MechyMarco
Mechanical
- Jun 5, 2014
- 39
Hi all,
I'm hoping someone can back me up here. I'm making some extreme stress parts out of 4340 round bar per AMS 6415 (air melt). They are machined in the normalized condition then send for hardening. Tempered at 475F to 50-52 HRC. Tensile tests on some test coupons done with the parts put the strength in the 220-240 ksi yield range with some reasonable ductility. So all good there. The issue is cost. The parts are quite rectangular so machining from round stock is very wasteful. I can save a lot of money by using plate instead. However, machinists and some other engineers say I need to consider grain structure. Normally I would agree if I wasn't hardening the parts as the grain structure would be different. Round bar superior in this case. But since the parts are being hardened, the grains will be completely reformed during heat treat and relatively isotropic so any directionality issues from the raw stock in plate form versus bar form are no longer an issue right? The only thing I can think of is the inclusions that are present will still be a factor. So round bar transverse still worse than longitudinal. Same with plate. The through thickness properties will be worse than the length / width properties.
Am I thinking this through logically? Anyone see any issues substituting AMS 6359 plate for AMS 6415 round bar?
Thanks for the insight.
I'm hoping someone can back me up here. I'm making some extreme stress parts out of 4340 round bar per AMS 6415 (air melt). They are machined in the normalized condition then send for hardening. Tempered at 475F to 50-52 HRC. Tensile tests on some test coupons done with the parts put the strength in the 220-240 ksi yield range with some reasonable ductility. So all good there. The issue is cost. The parts are quite rectangular so machining from round stock is very wasteful. I can save a lot of money by using plate instead. However, machinists and some other engineers say I need to consider grain structure. Normally I would agree if I wasn't hardening the parts as the grain structure would be different. Round bar superior in this case. But since the parts are being hardened, the grains will be completely reformed during heat treat and relatively isotropic so any directionality issues from the raw stock in plate form versus bar form are no longer an issue right? The only thing I can think of is the inclusions that are present will still be a factor. So round bar transverse still worse than longitudinal. Same with plate. The through thickness properties will be worse than the length / width properties.
Am I thinking this through logically? Anyone see any issues substituting AMS 6359 plate for AMS 6415 round bar?
Thanks for the insight.
