4340 - Mechanical Properties

[djm883]

I have been posed a question regarding 4340 (forged, round bar) mechanical properties. The specs. call for it to be annealed and to have the ultimate strength be a minimum of 101 ksi and the yield to be a minimum of 69 ksi.

According to the supplier, the only way to obtain these mechanical properties is to heat treat the shaft rather than anneal it. The annealing process gives properties approximately 15-20% lower.

According to Ryerson's website, their website says their annealed bars meet this however other suppliers do not. Unfortunately Ryerson doesn't make this product anymore.

Can somebody give me some advice regarding the annealing for heat treating?

Thanks.

 

[swall]

What is your application? Is annealing required for forming or for machinability?

 

[djm883]

The application is for a rotating shaft and I believe the annealing is for machinability. A concern with the heat treatment is that it will distort the shaft (approx. 18 ft. long).

 

[dbooker630]

With 4340 you can try a subcritical anneal by heating to 1250F, holding for about four hours, furnace cool to below 800F. Resulting Brinell is about 207-217 HB which meets your tensile requirement. This process should be less distortion than a full anneal or a normalize and temper treatment.

 

[mfgenggear]

Asking a question? why would you want your part soft?
machinibility is better went heat treated at 30 HRc