Description
S7 Tool Steel: Detailed Overview
S7 tool steel is a shock-resistant steel known for its high toughness, strength, and ability to withstand impact loads. It is ideal for applications that involve both shock and impact, such as heavy-duty tools, punches, chisels, and dies. S7 is characterized by its excellent combination of strength, toughness, and machinability.
Introduction to S7 Tool Steel
S7 is a versatile air-hardening tool steel designed to handle high-impact and shock-loading environments. It has excellent toughness and resistance to cracking, making it ideal for tools that must endure repeated heavy loads and shock. S7 is often used in cold-work applications, as well as in certain high-temperature scenarios due to its ability to retain strength at elevated temperatures.
Key Features of S7 Tool Steel:
- High Impact Resistance: Exceptional toughness and the ability to absorb shock loads without breaking.
- Good Hardness: Can be hardened to high levels while maintaining toughness.
- Wear Resistance: Moderate wear resistance compared to other tool steels but superior for shock applications.
- Machinability: Good machinability in its annealed condition.
- Air Hardening: This eliminates the need for complex heat treatment processes and reduces the risk of distortion.
Applications of S7 Tool Steel
S7 tool steel is used in a wide range of applications that require resistance to shock and impact, combined with high toughness. It is ideal for tools that experience heavy, repeated stress and loads.
Typical Applications Include:
- Punches and Dies: Cold and hot forming punches, trim dies, and shear blades.
- Chisels and Hammers: Hand tools like chisels, hammers, and jackhammer bits.
- Forging Dies: Dies used for impact forging processes.
- Air Hammer Tools: Tools subjected to extreme shock and vibration.
- Plastic Molds: Components in plastic injection molding that need both toughness and impact resistance.
Equivalent Grades of S7 Tool Steel
S7 is recognized under different standards, ensuring compatibility across various regions and industries.
| Standard | Equivalent Grade |
|---|---|
| AISI/SAE | S7 |
| DIN | 1.2355 |
| EN | 45CrMoV7 |
Chemical Composition of S7 Tool Steel
The chemical composition of S7 is designed to provide the balance of toughness, strength, and hardenability required for shock-resisting applications. The typical composition is as follows:
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.45 – 0.55 |
| Silicon (Si) | 0.20 – 1.00 |
| Manganese (Mn) | 0.20 – 0.80 |
| Chromium (Cr) | 3.00 – 3.50 |
| Molybdenum (Mo) | 1.30 – 1.80 |
| Vanadium (V) | 0.25 max |
This combination of carbon, chromium, and molybdenum gives S7 its unique balance of impact toughness and hardenability.
Mechanical Properties of S7 Tool Steel
The mechanical properties of S7 are essential for understanding its shock-resistant capabilities and its suitability for demanding applications. Typical values are:
| Property | Value (Typical) |
|---|---|
| Tensile Strength (MPa) | 850 – 1000 |
| Yield Strength (MPa) | 650 – 800 |
| Elongation (%) | ≥ 12 |
| Impact Toughness (J) | ≥ 80 (at room temp) |
| Hardness (HB) | 180 – 230 |
These values indicate the excellent toughness and resilience of S7 tool steel in impact-heavy applications.
Heat Treatment of S7 Tool Steel
Heat treatment is crucial for optimizing the performance of S7 tool steel, as it allows the steel to reach high levels of hardness without sacrificing toughness.
- Hardening: Heat to 950 – 980°C (1740 – 1800°F), followed by air cooling. This process hardens the steel and maximizes its toughness.
- Tempering: Tempering is done at temperatures between 500 – 600°C (930 – 1110°F) after hardening to reduce brittleness and maintain toughness. The higher the tempering temperature, the greater the toughness.
- Annealing: Heat to 790 – 840°C (1450 – 1550°F) followed by slow furnace cooling to ensure good machinability.
These treatments help S7 tool steel achieve a balance between toughness and hardness for high-performance applications.
Hardness of S7 Tool Steel
S7 tool steel can be hardened to high levels while maintaining excellent toughness. Typical hardness values are:
- Annealed Condition: 180 – 230 HB
- After Hardening and Tempering: 54 – 58 HRC
These hardness values make S7 suitable for applications where tools need to withstand both impact and wear without breaking.
Physical Properties of S7 Tool Steel
The physical properties of S7 play a significant role in its behavior under various operating conditions. Key values include:
| Property | Value |
|---|---|
| Density (g/cm³) | 7.81 |
| Melting Point (°C) | 1427 |
| Thermal Conductivity (W/m·K) | 25 – 29 |
| Specific Heat Capacity (J/kg·K) | 460 |
These properties contribute to S7’s performance in high-stress and high-impact environments, making it a reliable material for extreme applications.
Forging Properties of S7 Tool Steel
S7 can be forged at temperatures ranging from 1050 – 1150°C (1920 – 2100°F). After forging, the material should be cooled slowly to avoid the formation of internal stresses or cracks.
Stress Relieving for S7 Tool Steel
Stress relieving is performed by heating S7 tool steel to 600 – 650°C (1110 – 1200°F) to remove residual stresses from machining or forming operations. This process enhances dimensional stability and prevents warping during service.
Machinability of S7 Tool Steel
S7 tool steel offers good machinability, especially in its annealed condition. It can be machined with standard tools, but due to its hardness and toughness, tool wear should be monitored, particularly after hardening.
Welding of S7 Tool Steel
S7 can be welded, but it requires preheating to 200 – 300°C (390 – 570°F) and post-weld heat treatment to avoid cracking. Proper welding procedures help maintain the steel’s toughness and prevent embrittlement around the weld zone.
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