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? 

i would suggest since you didnt do full penetration welds, to forge weld them into one solid block first.

The forges in class aren't hot enough to forge weld. What if I were to use some penetrating weld through the faces? What then?

What type forge do you have in your class room?

Why do you need to heat treat a flatter? You are going to use it on HOT metal right?

I just didn't know wether or not the welding would make the spring facing brittle along the edge creating a weak point and delaminate under use. 

Well did you do the proper preheat and post heat for welding that alloy?  Is so, it should be fine. If not, not.

 If you're worried about them coming apart, perhaps try drilling a series of holes through your "bread and welding them back up?

Goodness, it's really hard to make suggestions without having taken a gander first, post some pics?

At first read I'm not sure what you did or your reasoning. For a simple flatter you can just bend a piece of leaf spring in a large hair pin, polish the contact surfaces and put it to work. Seriously the spring in a spring tool can be mild steel it isn't working against more resistance than the weight of the struck die.

For struck (top) tools in general you want the working surface hardened and the struck (hammer side) drawn pretty soft to avoid chipping. so if I'm reading your description correctly you have mild as the working surface and medium carbon steel for the struck surface. That's backwards from my experience. Sure a flatter is less sensitive than most top tools but it never hurts to observe the basic rules, especially about NOT hardening the hammer side of a top tool.

Frosty The Lucky.

Good Morning,

My reading the op, he hasn't tried it or broken it. He is just speculating.

Do not Heat Treat, try it first. The worst that will happen is he will learn a lesson.

Neil

Most of my spring tools are just mild steel through out. Kinder and safer all round.

The hammer tools made from Progen (hot sets and butchers) are left in the annealed state.

Alan

Thanks for all of your input and being patient with a newb! I decided to just put what I had together and beat the xxxx out of it to see if I could make it fail, so far so good. From here on out I will follow all of your advice and thanks again!

glad its working. please remember that this is a G rated forum, and that we have been asked to keep our language clean. see guide lines here.