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Cracking of Inconel after EB welding

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5.2K views 29 replies 9 participants last post by  PTR EB Welding  
S
#1 · (Edited by Moderator)
Hello together,

I would appreciate any advice or remarks regarding cracking after EB welding.

* We use material combination of Inconel and 42CrMo4.
* Inconel is produced by investment casting, then it's machined by grinding a weld together with 42CrMo4.
* After welding, cracks occur in the vicinity of the weld, mostly in longitudal direction, sometimes a crack touches the weld, sometimes not.
* Weld geometry is about 1,1 mm of depth and 0,8 mm of width.
* Generator 60 kV, beam current 7,5 mA, travel speed 28 mm/s etc.

Picture of a crack after section cut:



Etched structure of grains:


Picture of a crack by electron microscope:


Picture by optical microskope:


Thanks a lot for any feedback! :)
 
H
#3 ·
Egads, but that's some seriously coarse grain structure on that one piece (must be the casting). Also looks like there's a lot of "junk" packed into the grain boundaries. Doesn't seem all that surprising to me that the shrinkage stresses from the weld nugget would tear that piece along the grain boundaries like it's doing. I don't think you have a weld problem so much as you do a bad casting technique problem.
 
S
#6 ·
I agree that pre-condition of the part coming from casting has strong influence on cracking but...
* we have comparable cracking with more than one supplier of casted parts,
* it's almost impossible to change something on supplier's side so we want to focus at first on our in house process.

Therefore, I have been doing some tests to produce the weld with smaller width to reduce shrinkage. But the question is whether this effort makes sense OR how much do I need to change the weld geometry to get a measurable profit with respect to cracks occurrence (now about 5 %). Do you have any "feeling" for that? ;-)
 
T
#5 ·
I know when we would weld turbine parts with inconnel they always wanted us to preheat the part to 500 degrees. They also wanted each pass peened. Your grain structure is very course as stated by others. I have welded inconnel to mild steel cold with no preheat and had no problem also have welded inconnel with inconnel 82 and no preheat.
 
T
#8 ·
If you can't change material, I'd look more to joint configuration if possible. Can you move the weld seam closer to the center of the shown cutout in the first picture?
 
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S
#9 ·
I agree with above posters that the crack is resulting from weld shrinkage. Preheat will reduce weld shrinkage. Don't know if that is possible hold preheat during vacuum pumping though.
 
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S
#15 ·
If peening works for us, it would be great and probably the most simple solution. So we would need to find a way how to use electron beam instead of laser beam and apply it directly before welding itself.

Has anybody experience whether is electron beam peening even possible? I haven't found nothing about that on the internet.
 
H
#18 · (Edited)
stepan,

This individual was the key note speaker at a recent international conference on EB welding. I'd have to think that if any one could point you in the right direction for getting the kind of technical help you need to solve your problem it would be him.

Keynote Europe: Europe Business Developments
Current Development of the Electron Beam Technology in Europe
Dr. Phil Thorsten Löwer, pro-beam AG & Co. KGaA (Germany)

Edit: Here's his contact info

http://www.pro-beam.com/en/company/board-of-directors/
 
P
#20 ·
Hello Stepan!
Sorry for showing up late to the party here... in any case, I have spoke to our Application Engineers and they have one process recommendation that could help improve the quality of your weld:
We would add that you can locally preheat with the electron beam immediately prior to welding. Using a defocused beam, run over the weld seam several times before switching to the weld parameters without breaking vacuum in between. That will get some heat into your part and help reduce residual stress.

Good luck EB welding your Inconel application! Should your troubles persist, your company may reach out to PTR's Job Shop for other paid support options:
https://www.ptreb.com/eb-welding-services/weld-process-development

-The PTR-Precision Technologies Team
www.ptreb.com
 
S
#21 ·
Well what do you know. I have wondered how to preheat in a vacuum.

Good info.
 
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I
#22 · (Edited)
What Ive seen used for pre heating substrates in Hi-Vac was a glow bar. The glow bar is basically a "getter" like in a vacuum tube for electronics.

