MrBugatti

Found some info on the heat treating stages required for making leaf springs so leaving it here for later...

• Steps in making a leaf spring without special equipment
  
• Anneal the steel strip raw material - Heat to approx 800~850°C (cherry to bright red) and allow to cool s-l-o-w-l-y in air.
  
• Cut, machine and form and shape the individual leaves.
  
• Test assemble the complete spring assembly.
  
• When satisfied, disassemble the spring again and harden the leaves (individually). [Heat to approx 820°C (bright red) and quench in oil].
  
• Clean the surface with steel wool or similar to see the colours clearly when tempering (next).
  
• Temper the leaves. [Heat to approx 320°C (dark blue/grey) and quench in oil].
  
• Clean the leaves, and paint or apply final finish if desired.
  
• Assemble the spring.
  

These look promising, for the cost I'll give them ago.