Recommendation? Blue #2 Hardening Temperature

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Tenebr0s

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The materials from Hitachi indicate a fairly broad austenitizing range for Blue #2 (780 C - 830 C). To some extent, I understand that this may be to allow for water vs oil quenchants (I have seen both here in Japan for Hitachi blue). Murray Carter recommends 810 C. Another smith here says that 825 C is required to bring out the best qualities of this steel. Yet another I know recommends 800 C. Other than increasing hardenability for an oil quench, what are the advantages of the higher austenitizing range? It’s not hot enough to dissolve any of the tungsten carbides - and I’m not even sure it hot enough to dissolve the small amount of chromium carbides.
 
Will you be using a forge or a furnace to heat the steel?

Are you planning on a water or oil quench?

You are correct, use the higher end of the range for an oil quench.

Hoss
 
I heat treat with a kiln with good temperature control. I have a fast oil, but I’ve been experimenting with water lately. I’ve had great results in water, quenching from 800 C. Kind of scared to push it higher than that, if there’s no benefit from the higher temps.
 
The goal is not to dissolve the Cr or W carbides. Chromium carbides begin to dissolve roughly around 1650°F/900C and Tungsten carbides even higher than that. * That would blow the grain up and put WAAAY too much carbon in solution, and the hardness would be lower than what you're after. The goal is to put just enough carbon in solution to get the max hardness, and leave the rest of the carbon tied up in those Cr and W carbides. I use 1490°F/810C with a 15 minute soak, Parks 50 fast oil at 90°F/32C and get a good 66-67HRC. 400°F/200C tempers results ~63HRC. 800C thru 825C (1475°F-1517°F) isn't a huge range of temperature. But I have always been taught that with the low alloy hyper-eutectoid steels that exceeding 1500°F/815C puts too much carbon in solution, increasing retained austenite, and gives more plate martensite vs lathe martensite. This was evident with 52100 HRC testing, as there was a sweet spot around 1475°F/800C. The post quench hardness would rise as samples were quenched approaching that temp, and then the hardness would drop off as samples were quenched above that temp. If you have a hardness tester, you can try this for yourself and see what sweet spot your particular batch of Blue 2 lies at. I don't have a hardness tester, but have hardened/quenched Blue 2 knives at 1475°F/800C and also at 1490°F/810C. Both temps gave me excellent results.

*There is so little Chromium in Blue 2 I wouldn't expect much in the way of Chromium carbides. I think that small % is there to aid in heat treating. There is, however, a fair bit of Tungsten, of which the WC gives Blue steel it's wear resistance.
 
I use the same parameters as Stuart - 1485F, 15 minute soak, quench in room temp #50, double temper at 400F one hour each.
 
There are no chromium carbides. Even 52100 with 1.5% Cr is still cementite.
 
Thanks all for the replies.

I have trouble wrapping my brain around how alloying works. My understanding was that free chromium is what increases hardenability, so now I understand how the addition makes sense in blue steel if it's not forming carbides. So other than oil vs. water, there's no benefit to austenitizing in the higher range?

I'm puzzled by the numbers for white vs blue steel (white is given a minimum austenitizing temperature of 760 C, and 780 C for blue). If blue has better hardenability, why the higher temperature? Is it necessary for the free chromium to go into solution?
 
760C is only 1400F and 780C is only 1436F. Those are extremely low austenitizing temperatures, even for a "minimum". I found the link....http://www.hitachi-metals.co.jp/e/yss/search/aogami2.html. Note that they say 780C temp is for a water quench, while the 830C is for oil quench. Because we commonly use Parks 50 for shallow hardening steels, which mimics the speed of water, we use the lower hardening temps. Still, 780C is extremely low, and would be surprised if post quench hardness would be 66HRC+ with such a low temp. Just off my head, I wouldn't think enough carbon would be in solution (for max hardness) at that temperature.

The Hitachi data sheet that came with the Blue 2 I received had a recommended austentizing temperature of 1530F/832C (and an oil quench). That was a data sheet provided for that particular batch of Blue 2, direct from Hitachi/Yasuki. I also normalize and cycle Blue 2, just for peace of mind that any heavy spheroidizing/annealing is undone.

To try and answer the last question, I think higher temps are given because Blue 2 is often oil quenched, and the "oil" they're talking about likely is NOT a fast oil. If using a fast oil like P50 or DT48, stick with the lower hardening range.

Larrin....a few years ago I came across how there are no primary chromium carbides in 52100. Instead, you have "chromium-rich orthorhombic pro-eutectoid cementite". Say that 5 times fast. I was wondering the same about Blue 2. Like 52100, the carbon content is pretty close, and the alloying % are close, although Tungsten for Blue2 instead of Chromium in 52100. For Blue 2, there is only roughly 1%-1.5% Tungsten. Would Blue 2 contain primary WC? Or would it more than likely be like 52100, and have "Tungsten-rich orthorhombic pro-eutectoid cementite"? I could see Super Blue as having primary WC (tungsten carbides), as the carbon % is much higher (1.5%) and the Tungsten count is higher (2%-2.5%)
 
Larrin said:
If you want I can explain what “chromium-rich orthorhombic pro-eutectoid cementite” is. I wouldn’t use such wordy non-helpful descriptions in my writing.
Click to expand...

