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What's Going Wrong With This Hamon?


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I've made a half dozen hamons on chef knifes heat treating my blades with a forge and never seen this happen, and it's an issue that has occurred without fail on every single attempt I have made to produce one with a Paragon oven. 

 

The steel is W2 from NJSB, I profiled, rough ground, heated to 1600F, 1475, 1450, 1425, 1400, each for 15 minutes, air cooling to black in between, clayed and quenched in warm P50 from 1435.

 

On my first passes after tempering at 350 I could see a hamon than ran the length of the blade so I ground it out to completion and after 5 cycles of lemon juice and loose abrasive this is what I've got. A clean line that dissolves into a formation I don't recognize. The weird thing is that under it I can still see the shadow of what was the hamon that I observed during the initial stages of finish grinding. The edge still skates my files, and prior to grinding the hardened blade face did too, I don't know if it still does. 

 

This is the third time this has happened, roughly. Previously I could see after a pass on the grinder that the hamon ran off the blade, so I cycled it again and quenched again (omitting the 1600 degree cycle). Initially I was going from brine for 3 seconds to the oil, but I assumed the lag time between containers was costing me my quench line, so this time I went straight for the parks and let it sit for 15 seconds, put it in the snow till I could pick it up, and then tempered it. 

 

I have no idea what is going wrong here. I'm in over my head on this one. 

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looks like decarb, which wouldn't be surprising after 1 1/2 hours in a heavily oxidizing environment, but if that was the case it shouldn't skate a file on the face of the blade until you've ground off a lot of material. Could be alloy segregation from excessive normalization. if you're not forging, the 1600f normalization probably isn't needed, nor the 1400f one. Cut the soak time down to about 1 minute. Try quenching a piece from 1435f without normalizing to see what you get, to establish a baseline, and refine from there.

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On the contrary, if done by stock removal, you have to soak at high temp this steel to dissolve the carbides locked in a coarse spheroidized state. A 10 minutes hold at 1600 for the first heat sounds just fine. 5 minutes for the others is enough with most cross sections. 

 

1435 is a bit low for a p50 quench though, I would go a bit higher.

 

But first of all, get some anti scale coating! Atp-641 works very well and imo is crucial for electrical HT furnaces.

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I'm not inclined to think it's decarb, in my experience decarb is almost white without a visible grain like this, and a file skates all the way up the back of the heel. I am starting to question how much heat loss occurs at the oven door.

 

In my experience excessive clay causes cracking and this blade had only a strip 1/4" wide by about .04" thick along the spine, but none on the spine, and thin, opposing, diagonal ashi lines coming down off of it. I don't think that would have retained enough heat to have been an issue, but who knows. The blade is a gyuto, and roughly 2" wide at the heel. 

 

For the time being I'm thinking that it didn't harden all the way through at the heel due to inadequate heat, but strangely, another blade identical to it I did at the same time developed the opposite issue.

 

 

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I think there are several things that could be going on here, not least of which is W2 is a finicky steel and often does strange things. I have never used the W2 from NJSB, and I have heard widely varying reviews of its performance. The W2 I use is either Don Hanson's or Ray Rybar's. I have never used anything other than my Paragon oven for quenching and tempering W2, but  I have seen some funkiness in the hamon similar to the orgainized structures you show in picture #2. You can see the strange stuff appearing in this hamon. Although, these are not as prevalent or structured as what you have.

 

Activity 1 V2.jpg

 

I have been told this is because the Vanadium in the alloy doesn't get fully dissolved at the lower quench temps we tend to use for hamon and it collects in something like pools (or some such metalurgical talk). Anyway, I think you are doing way too many normalizing heats and holds for this steel, especially if doing purely stock removal and your quench temp is a tad too low to get fully dissolved carbides. I quench W2 at 1450-1460 now. I think the knife in the photo was quenched at around 1440.

 

The other thing to remember about shallow hardening steels is the depth of hardening is somewhere around 3 mm. When you clay a blde, that insulation does not extend in a perpendicular line to the surface either. It is conical and the hamon will move or totally wash out with a deep grind. You didn't say how thick the blade or edge were when you went for quench, so I don't really know if this is an issue.

 

If you want to determine whether it is an oven vs. forge issue, try a piece of the NJSB steel in your forge and see what happens. If the same thing occurs, it's either a steel or a heat issue. You don't say how you judged the quench temp with your forge, and it may be that you quenched at a much different heat in the forge than you did in the oven. It is also possible that the thermocouple in your oven isn't quite right.

 

There are many variables to consider. You need to go back to a method that you can reproduce and start eliminating each variable one by one.

 

Edit to add: Another thing about Parks 50 is the recommended working temp is 75*F - 120*F with the sweet spot right around 100. If your oil was hotter than 120, you are outside the recommended use range. That could affect the final product.

Edited by Joshua States
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I left the spine at basically the full 3/32, and too the edge to around .050".  1435 is probably a touch too cool for P50, I was planning on another brine/oil quench but chickened out. 

 

When I was heating my blades with the forge I would heat them to past magnetic 3x and then quench them. I was always keeping an eye out for the recalescence point and would quench them when the blade would just start to turn dull. I was also heating them edge up in the forge and trying to keep the heat concentrated at the edge with less attention to the spine. 

 

My oil was probably a bit on the warm side, but according to some posts by Jesus Hernandes it really doesn't seem to be a a problem. He also discovered that if he kept his oil really hot, around 180 (I think) it would consistently give him positive sori on his katana blades. 

 

More reading on NJSB W2 seems to indicate some issues with getting spheroidized carbides to dissolve at 1600 degrees and recommendations to go up to 1700 or 1750. So I'll give that a shot and bump the temperature up to 1455. 

 

During my initial attempt to harden these blades I used 1460, the second time around 1475, and this time I dropped it to 1435. 

Edited by Matt S
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1 hour ago, Matt S said:

More reading on NJSB W2 seems to indicate some issues with getting spheroidized carbides to dissolve at 1600 degrees and recommendations to go up to 1700 or 1750.

Good to know. 

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