ArtMetal

You are going to have to use heat to accomplish what you are desiring. The leaf spring is going to have to be heated to a dull orange color and then buried in wood ash so the heat dicipates slowly. You will then be able to cut it with the hacksaw and finish the edges. Once you are done with the shaping, you can reheat it to the dull orange and quench it in water to freeze the carbon on the outside of the blade. You can further heat treat to 500 degrees (blue color) to take a bit of the hardness/brittleness out of the blade so it won't break.

This is the simplest/minimal techniques required to work with the car spring.