The theory of how the glow bar worked was: once a certain level of vac was reached the glow bar would be turned on with its own power supply (not EB gun supply) and a controlled amount of Argon was bled into the vac chamber. The Argon would ionize from glow bar and heat up the chamber and parts. Heat doesnt conduct in a vacuum so I wont try to explain that. The other benefit of a glow bar is; the heat drives out moisture and helps the chamber reach ultra hi vac faster allowing more production time.

The EB guns Ive used and rebuilt were built to tight tolerances and not adjustable focus. To change focus would require shims or machine work and breaking vacuum. The focus was designed into the machining and fit. The deflection was done with electro magnets the same as crt's.

Im not saying the OP's guns or PTR's guns are not focusable just the ones Ive used. I didnt weld with them tho. I evaporated with smaller guns and melted with larger guns on a larger scale than evaporation tho.

IIRC a member here named A dab will do mentioned playing the E beam at lower powers over parts to pre heat in another similar thread. Kind of like using a TIG torch to boil out smut in the part to be welded. If I remember tho, you cant really do a proper pre heat this way.
 
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P
#23 · (Edited)
Insaneride It should be noted that EB evaporator equipment and EB welding equipment, despite both using an electron gun to deliver a stream of electrons to the workpiece, are VERY different machines and processes. (Let alone most shops have EB welding equipment that dates back to the 60-70's.) However I'm fairly sure whatever ineffective preheating "A Dab" was getting was purely a result of it being done an entirely different type of equipment altogether. Despite the fact that every material welds and behaves differently, so there are metallurgical considerations that come into play here as well.

If you are interested below you will find a link showing a video that utilizes one of the more advanced technologies we have in our EB generators (guns) called EBO Jump. This technology allows us to use ultra fast beam deflection to generate multiple weld pools- in this case 4 of them. The first two leading pools are preheating the application, the middle beam pool is a full penetration pass, and the final trailing beam is providing a cosmetic weld pass. This looks to be more than one electron beam, but actually the deflection technology is cycling between all the weld pools so quickly that the human eye (or welding equipment camera, lol) makes them all appear visible concurrently.
PTR EBOJump Multi Pool Welding video

-The PTR-Precision Technologies Team
www.ptreb.com
 
I
#25 ·
Forgive me A DAB will do for thinking it was your idea to lower power to pre heat parts in a vacuum. I like your eloquence and thinking but I was wrong to mention you this time.

The idea of induction heating sounds good and vacuum ports are not new. They are used for viewing, electrical, roughing, monitoring etc.

Another correction: I mentioned glow bar to pre heat but the actual name is "glow discharge bar". They do help to pre heat and aid the vacuum the same as a getter.

https://en.wikipedia.org/wiki/Glow_discharge

https://en.wikipedia.org/wiki/Getter

PTR, I understand the welding guns or generators as you put it are different than evap guns as are arc furnace guns that Im most familiar with. Can you share a pic of your generators (guns) and explain the de-focus? Your EBO jump technology is impressive and would need to re focus for each of the four beam spots since they would all have a different focal length to the gun. It has to be moving really fast because it did look like four separate beams tho. The human eye responds to about 1/20 of a second and the old TV EB gun rasters were about 1/30 of a second to trick the eye.

After looking at some old notes; the last EB guns I used did have a magnetic focusing in the vac chamber but was set and left alone. Never failed and never needed calibration.
The old CRT's had a curved surface to allow EB guns to have a fixed focal plane while watching TV. Im not familiar with focusable EB guns but if PTR say they exist then it must be so and simple as compared to lower power.

PTR, is de focusing actually better than using lower power or a glow discharge for pre heat?

BTW, no offense Stepan but the pics you took down belong in the failed weld thread or harber frate AC mig welder thread:p
 
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A
#26 ·
I wonder if the EB guns that can be focussed are controlled in a manner similar to the electron beam in an electron microscope? The scopes I worked with years ago had some fine and coarse image focus controls that were magnetic 'lenses' that bent the electron beam and changed the focus of the image. With high speed and high power electronics, I can imagine a combination of magnetic lenses and pulsing the E beam on and off at high speed. That might produce something akin to the EBO jump technology video shows.
 
