13 Myths about Heat Treating Knives

PEU said:
I always tell customers and colleagues that flexibility is not a function of hardness but of thickness and most of the times I get that face when someone is not sure to believe you... Now I have a place to send them so they can check by themselves. Thanks Larrin.

Here a 60RC O2 steel filleting knife bent 90 degrees.

Pablo

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I can bend an Rc64 z-wear fillet style knives to 90deg. People don’t believe this, even when I show them.
 
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I wouldn’t necessarily equate descending forging temperatures with descending normalizing cycles. They are somewhat different processes.
 
I think uneven heating during forging is an issue. I always figured there wasn't much good going on between the tang that remained black for the last 10 heats in contrast to the blade that was yellow, so everything gets a regular normalizing cycle when it's done in the forge.
 
Larrin said:
I wouldn’t necessarily equate descending forging temperatures with descending normalizing cycles. They are somewhat different processes.
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I suspect this is where that myth originated from. Japanese smiths and even info on hitachi white say this is for grain refinement.
 
Using sufficiently low forging temperatures may very well help with refining grain but it’s not the same as normalizing. Where is this Hitachi White information?
 
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Just to be clear, I wasn't equating forging at reducing heats to normalizing. After forging, most Japanese makers do a DET anneal, without any high heat normalizing. So that was where my question was coming from.
 
Larrin said:
Using sufficiently low forging temperatures may very well help with refining grain but it’s not the same as notmalizing. Where is this Hitachi White information?
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It used to be available on the dictum website. I don’t see it now. They send a paper, like a datasheet with the steel when you buy it. I couldn’t find it in the shop now that I moved everything around.
 
I heat treated a 5160 knife in used synthetic motorcycle racing oil.....

Turned out surprisingly good for a $20 BBQ grill heat treat with a magnet and mystery quench!!

Maybe I'll call it racing quench!!
 
samuraistuart said:
Take a look at this one, Warren....
https://oldbritva.ru/wp-content/uploads/2016/09/Yasuki-steel.pdf

"To maintain the highest quality crystalline structure, we recommend completing the final steps of forging at a somewhat reduced temperature (750°C/1382°F) and a higher frequency of hammer blows."
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Some of that data comes from Hitachi but I’ve never seen Hitachi give forging temperature recommendations. That might have been made up by the company doing that sheet.
 
Larrin said:
Some of that data comes from Hitachi but I’ve never seen Hitachi give forging temperature recommendations. That might have been made up by the company doing that sheet.
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I do have a data sheet from Hitachi in Japanese. It recommends an initial forging temperature of 850-900 C and a final forging temperature of 750 C for its steels having 1-1.4% carbon. It also does not list a normalizing temperature, which I always thought was interesting (it may simply be because this steel is made specifically for the Japanese knife industry and normalizing was never part of their process; I don't know). For heat treating, it only gives recommended annealing, hardening, and tempering temperatures.

Added: It also lists an absolute maximum temperature of 1060-1090 C for its steels having 1-1.2% carbon and 1050-1080 C for 1.2-1.4% carbon. For forge-welding to mild steel, it recommends that the mild steel should be around 1,100 C and the steel should be 900-950 C. This can be accomplished with kataha (two-layer blades) in a forge that has higher temps near the bottom (such as a coke forge), or it can be done with warikomi (hotdog in a bun weld) blades, in both cases with the mild steel being on the bottom. I am not sure how it can be done with sanmai. Ideally, from what I have seen in Japan, the billet it taken to welding heat and rapidly reduced under a power hammer.
 
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So who has a forge that can accurately and evenly heat a 15" blade? It seems like that a Hitachi forging info is highly dependent on accurate forging temps.
 
Tenebr0s said:
I do have a data sheet from Hitachi in Japanese. It recommends an initial forging temperature of 850-900 C and a final forging temperature of 750 C for its steels having 1-1.4% carbon. It also does not list a normalizing temperature, which I always thought was interesting (it may simply be because this steel is made specifically for the Japanese knife industry and normalizing was never part of their process; I don't know). For heat treating, it only gives recommended annealing, hardening, and tempering temperatures.

Added: It also lists an absolute maximum temperature of 1060-1090 C for its steels having 1-1.2% carbon and 1050-1080 C for 1.2-1.4% carbon. For forge-welding to mild steel, it recommends that the mild steel should be around 1,100 C and the steel should be 900-950 C. This can be accomplished with kataha (two-layer blades) in a forge that has higher temps near the bottom (such as a coke forge), or it can be done with warikomi (hotdog in a bun weld) blades, in both cases with the mild steel being on the bottom. I am not sure how it can be done with sanmai. Ideally, from what I have seen in Japan, the billet it taken to welding heat and rapidly reduced under a power hammer.
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Can you scan the datasheet and share it?
 
I find it interesting that a lot of highly experienced Japanese smiths do the cold forging, is that what we are talking about with the White steel? I have an old datasheet somewhere in the shop...

Great article Larrin! Thanks for taking the time to do all of this. Awesome web site too!
 
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