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 temperatures. 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.
SK85 material meaning (designation)
- “S” stands for “steel”,
- “K” stands for “Kougu”, the word “tool” in Japanese, and
- 85 denotes 0.85% carbon content.
Properties of SK5 steel
The density of SK85 tool steel is 7.84 g/cm3, the annealing hardness is ≤207 HB (the annealing temperature is 730-760 °C slow cooling), and the quenching and tempering hardness of the sample is ≥ 59 HRC (quenching temperature 780°C, water cooling; quenching temperature 180°C, air cooling).
Chemical composition
Based on fusion analysis
| Chemical Composition of SK5 Steel,% | ||||||
| Standard | Carbon steel | W | Yes | 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 | 7.87g/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 | 29×10 3 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
| Mechanical Properties of SK5 Material | ||||
| Steel | finish | Hardness (HV) | Tensile strength, MPa | To 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 bearing | 260-300 | 805-1000 | 1-5 | |
Uses and applications
The typical uses of SK85 material 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, fixture 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.
Equivalent material in SK5 steel
The equivalent material of SK5 carbon steel is listed in the table below, including US ASTM, ISO, German DIN, Chinese GB and European EN standard, etc.
| Equivalent material in SK5 steel | |||||||||||||||||||
| Japan | USA | European | ISO | Germany | China | Australia | India | Russia | Korea | ||||||||||
| Standard | Steel Grade | Standard | Steel Type (UNS) | Standard | Steel Name | Standard | Designation | Standard | Steel Name (Material Number) | Standard | Steel Grade | Standard | Note | Standard | Note | Standard | Note | Standard | Note |
| 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 | ||||||||
Observation:
- JIS G4401: Carbon tool steels;
- ASTM A686: Standard specification for tool steel, carbon;
- ASTM A29/A29M: Standard Specification for Hot Forged Steel, Carbon and Alloy Bars;
- 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
