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Grade 8 bolt hardness– material equivalent

Perk

Cast Iron
Joined
May 19, 2004
Location
Nebraska
I made some parts for a guy out of Grade 8 bolts because they had to be relatively hard, tensile strength was irrelevant. They worked fine and now he needs more but rather than using Grade 8 bolts I was thinking of using Pre-Hardened 4140. I can’t find any data which specifies the hardness of a Grade 8 bolt for a comparison. Any suggestions? If possible I don’t want to heat treat.
 
A couple of other current threads discuss the tensile strength of bolts. Grade 8 are in the 175 ksi range. A common pre heat treat 4130 is ETD 150. It is chemically relatively unspecified, but produced to 150 ksi strength. There also used to be an ETD 175, produced to 175 ksi tensile strength. I haven't used any in a long time, so I don't know about any current availability. The ETD 175 will be much closer to grade 8 bolts.

I also use some Sheffield #20 TG&P H.T., which is produced to 156 ksi.
 
They're not wrong. The spec for Grade 8 is 150K minimum.
175K is well within spec for Grade 8.
 
Then getting back to your question Perk, the 4142 prehard McMaster Carr sells is claimed to have 130,000 yield strength. This equates to something less than 140,000 tensile strength, or about 90% of the minimum requirement for grade 8.

Cruicible Steel sells Maxel 3 1/2 which is available prehard and is 4150S, so machines very nicely

John
 
Apples and Oranges guys..
1. there is no Grade 12..
There is a DIN (ISO) 12.9 and that is the 'Metric" for 170 K Tensile.
2. ANSO grade 8 is 157 k standard, and is for "average Batch strength" so some will be above and some below this level
3. The most important issue of good "High Strength" screw construction is "Roll Formed Threads" where the entire fastener is forged and formed, without cutting tools ! Otherwise you get stress cracking. failure WILL occur before you even reach the tensile level desired.

To answer the question
"they had to be relatively hard, tensile strength was irrelevant."
Then just make a screw out of 'Stress Proof Steel ( La Salle Steel ) and have it case hardened, or better yet, "gas nitrided "( C 60 !)
Rich
 








 
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