(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;
W1 (T72301);
EN ISO 4957 C80U;
ISO 4957 C80U;
DIN EN ISO 4957;
DIN 17350
C80U (1.1525,
C90U (1.1535);
C85W (1.1830)
GB/T 1298 T8Mn


  • 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

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