[TheForge] 4140 vs 4340

[Dave Brown]

At 22:54 04/04/02 +0930, you wrote:
>Well I just bought some 4140 after reading this discussion, its for my air
>hammer dies. The bar I bought is 38mm square and Im just going to grind it a
>little then weld it to the die plate, this bar is already heat treated and
>tempered by manufacturer, my question is welding it, does this stuff weld
>ok? Id like to keep the factory heat treatment intact so am not sure about
>preheat etc, I was going to use 7018 rod.

Shannell,

Over on the Principal Metals site under Alloy Steels and then to 4140, it 
says the following about welding:
"Weldable by all of the conventional methods. Note that welding with the 
alloy in the heat treated condition will affect the mechanical properties 
and a post weld heat treatment may be needed."

For annealing it says:
"Annealing is done at 1600 F followed by slow furnace cooling."

As for hardening, it says:
Hardens by cold working, or heating and quenching.

So, not being afraid to hazard a guess:  At 38mm (1.5") I think you have 
enough mass that you won't anneal anything far from the welding line.  Any 
moderate annealing that might take place will probably work harden 
relatively quickly.  But the working faces of your 4140 will probably stay 
just fine.

Note:  This is an educated guess on my part.  I could be just as wrong as 
right.  But I'm sure someone else will chime in if I'm all wet.  Right Grant?

Dave Brown


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