Can JTknives feel a bad HT when a knife is quenched?

[Ken H>]

I like turtles also, especially turtle Fricassee.

 

[John Cahoon]

Breaking Headline News: Turtles declare landslide victory, JT refuses to concede and demands a recount

 

[Mecha]

Breaking Headline News: Turtles declare landslide victory, JT refuses to concede and demands a recount

...and nobody thought it was impossible!

 

[Natlek]

...and nobody thought it was impossible!

Are you sure about that I just vote .................impossible

 

[Scott Hanson]

Yep, I bet he can.

 

[Mecha]

Are you sure about that I just vote .................impossible

You're the kinda guy who just has to kick a big perfect mushroom when you walk by one, aren't you?

 

[timos-]

New poll: can JT heat treat our knives while blindfolded? I dont think he can...

 

[Ian Fifelski]

Actually you're right about "Katana will develop positive sori when quenched in water and negative sori when quenched in oil"

I have seen this happened to almost every simple carbon not just tamahagane. From W2 to 1050. I still can't figured out why quenching in oil develop reverse sori tho..

I am no expert but I believe it is from the speed in which the water cools the steel.

When you quench in water the thin edge cools extremely quickly and pulls the edge in and the tip down. As the spine cools it pulls the spine in and the tip back up.
When you quench in oil, the same thing happens to the edge, but because of the slower quench speed of oil, it does not then cool the spine quick enough to pull the tip back up resulting in a negative sori.

 

[Stacy E. Apelt - Bladesmith]

That is a small part of it.

The negative sori is formed as the edge cools and contracts while the spine is still rubbery austenite.
Then, as the edge reaches the Ms at 400F it rapidly expands as it converts to martensite (martensite has a larger structure than austenite) at the same time the spine is contracting as it becomes pearlite. The spine becomes fairly rigid and the edge becomes very brittle as this happens. This makes the positive sori form. If there is too much stress caused by all this, it results in the dreaded PING as the edge tears itself apart.

I like JT and think he is doing a good job in his HT endeavors. However, I doubt anyone can tell if a blade hardened evenly or full by the feel. You can feel a vibrating blade in a rapid quench, you can feel/hear cracks forming, but I can't think of a metallurgical reason you could feel the difference between Rc 64 and Rc44 martensite forming in a normal blade.
I won't go as far as saying it is impossible, merely that I doubt it.

One thing in psychology is that we remember every negative event. It is evolutionary, and that is how you survive when the same circumstances arise again. This makes us think that certain things are far more common than normal. Read about two plane crashes and it will seem that planes are crashing at a greater rate than reality. See two snakes in a week and it seems like you will think snakes are taking over the garden. This also goes into combined memories and false deduction. "The blade vibrated when quenched; The blade was not as hard as it should be, Ergo - I could feel the difference." You felt the same vibrations in every quench, but your memory will only recalls them if there was a problem.

 

[shqxk]

That is a small part of it.

The negative sori is formed as the edge cools and contracts while the spine is still rubbery austenite.
Then, as the edge reaches the Ms at 400F it rapidly expands as it converts to martensite (martensite has a larger structure than austenite) at the same time the spine is contracting as it becomes pearlite. The spine becomes fairly rigid and the edge becomes very brittle as this happens. This makes the positive sori form. If there is too much stress caused by all this, it results in the dreaded PING as the edge tears itself apart.

Why quenching in oil result in negative sori as oppose to quenching in water?

 

[shqxk]

I am no expert but I believe it is from the speed in which the water cools the steel.

When you quench in water the thin edge cools extremely quickly and pulls the edge in and the tip down. As the spine cools it pulls the spine in and the tip back up.
When you quench in oil, the same thing happens to the edge, but because of the slower quench speed of oil, it does not then cool the spine quick enough to pull the tip back up resulting in a negative sori.

This actually sound reasonable. The slower quench speed of oil doesn't bring enough thermal contraction of the spine to overcome the volume expansion from martensite transformation at the edge.

 

[Stacy E. Apelt - Bladesmith]

shqxk is correct, the cooling rate is slower in oil and the two structures form at a more equal time. Personally, I rarely see much negative sori in an oil quench in oil. In Parks #50 I sometimes get a small positive sori.

