I'll tell you what is difficult sometimes to REALLY get your head around:
It often seems that many concern themselves, and get really focused on,"TEMPERING". Sort of thinking that if they temper their blade at this temp, and do it this many times for this long, then they'll end up with "X??X" hardness.
For ANY of those tempering "recipes" to predictably work correctly, and function along with industry standard proceedures, the steel must have reached FULL HARDNESS to begin with! All of those tempering times and temperatures have been determined by utilizing them on FULL HARD STEEL. This of course requires proper treatment up to the full hardening process with correct temperature control and steel/alloy heat treating procedures to begin with.
Sort of like saying that if you do not have your steel type up at the right temp, (not to high - not to low) -)for the proper amount of time, and then quench it in the correct medium to extract the heat at the proper rate FOR THAT STEEL to transform the austenite into martensite, then it doesn't matter how you temper it!
See what we're up against?
So, that behooves the knife maker to use the simplest steel that he can control with the equipment he has.
For example, 1084 is about the simplest steel going. If you get it non-magnetic and quench it in something wet, it'll get hard. How hard? Depends on the control of your processes up to that point.
If you harden something that you have overheated earlier, without going through post forging normalizing steps, and grain reduction steps, and then you harden it - you've got junk.
If you don't get it completely up to the temp for THAT steel, and quench it in the correct medium at the correct temperature for that steel, regardless of all the other steps being in place, it won't get hard!
Tempering is the easist of all the steps to accomplish.
Grain size, even carbon distribution, post foring techniques, proper temps and times for THAT STEEL, etc., are the hard parts.
Without those in place, tempering is just wasting gas and electricity.
I have found Lin to be a really good teacher, and he is one of my heros! Like he says, flex is, for the most part, determined by geometry. It's where the flex FAILS, and blades break, that is determined by heat treatment.
Which brings up another point!
Terminology.
"Heat treatment" begins at the mill, and ends with the final tempering.
Everything done between those two points can/will/might change the chemistry of the steel. That is all the "heat treatment". Simply said, anything that treats the steel with heat, is heat treating - milling, forging, normalizing, thermal cycling, annealing, hardening, tempering - are all one looooooooooooong heat treatment.
It's always easier to discuss these processes if all concerned use the term to describe the step/action.
That's all the bad news.
Good news is, steel is easily obtainable to match the maker's experience level.
I have been using my torch a lot lately, over the last few years, on my hunting sized knives.
The post I made a few weeks ago where the guy said he took 5 deer from "field to freezer" before he touched up his blade, was done with a torch.
Anybody can do it.
But! That steel was properly treated up to that point with concern to really watching forging and post forging steps for grain size and carbon distribution.
Why am I typing all of this and gettin' people mad at me? 'Cause I've got two blades in the oven just about done with their last tempering cycle and I've got some time on my hands.
When you get a steel up to the temp at which it is prescribed to be quenched, the steel is in the condition called "austenite". When you quench it, it transforms into a condition known as "martensite", which is the hardest condition of steel. But, it's also under a lot of stress and is quite brittle as a result of changing into a new structure.
However, ALL of the austenite does not make the transformation, and is known as "retained austenite". It is RETAINED in that condition.
When you do that first tempering cycle, on full hard steel, you are moving the "retained austenite". There was "left over" "stuff" that didn't get to transform into the "hard stuff" because the cooling process of the quench stopped it from occuring. As well, that first tempering cycle relieves stress, and some of the brittleness, created by the steel that DID make the transformation.
Now, since the "retained austenite" was able to make the transformation during the first tempering cycle into martensite, we need to relieve the stress created by its completion -hence, the second tempering cycle.
So, if you feel you've done a good job getting your steel hard in the first place, always give it two tempering cycles at the temp for that steel.
Almost sounds like I know what I'm talkin' about, but, for the most part, I've spent just enough time to learn the terms that define what I've been doing.
When I look at the graphs and photo-micrographs of steel - I'm a complete idiot. I haven't got a clue what they mean.
There are some really neat demos that can be done with steel, and I might do some photos that will show some of these. Just takes time.
Take an old file sometime, wrap it with tape, and bust it in two with a hammer. The tape keeps it from flying all over the shop like shrapnel.
Look at the grain. It's visibly fine and tight.
Now, get it TOO HOT and hold it there for a minute or so. By TOO HOT, I mean really yellow - yellow orange. HOT!!
Then quench it really quick in some warm oil.
Break it again.
The grain will be VISIBLY coarse and "grainy". Not good for a knife. If you get your steel too hot before you quench it, or right at the end of forging, and fail to do grain reducing steps, you've got junk.
Now, take the file, get it just above non-magnetic, the next color change above non-magnetic, and let it cool back to black. Do this three times.
You are reducing the grain size.
This is what you should do after forging your blade. It sort of "corrects" your forging errors.
Now, get that file just back up to barely above non-magnetic and quench.
Break it again.
The grain will be back to fine!
Easy demostration that what we are doing with time and temp effects the steel - either good or bad.
I'll give you two things I've heard over the years,
"Jesus Christ, Himself, could send a bar of steel down from Heaven. It'll only be as good as the heat treatment it gets."
and,
"The most a blacksmith can ever hope for is to end up with as good a piece of steel as the one he started out with."
Simply stated, we have far more opportunities to ruin good steel , than we have to improve it.
Anyway, have I gone on long enough?
You probably weren't expecting that Lin.
Sorry.
Everybody's probably mad at me now.
Topic: Tempering Question (Read 3220 times)
