There are a couple things I would comment on.
When doing the flex portion of the test, don't just go right to the square iron jaws of the vise. Either place a block of wood between the sides of the knife and the vise jaws, or make a steel clamp for the blade that has rounded edges where it meets the blade.
You're asking for failure with this method posted here.
Secondly, if you get decent martensite transformation on your quenches, you need a MINIMUM of 2 - two hour tempers.
I repeat - you ne a MINIMUM of 2 - two hour tempers.
If you giot good martensite the first time around, you barely accomplished anything in 1 one hour temper.
Something you've got to do - (besides the ABS Intro Course - Kevin!) is to get some basics about the transformation from austenite into marensite, and the resultant effects of tempering.
Even though a lot of the austenite WANTED to go into martensite when you get the temps and wuenches right, it was unable to because the steel just simply got too cool, too fast.
Thus, we have what is refered to as "retained austnite". It was steel in the process of going into martensite, but was "retained" in the austenitic stage.
When you do the first temper, you not only stress relieve the very brittle martensite that you DID get, but that first temper allows the "retained austenite" to go ahead and make the transfer into martensite.
Now, you have BRAND NEW brittle martensite that needs to be tempered!
So you let that steel come down to room temp from the first temper, and then give it a second temper to stress relieve that newly formed martensite.
If you don't, ---t happens.
Lin gave a great dissertation not long ago on the importance of thermal cycling and normalizing at the end of forging to reduce and "pin" grain size, which will also effect the toughness of your steel.
Even if you do all of the other steps right, if you have NOT reduced your grain size, failure is on the horizon as well.
Now, I'm not saying one way or the other about what I see here on your break, but take a look at this picture of my 5160 what the grain looks like - it looks like grey cream! Really fine in texture.
That's also a pretty short blade to flex, however, when doing an edge quenched 5160 blade that was not a whole lot different than yours, last year I did 32 180 degree bends - that's 90 degrees one way, and all the way to the other side 90 degrees! - before it cracked.
Don't short cut anything.
Keep your temps where they need to be.
Thermal cycle and normalize.
If you're confused about the difference between the two, a thermal cycle goes from above non-magnetic through decalescence, (when the shadow disappears), down until all color is gone in a dim room, to about 900 degrees.
Then back up to decalescence, back down to a black heat.
Then a normalizing cycle which cools all the way back to room temp.
Do everything the same every time.
Don;'t take short cuts or you will pay the price.
Don't over heat your steel when quenching or you can loose everything you gained up to this point.
Minimum two cycles of 2 hour tempers.
Call me.
I have made an absolute nuisance of myself to at least 3 or 4 other well known knife makers with questions over the years.
I have no ego.
I'm not embarrased to say when I don't understand something.
If stuff isn;t doing what you think it should, ask someone that knows.
I do it all the time.
Topic: Test Knife (Read 1130 times)
