Compare common steel grades by approximate tempering resistance, softening tendency, alloying characteristics and secondary-hardening behavior.
| Reference Level | General Behavior | Typical Steel Types |
|---|---|---|
| Low | Hardness decreases relatively readily during tempering | Plain carbon steels |
| Moderate | Alloying provides greater resistance to softening | Cr-Mo / Ni-Cr-Mo steels |
| High | Good retention of hardness at elevated tempering temperatures | Tool and hot-work steels |
| Very high | Strong high-temperature tempering response; secondary hardening may occur | High-speed and selected alloy tool steels |
Tempering resistance is the tendency of hardened steel to retain hardness and strength during tempering or subsequent exposure to elevated temperatures.
A steel with relatively low tempering resistance may soften considerably as tempering temperature increases. Alloy steels containing suitable carbide-forming elements can retain more hardness at elevated temperatures.
The comparison on this page is a qualitative reference rather than a replacement for grade-specific tempering curves or measured hardness data.
Carbon controls much of the hardness response in plain carbon steels, while alloying elements can alter carbide precipitation, diffusion, transformation kinetics and matrix stability during tempering.
Chromium, molybdenum, tungsten and vanadium are particularly important in many tool and high-speed steels. Nickel primarily contributes toughness and hardenability rather than producing the same carbide-related tempering response as strong carbide-forming elements.
Some highly alloyed steels show secondary hardening during elevated-temperature tempering. Instead of simply becoming progressively softer, hardness can remain high or increase within a particular tempering range as fine alloy carbides precipitate.
This behavior is especially important when selecting tool steels for applications involving sustained elevated temperatures.
| Grade | Relative Resistance | Secondary Hardening | General Character |
|---|---|---|---|
| AISI 1045 | Low | Minimal | Plain medium-carbon steel |
| AISI 4140 | Moderate | Limited | Cr-Mo alloy steel |
| AISI 4340 | Moderate–High | Limited | Ni-Cr-Mo high-strength alloy steel |
| AISI 52100 | Moderate–High | Limited | High-carbon bearing steel |
| AISI O1 | Moderate–High | Limited | Oil-hardening tool steel |
| AISI A2 | High | Moderate | Air-hardening cold-work tool steel |
| AISI D2 | High | Moderate–High | High-chromium cold-work tool steel |
| AISI S7 | High | Moderate | Shock-resistant tool steel |
| AISI H13 | High | Moderate–High | Hot-work tool steel |
| AISI M2 | Very High | Strong | High-speed tool steel |
Tempering resistance should not be interpreted as a single fixed temperature. Steel hardness generally depends on the complete heat-treatment history, including austenitizing temperature, quenching method, initial hardness, tempering temperature and tempering time.
For this reason, grade comparison is best treated as a screening reference. A published tempering curve for the exact grade and heat-treatment condition should be used when a specific final hardness is required.
Select two grades and use the comparison to identify which material has the stronger general tendency to retain hardness during tempering.
For production material selection, combine this information with required hardness, toughness, wear resistance, operating temperature, section size, machinability and the manufacturer's heat-treatment recommendations.
What does high tempering resistance mean? It means the steel generally retains hardness and strength better as tempering temperature increases compared with a lower-resistance steel.
Which steel has higher tempering resistance, 1045 or 4140? 4140 generally has greater tempering resistance because its chromium-molybdenum alloying provides greater resistance to softening than plain 1045.
Why is M2 considered highly temper-resistant? M2 contains substantial alloying with strong carbide-forming elements and can exhibit significant secondary hardening during elevated-temperature tempering.
Does higher tempering resistance always mean better steel? No. Tempering resistance is only one material characteristic. Toughness, wear resistance, hardenability, corrosion resistance, machinability and cost may be more important for a particular application.
Can this reference predict final hardness? No. It provides qualitative comparison only. Final hardness requires actual grade-specific heat-treatment data and appropriate tempering curves.
What is secondary hardening? It is a hardness-retention or hardness-increase phenomenon during elevated-temperature tempering caused by precipitation of fine alloy carbides in susceptible steels.