What temperature should I temper steel to achieve a specific HRC?

The tempering temperature needed depends strongly on the steel grade and the hardness after quenching. As a general guide for medium-alloy steels: 150–200°C gives HRC 58–62 (spring/cutting applications), 250–350°C gives HRC 50–55 (punches, dies), 400–500°C gives HRC 40–48 (shafts, gears), 550–650°C gives HRC 28–38 (structural toughness). Always consult the specific grade data sheet as alloy content shifts these ranges significantly.

Why do tool steels need double tempering?

High-alloy tool steels (H13, D2, M2) contain significant retained austenite after the quench. The first temper raises the martensite start temperature of this retained austenite, causing it to transform to untempered martensite on cooling. A second temper (at the same or slightly lower temperature) then tempers this fresh martensite. Skipping the second temper leaves untempered martensite that is brittle and prone to cracking.

How long should tempering soak time be?

A minimum soak of 1 hour per 25 mm of section (minimum 2 hours) is the standard guidance, with at least 1 hour at temperature after the thermocouple confirms the load has soaked through. For tool steels requiring double tempering, each cycle is typically 2 hours minimum. Undersoak causes inadequate stress relief; there is little benefit to soaking longer than 4–6 hours at temperature.

What is the 'temper embrittlement' zone and how do I avoid it?

Temper embrittlement (blue brittleness) occurs in many alloy steels when tempered in the 250–370°C range, causing a significant drop in impact toughness without an equivalent drop in hardness. This zone should be avoided for structural and impact-loaded parts. If your target hardness falls in this range, consider tempering slightly above 370°C and accepting the slightly lower hardness, or choosing a grade less susceptible to this effect.

Steel Tempering Calculator & Hardness Predictor — Tempering Temperature Chart

Tempering Temperature vs Hardness — EN24 (817M40) Example

Temper Temp (°C)	HRC (approx)	HV (approx)	Typical Application
150	57–60	620–650	Maximum hardness (not recommended — brittle)
200	54–57	570–620	Wear surfaces, gauges
300	50–53	513–555	Punches, dies
400	44–48	430–470	Crankshafts, high-strength bolts
500	37–42	360–405	Gears, shafts
600	28–33	270–310	Tough structural parts
650	22–27	230–270	Maximum toughness
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Calculator Features

Predicted post-temper HRC and HV from grade + temperature
Temper embrittlement zone warnings (250–370°C)
Double-temper cycle guidance for hot-work tool steels
Soak time by section thickness (mm or inches)
Cryogenic treatment option for retained austenite
Cooling method — air, oil, or water after temper

Steel Families Covered

Carbon steels — EN8, EN9, EN43
Alloy steels — EN24, EN36, EN40B
Hot-work tool steels — H11, H13, H21
Cold-work tool steels — D2, D3, O1, A2
High-speed steels — M2, M42, T1
Stainless steels — 17-4PH, 420, 440C

Tempering — Getting the Hardness–Toughness Balance Right

As-quenched martensite is hard but extremely brittle — unusable for most engineering applications. Tempering relieves the transformation stresses, allows carbon to partially precipitate as fine carbides, and dramatically improves toughness at the cost of some hardness. The tempering temperature is the primary lever controlling the hardness–toughness balance.

The relationship between temper temperature and final hardness is alloy-dependent: highly alloyed grades retain hardness to much higher temperatures (secondary hardening in high-speed steels occurs at 550–570°C). Accurate prediction requires grade-specific data, which the Bloor Engineering tempering calculator provides.

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Select your steel grade, enter quench hardness and target temper temperature — get predicted HRC instantly. Free with a registered account.

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Steel Tempering Calculator & Hardness Predictor

Calculator Features

Steel Families Covered

Tempering — Getting the Hardness–Toughness Balance Right

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