Bill,
I was attracted to and curious about the Al repair question, and became even more so when it began to appear he was repairing the Al with apparently a stainless filler. If the initial question was a bit unclear at least it's been straightened out, but you shouldnt feel it was your fault... the ambiguity got me too.
Its nice to see things on-track.
Also, it is difficult for me to avoid wisecracks about one-track minds. I can at least be thankfull that, if still only one track, it's the same track I was on when all the guys just thought of one thing. (coincidentally it was food even back then; we hung out at McDonalds and Mc-Fries was typically the subject du jour... (yah, that and sesame-seed buns))
:-)
d
Jer,
I cant give much direct advice, but I would be curious about the specific chemical activity going on with this molten Al to enable a "back-door" approach to finding the appropriate repair and alloy resistant to this action... providing I was unable to get advice from someone with experience of successful repair of the same stuff.
If not here, perhaps something more foundry oriented?
Perhaps also here at AWS but under "Technical"...good luck...
...I'd like to know whats going on with that myself, so I hope you find out; let us know how you do.
Are your patches the same thickness as the ladle body itself, and lacking specific information you need, might you be able to borrow material from elsewhere on the ladle to build the patch (for example, from a handle where the repair would be under less duress and where a compromise repair might hold up better)
Regards,
d
Hi jer
I am not in the casting industry, so I am really just giving advice on gut-feel here.
Firstly, we need to try and establish why the ladle is having problems in the first place. When we look at Al, we see that it is an extremely reactive metal. Given any opportunity, it will want to change to alumina. (Aluminium oxide) In fact, there is a welding process (thermit welding) that uses this fact to weld many metals very rapidly. Here Al filings are mixed with the oxide of the metal that it wants to weld (e.g. Iron oxide) and then heated to start the reaction. Once the reaction starts, there is a very rapid exothermic reaction that takes place, where the Al takes the Oxygen from the metal oxide and turns the Al to aluminium oxide. The metal is then left as a moulten "pure" metal which solidifies giving the weld.
I believe that the "corrosive" problem with Al is due to the above mentioned reaction. Stainless steels have an oxide layer that is the barrier rendering it corrosion resistant. I believe that the moulten Al is busy "corroding" this away rapidly by simply reacting with it.
To get to a satisfactory solution, I would like to know why you had to patch the ladle in the first place? Did the original material also just "erode" away, or was there some other reason? If it did erode away, how long did it last before the repair was necessary?
I believe that if there was a reasonable life to the ladle, then the material from which the ladle was made, was probably not "ordinary" stainless steel. It is probably some kind of Ni alloy or something simmilar. To effect this repair, you need to make sure of the material of the original ladle. Many people call all the "shiny" corrosion resistant materials "stainless steel".
At any rate, I do not believe that using 316 will make any difference because the extra Mo in the 316 is only really there to provide better pitting resistance in an electrolyte.
Another final question. You say that the 304 patch "disintegrated". How did it fail exactly? Did it crack along the repair weld? Did the edges of the patch "erode" away? Did the entire patch just thin very quickly untill it started breaking up? Did cracks develop all over the patch? If you can tell me this, we could possibly confirm the foregoing theory or look at something like liquid metal embrittlement.
Regards
Niekie Jooste
Hello Niekie, I have a custom fabrication and welding shop in wisconsin.
(The ladles) These are made of stainless steel and I think 316, I did not see the damaged ones yet that I used 304 on. Ladles evidently wear out in small areas, where customers maintenance trys welding ( actually looks like bird droppings from what I saw) So what I did was to cut out the droppings which protruded about 3/8" off ladles with my plasma cutter. Recently I found that these ladles must be coated before putting into service and allowed to dry, this gives some sort of protection to the ladles, customer said they definitely did this.
Having no history with this type of part, all I knew going into this was what customer told me ( cut and patch with stainless steel) well that evidently didn't work too good.
I called customer and offered to take three and try to patch differently.
First patch I placed on was cutted out with hand plasma cutter about 2" x 4" and covered with patch and tig welded around outer edge, weld looked like the color of a rainbow. This type of weld was a lap type joint, which left area inside of the cut out open, and I think created area for molten metal to wash out or get trapped in.
I am thinking of trying to patch inside the cut out so as to butt weld the joint there by creating a smoother edge inside of ladle, and use 316.
Hey Nieskie as far as where exactly the patch failed will have to wait until customer sends a few back, or I go and get a couple.
As far as stainless goes it was always my understanding that 304 is food grade and for corrosive properties use (316 or 316L what ever) is there a difference in 316 or 316L.
I'll keep posting any info I can find out on this matter.
The difference between the streight 316 and 316L grade is the carbon content. 316L has a low carbon content, (thus the "L") to prevent sensitization during welding and high temperature operation.
The big difference between 304 and 316 is that 316 contains a couple of percent of Molybdenum. This iscreases the pitting resistance of 316 over 304. It is for this reason that most people considder 316 a "superior" grade of stainless steel. It is superior, but only in instances where pitting corrosion is a problem. In your case (Liquid Al corrosion) I do not believe that there will be much of a difference in performance between 304 and 316.
Let us know how the failures occurred, then we will have a better chance of giving some usefull advice.
Regards
Niekie Jooste
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