!!!!!Really listen to the others advice before mine.!!!!!!
try to understand the key terms before hand,
Anneal, Tempering, normalize.
What I would do goes along the lines of a SWAG.
One thing that really will help is using a known steel, your leaf springs "may" be 5160 or it might be something entirely different.
If I were to use 5160 !not from a leaf spring! i would just start forging, with the forging range being a bright red to medium orange as seen in dim light.
hammer the steel to the max desired thickness using a straight or cross pien, then forge the tip.
The preform for the tip would be made by me hammering at 45 degrees to the face of the anvil, into the top corner(when the bar is held on edge), occassionally reducing
the thickness in an effort to get the other corner farther out. then bevel the steel by holding the bar at an angle to the anvil and the hammer at that same angle but from the steel.
this would be done on the side with the farther out corner, and it would cause the bar to warp along the spine side.
To fix this I would tap the flat part of the bar with the hammer flat to the anvil, which when done the whole length would hopefully make the whole thing straight.
Then I would form the tang through forging or with a grinder.
Normalizing should happen at this point, or if you like things to go easilly annealing.
What I do for normalizing is heat the entire thing to nonmagnetic, then just a tiny bit hotter. air cool to black, repeat with slightly less heat 2 times. This would be called a triple normalizing.
Clean up the flats with a grinder or files, then the bevels with files. sand to 220 ish. leave the edge slightly thick appx. dime thickness
Make everything as finished as possible because next is hardening.
Again heat as evenly as possible the entire blade area, to just past non magnetic, then carefully and quickly put the whole blade into hot vegie oil, (200 f ish )
wait untill its the same temp as the oil.
Now carefully and gently remove it, and wipe some excess oil off, then using a file, gently see if it is hard, if the file doesnt bite, its hard, or your file is really dull.
Carefully move to the tempering oven(here a kitchen oven.) now comes the individual part, if its a precision cutting knife, it can be hard, and tempered at 350 ish.
if the knife is to be a heavy chopping knife, you make the oven hotter, 450 perhaps.
Either way leave it in there for 1 hr, air cool on a safe surface like your stove. repeat one or two times.
Tempering is the thing i have the least experience in so others advice is prefered.
Now using sand paper or being slow and carefull with a quality belt sander/grinder bring it to a cutting edge.
Make your handle, or cord wrap etc.
call it done!
Anyone who knows better, can correct me, and make me better too.