All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (2023)

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Update 10/22/2020: I now have an article with how to heat treat D2, PSF27, and CPM-D2 and it also includes toughness testing of each steel and edge retention testing of D2. https://knifesteelnerds.com/2020/08/31/how-to-heat-treat-d2-psf27-and-cpm-d2/

D2 Steel

D2 is a common tool steel and knife steel. It is also known by other names such as the Japanese designation SKD11, German designation 1.2379, Hitachi SLD, Uddeholm Sverker 21, and many others. How long has it been around? Where did it come from? Who started using it in knives? How do its properties compare to other steels? Find your answers here!

Early Chromium Steels

The development of D2 steel coincides in part with the invention of stainless steel as well as high speed steel. You can read an article about the history of stainless steel here or the history of high speed steel here. D2 is part of a tool steel category called “high carbon, high chromium” steels. The production of chromium-alloyed steel wasn’t practical until ferrochromium was developed in 1821 and more practically in 1895 with the development of low carbon ferrochromium. The first commercially produced steel with a chromium addition was in 1861 by Robert Mushet, the inventor of the first tool steel [1]. A patent on chromium steel was granted to Julius Baur in New York in 1865 [1]. Robert Hadfield reported on the properties of chromium-alloyed steels in 1892 and also covered high carbon, high chromium steels which were in their infancy [2]. However, he concluded that the forgeability of the alloys was poor and often cracked, and said that a steel with 1.27% C and 11.13% Cr was at the limit.

Development of High Carbon, High Chromium Steels

After 1900 the number of people experimenting with chromium steels and tool steels in general exploded [1]. That date coincides with the discovery of high speed steels that I linked above. Also early in that period they developed high speed steels which used Cr-alloying rather than Mn-alloying for hardenability, where they used about 4% Cr. They also added large amounts of tungsten for hot hardness. The period of rapid development that occurred in the period shortly after 1900 is very difficult to nail down. Many companies and people were developing steel, and there was also widespread copying. James Gill (read about him here) writing in 1929 reported that he could not find which company was the first to produce high-carbon high-chromium steel [1]. In Becker’s High Speed Steel book in 1910 he reported that a steel with 2.25% C and 15% Cr was being used in Europe, particularly in France. In the USA a patent was granted in 1916 to Richard Patch and Radclyffe Furness for steel with 1-2% carbon and 15-20% chromium [3]. They gave an example composition of 1.35% C and 19.5% Cr which looks like it would be a stainless steel but was not patented as such. In the patent they stated that they had only heard of steels with carbon above 2% and chromium between 12-16%. High carbon, high chromium steels were frequently used in England during World War I for a range of applications including dies and cutting tools [4]. Cutting tools were more typically produced with high tungsten high speed steel at the time because of the superior hot hardness with high speed steel. You can read about hot hardness in the article on high speed steel. However, tungsten was expensive and difficult to obtain leading to the use of high chromium steel as an alternative. Those early high carbon high chromium steels were more similar to the modern D3 or D4 steels rather than D2 because their carbon content was higher, around 2.2-2.4%.

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (1)

Development of D2

In 1918 a patent was filed in England by Paul Kuehnrich [5] for a high carbon high chromium steel modified with cobalt, approximately 3.5%. The cobalt addition was to improve the hot hardness of the steels so that they were closer to high speed steel. You can read more about what cobalt does to steel in this article. The patent has fairly broad chemistry ranges: 1.2-3.5% carbon, 8-20% chromium, and 1-6% cobalt. However, interestingly the example alloy given had 1.5% C, 12% Cr, and 3.5% cobalt which without the cobalt would be very close to modern D2.

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While in the USA the high carbon high chromium steels were not used as a replacement of high speed steel, it did gain in popularity with die steels. Die steels required high wear resistance which was gained through the large amounts of chromium carbide present in those steels. These were initially the D3-type 2.2-2.4% chromium steels which had relatively poor toughness and machinability. These steels also did not typically contain vanadium or molybdenum. A composition consistent with D2 was not reported by Gill in 1929 [1] so even if it existed by that point it was likely not in widespread use.

