What is the difference between S7 and A2 tool steel?

The fundamental difference between S7 and A2 tool steel is that S7 is engineered for excellent toughness and impact resistance, and A2 offers excellent wear resistance. In terms of classification, S7 belongs to impact-resistant steel among cold-work tool steels; A2 belongs to hardenable medium alloy cold-work steels.

1. Core Distinctions: S7 vs. A2

1.1 Toughness and Wear Resistance

The main difference between S7 tool steel and A2 tool steel lies in their toughness and wear resistance.

S7 has the highest toughness of all tool steels and is characterized by its strong resistance to fracture under impact loads.

A2, on the other hand, is characterized by its excellent wear resistance. A2 has higher toughness than oil-hardened steel but lower than the S series steel. However, A2 has better wear resistance than the S series steel.

Chemical Composition

The difference between S7 and A2 ultimately comes down to their different alloy compositions.

A2 has a higher carbon content (typically 1.00-1.05%) than S7. It also contains approximately 5% chromium, as well as molybdenum and vanadium. The higher carbon and chromium content results in the formation of hard carbides, giving A2 better wear resistance.

S7 has a moderate carbon content (typically 0.50%), along with chromium (approximately 3.25%) and molybdenum (approximately 1.40%), as well as silicon and manganese. The lower carbon content gives S7 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. If the machinability of W1 steel is set to a score of 100, then the machinability score for S7 is 70-75, and that for A2 is 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

A2 tool steel is typically used in work environments that require wear resistance.

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)

S7 is used for applications requiring high impact resistance and high toughness.

Summary

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.