Bringing W2 up to hardening temp.

Jason Volkert

KNIFE MAKER
I have never heard of having to that with W2. As far as I know you want to get up to temp as quick as possible to prevent any unwanted grain growth. But I was wrong once before:rolleyes:
 

Sean Jones

Well-Known Member
Faster rates of heating can result in finer structure but also increases the effects of hysteresis, necessitating more time for to things to equalize. Most of it will depend on the condition going into the heat.
I had to look up the meaning of hysteresis. If I understand it correctly does this mean that you don't want it too hot but not too cool either? It will essentially stabilize at it's own rate?
 

Kevin R. Cashen

Super Moderator
One can push Ac1 or Ar1 (i.e. critical temperatures in heating or cooling) as much as 100°F off its expected point simply by changing rates of heating or cooling. Say your target temperature is 1475°F, with a reasonable rate of heating the diffusion rate of the carbon will allow the desired solution shortly after the temperature is achieved, but if your rate of heating outpaces the rate of diffusion enough, you will have to either increase your target temperature or increase your time at temperature in order to compensate and allow the carbon to catch up and give you the desired solution. This is another instance where soak times can play a significant role in proper solution, even in simple steels.

If you wish to see a very clear demonstration of hysteresis, heat a piece of steel through decalescence (Ac1), observe the "shadow" and the loss of magnetism, then air cool the steel and observed recalescence, where the brighter wave of energy moves though the steel and the magnet sticks again (Ar1). Theoretically Ac1 and Ar1 should be the same temperature, however the very different rates of heating and cooling pulls these two points to radically different temperatures.

This is one of the fundamental reasons for soak times, and the quicker you heat the steel the more time you need at the target temperature for the system to catch up. But… the finer the structures you are heating, the more readily they will go into solution, and thus the less compensation you will need for this issue.

Forge a piece of steel and simply normalize, with no anneal, and the carbon has very little distance to travel for full solution, so faster rates of heating can be used, with less need for compensation for the lag. Anneal that same piece of steel and the distance the carbon atoms need to travel increases enough that you either need to slow the heating (not the best approach for fine and uniform structures), or increase the time at temperature for proper solution.

Steel is not just steel, its properties change depending on what we have done to it and how we prepare it. If it was as simple as I thought it was when I was 25, I wouldn't have needed the last 27 years to understand how much I didn't know;) .


Edited to add- In case you haven't noticed, I LOVE steel. It is one of the most absolutely fascinating things I have ever studied, an entire universe of possibilities in one little piece. And when you make that piece into a blade it is the coolest thing that has ever been:D.
 
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Sean Jones

Well-Known Member
One can push Ac1 or Ar1 (i.e. critical temperatures in heating or cooling) as much as 100°F off its expected point simply by changing rates of heating or cooling. Say your target temperature is 1475°F, with a reasonable rate of heating the diffusion rate of the carbon will allow the desired solution shortly after the temperature is achieved, but if your rate of heating outpaces the rate of diffusion enough, you will have to either increase your target temperature or increase your time at temperature in order to compensate and allow the carbon to catch up and give you the desired solution. This is another instance where soak times can play a significant role in proper solution, even in simple steels.

If you wish to see a very clear demonstration of hysteresis, heat a piece of steel through decalescence (Ac1), observe the "shadow" and the loss of magnetism, then air cool the steel and observed recalescence, where the brighter wave of energy moves though the steel and the magnet sticks again (Ar1). Theoretically Ac1 and Ar1 should be the same temperature, however the very different rates of heating and cooling pulls these two points to radically different temperatures.

This is one of the fundamental reasons for soak times, and the quicker you heat the steel the more time you need at the target temperature for the system to catch up. But… the finer the structures you are heating, the more readily they will go into solution, and thus the less compensation you will need for this issue.

Forge a piece of steel and simply normalize, with no anneal, and the carbon has very little distance to travel for full solution, so faster rates of heating can be used, with less need for compensation for the lag. Anneal that same piece of steel and the distance the carbon atoms need to travel increases enough that you either need to slow the heating (not the best approach for fine and uniform structures), or increase the time at temperature for proper solution.

Steel is not just steel, its properties change depending on what we have done to it and how we prepare it. If it was as simple as I thought it was when I was 25, I wouldn't have needed the last 27 years to understand how much I didn't know;) .


Edited to add- In case you haven't noticed, I LOVE steel. It is one of the most absolutely fascinating things I have ever studied, an entire universe of possibilities in one little piece. And when you make that piece into a blade it is the coolest thing that has ever been:D.
Thanks for the further explanation Kevin. That really helped.
 