Update 4/11/2019:I finally found the patent for D2, the application was filed June 30, 1927 by Gregory Comstock of Firth-Sterling Steel company. Comstock, Gregory J. “Alloy steel.” U.S. Patent 1,695,916, issued December 18, 1928.

By 1934 a composition consistent with D2 was discussed with 1.55% C, 12% Cr, 0.25% V, and 0.8% Mo [6]. It wasn’t yet named D2, of course. The molybdenum was added to make it a true “air hardening” steel which allows the steel to fully harden in thick sections or without oil. Without Mo, the high Cr did make the steel quite hardenable but not enough to make it truly air hardening. The vanadium addition was made to improve toughness which it does by refining both the grain size and also the carbide structure. This new D2-type steel was gaining in popularity because of its “air hardening property, low distortion and better machining quality than the other [high carbon, high chromium steels]” [6]. It was also reported to be, “the most universally adaptable of the…high carbon high chromium steels” [6]. And as mentioned previously the lower carbon meant much greater toughness than the earlier D3-like steel which you can see in the figure below. Vanadium and nickel additions had been experimented with the D3-type, 2.2% carbon steel, but while that improved toughness, the lower carbon D2 was much tougher.From that point D2 became one of the most popular tool steels, particularly in dies. New “better” steels made for dies continue to be compared to D2 because of its ubiquity.

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (2)

D2 in Knives

It took some time before D2 was used in knives. The first recorded use I can find is by D.E. Henry in 1965 or 1966 [7][8]. He tried the higher carbon D3 first followed by D2, unintentionally mimicking the order in which they were developed. Due to its popularity as a tool steel, it was only a matter of time before someone used D2. Its relatively high wear resistance along with good hardness and toughness made it work well as a knife steel. With its high chromium content it had a unique position in the stainless vs carbon steel debate. D2 has somewhat better wear resistance and toughness than 440C, the most commonly used stainless steel in the 70’s, so for makers who felt that the stain resistance of D2 was “good enough” it could offer superior properties. You can read more about how corrosion resistant D2 is in this article. It also had much greater wear resistance than the carbon steels commonly used by forging bladesmiths, so was used by some knife makers that wanted a high wear resistance steel.D2 has since been used in many knives, famously by makers such as Bob Dozier.

Carbide Structure of D2

The large carbides in D2 limits its toughness and also its edge stability. A powder metallurgy version, CPM-D2, was released around 2007 [9] to reduce the carbide size, which is reported to improve the toughness, corrosion resistance, and heat treatment response. You can read more about why D2 has large carbides andthe powder metallurgy process in this article. Sprayform is a somewhat similar technology that leads to a somewhat larger carbide size than powder metallurgy. There is a sprayform version of D2 called PSF27 produced by Dan Spray in Denmark, made at least since 2002 [10]. You can see the decreasing carbide size in conventional (well, ESR anyway), spray form, and PM D2 in the images below [10]. Note the PM is at a higher magnification.

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (3)

Those are pretty low resolution micrographs. I took micrographs of D2, PSF27, and CPM-D2 which are shown below:

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (4)

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Conventional D2

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (5)

PSF27

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (6)

CPM-D2

Properties of D2

Bohler Uddeholm measured the edge retention of D2 along with other steels with CATRA testing and found it to be somewhat better than N690, ATS-34/154CM, and 440C, on par with 3V, but worse than S35VN, Vanadis 4 Extra, Elmax, S30V, M4, and M390 [11]. I also calculated the edge retention relative to 440C which is a value that Crucible has reported in the past.

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (7)

Crucible reports that D2 has toughness roughly equivalent to 10V, better than 440C and S90V, but worse than 3V, CruWear, and A2 [12][13][14].

