AISI S7 tool steel.
AISI S7 tool steel is a shock-resistant steel with the highest hardenability and resistance to elevated temperature softening of the S series steels. Due to these properties, S7 material is popular in shock-resistant applications. They are moderately resistant to decarburization and grain growth.
Properties of S7 tool steel
The properties of S7 tool steel such as chemical composition, physical and mechanical properties are summarized below.
Chemical composition
| Chemical composition, % | |||||||||
| Standard | AISI (UNS) | W | Yes | Mn | P, ≤ | S, ≤ | Cr | Mo | V, ≤ |
| ASTM A681 | S7 (T41907) | 0.45-0.55 | 0.20-1.00 | 0.20-0.90 | 0.030 | 0.030 | 3:00-3:50 | 1:30pm-1:80pm | 0.35 |
Physical properties
| Physical properties | Metric | Imperial |
| Density | 7.76g/cm3 | 0.280 lb/in3 |
| Coefficient of thermal expansion (CTE) | 12.6 μm/m·K (20-200 °C) | 7.0 μin./in.°F (70-400 °F) |
| 13.3 μm/m·K (20-425 °C) | 7.4 μin./in.°F (70-800 °F) | |
| 13.7 μm/m·K (20-500 °C) | 7.6 μin./in.°F (70-930 °F) | |
| 13.3 μm/m·K (20-200 °C) | 7.4 μin./in.°F (70-1200 °F) |
Mechanical Properties of S7 Steel
Nominal mechanical properties at room temperature of S7 steel
| Steel | Condition, Fan cooled from 940°C (1725°F) and simple tempered in: | Tensile strength, MPa (ksi) | 0.2% yield strength, MPa (ksi) | Stretch by 2 in. (50mm),% | Reduction area, % |
Hardness, HRC | Charpy impact without notch, J (ft·lbf) |
| S7 | 205°C (400°F) | 2170 (315) | 1450 (210) | 7.0 | 20 | 58 | 244 (180) |
| 315°C (600°F) | 1965 (285) | 1585 (230) | 9.0 | 25 | 55 | 309 (228) | |
| 425°C (800°F) | 1895 (275) | 1410 (205) | 10.0 | 29 | 53 | 243 (179) | |
| 540°C (1000°F) | 1820 (264) | 1380 (200) | 10.0 | 33 | 51 | 324 (239) | |
| 650°C (1200°F) | 1240 (180) | 1035 (150) | 14.0 | 45 | 39 | 358 (264) | |
| Annealed | 640 (93) | 380 (55) | 25.0 | 55 | 95 HRB | – |
Heat Treatment for S7 Shock Resistant Tool Steel
The heat treatment of S7 tool steel is listed below.
Normalizing and annealing temperatures
- Normalizing: Don't normalize.
- Annealing: 815-845°C (1500-1550°F), the upper limit of the range should be used for large sections and the lower limit for smaller sections. The time held at temperature varies from 1 hour for light sections to 4 hours for heavy sections and large high-alloy steel furnace charges.
- Cooling rate: ≤ 14°C/h (25°F/h)
- Annealed Brinell hardness: 187-223 HB.
Hardening and Tempering of S7 Materials
- Heating Rate: Slowly
- Hardening
- Preheating temperature 650-705°C (1200-1300°F);
- Austenitizing temperature 925-955°C (1700-1750°F)
- Time at temperature: 14-45 minutes for heat treatment in an open oven
- Quenching medium: Air or oil
- Hardened Rockwell C hardness, 60-61 HRC
- Quenching Temperature: 205-620°C (400-1150°F)
- Approximate tempered Rockwell C hardness: 45-57 HRC
Forms
S7 steel is mainly used for chisels, punches, rivet sets, stamps, screwdrivers and other applications that require high toughness and resistance to shock loads. Also used for punching and hot shearing where some heat resistance is required.
AISI S7 steel equivalent material
The material equivalent to AISI S7 steel is listed in the table below, including European EN, ISO, German DIN, Chinese GB and Japanese JIS standards, etc.
| AISI S7 tool steel equivalent material | |||||||||||||||||||
| USA | European Union | ISO | Germany | China | Japan | Australia | India | Russia | Korea | ||||||||||
| Standard | Steel (UNS) | Standard | Steel Name (Material Number) | Standard | Designation | Standard | Steel Name (Material Number) | Standard | Steel Grade | Standard | Steel Grade | Standard | Note | Standard | Note | Standard | Note | Standard | Note |
| AISI, SAE; ASTM A681 |
S7 (T41907) | EN ISO 4957 | 5OCrMoV13-15 (1.2355) | ISO 4957 | 5OCrMoV13-15 | DIN EN ISO 4957; DIN 17350, |
5OCrMoV13-15 (1.2355) | GB/T 1299 | 5Cr3MnSiMo1V | – | – | ||||||||
