316 Class 2 Bolts

[dawgs83]

It is my understanding that class 2 316 and 304 bolts under the A193 and A320 specs are not to be hot forged because the material is strain hardened. We received some bolts that were hot forged from class 2 material and were full size axially tensile tested. The test show the bolts exceeding the required mechanicals (tensile and yield) for both specs. Is there something else I'm missing or are the bolts acceptable under those specs as long as they have the required chemicals and mechanicals even though it is suggested they not be hot forged? Any help is appreciated.

 

[EdStainless]

I would check microstructure and require a ASTM A262 practice E test.
These may have been warm worked from previously strain hardened bar.
If they weren't careful with the temps they could be seriously sensitized.
If they were truly hot formed they would be dead soft.

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P.E. Metallurgy, Plymouth Tube

 

[CoryPad]

Class 2 does not mean the parts cannot be hot forged (for example to produce the head), it means that after solution treating, the part is strain hardened (e.g. extrusion/thread rolling). Other things you are missing are considerations for corrosion resistance, creep strength, and product liability due to the head code not matching the requirements inside the standard.

 

[dawgs83]

Can you all give me a little more information regarding the part being sensitized and also the head code not matching the requirements inside the standard. Also is the microstructure applicable to the part being acceptable if the mechanicals are measuring correctly? I guess what i'm asking there is if the bolt is strong enough does the microstructure matter? I really appreciate the help.

 

[CoryPad]

Do you have ASTM A193 so that you can read and understand the requirements?

Sensitization is a condition detrimental to corrosion resistance of the parts, and the solution annealing process is meant to avoid sensitization.

ASTM A193 requires specific head markings based on the grade and class. For example, Grade 8 Class 1 is marked B8. Grade 8 Class 2 is marked B8SH.

 

[dawgs83]

Thanks for the explanation. I am familiar with A193 but I did not understand what you meant by head code not matching the requirements. Could the parts not be marked B8SH if it were hot forged from strain hardened round bar?

 

[CoryPad]

You need to read section 6 and Table 5 to know what head marking to use.

 

[dawgs83]

I'm sorry I guess I am not following if the bolts were made from 316 Strain hardened material but were hot forged would they not still have the marking of B8MSH if they were 304 strain hardened they would be B8SH correct? I am not seeing in the spec were it clarifies if the bolt can be classified as class 2 if it is hot forged. Sorry if I'm not making sense.

 

[CoryPad]

As you have described your process, I do not think you meet the requirements for any of the classes in ASTM A193.

 

[dawgs83]

I'm confused we did not make these parts. These are parts that we received from another vendor that were hot forged, and annealed from strain hardened material and then tensile tested and met the mechanical requirements. I am not sure how they would not meet requirements if they are chemical, mechanically and have dimensions within spec. ll the spec says is that they are to be "carbide solution treated and strain hardened" it does not say that the need to be "carbide solution treated and strain hardened in the finished condition" like B8A and B8MA

 

[EdStainless]

It clearly says that they must be strain hardened after being solution annealed.
That is not a hot formed fastener.

If they are hot forged it does not matter what you started with, it will be annealed when you are done.

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P.E. Metallurgy, Plymouth Tube