sharpness and edge retention test

[Coutel]

Hi.

I thought maybe some would be interested in this test I did with one of my knives yesterday.

After heat treatment and before I begin final building, I test knives for durability...one test I do is cutting rope which gives me an idea of sharpness , geometry and durability.

I use 1/2 inch diameter manila rope and cut the entire 1/2 inch thickness (not unwinding it ).

Measure 2 inches of cutting edge on my blade and just cut within those 2 inches.
Each cut needs to be a push and one draw...NOT a sawing motion,..so the rope is completely severed in one attempt.The idea being to count how many total cuts can be made before the blade loses its sharpness...noticable when it slides and does not make the cut.

The cuts were done on a wooden bench so the edge was also cutting into the wood to severe the rope completely.

No re sharpening, or honing the edge between cuts.



This blade made 1300 cuts and was still going strong (my best before this was 700 cuts).....This test consummed 120 feet of rope!!

The blade is 52100, used Even heat oven and Chevron 70 quenching oil.

[Coutel]

I forgot to mention hardness. Someone asked me if I am cutting at full as quenched hardness?.....

The blade is triple tempered, and I stop tempering when a 60Rc file just starts to cut....so, unscientificaly, I estimate the blade is around 59/60Rc....The temper colour is actualy begining to hit vermillion by the time the file cuts.

[circlepknives]

Wow now that is some cutting power and edge retention wonder how many more cuts it could do. Bet you could more than double you best result.

I know I would feel good about having a knife that had such good edge retention.

Love the pic!

Have a good one!

[raker]

Kevin, You did good and the results show it. What temp was the tempering temprature or close to it. I know that all the ovens are close and some are not the same as others. That is a pretty blue ins't it?

[Coutel]

Originally Posted by raker

Kevin, You did good and the results show it. What temp was the tempering temprature or close to it. I know that all the ovens are close and some are not the same as others. That is a pretty blue ins't it?

Hi Ray.

I used to temper at 400 x 2 hrs, three times when I used peanut oil...but I know use Chevron 70.

When I changed to Chevron 70 quenching oil, my blades were a point or so harder (estimated using my Rc files) after a triple quench sequence ...The temperatures I now use are 400F (2 hrs), second 420F (2 hrs), then on the third I hit 440F... an hour or so at 440 seems to put it where I want (60 file just begins to cut).

[raker]

Kevin,
That is pretty close to what I do. I do a double temper and start on the high end, 460, for two hours and then 450 for two more hours. On the large knives, I still do the double temper at 475 both times. I still use the transmission fluid at around 300 degrees for quenching. That is in the middle of the transformation zone so it drops fast to there and then a slow cool to Mf temperature. When the oil gets to about 150 degrees, I take the knife and and wash it up before tempering. I have a Rc testor but the readings are always all over the chart, I may need to learn more or get another point.
I had heard a long time ago of tempering 3 times and dropping the temperature about 25 degrees each time for equal periods of one hour. The thinking was that each temper got 90% of the transformation and you would end up with some hard carbides in a slightly softer matrix. I don't know for sure but it hasn't hurt anything so far. I am sure a lot of it will be determined byt the condition of the steel before tempering.
I have enjoyed your posting and thanks for doing it.

[jdm61]

question....what time and temp would you guys recommend for tempering 1075, 0-1 and 5160/9260? ihad some brittleness issues with an O1 blade early on. I tempered my last one until it was blue (over 400 degrees)and it seems to be pretty tough, but i have no idea what the hardness of the edge is. I have tempered 1075 at 375-400 degrees to a nice straw yellow and it seems to hold a good edge and remain flexible. I was using my old kitchen oven which was not very good about keeping the indicated temp. My new oven is spot on. (you may have guessed that i am single since i use my kitchen oven to temper blades..lol)
Joe Mandt

[raker]

Sounds like you are pretty close to me. All I know is to temper and test each batch of steel to get closer to being right on. If you temper and it is brittle, temper it again at about 25 degrees higher until it doesn't chip. That is basically what you should do with any new steel you start using. All ovens are close but not quite the same.
I always do a double temper for two hours each with a cooling in between to below room temperature, cold water will work.
A good woman would let you use the stove if you let her use it too. Mine did.

[ZDP-189]

Kevin, have you tried Texaco Type A?

[Coutel]

Originally Posted by ZDP-189

Kevin, have you tried Texaco Type A?

I made paper comparisons of several industrial quenching oils.....Texaco Quenchtex being one of them .

Using the information gained from Drayton Quenchalyzer curves (industy standard)....Quenchtex A is a slower quench than Chevron 70.

As an example....
Quenchtex A ..... 12.625 seconds to reach 600F (about 1100F),
Chevron 70 ..... 7.5 seconds.

Parks Heat Bath AAA comes recommended by many makers (Kevin Cashen being one), and comparing it on paper to Chevron 70, they are very close (AAA is less tha a second slower to reach 600C than Chevron 70). ..I wasnt able to get hold of any Parks Heatbath products.

I have 5 gallons of Texquench A in my shop (its getting difficult to find these days) and I know its also a recommended popular oil (Ed Fowler) but I havent used it as I personaly do not think that slowing the quench speed will gain any benefits over the faster Chevron 70....I would welcome others views on this as I may be missing something.

I would expect that the difference in oils agaisnt performance in my shop would be negligable, if at all noticeable......When I have some help in my shop, I will make some comparisons.

[jonwelder]

Kevin, thats a very impressive picture!! You didn't mention how or how many times you heat-treated the blade before you tempered it. By going to well over 400 degrees tempering, were you trying to get that 52100 just a little softer than you usually like it? Edge quench or full quench? --jon

[Coutel]

Originally Posted by jonwelder

Kevin, thats a very impressive picture!! You didn't mention how or how many times you heat-treated the blade before you tempered it. By going to well over 400 degrees tempering, were you trying to get that 52100 just a little softer than you usually like it? Edge quench or full quench? --jon

Hi John.

Triple normalising and triple full quenching.....using a digital overn for accurate temp control. I use Chevron 70 quenching oil.

I temper until my 60Rc file just begins to cut.... (I think I am around 59 to 60Rc....though I appreciate an accurate Rc test may show a slight difference one way or another.

I can leave the blade several points higher if I wanted, but I tend to think there is an optimum hardness of this steel to the performance I want...... I experimented with harder blades, but as well as the obvious that they were harder to sharpen, I found that my sharpening technique (slack belt and leather strop) would leave a polished edge, and rope cutting with a polished edge is very poor because it slides rather than have that agressive bite I wanted.

After 1300 cuts, I can re hone the edge with a few strokes on a leather strop at the hardness I am using which to me, seems a good compromise.