This is also known as bimetal, which is layers of different metals.
It is a sharp and tough additional or replacement blade for use with your TOTAL Hacksaw. D6A steel is an alloy with chromium, molybdenum, manganese and others which separately and together improve corrosion resistance, wear resistance, and toughness.
Hardness and tensile strength are also improved.
M42 steel is a high-speed alloy including some additional percentage of cobalt.
This gives it superior hardness as compared to more conventional high-speed steels.