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Effect of Prolonged Temp On Cr-Mo Alloys

Effect of Prolonged Temp On Cr-Mo Alloys

Effect of Prolonged Temp On Cr-Mo Alloys

(OP)
We have two large Cr-Mo forgings (supposed to be normalized condition) that were left in the preheat oven over the weekend and forgotten. The temperature crept up to 950 deg F and held there for 56 hours. The first alloy is an F22V (2.25%Cr, 1%Mo, .25%V, .12%C) and the second alloy is 4130 (.9%Cr, .2%Mo, .5%Mg, .3%C). When this was discovered I told them to drop temp at 100 deg per hour until they reached 400 deg F (our typical weld repair preheat temp).

I am guessing that the only negative affect of the long 950 deg excursion would be that grain size has enlarged and perhaps lost toughness?  If so, is there any way to estimate what extent that toughness may have been lost in the areas that won't be weld repaired?

Any other concern that I should be aware of? ( aside from our own ignorance)?

Thanks.

RE: Effect of Prolonged Temp On Cr-Mo Alloys

tc7;

Quote:

I am guessing that the only negative affect of the long 950 deg excursion would be that grain size has enlarged and perhaps lost toughness?

There should be no increase in grain size at this temperature for this short duration.



Quote:

If so, is there any way to estimate what extent that toughness may have been lost in the areas that won't be weld repaired?

The easiest way to evaluate embrittlement from thermal exposure is to calculate the susceptibility to temper embrittlement using the J-Factor

J = [ ( Mn + Si ) x ( P + Sn ) ] x 104

elements are expressed in mass percent amounts


If you are less than 150, I see no issues.
 

RE: Effect of Prolonged Temp On Cr-Mo Alloys

(OP)
for F22V (from ASTM A182 max values)
J=[(.60+.1)x(.015+0)]x10,000   =   105<150 so wer're OK.

I wonder why C content doesn't contribute?

Can you recommend your best reference on "j-factor" ?


Thanks Met, as always!


 

RE: Effect of Prolonged Temp On Cr-Mo Alloys

tc7:
Carbon in low alloy steel does not segregate to the grain boundaries, under normal heat treatment conditions before service – it exists in carbide form and some is dissolved in iron. The embrittling agents that result in loss of toughness, besides P, are the tramp elements like Sn and Sb and several others. These elements segregate with P and Mn to grain boundaries upon exposure to elevated temperature service.  

For reference;

http://www.google.com/search?hl=en&;q=temper+embrittlement+factors&btnG=Google+Search&aq=f&oq=
 

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