Cr-Mo Weld & HAZ Property Data 2

[Guest102023]

I have just run into yet another case of extremely high hardness in Cr-Mo weld and HAZ. Since I never had the joy of working with these much in a production environment, I don't know that much about the as-welded mechanical properties, especially when things have gone wrong.

So I am seeking any and all data on as-welded hardness for 1¼Cr-½Mo up to 12%Cr alloys and everything in between (conventional alloys, not the newer CSEFs). Process, preheat as well as base metal thickness are pertinent to the data. CCT diagrams would be very useful.

Thanks in advance!

 

[metengr]

brimstoner;
Find someone that has EPRI technical reports for you to review. Some of the B&W Intermediate Croloy boiler tube reference brochures had excellent information on these alloys - hardness and weldability.

Try to search the internet for EPRI temper bead welding documents released to the public or other similar publications because there you might find as-welded and typical PWHT hardness values for P-No 4 and
P-No 5A base materials.

 

[Metalhead97]

brimstoner,

What condition are you welding the alloy steel in? Sounds like the precipitation hardening kinetics are fast. If the kinetics are anything like some high Al/Ti Ni superalloys you may need to try over-aging prior to welding. The worst thing you can do is weld in the solutioned condition. The fast precipitation hardening alloys are always a pain.

Metalhead

 

[metengr]

The Cr-Mo (Croloy) materials are very well known and have been used extensivly in the Power Generation field for over 50 years. They are typically low carbon and supplied in an annealed or normalized or normalized and tempered condition by specification. The croloys are very stable at elevated temperature and are not subject to precipitation hardening kinetics.

These alloys can be welded with or without PWHT - it depends on thickness. They respond very well to tempering from PWHT.

 

[metengr]

http://www.scribd.com/doc/36576094/A335-GR-P11-and-P22

 

[stanweld]

The as-welded hardness range is quite large based on thickness, preheat and interpass temperature and welding process (GTAW and GMAW being hardest with the aforementioned variables being the same). P-4 welds can readily have hardness > 300 BHN and P-5A welds can readily have as-welded hardness > 350 BHN (based on actual hardness checks). I have rarely measured as-welded hardness < 220 BHN on P-4 welds and < 240 BHN on P-5A welds.

 

[Guest102023]

Metengr,
I could find almost no info on the Croloy alloys on the www.
But I do have a number of temper bead reports and they are useful in demarcating the line of optimum preheat/no PWHT. Any hardness higher than this indicates less than optimum preheat/no PWHT. So a good suggestion.
Ultimately I wish to be able to comment intelligently on the extreme hardness numbers I am seeing - 400-450 HV in the weld and HAZ of Grade 9 piping. Composition checks out OK in weld and base.
There is no substitute for procedure development and PQR data though.

 

[Metalhead97]

There is at-least one Croloy PH. However, if PH isn't a factor then the only other thing that could cause hardening is a martensitic/banitic transformation if the section thickness was thick enough.

metalhead

 

[mrfailure]

Brimstoner,

My reference materials indicate typical base metal hardness of Grade 9 should be about 87 - 88 HRB (175 HV). Sounds like you need to look at preheat and PWHT parameters to bring down the HAZ and weld hardness.

Aaron Tanzer

http://www.lehightesting.com

 

[Guest102023]

I should have clarified that this is not MY welding problem - it is a failed spool that was made several decades ago.
I understand the metallurgy and how to weld these alloys, I only lack data points at the extremes of 'doing it wrong'.

 

[stanweld]

brimstoner,
The P9 alloy weld would have to have received PWHT. The >400 BHN is not atypical in the as-welded state. The weld was obviously not subject to the Code(s) mandated PWHT requirements.

 

[Guest102023]

I am stunned at how frequently field heat treaters completely mess up. Then they are asked to check their own work with hardness testers.

Think I'll stop my favorite rant right here before it gets started!!

 

[Guest102023]

Last call for a CCT diagram for 9%Cr-1%Mo steel ...