San Mia San sad.... why did the steel split?

[James M. jones]

Thank you for the time , and info. Tried the o1 /wrought Sam mai again today with great success....so far , haven’t hardened it yet , no canola in the house. Ended up forging a bit hotter , a bit slower...I have a 75 lb sahinler... and letting the cool down take substantially longer by bathing it in the forge exit . All seemed to add up to success.

 

Edited September 25, 2019 by James M. jones

[John N]

Ive split loads of wrought iron clad san-mai, right down the middle of the spine. O1 seems particularly prone.

Ive had them perfect from the quench, and then they split 10 mins later!

I have not had the problem since I switched to a fast commercial quench oil, Not sure if that was the sole reason for my success rate improvement, as I was also changing things in the thermal cycling, and forging temps etc at the same time.

I tend to use Aogami blue paper, and super blue for my core steels now. I have very high success rates now with these steels (touch wood) - but I will never know if its the steel, or my technique improved by messing up so many O1 ones !

I do like O1 as it does go strikingly black in use ! I will revisit using it at some point.

[James M. jones]

I,ve heard of the blue paper, might be a while before trying it for the price. Looks like good stuff. I have bunches of the o1 from another job making turning tools, air harden with no temper as per request... so really want to see if process is key, or if there is some issue with o1 in laminate “out of the gate” so to speak . the big plan is to get a heat treat oven to dial things in.

When you say your quench is good but then it splits ten minutes later..... is that after cooling to room temp without tempering? If so , could that be the problem? They say o1 needs to not cool to room temp before temper, might have to test that ..today... After reading the material Allen  suggested It seems that time to harden o1 , needs to be about nine seconds to be best, as well as an extended soak at the Aust temp to fully convert, when compared to a water hard that need to quench as soon as aust temps are reached and to cool quick. Have I got that right? Would be nice to have a full poster size spread sheet for the shop . Lots to learn... I,ve been quenching the o1 hard , with hot transmission fluid....will try canola next...and clamping in copper bars, cooling down to probably 300f and straight into temper for an hour or so at about 420 f in a household oven, Seems to work on single steel blades.  

15 hours ago, John N said:

Ive split loads of wrought iron clad san-mai, right down the middle of the spine. O1 seems particularly prone.

Ive had them perfect from the quench, and then they split 10 mins later!

I have not had the problem since I switched to a fast commercial quench oil, Not sure if that was the sole reason for my success rate improvement, as I was also changing things in the thermal cycling, and forging temps etc at the same time.

I tend to use Aogami blue paper, and super blue for my core steels now. I have very high success rates now with these steels (touch wood) - but I will never know if its the steel, or my technique improved by messing up so many O1 ones !

I do like O1 as it does go strikingly black in use ! I will revisit using it at some point.

 

Edited September 26, 2019 by James M. jones

[Joël Mercier]

9 minutes ago, James M. jones said:

I,ve heard of the blue paper, might be a while before trying it for the price.

26c3 is a fantastic alternative that's also much cheaper. AKS is the supplier.

[Alan Longmire]

For best results with O-1, soak time at aus temp for a blade-sized object is 5 to 10 minutes, although Kevin Cashen likes to go for up to 30 minutes.  He has the micrographs showing superior carbide distribution to back him up, but agrees most people will not want to soak that long.  5-10 is enough to get it "good enough."  As for the nine seconds thing, that just means you have nine seconds to drop the temperature from 1500 to below 1000 degrees, and in my opinion that means slower is better.  I don't know which oil the esteemed Mr. Nicholson (and he is seriously esteemed, no joke!) is using, but industry standard is Parks AAA or equivalent, which is slightly slower than warm canola.  When I do O-1 in canola I take it out of the forge and hold in air for a count of three, then gently into the 120-degree oil.  This is fast enough to blow the scale off, which means it is fully hardened.  VERY unlike when I do W-1 in warm oil!  Then I get from the forge into the oil as fast as humanly possible since with W-1 you have about 3/4 of a second to drop the temp from 1425 degrees to below 900 degrees.  

Don't get confused by quench oil speed ratings, they do not mean what they sound like they mean.  For instance, Parks 50 and equivalents are 7-second oils, warm canola is 10 to 11-second, and AAA and equivalents are 13-second oils.  The number refers to the GM quenchometer test in which a 1" nickel ball is quenched from 1625 F to 670 F measured in time only, not taking into account the various curves in cooling rate, which are far from linear depending on the oil and additives.  So you see it's not really a direct comparison.  

