thinking about stainless...

S

siguy

Joined
Aug 26, 2006
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i was walking around earlier and a thought on stainless occurred to me.

i have often heard that stainless steel should not be forged because it imparts undue stress to the metal.

but then i thought: stainless is essentially basic carbon steel with extra chromium (at least that's how i understand it)

so does chromium really make steel that much more susceptible to stress in the forge over the simpler carbon steels that are commonly forged?

or am i missing a step in my logic?

and all steel is forged to shape (stock, round rod, etc) in the first place, so what is the difference between the original forging and hammer forging?

is this a myth that has been busted and i somehow missed it?

thanks very much for your thoughts, i'm curious about this...
 
Stainless and Semi-Stainless can be forged, Jim Hirsoulas forges A2 & D2. Listed below is a quote form his forum:

"For daggers and knives we use mostly 1095 or 1084. Both are very good high carbon steels for knives and "smaller" blades. Their higher carbon levels mean a higher "over all" hardness than a sword, which is fine for a knife where cutting ability/edge holding is more "important" than flexing ability. However, we can on request use other materials such as: 0-1, W-2, 1060, WHC, A-2, D-2, Vasco-Wear, 1045, 52100 and others.

"We will even hand forge stainless steels, but we will NOT fashion any blade longer than 10 to 12 inches in length out of this material as it is unsuitable for "larger" pieces due to its inherent brittleness. (Stainless steels are available at additional cost...) There very few smiths out there that are wiling or able to forge a decent blade from stainless steel but it can be done. Excellent choice for blades in moist or humid conditions".

I hope this helps
 
thanks for that...so it can be done...

hoping to hear from some of the metalurgists here to say whether it should be done.
 
You usually run a normalizing cycle on any carbon steels you work with. Most folks I know don't run normalizing cycles on their stainless, maybe this could be a factor. I think the big reason it's cautioned against is the heat treating aspect, not the actual forging.
 
so maybe people are just not normalizing their stainless, leaving "undue stress" where carbon steels are typically normalized, which reduces the stresses in the steel...

but i wonder if a knifemaker that is familiar with forging carbon steels would leave out a step just because they are working with stainless...

i see what you mean about the heat treat, not being capable of differential hardening, but as seen in the "flex" thread, it really shouldn't matter whether it can be hardened differentially or not, but purely based on the capabilities of the steel...
 
I've tried forging some stainless, and I've tried some A2, too.

Very, very tricky. Not hot enough and it won't move. Too hot, and it crumbles.
And not-hot-enough and too-hot are very close together. :grumpy:

No fun!
 
A couple of comments:

While chromium is the largest alloying element in stainless steel at
13%+, it's not the only one in many steels.

I think that the problems with forging stainless are that the required
temperature range is both high and narrow and the steel still hard to
move. In addition, all stainless steels are air hardening so the steel
will harden if you ever let it cool down. I.E. it's a lot more work and
there's much less margin of error.

Also, heat treating stainless steel requires carefully controlled high
temperatures and protection from oxygen (because scaling and
decarb are real problems at the required temperatures). This isn't
a problem if you have the right setup in addition to a forge, but it's
undoubtedly a limit for many.
 
Not all stainless is air hardening. The sanvick steels come to mind. 13c27 is an oil hardening stainless. Not that this changes the fact that stainless is a pita to forge from everything I have heard.

dlpierson said:
A couple of comments:

While chromium is the largest alloying element in stainless steel at
13%+, it's not the only one in many steels.

I think that the problems with forging stainless are that the required
temperature range is both high and narrow and the steel still hard to
move. In addition, all stainless steels are air hardening so the steel
will harden if you ever let it cool down. I.E. it's a lot more work and
there's much less margin of error.

Also, heat treating stainless steel requires carefully controlled high
temperatures and protection from oxygen (because scaling and
decarb are real problems at the required temperatures). This isn't
a problem if you have the right setup in addition to a forge, but it's
undoubtedly a limit for many.
Click to expand...
 
Sorry, I wasn't really talking about differential heat treatment. I'm speaking more of any heat treatment at all in the forge. Heat treatment and normalizing for stainless steels is just not the same as carbon steel and can't be done appropriately in a forge.

Great points also about the forging temps, which I had forgotten.



siguy said:
so maybe people are just not normalizing their stainless, leaving "undue stress" where carbon steels are typically normalized, which reduces the stresses in the steel...

but i wonder if a knifemaker that is familiar with forging carbon steels would leave out a step just because they are working with stainless...

i see what you mean about the heat treat, not being capable of differential hardening, but as seen in the "flex" thread, it really shouldn't matter whether it can be hardened differentially or not, but purely based on the capabilities of the steel...
Click to expand...
 
Yes you found another myth ! Every steel is different and should be treated for it's own characteristics. If you can roll it out in a mill you can forge it .You can even make damascus .The stainless steels require more precise control of temperatures for both HT and forging .Learn about the steel first then play with it.
 
Stainless can be forged absolutely. Gill Hibben used to forge all his 440C blades because he could only get it in round. There are some things to think about, Chromium and some of the other alloying elements cause it to be very stiff under the hammer, High temperatures will cause the material to "fall apart" or turn to oatmeal as I like to put it. Also most all of the martensitic stainless I can think of is air hardening so each time you allow it to cool you need to do it slowly as to prevent stresses from causing the cracks I believe you are referring too. Many Years ago there was an article in one of the magazines in which Mr Hibben compared forged and non-forged SS under a microscope. There was little or no grain refinement between the two samples so his hypothesis was there was that is was not worth the effort to forge SS. Many have done it since and continue to do so. I do not know what the effects are of forging CPM steels. I know they drop forge it but under the hammer may be a different story. I tried to forge a piece of D2 ONCE. It is very difficult to move, like trying to forge a piece of cold rolled cold. So I prefer to stick with carbon steels.
 
Dustin Golat said:
Not all stainless is air hardening. The sanvick steels come to mind. 13c27 is an oil hardening stainless. Not that this changes the fact that stainless is a pita to forge from everything I have heard.
Click to expand...

The instructions for 13C27 do say to use oil but a number of people on this forum have had success plate quenching it.

In any case, but "air hardening" I didn't mean that the recommended quench was in air, but rather that if you heat it to the austentite range and let it air cool it will get hard. I.E. "Normalizing" it, will harden it instead.
 
dlpierson said:
The instructions for 13C27 do say to use oil but a number of people on this forum have had success plate quenching it.

In any case, but "air hardening" I didn't mean that the recommended quench was in air, but rather that if you heat it to the austentite range and let it air cool it will get hard. I.E. "Normalizing" it, will harden it instead.
Click to expand...

I see you point there, I wonder if something like 13c27 would be easier to forge then an air quench steel? Maybe giving you more working time before you have to go to the next heat or stuff it in vermiculite.
 
I forge D2 because I have to forge, if anyone forges air hardening steels for me he/she has to have at least a good kiln to anneal that steel. You cannot normalize as carbon steel, If you slow cool under vermiculite the results are too variable. Also forging needs too much experience and serious knowledge of color reading of heat, 30 % of my forging results cold shut cracks, even I take huge care to stay at proper forging heats during hammering, as the stock gets thinner it is virtually impossible to get the stock from forge to anvil without dropping to out of margin. So forging is only for to shape the stock to your needs, but you have to forget to forge the bevels. It is somewhat guaranteed you'll have at least micro cracks, which will be not noticed until the blade cracks from the edge during hard usage....
Emre
 
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