stainless steel welded part getting rust after dishwasher test.

[gmensing]

Hello,

The area where the stainless steel is welded, is getting rusty after doing the dishwasher test...
Why is this and can we avoid this?

Regards,

GM

 

[Metalguy]

What SS was used? Sounds like a case of sensitization. Low-carbon or stabilized grades should be used for welded items.

 

[arto]

did you passivate it? also, don't use the same wire wheel or grinding wheels as used on carbon steel in the shop.

 

[stanweld]

If rusting covers a relatively wide area (4 mm to 8 mm)from the weld, most probably the rustingcis due to improper cleaning prior to welding by using contaminated brushes, grinding wheels, other abrasives. If rusting is narrow, confined to the Heat Affected Zone, rusting is most likely caused by sensitization.

 

[gmensing]

Hi y'all,

The stainless steel is 18/10.
Thanks for the thoughts.
>> arto - Passivate? Can I passivate it after welding? How? heat treatment?

cheers,

GM

 

[kenvlach]

Lots of threads describe passivation, e.g.,
Stainless Steel Passivation
thread404-64445

 

[arto]

Lotsa info from NiDI:

http://www.nidi.org/index.cfm/ci_id/11931/la_id/1.htm

Basically, the metal is dunked in a Nitric Acid solution to dissolve embedded iron particles

 

[arto]

also see ASTM A-380 "Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems "

 

[ibrahimdemir]

gmensing,

I suggest you to check your manufacturing and/or welding procedure as well.
If you work with austenitic steels you need to know about formation of Chromium Carbide. Solution treatment between 1050 and 1150 deg C will take all of carbon into solution and rapid cooling from this temperature range will give a supersaturated austenite solid solution at room temperature.

However, slow cooling or reheating within the range 550-800 deg C will lead to the rejection of carbon fron the solution, usually as chromium rich carbide even when carbon content of the steel is very low.

This carbide nucleates preferentially at the austenitic grain boundaries as faceted particles or often as complex dendritic arrays.

The most significant result is the deplation of the regions adjacent to the grain boundaries with respect to cromium.
The surface film in this regions is deplated in cromium and as a result the steel is more prone to corrosive attack. Consequently, a classic form of intergranular corrosion is experienced which, in severe cases, can lead to disintegration of the steel. This type of corrosion is also experienced in martensitic chromium steels.

Welding, in particular, provides these conditions in the heat effected zone leading the localised attack in certain chemical media.

I refer you to see the following reference:

Steels
Microstructure and Properties, 2nd Edition
Sir Robert Honeycombe and H.K.D.H. Bhadeshia

Hope this helps.

Ibrahim Demir

 

[INBCPE]

What about glass beading? We use beading in lieu of passivation for non-critical parts (non WFI, etc). Works like a charm, and it's a lot cheaper and cleaner.