FINSH AFTER HEAT TREATING

[DANA HOLMAN]

GOOD MORNING GUYS
TO START, I TOUGHT I HAD TO FINSH THE BLADE TO FINAL FINSH BEFORE I HEAT TREATED AND TEMPERED
SO I DID ON THREE BLADES, NOW AFTER HEAT TREATING AND TEMPERING I'M DOING THE SAME WORK ALL OVER AGAIN, I GUESS MY QUESTION IS, TO WHAT GRIT OR FINSH DO MOST OF YOU TAKE YOUR BLADES TO BEFORE HEAT TREATING? THERE IS ALOT OF ELBOW GREASE IN THESE BLADES BEFORE HEATING THEM.
ANY AND ALL INFO PLEASE
DANA

[mwmwmb]

I usually just shape and 80grit. because like you said there is a lot of work after the temper. but i am no expert

[DANA HOLMAN]

THANKS
I DON'T MIND THE WORK BUT I REALLY DON'T WANT TO DO IT TWO TIMES (WORK SMARTER NOT HARDER)
THANKS FOR YOUR INPUT

[Phoenix 1967]

I usually take it to 220 prior to hardening, then hit it witha scotch brite pad to give myself a shiny spot on the blade before tempering. After tempering, the color on the shiny spot will give you and Idea of how hard it is.

[DANA HOLMAN]

LAWREN
WHAT DO YOU MEAN, WHAT WILL THE SHINY SPOT LOOK LIKE?

[Phoenix 1967]

When steel is heated in tempering, oxides form on the surface. The color tells us how hot the steel has gotten (and how evenly if you cleaned the whole blade) the chart below gives an idea of the colors (though the temps on the left are in C, not F)

 

Knowing the type of steel, and the hardness at a certain color (The Machinist handbook has charts for many different steels) will help decide how hot, and how long we temper for the desired properties. Most blade steels do well at a straw, to deep straw color.

[DANA HOLMAN]

THANKS LAWREN
I LEARNED SOMETHING TODAY, OLD DOGS CAN LEARN NEW TRICKS
THANKS AGAIN

[Jeremy]

I take it to 220 grit normally before hardening.  If you don't go to at least that fine a grit you run the risk of cracking the blade due to stress risers on the blade... the same thing can happen if you don't round over all your edges.  Remember that quenching hot steel in oil or water is a violent process that introduces lots of stress into the blade.

After hardening I check it with a file to make sure the blade hardened properly, then hit at least part of it with 180-220 grit (what ever is on the grinder at the time really) to get down to bare steel.

[DANA HOLMAN]

thanks jeremy
the blades that i hardened there was only one or two little scratch in the blade. is this going to hurt anything, is it hard enought
thanks
p.s. a frind told me about the caps, did not mean to offend anyone, i just don't use the little finger very much.
dana

[kbaknife]

Dana, your tempering times and temperatures will only be relevant if you got a full transformation to martensite in the first place.
That requires proper set up of the steel's condition prior to austenizing, steel alloy type, temperature control and and soak time at the correct temp, and achieving full hardness by using the proper quench media.
You can heat up a piece of steel and get it any color you want, but that color is irrelevnat if you did not acquire full hardness in the first place.
Focus on getting your KNOWN steel fully transfered to martensite and THEN concern yourself with tempering.
All of those tempering times and temperatures are designed to complete retained austenite transformation to martensite, and to relieve induced stresses from creating the martensite formation in the first place.
They mean nothing without full hardness achieved in the first place.
You can put any old piece of steel in an oven and turn it some color, but that has nothing to do with its hardness.
It all depends on your successes prior to that point.
Even the atmosphere of the oven will effect the color. But what we need to do FIRST is get full hardness of the steel.
that is done with knowing the alloy of the steel you have, proper temp control and soak times for that alloy, and creating martensite with the right quench media.

[Phoenix 1967]

That is, of course true, I was pre-supposing that Dana already knew how to harden the steel he had. The tempering colors only mean something if you start with a fully hardended piece.
Thank you for clarifying KBA

[Todd Robbins]

I use a hand held orbital sander from Harbor Freight to take mine to 600 grit, and then hand sand with 600 grit sandpaper, keeping the scratch pattern parallel to the edge.  I also do the edge and spine the same way.  It's a little overkill, but I haven't cracked a blade, even quenching a lot in brine, in a pretty long while.  The orbital sander makes it a lot easier for less than 20 bucks.

Todd