Solution Annealing Hot Forged Fasteners

[dawgs83]

There are few common ASTM specifications in our industry including A193 and F593. These spec call for a solution anneal after the hot forging process. We are using round bar that has already been through a solution anneal treatment, heating it to forging temp., forging, and then water quenching the part. We have tested the parts to A262 practice A for corrosion resistance and they pass. They also pass all requirend mechanical testing. My question is, is it still necessary to solution anneal the bolts after hot forging if they are passing the corrosion test? Isn't the purpose of the solution anneal to keep the material in a corrosion resistant state? Any help is appreciated.

 

[TVP]

I'm assuming you are referring to austenitic stainless steels within ASTM A193 and F593? Table 3 and Section 7.2 explain the requirements. Some heat treatments must be performed on fully finished fasteners (carbide solution treated in the finished condition), meaning after all machining, threading, etc. Some heat treatments may be performed on the bar or wire only as explained in those two sections of the standard.

 

[dawgs83]

Yes i am referring to the austenitics. Mainly 304 and 316. I am interpreting it the same way as you I think. If it does not explicitly say that the anneal needs to be done on a finished part then I assume that we do not need to anneal after forging if the mechanical and corrosion requirements are being met. Does that sound accurate or am I way off base here?

 

[TVP]

Yes, that is accurate.

 

[TVP]

I just re-read section 6 in the 2014 revision of ASTM A193, and it does not appear that you can certify your proposed process to meet Class 1, 1A, 1B, 1C, or 1D. Solution treated bar can be subsequently machined into bolts without re-solution annealing, but not forged. ASTM F593 is not so stringent, since these are not intended to be used for boiler and pressure vessel applications.

 

[EdStainless]

What you are doing would be termed a process anneal.
So you have controls in place to assure that you are not dropping below the required anneal temp during the forging operation? That would be a requirement.
Some specs allow this, some don't address it, and some specifically prohibit it. You need to read the heat treat sections very carefully. And be aware that the ASME may be different from the ASTM specs on this.

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P.E. Metallurgy, Plymouth Tube

 

[dawgs83]

Thank you all for the feedback. I guess what seems murky to me is that if we are using the correct material, meeting the required mechanicals, and maintaining the required corrosion resistance I am not sure what solution annealing further would accomplish. In fact it would seem further heat treatment could jeopardize the integrity of the part. Is there something I am missing there?

 

[CoryPad]

I believe the standard is written that way because it would be hard to guarantee that the hot forging process does not reduce the corrosion resistance of the annealed bar, especially for large diameter parts that may require long times to heat and cool. Also, I believe the thinking is that if you perform the anneal afterwards, you would not have to do corrosion testing like ASTM A262.

 

[OGMetEngr]

CoryPad is correct, I saw this at my last job. Suppliers were giving us process-annealed barstock. The bar ASTM allows this, but others such as sheet do not. We had 13.6N HNO3 which requires fully solution annealed material for adequate corrosion resistance. The process-annealed bar would fail ASTM A262 Practice C much more often than solution annealed material.