AISI 4340 Plate Fatigue Limit

[Neubaten]

Hi,

I've been looking for the fatigue limit of AISI 4340 steel in the form of plate.

I found data (S/N curves) for bar at the MIL-HDBK-5, but not for plate. Could those curves be used also for the plate form?

If not, please any guide to where I can find fatigue data on plate (or any way to calculate it) would be greatly appreciated.

Thanks in advance for your help.

 

[metengr]

For high cycle fatigue, I would approximate the value based on 0.5 x UTS if you cannot obtain published S/N data. The S/N curves in MIL-HDBK-5 apply to a specific strength level and if your material is either above or below this strength level, the HCF limit will be incorrect for your application.

 

[TVP]

The MIL-HDBK-5 curves should be a reasonable approximation for plate, as long as the strength level is similar.

 

[tbuelna]

Neubaten,

The S/N data for 4340 wrought plate should be similar to wrought bar if the plate part's grain direction is primarily longitudinal. The 4340 bar S/N curves in MIL-HDBK-5 are for longitudinal grain orientations.

Also, pay attention to whether the material properties are for air melt or vacuum melt 4340 alloys. Air melt 4340 alloys (like AMS 6415) will have much lower fatigue limits than vacuum melt 4340 alloys (like AMS 6414).

Good luck.
Terry