The "Standard" High Speed Steel. M2 offers the best balance of toughness, wear resistance, and hot hardness. It is far superior to D2 in terms of toughness and heat resistance, making it ideal for cutting tools that get hot during operation.
M2 with the addition of 5% Cobalt. This significantly improves "Red Hardness" (the ability to stay hard at high temperatures). Essential for cutting hard materials like Stainless Steel or Titanium where high heat is generated at the cutting edge.