Weld repairing a Quenched and Tempered cast steel

[theedudenator]

I have a steel casting that is quenched and tempered and then machined

Weld repairs were performed after the machining.

I am assuming the casting should be re-heat treated.
Is it typical to just re-temper? or a full Q&T?

Is there a time frame to complete this after the welding is performed?

Are there any specs or standards I should be looking at?

Any specific tests/analysis to check the welds?

 

[unclesyd]

with a few more details.

What is the material?

How much welding and where?

What was the welding process?

 

[arunmrao]

Your process chart seems to be wrongly drafted. Normally the heat treatment cycle is after the machining. Issues like distortion loss of acuracy will arise after heat treatment. To get over this,leave some stock for final machining operation.

In Q& T condition, machining is difficult,expensive and also might lead to build up of internal stress. I have another customer like you from US who machines in Q&T (Rc 30) condition 4318 grade castings. No amount of convincing has produced a change.

In your case now it will be necessary to go through the complete cycle if the repair is more than 20% of the wall thickness

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[theedudenator]

The material is genericly ASTM A148 grade 90 60

We have a very tight tolerance on the final machining. ±.0005
We have been quench and tempering, then final machining for 20 years.

This is the weld process: metal-electrode arc welding.
The defect was completely removed first.

 

[EdStainless]

My gut feel is if the weld is small (less than 25% of thickness) and not near an edge AND this part is low strength, then I might temper only.
We used to do some parts that we Q&T, rough machined, re-tempered, and then finished machined.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[metengr]

If the defect is less than 20% of the wall thickness, you do not need to re-heat teat or even temper at the original tempering temperature. All you need to do is to perform a local stress relief of the weld repair region that is 50 deg F below the original tempering temperature. NDT should be performed of the weld repair region and surrounding base material.

If the defect is deeper than 20% of the wall thickness, I would use a temper bead weld repair. A temper bead weld procedure can be qualified using ASME B&PV Code, Section IX guidelines. The same requirement for NDT would apply.

 

[theedudenator]

It was not 20% of the section.
But this is in a critical area in a highly stressed part.

Normally all defects are repaired prior to quench and temper.

 

[arunmrao]

Gr 90/60 casting is a high strength steel casting. However, your composition is perhaps 0.27-0.30 %C, 1-1.2% Mn, 0.5% Si,0.2-0.3% Ni and 0.2% Mo,I feel a stress relief in the weld repair zone is adequate. I have got away with this mode of salvaging this far .

Your heat treatment Q& T is interesting. we follow forced air cooling followed by tempering.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[theedudenator]

How is a stress relief in the weld zone typically applied?

 

[arunmrao]

Very simply it is a portable coil/induction heater wound around the region and heat applied.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[theedudenator]

This was not available.

I believe the casting was normalized.. now the hardness is too low.

I am assuming the process destroyed the structure created from the quench and temper..

I think the casting is scrap now

 

[metengr]

theedudenator;
What process, the welding process? If you used a local preheat, welded and did not stress relief (as you indicated above), you did not destroy anything. It would appear to me that this component was not properly heat treated from the start.

 

[theedudenator]

You did not read my last post...

The casting was normalized after the welding.

I would assume this would destroy the structure.

I would have thought a temper would be ok.

 

[metengr]

Yes, I see that you mentioned the casting was normalized in your post. I guess my question is why was the casting re-heat treated after welding, when you were concerned with preserving a Q&T structure?

 

[dbooker630]

What is the desired hardness after quench and temper - I use this material in a range of 187-241 HB and prefer a forced air cooled HT as arunrao recommends.
The weld repair I assume in this case was structural in nature as opposed to cleaning up a cosmetic blemish. I would always perform some sort of heat treatment after a structural weld repair, at minimum a stress relieve at or above 1000F. Depending upon the Mn/Si and any alloying levels the hardenability may be rather high. If you have finish machined the part already at the tolerances you reported it may indeed have to be scrapped. Perhaps the temperature generated by the portable heater approached the critical temp.

 

[EdStainless]

Since it is finish machined, you are probably right, junk. You could re-Q&T it just to make sure of the results. That is to check out the weld repair. Maybe use it for some destructive testing. It will probably be out of tolerance.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[theedudenator]

I have a question on what is considered cosmetic type weld repair.

If the part is subjected to high stress in a cyclic condition I would assume any surface cosmetic repairs would also be considered stress risers.

Any thoughts on this?

 

[metengr]

theedudenator;
Yes. There is really no such terminology in welding as a "cosmetic weld repair". You have weld repairs that may or may not require post weld heat treatment - some may call these major or minor weld repairs, respectively.

In my opinion, any weld repair requires careful consideration as to it's location based on applied stress and service conditions. When welding is performed you have altered the original structure of the metal, and under certain service conditions (like fatigue) this can result in a preferred location of weakness.

For some high hardenability alloy steels any weld repair, regardless of depth, requires PWHT. In other less hardenable alloys, repairs can be performed without post weld heat treatment.

Now, back to your post. In certain situations weld repairs are optimzed to locate the base metal heat affected zone in an area of the component that is lower in stress or under fatigue loading conditions.

 

[arunmrao]

theedudenator,
I go along with metengr's comments above. The same weld repairs for WCB or lower grade will be different(i.e less serious issue) as compared to 90/60 grade.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[tc7]

Very interesting thread! and answers similar issues I have had.

Follow-up to Ed and Metengr: you both have indicated that if defect depth is 20% or 25% of wall thickness (I presume that is the excavation depth) that tempering or a full Q&T may not be required. We have a guideline that says 1/4" depth is the limit on whether we temper or simply stress relief. I don't know where my 1/4" parameter comes from, can you advise on where you 25% wall thicknes parameter comes from? looking for a reference or a theory (or is it just a Code reqt?)

thanks