Bolt material selection

[D6c]

I have a couple of custom bolts to make. What's your favorite steel to use to approximate a grade 8 bolt and heat treatment? (150,000 psi tensile strength)
Not a super critical application....anything grade 5 and above would probably be adequate.

 

[Milland]

I have a couple of custom bolts to make. What's your favorite steel to use to approximate a grade 8 bolt and heat treatment? (150,000 psi tensile strength)
Not a super critical application....anything grade 5 and above would probably be adequate.

More information about what the bolt is supposed to do, the size, and what loading/flexing it'll see would help, but this has been recommenced before on PM:

Niagara Lasalle Steel Products - Stressproof ®, ASTM A311, Cold Rolled Steel 1144 Round Rod

Edit: Just realized I used the wrong link, what I'd intended to use was this:

http://www.niagaralasalle.com/pdf/fatigueproof.pdf

Which should be better for fasteners with cut threads.

 

[Laverda]

Any time I need to make a custom grade 8 bolt, I just go to the hardware store and get a grade 8 bolt bigger than what I need and machine it down to size. No heat treating required. Same for making custom grade 8 nuts. If starting with round bar you are gonna make a mountain of chips in order to make a bolt due to the much bigger size of the bolt head.

 

[cyanidekid]

all kinds of wrong about this if you don't understand fastener and material engineering. one fact is, cut threads are vastly inferior to rolled threads.

a lot of machinists absolutely refuse to believe this. their beautiful H2 threads couldn't possibly be inferior to rolled threads.
well, they are. vastly.

particularly critical for single shear suspension parts. quite a few drivers have died when custom steering arms, front wheel mounts, pitman arms etc fatigued and snapped.

see Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook. a bit dated, but if you don't own this, you shouldn't even think about making a bolt.

 

[Blazemaster]

I would prob use something like 4140 ht

 

[MrWhoopee]

ETD150

 

[jim rozen]

"a lot of machinists absolutely refuse to believe this"

A lot of machinists don't know what an Instron is.

 

[Milland]

"a lot of machinists absolutely refuse to believe this"

A lot of machinists don't know what an Instron is.

It's the opposite of an Outstron, of course...

OP says it's for a non-super-critical application, but it would still be better to have more information to help with material and process selection.

 

[john.k]

Dont go to a bolt shop either .....if'n ya dont want prefractured chinesium.......buy the bolts ,studs, nuts,washers ,etc at a Caterpillar spare parts outlet.

 

[Halcohead]

I second ETD150. 17-4 H900 or 15-5 H900 (or H1025 if you want more toughness for a little less strength) also make a fine screw if you also want it to be shiny, and if you want insane strength and ductility/toughness, heat treated 718 inconel. But don’t do that you’ll hate machining it.

I would do ETD150 over 1144, just because 1144 has lower yield and ultimate strength and ETD150 is easy enough to machine.

As for suggestions about rolled vs cut threads, don’t worry and don’t over-engineer things. Rolled threads only have advantages in applications where fatigue is an issue, and maybe some exotic corrosion cases. Many fasteners never see meaningful fatigue loads (even if the joint is cyclically loaded). If the application is failure-critical or super highly loaded, this isn’t the place to look for guidance and there are a lot of fastened joint fundamentals to brush-up on before specifying the fastener. If you’re really worried about fatigue you can consider using a UNJ thread form, but once again this is likely overthinking things.

 

[atex57]

Halcohead has the gist of it.

I make custom rolled thread fasteners and have made several videos on testing them and the lubricants for them.

Cut threads in tension have between 10 and 20 percent less tensile strength and when tested to failure fail more abruptly, less elongation. I have videos on Youtube about this.

Cut threads in shear are to be avoided.

Ed.

 

[Mtndew]

A lot of machinists don't know what an Instron is.

A lot of machinists don't need to know what that is.

 

[cyanidekid]

I make custom rolled thread fasteners and have made several videos on testing them and the lubricants for them.

Cut threads in tension have between 10 and 20 percent less tensile strength and when tested to failure fail more abruptly, less elongation. I have videos on Youtube about this.

Cut threads in shear are to be avoided.

