[TheForge] 4140 vs 4340

[John Newman]

Does this mean that power hammer dies made from 4140 or 4340 quenched in oil
do not need to be tempered?

John Newman

Grant Neil Sarver wrote:

> 4140 and 4340 both have advantages. 4340 will harden deeper and in
> larger cross-sections. When you get past around 1 1/2 inch thick 4140
> won't get nearly as hard. "The Book" says that a 1" round 4140 quenched
> in oil from 1550 F. will be about 55 Rockwell on the surface and around
> 50 Rc in the center. A 2" round 49 surface and 38 center and a 4" round
> 36 surface and 34 center. 4340 on the otherhand, in 4" section will give
> 53 surface and 47 center.
>
> I prefer working with 4140 but use 4340 when I have to. 4140 is easier
> to forge, easier to heat treat and gives wonderful results if the
> thickness is under 1 1/2 to 2". 4340 is harder to forge, has heavy, ugly
> scale (the nickel content causes this) that is a real bitch to remove,
> more difficult to heat treat, but when I need a heavy sections I have to
> use it.
>
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