pre heat treat finish requirements

samuraistuart

samuraistuart

Joined
Dec 21, 2006
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How critical is it to remove the previous grit's scratches in a pre heat treat finish? I know the FINAL polish depends heavily on removing every single scratch left from the previous grit. I take my progression up to 220 pre heat treat (all hand done...no belt sander), and I know that it's important to have the 220 finish running lengthwise prior to hardening, just wondering if I can get away with some cheating, and go from my smooth file, to 220, as long as the edges, corners, etc don't have scratches on them as a place for a crack to propagate.

I guess this might affect your answer.....post heat treat I go back to 80 grit to remove the decarb layer, and then on up to 600 or whatever the blade requires. So doing nice detail finishing work pre heat treat will be erased by the 80 grit post heat treat.

Thanks for your thoughts! Looking forward to see if I can save a bit of time. Trial and error may be necessary here, but thought I'd call in the experts first!
 
I'm saying to go to 400 pre heat treat if you are doing the working all by hand and thin down that edge. I reasonable heat treat will let that work. Frank
 
On carbon steel I only go to 120X before H/T. I also just do a belt finish, no hand sanding. On air hardening stuff I got to about 220X or 320X.
 
Darrin certainly knows the steels much better than I do. As well I only work with carbon Damascus or stainless. Frank
 
If you have a grinder, getting deeper and heavier scratches out after HT isn't all that big of a deal. With a grinder 220 grit, or even 120 grit will get things flat and pre-shaped.
When doing it by hand, make dead sure every scratch and bump is gone before HT. I suggest 400 grit pre-HT.
 
Frank Niro said:
Darrin certainly knows the steels much better than I do. As well I only work with carbon Damascus or stainless. Frank
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I don't claim to know steels better than anyone Mr. Frank. Especially someone who has been doing this for as long as you have. I was just sharing what works for me. I somehow missed that he was doing everything by hand. Now that I've read that, I agree with you and Stacy, every bit of work you can do before H/T will save you time and effort after H/T.
 
When doing blades by hand, I went to 400 pre heat treat. With the 2x72, I rough grind, do a quick cleanup with a 120 or 220g belt to make sure there are no flaws to take out post heat treat, and then heat treat. The structured abrasives have no problem cleaning up the blades post heat treat. I can leave the edge a little thicker which helps prevent warps on the blades larger than 5". With stainless, I go to my final grit prior to heat treat. I mistakenly did my first s35vn kitchen knife like I did my carbon steel blades, and man did it suck cleaning that one up post heat treat! :grumpy: :eek:

Whoops, I missed that Stacy posted the exact same thing.
 
Correct me If I am wrong as I am still new to this. The main difference is with oil hardening steels you cant take em to final shape before heat treat without risk of warping. So why bother finish sanding? With the air hardening steels you can get pretty close to finish shape so take em up to higher grits as mentioned above.
 
The air hardening steels are shielded in foil, so they don't decarb. With oil hardening steels, there isn't time to get the steel out of the foil to quench, so decarb is the issue. You have to grind the decarb off of the blade after heat treat. If you are finishing by hand, getting close to final shape is better as hardened steel is a pain to finish by hand.
 
I grind to 120gt. then hand sand to 220 before HT. That said, most of my blades get heavily etched when finishing. Have you tried to reduce decarb with a thin layer of clay slip?
 
Rick, I LIKE decarb. I do NOT want to prevent it. Why? I hand sand all my blades (all carbon steel...no stainless yet), and as such, it is VERY nice to have a soft layer of steel to grind off before reaching a hard edge. I have to leave the edge around .030 before heat treat, and I like to have an edge around .010 or 005 before sharpening. So having a soft layer of steel to sand thru post heat treat is beneficial to me, that layer being the decarb layer. I hope this makes sense. To be honest, I don't think I'm making my point very well. I should have said before hand that I do not use any stainless, all carbon steel. I'm trying to save time pre heat treat finish, and with carbon steel I see no need at all to go beyond 220 pre heat treat, with my set up and work procedure, as I MUST come back after heat treat with 80 grit to get thru the decarb layer, and have a nice thin (005) edge before sharpening. When I thermal cycle my carbon steel for grain refinement (I think Rick and I talked about this in another thread), I sand off the scale buildup between each cycle, to INDUCE decarb. Leaving the scale will help to reduce decarb, as I understand. Again, since my edge is 030 pre HT, and I want it 005 or os post HT, I like decarb....as it is easier to sand thru than hardened steel.
 
timos- said:
Correct me If I am wrong as I am still new to this. The main difference is with oil hardening steels you cant take em to final shape before heat treat without risk of warping. So why bother finish sanding? With the air hardening steels you can get pretty close to finish shape so take em up to higher grits as mentioned above.
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I'm new to the area of HT. Does oil hardening and air hardening only apply to carbon steels?

