Re-hardening?

Hi All,

Well I have finished making my first razor out of 1084fg steel but it will not take an edge.
I have triple tempered in a precision oven at 230°c (446°f) and the steel is soft enough but I keep getting microchips at the edge when I go to hone it.
When I first hardened it I think the steel was not hot enough. I left it in the oven at 815°c (1499°f) for about 4 minutes.
It was glowing a dull orange and there was no flame up when quenching it in warmed vegetable oil.
I suspect that if the blade is not hardened properly then the austenite did not all get converted to martensite and so the grain will be weird.

My question is, can I just repeat the hardening/tempering process with the blade fully ground?
Do I need to normalise before re-hardening or can I just go ahead and whack it in at 815°c again?

It is a 1/4 hollow grind so I suspect that the edge will warp but at this point I have little choice.

Cheers,

Ash.

I had this problem before, I asked a couple of our resident experts and they mentioned decarburization(spelling?). On one occasion I completely re_cooked the blade, then reground and ended up with a little smaller blade, the other time I kept honing until I got to good steel, then reground to tighten up the bevel.
Good luck,
Eric

Edit: Im not to familiar with 10xx series steels, but I was under the impression that with 10xx you heat to critical and quench immeditely... 4 mins may have been too much.

Quote:

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Originally Posted by epd

I had this problem before, I asked a couple of our resident experts and they mentioned decarburization(spelling?). On one occasion I completely re_cooked the blade, then reground and ended up with a little smaller blade, the other time I kept honing until I got to good steel, then reground to tighten up the bevel.
Good luck,
Eric

Edit: Im not to familiar with 10xx series steels, but I was under the impression that with 10xx you heat to critical and quench immeditely... 4 mins may have been too much.

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Thanks for the reply. Well I'm not certain it made it to critical in that time in the furnace. It's an electronic furnace so air heating only.
So did the one you re-cooked work out OK and take a good edge even though you needed to regrind?

Edit: Ah so decarburization is the effect of loss of carbon on the surface of the steel. I thought this was limited to the depth of the scale. So it turns out that in an oven, decarburization is pretty high due to the oxidative environment. This still cannot explain what I am seeing though, since I left about 0.5mm of steel to final grind and I am sure that this is good steel.

Four minutes is not too long for this steel, not at that controlled temperature. Microchips sound like the steel is fracturing and that would be typical for a through-hardening steel like this one. Almost certainly the edge will have shifted to austenite in a thin section like a razor.

Possibilities:

Did you forge this blade? The heat history of the bar itself may tell the story of what's going on. This is where I would look for either grain growth and/or decarburization. Eric's idea is a good one though, maybe keep working on the hone and see if you get past the outer skin and find a less crumbly solid portion.

The oil quench temperature? It may have been too high to bring the blade down past the nose of the TTT curve and you missed hardening. For this steel some diagrams show that you have between 0.5-2.0 seconds to get from the austenitizing temperature to below 3-400 degrees C to miss that curve and have a hard blade. Try a cooler oil. Definitely not water unless you like "The Dreaded Ping."

You can definitely reheat the blade but at a razor's edge there is no meat to allow for warping and it could do that (potato chip edge). The steel doesn't care how many times it's heated. With the temperature control of your oven you're not overcooking it for sure.

Edit: you responded before I got in there. You can cover the blade with a surface coating of refractory to prevent scale formation in an electric oven. See here: http://www.brownells.com/gunsmith-to...urce=CJ&ch=aff

Sorry I just re-read that, I also have an air kiln. 4 mins is not enough time you are correct. I let oven reach critical temp, insert razor, check with magnet until non-magnetic, or use a oxy acet torch until non magnetic and quench (my experience with 1095)

After ht all blades get re-ground, slower, and sometimes with water, to keep the temperature well below where you set your temper.

Hope that helps, there are a LOT of guys here with way more experience, someone will chime in soon.

Edit: Forget everything I said and listen to Mike!

Quote:

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Originally Posted by Mike Blue

Four minutes is not too long for this steel, not at that controlled temperature. Microchips sound like the steel is fracturing and that would be typical for a through-hardening steel like this one. Almost certainly the edge will have shifted to austenite in a thin section like a razor.

Possibilities:

Did you forge this blade? The heat history of the bar itself may tell the story of what's going on. This is where I would look for either grain growth and/or decarburization. Eric's idea is a good one though, maybe keep working on the hone and see if you get past the outer skin and find a less crumbly solid portion.