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (8)

In our toughness testing D2 was not very impressive though we have only tested one heat treatment and have not compared to many other low toughness steels like 10V, 440C, and S90V:

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All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (9)

I previously wrote about the potential corrosion resistance of D2 in this article. Its corrosion resistance has been somewhat over-promoted in some cases because of its high chromium content. Approximately half of that chromium is tied up in carbides where it doesn’t contribute to corrosion resistance. Therefore, it has good corrosion resistance for a tool steel, though there are some non-stainless steels that potentially have better corrosion resistance, particularly many of the 8% Cr steels like 3V or CruWear. Here is the chart from that article with the steels ranked by “chromium in solution” which is approximately equal to the corrosion resistance of each steel:

All About D2 Steel - Development, Use in Knives, and Properties - Knife Steel Nerds (10)

D2 in Knives Today

D2 continues to see use in knives; a search on BladeHQ brings up 1,690 available knives in D2. Knifemakers like Bob Dozier have built their reputation on making a superior knife with D2. With the rise of powder metallurgy vanadium-containing steels, there are now other options with both higher wear resistance and toughness. Or powder metallurgy stainless steels that can match or exceed its wear resistance and toughness but with better corrosion resistance. Powder metallurgy steels are much more expensive than D2, as D2 is conventionally produced and widely available from virtually every tool steel company. Therefore from a cost perspective D2 still has an advantage over many newer steels. The newer sprayform and PM versions of D2 help to make up some of the difference in properties relative to other powder metallurgy steels. Due to its good properties and reputation built over decades, D2 will likely continue to be seen in knives.

Conclusions

High carbon, high chromium steel was developed as an alternative to high speed steel in England in the early 20th century. These steels were similar to the modern D3 tool steel with very high carbon (2.2%). The carbon was reduced to 1.5%, and additions of Mo and V were made to improve the toughness and hardenability of the steel which was in use by 1934. This steel became what we know as D2, which is popular as a die steel. The steel was first used in knives by D.E. Henry in 1965 or 1966 and became popular in knives. Sprayform and powder metallurgy version have been produced to improve the toughness and refine the microstructure of D2. D2 has good wear resistance, hardness, and adequate toughness.

[1]Gill, J. P. “High-carbon high chromium steels.”Trans. ASST15 (1929): 387-400.

[2]Hadfield, Robert Abbott. “Alloys of Iron and Chromium, Including a Report by F. Osmond.”J. Iron Steel Inst.42 (1892): 49.

[3]Patch, Richard H., and Radclyffe Furness. “Tool-steel alloy.” U.S. Patent 1,206,902, issued December 5, 1916.

[4]Gill, James Presley, Robert Steadman Rose, George Adam Roberts, Harry Grant Johnstin, and Robert Burns George.Tool steels. American Society for Metals, 1944.

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[5]Kuehnrich, Paul Richard. “Steel.” U.S. Patent 1,277,431, issued September 3, 1918.

[6]Wills, W. H. “Practical Observations on High-Carbon High-Chromium Tool Steels.”Trans. ASM23 (1935): 469.

[7]Warner, Ken.Knives,’84. DBI Books, 1983.

[8]Henry, D.E.Collins Machetes and Bowies, 1845-1965. Krause Publications, 1995.

[9] https://www.bladeforums.com/threads/cpm-d2.470623/

[10]Schruff, I., V. Schüler, and C. Spiegelhauer. “Advanced tool steels produced via spray forming.”The Use of Tool Steels: Experience and Research2 (2002): 973-990.

[11] https://knifesteelnerds.com/wp-content/uploads/2018/08/Bohler-Uddeholm-CATRA.pdf

[12]https://www.alphaknifesupply.com/Pictures/Blade-Steel/CPMS90V-Crucible.pdf

[13]http://www.crucible.com/PDFs/DataSheets2010/ds10Vv1%202010.pdf

[14]http://www.crucible.com/PDFs/DataSheets2010/dsD2v12010.pdf

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Related

FAQs

What is D2 tool steel for knives? ›

D2 steel is air hardened and contains between 10% and 13% chromium (which is unusually high). D2 steel has a hardness in the range of 55 to 62 HRC, which makes is a very durable and high- end knife steel. D2 steel will retain its hardness up to a temperature of 425 °C (797 °F).

Is D2 steel good for making knives? ›

D2 in Knives

Due to its popularity as a tool steel, it was only a matter of time before someone used D2. Its relatively high wear resistance along with good hardness and toughness made it work well as a knife steel.