 

[jake pogg]

some folks would dismiss this as part of the forged grain flow

Once,many moons ago,i had a discussion with Grant Sarver and an older machinist gent from Australia on the subject of directional "grain" in rolled stock.(Both believed in it implicitly).
The Australian gent recalled being officially regularly inspected on this very matter while doing some Mil-spec forging in the yards during WWII.
Being an utter hick myself i was loath to doubt either of these very respected elders(rest in peace,Grant...),but with my own pea-brain i could neither understand nor account for anything of the sort.
Till some time later i came across a mention of how the crystallization takes place along the original dendritic structure(as a casting cools from liquidus);and any future re-crystallization similarly will be formed along those same sites(as distorted as it may become with any degree of deformation short of being brought back up to liquidus)...

So,is that what is meant by "forged grain flow"?...And if so,is this still a controversial issue?

 

[JTknives]

I hate to argue my point but it is indeed different. For some reason the steel that does not harden takes longer to quench and does not bubble the oil as vigorously. It could be in my mind but the fact was my wife was there as oven opener and right when I quenched the first blade I said oh man I think this is bad steel.

I will try and recreate it and see if I can capture it on camera. I still think it has to do with the scale formation not popping off the soft steel and disrupting the vapor jacket.

 

[Cushing H.]

This comment/question is i think really for Larrin (and others who want to dig into the materials science) ... i still wonder if some of what we are seeing here is related to anisotropy of thermal and thermomechanical properties arising from different rolling processes during manufacture??? See for example Hutchinson, Materials Science and Technology, volume 31, pp. 1393-1401 (2015). I wonder if JTs observation regarding scale delamination (and resulting differences in heat transfer rates) isnt a clue about this...

 

[Randy3000]

• 00:13:44 Write up a brief summary and have it to me by the end of the day.
  
  
• 00:13:47 My pleasure.
  
  
• 00:13:48 Layman's terms. None of that inside, bullshit jargon that nobody understands.
  
  
• 00:13:52 Yes, sir.
  
  
• 00:13:57 Oh, Mr. Shirley...
  

 

[Cushing H.]

• 00:13:44 Write up a brief summary and have it to me by the end of the day.
  
  
• 00:13:47 My pleasure.
  
  
• 00:13:48 Layman's terms. None of that inside, bullshit jargon that nobody understands.
  
  
• 00:13:52 Yes, sir.
  
  
• 00:13:57 Oh, Mr. Shirley...

Not sure if this is directed at me but .... the specifics of a process in which a piece of steel is rolled down to thickness can affect its properties - including how fast is cools in different directions (those directions being the rolling direction, the in-plane direction perpendicular to that, and the vertical direction). If we are looking at something here where this steel has some lower level of conductivity in the vertical direction (due to the way it was processed) (and it crosses a critical threshold in terms of being too slow), might that explain what JT is seeing. The paper I cite above indicates these properties can differ on the order of a factor of three between the different directions.....

 

[timos-]

i enjoy reading the jargon lol ..thx for google i now know what anisotropy means BTW you know its inside jargon when spell check underlines it in red!

 

[Stacy E. Apelt - Bladesmith]

While we all love jargon, some can be said just as easily in layman's terms. Anisotropy is the directional properties of a material. Consider a 2X12X24" board. It is very strong with a force applied by an axe in the 2" direction, fairly strong in the 12" direction, and very weak in the 24" direction. Steel is cast, forged, rolled, re-rolled, etc. many times before we get it as a bar of steel. Personally, I think anisotropy is of minimal concern to a knifemaker. Bad mixes and other errors/flaws in the steel are a different thing. They matter a lot to knifemakers.

I wanted to clarify my earlier statement about whether JT can feel the difference between a good blade and a bad blade in the quench. I wasn't saying a problem doesn't exist, just that I doubt it can be felt. HIs farther testing and results clearly showed a problem in the steel. The reasons are still undetermined, but the fact a single blade has a wide range of hardness side by side is very concerning.

I would suggest testing the steel with flat surface ground rectangular bars and after re-grinding post HT. This will eliminate testing errors. If that shows similar results, then there is a serious error/defect in the steel.

One thing that I don't recall being mentioned is the quenchant. If large amounts of vapor jacket form, there could be a variety of hardnesses formed along the blade. The places with heavier scale would likely have a different cooling speed and lower hardness. Perhaps the quenchant is not performing efficiently. There could be may reasons for this - wrong type quenchant, degradation, overheated/too cold, contaminated, etc..

 

[Cushing H.]

While we all love jargon, some can be said just as easily in layman's terms

Agreed - but I really did intend that as a question directed to Larrin (and I did qualify my statement to those interested in the technical stuff ). He would have a better experienced insight as to whether the variations could be significant enough to cause what JT is seeing. I am also wondering about local and directional variations in the coefficient of thermal expansion (hence the "thermomechanical"), and whether that could give rise to the differences in release of scale that JT is observing.......