Larrin
Knifemaker / Craftsman / Service Provider
- Joined
- Jan 17, 2004
- Messages
- 4,970
Hello Friends. I have made a grave mistake. You can read my mistake in the title. It should be self-evident. The mistake is using the word Infi within any context. Only a man truly brave would attempt to say anything metallurgically about the mythical steel. Or a truly stupid man. There was a thread a few days back about the composition of Infi but I grew tired of making little headway in that thread and also did not have the patience to provide more complete answers about its composition. Today, on this Friday afternoon where I don't feel like working I have gotten my second wind.
There are two published compositions of Infi:
http://zknives.com/knives/steels/infi(pre_2002).shtml
http://zknives.com/knives/steels/infi.shtml
I am reliant on the information above for those published compositions. I have not checked the original sources. The first says that it was analyzed by "a lab in Germany" and the second was analyzed with "X-Ray SEM" analysis. I believe the lab in Germany used Optical Emission Spectroscopy or a similar technology but I am not sure. OES is pretty common for measuring the bulk composition of steel though there are a couple other technologies used. It is pretty reliable though there are occasional issues with calibration. "X-ray SEM" is likely referring to "Energy-dispersive X-ray spectroscopy" or EDS for short. It is only rarely used for bulk composition measurements of steel because its accuracy is not very high, particularly for light elements like carbon or nitrogen. EDS generates a series of "peaks" that must be identified because most peak locations can be for several elements though in many cases we have some idea of what might be in the steel and can therefore assume that such and such peak is for silicon and not tellurium. I would not personally use EDS to measure the bulk composition of steel except for getting a broad idea of composition. I have used it to give the approximate chromium and molybdenum "in solution" for a few steels: https://knifesteelnerds.com/2018/03/16/micrographs-of-niolox-cpm-154-and-aeb-l/ EDS is the best method for determining alloy in solution and Cr and Mo are good elements for detecting with EDS, at least in sufficient amounts.
Busse apparently confirmed that nitrogen and cobalt were indeed removed between the first and second reported compositions, though honestly if Busse had not confirmed that fact I would not necessarily see EDS measurements as definitive in terms of showing that no nitrogen is present. The original steel is also reported to have nickel in it, above the levels that are typically present due to the common use of recycled steel. The new composition analysis does not show nickel though that could also be due to the small amount not being detected through EDS.
What is A8 mod? A8 mod or chipper knife steel is used for wood chippers. It is called "mod" because it has ~8% Cr rather than 5% in regular A8. Regular A8 also has a small tungsten addition which is lacking in A8 mod. The increase in Cr gives A8 mod a little less toughness but better wear resistance than A8. A8 mod has a good balance of toughness and wear resistance and seems like a fine choice for chopping knives. The reported composition can be found here: http://cdna.terasrenki.com/ds/1.2631_X50CrMoW9_AISI-L8_LSS-Chipper-Knife_Datasheet_3.pdf I am aware of no official composition or agreed upon composition ranges for A8 mod or chipper knife steel. It is somewhat of an industry standard but does not have an official specification. Therefore the composition of A8 mod can be a little blurry.
The Latrobe A8 mod composition is: 0.5C-8.0Cr-1.3Mo-0.45V-1.3Mo. It also has Mn and Si which are present in virtually all tool steels in some amount up to 1% or so. Both Mn and Si are missing from the pre-2002 Germany analysis and Mn is missing from the newer EDS analysis. Neither of those measurements can be taken as confirmation that Mn and Si is missing from the steel, as it would be very surprising for them to be missing.
The pre-2002 Germany analysis shows 0.5% C and the newer EDS shows 0.63%. Obviously the earlier analysis is dead on with A8 mod and the newer is perhaps a little high. I am aware of no published ranges of composition for A8 mod, for reference the A2 standard specifies 0.95-1.05%C acceptable though some steels are wider like 440C with 0.95-1.2%C. Because EDS is notoriously poor at getting accurate measurements for light elements like carbon, the value could very well be significantly off.
The pre-2002 analysis shows 8.0% Cr and the newer EDS shows 8.12%. Both are well within tolerances for A8 mod, for comparison the A2 standard is 4.75-5.5%. The pre-2002 measurement shows 1.3% Mo and the EDS shows 0.85%. The EDS value is again a little off but I'm not sure if that is due to an actual change from A8 mod or simply again due to the limitations of EDS. Vanadium measurements from both are in the mid 0.30s% which is within tolerance for a 0.45% vanadium target such as given in the Latrobe datasheet or perhaps the target for whatever company is making Infi is a little different.
So is Infi the same as A8 mod? At the very least it is in the same "family" of A8 mod-like steels with medium carbon, ~8% Cr, Mo, and V. Perhaps one could argue that if it is modified with Co and Ni then it would no longer be the same steel. If there was a patent for A8 mod (I can't find one), then it would certainly state that Co and Ni additions would fit within the patent. If it had been patented it would be long expired now. You can't just add small amounts of certain elements to get around patents because you would have to demonstrate that the addition is greater than is allowed by the patent and also that there is some significant change to the material's behavior to require the difference. But it would still be in the same family, or class, or material. Steels are often grouped into familes such as the A-series of steels which are air hardening steels usually with around 5% Cr like A2. Or the high chromium D-series like D2. My personal view is that if reports are correct that the Co and Ni were removed for the "new" Infi then it is either A8 mod, or such a small modification of A8 mod (A8 mod mod, if you will) that the difference is hardly worth writing home about. It is a medium carbon 8% Cr steel in the Chipper knife steel family.