What is D2 tool steel used for? ›

D2 tool steel is often used to make blanking dies, cold forming dies, stamping dies, slitters, punches, trim dies and thread rolling dies for applications when exceptional toughness is not necessary.

Is D2 better than VG10? ›

VG10 VS D2

VG offers better Edge retention, and corrosion sharpness compared to the D2, but for toughness, d2 is better since it's high carbon steel.

Why are D2 knives good? ›

The D2 steel has a high wear resistance, hardness, and good toughness, which make it an excellent choice for knife makers, and if you do a little search on the market (example: go to baldehq.com) you 'll find out how cheap are the knives compared to their high quality, but it doesn't mean that the D2 is better than the ...

What quality is D2 steel? ›

D2 steel is an air hardening, high-carbon, high-chromium tool steel. It has high wear and abrasion resistant properties. It is heat treatable and will offer a hardness in the range 55-62 HRC, and is machinable in the annealed condition. D2 steel shows little distortion on correct hardening.

Is Chinese D2 steel any good? ›

D2 Steel – This steel This is not technically Stainless, but Tool Steel. However, it Because of this it has good rust resistance. It is much tougher than most stainless steels, but not as tough as most of the other tool steel. This steel does have excellent wear resistance.

Is D2 better than AUS 8? ›

D2 is higher-quality steel that is harder and has better edge retention than AUS-8, but D2 does not have as much corrosion resistance. AUS-8 is the opposite. So, if you're looking for a cheaper, more water-resistant knife, go with AUS-8. If you want a high-end, less water-resistant knife, go with D2.

Does D2 take a good edge? ›

D2 Durability:

In the realm of steel, having a high hardness is the ideal recipe for having an excellent edge retention. With the D2 tool steel, this is the case. It has a high carbon content, which makes it harder and allows it to maintain a sharp edge for a lot longer than other inexpensive steels.

What is D2 steel composition? ›

Chemical Composition
ElementContent (%)
Mn0.60
Si0.60
Co1.00
Cr11.00 – 13.00
7 more rows
13 Sept 2012

What type of steel is D2 steel? ›

What is D2 Tool Steel? D2 tool steel is an air-hardening, high carbon, high chromium tool steel with extremely high wear-resisting properties.

Is D2 carbon steel good for knives? ›

The high wear resistance and edge retention make D2 steel a perfect choice for knives. You might struggle a bit with sharpening, but D2 knives are quality and affordable options.

Is D2 better than 420HC? ›

Here is the short answer: D2 is harder and has better edge retention, but 420HC has a lot better corrosion resistance. If you wanted a knife that had good corrosion resistance then you would want 420HC, but if you were looking for edge retention and durability then you would want D2.

Is D2 steel better than S30V? ›

S30V is a higher-tier knife steel compared to D2. It generally has higher corrosion resistance, toughness, ease of sharpening, and edge retention. It's a really well-balanced steel, but it's more expensive. D2 is cheaper, but not as good as S30V as it rusts easier and is harder to sharpen.

Does D2 steel hold an edge? ›

While D2 may not be stainless, it remains a top performer due in no small part to its high wear resistance/edge-holding ability. “It will hold an edge for a very long time before it will go dull,” says Paul Tsujimoto, director of engineering at Ontario Knife Co.

Is D2 carbon steel good for knives? ›

The high wear resistance and edge retention make D2 steel a perfect choice for knives. You might struggle a bit with sharpening, but D2 knives are quality and affordable options.

Is D2 better than S35VN? ›

Well, here's the short version: CPM-S35VN is better than D2. It has more edge retention, corrosion resistance, ease of sharpening, and about the same toughness. The main difference between the two is that D2 rusts easier.

Is D2 steel better than stainless steel? ›

D2 Steel – This steel This is not technically Stainless, but Tool Steel. However, it Because of this it has good rust resistance. It is much tougher than most stainless steels, but not as tough as most of the other tool steel. This steel does have excellent wear resistance.

Is D2 better than 420HC? ›

Here is the short answer: D2 is harder and has better edge retention, but 420HC has a lot better corrosion resistance. If you wanted a knife that had good corrosion resistance then you would want 420HC, but if you were looking for edge retention and durability then you would want D2.

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