Medium Temper
Tempering · Through-hardening
Medium-temperature tempering reheats quenched steel around 300–450 °C to trade some hardness for strength, elasticity, and improved toughness.
Reference page — Medium 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.
Medium 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 Medium temper?
Medium-temperature tempering reheats quenched steel around 300–450 °C to trade some hardness for strength, elasticity, and improved toughness. It is used for springs, shafts, gears, and high-strength fasteners when roughly 38–50 HRC is required.
How it works
At 300–450 °C, transition carbides evolve toward cementite, martensite loses carbon and tetragonality, and recovery reduces dislocation and residual-stress density. Hardness and tensile strength fall while ductility and impact resistance generally improve. Silicon-alloy spring steels retain strength well in this range. Some carbon and low-alloy steels are vulnerable to tempered-martensite embrittlement across roughly 250–400 °C, so the selected temperature must follow qualified impact and hardness data rather than a generic band. Cooling is normally in air; susceptible alloy steels may require rapid cooling from higher tempering ranges.
Why specify it
- Produces about 38–50 HRC on common quenched alloy steels
- Balances wear strength with more toughness than a 150–250 °C temper
- Supports spring and high-strength shaft applications
- Relieves quench stress throughout the section
Where it falls short
- Some steels lose impact toughness in the 250–400 °C embrittlement range
- Lower wear resistance than low-tempered martensite
- Final hardness depends strongly on alloy and as-quenched condition
- Not applicable to precipitation-hardening nonferrous alloys
The Medium 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 | 300–450 °C (572–842 °F) — Medium-temper range; avoid grade-specific tempered-martensite embrittlement bands. |
|---|---|
| Soak | 1–2 h — Typical hold after equalization; use at least about 1 h per 25 mm where the procedure requires. |
| Cooling | Still air |
| Atmosphere | Air / nitrogen / vacuum |
| Door to door | 3–7 h — One temper including heat-up and cooling. |
Stages
- 1Quench from the grade-specific hardening temperature
- 2Temper promptly at the qualified setpoint
- 3Hold 1–2 h after equalization
- 4Air cool
- 5Verify hardness and impact requirements
What Medium temper does to the part
| Hardness | 38–50 HRC (353–481 HB) — Representative alloy-steel range; 4140 around 400 °C is approximately 46–50 HRC. |
|---|---|
| Section affected | The whole section transforms. |
| Toughness | Toughness is intermediate, but susceptible steels require care around the 250–400 °C tempered-martensite embrittlement range. |
| Distortion | Low risk. Tempering movement is usually small and can improve dimensional stability by relieving quench stress. |
| Surface after treatment | Blue-gray temper oxide in air at the upper range; bright under protective atmosphere or vacuum. |
| Machining sequence | Finish machine or grind after hardness verification; control grinding heat to avoid local overtempering. |
Specifications for Medium 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 TEMPER PER AMS 2759/1 TO 40–44 HRC THROUGH SECTION; TEMPER 2 H MIN AT QUALIFIED TEMPERATURE; HARDNESS PER ASTM E18Which alloys take Medium 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, 4340, 5160, 6150, 9260, S7.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | AM martensitic steels can be tempered after qualified hardening.
| |
| Yes | Quenched carbon, alloy, spring, and tool steels are suitable.
| |
| With care | Fully sintered hardenable steel can be tempered after quenching. | |
| Limited | Martensitic stainless uses grade-specific tempering restrictions.
| |
| No | Aluminum is aged rather than martensitically tempered. | |
| No | Brass does not contain martensite to temper. | |
| No | Bronze does not use this tempering mechanism. | |
| No | Cobalt-chrome is not quenched and tempered as steel. | |
| No | Copper alloys do not use quenched-steel tempering. | |
| No | Magnesium alloys use aging schedules. | |
| No | Nickel alloys use solution and precipitation treatments. | |
| No | Precious metals do not contain quenched steel martensite. | |
| No | Refractory metals do not use steel tempering. | |
| No | Titanium uses alloy-specific anneal and age schedules. | |
| No | Tungsten heavy alloys do not use this treatment. | |
| No | Zinc alloys do not use martensitic tempering. |
Design rules for Medium temper
What to decide on the drawing before the part goes to the heat treater.
- Select temperature from the alloy's tempering curve.A generic 400 °C setpoint does not produce the same hardness in 1045 and 4340.
- Review impact data in the 250–400 °C range.Tempered-martensite embrittlement can reduce toughness despite lower hardness.
- Specify final HRC and minimum hold time.Hardness is the inspectable result; furnace setpoint alone is not.
- Temper promptly after quench.Delay leaves high residual stress in brittle as-quenched martensite.
- Keep service temperature below the qualified temper.Higher exposure continues softening the microstructure.
Medium temper versus the alternatives
Treatments engineers weigh against Medium temper, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Medium temper this page | 47 | 45 | 78 | $ | — |
| 70 | 10 | 72 | $ | when wear hardness above 50 HRC is the priority | |
| 18 | 82 | 85 | $ | when impact toughness and ductility are the priority |
Cost, lead time and applications
Relative cost
Medium 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 | 3–7 h |
What Medium temper is used for
- Coil and leaf springs
- Axles and shafts
- Connecting rods
- High-strength bolts
- Gears
- Impact tooling
Medium temper — frequently asked
What temperature is medium tempering?
This catalog uses 300–450 °C. Designers must check the alloy's impact data because some steels are embrittlement-sensitive between about 250 and 400 °C.
What hardness does medium tempering produce?
A representative range is 38–50 HRC. For 4140, tempering near 400 °C can produce roughly 46–50 HRC.
Is medium tempering suitable for springs?
Yes, especially for silicon and chromium spring steels such as 5160, 6150, and 9260. The drawing should specify final hardness or mechanical properties, not only a temperature band.
What is tempered-martensite embrittlement?
Some steels show reduced impact toughness after tempering in roughly the 250–400 °C range. For impact-critical 4140-type parts, engineers commonly select below 250 °C or above about 450 °C after reviewing qualified data.
Does a medium temper affect the entire part?
Yes. Unlike surface hardening, tempering changes quenched martensite throughout every region that reaches the soak temperature.