I'm other words, are there stainless steels that are oil hardened or are all stainless steels air hardened?
 
Just to be sure, when you guys sand to a higher grit like 400 pre-HT, you then go back down to the lowest grit and work your way back up pre-HT, right? If that's the case, then why do you sand to a higher grit in the first place, only to have it taken back down? Maybe I missed something when researching this.
 
Masterjuggler said:
Just to be sure, when you guys sand to a higher grit like 400 pre-HT, you then go back down to the lowest grit and work your way back up pre-HT, right? If that's the case, then why do you sand to a higher grit in the first place, only to have it taken back down? Maybe I missed something when researching this.
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Think of a sanded surface as rows of peaks and valleys. The higher and sharper the peaks, the more they are sensitive to heat. The thinner, the hotter so-to-speak. Those variances in temperature(especially the overheated peaks) cause "heat/stress risers" and the deep valley are perfect places for fractures to start(think of those snap off exacto-blade scorings). Hardening puts a tremendous amount of stress into the steel, so you want it as smooth as possible to uniformly spread out all that pent up energy.
 
The higher grit pre-HT is to make sure the lower grit scratches are gone.
Once HT is done, you have to grind/sand off the scale, decarb, and remove enough metal to get the blade down to finished thickness. This is done easier at lower grits. Thus, you drop back one grit when sanding post HT.
 
samuraistuart said:
Rick, I LIKE decarb. I do NOT want to prevent it. Why? I hand sand all my blades (all carbon steel...no stainless yet), and as such, it is VERY nice to have a soft layer of steel to grind off before reaching a hard edge. I have to leave the edge around .030 before heat treat, and I like to have an edge around .010 or 005 before sharpening. So having a soft layer of steel to sand thru post heat treat is beneficial to me, that layer being the decarb layer. I hope this makes sense. To be honest, I don't think I'm making my point very well. I should have said before hand that I do not use any stainless, all carbon steel. I'm trying to save time pre heat treat finish, and with carbon steel I see no need at all to go beyond 220 pre heat treat, with my set up and work procedure, as I MUST come back after heat treat with 80 grit to get thru the decarb layer, and have a nice thin (005) edge before sharpening. When I thermal cycle my carbon steel for grain refinement (I think Rick and I talked about this in another thread), I sand off the scale buildup between each cycle, to INDUCE decarb. Leaving the scale will help to reduce decarb, as I understand. Again, since my edge is 030 pre HT, and I want it 005 or os post HT, I like decarb....as it is easier to sand thru than hardened steel.
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I get ya, Stu... but what if...

You thermal cycled after forging, prior to stock removal(without sanding in between). Worked that(Uniformly softened) steel to shape(once) down to .015. Then did your best to prevent decarb(clay slip). It sounds like a LOT less work and cost to me than heat-sand-heat-sand-heat... and hoping you still have a decent amount of carbon content at the end of it.

To me, it's a no brainer and I went the way of files and paper for a long time so I know your pain.
 
Rick Marchand said:
I get ya, Stu... but what if...

You thermal cycled after forging, prior to stock removal(without sanding in between). Worked that(Uniformly softened) steel to shape(once) down to .015. Then did your best to prevent decarb(clay slip). It sounds like a LOT less work and cost to me than heat-sand-heat-sand-heat... and hoping you still have a decent amount of carbon content at the end of it.

To me, it's a no brainer and I went the way of files and paper for a long time so I know your pain.
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Truth.

Intentionally allowing carbon to be removed with NO control over how much is being removed...? Not so good.
 
M.FREEZE said:
I'm new to the area of HT. Does oil hardening and air hardening only apply to carbon steels?

I'm other words, are there stainless steels that are oil hardened or are all stainless steels air hardened?
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I'm no stainless expert, but from what I understand, the chromium in the stainless slows the cooling rate so much that the steel will harden as it air cools. I have read that 440c can be oil or air quenched, but I have assumed, possibly incorrectly, that this is for larger pieces. Carbon steels need a faster quench, but a few will air harden a certain amount such as L6, 52100, but they won't reach full hardness that way. The higher chromium steels like A2, D2 will air harden, but I don't know much about them as I haven't worked with them.
 
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