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Hitachi Carbon Steels for Knives

Discussion in 'Shop Talk' started by Rick, Nov 12, 2017.

  1. Rick

    Rick aka Pensacola Tiger Founding Member Gold Contributor

    There was a question about white #1 and white #2 on another forum that made me think that an explanation that Jon Broida (of Japanese Knife Imports) made in 2012 might be of interest here, so I'm reposting what Jon wrote.

    Hitachi makes a number of carbon steels. Here are the common ones found in knives.

    SK Steels (SK5, SK4, SK3) - the least expensive of the carbon steels and the lowest carbon content (#5 has the least carbon, #3 the most). This steel has higher amounts of phosphorus and sulfur than the other steels i'm about to mention. This steel tends to be tough (due to the lower carbon content and thus lower hardness). It also tends to be more reactive.

    Yellow Steel (Yellow 3, Yellow 2) - This steel is more pure (less phosphorus and sulfur than the SK Steels). It also has higher carbon content (#3 has less carbon than #2 in this case as well). This steel is commonly found in saws and wood working tools. It is also sometimes found in knives.

    White Steel (White 3, White 2, White #1) - This steel is even more pure than yellow steel (which is relatively pure). Once again, the lower the number, the higher the carbon content, so white #1 has the most carbon and white #3 has the least. The higher carbon (and hardness) leads to white #1 having the best edge retention of the white steels and also the best ability to hold an acute angle. White #3 has the best toughness.

    Blue Steel (Blue #2 and Blue #1... i'll talk about blue super later) - Blue steel is white steel with chromium and tungsten added to it. Blue #2 has the same amount of carbon as white #2 but has the added elements. Same for blue #1 and white #1. The added elements lead to better corrosion resistance and edge retention (as well as deeper hardening). This also comes at the cost of being more difficult to sharpen and not taking quite as keen of an edge. Blue steel also tends to be more brittle (ever so slight).

    Blue Super - Blue super is blue #1 with even more carbon, chromium, and tungsten added to it. Its the best of the hitachi carbon steels with regard to edge retention and ability to hold an acute angle (due to the higher carbon/hardness and added elements). This comes at the cost of being more difficult to sharpen, not getting quite as sharp, and being the most brittle of the bunch.

    So, in conclusion, the white steels take the best edge (#1 holding the most acute angle and #3 being the toughest), while the blue steels hold the best edge (Blue super being the best at this while blue #2 and #1 have better toughness).
     
  2. HHH Knives

    HHH Knives Professional Craftsman Founding Member

    Awesome post. and very accurate information. Jon knows his stuff!
     
  3. Thanks for that Rick.

    A bit off topic but related I think - I have never seen a white3 honyaki that is quenched in water, they seem to be always in oil.

    I am aware of the difference in oil quenching vs water quenching. So is this because white3 cannot 'handle' (for the lack of a better term) being quenched in water?
     
  4. MotoMike

    MotoMike Founding Member

  5. Rick

    Rick aka Pensacola Tiger Founding Member Gold Contributor

    A good question. I haven't seen one, either. Perhaps someone with the answer will reply.
     
  6. I've not worked with it but looking at the composition, it's sort of similar to 1084 but a bit cleaner. Water is faster than needed for 1084 quenching, so I bet the same holds for W#3. So it can work but you risk losing a lot of blades to the "tink of death". :eek::(

    Also, W#3 honyaki probably do not sell for as much price as other steels? So that combined with a high failure rate may make the mizu-honyaki version rarer to see. This is just conjecture on my part based on metallurgy.
     

  7. Makes an awful lot of sense.

    Out of curiosity, what makes the lower carbon white3 more susceptible to the 'tink if death', compared to a slightly higher carbon white2?
     
  8. I don't know if it's actually more susceptible to cracked blades in water quench versus white 2 or 1 but maybe that it's so amenable to oil quench that the bladesmiths prefer not to risk water quench with this steel? Especially if there isn't as high a premium for honyaki in W#3... I'm just guessing tho...
     
  9. understood. so the rationale is economical rather than metallurgical
     

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