Doug Lester

Well-Known Member
When I cool my steel during heat cycling I hold the steel at a black heat as it is cooling and check for magnetism to return as a sign that the iron crystals have converted back to a body centered cube and I have noted that this take a while. Is this because the steel is cooling slower than I think it is or does the point where magnetism returns shift to a lower temperature when the steel cools?

Doug
 

flatblackcapo

Well-Known Member
One can push Ac1 or Ar1 (i.e. critical temperatures in heating or cooling) as much as 100°F off its expected point simply by changing rates of heating or cooling. Say your target temperature is 1475°F, with a reasonable rate of heating the diffusion rate of the carbon will allow the desired solution shortly after the temperature is achieved, but if your rate of heating outpaces the rate of diffusion enough, you will have to either increase your target temperature or increase your time at temperature in order to compensate and allow the carbon to catch up and give you the desired solution. This is another instance where soak times can play a significant role in proper solution, even in simple steels.

If you wish to see a very clear demonstration of hysteresis, heat a piece of steel through decalescence (Ac1), observe the "shadow" and the loss of magnetism, then air cool the steel and observed recalescence, where the brighter wave of energy moves though the steel and the magnet sticks again (Ar1). Theoretically Ac1 and Ar1 should be the same temperature, however the very different rates of heating and cooling pulls these two points to radically different temperatures.

This is one of the fundamental reasons for soak times, and the quicker you heat the steel the more time you need at the target temperature for the system to catch up. But… the finer the structures you are heating, the more readily they will go into solution, and thus the less compensation you will need for this issue.

Forge a piece of steel and simply normalize, with no anneal, and the carbon has very little distance to travel for full solution, so faster rates of heating can be used, with less need for compensation for the lag. Anneal that same piece of steel and the distance the carbon atoms need to travel increases enough that you either need to slow the heating (not the best approach for fine and uniform structures), or increase the time at temperature for proper solution.

Steel is not just steel, its properties change depending on what we have done to it and how we prepare it. If it was as simple as I thought it was when I was 25, I wouldn't have needed the last 27 years to understand how much I didn't know;) .


Edited to add- In case you haven't noticed, I LOVE steel. It is one of the most absolutely fascinating things I have ever studied, an entire universe of possibilities in one little piece. And when you make that piece into a blade it is the coolest thing that has ever been:D.
Thanks to all for taking the time to reply.

Kevin, I am using 1/8" W2 bar stock from Aldo , using a electric HT oven and Parks 50 for quench.
I haven't done anything to it prior to hardening.
I had read that it was important to bring W2 up through the 900* f range slowly but I did not see why it was important.
Are there other steps that I should be taking to improve the performance ?
 

flatblackcapo

Well-Known Member
I have been doing some more reading about Normalizing and grain refinement.
I have a few blades that are ground and ready for HT. ( stock removal )

Should I foil wrap these when I do the normalizing and grain refinement ( is this just called thermal cycling?)? Will leaving it in the foil to cool cause it to cool too slowly ?

Last question ( today ;)) does grain growth only start happening above austenitic temps?
 

tkroenlein

Well-Known Member
Thanks to all for taking the time to reply.

Kevin, I am using 1/8" W2 bar stock from Aldo , using a electric HT oven and Parks 50 for quench.
I haven't done anything to it prior to hardening.
I had read that it was important to bring W2 up through the 900* f range slowly but I did not see why it was important.
Are there other steps that I should be taking to improve the performance ?
Because of some things I've read in other forums, I think you should do a test coupon of this W2 before you HT blades. Apparently there are some reporting standard normalization and HT practices are not achieving full hardness. Perhaps you're already aware. I haven't experienced this myself, and don't intend to fear monger or dis anyone. But I'd test it if it was my own.
 

flatblackcapo

Well-Known Member
Because of some things I've read in other forums, I think you should do a test coupon of this W2 before you HT blades. Apparently there are some reporting standard normalization and HT practices are not achieving full hardness. Perhaps you're already aware. I haven't experienced this myself, and don't intend to fear monger or dis anyone. But I'd test it if it was my own.
Thank you, tkoenlein for the heads up.
 

Doug Lester

Well-Known Member
Part of the recommendation for doing coupons to test the heat treatment before making blades from a given order of W2 is that there is W2 and then there's W2. I know that buyers ask the foundry for a target range for the alloy but the carbon content, even though it's the easiest to manage, can vary a bit and ask for a random melt of W2 and the carbon content can differ a whole lot.

Doug
 

flatblackcapo

Well-Known Member
Part of the recommendation for doing coupons to test the heat treatment before making blades from a given order of W2 is that there is W2 and then there's W2. I know that buyers ask the foundry for a target range for the alloy but the carbon content, even though it's the easiest to manage, can vary a bit and ask for a random melt of W2 and the carbon content can differ a whole lot.

Doug
Thanks, I have done a bit more reading and will definitely do some testing.
Thanks for the help
 
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