What type of material are the blades made from?

The Martha secateurs are made with S58C steel. 

S58C (JIS G4051) is a kind of high strength medium carbon steel with high strength, hardness and elasticity.

This type of steel is also commonly used in the following: 

• Bridge steel plate
• Boiler steel plate
• Shipbuilding steel plate
• Armor steel plate
• Automotive steel plate
• Roof steel plate
• Structural Steel 
• Electrical steel (silicon steel)
• Stainless steel spring plate
• Solar panels