Heat treat issues

[wingnutgabber]

I am a beginner knife maker doing stock removal. I am having difficulty getting my blades hard. For heating I am using a knife dog heat treat kiln. I am using 80crv2 and SUP9 for my metals. I use the heat treat guide posted by New Jersey Steel Baron. First cycle at 1650 for 18 minutes then air cool. Second cycle at 1500 for 18 minutes then air cool, third cycle at 1350 for 18 minutes and air cool. Austenizing is use knife steel nerd recommend temp of 1525 soak for 18 minutes. I quench in heated canola oil. Thermometer says it’s between 125-140 when I quench. Tank is below oven so blade comes out and straight in. After 15 seconds in oil then into aluminum plate vise for final cooling. I was able to get two blades hardened. All the others I’ve done have my hardness files dig in. I sand away all scale before testing. Can anyone give some advice on what I am doing wrong?
Thanks

 

[DevinT]

Good job .

I would change a couple of things.
Normalize @1600’f for 10 minutes and air cool.
Cycle @1450’f twice for 5 minutes to refine the grain, air cool or plate quench.

Austenitize from 1525’f for 10 minutes and quench in parks 50 oil.

Temper at 350-400 depending on desired hardness.

The two problems I see are too much time at thermal cycling causing excessive decarb.
Wrong quench oil.

Maybe coat the blade in turco to prevent scaling. Canola oil is not a good quench oil.

You’re on the right track just need a couple of small adjustments.

Hoss

Edit: I looked it up and Larrin recommends using 1525’f for normalizing

 

[Larrin]

Likely the issue is you have decarb under the scale that you aren’t removing

 

[Stacy E. Apelt - Bladesmith]

Yup, decarb. Grind away a good bit (two or three thousandths) and you will suddenly see sparks. Test again and I bet it is hard.

Hoss and Devin are giving good advice.

 

[wingnutgabber]

Good job .

I would change a couple of things.
Normalize @1600’f for 10 minutes and air cool.
Cycle @1450’f twice for 5 minutes to refine the grain, air cool or plate quench.

Austenitize from 1525’f for 10 minutes and quench in parks 50 oil.

Temper at 350-400 depending on desired hardness.

The two problems I see are too much time at thermal cycling causing excessive decarb.
Wrong quench oil.

Maybe coat the blade in turco to prevent scaling. Canola oil is not a good quench oil.

You’re on the right track just need a couple of small adjustments.

Hoss

Edit: I looked it up and Larrin recommends using 1525’f for normalizing

Thank you. I will change those things you recommended. I ordered some speed oil two weeks ago but it will be a while before it will show up.

 

[wingnutgabber]

Likely the issue is you have decarb under the scale that you aren’t removing

Thank you for the tip. I am sanding to bare metal and then some. I’ll try more.

 

[wingnutgabber]

Yup, decarb. Grind away a good bit (two or three thousandths) and you will suddenly see sparks. Test again and I bet it is hard.

Hoss and Devin are giving good advice.

Thank you. I will try sanding more.

 

[DevinT]

Be aware that you can get under the scale and still have decarb.

Hoss

 

[wingnutgabber]

Be aware that you can get under the scale and still have decarb.

Hoss

Thank you. I sanded really heavy to the point I sanded off my makers mark and still not hard.

 

[wingnutgabber]

Good job .

I would change a couple of things.
Normalize @1600’f for 10 minutes and air cool.
Cycle @1450’f twice for 5 minutes to refine the grain, air cool or plate quench.

Austenitize from 1525’f for 10 minutes and quench in parks 50 oil.

Temper at 350-400 depending on desired hardness.

The two problems I see are too much time at thermal cycling causing excessive decarb.
Wrong quench oil.

Maybe coat the blade in turco to prevent scaling. Canola oil is not a good quench oil.

You’re on the right track just need a couple of small adjustments.

Hoss

Edit: I looked it up and Larrin recommends using 1525’f for normalizing

I tried everything you suggested minus the parks50 since it’s not here and I still can’t get a hard blade. For the life of me I can’t figure out why I was able to get two blades hard and the rest not.

 

[DevinT]

I tried everything you suggested minus the parks50 since it’s not here and I still can’t get a hard blade. For the life of me I can’t figure out why I was able to get two blades hard and the rest not.

How thick is your material?

Hoss

 

[DevinT]

I tried everything you suggested minus the parks50 since it’s not here and I still can’t get a hard blade. For the life of me I can’t figure out why I was able to get two blades hard and the rest not.

Soak a coupon at 1525’f for 10 minutes and quench in water to see if it’s the oil. Try it from the as received condition.

Hoss

 

[wingnutgabber]

How thick is your material?

Hoss

A bit less than 5/32.

 

[wingnutgabber]

Soak a coupon at 1525’f for 10 minutes and quench in water to see if it’s the oil. Try it from the as received condition.

Hoss

By coupon I am assuming you mean scrap pieced metal and not a printed piece of paper that gives a discount. I will try tomorrow. Do you recommend I do the full cycle or just heat to 1525 and dunk?

 

[Alex Topfer]

You could test one in water. Don't expect it to survive but that will give you a very fast quench to compare to, in case it's something to do with the starting structure of your steel
Do you have any way to calibrate the oven?

