Welding Myths Part 2: If it’s metal, I can weld it

Topics: Laser welding

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This misconception about welding comes up far more often than I’d like.  An engineer calls in a rush to get a prototype stainless steel part welded.  To save time and cost, he had the parts made from free machining material.  Frantic on the phone, the conversation generally goes something like this:

Customer: “This is so and so, and I’ve got 3 stainless steel housings I need laser welded ASAP.  The machining is done, I just need a full penetration laser weld to hold them together, and they have to be absolutely leak tight.”

Me: “Ok, a couple of questions.  1 - What is the size and shape of the part?  2 – How much penetration?  3 – What grade of stainless?”

Customer: “It’s a round housing about 2 inches in diameter, it has a step behind the weld to align the parts.  The wall thickness at the weld is .030”, and the material is 303 stainless steel.”

Me: “Alright, a couple more questions now.  1 – Is there a cosmetic requirement for this part?  2 – Can you tolerate filler material in the weld?  3 - (in my head) Why did you make these out of 303?”

Customer: “Looks are very critical.  I need the weld very small, which is why I want laser welding.  I can’t tolerate filler material unless it won’t affect the cosmetic appearance.”

Well, this back and forth usually goes on and on.  During the conversation, I mention that 303 is not ideal for welding.  There is a rapid and fierce push back about how all 300 series stainless steels are easy to weld. 

Reality check

Here’s the thing - 303 stainless steel is GREAT for machining.  Wonderfully easy to work with, readily available, and fairly inexpensive.  That said – it’s just not meant for welding, no matter how you slice it.  The stuff they add to make it free-machining, sulfur and phosphorus, don’t mix well with welding.  They evaporate with fervor - to put it mildly - during the laser weld process, leading to copious weld spatter and frequently cracking, not to mention porosity (a topic for a later post).  

The conversation will end with one of three outcomes: 

  1. Customer will have us work with the 303 parts, and add a ductile filler wire (such as 308L or Hastelloy W) to add some good material back into the “ugly” weld, and Mr. Customer will tolerate the resulting cosmetic blemishes.
  2. Customer remakes parts out of 304L and everything is hunky-dory.
  3. Customer hangs up in anger because his parts can’t be made exactly as he wants them from the material he already had purchased.

I’d like to say option 3 never happens, but unfortunately it’s a real situation that occurs regularly. So, the lesson to be taken from this – always check with your weld house BEFORE manufacturing parts.  Make sure that the material that you want welded is actually weldable, please.  I’ll speak more about weldable and non-weldable materials in other posts.

 Check back soon for the next post in our series on welding myths: “A weld is never as strong as the parent material.”


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