The Steels, Stainless, Carbon, and Tool Steels
High Carbon, Stainless, Tool Steel, CPM Steels
Hint: They're not all the same!
The steel a knife is made from imparts its "personality" on the finished blade. Some sharpen easier, some are tougher, some hold an edge better, and some have a higher working hardness. All the steels in my shop are chosen for their high potential hardness, ease of sharpening, good toughness, availability, and affordable prices, except a couple. The heat treatment, profile, bevel grind, and final sharpening will matter deeply in how your knife performs in your hand, but the steel must have suitable properties for the desired blade geometry.
Some steels excel at specific properties such as toughness, strength, edge retention, stain resistance, or sharpenability. No steel exists that excels in every category.
This list may grow with time, but SLOWLY. If your favorite knife steel isn't on the list, contact us, and we'll work something out!
Learn Heat Treating Terms HERE!
A2 steel is traditionally a tool and diemaker's steel and has been used to make custom knives for several decades. The "A" designation denotes it is from the family of "air hardening" steels. After heating to austenitizing temperature(1725 to 1775), A2 can be cooled in still air and attain full hardness. Other steels like D2 and most all stainless steels possess the same characteristic since additions of Chromium increase the "hardenability" of steels.
At around 5% chromium, there is not enough Cr to be "stainless" but plenty to make A2 air hardening. A2 has 1% carbon and 5% chromium, 1% Molybdenum, and .4 Vanadium. Mo also increases hardenability, and the V helps grain structure to remain small, while the 5% chromium increases edge retention and hardenability over simple carbon steels.
A2 is capable of as-quenched hardness well above 64Rc and has typically been tempered to 58-60Rc for use in custom knives. It is more than adequate at that hardness, but edge retention is improved with a bump to around 62Rc, with negligible loss of toughness. A soak at cryo temperature (-320F, liquid nitrogen bath) enhances the hardness and strength of A2, so every knife receives cryo immediately after austenitization and before tempering cycles begin.
I chose AEB-L steel as the "house stainless" at Keith Nix Knives for its high potential hardness, excellent toughness, good stain resistance, and edge retention.
Stainless steel chef's knives have gained a reputation through the years, particularly perhaps in the 50s and 60s, as not being very tough, hard, or great at holding an edge. This probably has to do with a flood of factory knives made from 420 series stainless. With .3% carbon, it was never going to get hard enough for a quality knife. But it blanked well (making knife blanks with a press and dies), machined well, was very stain resistant, and polished well. So there was that.
About 100 years ago, Uddeholm in Sweden began tinkering with a new stainless steel for razor blades. This new steel had to attain high hardness(62 HRc or above), have fine blanking ability(see above), and a carbide structure fine enough to be suitable for razor blades. AEB was the first iteration, but the chromium carbides were too large, creating a toothy edge unsuitable for razors. AEB-L came into being sometime later and was a perfect balance of all the attributes necessary, Such as fine blanking, edge retention, hardness, ultra-fine carbides, and stain resistance.
From Devin Thomas at devinthomas.com:
"Few know what AEB-L steel is, and those that do, only have heard that it is similar to 440B or 440A. The only similarity between AEB-L and 440B or 440A is the amount of carbon. The fact that AEB-L has only 12.8% chromium by weight compared to the 16-17% in 440A and 440B makes the steels quite different. AEB-L is more similar to a stainless 52100 than 440A. A copy of AEB-L called 13C26 is made by Sandvik.
AEB-L naturally forms what is called the K2 carbide, the harder of the two chromium carbides, compared to the K1 carbide, which is formed in steels such as 440C. The K2 carbide is about 79 on the Rockwell C scale, compared to 72 for the K1 carbide. Through proper heat treatment, AEB-L has fine, evenly distributed K2 carbides. AEB-L lies almost perfectly on what is called the "Carbon Saturation Line," which means that all of the carbides formed are precipitated carbides, not primary carbides like are formed in 440C, and there is more carbon and a similar amount of Chromium in solution as compared to 440C. Primary carbides are very large. So, through a balanced composition, AEB-L has excellent toughness, edge retention, workability, ease of sharpening, and ease of polishing."
Learn more about AEB-L at Knife Steel Nerds
D2 tool steel is an air-hardening tool or die steel used to make various cold-work stamping dies for metalwork. It offers excellent hardness, great abrasion resistance, excellent edge retention, and SOME stain resistance. Best sharpened with diamond stones due to high abrasion resistance. Cryo treatment benefits D2 with higher hardness, slightly better edge retention, and abrasion resistance. Not high on toughness, D2 works best in smaller, more robust blades.
Learn more about D2 Steel at Knife Steel Nerds.
