Flat spring steel with a thickness of less than 3 or 4 mm:

Those products are flat spring steel with a thickness of less than 3 or 4 mm:

carbon spring steel strip (annealed)
Material C75S/C85S+LC
Standard tensile strengths 490-640 N/mm²
Dimensions From 0,05 mm thickness to max. 4 x 200 mm
If you need wider Dimensions maybe 75Cr1 is an alternative
Product Strips and sheets
Optional: round Edges

 

carbon spring steel strip (hardened & tempered)
Material C75S/C85S+QT
Standard tensile strengths 1320-1520 N/mm²
1570-1770 N/mm²
not that common but possible:
1100-1300 N/mm² and further ranges
Dimensions From 0,02 mm thickness to max. 3 x 230 mm and 4 x 30 mm
If you need wider Dimensions maybe 75Cr1 is an alternative
Product Strips and sheets
Optional: round Edges

 

spring steel strip (stainless)
Material 1.4310 (X10CrNi18-8)
Standard tensile strengths 1100-1300 N/mm²
1300-1500 N/mm²
1500-1700 N/mm²
Dimensions From 0,05 mm thickness to max. 3 x 300 mm
Product Strips and sheets
Optional: round Edges