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How to Weld Q&T 5150 !!!

How to Weld Q&T 5150 !!!

How to Weld Q&T 5150 !!!

(OP)
I have never seen this alloy mentioned in this forum. This is the chemistry taken from a spectrometer test on a machinery link that I have to weld on an extension:

C    0.495
Si   0.167
Mn   0.833
Cr   0.522
Ni   0.004
Mo   0.0
Cu   0.168
Al   0.047
V    0.0
W    0.058
Ti   0.048
S    0.020
P    0.016

Our best guess is that it a very good match for 5150 as listed in ASTM A304. The link is presently hardened to an HRc of 53 (!)    My purpose is to modify this link by extending it with a section of 4340, which is as close as I can get to a material match. The weld process will be GTAW and use a matching 4340 filler)

I have been told by the engineer in charge that the end article only needs to have a final strength of 150-160ksi (i.e. HRc 33-35)


What are my welding and post weld options?
my preference is to leave the 5150 in hardened state, then weld on my normalized 4340 extension ( using a matching 4340 filler, GTAW process) and then Q&T the entire thing such that the 4340 extension portion reaches the desired HRc 33-35 hardness.  This would mean that the 5150 becomes double Q&T'ed.    

What issues arise from double Q&T'ing a 5150 alloy?   

Opinions please and thanks.
 

RE: How to Weld Q&T 5150 !!!

tc7;
If you absolutely need to weld the link with an attachment, and you intend to reheat treat, I would over temper the link first to reduce hardness to as low as possible before welding. Why? Attempting to weld this link in the hardened condition and carbon content can result in cracks.

The carbon equivalent of this steel calls for a high preheat. Your Q&T heat treatment after welding looks acceptable.
 

RE: How to Weld Q&T 5150 !!!

(OP)
Hello and thanks-

What would you suggest for the overtempering recipe?    1100 deg F for  ?x? hours?

Would there be any benefit to normalizing the thing at 1650 deg F (with a soak time of one hour) instead ?

On the postweld re-Q&T......oil or water quench and why?
 

RE: How to Weld Q&T 5150 !!!

tc7:
What I would do is to temper at 1200 deg F for one hour per inch thickness before welding. Slow cool, prep for welding, preheat, weld, slow cool, and perform NDT.

As far as heat treatment, I would favor oil quench versus water quench. However, the thickness will dictate quench medium. The 5150 is not a deep hardening steel. You need to review what core hardness is desirable after welding and work from there. The 4340 is a deeper hardening steel so this will go along for the ride a far as optimizing the heat treatment for the 5150. I would do a final NDT of the weld and surrounding base materials after re-heat treatment.
 

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