Heat Treatment Calculator
Pick a steel, enter a target HRC (or a tempering temperature) and section thickness to get the tempering temperature (or hardness), hardening and quench data, soak and temper times, and the datasheet the numbers come from.
The higher the tempering temperature, the softer the steel: per manufacturer datasheets O1 is 60 HRC after tempering at 200 °C and 50 HRC at 400 °C, A2 and D2 stay at 58–62 HRC up to 480 °C and drop to 55 HRC at 540 °C, and water-quenched 1045 falls from 57 HRC at 100 °C to 42 HRC at 350 °C.
Use the Heat Treatment Calculator
Heat Treatment Parameters
Select a grade and target hardness, then click Calculate.
Steel Grade
Tempering Temperature
Approximate curve: no cited tempering datasheet for this grade. Confirm with your supplier's tempering diagram.
Preheat
Hardening (Austenitizing)
Quench
As-quenched hardness
Tempering
Notes
Sources:
Planning values only, not a guaranteed recipe. Section size, chemistry, furnace atmosphere, quench speed and hold time change the result; confirm with a hardness test.
Tempering Temperature vs Hardness Chart
Hardness (HRC) after tempering, from the datasheets cited for each grade. 4140 and 4340 are approximate typical values.
| Steel | Hardening / quench | As quenched | Tempering °C (°F) → HRC |
|---|---|---|---|
| AISI 1045 (C45) | 820–850 °C (1510–1560 °F) water or brine; 830–860 °C (1525–1580 °F) for oil; Water or brine (oil for lower hardness) | 57 HRC | 100 (212) → 57 · 200 (392) → 54 · 300 (572) → 49 · 350 (662) → 42 |
| AISI 4140 (42CrMo4) approximate |
820–860 °C (1510–1580 °F), oil or water; Oil (water for simple shapes) | 58 HRC | 150 (302) → 58 · 175 (347) → 57 · 205 (401) → 55 · 260 (500) → 52 · 315 (599) → 50 · 370 (698) → 47 · 425 (797) → 43 · 480 (896) → 39 · 540 (1004) → 34 · 595 (1103) → 29 · 650 (1202) → 24 |
| AISI 4340 approximate |
About 830–860 °C (1525–1580 °F), oil (typical); Oil | 60 HRC | 150 (302) → 60 · 175 (347) → 59 · 205 (401) → 57 · 260 (500) → 54 · 315 (599) → 51 · 370 (698) → 48 · 425 (797) → 44 · 480 (896) → 40 · 540 (1004) → 35 · 595 (1103) → 30 · 650 (1202) → 25 |
| O1 (1.2510) | 790–820 °C (1454–1508 °F); Oil (or hot bath 180–225 °C) | 64 HRC | 100 (212) → 63 · 200 (392) → 60 · 300 (572) → 56 · 400 (752) → 50 · 500 (932) → 42 · 600 (1112) → 38 |
| A2 (1.2363) | 955–980 °C (1750–1800 °F), hold 30–45 min; Air or positive-pressure gas (2 bar min.) to below 65 °C | 64 HRC | 150 (302) → 62 · 205 (401) → 61 · 260 (500) → 60 · 315 (599) → 59 · 370 (698) → 58 · 420 (788) → 58 · 480 (896) → 58 · 540 (1004) → 55 · 595 (1103) → 51 |
| D2 (1.2379) | 995–1025 °C (1825–1875 °F), hold 30–45 min; Air or positive-pressure gas (2 bar min.) to below 65 °C | 63 HRC | 150 (302) → 62 · 205 (401) → 61 · 260 (500) → 60 · 315 (599) → 59 · 370 (698) → 58 · 420 (788) → 58 · 480 (896) → 58 · 540 (1004) → 55 |
| H13 (Uddeholm Orvar Supreme) | 1010–1050 °C (1850–1920 °F), normally 1030 °C (1885 °F); Inert gas, oil or circulated air (≥ 28 °C/min at 16 mm depth) | — | 549 (1020) → 48–52 · 566 (1051) → 46–50 · 582 (1080) → 44–48 · 599 (1110) → 42–46 · 616 (1141) → 40–44 |
Temper Color Chart (Oxide Colors on Bright Steel)
Rule-of-thumb oxide colors for plain carbon steel heated in air (after Blandford, Practical Blacksmithing and Metalworking). The film keeps darkening with time at temperature, and alloys such as stainless show different colors, so treat this as a rough check only.