Ed.

thank you for that info. 10-20% less tensile strength and abrupt failure is significant. (it's not just fatigue resistance.)
puts a fastener in grade 5 territory even if made with the same spec material as a gr.8

 

[Laverda]

all kinds of wrong about this if you don't understand fastener and material engineering. one fact is, cut threads are vastly inferior to rolled threads.

a lot of machinists absolutely refuse to believe this. their beautiful H2 threads couldn't possibly be inferior to rolled threads.
well, they are. vastly.

particularly critical for single shear suspension parts. quite a few drivers have died when custom steering arms, front wheel mounts, pitman arms etc fatigued and snapped.

see Carroll Smith's Nuts, Bolts, Fasteners and Plumbing Handbook. a bit dated, but if you don't own this, you shouldn't even think about making a bolt.

I most certainly agree that rolled threads are stronger than cut but if the 20% at most a cut thread bolt is weaker than a rolled thread and it fails, you were not using the correct size hardware in the first place. Many race car builder are so obsessed with weight that they often times don't make the part or use hardware that is strong enough for the application.

After 45 years of making bigger grade 8 bolts in to smaller grade 8 bolts, I have never had one fail.

It is common for people to swap steel bolts for titanium of the same size not realizing that titanium has about half the tensile strength of steel.

A friend of mine mine copied the front and rear axles of his dirt bike and made them out of titanium. The front one snapped on the first jump.

 

[D6c]

The "bolts" I'm working on are for a restoration project on a GMC 2 1/2 ton 6x6 truck. The bolts are double ended studs that retain the spare tire carrier in the stowed position. By double-ended I mean it's a 3/4" stud that has a 1" hex in the center. One end bolts through the frame and the other has a large nut that retains the carrier in the stowed position. Like I said, not a super critical part. At first glance the ETD150 material looks like it might work fine. Thanks for the replies.

 

[cyanidekid]

I most certainly agree that rolled threads are stronger than cut but if the 20% at most a cut thread bolt is weaker than a rolled thread and it fails, you were not using the correct size hardware in the first place. Many race car builder are so obsessed with weight that they often times don't make the part or use hardware that is strong enough for the application.

After 45 years of making bigger grade 8 bolts in to smaller grade 8 bolts, I have never had one fail.

It is common for people to swap steel bolts for titanium of the same size not realizing that titanium has about half the tensile strength of steel.

A friend of mine mine copied the front and rear axles of his dirt bike and made them out of titanium. The front one snapped on the first jump.

please note the 20% reduction is in pure tension, fatigue resistance in a cut thread is much, much less.

totally agree about builders being obsessed with weight to the detriment of driver safety. ("if we win the title, I can get another driver, they will line up to drive for us").

not necessarily on the Ti. some alloys properly heat treated and work hardened can approach 200KPSI if I recall.

 

[Halcohead]

thank you for that info. 10-20% less tensile strength and abrupt failure is significant. (it's not just fatigue resistance.)
puts a fastener in grade 5 territory even if made with the same spec material as a gr.8

Fair enough, yes a torque-to-yield fastener application can also benefit from the grain refinement associated with rolling. But if a fastener is not being loaded to yield or severely cyclically loaded, cut threads are perfectly acceptable. For example many JIS/AN fittings use cut, rather than rolled threads, and they work just fine. More generally I disagree with the assertion that a successful fastener or fastened joint cannot be designed without consulting a fastener design textbook. That is certainly true in some applications, but the people seriously engineering for those applications aren't asking a machinist forum to help them select a material.

D6c, ETD150 should work just fine for that, and if it's too expensive, 1144 should be a fine substitute. Not that anyone has suggested them, but I would stay away from the free machining steels like 12L14 or 303; the additives that make those easy to cut also sacrifice their strength and toughness. Good luck with the project, it sounds like a fun one.

 

[jim rozen]

"A lot of machinists don't need to know what that is."

Yeah, who cares how strong the part you made is. Just make it out of some super strong unobtainium and it will work just fine. Until the spare tire falls off and goes through somebody's windshield. Or until the axle snaps....

 

[cyanidekid]

" More generally I disagree with the assertion that a successful fastener or fastened joint cannot be designed without consulting a fastener design textbook.

haha! that book is far, far from a textbook. it's actually a good read, and he's a "character" a cranky opinionated guy... much like some here...
totally worth getting.

 

[guythatbrews]

As has been pointed out this forum is not the place for critical bolt design, but is just fine for the OP's application.

Nevertheless I thought I'd chime in with something about corrosion.

Regarding rolled threads and corrosion resistance, I always thought rolled equals better, but the jury is still out. I am in no way an expert, but I have a customer that is. Safety critical parts. They allow no rolled threads due to the possiblity of Hydrogen Stress Cracking. I believe studies are ongoing but apparently this is a concern due not only to internal hydrogen embrittlement but also enviormental hydrogen embrittlement.