making of a grade 8 bolt

[jakieboy]

To make a grade 8, 1 inch diameter bolt out of 2.875" round bar 4340 ; 1) Should I start out with untreated 2 1/2" round bar and machine down to with 10% of bolt shank dimension, then heat treat to hardness requirements and finish machining shank, than machine the threads, or 2) heat treat the full 2.875" round bar and machine to final dimension.
I am using a 4340 material and want to achieve a bolt having a 321-388 brinell hardness, 150000 psi tensile, 130000 psi yeild and elongation of 12%.
Presently sending out the round 2.875' bar to a Heat Treater shop to obtain the above numbers, but upon testing a 1" bolt machined from the core of the material the numbers come in slightly below strength requirement.
Any ideas for the best method to achieve desired results and keep the cost down.

 

[swall]

The normal way of doing things would be to machine the bolt preform then heat treat and final machine.

 

[JStephen]

Now, you've got me curious...why machine a bolt? Do they not sell them that big or something? If so, seems it would be easier to change bolt specs than to make one from scratch.

 

[Lutfi]

Go to Portland Bolt company web site and search under Technical information. They have great wealth of data and technical expertise. Even try calling them for an advise. Here is the link:

http://www.portlandbolt.com/

Regards,
Lutfi

 

[Ron]

Sounds like your heat treatment wasn't fully effective. 4340 should be treatable through the section; though would be easier on smaller section.