| Color | °C | °F | Typical use |
|---|---|---|---|
| Faint yellow | 176 | 349 | Gravers, razors, scrapers |
| Light straw | 205 | 401 | Rock drills, reamers, metal-cutting saws |
| Dark straw | 226 | 439 | Scribers, planer blades |
| Brown | 260 | 500 | Taps, dies, drill bits, hammers, cold chisels |
| Purple | 282 | 540 | Surgical tools, punches, stone-carving tools |
| Dark blue | 310 | 590 | Screwdrivers, wrenches |
| Light blue | 337 | 639 | Springs, wood-cutting saws |
| Grey-blue | 371 | 700 | Structural steel (371 °C and higher) |
Soak time rule of thumb: once the whole section is at temperature, hold about 1 hour per 25 mm (1 in) of the thickest section when tempering. The calculator uses the specific datasheet rule where one is cited for the grade.
Quick answer
The higher the tempering temperature, the softer the steel: per manufacturer datasheets O1 is 60 HRC after tempering at 200 °C and 50 HRC at 400 °C, A2 and D2 stay at 58–62 HRC up to 480 °C and drop to 55 HRC at 540 °C, and water-quenched 1045 falls from 57 HRC at 100 °C to 42 HRC at 350 °C. A common rule of thumb is to soak about 1 hour per 25 mm (1 in) of thickness at tempering temperature, with tool steels tempered twice for at least 2 hours each.
Examples
| Steel | Tempering temperature | Hardness |
|---|---|---|
| O1 (oil quenched) | 200 °C (392 °F) | 60 HRC |
| A2 (air quenched from 970 °C) | 205 °C (400 °F) | 61 HRC |
| D2 (air quenched from 1010 °C) | 540 °C (1000 °F) | 55 HRC |
| H13 (hardened from 1030 °C) | 566 °C (1050 °F) | 46–50 HRC |
| 1045 (water quenched) | 300 °C (572 °F) | 49 HRC |
Choose your steel and enter a target HRC or a tempering temperature below.
Summary
A tempering temperature calculator for common steels. Enter a target Rockwell C hardness to get the tempering temperature, or enter a tempering temperature to get the expected hardness, for 1045 carbon steel, 4140 and 4340 alloy steel, and O1, A2, D2 and H13 tool steel. Each result comes with the hardening (austenitizing) temperature, preheat, quench medium, soak and tempering times, and a link to the datasheet the numbers come from. A tempering table and a temper color chart are included below.
How it works
- Each grade stores the tempering temperature → hardness points from its datasheet. The calculator interpolates linearly between them, forwards (temperature → HRC) or backwards (HRC → temperature).
- Where several temperatures give the same hardness (the A2 and D2 plateau near 58 HRC), the whole temperature range is shown.
- Soak and tempering times are scaled from the section thickness using the datasheet rule for that grade, or the 1 hour per 25 mm rule of thumb where no datasheet rule is cited.
Use cases
- Choose the tempering temperature that leaves O1, A2 or D2 knives, punches or dies at 58–62 HRC.
- Check how hard 1045 will be after a 200 °C or 300 °C temper.
- Plan the tempering cycles for H13 hot-work dies at 44–50 HRC.
- Estimate soak and tempering hold times from the section thickness.
- Read the oxide color on bright steel to judge the tempering temperature reached.