01 steel heavy scale

[Txcwboy]

What causes this ? Is it heavy scale ? its 1/8 01 steel.

thanks

Dave

[Doug Lester]

Dave, what was happening with the steel when this occured; were you heat treating?

Doug Lester

[Txcwboy]

Yes..I had just HT it. 6" gas single Roy type burner.Let it soak some to make sure it was all uniform color..Its a 8" chef knife.

Dave

[pipecrafter]

I've found that O1 is very sensitive to overheating, and when you do overheat it, you get that lizard skin pattern on the surface. I'll bet that that the steel has got absolutely huge grain structure, and while it might be very hard, it may be fragile as well.

What I would do in an attempt to salvage it is grind it down, then go through the whole HT process again, including normalizing prior to hardening.

[Doug Lester]

Soaking in white vinegar overnight followed by a scrub with a wire brush will take care of most of the scale. I agree with Kurt's advice to re-heat treat with multiple normalizations to reduce grain size. I found that one of my big problems with heat treating was running my forge too hot. Now I run my forge wide open only long enough to get it heated up evenly and then I turn the gas and air back to where the forge glows red, not yellow. I found that the blade heated more evenly and I didn't have as much problem with the edge getting yellow while the spine was still non-magnetic and soaking didn't overheat the whole blade. With the burner cranked back it is easier to bring the whole blade up to an even heat and soak for about a minute after reaching non-magnetic without worrying so much about grain growth. Good heat treating requires good heat control.

Doug Lester

[B.Finnigan]

Without a good vortex swirl of heat in a forge you will have hot spots but not be able to know exactly where.

I do the same thing as Doug. The only flame I see in my forge is the rich purple/yellow coming out the front. Inside is nice even heat with no visible flame.

Using forced air gives you infinite control of the atmosphere for the needed task. 80% of my knife forging/Hting problems were gone when I switched over from a venturi.

It's supposed to be fun not frustrating.

[Txcwboy]

I havent ever normalized . I ve been one of those Heat and Dunk guys ..I know.
I do try to watch for colors though.So to do this correctly.. heat to nonmagnetic then pull out and let it air cool to what temp ? Then HT and temper ? I normally dont do blades this big and have had good luck with those.

it did slip in my tongs and ended up going tip first in oil ..it warped a tiny bit near tip. But I fixed that when i tried to straighten it...it broke ! hahaha Its now a shorter chefs knife .

Dave

[Doug Lester]

To normalize, heat to non-magnetic, let the steel soak for several seconds to assure thorough austinization, then pull it out and let it cool. I cool my blades until they are cool enough to touch, not necessarily to ambient temperature. Others have noted that they cool to a black heat. I don't know if it really matters. Once the phase conversion is complete, I don't know what the additional cooling does but it doesn't hurt. What you are doing is forming new crystals on the boundries of the old crystal; the type of crystal that is forming depends on the phase that the steel is in. Unless you overheat the steel, the new crystals will be smaller than the crystal that they are replacing, refining the grain. The reforming of the crystals also allows for the reduction of the stress between the crystals that is caused by having them shoved around by a hammer during forging.

Doug Lester

[Kevin R. Cashen]

Txcwboy, B.Finnigan has some good tips here. Everything I see on your blade can be controlled with atmosphere. Heat plays a factor in that it accelerates the effects of atmosphere. There are two thing happening with the surface of steel when you heat it and expose it to the atmosphere- scaling (the loss of iron to oxygen) and decarburization (the loss of carbon to oxygen). Clean forgings and heat treated parts come from either eliminating the oxygen entirely (foil wraps, antiscale compounds, or inert gas or vacuum ovens) or finding a healthy balance between the scale and the decarb while controlling excess O2 to reduce both.

Adjusting your forge to a good carburizing flame to reduce the amount of free O2 could reduce both, but when forging and doing other longer heat operations a very fine scale is your friend as it removes iron in balance with the decarb. Huge sheets of scale flaking off your blades is way too much oxidation- reduce both your heat and your oxygen.

What I see mostly on you blade is decarb, this will result in one of those pesky blades that will not hold a proper edge until it has been resharpened two or three times. If you cannot eliminate that mottled surface effect then always leave around 3-5 thousandths to grind off after you are done.