Glenn

What is Grade 8 (bolts, metal)

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I have encountered some Grade-8 bolts and would like to know the composition, and any suggestions on forging this metal.

From the internet:
Grade 8 bolts are comprised of carbon alloy steel, thus giving them a high psi rating. Zinc or yellow zinc grade 8 bolts are available to resist corrosion. The factor that makes a grade 8 bolt different from a lower grade bolt is its preload strength. Higher grade materials, such as carbon alloy steel, allow for greater torque strength in the threads of the bolt. The preload, or thread tension in a fastener is higher when the type of steel being used is grade 8 in quality. Mark's Standard Handbook for Mechanical Engineers lists Grade 8's as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch.

Grade 8 bolts are medium carbon alloy steel, quenched and tempered at a minimum temperature of 800 degrees Fahrenheit. They are then heat-treated to achieve a hardness of 33 to 39 on the Rockwell C scale.


Another thought, if you use a grade 8 bolt for a particular application, do you also have use grade 8 nuts and washers (if they make such things).

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washers are compressive so it wouldn't matter what their rating was. I would think you would need at least the same grade nuts otherwise the weakest link.

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American Fastener - ASTM, SAE, and ISO Grade Markings
IHS SAE J429 - Mechanical and Material Requirements for Externally Threaded Fasteners
AISC | Steel Interchange


pretty sure that the applicable standards from the governing organizations ( ASTM, SAE & ISO) don't specify a specific alloy, carbon content ect. But rather the physical properties the bolts must test to. Thus depending on the manufacturer some variation is likely

Search: temper
(unfortunately a deep link that leads nowhere without a logon, but it is fun to play with the advanced search)
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For my applications I use grade 5 bolts and nuts for most stuff. I really could care less about the price. Grade 2 is yes used though. Grade 8 is for when I want something married ( reciever hitch etc ). Yes I use appropriate grade nuts. Intresting example. shear bolts will be ( my experience ) grade 5. Grade 2 won't shear but sometimes just bend a bit. The purpose of a shear is to break and save machine parts. Some will go to grade 8 when they continue to break 5's. Some will use 2's and wonder why they don't shear. I'm sure Junior has much more experience in this. Thanks for the links to the specs folks. DON'T breathe the cadnium on the bolts when you heat them. Even the galvanized. More than an answer about grade 8 I know.....BTW, some manufacturers make grade bolts to be guaranteed at LEAST that grade. Caterpillar ( example ) has bolts that are guaranteed grade 5 if they marked grade 5 ( no more less ).

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Nothing worse than a bolt that *won't* break when it was designed expecting it to---sort of like a circuit breaker that won't trip at it's rated value.

Where it gets fun is when folks have mixed up grades through re-using old ones from the bolt can.

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Yea, you want to use matching nut and bolt grades, whashers really don't matter.
Caterpillar hardware is specifically meet or exceed SAE grade 8 and have a larger head than SAE specs makeing them less likely to strip also use a higher quality of steel than most manufactuers, also have a much better thread than most manufactures giving them a better clamp load, more strip and shear resistant than your average bolt, the standard Cat bolts are Rckwell C 37-45 but go higher with the specialty bolts.
Cat hardware is among the best you can buy and definitly surpasses the average hardware or automotive store hardware, if you have a Cat dealer near by then I would highly recomend going there to buy your nuts and bolts standard or metric.

welder19

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In a critical application (for example, aircraft), washers do matter because of compressive strength. The washer is part of the fastener so they should match - although I agree you couldn't see it in routine situations.

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Well if and when you buy your hardware from a quality source the washers (and nuts) will automatically match the grade of the bolt.

welder19

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Grade 8 bolt: a.k.a. a quick and readily handy replacement for a lost/misplaced tractor hitch pin :)

I tried making a specialty drift punch for something or other out of a grade 8 bolt once. It seems I water hardened it from non-magnetic, for some reason (probably just wasn't thinking), then drew the temper back from the point. It worked for what it was needed for, but cracked when I was using it on something else afterwards. I'll definitely oil harden if I ever do it again.

-Aaron @ the SCF

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Hollis is right about aircraft fasteners/washers. Been a long time. They ( fasteners ) will also have safety wire holes in bolt heads/nuts.

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I beg to differ on it doesn't matter about washers, If a fastener needs to be torqued to a certain poundage and the washer is not of the same grade as the bolt and nut, the washer will compress and thus the requirement for the specific application is lost.

The same with the quality of nuts. If a lower grade nut is used the elasticity of then nut material will actually pull the center part of the nut down and raise the outer edges of the nut, thus comprimising the efficiency and contact surface required for the nut.

The rule of thumb in critical applications is that a nut must not be reused as the torquing of the fastener stretches the threads in the nut and the reuse of the nut will result in its holding power made unexceptable.

