Can stainless steel be forged ? And how ? 04 January 2024
It's a question that comes up very regularly among our customers... And the sources on the internet are sometimes contradictory! Rather than offer you a summary of the information we could have found on the net, we decided to ask Larrin Thomas, PhD in Metallurgy - whom many of you will know from his blog Knife Steel Nerds, THE bible for knifemakers, and also the originator of the famous MagnaCut knifemaking steel! Find out what he has to say in the interview below.
Can one forge stainless steels ?
Yes!
Why is it so difficult to forge stainless steel grades ? Can one forge it with « basic tools » in his/her workshop ?
You can indeed forge stainless steel with basic tools. Stainless steels have a narrower window for forging, as they can crack when forged at higher temperatures than simple carbon steels. Another common mistake is that many bladesmiths think they need a higher forging temperature than carbon steel. This is not the case, and some stainless steels are actually more sensitive to overheating. This can lead to crumbling while forging and the bladesmith thinks they need even higher temperature, which of course will only make the problem worse.
This can also be a common mistake when bladesmiths transition from simple 1080-type steels to higher carbon steels because the higher the carbon, the lower the melting temperature. This is why "cast iron" has extremely high carbon content, so that it can be more easily melted for casting. The grain boundaries melt first, which leads to problems while forging.
Is there any real technical advantage to forging stainless steel, other than creating stainless damascus?
There is at least as much potential advantage to forging stainless steel as there is to simple carbon steels and low alloy tool steels. Though we can argue how much performance potential there is to forging any knife to shape, which may not be very much in many cases.
With simple steels, the carbides dissolve at typical forging temperatures, meaning the forging isn't needed to improve the carbide structure. With high alloy tool steels and stainless steels, those carbides hang around all the way up to melting, so there is potential to break them down further during forging. Also, when forging knives to shape the orientation of the carbide "stringers" can be manipulated to follow the shape of the knife.
Why do martensitic stainless steels weld so difficultly together ? What are the conditions required for successful welding ?
Stainless steels form tenacious chromium oxides that conventional fluxes cannot remove. Therefore avoiding the formation of oxides in the first place is generally the best approach, by ensuring an oxygen free environment.
Which stainless steel grades are suitable for forging – and which ones are NOT ?
Virtually any stainless grade can be forged. The steel company forged them before they were sold to the knifemaker. Steels with less carbide at the forging temperature, and smaller carbides, are generally easier to forge. AEB-L is a good steel to start with for this reason, plus the benefit of its relatively low cost. The biggest disadvantage is that AEB-L is typically not available in thicker sizes which are sometimes preferred by forging bladesmiths.
What are the grades that give the best contrasts when etched properly ?
I think this is an area that could see further exploration in the future. The very best contrast is typically seen between martensitic stainless (440C, AEB-L, 154CM, S30V, MagnaCut, etc.) and austenitic stainless (302, 304, etc.) or nickel. However, the large carbon difference between the two, and the high chromium of the austenitic stainless steels can lead to large carbides in the austenitic stainless, leading to reduced toughness.
A semi-common "double high carbon" mix was popularized by Damasteel with PMC27 and RWL34, which can also be achieved with similar steels like AEB-L/12C27 and 154CM/ATS-34. The high molybdenum content in the 154CM gives it contrast when etched with hydrochloric acid. However, many more "double high carbon" mixes have been used which do not contain a high Mo steel and there may be other elements contributing to the contrast.
For example, Balbach has used Nitro-B and N690, or 7C27Mo2 and 19C27. You can always start by copying the mixes of others before experimenting with your own.
A huge thank you to Larrin Thomas for his time and precious answers! His research work can be found on theKnife Steel Nerds blog, as well as in his book, « Knife Engineering », available on Amazon. Last year, he also published an exhaustive study of the history of cutlery steels, « The Story of Knife Steels »,, also available on Amazon.
