Grade 8 hardware, through hardened?

Is grade 8 Hardware through hardened? specifically, BHCS? and SHCS?

Thanks,
Nate.

This is what I found, Grade 8 - Medium Carbon Alloy Steel, Quenched and Tempered.

Here's the link,

Bolt Depot - Bolt Grade Markings and Strength Chart

Cheers,
Chazz

Chazz said:

This is what I found, Grade 8 - Medium Carbon Alloy Steel, Quenched and Tempered.

Here's the link,

Bolt Depot - Bolt Grade Markings and Strength Chart

Cheers,
Chazz

Click to expand...

Thanks. That helps a bit, although, it does not specifically address not it is through or case hardening...

Anyone know?

My thoughts are it is heat treated to a higher ultimate tensile strength, but it isn't nearly as hard as a dowel pin or a shoulder bolt. A regular drill bit will make short work of a Grade 8 fastener. Thinking the thread form and the bolt head have slightlty improved material properties due to the compressive stresses imparted by the cold-forming process, but its basically the same material throughout, whereas a dowel pin can be case hardened.

It a very loose spec that states a minimum strength of 150,000 tensile.

It is not "case hardened"

It is "through hardened" as any directly hardenable alloy steels, but sure isn't very "hard"

question of "is it through hardened" is unquantified, and so not super-specifically answerable.


generally harder throughout than a grade 3 or 5, yes.

case hardened, no. that would mean they use lower carbon steel and add carbon to the outside and harden just the outside. or quickly heat the outside, and leave a cool inside. they do not. they use a carbon steel wire and forge the head on it. They heat treat them in batches in a furnace I think i saw this in a video from holokrome.

is it a little harder on the outside than the core, maybe a little. as are many heat treated materials.



cut one down and check it with hardness files. I doubt the accuracy of the files can detect a change in a 1/2" thick bolt shank from the outer 10% to the core.


is thisn answer good enough for your rather vague question?

Not a complete answer to your question, but one can infer from the way its stated that grade 8 bolts are not carburized but through hardened. Cut one open and do a hardness cross section.

American Fastener - ASTM, SAE, and ISO Grade Markings

Drag out the SAE or ASTM specs.

Tom

"question of "is it through hardened" is unquantified, and so not super-specifically answerable."


"is this answer good enough for your rather vague question?"

Awful snarky aren't we?

Through hardening differs from case hardness and is generally accepted as have been hardened all the way through, whereas case hardening is generally accepted as having a hardened case (outer layer) regardless of alloy.

I dont know what was so vague. I did not ask anything except if Grade 8 generally was "through hardened" or not.

I did not ask what the alloy was, the level of hardness, if the hardness varied throughout the part, etc. ONLY if it was hardened all the way through.

So, answer the actual question or not. I don't care. but don't rag on my question for not being exactly as you would have wanted it.

So - did you read Post #5?

things hardened have a gradient of hardness.

we did say they aren't carburized.
and that they are headed from alloy/carbon steel wire.
and batch heat treated.
so a LOT of gradient is kinda thrown out.

what level of precision were you looking for in an answer?

had you been really specific we might reason that you really needed a quite specific answer.
-
(however, had you been really specific it's unlikely you would have asked, because you would have had the knowledge or means to find out yourself and the need of a more trusted answer than likely to find on the internet)


I did suggest an easy & economical test method

John seemes to have beat me to it.

& I am a bit snarky. it's just a character trait (flaw) I have.

Just an FYI - socket head cap screws are not grade 8; they have their own standard (ASTM A574-6 on my ancient Holo-Krome slide chart). Holo-Krome states the hardness of theirs is as follows:

socket head (and low head) cap screws: 39-45 Rockwell C up to 1/2", 37-45 over 1/2"
flat head cap screws: 36-45
button head cap screws: 36-45 up to 1/2", 36-43 over 1/2"
set screws: 45-53

Andrew

Since the bolt grades relate to tensile strength rather than surface hardness, they will be through hardened to meet the grade. Surface hardening makes little difference to tensile strength.

Really!

Common fasteners like Cap Screws are NOT HARDENED at all.They are HEAT TREATED to achieve specifications such as tensile strength. Any "hardening" is purely coincidental.

CalG said:

Really!

Common fasteners like Cap Screws are NOT HARDENED at all.They are HEAT TREATED to achieve specifications such as tensile strength. Any "hardening" is purely coincidental.

Click to expand...

That's just lawyering up. Heat treatment is a process where, through the use of time, temperature and environment, that physical properties of materials are altered. Hardening is just one of them.

Tom

CalG said:

Really!

Common fasteners like Cap Screws are NOT HARDENED at all.They are HEAT TREATED to achieve specifications such as tensile strength. Any "hardening" is purely coincidental.

Click to expand...

Read what I wrote

One can harden a steel part by case hardening it. This will have almost no effect on the yield strength of the part. To affect a yield strength increase, one needs to through harden it and the Yield strength increase comes hand-in-hand with the hardening. Yes, the process is via heat treating, but the result is hardening.

post holiday blues?or maybe bad gas got you fellows per snickity?
shcs, i call them tuff not hard, i know, i know, not real smart am I?
ha guys, liten up.
Gw

I hadn't got any Tabasco sauce, so I made a Bloody Mary with some of the vinegar out of my (dangerous) chilli storage jar. My tongue is twice the size of my mouth and my head's still reeling.

That's my story and I'm drooling to it

Mark

My comment was in support of yours! And directed as a general bit of blather.

"Words are the source of ALL misunderstanding"

Come on children, play nice. To answer the original question a little more accurately, steels have various crystalline forms which have various strengths and hardness. In hardening a metal like medium carbon steel, the basic mechanism is heating it to change the structure from one crystal to a different one by heating it to a temperature where a certain crystal type forms, then cooling it so rapidly that it does not have time to change form as it cools, quenching. That normally results in a crystal that has high hardness but is brittle. Tempering is heating it to a lower temperature that allows crystal growth and reduces brittleness and coincidentally hardness, but not high enough for it to revert to the soft state. I am aware of migration to grain boundaries, precipitation, and so on, but this is an attempt to stay simple. So far I have not said anything that most readers don't know. Now the punch line. Quenching cools the surface very quickly and the inner material more slowly so some of the structure will not be locked in the initial state. As you increase the cross section, it will reach a size where the core will stay soft by virtue of slow cooling. The answer to the question is that the bolts are more or less through hardened, but not uniformly and not the same for different sizes. In the sizes we use in our daily lives, this effect is probably not very important, but it is there.

Early metallurgical experimenters measured this quality by heating a chunk of the test metal with enough soak time to have uniform temperature throughout, directing a strong stream of water against one surface, then sectioning it and measuring the hardness at different depths.

A little OT, but interesting is that jet turbine manufacturers regard the grain boundaries as the most likely places for a failure so they heat treat to produce a single grain from one end of the blade to the other.

Bill

nateman said:

Is grade 8 Hardware through hardened? specifically, BHCS? and SHCS?

Thanks,
Nate.

Click to expand...

SUMMARY:
Grade 8 fasteners are not hardened, just heat treated to meet tensile strength specifications.