M-sub-S for SA182 F22V Alloy 1

[tc7]

Hello-
Can anyone advise on the martensite start temp of ASME SA-182 alloy F22V? The alloy is not listed in Heat Treater’s Guide or ASM Handbook Volume 6 (Heat Treating) and I cannot find an online reference.

I have used the following equation in Dr. Kotecki’s book on stainless but not sure it applies to this low alloy: Ms(deg C) = 539 - 423C – 30.44Mn – 17.7Ni – 12.1Cr – 7.7Mo

With the above I calculate ~424 deg C or 795.2 deg F which seems reasonable. Confirm by other reference please?

I have an idea that I may be able to prevent welding cracks by holding very high preheat temps of 800-900 deg F (trying to stay above M-sub-s)and then go right into post weld stress relief of 1150 deg F. Comments welcome. By the way, the welding in question is for hardfacing valve seats using Stellite on the F22V base. PQR will be accomplished.

Thanks for all advice.

 

[metengr]

tc7;
You have several options. You can use the web site below for an approximate M_s for this low alloy steel.

http://homepage3.nifty.com/yurioka/exp.html#E1

or here is another similar equation for low alloy steel cited from the Journal of Iron and Steel by an article from KW Andrews


M_s = 539-423C-30.4Mn-17.1Ni-12.1Cr-11.0Si-7.0Mo

elements are expressed in percent mass and the start temperature is deg C.

You do not want to hold preheat temperatures this high because of the potential fo reheat cracking! You want to hold preheat at 200 deg C, the maximum interpass temperature should only be 500 deg C, weld and go right into PWHT.

There is no need for this type of elevated preheat. This is only a low alloy steel, and the vanadium addition is to increase creep strength at elevated temperature. This is a common alloy addition.

 

[tc7]

I suppose I should have mentioned the anomaly I am trying to cope with: when we apply new stellite hardfacing to a new F22V base, we rarely have a problem. Our qualified process is by GTAW and the preheat and interpass is 400 deg F and 650 deg F respectively, very similar to what you have suggested. However, when we make repairs on existing in-service equipment and attempt to repair cracks (instead of complete removal and refacing) in the existing applied stellite valve seats we get unpredictable results - sometimes they will crack in the same spot, sometimes no crack. After some trial and error, we find that our best success was with very high preheat. Why would high preheat seem to improve success? I reasoned that managing the heat to control austenite to bainite or pearlite transformation with very slow cooling (vermiculite or double blanket wrap) might explain it. I know the cobalt based stellite will not form martensite so I began to believe the entire problem was caused by the F22V behavior.

Strangely, we do NOT have similar cracking problems when we repair hardface on 4130 or 9310 base materials.

Thoughts? Comments?

Thanks Met.

 

[metengr]

tc7;
The Cr-Mo and Cr-Mo-V alloys will suffer from thermal embrittlement upon exposure to prolonger service temperatures at or above 1000 deg F. This is the nature of these alloys. I suspect that the cracking problem is reheat cracking. In this case, reheat cracking is quite unpredictable and results from welding on aged Cr-Mo alloys containing vanadium.

The high preheat will reduce thermal stresses and reduce susceptibility to reheat cracking.

 

[tc7]

Thanks for the mention of reheat cracking - now I will research the literature and see what I can learn about that. There is always some new twist to keep us from thinking we have finally learned something.


So I gather you agree with the principal of my high preheat/slow cool approach to this repair procedure?

 

[metengr]

Yes.