 

[wingnutgabber]

You could test one in water. Don't expect it to survive but that will give you a very fast quench to compare to, in case it's something to do with the starting structure of your steel
Do you have any way to calibrate the oven?

I will try water quench. The oven is brand new but idk about a way to check to see if it’s calibrated to exact temp.

 

[DevinT]

By coupon I am assuming you mean scrap pieced metal and not a printed piece of paper that gives a discount. I will try tomorrow. Do you recommend I do the full cycle or just heat to 1525 and dunk?

Coupon is a word used in metal working to mean small piece. A welding coupon or a heat treating coupon etc.

I would try it without any cycling, in the as received condition.

Hoss

 

[wingnutgabber]

Coupon is a word used in metal working to mean small piece. A welding coupon or a heat treating coupon etc.

I would try it without any cycling, in the as received condition.



Hoss

I am to new to metal working to understand terms. I went to my paper recycling bin and dug out some just in case thats what you were actually talking about. I will give the scrap metal in water a try tomorrow and let you know results.

 

[Stacy E. Apelt - Bladesmith]

I'll explain decarb a bit:
When the steel is in the HT oven for long periods of time the oxygen in the air reacts with the carbon in the steel and removes it from the surface as carbon-dioxide.
This leaves a thin layer of metal on the surface that has lower carbon content ... called decarb. It can be very deep in some cases and go several thousandths into the steel bar/knife. This isn't the scale on the surface, it is a layer of the bar that is still steel ... just low carbon content. If you remove the scale and sand the bar the decarb layer will be shiny bare metal. However, a test for hardness will say the bar is not hard. This is because decarb is very soft.
Below the decarb is hard steel. You must remove the decarb on all knife blades that were hardened in an open-air chamber (or forge). This is more than just sanding it to shiny. You have to grind away a few thousandths of an inch of the surface. Once through the decarb you will usually find the blade fully hardened.

The three main ways to prevent/lessen decarb are:
1) Use a foil packet to encase the blade. This is the normal method used for stainless steel blades. These steels are hardened at higher temperatures for longer time and decarb would ruin the blade. Some carbon steels that need long soak times are also done in foil packets. The foil is called Stainless HT foil and is a thin stainless-steel sheet. Wear gloves, as it will cut you severely if not careful ... especially after the HT is done and the foil has hardened. The packet must be sealed tightly by double folds and hammering the seams tight.

2) Coat a carbon steel blade with an anti-oxidation coating. These are various clays or "paints" that makes a thin coat on the blade surface and keep the oxygen away from the carbon. Some folks use a thin wash of satanite, others use pre-made commercial coatings like Brownell's anti-scale, ATP, Turco, and Nu-Clayer. Coatings do not work at stainless steel HT temps.

3) The other way to lessen/eliminate decarb is to keep oxygen out of the HT oven. There are special HT ovens that use nitrogen or argon to fill the chamber and exclude oxygen. In industrial setups, the ovens are vacuum sealed, and the air is removed. These ovens are very expensive, and the gas can also be expensive. It is not practical to convert a normal knife HT oven to these types.

 

[wingnutgabber]

I'll explain decarb a bit:
When the steel is in the HT oven for long periods of time the oxygen in the air reacts with the carbon in the steel and removes it from the surface as carbon-dioxide.
This leaves a thin layer of metal on the surface that has lower carbon content ... called decarb. It can be very deep in some cases and go several thousandths into the steel bar/knife. This isn't the scale on the surface, it is a layer of the bar that is still steel ... just low carbon content. If you remove the scale and sand the bar the decarb layer will be shiny bare metal. However, a test for hardness will say the bar is not hard. This is because decarb is very soft.
Below the decarb is hard steel. You must remove the decarb on all knife blades that were hardened in an open-air chamber (or forge). This is more than just sanding it to shiny. You have to grind away a few thousandths of an inch of the surface. Once through the decarb you will usually find the blade fully hardened.

The three main ways to prevent/lessen decarb are:
1) Use a foil packet to encase the blade. This is the normal method used for stainless steel blades. These steels are hardened at higher temperatures for longer time and decarb would ruin the blade. Some carbon steels that need long soak times are also done in foil packets. The foil is called Stainless HT foil and is a thin stainless-steel sheet. Wear gloves, as it will cut you severely if not careful ... especially after the HT is done and the foil has hardened. The packet must be sealed tightly by double folds and hammering the seams tight.

2) Coat a carbon steel blade with an anti-oxidation coating. These are various clays or "paints" that makes a thin coat on the blade surface and keep the oxygen away from the carbon. Some folks use a thin wash of satanite, others use pre-made commercial coatings like Brownell's anti-scale, ATP, Turco, and Nu-Clayer. Coatings do not work at stainless steel HT temps.

3) The other way to lessen/eliminate decarb is to keep oxygen out of the HT oven. There are special HT ovens that use nitrogen or argon to fill the chamber and exclude oxygen. In industrial setups, the ovens are vacuum sealed, and the air is removed. These ovens are very expensive, and the gas can also be expensive. It is not practical to convert a normal knife HT oven to these types.

No mater how much I grind off, there is no hard metal on the blades that I have quenched. I have not tempered these since the were not hard post quench.