A2 Tool Steel Hardness

A2 tool steel is a popular and versatile air-hardening, cold-work tool steel, and its performance relies heavily on achieving the correct hardness. This guide details A2 tool steel hardness, drawing directly from technical data to aid your decision-making. At the bottom of the page, you can download a free PDF technical file on D2 tool steel hardness.

An Overview of A2 Tool Steel

A2 tool steel is an air-hardening, cold-work tool steel. This classification is key to one of its primary advantages: its method of hardening. A2 hardens upon cooling in air from its austenitizing temperature. This air quenching process is gentler than oil or water quenching, leading to:

• Minimized distortion during heat treatment.
• Excellent dimensional stability in the finished tool or component.

These characteristics make A2 a reliable choice for applications where precision is paramount.

Effect of heat treatment on the hardness of A2 tool steel

The A2 tool steel hardness you achieve is a direct result of precise heat treatment. The process involves:

Austenitizing, Quenching, and As-Quenched Hardness

The initial step involves heating the A2 steel to an austenitizing temperature, typically around 1740°F (950°C) to 1775°F (968°C), followed by air quenching. In this as-quenched state, A2 can reach a hardness of approximately 65 HRC. However, steel in this condition is too brittle for most applications.

Effect of tempering on the final hardness of A2 tool steels

Tempering is a critical subsequent step. This process involves reheating the quenched steel to a specific, lower temperature to reduce brittleness and achieve the desired balance of hardness and toughness. The final A2 tool steel hardness is dictated by the chosen tempering temperature.

Typical Working Hardness of A2 Tool Steel:

For most applications, the normal working hardness for A2 tool steel falls within the 58–60 HRC range. However, this can vary:

• Some applications may utilize A2 at 56-58 HRC.
• For bending and blanking dies, a range of 58-64 HRC is common.
• Aluminum extrusion dies often use A2 in the 56-62 HRC range.

The relationship between tempering temperature and hardness is inversely proportional: higher tempering temperatures generally result in lower hardness but increased toughness.

Table: Example Tempering Temperatures vs. Resulting A2 Tool Steel Hardness

(For a 1″ diameter specimen quenched from 1775°F / 968°C)

Tempering Temperature	Resulting Hardness (approx.)
300°F (149°C)	61 HRC
400°F (204°C)	60 HRC

Secondary Hardening Characteristics of A2 Steel

A2 tool steel exhibits a slight secondary hardening effect when tempered in the region of 950°F (510°C) to 1000°F (538°C). At these temperatures, the hardness might slightly increase or stabilize before decreasing with further temperature increases. After hardening and tempering, A2 die steel typically shows a microhardness of 630-700 HV.

For more information about A2 heat treatment, please click A2 steel heat treatment guide.

Deep Dive into A2 Tool Steel Hardness Properties

Several inherent properties of A2 contribute to its performance beyond the Rockwell C numbers.

Hardenability: Ensuring Consistent A2 Tool Steel Hardness in Larger Sections

A2 possesses excellent deep hardenability. This means it can achieve full hardness through substantial cross-sections.

• It can fully harden in sections up to 4.5 inches (114.3 mm) round or square when air quenched.
• Remarkably, an A2 tool steel hardness of 60 HRC can be developed even in the center of a 5-inch (125mm) square section.

This deep hardening capability makes A2 suitable for larger tooling components where consistent through-hardness is essential.

The relationship between hardness and wear resistance of A2 tool steel

Hardness is directly related to a material’s ability to resist wear. A2 tool steel’s good wear resistance stems from its chemical composition and microstructure:

• Composition: Approximately 1.00% Carbon and 5.25% Chromium.
• Microstructure: The dispersion of fine carbides after proper heat treatment.

Comparing A2’s Wear Resistance and Toughness:

• vs. S-Series (e.g., S7): A2 offers significantly more abrasion resistance than shock-resistant tool steels like S7.
• vs. D-Series (e.g., D2): High-carbon, high-chromium D-series steels (like D2) exhibit superior wear resistance (30-40% better than A2). However, A2 provides a better balance with improved toughness and ductility than D2.

A2 makes a compromise for improved toughness compared to the highly wear-resistant D-series, while still providing good wear resistance.

Enhancing Surface Properties: Advanced Treatments for A2 Tool Steel

For applications demanding even greater surface hardness to combat abrasion or wear, A2 tool steel can undergo surface treatments while maintaining its core A2 tool steel hardness and toughness:

• Ion Nitriding: This process can yield a surface hardness of 750–1200 HV to a typical depth of about 8 µm, while the core remains at its tempered hardness (e.g., 54–60 HRC).
• Boriding: Boriding treatments can create an extremely hard surface layer, with microhardness values around 1900 HV reported on treated steels.

Machinability of A2 Tool Steel

In its soft-annealed condition (typically a maximum hardness of 235 HB), A2 tool steel offers good machinability for a tool steel. It has a machinability rating of approximately 60-65, compared to a 1% carbon steel rated at 100. This makes it relatively easier to shape and prepare for heat treatment.

Summary

A2 tool steel is an excellent choice for applications requiring a good balance of wear resistance and toughness, especially where dimensional stability during heat treatment is crucial for parts up to about 4.5 inches in section. With a typical working A2 tool steel hardness of 58-60 HRC, it serves a wide array of cold-work applications.

This detailed breakdown should assist in determining if A2 tool steel fits your specific factory processes. For further questions regarding its heat treatment or comparisons with other grades for your tooling requirements, please consult our technical team.