Cracking of Inconel after EB welding
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  1. #1
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    Cracking of Inconel after EB welding

    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! :-)
    Last edited by MinnesotaDave; 01-05-2017 at 04:46 PM.

  2. #2
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    Re: Cracking of Inconel after EB welding

    The grain structure of your base material looks questionable. The shrink of the weld looks to be sucking it in. May be a pre heat issue.
    I really know nothing about this but your QC pictures are great.

    Dan D,
    Manipulator Of Metal

  3. #3
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    Re: Cracking of Inconel after EB welding

    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.

  4. #4
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    Re: Cracking of Inconel after EB welding

    Is this a new part or process, or is this a new problem with an existing part/process?
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  5. #5
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    Re: Cracking of Inconel after EB welding

    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.

  6. #6
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by HT2-4956 View Post
    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.
    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? ;-)

  7. #7
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by Teggy1 View Post
    Is this a new part or process, or is this a new problem with an existing part/process?
    The problem has been there since the start of production and now comes the effort to reduce scrap. Furthermore, the same issue occurs on more machines (with the same welding parameters) as well as on parts from different suppliers of raw material.

  8. #8
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    Re: Cracking of Inconel after EB welding

    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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  9. #9
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    Re: Cracking of Inconel after EB welding

    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.
    Weld like a "WELDOR", not a wel-"DERR"
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  10. #10
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by thegary View Post
    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.
    Ok, thanks for info.

    I am quite attracted by the idea of peening. Do you (or anybody else) have any experience with peening by laser or electron beam directly before welding itself? Could it help?

  11. #11
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by Teggy1 View Post
    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?
    You mean little bit lower? I will try finding a way how to do it. Anyway, tolerances of the workpiece and the machine will be still there and 50 um is really nothing.. What about full penetration weld, could it be beneficial?

  12. #12
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by stepan.b View Post
    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? ;-)
    stepan,

    As much as I'd like to help you out I'm afraid that when it comes to the practical application of EB welding I'd be way in over my head.

    Have you tried contacting the application / technical department of the company that makes your EB welding equipment? I would think those people would be far more likely to be able to give you the kinds of expert help you seem to be needing than what you're likely to find here.

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    Re: Cracking of Inconel after EB welding


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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by HT2-4956 View Post
    stepan,

    As much as I'd like to help you out I'm afraid that when it comes to the practical application of EB welding I'd be way in over my head.

    Have you tried contacting the application / technical department of the company that makes your EB welding equipment? I would think those people would be far more likely to be able to give you the kinds of expert help you seem to be needing than what you're likely to find here.

    Yes, I have contacted the supplier of our machines, of course, but they have no experience with such a kind of the issue so far. They are able to provide interesting but very general information but when it comes to this specific application, we know already more then they do.

  15. #15
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by HT2-4956 View Post
    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.

  16. #16
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    Re: Cracking of Inconel after EB welding

    stepan,

    I checked the AWS research section papers and I couldn't find any thing on it.

    https://app.aws.org/wj/article_search.html

  17. #17
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    Re: Cracking of Inconel after EB welding

    So can you introduce a preheat while drawing the vacuum?
    Weld like a "WELDOR", not a wel-"DERR"
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  18. #18
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    Re: Cracking of Inconel after EB welding

    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/
    Last edited by HT2-4956; 01-02-2017 at 10:51 AM.

  19. #19
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    Re: Cracking of Inconel after EB welding

    Thanks everybody for support.

    Based on recomendations above, we will now focus mainly on shrinkage and evaluation of residual stresses both before and after welding.

    Wish me luck ;-)

  20. #20

    Re: Cracking of Inconel after EB welding

    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-ser...ss-development

    -The PTR-Precision Technologies Team
    www.ptreb.com

  21. #21
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by PTR EB Welding View Post
    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-ser...ss-development

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

    Good info.
    Weld like a "WELDOR", not a wel-"DERR"
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  22. #22
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    Re: Cracking of Inconel after EB welding

    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.
    Last edited by Insaneride; 01-11-2017 at 12:01 PM.
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  23. #23

    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by Insaneride View Post
    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.
    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
    Last edited by PTR EB Welding; 01-11-2017 at 04:42 PM.

  24. #24
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    Re: Cracking of Inconel after EB welding

    Quote Originally Posted by PTR EB Welding View Post
    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 every material welds and behaves differently as well, so there are metallurgical variables 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
    My ears were burning...

    I don't think it was me that mentioned anything about electron beam welding. That's one area I don't have any prior first hand experience.

    But since we're on the subject, I don't see why you couldn't use resistance or induction heating on parts in the vacuum chamber of an E-beam welding system. You just have to come up with a way to pass power cables through the walls of the vacuum chamber. NOTE: I have no idea if the OP's application lends itself to preheating with either of these types of equipment. I'm just saying if pre-heat would help, you should be able to use either method in a high vacuum environment.
    Benson's Mobile Welding at your worksite or place of business. Serving Dayton, Ohio and the surrounding metro areas.
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  25. #25
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    Re: Cracking of Inconel after EB welding

    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
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