Bolts grades and materials 2

[Pucp]

I have purchase bolts for my company, but I have only specify the material (AISI 4140). This is because we have calculated that in the annealed condition it would work well. But I have read in some paper that this material could be use or could correspond to bolts - Grade 8. I know that AISI 4140 corresponds to ASTM A193 Grade B7, that has less yield stress than a Grade 8. So I would like to know in what condition (heat treatment or anything else) it corresponds to ASTM A193 Grade B7 and in what condition it corresponds to Grade 8.
Everytime I purchase a bolts I have to specify the Grade or it is only necessary to specify the material (but I do not know in what condition they sale the bolt) so what is the right method. Is possible to obtain different grades than the comercial ones with the same materials or the manufacturers only follows the standard (in this case AISI 4140 would only be manufactured as A193 Grade B7).

Thanks in advance. I will appreciate a lot your repply, because I get a little confused with the theme. Bye.

 

[jackboot]

What you need is the actual specification for ASTM A193. You can go to their (ASTM) website and download the spec in PDF format.

-The different grades are listed in the spec. You can see that a ASTM A193 can be made of many different materials.

I think the actual specification will clear this up for you.

Jackboot

 

[TVP]

First, mechanical fasteners like bolts, nuts, rivets, etc. should NEVER be specified according to a chemical composition only. Mechanical fasteners should always be specified according to some type of specification, whether it is an industry specification (ASTM A 193 or SAE J429) or a government specification (MIL, AN, etc.), or some other specification (internal, customer, etc.). These standards have extremely important requirements for mechanical properties, manufacturing guidelines for heat treatment, testing and quality control procedures, etc.

Now, I assume when you mention Grade 8, you are referring to a Grade 8 fastener according to SAE J 429, Mechanical and Material Requirements for Externally Threaded Fasteners. There are many steel grades that will meet the chemical composition requirements for SAE J 429 grade 8, because the specification is only as follows:
C 0.28 to 0.55
P 0.030 max
S 0.050 max

So, as you can see, SAE 4140 meets this requirement, but so do many other grades.

Next, the reason that SAE 4140 can meet the requirements of both SAE J 429 and ASTM A 193 Grade B7 is because the heat treatment of steel allows for a fairly wide range of mechanical properties to be developed. Specifically, grade 4140 would be tempered at a higher temperature to meet the lower strength requirements of the ASTM spec. As the tempering temperature is increased, strength decreases but elongation increases. One thing to keep in mind is that ASTM B 193 is a specification for HIGH TEMPERATURE bolts, while SAE J429 is not. If the use temperature is high enough, plain carbon steel fasteners that meet the requirements of SAE J 429 because they have been tempered at a relatively low temperature may not perform adequately.

And last, depending on the quantity of fasteners you purchase, many fastener manufacturers will produce a part to whatever requirements you specify. By this I mean that if you want to specify the chemical composition to be SAE 4140, the mechanical properties to be something other than those required by SAE J 429 Grade 8 or ASTM B 193 Grade B7, etc., and that they are painted purple and orange, you can order them to this "specification". If you are only purchasing a small number of fasteners, then it may be difficult for you to obtain something other than the standard industry specification grades.

 

[Pucp]

TVP: Thank you very much for your soonest and excellent reply. Now I know what to specify when I have to purchase bolts.

 

[trustmfg]

You may also consider A-354 Grade BD or BC.