There are two published compositions of Infi:
http://zknives.com/knives/steels/infi(pre_2002).shtml
http://zknives.com/knives/steels/infi.shtml
I am reliant on the information above for those published compositions. I have not checked the original sources. The first says that it was analyzed by "a lab in Germany" and the second was analyzed with "X-Ray SEM" analysis. I believe the lab in Germany used Optical Emission Spectroscopy or a similar technology but I am not sure. OES is pretty common for measuring the bulk composition of steel though there are a couple other technologies used. It is pretty reliable though there are occasional issues with calibration. "X-ray SEM" is likely referring to "Energy-dispersive X-ray spectroscopy" or EDS for short. It is only rarely used for bulk composition measurements of steel because its accuracy is not very high, particularly for light elements like carbon or nitrogen. EDS generates a series of "peaks" that must be identified because most peak locations can be for several elements though in many cases we have some idea of what might be in the steel and can therefore assume that such and such peak is for silicon and not tellurium. I would not personally use EDS to measure the bulk composition of steel except for getting a broad idea of composition. I have used it to give the approximate chromium and molybdenum "in solution" for a few steels: https://knifesteelnerds.com/2018/03/16/micrographs-of-niolox-cpm-154-and-aeb-l/ EDS is the best method for determining alloy in solution and Cr and Mo are good elements for detecting with EDS, at least in sufficient amounts.
Busse apparently confirmed that nitrogen and cobalt were indeed removed between the first and second reported compositions, though honestly if Busse had not confirmed that fact I would not necessarily see EDS measurements as definitive in terms of showing that no nitrogen is present. The original steel is also reported to have nickel in it, above the levels that are typically present due to the common use of recycled steel. The new composition analysis does not show nickel though that could also be due to the small amount not being detected through EDS.
What is A8 mod? A8 mod or chipper knife steel is used for wood chippers. It is called "mod" because it has ~8% Cr rather than 5% in regular A8. Regular A8 also has a small tungsten addition which is lacking in A8 mod. The increase in Cr gives A8 mod a little less toughness but better wear resistance than A8. A8 mod has a good balance of toughness and wear resistance and seems like a fine choice for chopping knives. The reported composition can be found here: http://cdna.terasrenki.com/ds/1.2631_X50CrMoW9_AISI-L8_LSS-Chipper-Knife_Datasheet_3.pdf I am aware of no official composition or agreed upon composition ranges for A8 mod or chipper knife steel. It is somewhat of an industry standard but does not have an official specification. Therefore the composition of A8 mod can be a little blurry.
The Latrobe A8 mod composition is: 0.5C-8.0Cr-1.3Mo-0.45V-1.3Mo. It also has Mn and Si which are present in virtually all tool steels in some amount up to 1% or so. Both Mn and Si are missing from the pre-2002 Germany analysis and Mn is missing from the newer EDS analysis. Neither of those measurements can be taken as confirmation that Mn and Si is missing from the steel, as it would be very surprising for them to be missing.
The pre-2002 Germany analysis shows 0.5% C and the newer EDS shows 0.63%. Obviously the earlier analysis is dead on with A8 mod and the newer is perhaps a little high. I am aware of no published ranges of composition for A8 mod, for reference the A2 standard specifies 0.95-1.05%C acceptable though some steels are wider like 440C with 0.95-1.2%C. Because EDS is notoriously poor at getting accurate measurements for light elements like carbon, the value could very well be significantly off.
The pre-2002 analysis shows 8.0% Cr and the newer EDS shows 8.12%. Both are well within tolerances for A8 mod, for comparison the A2 standard is 4.75-5.5%. The pre-2002 measurement shows 1.3% Mo and the EDS shows 0.85%. The EDS value is again a little off but I'm not sure if that is due to an actual change from A8 mod or simply again due to the limitations of EDS. Vanadium measurements from both are in the mid 0.30s% which is within tolerance for a 0.45% vanadium target such as given in the Latrobe datasheet or perhaps the target for whatever company is making Infi is a little different.
So is Infi the same as A8 mod? At the very least it is in the same "family" of A8 mod-like steels with medium carbon, ~8% Cr, Mo, and V. Perhaps one could argue that if it is modified with Co and Ni then it would no longer be the same steel. If there was a patent for A8 mod (I can't find one), then it would certainly state that Co and Ni additions would fit within the patent. If it had been patented it would be long expired now. You can't just add small amounts of certain elements to get around patents because you would have to demonstrate that the addition is greater than is allowed by the patent and also that there is some significant change to the material's behavior to require the difference. But it would still be in the same family, or class, or material. Steels are often grouped into familes such as the A-series of steels which are air hardening steels usually with around 5% Cr like A2. Or the high chromium D-series like D2. My personal view is that if reports are correct that the Co and Ni were removed for the "new" Infi then it is either A8 mod, or such a small modification of A8 mod (A8 mod mod, if you will) that the difference is hardly worth writing home about. It is a medium carbon 8% Cr steel in the Chipper knife steel family.
