Passivation & laser marking 1

[frank72]

is there anyone with experience on passivation of martensitic & austenitic steels that need to be passivated and laser marked. I do know the procedured according to ASTM A 380 / A 967 but this conflicts with laser marking. I am lookin g foreward to get some input.

Regards
Frank

 

[limey1]

From what I understand, you will have to passivate the material after laser marking, due to the heat generated. Could you consider line marking instead?. Otherwise, you are going to have to add more steps in your process for the same result.

 

[frank72]

we already do line marking - the problem is that we need to do passivation due to corrosion issues but if we do Nitric 3 for 30 minutes the lasermarking is gone....

 

[EdStainless]

If Nitric is removing your laser marking then you have not etched the surface with the laser. The nitric will not remove any bulk metal.
Crank up the laser.

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[limey1]

Can you better explain your process steps. What is wrong with line marking in place of laser?

 

[unclesyd]

In your process are you pickling and ten passivating or just passivating?
If you are pickling you can remove some metal. As stated above, passivation in itself will not cause loss of metal.

Depending on your service I see not problem with Laser Marking SS. I ran some bench scale corrosion tests on 304, 316, 430, and 17/4 SS in a very corrosive mixture of nitric and organic acids along with a couple of Huey tests. There was no evidence of any accelerated corrosion in the area of the Laser. In our process of manufacturing some of our component we reach extremely high temperature around areas where we are working.

If you have an very light oxidized surface, like you get from steam air oxidation, you have the most corrosion resistance surface as far as corrosion is concerned unless you are in highly reducing media.

 

[EdStainless]

I have seen very light laser marking where you are relying on a slight surface discoloration to be the mark. These will come off with passivation.
The good side is that without passivation laser markings are often seen with rust stains. Not good on stainless parts.

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[frank72]

actually we are doing only light laser marking - when examined microscopically at 100x you will see discoloration of the surface. the reason for mot going up with the power is that we do not want to damage the surface too much - the marking shall visible, not influencing them mechanical behaviour and it shall not vanish by time.

actually I agree with the comment that passivation does not dissolve bulk material but as far as I know the reason for passivation is to remove disturbed oxides from the surface and generate a uniform oxide layer that guarantees optimum corrosion resistance. am I correct?

 

[EdStainless]

The actual purpose of passivation is to remove free iron from the surface.
Right now you are relying on oxides and dust for your marking. You need to burn into the surface a bit. It won't hurt the parts.

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[limey1]

Doesnt passivation also remove potential thermal oxide layers too?, or is thermal oxide and free iron one of the same? As I understood it, the laser marking is a thermal generated form of identification, which is why it is being removed at passivation/pickling??

 

[EdStainless]

pickling will remove oxides, passivation won't.
are you using straight nitric acid for passivation?

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