52100 steel is a "fast oil" hardening steel developed and still used for ball bearings and bearing races, capable of high hardness and excellent toughness. 52100 is known for taking an extremely fine edge and is my choice for high carbon, low alloy steels for its high working hardness, excellent toughness, and overall balance of properties. Developed in the early 1900s, 52100 has about 1% carbon for high hardness. 1.5% chromium makes this steel more deeply hardenable, and the Chromium also decreases grain size within the steel and slightly increases edge retention. This steel has been used to make many fine knives for years. Previously it was a forging steel, mainly coming in round stock, and from salvaged bearings and races. These days it can be found in flat bars suitable for custom knifemakers who employ stock removal.
52100 is a very tough steel due to the small, evenly distributed carbide throughout the steel matrix. In extensive toughness testing, 52100 comes out on top of O1, 1095, 440C, D2, A2, and many other knife steels held in high regard in the knifemaking world. Its high attainable hardness makes 52100 a great choice when corrosion isn't an issue. I highly recommend it for hard-use Outdoor Knives or in the kitchen when the chef prefers a non-stainless option for a slightly keener edge. To get your custom knife in 52100 steel, visit the Shop NOW.
Learn more about 52100 steel at Knife Steel Nerds.
26C3 steel is a high carbon, low alloy, non-stainless steel. It's called 26C3 in the US, 1.2002 in Germany. Uddeholmstrip produces 26C3 for use as razor and scalpel blades. 26C3 has a very fine grain and carbide microstructure and is exceptionally clean/pure. As such is capable of very high hardness (above 67HRc as-quenched) while maintaining good toughness. High Hardness Carbon Steel Kitchen Knives!
Chefs and professional cooks who prefer carbon steel should consider 26C3, which is very close in composition to Hitachi White #1, a well-known Japanese blade steel. Both steels are extremely clean (low impurities) and have a very high carbon content with low alloying, allowing for extreme hardness in simple carbon steels.
Hard, Yet TOUGH
While high hardness is desirable, good toughness matters too. Toughness determines whether a blade will hold a keen edge or suffer chips. 26C3 holds up well in toughness comparisons, testing equal or better to more mainstream steels such as 1095, O1, M2, A2, and PSF27. I run these chef's knives at 64-65 HRc, and tests show they'll be tougher than D2 at 60 HRC! It's important to note here that this steel is NOT stainless. It will rust and develop pitting very quickly without proper maintenance. It will also develop a patina that many find attractive and quite desirable over time. Refer to "How to Care For Custom Knives" to learn more about the care of carbon steel knives. So if you're looking for a really hard, very fine-grained custom chef's knife, we have the steel for you at Keith Nix Knives! Give me a call today at 828-337-7836...
Learn more about 26C3 at "Knife Steel Nerds."
CPM MagnaCut is a newer steel composition developed by Knife Steel Nerd Author and Metallurgist Dr. Larrin Thomas and produced by Crucible. Explicitly designed as a KNIFE STEEL, MagnaCut is a high hardness, high toughness stainless steel with excellent stain and wear resistance. It is capable of a working hardness in the 63-65HRc range while maintaining excellent toughness. Additions of Vanadium and Niobium help keep grain and carbide size very small and significantly increase edge retention. While it's expensive compared to conventionally produced steels, it offers an outstanding balance of properties not found in any other steel composition.
Learn more about CPM MagnaCut at Knife Steel Nerds HERE!
Learn about CPM technology here!
CPM M4 is a high hardness high-speed tool steel with good toughness and excellent edge retention. Its composition includes 4% chromium, 4% Vanadium, 5.25% Molybdenum, and 5.5% Tungsten. The high carbon improves steel hardness and provides enough carbon to create carbides from the Chromium, Vanadium, Molybdenum, and Tungsten. 4% Chromium improves steel hardenability, tensile strength, and edge retention. 4% Vanadium guarantees fine grain size and increases wear resistance and edge retention with extremely hard, fine carbides. The high 5.25% of molybdenum increases strength and machinability. The Tungsten improves wear and corrosion resistance. CPM technology produces the fine grain and carbides needed to give this steel its excellent toughness. This is SUPER steel, where stain resistance is not a concern.
Learn more about CPM M4 HERE!
What is Cryogenic Treatment?
And What Does It DO??
Simply put, Cryogenic Treatment is a continuation of the "quench", down to -320F. That is, when the knife comes out of the oven at its austenitizing temperature, it is quenched to room temperature according to the standards and protocols for that particular steel. Cryo treatment EXTENDS the quench to -320F. This aids the steel in converting the retained softer phase Austenite to harder and stronger Martensite. Thus we finish the quench with liquid nitrogen, for an hour or overnight. Afterwards, the tempering cycles are performed as usual. Your custom knives deserve the very best heat treat I can give them, and cryogenic treatment improves knife steels in easily measurable ways.
Dr Larrin Thomas wrote a three part article on his blog "Knife Steel Nerds" about cryogenic temperatures and the effect on knife steels. If you're a knife steel nerd like me, click on the link!
Dr Larrin Thomas explains cryo treatment of knife steels