Greetings!
I have a particularly quarrelsome time with a blade this week and would like to understand the causes from it to better my knowledge and learn if I potentially did something wrong....
As my usual lately, I heat treat 7 blades at a time in my kiln. I do a staggered normalization cycle 1650-1550-1475. Normally i might have one that warps despite marquench-straightening. Usually I temper 2x @ 2 hrs each for targeted tempered hardness and then toss it back in the kiln to get to temper heat and then straighten in my 3 point jig.
The blade in question was damascus made from 1080 / 15n20. Anyway, this blade was straightened 4 times and quenched in water and checked on my surface plate for straightness with satisfactory results. Back to the grinder and after about 5 minutes of grinding i get a big horseshoe almost... Long story short, I raised the temper temp 25 degrees and straightened one last time (seems like it will survive)
Is the heat from the grinder tempering retained austenite and causing the sets? Is the "grain" over forged on one side causing memory (this i never have been able to buy- this only happens one out of a 100 blades) Or is there some other metallurgical consideration?
In a batch of 7 I usually have 1-2 with minor straightness issues that i then correct as mentioned above and never have a problem again.
|quoted:
Greetings!
I have a particularly quarrelsome time with a blade this week and would like to understand the causes from it to better my knowledge and learn if I potentially did something wrong....
As my usual lately, I heat treat 7 blades at a time in my kiln. I do a staggered normalization cycle 1650-1550-1475. Normally i might have one that warps despite marquench-straightening. Usually I temper 2x @ 2 hrs each for targeted tempered hardness and then toss it back in the kiln to get to temper heat and then straighten in my 3 point jig.
The blade in question was damascus made from 1080 / 15n20. Anyway, this blade was straightened 4 times and quenched in water and checked on my surface plate for straightness with satisfactory results. Back to the grinder and after about 5 minutes of grinding i get a big horseshoe almost... Long story short, I raised the temper temp 25 degrees and straightened one last time (seems like it will survive)
Is the heat from the grinder tempering retained austenite and causing the sets? Is the "grain" over forged on one side causing memory (this i never have been able to buy- this only happens one out of a 100 blades) Or is there some other metallurgical consideration?
In a batch of 7 I usually have 1-2 with minor straightness issues that i then correct as mentioned above and never have a problem again.
A hardened blade that is still straight is actually an incredible feat in a very well balanced system of incredible levels of strain and stored energy. Grinding down one side will definitely throw this balance off a bit. 15n20/1084 is eutectoid at best, one should have to really try to make retained austenite to get it in such a steel, so I seriously doubt this would be the issue. The whole steel memory from forging is a bit of a myth if normalizing is part of the process. I would say that you probably removed a little too much off one side of a hardened blade versus the other side. Try grinding a rapier blade after it is hardened and watch that bow form on every pass until you finally get the grind passes balanced.
On a side note, 2 hours twice for the temp would equate to 4 hours total, which is a bit of overkill. 2 hours total is all that is really necessary. It should be too much of concern if the HRC remains steady but time and energy is worth something.
"One test is worth 1000 'expert' opinions" Riehle Testing Machines Co.
|quoted:
A hardened blade that is still straight is actually an incredible feat in a very well balanced system of incredible levels of strain and stored energy. Grinding down one side will definitely throw this balance off a bit. 15n20/1084 is eutectoid at best, one should have to really try to make retained austenite to get it in such a steel, so I seriously doubt this would be the issue. The whole steel memory from forging is a bit of a myth if normalizing is part of the process. I would say that you probably removed a little too much off one side of a hardened blade versus the other side. Try grinding a rapier blade after it is hardened and watch that bow form on every pass until you finally get the grind passes balanced.
On a side note, 2 hours twice for the temp would equate to 4 hours total, which is a bit of overkill. 2 hours total is all that is really necessary. It should be too much of concern if the HRC remains steady but time and energy is worth something.
Thanks for this response. I guess that could play into affect here. I never thought about grinding one side and having the other side pull the curve in it. BUt i can see how that would be the case. This was a very thin kitchen knife anyway.
On the tempering note, I was under the impression that 2- 1 hr cycles was for low temp salt- liquid conduction, and taht air conduction would need to be a full 2 hours to ensure the steel was thoroughly to temp? I only have RC chisels and have been getting consistent results with the current process. BUt 2 less hours in the oven wouldnt make me angry if i were being redundant unnecessarily
|quoted:
Thanks for this response. I guess that could play into affect here. I never thought about grinding one side and having the other side pull the curve in it. BUt i can see how that would be the case. This was a very thin kitchen knife anyway.
On the tempering note, I was under the impression that 2- 1 hr cycles was for low temp salt- liquid conduction, and taht air conduction would need to be a full 2 hours to ensure the steel was thoroughly to temp? I only have RC chisels and have been getting consistent results with the current process. BUt 2 less hours in the oven wouldnt make me angry if i were being redundant unnecessarily
so 15 minutes to achieve temp in a preheated oven, add 1 hour, cool and repeat
Is this the recommended procedure for my resources?
Ideally 1 hr in low temp salt?
