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Alloy choice to match grade 8 bolts

crickets

Hot Rolled
Joined
Jul 3, 2021
Folks,

I need to machine some hardware that will have tensile strength similar to grade 8 bolts. Don't want to deal with heat treatment. What are the possible options ? Thanks!
 
ETD 150 has the same tensile strength. If you are threading you lose about 10 to 15% of the strength if you cut the thread vs rolling them.

Ed.

Yes, ETD-150. The best of both worlds, machinability and strength.
 
grades are not given an alloy restriction (type 1 or 3 is the alloy call out). Grade 8 is heat treated after threading with tensile of 150k psi. Grade 490 which is what your 2 inch bolt would be is 120k - sometimes tempered after threading. a490, a325, b7 are twins from another mother, and slightly better than grade 5- way better to use.
I am for doing work yourself; when spec is grade 8 there is no room for error. St Louis bolt and screw or Portland bolt would be the ones to call.
 
thanks, mom :D

You are already removing two of the requirements of grade 8 - heat treat after threading and rolling threads - It might be time to get engineer or at least client to sign off. You still need to know if it is type 1 (plain steel aka secret 4140 derivative) or type 3 (corten derivative).

Grade 8 bolts are not very expensive, why not just get a 10 or 12 in long bolts?
 
You are already removing two of the requirements of grade 8 - heat treat after threading and rolling threads - It might be time to get engineer or at least client to sign off. You still need to know if it is type 1 (plain steel aka secret 4140 derivative) or type 3 (corten derivative).

Grade 8 bolts are not very expensive, why not just get a 10 or 12 in long bolts?

So why do rolling threads / heat treat after threading matter if the tensile strength of the material matches or exceeds such of the grade 8 bolt ? Okay, say if it only matches it, then the resulting part will be somewhat weaker due to difference in threading. But if it exceeds, like some of the alloys suggested above ?


Not quite sure what you're suggesting. Getting a long bolt and using it as a donor stock ? Just for funzies I checked McMaster - closest to what I'd need is 1-3/4x10" at $65.15 a piece... except my part is 12" long. Still, seems like raw stock would be cheaper.
 
hardware? how critical? edt 150 is a free machining 4142 type steel. so its "dirty". supposedly 0.06% sulphur and other stuff. the 10.9 bolt (bossard) im looking at has 0.004%. they say elongation is 7% as compared to 9% for 10.9 bolts (iso 898). 12.9 is 8%. i would try and find out some fracture toughness data, e.g 10.9 is 20j cvn minimum*. those free machining steels dont excel in stress corosion cracking and fatigue either.

i never used edt 150 but would be much more comfortable with 4340 pre hard, even if it should look a bit weaker "on paper".

a fantastic steel, btw, is toolox44 (1450/1300 mpa, 20-30 j cvn).

* those elongations dont mean much. they are total elongations (part braks long before that). nobody gives out uniform elongations for bolts.
 
heat treat after is for stress releiving, which makes part stronger. Cutting into material drastically changes its properties compared to forming/forging. The tiny little bit cut on threads weakens it by about 15% on yield.

grade b7/490 is heat treated before threading, 150k vs 120k - just by heat treating after the processing.

Steel is not homogenous soulless material, it has grain and cell structure.

A 2' section of non-heat treated 41xx is over 60$, I would expect the secret corten high strength weathering alloys to be a lot more. Bolts are a cheap way to get small amounts of alloy steel.
 
So why do rolling threads / heat treat after threading matter if the tensile strength of the material matches or exceeds such of the grade 8 bolt ? Okay, say if it only matches it, then the resulting part will be somewhat weaker due to difference in threading. But if it exceeds, like some of the alloys suggested above ?


Not quite sure what you're suggesting. Getting a long bolt and using it as a donor stock ? Just for funzies I checked McMaster - closest to what I'd need is 1-3/4x10" at $65.15 a piece... except my part is 12" long. Still, seems like raw stock would be cheaper.

It's obvious you need this engineered, and not by you....
 








 
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