 230 | 36 | 770 | |
| 18 | 210 | 215 | 34 | 730 | |
| 15 | 195 | 200 | 31 | 680 | |
| 12 | 180 | 185 | 28 | 630 | |
| 10 | 170 | 175 | 26 | 600 | |
| 8 | 160 | 165 | 24 | 560 | 1045 steel as-rolled |
| 5 | 145 | 150 | 22 | 510 | 1020 steel |
| 0 | 135 | 140 | 20 | 470 | Mild steel |
Conversion Notes
- Conversions are approximate — the relationship between hardness scales varies slightly by steel chemistry and heat treatment
- For austenitic stainless steels (304, 316), use the ASTM E140 conversion for austenitic steels, which differs from the non-austenitic table above
- For non-ferrous metals (aluminum, copper, titanium), standard steel conversions do not apply — use material-specific conversion charts
- Tensile strength conversion (Rm) is an estimate for carbon and alloy steels only
Tensile Strength Quick Reference
| Hardness (HB) | Rm (MPa) — Carbon Steel | Rm (MPa) — Alloy Steel |
|---|---|---|
| 100 | 350 | — |
| 150 | 520 | 500 |
| 200 | 690 | 670 |
| 250 | 860 | 840 |
| 300 | 1,030 | 1,010 |
| 350 | 1,200 | 1,180 |
Quick Reference for Common Deep Hole Drilling Materials
| Material | Condition | Typical Hardness | HRC | HB | Machinability |
|---|---|---|---|---|---|
| 1020 carbon steel | Annealed | — | 0–5 | 135–145 | Good |
| 1045 carbon steel | As-rolled | — | 8–12 | 160–180 | Fair–good |
| 1045 carbon steel | Heat treated | — | 25–30 | 255–285 | Fair |
| 4140 alloy steel | Annealed | — | 18–22 | 210–235 | Fair |
| 4140 alloy steel | Q&T (prehardened) | 28–32 HRC | 28–32 | 270–300 | Fair–poor |
| 4140 alloy steel | Q&T (high strength) | — | 35–42 | 330–400 | Poor |
| 4340 alloy steel | Annealed | — | 18–24 | 210–250 | Fair |
| 4340 alloy steel | Q&T (aircraft grade) | — | 36–45 | 340–430 | Very poor |
| 8620 alloy steel | Case hardened | — | 28–32 (core) | 270–300 | Fair |
| 4130 alloy steel | Normalized | — | 15–22 | 195–235 | Fair–good |
| P20 mold steel | Prehardened | 28–32 HRC | 28–32 | 270–300 | Fair–good |
| H13 tool steel | Annealed | — | 18–22 | 210–235 | Fair |
| H13 tool steel | Hardened | 45–55 HRC | 45–55 | 430–560 | Poor |
| A2 tool steel | Hardened | 57–62 HRC | 57–62 | 600–700 | Very poor |
| D2 tool steel | Hardened | 58–64 HRC | 58–64 | 600–750 | Extremely poor |
| S7 tool steel | Hardened | 48–58 HRC | 48–58 | 460–600 | Poor |
| AISI 304 stainless | Annealed | — | 0–5 | 135–175 | Fair |
| AISI 316 stainless | Annealed | — | 0–5 | 135–175 | Fair |
| 17-4 PH stainless | H900 aged | — | 38–45 | 350–430 | Poor |
| Ti-6Al-4V | Annealed | 33–36 HRC | 33–36 | 310–340 | Poor |
| Ti-6Al-4V | STA (aged) | — | 38–42 | 370–400 | Very poor |
| Inconel 718 | Solution treated | — | 34–38 | 330–360 | Very poor |
| Inconel 718 | Aged | 40–47 HRC | 40–47 | 370–470 | Extremely poor |
| Inconel 625 | Annealed | — | 20–28 | 235–270 | Very poor |
| Hastelloy X | Solution treated | — | 20–28 | 235–270 | Very poor |
| Aluminum 6061-T6 | T6 | — | — | 95–100 | Excellent |
| Aluminum 7075-T6 | T6 | — | — | 150–160 | Excellent |
| Brass C360 | As-drawn | — | — | 80–100 | Excellent |
| Bronze C932 | As-cast | — | — | 60–80 | Good |
| Gray iron Class 30 | As-cast | — | — | 187–241 | Good |
| Ductile iron 80-55-06 | As-cast | — | — | 170–230 | Good |
Application Notes for Deep Hole Drilling
| Hardness Range | Tooling Recommendation | Speed Adjustment | Coolant |
|---|---|---|---|
| HRC < 25 (HB < 255) | Standard carbide (K15–K25) with TiAlN coating | Standard parameters | Standard pressure |
| HRC 25–35 (HB 255–330) | Carbide (K20–K30) with TiAlN coating | Reduce speed 15–25% | Recommended ≥ 40 bar |
| HRC 35–45 (HB 330–430) | Carbide (K25–K35) with AlTiN or AlCrN coating | Reduce speed 30–50% | Required ≥ 60 bar |
| HRC 45–55 (HB 430–560) | AlCrN-coated carbide or PCBN | Reduce speed 50–70% | Required ≥ 70 bar |
| HRC > 55 (HB > 560) | PCBN or ceramic; carbide not recommended | Reduce speed 70–85% | Critical — ≥ 100 bar |
NACE MR0175 / ISO 15156 (Sour Gas Service): Limits carbon steel hardness to ≤ 22 HRC (HB 235) to prevent sulfide stress cracking. Components destined for sour gas service must be verified to meet this maximum.
For related reading, see the Material Machinability Ratings for Deep Hole Drilling, the ISO Tolerance IT Grade Reference, and the Surface Finish Conversion Chart.