[John N]

Esteemed! I am honoured Alan  (you might just be being influenced by my stove pipe hat) - I hope you are keeping well. All is good with me and the family on the murky side of the pond!

When I was bursting a lot of spines I was using a hydraulic oil to quench in. I now use a commercial quench oil that claims to be as fast as parks 50 (which is unavailable here) - Jesus, and Owen are confident it is not as fast! - I have not shot for hamon in anger with the oil, but the SC125 blades I did clay up ran a very low hamon, which supports this observation. I may have reduced grain size too much in the ones I did, so more testing necessary before I can draw a proper conclusion.

A wise man (Col KC) once said ' O1 hardens if you so much as fart in its general direction' - It is a very interesting steel, and a lot more complex than it seems on face value. It really makes an excellent knife. I switched to 'blue' steel as it is 'sexy' to chefs. I'm not sure its a lot better than O1 in my limited testing (again, I don't get enough making time to quantify my gut feelings) - whilst expensive, pound for pound, it is still cheap.

I use the Takefu, and occasionally Hitachi - In a san mai chefs knife,  it is still only ten or fifteen bucks of core steel. Its probably the lowest cost bit of the finished knife, and it is an excellent steel, and people buy because its 'blue paper' - im not going to argue if the numbers stack up  

[John N]

@James M. jones - they split after quench, well after Mf finish, but before tempering. I don't currently  have a tempering over at my workplace so they generally sit for a couple of hours brittle. 

The problem is really the differences in thermal properties between the core and the cladding tearing it apart. Ive done O1 between 303 stainless cladding. The only way to make that work is normalise the crap out of it immediately after forging, and temper very soon after quench (I torch tempered them as a temporary save, before they went in my household oven a couple of hours later).  Makes O1 and wrought, or normal mild cladding seem very easy!

[James M. jones]

Still getting to know folks here so , ....thanks for the inputs. Ten bucks for core steel, seems like a lot on the surface of things but if folks like and it sells ...who,s to argue. Lots to consider, still have a long way to go before I feel like a knife maker. 

[John N]

51 minutes ago, James M. jones said:

Still getting to know folks here so , ....thanks for the inputs. Ten bucks for core steel, seems like a lot on the surface of things but if folks like and it sells ...who,s to argue. Lots to consider, still have a long way to go before I feel like a knife maker. 

Its too expensive to do your learning on for sure! Makes messing a billet up all the more painful !

The $15 is money well spent when it turns a knife from a $250 dollar one to a $300 one, all other things being even!  

[Jeremy Blohm]

This is my experience with O1 san mai. It wasn't wrought iron jacket but still had the same type of crack. Mine might have been between layers but a good portion of the crack runs right down the center of the O1. I kinda suspected the the O1 was so thin it was able to air harden and I quenched in oil. 

Before failure.

After failure.

[James M. jones]

Nice to know I,m not the only one , can anyone say if in welding , does the weld get stronger during thinning? Heard it develops as the weld is worked down to about half the original thickness ? 

On 9/28/2019 at 8:43 PM, Jeremy Blohm said:

This is my experience with O1 san mai. It wasn't wrought iron jacket but still had the same type of crack. Mine might have been between layers but a good portion of the crack runs right down the center of the O1. I kinda suspected the the O1 was so thin it was able to air harden and I quenched in oil. 

Before failure.

After failure.

Looks like some weld failure and split....fancy! 

[Alan Longmire]

Forge welds being a diffusion-bond thing, the more time spent at welding heat the better the bond.  Of course, hammering and stretching at lower than welding heat isn't good for the weld.

So, yes and no. 

[Joshua States]

@John N I am suddenly very curious about this blue paper steel. It seems like a lot of guys like using it, especially for chef's blades. Where does one acquire said steel?

Edited October 2, 2019 by Joshua States

[John N]

On 10/2/2019 at 3:19 AM, Joshua States said:

@John N I am suddenly very curious about this blue paper steel. It seems like a lot of guys like using it, especially for chef's blades. Where does one acquire said steel?

Its not easy to get hold of outside Japan. I used to buy the Hitachi blue paper from 'Workshopheaven' in the UK, it is crazy expensive from them. More recently we have a UK distributor (Barmond Steels) for Takefu steels. I can get Blue, and Super blue (which is a juiced up version, with 1.3C and more Tungsten! ) in 6mm thick bar, which is perfect for my san-mai.

