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A recent Spyderco Byte has announced a replacement for H1 steel – H2. H1 is known for being a very high corrosion resistance steel used primarily in Spyderco’s Salt line of knives. I have a previous article about the design of H1 and how it “works” which you can read here. I am somewhat tempted to re-write large chunks of that article here because H1 is one of the most misunderstood knife steels but I am going to try to hit a few of the highlights without much explanation and I hope you will read the earlier article to understand what I am referring to:
H1 is an “austenitic” stainless steel. This category of steels includes grades like 301, 302, and 304 and are best known for being used in non-knife applications like pots and pans. Though they are used in butter knives, I suppose. They have very high corrosion resistance and excellent formability, and are non-magnetic. The grades are not known for their high hardness, which is generally a requirement for knife steels. Austenitic stainless steels will transform to hard martensite with cold working, however. The degree to which it transforms to martensite is dependent on its composition and the temperature at which the steel is cold rolled. Colder temperatures will lead to more transformation to martensite with less cold working. There are many models and equations for predicting how readily the steel will transform to martensite but no real consensus about how to predict it because of the difficulty of modeling the behavior. One measurement is the temperature at which 50% martensite will form from 30% strain. Here is an equation to predict that temperature:
MD30 (°C) = 413 – 462*(C+N) – 9.2*Si – 8.1*Mn – 13.7*Cr – 9.5*Ni – 18.5*Mo
So for a steel that is designed to be transformed to martensite through cold rolling we want that MD30 temperature to be relatively high so that when it is cold rolled at room temperature it will transform nearly 100% to martensite (without cracking). That achieves the relatively high hardness of H1 steel in finished knives, which has been measured in the 55-58 Rc range.