What is the difference between S7 and A2 tool steel?

When selecting between S7 and A2 tool steel, the fundamental difference is: S7 is engineered for superior toughness and impact resistance, whereas A2 offers excellent wear resistance. Understanding this is crucial for choosing the optimal grade for your applications.

Both A2 and S7 are cold-work tool steels; however, S7 is primarily classified as a shock-resisting steel, and A2 is an air-hardening, medium-alloy cold-work steel. Their distinct properties determine their best uses.

Core Distinctions: S7 vs. A2

Toughness and Wear Resistance

This is the primary area of differentiation.

S7 tool steel is designed for high toughness and fracture resistance under impact loading. It possesses a very high toughness (rating 8) and is noted for having the highest shock resistance among tool steels. Its wear resistance is generally low to medium (rating 3).

A2 tool steel provides excellent abrasion resistance, its main strength in cold-work applications. It has higher toughness than oil-hardening steels but less toughness than S-series steels. A2’s wear resistance is rated very high (rating 6-8), while its toughness is good (rating 4). A2 exhibits more abrasion resistance than S-series steels.

Chemical Composition

The alloying elements define their characteristics.

A2 has a higher carbon content (typically 1.00-1.05%) compared to S7. It also contains approximately 5% Chromium, along with Molybdenum and Vanadium. This composition, particularly the higher carbon and chromium, results in hard carbides that provide A2’s superior wear resistance.

S7 has a medium carbon content (typically 0.50%), with Chromium (around 3.25%) and Molybdenum (around 1.40%), plus Silicon and Manganese. The lower carbon content in S7 is a key factor in its higher toughness.

Hardenability and Heat Treatment

Both are air-hardening tool steels, offering good safety in heat treatment and minimal distortion.

A2 typically hardens deeply, achieving full hardness through cross-sections up to 4.5 to 5 inches (114.3-127 mm). Its hardening temperature is generally around 1775°F (968°C).

S7 has medium to deep hardening depth, fully hardening through cross-sections up to 2.5 inches (63.5 mm) when air-cooled. Full hardness cannot be attained in S7 beyond a 2.5-inch (63mm) cross-section with air cooling. Its hardening temperature is typically around 1725°F (941°C). For more information, please click S7 tool steel heat treatment.

Machinability

In the annealed condition, S7 generally has better machinability than A2. Compared to W1 tool steel (rated 100), S7 has a machinability rating of 70-75, while A2 is rated at 60-65.

Typical Applications

Selection depends on the primary demands of the application.

When to Use A2 Tool Steel

A2 is a general-purpose cold-work steel for applications where high abrasion resistance is needed. For more information, please click A2 tool steel properties.

• Blanking, forming, and drawing dies (especially for abrasive materials like hot-rolled unpickled steel)
• Punches
• Molds
• Shear knives

If combating abrasive wear is the main challenge, A2 is often the suitable choice.

When to Use S7 Tool Steel

S7 is used for applications requiring shock resistance. It is also suitable for medium cold-work tools and dies, and even medium hot-work dies, as it maintains a degree of hardness up to 1100°F (600°C) and exhibits excellent shock resistance at higher temperatures.

• Chipping chisels
• Punches
• Shear blades
• Rivet sets
• Molds (especially small to medium sizes)

If tools experience impacts or sudden shocks, S7’s toughness is required.

Summary

The decision between A2 and S7 tool steel hinges on the primary operational challenge: A2 is the choice for jobs demanding high wear resistance and minimal distortion during heat treatment. S7 is selected when impact strength, toughness, and some heat resistance are the primary requirements.

If you require further assistance in selecting the right tool steel for your application, please feel free to contact us at Aobo Steel. Our experience can help you find the optimal solution.