Hydrogen Embrittlement of 8620 Pickled

[mewhg]

If we acid pickle 8620 steel in the as cast condition and then machine and heat treat (carburize at 1700F) will the heat treating drive off any hydrogen or acid that is present in surface defects?

TIA

 

[Goahead]

If you machine the surface you probably remove any affected volume. Hydrogen should not cause cracks in low carbon, low hardness (machinable) steel. It would be good practice to neutralize and rinse the steel after pickling.

http://www.welding-advisers.com/

 

[unclesyd]

Are you pickling just to remove molding sand or something else?
Can you use mechanical claning?
What is you acid/acids for pickling?

 

[CoryPad]

Hydrogen is very mobile in steel at 1700 [°]F, so it will diffuse throughout the volume and even leave the steel and enter the atmosphere. I wouldn't worry about hydrogen embrittlement in the situation you describe.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Carburize]

I would not worry about the hydrogen from the acid pickling there is going to be a whole lot more hydrogen introduced during carburizing.

 

[arunmrao]

Your need to pickle before machining is not clear. The as cast skin may pose a problem. You can machine,pickle(If essential!!),and then carburize followed by case hardening.

 

[mewhg]

Guys,

I wanted to be general when I mentioned 'pickling'. Its actually a type of vibratory finishing process that polishes the small castings we use in our products. There have been some fatigue failures that we think are related to the shot blasted finish from the foundry....we wanted to smooth up the outside surfaces.

The reason I mentioned pickling is that yesterday I was informed that the vibratory finishing process uses an acidic base wash (the parts are actually black from the acid).

The parts were rinsed after the finishing process.

Machining consistes of some holes drilled and a skim cut at a couple of locations.....so most of the casting surface is not removed.

Sorry for the mis-communication.

TIA

 

[arunmrao]

Small castings sand cast?? Why not accept investment cast. Also vibratory polishing is a good technique to remove burrs and other surface projections. The components are later ,neutralised washed and dried. I have used this technique with success and no embrittlement was observed

 

[mewhg]

They are investment castings. The ceramic is cleaned off at the foundry in a shot blast machine and the outer surface is not smooth.

This process is not a vibratory finish process that uses a soap based liquid medium.....but a speciality acid based medium. Supposedly it is supposed to polish the surfaces without very agressive ceramic media needed.....this way the corners do not get rounded off so much.

 

[NickE]

mewhg- is it REM Isotropic finishing?

If so thats a pretty mild acid they use, in fact I think its weaker than the citrisurf citric acid passivation solutions.

 

[mewhg]

Nick,

It's a proprietay process developd by the chemist at a finishing hose here in eastern PA. I don't know much about the specifics but I think I need to give them a call to find out.