Grade 5 vs Grade 8

[8Mud]

I rarley see nuts, with a rating. Makes me wonder, I see a few. Is it possible the unmarked nuts, I´m using, are grade 3 or lower? I have picked up a few pounds, of some really soft washers from time to time.
Have a load of nuts I picked up military surplus. They have a parrallelagram or a diamond sign on the ends. They seem pretty darned hard. Anybody seen this sign before. And maybe know what it indicates.

 

[Jeep'nD]

But no-one has tackled this question:

When rocks start smashing the fastener heads, which will put up with it better? A medium carbon steel or a medium carbon alloy steel.

Anyone?

 

[8Mud]

Depends on the alloy, most are softer than steel. I´d be tempted to use stainless bolts, with an index of 10.9 or higher. High carbon bolts, will rust (slowly), but not ding very easily. Diamond stamped bolts, will dent most any punch, chisel or hammer, forget about a drill bit. Basalt rock, some granite or most rock, not sedimentary is some harder than most steel. They usually use carbide and high carbon tools to work the stone.
I have an antique rockwell drop tester, that I play with on occasion. The carbide tips, ding most everything somewhat.

 

[Ghost]

They are expensive but.......

Advanced Auto usually has waht I am looking for in metric stuff. Around here Grade 8 bolts are easy to come by. It's the Grade 10.9 that are rare as hell. Those symbols are the hardness of the bolt too I believe. But cannot remember where I saw it.

 

[Jeep'nD]

For metric info see:

http://www.mech.gla.ac.uk/~paulk/pde/nutnbolt.htm


And to get an idea of what the different fasteners look like, peruse:

http://www.fastenerhut.com/

And for an explanation of course vs fine threads see:

http://www.tapmatic.com/tech_manual/coarse_fine.html

 

[Jeep'nD]

After having poked around the fastenerhut site I listed above, I think I found the solution to my plating dilema. Instead of using bolt heads on the armor that will be exposed to rock, I could use flat head bolts that sit flush with the surface of the plating. All that I need to do is contersink the hole and all should go well. Now when rocks scrape by, they should not catch on the bolts at all.

Since I am assuming that there won't be much stress on these bolts I think this bolt head type should suffice. Besides when in doubt, make it stout, i.e. the more bolts the better.

Check these out:

Flat Head Socket Cap Screws

 

[FarmerMatt]

That is until you booger up the head & can't get your allen or torx bit in it to back the bolt back out. At least you can get vise grips or weld a nut onto hex head bolts. I would not use those types of fasteners under a crawler. Now recessing the hex head bolts up into the metal is a cool deal.

BTW grade 2 bolts are where it's at.

Matt

 

[C-ROK]

BTW grade 2 bolts are where it's at.

Matt

No way man - it's all about nylon these days.

BTW, do you know anyone that can turn threads in rubber?

 

[MudDawg]

I agree that in a lot of cases, the condition of the fastener and it's installation have a drastic effect on the performance. I have seldom failed a properly applied and installed Grade 8 fastener. Those few times, the components failed along with the fastener.

 

[robs]

But no-one has tackled this question:

When rocks start smashing the fastener heads, which will put up with it better? A medium carbon steel or a medium carbon alloy steel.

Anyone?

It's all about hardness, not the material type...

Carbon is responsible for hardness... alloy lets the carbon do it's job....

From a strict "deformation" application... any plain carbon or engineering alloy that achieves a hardness of say 38 HRC will behave roughly the same... (that's roughly how hard Grade 8 is)...

Where material comes into play is for larger fasteners... there has to be enough alloy to allow proper transformation during heat treat and provide tempering resistance... For 1/2" size fasteners... a C1045 will work fine for Grade 5, but normally don't have enough hardenability to achieve Grade 8 properties... Most Grade 8s of this size are from 4140... Both these alloys have roughly the same carbon... but the 4140 has Chromium and Moly to enhance it's hardenability.

They do make fasteners harder than this for specific applications, but they are normally restricted to internal engine components where they aren't subject to corrosion... Once the hardness gets much above 40 HRC, the steel will be susceptible to environment damage (hydrogen enduced stress corrosion cracking and the like)... that's why GM outlawed 12.9 fasteners and recalled millions upon millions of them...

