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I Forge Iron

Steel Grade for "Grade 8 Bolt" ???

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Bolt grade are by physical specification not by chemistry.  Basically a grade 8 bolt can be made from any alloy as long as it meets the physical specs.  The following company site explains a little but because it does not list the alloys only the carbon content it's hard to say what kind of steel is used.


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I would assume heat treet, as what I learned in the automotive industry indicates that the grade 8 can provide higher clamping loads but is not recomended for loads in shear, wile the grade 5 provides adiquate clamping force but as it is a bit more malluable it serves better in shear. If the range is 3 and 5 point carbon, i would bet that most grade 5 are the lower and the 8 the higher tho depending on the costs, they may make them both from the same (say mid way) just making grade five as forged, wile quenching the grade 8 (not unlike japanise sword smith choses his corbon content to obtain a one step heat treat). Manufacturing is about cost cutting, so if the proces can be stream lined, handling and material costs cut that is the way they will go, 

i bet a 2" grade 5 would make a nice post anvil

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I have some shafting from a manual trans. Big stuff like 1 3/8" etc. I can't cut that with a file. I think that may be forged into a hardie cut and left to cool w/o hardening it...it may be ok. I don't need it to be super hard for a hardie /hot cut.

If you can't cut into steel with a file that may be 60 or 80 point carbon I bet (???)


Did you mean to reference .30 to .50 point carbon,,,,,, as opposed to 3 to 5 point? You can't buy 5 point carbon. Lowest I have seen is .18 point.

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A safety note for those who don't know, most common coating on a grade 8 bolt is cadmium.  That yellowish/gold/blue tint.  If you think breathing zinc fumes is a fast way to get sick or die, putting cadmium coated stuff in your forge is nastier.  Don't do it.  Scary s**t.



but, grade 5 and grade 8 are both .28 to .55 carbon.............????????? Then why have  a 5 and also an 8? 


Why do folks demo tool making and insist upon grade 8 (not grade 5?)

​There are other elements used in alloying steel in addition to carbon.  Grade 5 has one set of characteristics that include yield strength, carbon content, perhaps other characteristics.  8 has a higher required strength, therefore perhaps different carbon, perhaps different other alloyed elements.  And when we blacksmiths use a mystery steel "off label" as it were with atypical use and heat treatment then we enter the world of experimentation rather than cook book technique.  

When I use a scrap steel (anything I don't have certs for) I write down what it was, what I used it for, what heat treat I did, and how it held up.  After 25 years looking back on that list I've found that it's much more economical to buy known steel.  

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How many desimal point off am I Artist? .1 or 1 percent should be .001, that is 1/10th of 1/100th is 1/100th. Not the greatest at math, but i got the basics, have I mis understood that a "point" of carbon is .1 of 1 pecent? Or is it .01 of 1 percent?  (1/10,000th?

that would make bolts 10-30 point?

Edited by Charles R. Stevens
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