On over the road semi tractors if you look each and every frame nut has a hardened washer under it to distribute stress on the frame.

And if you look at the engine mounting of a small airplane motor you will see that it is held to the fuselage with usually 3, 3/8inch or so bolts with more than the usual 5 marks of a grade 8 bolt. Its not a good experience if you are flying and your engine takes off flying on its own ahead of you.

I am not sure it ever passed, but there was an attempt at making it a crime to replace a bolt with other than what was originally speced for the application, expecially in the Automotive industry.

On some engines it is not recomended to use head bolts over due to the torqueing and the stressed put on them by the many explosions of the engine fuel over time.

Grade 2 bolts are almost useless, you can twist a 3/8 bolt off when tightening it with a small crescent wrench. Just think of this when going down the road with your family in your car and something traveling in the opposite direction coming at you and some fool used a grade 2 bolt replacement on some trailer or piece of equipment and it fails at the time it is passing you.

when the investigators get done with their investigation, the one who used the grade 2 bolt will be charged with neglient homicide or murder, but it won't make much difference to the ones that person killed.

The same goes for welds, you would not believe the faulty welds that some people put on things that go down the hiway because they are trying to save a buck by doing it themselves.

Remember you are responsible for your actions, could you live with yourself if in your attempt at penny pinching your actions killed or maimed a family.

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That's a big problem today, people don't think about their actions and how they could effect others, just like all the idiots that we let drive 2000lb+ murder weapons down the road, women doing their make up, evryone talking on their cell phones, playing with some kind of gadget that has all their music stored on it or just the radio, looking at the stupid computor built in the dash, laughing and goofing off with their friends, having meetings in the car going down the road, eating......basically doing everything and anything except paying attention to their driving and the people around them.

A woman crashed into my yard a week or so ago, I live on a straight road, she was playing with her phone, well fortunately no one got hurt (other than 2 of my shrubs that she destroyed), but just 1 1/2 hours earlier my with and daughter were standing about 10-15 ft away from the pole she hit waiting for the school bus.....how important is that call your trying to make or take while driving? take your eyes off the road for a split second and anything can happen.

So many people just don't care, like not paying any mind to the hardware they are using or the quality of parts they put on the 2000lb+ murder weapons that are going to be going 60 mph down the road. It's just a matter of knowing and paying attention, if you don't know how to do something then don't, have someone teach you, if your doing a job and too much on your mind to thouroghly pay attention then either don't do it or take a break and clear your mind.

Always think about what could happen due to your actions.

When I said that the grade of washers don't really matter I should have been a little more specific, but I guess I was mainly thinking along the lines of blacksmithing and machineing and fabricating and such, more specific to the things that go on here on the forum.

welder19

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The IForgeIron forum self moderates and self corrects, and that is a good thing. In this case one fellow thinks blacksmithing application, the next fellow thinks aerospace applications. You both are right, but both need to be posted as the next guy reading the article can easily misunderstand which application is being talked about. With both comments posted, they can then be better informed and decide for themselves which application they need.

Thanks to everyone that posts. Keep the discussion going so I can keep reading and learning.

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Off on another small tangent. Mercedes Benz for one does not torgue engine bolts in the way we we do with a torgue wrench, They measure the length of the bolt and torgue until the bolt stretches a certain amount. If you think about that it seems like a good way to go. They have set ups that make this an easy task. for everyday shop use it would require al ot of set up time to measure with this method.

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yes torque to yield I think they call that and it is showing up in domestic cars now you can even by them in rebuild kits now for custom engine work . not that it has any bearing on this .

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Quite often, Grade #8 hardware is specified, because of the shear strength of the bolt, rather than issues of compression, or streach.

 

In those cases, it's common to use a "high grade" bolt, with Grade #2 Nuts and Washers, to retain it in position.

 

Also, it's common practice to use a "low grade" bolt, as a cheap alternative to a proper Shear Pin.

 

Applications vary too much, to make any sort of "rule" about matching the grades of Nuts, Bolts and Washers.

 

 

As for Forging a grade #8 bolt, ... how do you think the head of that bolt was formed ?

 

Of course it can be successfully Forged.

 

 

I'd be more concerned about the fumes that will result from heating the Zinc/Cadimum, ... or whatever protective coating might be on the bolt.

 

I wouldn't let that stop me, ... but I'd be aware of that issue, and be sure I had very positive ventilation.

 

 

 

.

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When it comes to any type of Grade of bolt YES use the same washers and nut to match the Grade bolt ! the reason why is a softer washer,or nut  will mash,distort and/or fail when torqued to the specifications of the grade of the bolt . as for forging them they a grade 8 or 10 bolt that is specked out for outside use (***normally has a zink or galvanized coating on them and is bad for your health***) if burnt off out side or very well ventilated area will yield a good punch  or other tools as desired .

 

Sam

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