I wanted to make a spring flatter for a class I'm in but I didn't have thick plates of high carbon steel to make the striking plates. I decided to take two pieces of mild plate steel that were 2"x2"x1/2" and weld four pieces of auto leaf spring pieces that were 2"x2"x1/4" on the top and bottom with a MIG welder,I welded all around the edges essentially making a steel sandwich with the leaf spring as bread and the mild as the meat. What would be the best method of heat treating so that all three of the different metals used in the construction can stay stuck together and survive the hammer blows?