455 S.S. tube rusting after welding 1

[Phil174]

I am welding a handle made from 17-4 S.S. to a machined tube made from 455 S.S., parts are joined together via GTAW with 17-4 S.S. filler , units are cleaned heat treated and passavated , the completed part is a Orthopedic Surgery Tool, problem is that we are getting rust on the 455 tube bore , mostly in the welded area , any thoughts would be appreciated.
Phil L.

 

[israelkk]

By 455 ss do you mean Carpanter's Custom 455?
Are you sure it is rust and not heat tint?
What is the heat treatment aging temperature?

 

[Phil174]

Yes it is Carpanter's 455 SS , I belive the Co. that I sub contract for heat treats at H900 or 482 C for 1 Hour , and yes it is very much rust .

 

[israelkk]

The rust can come from the machining process. If the cooling fluid used in the machining was previously used with carbon alloys that creates iron based particles which may embed themselves into the stainless during machining. The cooling fluid should be new and the machine must be cleaned from any traces of previous machining fluid prior to the machining of the 455 and 17-4 tubes.

Another possible source of contamination can come from the cutting tool itself which may contain iron. It is better to use diamond cutting tool at least for the final machining.

Did the plater pickled the part before passivation. The pickling dissolves the iron parts that came from the m machining process.

However picking produces hydrogen. Therefore, if the parts are treated to H900 there is a real risk of hydrogen embrittlement of the parts.

The correct cleaning method should be abrasive cleaning such as aluminum oxide blast of the part surfaces before and after welding. If the inside diameter of the tube is too small you can use a paste abrasive cleaning as used for stainless tubes used for microelectronic industry where a paste with abrasive particles is pushed/flow through the tubes using pressure.

After abrasive cleaning there is no need for pickling just solvent cleaning and passivation.

 

[Phil174]

First of all thank you for the information , I have only been working for this Company for a few months and am not completely sure as to the history of the Tool in question , I don't know the exact procedure as to cleaning and handling before and after surgery and at this point we are looking for any and all help, one concept that has been suggested by our QC man was to either reduce or eliminate the bore in the weld area until after welding and then finish to size , if you are saying that iron contamination could be the problem then we will still need to change our procedure , most of the Surgical Tools are made from 17-4 SS and to my knowledge they haven't had a similar problem , only with the bore of a welded 455 tube .
Thank You Again
Phil Lohiser

 

[btrueblood]

Was the tube bore purged (with Argon or similar inert gas) during welding? Was the i.d. cleaned and degreased prior to welding?

 

[limey1]

You need to verify that the i/d is treated after welding to encourage passivation to take place, either by pickling or paste, otherwise the heat generated would create a thermal oxide layer = rust.

 

[Phil174]

Yes , we use fittings on the 455 tube and have a source of Argon that purges during welding , parts are washed in kerosene and then washed with soap and water.

 

[EdStainless]

I have to go with the opinions already mentioned.
I believe that the surface in question may not be clean enough to start with, isn't purged enough, and has not been passivated.
What are you using for passivation?
You may have too much surface damage for passivation to do its job.

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