Please? I'd like to better understand the role of chromium in 52100
 
Cementite is a carbide formed between iron and carbon, its composition given as Fe3C, or sometimes as M3C because the iron can be partially replaced with other elements, such as chromium. The "M" referring to any metal atom that is part of the cementite structure. Cementite is harder than steel so it contributes to wear resistance. Cementite has an orthorhombic structure, which refers to the arrangement of the atoms. If interested you can see images of the orthorhombic structure: https://www.phase-trans.msm.cam.ac.uk/2003/Lattices/cementite.html. Its orthorhombic structure is not changed by chromium additions so "orthorhombic" is a useless modifier in "chromium-rich orthorhombic pro-eutectoid cementite." The chromium-rich refers to the partial replacement of Fe with Cr in the cementite.

phasediag.jpg

The "pro" in proeutectoid means "before" because in slow cooling from high temperature carbides will form first as it passes from point 4 (only austenite) to 3 and 2 (austenite plus cementite) until it cools to point 1 where the "eutectoid" transformation occurs where both ferrite and cementite form at the same time making pearlite with its alternating ferrite and cementite. Therefore the steel would have a combination of proeutectoid cementite and pearlite after slow cooling from high temperature. The "proeutectoid" cementite forms "before" the "eutectoid" transformation. Steel with sufficient carbon to have that austenite+cementite region have proeutectoid cementite. However, both the "proeutectoid" and "eutectoid" cementite has its iron partially replaced by chromium, so "proeutectoid" is also a useless modifier in "chromium-rich orthorhombic pro-eutectoid cementite." Also proeutectoid is a single word and does not need a hyphen in between pro and eutectoid.

Therefore a better description would be "chromium-rich cementite" or "cementite with partial replacement of iron with chromium."
 
I was just quoting from a Tool Steel book, but agree that such a term is sort of repetitive. Like saying a "cubical cube".

The role of Chromium in 52100 would be to give higher wear resistance over a simple 1% carbon steel that had no chromium. Hence it's application in ball bearings. There are no primary chromium carbides in 52100, but the "chromium rich cementite" would be harder than plain "cementite".
 
samuraistuart said:
I was just quoting from a Tool Steel book, but agree that such a term is sort of repetitive. Like saying a "cubical cube".

The role of Chromium in 52100 would be to give higher wear resistance over a simple 1% carbon steel that had no chromium. Hence it's application in ball bearings. There are no primary chromium carbides in 52100, but the "chromium rich cementite" would be harder than plain "cementite".
Click to expand...
Yes I was criticizing your source not you.
 
Thanks Larrin. I honestly was wondering. As if I could come up with such a term! Sorry for a thread derail from Blue 2. To get back on topic, and thanks to Larrin’s link to his excellent article on Tungsten steels, the simulation does indeed show primary tungsten carbide in Blue2. Albeit very small percentage, and most of the carbide content of Blue2 being cementite.
 
It's interesting that the higher carbon in blue #1 negatively impacts its performance due to the excess of cementite. I wonder if it's not there to account for carbon loss due to diffusion in mild-steel-clad blades. So perhaps there's significantly less cementite in a finished blade of this type.

Larrin, I noticed you didn't list the Takefu VToku steels as having any vanadium, but they do seem to have at least a pinch (up to 0.2 %):
http://www.e-tokko.com/eng_vspe_1_2.htm
 
Tenebr0s said:
It's interesting that the higher carbon in blue #1 negatively impacts its performance due to the excess of cementite. I wonder if it's not there to account for carbon loss due to diffusion in mild-steel-clad blades. So perhaps there's significantly less cementite in a finished blade of this type.

Larrin, I noticed you didn't list the Takefu VToku steels as having any vanadium, but they do seem to have at least a pinch (up to 0.2 %):
http://www.e-tokko.com/eng_vspe_1_2.htm
Click to expand...
It's not clear to me if they are making an intentional addition of vanadium, since it is only listed as a max with no minimum. A 0.1% vanadium addition (the mid-point between zero and 0.2) is pretty small for tool steels. For example, W2 has 0.15-0.35% vanadium and 1.2519 has 0.15-0.25%. A potential counter to my reasoning is that Takefu does not list a V max for V1 and V2 steels. However, all of them have a nickel max of 0.25 listed and I doubt they are adding any nickel. So because I couldn't be sure that they are making an intentional V addition I left it off.
 
Yeah, I'm not sure. It does say in both the English as well as Japanese write-up that they add vanadium ("As for the adjustment of component, hard and fine carbides are formed in the substrate by adding Cr, W, and V(vanadium), and the durability increases.") But I guess if it's a maximum of 0.2% its effects would be minimal.
 
Tenebr0s said:
Yeah, I'm not sure. It does say in both the English as well as Japanese write-up that they add vanadium ("As for the adjustment of component, hard and fine carbides are formed in the substrate by adding Cr, W, and V(vanadium), and the durability increases.") But I guess if it's a maximum of 0.2% its effects would be minimal.
Click to expand...
That's a good point that they do at least say that they are adding the vanadium.
 
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