theimi

stainless steel fire scale

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Hello guys,

wasn't there for a very looong time (years!, sorry for that) but if one has a blacksmithing related question this forum is the way to go!

I'm doing a lot of work in stainless at the moment because my customers like the 'bare' steel finish without rust. So the fire scale it develops during forging is a necessary feature in my work as it looks as "normal" mild steel.

What I don't really understand is how and when the scale develops (and if not, why!!). After doing welds (sometimes) or after working with the grinder I often have the problem to get the scale back on the ground spots which looks really ugly (I have really problems to explain it as English is not my mother tongue, but if you work with SS you should know what I'm talking about)

 

Greetings from South Africa

Frank

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Have you tried putting the freshly ground/ welded piece back on the fire to re establish the scale in those areas, and even it out?

Steve

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You have to do the same amount of work to it to return the surface condition as it took to create it the first time.

Grinding is the last thing, next time work out the roughness with forge and hammer...voila.

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Stainless steels are also pretty good at handling high heat situations due to the chrome and nickel content, so you have to get them really hot, and have enough oxygen around the item for the scale to form.

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Thanks for the answers guys.

Sometimes there is no other possibility than using the grinder even if I try to avoid it. Ok, in any case you can start from scratch and make a completely new part :rolleyes:, but that's not really economical...

I realized there are many factors which affects the development of fire scale. surface texture, smoothness and - of course - time. The funny thing is whenever I put the part under the (power) hammer the scale develops much easier even if the part is not that hot and was in the forge for a short time only... something I don't have an explanation for and that was the reason for my confusion...

hinge2.thumb.jpg.608fb054a2b26af669571ea0bea8e3af.jpg

hinge1.jpg

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First a disclaimer, I have limited experience and my comments may need correcting by those who know more. My understanding is that nickle passivates easily and forms an oxide layer which contributes to its stainless nature. When you work with the power hammer you are working hot and drawing out and so breaking the surface layer which exposes the fresh hot surface to oxygen. When grinding, you are working cold. The passivated layer can reform and interfere with regaining the finish you are looking for. I hope those who are more knowledgeable will either validate or refute this. 

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My question would be: are you using stainless dies on the powerhammer?   Not using stainless tooling can result in oxidation  for regular uses of stainless perhaps with the PH as well?

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1 hour ago, 4elements said:

. My understanding is that nickle passivates easily and forms an oxide layer which contributes to its stainless nature.

Chrome

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9 hours ago, theimi said:

Thanks for the answers guys.

How did all those blacksmiths manage for the thousands of years before grinders were invented?

No matter if you have it figured out but since you asked here...

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I think they hadn't to compete with cheap welding "wrought iron" shops on every corner and cheap mass imported Chinese junk....

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That's a different topic. Customers pay for the end product, they don't pay me for a few extra hours because I had to avoid a grinder as all those blacksmiths did it without before it was invented ;)

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In the history of technology, abrasion predates metalwork.

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Lol back when you could go to a supermarket snag a homeless orphan street rat and give him a job... Nowadays you gotta pay people.

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