The oil quench temperature? It may have been too high to bring the blade down past the nose of the TTT curve and you missed hardening. For this steel some diagrams show that you have between 0.5-2.0 seconds to get from the austenitizing temperature to below 3-400 degrees C to miss that curve and have a hard blade. Try a cooler oil. Definitely not water unless you like "The Dreaded Ping."

You can definitely reheat the blade but at a razor's edge there is no meat to allow for warping and it could do that (potato chip edge). The steel doesn't care how many times it's heated. With the temperature control of your oven you're not overcooking it for sure.

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Thanks for your reply :)

It is not forged so I didn't normalise.
It was ground on a bench grinder and probably reached temperatures around the 250°c mark initially but I don't think that is anywhere near high enough to grow the grain.
It is 1084fg so has some vanadium to pin the grain anyway.

I heated the oil to 55°c. Is this too hot or too cold?
I agitated during the quench as well.
The blade was hard enough to skate a file after the heat treat.

The tempering process has softened the steel quite a bit.
In fact it's quite soft, soft enough to be scratched by a stainless steel rule.
Honing is fast but the edge is still chipping.
This is my problem.

I don't mind losing a few mm at the edge, it's a 9/8 blade anyway so going down to 8/8 or 7/8 would not be a huge loss.
If the edge does potato chip, how much could I expect to lose?
I've included a photo to help show the grind.

imgur: the simple image sharer

OK well I decided to re-burninate again and I had good colour temperature this time. It was in the furnace for 6 minutes so hopefully I didn't manage to grow the grain.
Quenching went very well and the steel actually feels different this time.
I heated the oil to 60°c instead. I based this temperature on tests performed at the following URL: Quenchants Derived from Vegetable Oils as Alternatives to Petroleum Oil | 2011-08-31 | Industrial Heating
I'm lucky, the edge didn't warp at all! All that tempering probably removed the internal stresses.

I'll temper the blade in a few mins when the furnace cools and let everyone know how it all went.

Cheers,

Ash.

I usually leave everything at room temperature. That seems to work well, though I always leave some extra meat to prevent warp.

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Originally Posted by Bruno

I usually leave everything at room temperature. That seems to work well, though I always leave some extra meat to prevent warp.

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This is what I do, why? Mike told me to do it...when I didn't listen: potato chip

Lesson learned.

Listen to Mike.

One other thing I could be curious about is your tempering temperature (the post hardening stress relieving aspect), that might lower the final hardness. But, if it skates a file, it's probably hard enough that it shouldn't be giving you so much trouble. Other factors are that scale can be hard sometimes and tempering the scale will make it seem much softer than the meat underneath.

This is where a keen observer will rise to his full strength. You're there with the blade in hand, while the rest of us depend on your description, times, temperatures etc. And, there are a lot of variables. Sounds like you're working a good program though.

Quote:

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Originally Posted by Mike Blue

One other thing I could be curious about is your tempering temperature (the post hardening stress relieving aspect), that might lower the final hardness. But, if it skates a file, it's probably hard enough that it shouldn't be giving you so much trouble. Other factors are that scale can be hard sometimes and tempering the scale will make it seem much softer than the meat underneath.

This is where a keen observer will rise to his full strength. You're there with the blade in hand, while the rest of us depend on your description, times, temperatures etc. And, there are a lot of variables. Sounds like you're working a good program though.

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Well what I discovered in the end is that I definitely didn't have it in the furnace long enough the first time to through harden. Maybe it case hardened?
In any case there was no visible decarburized pattern underneath the scale first time; there is this time.
Secondly the tempering process was done at the same temperature as last time (230°c) but this time it turned a nice shade of bronze, which it didn't do last time.

I haven't had a chance to regrind and start honing but it all feels better this time. More "right".

Thanks for all your help :)

Ash

Quote:

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Originally Posted by shooter74743

This is what I do, why? Mike told me to do it...when I didn't listen: potato chip

Lesson learned.

Listen to Mike.

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Room temperature slows the quench, so I believe. It's due to the viscosity of the oil being much higher at room temp, thus heat transfer slower even with agitation. That is probably why potato chip but I guess I am lucky that my edge didn't go all crinkle cut on me.

Bronze sounds really good. Cool. Pix when done, don't just keep us all on edge.... ;)