P
#27 · (Edited)
A Dab Will Do Correct about the magnetic focusing lens', I would steer you to the paper below as well if you wish to read more about the EB process. Actually, we have a whole website category dedicated to Electron Beam Welding Information if you are feeling froggy.

InsaneRide regarding your request to see our generator; we have a technical paper up on our website that on the very first page describes how the EB welding process works, along with a schematic representation on the type of EB gun and column assembly commonly employed to perform EB welding tasks:
Electron Beam Welding in the United States by Donald E. Powers

Regarding your next question; "Is defocusing actually better than using lower power or a glow discharge for preheat? "

It's to be noted that the EB generators in our standard fixed gun EBW systems have an independent vacuum system to that of the work chamber. Also, most everything is done electronically now including focusing which is simply an independent machine parameter that can be adjusted at the touch-screen control console by the operator.

• Power adjustment is another adjustable weld parameter that can be changed on the fly. When you are doing this preheating with the defocused beam, lower power could be used (if desired), but generally you will need this power to heat the application. Defocussing the beam effectively makes the beam spot on your workpiece larger + more spread out which in turn makes the beam less apt to damage your application surface. It also allows for greater control of 'what portion' of the application material is actually being preheated.
• PTR’s Job shop has never been asked to use a glow discharge bar by a customer when we can effectively use the EB welding systems beam to carry out the same task. This being the case we will not truthfully be able to comment on its effectivity “in the field”, however our Engineers suspect that this method could possibly work as well. Whether it makes sense to deal with the extra cost of another accessory, plus the hassle of having to connect it when it’s required for welding is the question that we would pose to you if it was your company that was in charge of this welding task.

That being said, there have been a few alternative methods used here in the past including a traditional preheating of the application in an oven prior to EB welding. Or another method that overcomes the oven’s disadvantage of heat loss in the transfer time between coming out of the oven and being brought over to the EB welding system, the part being fixtured, and then the time for the vacuum chamber to evacuate… we have also used is in-chamber induction heating (as “A Dab” mentions above). There are power feeds accessible within the chamber where this induction heater could be connected.

But quite simply, if you would like to know how an EB welding Job Shop and EBW system manufacturer would handle the task.... we find that the beam is the most effective method. :)
 
I
#29 ·
A DAB will do, you are rite, a magnetic lense is used and shown in PTR's last link.

PTR, thanks for sharing your proprietary information. The de-focus does sound like the best solution to pre heat for the OP's problem.

Before the internet/web, information was not readily available or shared. With the information age, information is shared in some areas. The Hi Vac society only shares information thru expensive publications and paid web sites that I know of. And theres no schools for HiVac technology so on the job training is about the only way to learn HiVac. So again, thanks PTR.

Stepan, forgive me for hi jacking. I hope you have been able to pre heat. PTR engineers suspect the glow discharge works but dont need it with there de focus system being able to do pre heat without the extra power supply. If you have a way to de focus then forget the glow discharge but the main advantage of glow discharge is faster pumping speed. The entire chamber is electrically connected to the discharge and the discharge helps evacuate the chamber and heat.

Another thing to think about is: why cant you use the laser peening procedure to peen with Electron Beam guns. They are different types of energy but it seems like it would be worth a try and similar in my opinion.
 
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P
#30 ·
Insaneride said:
Another thing to think about is: why cant you use the laser peening procedure to peen with Electron Beam guns. They are different types of energy but it seems like it would be worth a try and similar in my opinion.
Click to expand...
You are correct to assume that with EB the beam can be controlled in the same fashion as a laser (even more robustly in fact), unfortunately the only real similarity shared here is that they are both "surface modification processes". You can read more about that technology here on our sister companies website:
http://www.sst-ebeam.com/en/application-areas/surface-treatment.html

Again, apologies to Stepan for this off-topic conversation.
 
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