Takefu also do a range of pre-laminated blue and super blue which makes a very nice blade. I heard, but can not substantiate that the core steels in the pre-lam is HItachi. I understand there are distributors for Takefu steel in the states now. 

The blades below are Takefu super blue core, pre-laminated stainless, with Ni barrier. Its a really nice laminate that I find easy to work, especially given the metallurgy of it. Even though this is expensive material, there is probably only $15 bucks per blade. I really get my moneys worth by forging very close to nett shape though (1mm at edge after forging)!

 

[James M. jones]

On 10/4/2019 at 1:26 PM, John N said:

Its not easy to get hold of outside Japan. I used to buy the Hitachi blue paper from 'Workshopheaven' in the UK, it is crazy expensive from them. More recently we have a UK distributor (Barmond Steels) for Takefu steels. I can get Blue, and Super blue (which is a juiced up version, with 1.3C and more Tungsten! ) in 6mm thick bar, which is perfect for my san-mai.

Takefu also do a range of pre-laminated blue and super blue which makes a very nice blade. I heard, but can not substantiate that the core steels in the pre-lam is HItachi. I understand there are distributors for Takefu steel in the states now. 

The blades below are Takefu super blue core, pre-laminated stainless, with Ni barrier. Its a really nice laminate that I find easy to work, especially given the metallurgy of it. Even though this is expensive material, there is probably only $15 bucks per blade. I really get my moneys worth by forging very close to nett shape though (1mm at edge after forging)!

 

Beautiful, ..... 

[Brian Dougherty]

On 10/4/2019 at 5:26 PM, John N said:

... I really get my moneys worth by forging very close to nett shape though (1mm at edge after forging)!

 

Most impressive.  I did this once on a pair of 10" ss/1084 sanmai blades.  That is a real trick to keep things centered, and I don't think I could do it repeatedly! 

[James M. jones]

So now this has me wondering, are there any general guidelines as to how thick to forge in order to grind back. .? 1mm on the edge, ? I can see how shooting down that straight and centered would require great skill, so , the question becomes what are some good thickness  , to shoot for off the forge, before cleaning up on the grinders  , been mostly wanting to go thinner but not wanting to thin overly, concern for De carb, centerline straight, clean up , quench warping... suggestions?

[Alan Longmire]

Depends on how good you are at forging a true flat.  I usually go for about 1.5 - 2 mm so the grinder can take care of any stray hammermarks.  Unless I'm going for a major brut-de-forge look, in which case I'll take down to 1mm or less.  

[John N]

I usually do laminates, so give them a real good pasting stone cold under the power hammer (after annealing), lets me forge thinner, and more accurately. 

 

When you look at san-mai blades you can often get an idea how close to finished they have been forged. Small bit of hardened edge showing = forged very close! 

[James M. jones]

2 hours ago, John N said:

I usually do laminates, so give them a real good pasting stone cold under the power hammer (after annealing), lets me forge thinner, and more accurately. 

 

When you look at san-mai blades you can often get an idea how close to finished they have been forged. Small bit of hardened edge showing = forged very close! 

Thanks for that, I assume you must anneal after cold working , before the quench. Interesting. Now the question becomes , on threads like this where the initial question has been ..... effectively answered.... should I consider starting new topic threads or is it ok to diversify the discussion, fine either way...... real glad you all have this resource for us. 

[John N]

2 minutes ago, James M. jones said:

Thanks for that, I assume you must anneal after cold working , before the quench. Interesting. Now the question becomes , on threads like this where the initial question has been ..... effectively answered.... should I consider starting new topic threads or is it ok to diversify the discussion, fine either way...... real glad you all have this resource for us. 

 

I don't anneal (which I think of as 'slow cool in vermiculite or ashes) after the cold forging. I do normalise accurately at least 3 times though. ( heat to desired temp, and cool in still air)

 

I find the normalising very important, obviously for the grain refinement, but also to straighten and remove twists etc between each normalisation cycle. After 3 they generally 'stay put' and behave themselves in the quench. Gentle bows from the quench are easy to take care of, but any twisting etc can scrap the blade when you have forged it so close to finish. There is no margin for error when you dont have the luxury of 'ill grind it out after'