Low Temper
Tempering · Through-hardening
Low-temperature tempering reheats freshly quenched steel at about 150–250 °C to relieve stress while retaining high martensitic hardness.
Reference page — Low 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.
Low 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 Low temper?
Low-temperature tempering reheats freshly quenched steel at about 150–250 °C to relieve stress while retaining high martensitic hardness. It is specified for bearings, cutting tools, dies, and wear parts where 50–60 HRC is more important than impact toughness.
How it works
Quenched martensite is supersaturated with carbon and carries high transformation stress. During a 150–250 °C temper, carbon clusters and transition carbides precipitate, tetragonality and residual stress decrease, and some retained austenite may change. Hardness falls only modestly, so abrasion and contact resistance remain high, but toughness remains lower than after hotter tempering. The exact response depends on alloy, as-quenched hardness, section size, and hold time. Tool and bearing steels often require a second temper or a cryogenic step between tempers to address retained austenite.
Why specify it
- Retains about 50–60 HRC on suitable quenched steels
- Relieves a significant portion of quench stress at only 150–250 °C
- Preserves wear and rolling-contact resistance
- Provides a stable condition for bearings, dies, and cutting edges
Where it falls short
- Lowest toughness of the three tempering ranges
- Not suitable for shock-loaded structural parts
- Retained austenite may remain in high-alloy tool steel
- Service temperature should remain below the tempering temperature
The Low 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 | 150–250 °C (302–482 °F) — Low-temper range for quenched carbon, alloy, bearing, and tool steels. |
|---|---|
| Soak | 1–2 h — Typical minimum hold after the part reaches temperature; tool-steel procedures may require multiple tempers. |
| Cooling | Still air |
| Atmosphere | Air / nitrogen / vacuum |
| Door to door | 2–6 h — One temper; double tempering extends the total cycle. |
Stages
- 1Quench from the grade-specific hardening temperature
- 2Transfer promptly to temper
- 3Hold 1–2 h at 150–250 °C
- 4Air cool
- 5Repeat when the material specification requires
What Low temper does to the part
| Hardness | 50–60 HRC (481–654 HB) — Representative range across suitable quenched medium-carbon, bearing, and tool steels. |
|---|---|
| Section affected | The whole section transforms. |
| Toughness | Residual stress is lower than as quenched, but impact toughness remains limited at 50–60 HRC. |
| Distortion | Low risk. Tempering itself causes low movement, though it can reveal distortion already created by quenching. |
| Surface after treatment | Light straw-to-brown temper color in air; bright under vacuum or protective gas. |
| Machining sequence | Finish grind after tempering with controlled coolant; avoid grinding burn that locally retempers or cracks the surface. |
Specifications for Low 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 LOW TEMPER PER AMS 2759/1 TO 54–58 HRC THROUGH SECTION; TEMPER 2 H MIN AT QUALIFIED TEMPERATURE; HARDNESS PER ASTM E18Which alloys take Low temper?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: 1045, 4140, 52100, O1, A2, D2, M2.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | AM martensitic tool steels can be low tempered after qualified hardening.
| |
| Yes | Quenched carbon, alloy, bearing, and tool steels are the intended substrates.
| |
| With care | Fully sintered hardenable steel may be tempered after a qualified quench. | |
| Limited | Quenched martensitic stainless may use a grade-specific low temper.
| |
| No | Aluminum uses precipitation aging, not martensite tempering. | |
| No | Brass does not contain quenched martensite. | |
| No | Bronze does not use this tempering mechanism. | |
| No | Cobalt-chrome is not tempered as quenched steel. | |
| No | Copper alloys do not use martensitic tempering. | |
| No | Magnesium alloys use solution and aging schedules. | |
| No | Nickel alloys are solution treated and aged rather than tempered as martensitic steel. | |
| No | Precious metals do not contain quenched steel martensite. | |
| No | Refractory metals do not use martensitic steel tempering. | |
| No | Titanium uses annealing or solution-and-aging schedules. | |
| No | Tungsten heavy alloys do not use this treatment. | |
| No | Zinc alloys do not use martensitic steel tempering. |
Design rules for Low temper
What to decide on the drawing before the part goes to the heat treater.
- Temper immediately after quenching.Unrelieved martensite can crack during delay or handling.
- Specify final hardness, not temperature alone.Different alloys reach different HRC at the same tempering temperature.
- Keep maximum service temperature below the tempering temperature.Hotter service exposure continues tempering and lowers hardness.
- Use generous radii and avoid impact duty.A 50–60 HRC through-hardened section has limited notch toughness.
- State the number of tempers for tool steel.High-alloy steels may transform retained austenite after the first cycle.
Low temper versus the alternatives
Treatments engineers weigh against Low temper, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Low temper this page | 70 | 10 | 72 | $ | — |
| 47 | 45 | 78 | $ | when more impact resistance is needed at moderate hardness | |
| 18 | 82 | 85 | $ | when structural toughness outweighs maximum wear hardness |
Cost, lead time and applications
Relative cost
Low 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 | 2–6 h |
What Low temper is used for
- Rolling-element bearings
- Cold-work dies
- Cutting tools
- Wear plates
- Gauges
- High-hardness pins
Low temper — frequently asked
What temperature is low tempering?
A practical engineering range is about 150–250 °C. The exact setpoint is selected from the grade's tempering curve to meet final hardness.
What hardness results from low tempering?
Suitable quenched steels commonly remain around 50–60 HRC. For 4140, a 200 °C temper can leave roughly 54–57 HRC.
Why temper immediately after quenching?
Fresh martensite contains high residual stress and can crack before use. A 1–2 hour low temper reduces that stress while preserving most hardness.
Does low tempering make steel tough?
It improves toughness relative to the as-quenched condition, but 50–60 HRC remains notch-sensitive. Shock-loaded shafts usually use a higher temper.
Can a low-tempered part run at 300 °C?
Not without property change. Exposure above its 150–250 °C tempering temperature will continue tempering and reduce hardness.