Steel tempering is a heat treatment performed after hardening to achieve the required combination of hardness and resistance to fracture. It involves heating the material below the temperature at which austenite begins to form, holding it at that temperature, and then cooling it under appropriate conditions.
The tempering temperature and holding time depend on the steel grade, component dimensions, and service conditions. No single set of parameters is suitable for all parts.
Why Does Steel Need Tempering After Hardening?
After hardening, steel may have high hardness but also significant brittleness and internal stresses. Tempering reduces these undesirable effects and adjusts the material’s properties to suit its intended application.
A punch subjected to abrasive wear requires different properties than a shaft exposed to fluctuating loads. The purpose of tempering is to achieve the right balance of hardness, strength, and ductility. Process overview — Bodycote.
Types of Steel Tempering and Temperature Ranges
In practice, tempering is classified as low-, medium-, or high-temperature tempering. The boundaries between these ranges are approximate and do not replace recommendations for a specific steel grade.
| Type | Approximate Temperature | Typical Applications |
|---|---|---|
| Low-temperature | Approximately 160–300°C | Components requiring high hardness, including carburized and hardened parts and selected cold-work tools |
| Medium-temperature | Approximately 300–500°C | Springs and components requiring a high elastic limit |
| High-temperature | From approximately 500°C, below the temperature at which austenite begins to form | Quenched and tempered steels, hot-work tools, and high-speed steels |
Not every temperature range is suitable for every steel. Certain grades exhibit temper embrittlement within specific temperature ranges. Process selection should take the material manufacturer’s documentation into account. Temperature ranges and limitations — Bodycote.
How Long Does Steel Tempering Take?
It is important to distinguish between the holding time at the tempering temperature and the total cycle time, which also includes heating and cooling.
For example, the manufacturer of Uddeholm Sverker 21 tool steel, corresponding to grade 1.2379 / D2, recommends tempering twice, with cooling to room temperature between cycles. The minimum holding time is 2 hours per tempering cycle.
This means at least 4 hours of holding time alone. The complete process takes longer because the load must also be heated and cooled. However, this is not a universal schedule for all steels. Uddeholm Sverker 21 technical data sheet.
How Do You Select the Temperature for the Required Hardness?
The starting point is the tempering curve for the specific material, taking into account the conditions of the preceding hardening process. Information such as “tool steel” or “required hardness: 60 HRC” alone is insufficient to define the heat treatment procedure.
For Sverker 21, the manufacturer specifies that the temperature should be selected according to the required hardness and the tempering curve. The curve applies to specific treatment conditions, so its values should not be transferred directly to another steel grade. Steel manufacturer’s recommendations.
Why Are Multiple Tempering Cycles Used?
The number of cycles depends on the material and the required properties. For tool steels, manufacturers often specify multiple tempering cycles with cooling between treatments.
For example, at least two tempering cycles are recommended for Uddeholm Vanadis 4 Extra. To achieve high dimensional stability and ductility, the manufacturer recommends three cycles and a minimum temperature of 540°C. This illustrates why a single heat treatment schedule cannot be applied to all tools. Uddeholm Vanadis 4 Extra technical data sheet.
What Information Should You Provide When Ordering Hardening and Tempering?
To help select the appropriate process and prepare a quotation, provide:
- The material grade, preferably accompanied by a material certificate.
- A technical drawing and the number of parts.
- The required hardness and its tolerance.
- Details of any previous heat treatment.
- Requirements for distortion, surface condition, and post-treatment inspection.
- A description of the intended application, if it is not clear from the documentation.
A detailed specification makes it easier to agree on the process and the acceptance criteria for the finished components.
Component Heat Treatment at Sacher
Do you need hardening and tempering for steel components? Explore Sacher’s heat treatment services Explore Sacher’s heat treatment services.
Send your drawing for a quotation — specify the material grade, required hardness, and number of parts.