(SK85) SK5 Carbon Steel Properties, Composition & Equivalent
SK5 Carbon Steel (SK85 Material)
SK5 steel (SK85 material) is a carbon tool steel commonly used in Japan. After quenching and tempering, it has high hardness and good wear resistance, but the hardness decreases at high temperature. It is often used as a material for tools such as hammers and saws. SK85 is the name of the new JIS G4401 standard to replace the old name SK5. But the name SK5 is still widely used in Japan.
Material SK85 Meaning (Designation)
- “S” means “steel”,
- “K” means “Kougu”, the word “tool” in Japanese, and
- 85 denotes 0.85% carbon content.
SK5 Steel Properties
The density of SK85 tool steel is 7.84 g/cm3, the annealing hardness is ≤207 HB (annealing temperature is 730-760 °C slow cooling), and the quenching and tempering hardness of the specimen is ≥ 59 HRC (quenching temperature 780 °C, water cooling; tempering temperature 180 °C, air cooling).
Chemical Composition
Based on melting analysis
| SK5 Steel Chemical Composition, % | ||||||
| Standard | Carbon Steel | C | Si | Mn | P, ≤ | S, ≤ |
| JIS G 4401 | SK5 (SK85) | 0.80-0.90 | 0.10-0.35 | 0.10-0.50 | 0.030 | 0.030 |
Note: For impurities, Cu must ≤ 0.25%, Cr ≤ 0.30%, and Ni ≤ 0.25%.
Physical Properties
| Physical Properties | Metric | Imperial |
| Density | 7.87 g/cm3 | 0.284 lb/in3 |
| Specific heat capacity | 490 J/kg·K | 0.117 Btu/lb ·°F |
| Electrical resistivity | 0.18 μΩ·m | 7.09 μΩ·in |
| Elastic modulus (Modulus of Elasticity) | 208 GPa | 29 x 103 ksi |
| Coefficient of thermal expansion (CTE) | 11.0 x 10-6/K at 0-100 °C | 6.39 μin./in.·°F at 32-212 °F |
| Thermal conductivity | 50.2 W/m·K | 30.1 Btu/ft·h·°F |
Mechanical Properties
| SK5 Material Mechanical Properties | ||||
| Steel | Finish | Hardness (HV) | Tensile Strength, MPa | Stretch, % |
| SK5 (SK85) | Annealed | 150-190 | 460-625 | 26-37 |
| Skin pass | 170-210 | 510-685 | 15-35 | |
| Rolled | 240-280 | 725-930 | 3-16 | |
| Strong rolling | 260-300 | 805-1000 | 1-5 | |
Uses and Applications
SK85 material typical uses are hammers, axes, saw tools, but the application of SK material is not limited to tools, it is also widely used in materials that require hardness and wear resistance, such as pins and shafts in mechanical parts; engraving, chisels, stamping dies, band saws, circular saws, clamp and jig tools, cold steel knives, blades, daggers, gauges, needles, etc. Some popular brand knives such as Cold Steel SRK SK5, Recon Tanto SK5, Ontario Blackbird SK5 all use SK5 material.
SK5 Steel Equivalent Material
SK5 carbon steel equivalent material is listed in the table below, including US ASTM, ISO, German DIN, Chinese GB and European EN standard, etc.
| SK5 Steel Equivalent Material | |||||||||||||||||||
| Japan | US | European | ISO | Germany | China | Australia | India | Rusia | Korea | ||||||||||
| Standard | Steel Grade | Standard | Steel Type (UNS) | Standard | Steel Name | Standard | Designation | Standard | Steel Name (Material Number) | Standard | Steel Grade | Standard | Grade | Standard | Grade | Standard | Grade | Standard | Grade |
| JIS G4401 | SK5 (SK85) | AISI, SAE; ASTM A686; ASTM A29/A29M | W1 (T72301); 1086 | EN ISO 4957 | C80U; C90U | ISO 4957 | C80U; C90U | DIN EN ISO 4957; DIN 17350 | C80U (1.1525, C90U (1.1535); C85W (1.1830) | GB/T 1298 | T8Mn | ||||||||
Note:
- JIS G4401: Carbon tool steels;
- ASTM A686: Standard Specification for Tool Steel, Carbon;
- ASTM A29/A29M: Standard Specification for Steel Bars, Carbon and Alloy, Hot-Wrought;
- BS EN, DIN EN ISO 4957: Tool steels
- DIN 17350: Tool steels, has been replaced by DIN EN ISO 4957.
- GB/T 1298: Carbon tool steels
