Does forging stainless reduce the corrosion resistance?

[JamesBBrauer]

Wasn't quite sure what forum this fits in, but it is mostly related to how heat and pressure change metal, so here you go:

 

If I heat stainless up to an orange heat in the forge a few times, and hammer on it, does that wreck whatever they alloy in for the corrosion resistance?  I would guess that it depends on the type of stainless.  So if it does, is there a type of stainless that is particularly good for this?  I want to make some hand forged cutlerly.

 

thanks

James B

www.hotworksgallery.com

[Rich Hale]

A lot of stainless that contains enough carbon for knife making is not a starting point for knife making. For a couple of reasons:  Forged stainless may end up with a lot of cracking. If you pick any of the knife making grades of stainless and research the temps and times needed to properly heat treat you will see that it will not be something most home shops can do. http://www.simplytoolsteel.com/heat-treating-tool-steel.html

That link gives heat treat information for 440C, A stainless that makes great knives if done correstly.

So with all that said I think you can forge stainless into a working blade.. After yoiu spend the houirs needed to learn how it works and keep it in the proper heat range for forging. And you can work out how to heat treat it properly.

If you are not forging yet you may want to consider spending a lot of time forging basics first,,,drawing roiund to square, tapering, etc,,,those basics will build not only body mechanics but also fire management.

Lots of that covered in the knife making lessons on this site.

[Frosty]

Yes but not permanently. Heating SS causes surface corrosion which will continue. However passivization will clean it up and return it to stainless. (The adjective, not noun)

 

You'll need to look passivization up, I just ask the gang and get the correct acid I believe citric acid is enjoying success. You can also "electro polish" stainless. It literally polishes it, neat process and results.

 

As for altering the internal metallic composition or such, NO it won't. Well, not more than regular steel, eg. grain growth, hardening, embrittlement, etc. the normal stuff.

 

Rich posted just about the time I was hitting "Post." Rich speaks with the knowledge of an experienced bladesmith. I was addressing only the visual finishing of stainless: surface corrosion polish, and potential alloy altering. For advice go with Rich, I would.

 

Frosty The Lucky.

[JamesBBrauer]

Frosty, thanks for the search tip (passivization), I'll check that out.  I might be able to convert one of my plating tanks for an electro polish.  I've done the electrolysis rust removal thing, and have an even better constant current power supply now.   

 

And Rich, I've been pretty successful making edged tools with tool steels, and forged stainless, just never tried polished or edged stainless.  I scratch built and programmed a controller for an atmospheric digital kiln.  I use it for tempering borosilicate glass (which shatters if you do it wrong), so I can dial in ramps and soaks with good precision and accuracy.  More interested in what the forging does or doesn't do to stainless, but Frosty's search suggestion got that answered.

 

thanks fellas

 

[edit]

 

I found a couple of good descriptions of passivation:

 

http://www.mmsonline.com/articles/how-to-passivate-stainless-steel-parts

http://www.delstar.com/passivating.html

 

and some formulae with temp/voltage/current for electropolish on different types of stainless:

 

http://www.fischione.com/product_support/model_110_application_notes.asp

 

Looks like a good cleaning and some quality time in citric acid is a good place to start for a corrosion resistant finish.  I didn't realize the corrosion resistance was a surface film. 

 

I have a couple temp controlled plating baths with fume extraction that I might use for an electropolish tank.  I guess I'll have to do the final sharpening after it comes out, since that whole point charge collection thing will erode a sharpened edge along with any metal contaminants. 

 

I'll go practice drawing out a taper now, do you hold the metal end of the hammer, or the wood end?  :-)

[Rich Hale]

I'll go practice drawing out a taper now, do you hold the metal end of the hammer, or the wood end?  :-)

How would anyone be able to guess wot your skills are? Yoiu experience or for that matter wot tools you have on hand?

 

I will trouble you no more!
 

[Robert Yates]

I have to admit I have meet many a smith that works with metals that have said that many metals would NOT work together and yet have forged them in many layers to form a 100% welded billets from them . However you must understand as I did learn it you do not explain your abilities first you will get an adverse reaction to anything you post that is Not the Normal Forgings just like the MBSA they like and want traditional knives and frown upon any type that is different . Yes ! it Blows ! yet if you want the stamp of a Master Blade Smith you need to do every thing perfect to get the MBS Stamp .

 

many a book and DR. Level Smiths (Metallurgist) have written and done work on working with metal that should Never work together yet it did and does ! traditional Smiths Do Not work with them and will discourage you from doing this type of work . I say drive on do it and prove your ability as processable. yet be kind to the rest of the folks here as well that is the best I can offer you Brother .

 

Sam

[ianinsa]

The wood end? Where on your power hammer is the wood end? :D

Great link on the recipies Thank you!

[BIGGUNDOCTOR]

The passivation most of our customers spec out is either nitric, or citric acid.