Doubts on 4140 steel microstructure
Doubts on 4140 steel microstructure
(OP)
Hello everyone,
I would like to hear (read) your thoughts on the image I'm posting. It belongs to a 4140, 2" diameter steel bar . Notice the coarse acicular structure + fine pearlite grains (?). I was told by a material specialist that it corresponds to the absence of heat treatment after rolling (uncontrolled cooling) but I could not find any similar image in the bibliography to support it. Do you agree with that statement?
Best Regards,
Gonzalo M.
Magnification 100X
I would like to hear (read) your thoughts on the image I'm posting. It belongs to a 4140, 2" diameter steel bar . Notice the coarse acicular structure + fine pearlite grains (?). I was told by a material specialist that it corresponds to the absence of heat treatment after rolling (uncontrolled cooling) but I could not find any similar image in the bibliography to support it. Do you agree with that statement?
Best Regards,
Gonzalo M.
Magnification 100X





RE: Doubts on 4140 steel microstructure
RE: Doubts on 4140 steel microstructure
RE: Doubts on 4140 steel microstructure
RE: Doubts on 4140 steel microstructure
WHAT material spec [and HT, etc] was the 4140 bar SUPPOSED to be made per: ASTM, AMS, MIL-, foreign, etc?
Did wet chemistry verify the alloy chemical constituents/ratios... or perhaps by spectroscopy?
CAUTION. Materials definition/requirements should be crystal clear and unambiguous from the beginning of procurement... thru to to the final packing of the finished parts.
An old engineer acquaintance in the fastener business wisely advised me: "You deserve to get what you ask for: but if You don’t ask for very much, don’t-expect to get very much."
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Doubts on 4140 steel microstructure
Thank you all for your help! I think I got enough information to reduce my bibliographic search.
RE: Doubts on 4140 steel microstructure
More than once my shops have complained that raw steel stock 'wouldn't harden' like it was supposed to; or it cracked; or warped; etc.
When pressed, I found out that the shop was sure' it was a specific alloy because it was 'in the right scrap bin'... but was otherwise was unmarked.
This is precisely why aircraft/aerospace/ordnance parts mandate [anal] traceability. Detailed material certs [from a recognized lab] directly accompanying raw-stock made per a recognized spec is worth the effort and expense. Yeah, trust is still required that the 'system worked' [integrity prevailed]... but the ground-work is a solid foundation with checks/balances.
I am working a somewhat similar issue... but with a steel finish processing bath solution that 'went out-of-spec' for several months [getting more acidic]. Traceability has finally caught-up and we've been able to identify the discrepant parts in various assemblies and place them under quarantine. Imperfect as this system is, the 'system eventually worked'... better late than never.
BTW a couple of other Eng-Tip threads are also dealing with 4140 steel discrepancies... worth a look.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Doubts on 4140 steel microstructure
RE: Doubts on 4140 steel microstructure