FWIW, here's 12C27: A Steel that Gets No Respect by Butch Winter from Tactical Knives, probably 1998:
My introduction to 12C27 came at one of the Knifemaker Guild Swedish shows so long ago I don't want to think about it. Sandvik, the Scandinavian steel company that produces 12C27, put on a demonstration for all the knifemakers to introduce their new steel designed especially for knives.
Sandvik, in my opinion, was unlucky in choosing this time to promote 12C27. Bob Loveless had just discovered 154CM, and most knifemakers thought it was going to be the answer to their woes, a stainless steel with super edge-holding ability. And it was, at the time.
Despite the lackluster reception the Sandvik people were given, what they said made perfect sense to me. I'll quote from Sandvik's bulletin on the steel:
Sandvik's Reasoning
"When selecting steel for edge tools, it is important to balance the different requirements regarding corrosion resistance on one side and hardness, cutting edge durability, and wear resistance on the other. When doing this it is important to be aware of the fundamental metallurgical facts concerning chemical composition, microstructure and the effects of the necessary heat treatments.
"12C27 is a grade developed by Sandvik AB. The objective of this development work was to produce a grade for application where high demands are placed on both corrosion resistance and hardness. In many applications where corrosion resistance is not required, 12C27 still is the best solution thanks to its very good wear resistance."
What did Sandvik do that makes them think that 12C27 is so great? Quoting again, "Corrosion resistance is determined by the chromium content of the martensite/austenite (hardstuff/softstuff). It increases rapidly with increasing chromium content of the matrix up to a value of 11.5% chromium. At this content the steel is stainless in not too aggressive environments. Above this threshold value the corrosion resistance is only slowly increased by additional chromium."
What they're saying is that about 11.5% chromium is going make the steel stain-resistant to an appreciable degree and adding more chromium will help but with diminishing returns.
Quoting further, "A very high corrosion resistance and a very high hardness can never be achieved at the same time. The reason is that both chromium and carbon suppress the temperature where the transformation from austenite (unhardened steel) into martensite (hardened steel) starts." This keeps the austenite from completely transforming into martensite (retained austenite).
"A steel with good corrosion resistance and the highest possible hardness should thus have a matrix composition of about 11.5% chromium and .50% carbon...for most hardenable stainless steels...carbon and chromium are bound in the undissolved carbides where they contribute neither to the hardness nor to the corrosion resistance.
"A certain amount of excess carbides is desirable in order to avoid grain growth which would occur if all carbides were dissolved during hardening. Grain growth would cause a coarse hardening structure and brittleness. The wear resistance is improved by the presence of undissolved carbides. Primary carbides should be avoided when a smooth edge is needed. The reason is that the primary carbides… tend to cause 'tear-outs' in the edge at the grinding operation."
What all this is about is that Sandvik is trying to explain that 12C27, after heat treating, because of its chemical composition, is a fine grained steel. Notice the number and amount of the elements: carbon .6%, chromium 13.5%, silicon .40%, manganese .40%. Compared with 440C, for instance, they are fewer and lesser. 440C has .9-1.25% carbon, 16-18% chromium, 1% manganese, .75% molybdenum, .04% phosphorus, 1% silicon, and .03% sulfur. So, 12C27, compared with most other stainless steels is a rather simple alloy. And, Sandvik says, this makes for a fine grained, hence better, knife steel.
How does it work? Very well indeed. I have had several knives made from the sample strip of steel all who attended that seminar received. One of the knives has been cutting cardboard for over 10 years. Wayne Clay and Larry Downing have also contributed blades for test. Neither of them really cared for the steel, but I don't feel they gave it a fair test. The only knifemaker I have found who has used the steel and likes it is Darrel Ralph, and he agrees with me that 12C27, properly heat-treated, is a steel to be reckoned with.
Any knifemaker out there who isn't happy with his stainless steel should think about giving 12C27 a try. At times the answer to a complex problem is the simplest one.