High Temper
Tempering · Through-hardening
High-temperature tempering reheats quenched steel around 500–650 °C to produce tempered martensite with high toughness and moderate hardness.
Reference page — High temper is not in the instant-quote configurator. Upload the part, name the treatment in the notes with the call-out below, and an engineer quotes it with the part.
High temper at a glance
Four scores, each 0–100 against every heat treatment in this catalog. Hardness is derived from the HRC target (20 HRC = 0, 70 HRC = 100) — treatments without a hardness target (anneals, stress relief, HIP, cryo) are not rated. Toughness, dimensional stability and cost are FabDigit's engineering assessment.
What is High temper?
High-temperature tempering reheats quenched steel around 500–650 °C to produce tempered martensite with high toughness and moderate hardness. It is the standard strength–ductility condition for heavily loaded shafts, gears, pressure parts, and structural machinery.
How it works
At 500–650 °C, martensite recovers extensively and carbon forms coarser, more stable carbides in a ferritic matrix. Residual stress drops, hardness decreases, and ductility plus impact resistance rise. Alloy carbides can cause secondary hardening in some tool steels, so their grade-specific curves do not follow simple carbon-steel trends. For 4140, increasing tempering temperature through this range reduces hardness from the high 30s toward the low 20s HRC. Susceptible alloy steels should be cooled promptly through the temper-embrittlement range after soaking.
Why specify it
- Produces about 22–38 HRC with high structural toughness
- Relieves quench stress throughout heavy sections
- Provides a practical strength–ductility balance for 4140 and 4340
- Raises usable impact resistance compared with low and medium tempering
Where it falls short
- Lower wear resistance than low-tempered steel
- Can overtemper a surface that must later be nitrided unless sequence is planned
- Slow cooling can promote temper embrittlement in susceptible alloy steels
- Tool steels may show secondary-hardening behavior outside simple hardness trends
The High temper cycle
Typical furnace parameters from the governing specifications and shop practice; the heat treater sets the exact recipe from the alloy, section size and required result.
| Temperature | 500–650 °C (932–1,202 °F) — High-temper range for quenched structural steels. |
|---|---|
| Soak | 1–3 h — Commonly at least 1 h per 25 mm after equalization, subject to the governing procedure. |
| Cooling | Forced air |
| Atmosphere | Air / nitrogen / vacuum |
| Door to door | 4–10 h — One temper including heating and controlled cooling. |
Stages
- 1Quench from the grade-specific hardening temperature
- 2Temper promptly at 500–650 °C
- 3Hold through section
- 4Cool promptly through embrittlement-sensitive range
- 5Verify final hardness
What High temper does to the part
| Hardness | 22–38 HRC (235–353 HB) — Representative 4140-type range across 500–650 °C. |
|---|---|
| Section affected | The whole section transforms. |
| Tensile strength | 850–1,200 MPa — Representative 4140-type range across the high-temper window; section and chemistry govern. |
| Toughness | High tempering gives the best toughness of the three catalog temper ranges; susceptible Ni-Cr steels still require temper-embrittlement control. |
| Distortion | Low risk. The temper relieves quench stress and generally improves stability, though large sections can move as stresses relax. |
| Surface after treatment | Blue-gray oxide in air; bright in vacuum or protective atmosphere. |
| Machining sequence | Parts at 22–38 HRC remain machinable with appropriate tooling; precision grinding can follow hardness verification. |
Specifications for High temper
The documents a drawing cites to define this treatment. Each links to a page explaining the standard, its classes and the tests it invokes.
| Standard | Role | Classes used | Status |
|---|---|---|---|
Heat Treatment of Carbon and Low-Alloy Steel Parts, Minimum Tensile Strength Below 220 ksi (1517 MPa) | Governing | — | Active |
Heat Treatment of Parts in a Vacuum | Alternative | — | Active |
Test and related methods: ASTM E18 (Standard Test Methods for Rockwell Hardness of Metallic Materials), AMS 2750 (Pyrometry), ASTM E140 (Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness).
