What's the difference between high carbon steel SK2, SK4, SK5 and SK7?

S stands for steel, K stands for tools (such as knives and saws), and the serial number is the one selected at the beginning. The new Japanese standard has been changed to SKXX(XX stands for carbon content).

SK5, with a carbon content of about 0.85%, seems to be a better one, with balanced strength, toughness and price.

SK2 is a high-grade high-carbon tool steel, cold stamping die steel. The steel has high hardness, good wear resistance, good toughness deviation and machinability, and more excess carbide after quenching.

The strength and wear resistance of SK4 steel are higher than T8 and T9, but it has low thermal hardness, low hardenability and large quenching deformation. SK4 is suitable for manufacturing with poor cutting conditions and high wear resistance requirements.

SK5 is carbon tool steel, and the standard is JIS G440 1. After quenching and tempering, it has high hardness and wear resistance, but low thermal hardness, poor hardenability, easy deformation, poor plasticity and strength.

SK7 is a high carbon steel with a carbon content of 0.6. After quenching and hardening, SK7 has excellent wear resistance and is a cheaper tool steel. Suitable for sliding parts requiring high hardness and making cold working die parts.