Getting negative sori

L

Lucasberg

Joined
Feb 17, 2016
Messages
29
Hey Guys,
I have noticed on my last two blades that they got negative sori during quenching. I'm using an Evenheat KF27 and parks 50. Both blades were made from Aldo's 1095 steel and both were Sataninte clayed on the spine. The first one was a straight spine 17in overall tanto 3/16 thick quenched vertically . I noticed it is now a slight recurve. The next blade is a 1095 1/4 thick 24in overall wakisashi quenched horizontally. It had ground in Sori and went slightly negative.

I searched and only found to try an upside down quench or a water for 3 seconds then into Parks 50. Is this happening because of the clay backed spine ? If I didn't go for a Hamon with no clay what would happen?

Any help would be great.
 
happens every time with parks cooling rate is just different enough to do that vs water quench. when i did my tuna sword and it needed to be straight not tip up or down i part quenched in water then finished in parks 50
 
Years back on this forum someone asked me to explain the curve and I refused as too many things are happening ,too hard to predict. The japanese steels are not high carbon ,1070 at most. They are water quenched .You have really complicated the whole process. I don't really know what to suggest .
 
In yaki-ire, the blade first bends down as the spine converts to pearlite, and then, as the martensite starts to form along the edge, bends upward. This is the highly stressed change that creates cracked/broken blades.

On thin blades, especially when using a slightly slower quenchant on a really shallow hardening steel, it may only bend downward and not have enough "force" to pull it up as the austenite converts to martensite. This is also why thin blades often crack along the edge ... it just give way to the stress. Other factors that can make the upward curve resist the change is the spine cooling too much before the edge converts. If the spine gets exposed ( by intent or accident of the clay popping off), and converts to martensite along the top, this can stop the upward curve completely. Some people do this on purpose to keep a blade straight.

I usually forge in some sori and use Parks #50. It may take a few test quenches to get it balanced right. Different steel batches will curve differently, too. So using steel that all comes from the same batch for years is well worth the initial large quantity purchase. Ask Don Hanson about the wisdom of that :)

Here is a great video of the process:
https://www.facebook.com/photo.php?v=245811752214385&set=vb.100003566854392&type=2&theater
 
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Thanks for the replies guys. I bought parks 50 because people said your blades won't crack and after 30+ blades no problem with that. I didn't read about the negative sori though :). Since i have an oven I should have a good chance at a successful water quench I would think. If i try a water quench on a longish blade should I keep the bevels a little thick, and heat the water to around 150? Any other major details?
 
There is a formula for calculating this: ASB + H2O = BB.







ASB - Austenite Sword Blade
H2O - water quenchant
BB - Broken Blade

This formula is accurate about 90% of the time.
 
I heard rumor long ago that if you quench W2 a second time in oil, you have even more chance of getting that negative "sori" Don't know if it is true.
 
Even if you do stock removal, the sori can be formed hot in the bar before shaping and grinding. You are best to heat to about 1600F and use a wooden mallet to make the bar curve> this is very simple, and only takes the lightest blows.
It can be also done at 400-700F with a regular hammer. Just set one end on the bench top/floor/anvil and the other end on a piece of 2X4. Use moderate blows and work along the spine with the hammer.

A trick for holding the hot bar while working it is to put a C-clamp on one end and use it as a handle.
 
Is there a known amount of curve from oil? On my 10in blade it was about 1/8in and on my 17in blade it was about 1/4in. On both it was just enough to make a tiny recurve about 1/4 the way down the blade from the tip. Ill try the hot bar shaping. Thanks!
 
All my blades curve downward when quenched in oil. 1084, 5160, O-1, L6. Anything I have tried to water or brine quench went the other direction. You just have to account for it in the pre-heat treat shape. Usually I get the tip dropping 1/16" to as much as 1/4" depending on blade length. Multiple quenches will add more drop.

Darcy:)
 
jdm61 said:
I heard rumor long ago that if you quench W2 a second time in oil, you have even more chance of getting that negative "sori" Don't know if it is true.
Click to expand...


Yup, I did now grind a Sori into the profile, which I can adjust after quench as needed. If I try a second time for a better hamon, the tip drops noticeably more than the first time I quenched. My first sujihiki looks like a dirk. Tip dropped about 1/2" between the two quenches.
 
Not really. It has to do with the different thicknesses converting at different rates. The way to reduce or stop it is to have the spine exposed during quench ... or have extra sori pre-set in the shaping before HT.

TIP:
Leave extra width - especially toward the tip - to grind away post-HT. This allows you to adjust for the small amount of variation in sori. Generally, I put an extra 1/8" to 1/4" in the blade width to allow a cleanly shaped edge. This also gives me some room to grind away any edge warps or ripples.
 
I measured the droop on my last 3 blades and from about halfway down the blade it was 1/8,1/4,1/4. I just put a straight edge on the spine. So if I did not put clay on the spine it would droop less? For a chopping sword is there an advantage to the soft spine or would fully hardened be better? I have been claying the spine to practice the hamon but I usually just blue the blade anyway.
 
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