Drawing call-out
HARDEN AND HIGH TEMPER PER AMS 2759/1 TO 28–32 HRC THROUGH SECTION; TEMPER 2 H MIN AT QUALIFIED TEMPERATURE; HARDNESS PER ASTM E18Which alloys take High temper?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: 1045, 4130, 4140, 4340, 4330V, 8630.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | AM martensitic steels can be high tempered after qualified hardening.
| |
| Yes | Quenched carbon and low-alloy structural steels are primary candidates.
| |
| With care | Fully sintered hardenable steel can be tempered after quenching. | |
| With care | Martensitic stainless may lose corrosion or toughness if tempered in restricted bands.
| |
| No | Aluminum uses solution treatment and aging. | |
| No | Brass does not contain quenched martensite. | |
| No | Bronze does not use this tempering mechanism. | |
| No | Cobalt-chrome is not quenched and tempered as steel. | |
| No | Copper alloys do not use martensitic steel tempering. | |
| No | Magnesium alloys use solution and aging schedules. | |
| No | Nickel alloys are solution treated and precipitation aged. | |
| No | Precious metals do not contain martensitic steel. | |
| No | Refractory metals do not use this treatment. | |
| No | Titanium uses alloy-specific annealing and aging. | |
| No | Tungsten heavy alloys do not use martensitic tempering. | |
| No | The process temperature approaches or exceeds zinc-alloy limits. |
Design rules for High temper
What to decide on the drawing before the part goes to the heat treater.
- Specify final hardness or tensile class, not only the tempering temperature.Chemistry and section size change the response at a given setpoint.
- Cool susceptible alloy steels promptly after soaking.Slow passage through roughly 375–575 °C can promote reversible temper embrittlement.
- Place nitriding after the high temper.The prior temper should exceed the later nitriding temperature to preserve core hardness.
- Allow stress-relief movement on large asymmetric parts.A 500–650 °C soak releases quench and machining stresses.
- Verify hardness at the controlling section.Heavy sections may not have achieved uniform as-quenched martensite.
High temper versus the alternatives
Treatments engineers weigh against High temper, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
High temper this page | 18 | 82 | 85 | $ | — |
| 47 | 45 | 78 | $ | when hardness above about 38 HRC is required | |
| — | 75 | 65 | $ | when grain refinement and machinability matter more than quenched strength |
Cost, lead time and applications
Relative cost
High Temper is a budget-cost treatment ($) relative to the other heat treatments in this catalog.
Heat treatment is priced per lot with a furnace minimum. The exact figure appears on the instant quote once the part is uploaded.
Lead time
| Added lead time | 2–5 working days |
|---|---|
| Furnace time | 4–10 h |
What High temper is used for
- Heavy-duty shafts
- Crankshafts
- Structural gears
- Pressure-equipment components
- Oilfield tools
- Landing-gear structural parts
High temper — frequently asked
What temperature is high tempering?
This catalog uses 500–650 °C for quenched structural steels. The exact temperature comes from the alloy's tempering curve and target hardness.
What hardness does high tempering produce?
4140-type steels commonly span about 22–38 HRC over 500–650 °C. At about 550 °C, 4140 often falls near 32–38 HRC.
Why high temper 4140?
It trades peak martensitic hardness for useful ductility and impact resistance. Around 600–650 °C, 4140 commonly reaches roughly 22–32 HRC for tough shafts and structural parts.
What is temper embrittlement?
Some alloy steels become less impact-tough after slow cooling or long exposure through roughly 375–575 °C. Chemistry control and prompt cooling after the temper reduce susceptibility.
Can a high-tempered part be nitrided?
Yes, and the sequence is preferred when the core tempering temperature exceeds the later 495–565 °C nitriding temperature. Otherwise nitriding can unintentionally soften the core.