 

[Erik the Red]

This is a very interesting discussion, and one I've agonized over when replacing exhaust manifold bolts. I've been told by some to use grade 8 bolts because of their obvious tensile strength advantages, while others have said I should use grade 5 bolts because, while weaker, a broken grade 5 can be tapped out whereas a broken grade 8 cannot be easily removed.

Any opinions on which grade to use for exhaust manifolds?

Erik
88 Comanche

 

[8Mud]

I´ve always used OEM bolts, grade 8. Can´t remeber having a bolt seize or break off. The cone/spring washers allow for expansion and contraction. I have a brass drift 1/2 diameter, a foot long. A few sharp raps on the bolt head, with the brass drfit, has always loosened them enough for removal. Use an anti-seize compound (labeled very high temperature grease, with teflon), when replacing, doesn´t work like it was inteneded, it bakes into a crust, but still retains some of it´s anti-seize properties. Grade 5 are probably too soft to let the cone/spring washer do it´s job.
Studs are more of a problem, use of a soft nut, has worked for me. Brass, if it strips, is no big deal, a few minutes with a thread file. Cutting off the excess threads and an anti-seize compound, helps.
When drilling out grade 8 bolts, a bit labeled HSS (high speed steel) works. Slow speed, frequent oil, screw/nut driver drill with a clutch. Heat and hanging are the enemy when drilling out hardened bolts. High speed drilling heats up the drill bit, a little stepper pitch, when resharpening and a slow speed will work.

 

[robs]

If it's on the exhaust... smack that baby with mapp gas until it starts glowing red.. It won't be a grade 8 no more and will drill fine....

Most grade 8's are tempered around 900-1000°F during heat treatment... Glowing red is about 1200°F and will knock the hardness clean out of it.

 

[5-90]

Undercar exhaust? Use something nonferrous, like brass or bronze. I've been doing it for about 20 years, and the only difference I've seen between putting them on and taking them off is they're a little duller when I take them off a few years later. No need for anything beyond a plain ol' wrench when it's time for them to come off - I haven't been able to MAKE them sieze!

I also use brass or bronze bolts on exhaust manifolds - the torque (and therefore strength) requirements are low enough that it's not a factor for any metal, and the same reasons apply as for undercar brass or bronze. Sieze? Doesn't happen.

You can find brass (usually half hard marine grade) at a good hardware store or boat shop, and Fastenal carries both brass and silicon bronze (both of which will work nicely, silicon bronze is significantly stronger than brass if you worry about it... Expect Fastenal to need a couple days to bring in si-bronze, they come from the central warehouse in MN...)

5-90

 

[Majo]

It's all about hardness, not the material type...
...

Material type and composition is very much a factor here. Look at a Equilibrium Microstucture Development plot for Fe-Fe3C. I'll post a pic of it soon. It's all about the eutectic tempure, and composition as the C is what does the job. Any where below the eutectic temperature the melted material will become a solid, containting precipates of both Fe and Fe3C.

Lets take a 50/50 solution to work with. Ideally an equal solution(liquid as in melted) would precipated equally when hitting the eutectic temperature for Steel/Iron. That temperature being 1153 degrees farenheit. At this temperature the material (Steel or Iron dependent on Compisition) is a eutectoid(mixture of fine graded particals). When that compostion hits the eutectioid temperatore of 727 degrees farenheit both materials in the composition Fe and Fe3C will become full solids.

Now lets look at a different case. Say the weight percent of carbon in this solution is 3%. Melt the compostion to a liquid. Now let it begin its cooling and formation process. It will first reach a stage where it has
Fe precipates in liquid Fe3C solution. After this stage a eutectiod compostion of Fe and the precipated Fe3C forms. (Draw a box and put cirlces in it to represent the Fe3C and blank space to be the Fe.) Now we hit a point where the eutectoid comes into play, the Fe starts to become fine microstructures, and becomes what is referred to as Austenite. Now further cooling of the substance would result in Steel. So the going back to the little box and picture you would now draw straight lines all over except where the Fe3C is. As you can see a varying percent compositon of Fe3C or Carbon would dramatically change the chemical properties of the steel. Going from one extreme of Iron or Ferrrite to one extreme of Graphite, it's ALL composition.

questions just PM or make some noise and i'll be back