Hypereutectoid steels and soak

J

JeffreyFogleboch

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May 13, 2009
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Hey guys I've been wondering about how different the performance is with hypereutectoid steels when comparing one that is held at critical for 5-10 min vs one that is simply brought up to temp and quenched. Let's use W1, Hitachi blue 2, and cruforge V as examples. I've made knives out of W1 and cruforge and they both seem to perform very well and have excellent edge retention using with no soak. However, I have been reading that a 5-10 min soak with these 3 mentioned steels will yield better results. So my question is how much better? Is it necessary? I'm trying to determine whether or not I should heat treat my own blades made from the blue steel or have them heat treated properly with a temperature controlled kiln? What really peaked my curiosity was watching Murray carter and Japanese smiths heat treat their white and blue steels in a charcoal forge with no soak time. I know they yield fantastic blades but would they be potentially better if they were to use a kiln? Sorry for the long post and thanks guys!

-Jeff


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I wish it was as simple as that.
I use my forge, but how the steel is treated BEFORE austenizing is a very important part as well.
And I'm running my forge as about low as it will go and actually do get some soak time. So it's not just brought through the decalescent stage and then quenched.
The performance I've got out of Precision Marshall W1 is often quite extraordinary. This is forged down from large round stock, so a lot of set-up steps are necessary after forging and grinding.
DH III W2 stands alone and exceeds many other steels by following the steps I already mentioned.
I forge my CruV from large round stock, as well, and it gets some forge-soak-time and performs as well as I could ever expect a steel to.
 
Are you using a thermocouple at all? I think I can get my forge to soak if I'm careful but I can't be certain that the temp will remain constant without some sort of thermometer.


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As Karl said - "I wish it was as simple as that."
What a soak does is allow time for things to go into solution and get evenly distributed. In some cases, that is what you want .... and in others it isn't. The higher the alloy content, the more the soak time ( usually*).



*When working for hamon, the reverse may often be the case. You only want the steel to release the eutectoid in carbon and keep everything else locked up. Thus, you use lower temperatures and minimal soaks. This is why the Japanese smiths judge by eye and quench immediately upon deciding the steel is just right. They aren't necessarily trying to get the most from the steel, but are trying to get what they want from the steel.
 
have a look at this - http://www.bladeforums.com/forums/showthread.php/1397121-laminated-Hitachi-White-and-Blue-Steel-Heat-Treat-Process?p=16104069#post16104069

you can also see Tenebros comment about other Japanese smiths

Murray's method's aren't that popular I think, I may be the only one using it! haha
This is the way I learned so this is the only I've been doing it, little to no soak.

I can't answer your question since I don't have that testing or experience, but I wonder if at some point you (we) are chasing a point of diminishing returns...?

Harbeer
 
Very informative Stacy and very interesting! I too wish it were simple as that [emoji28] hsc- that's what I am trying to figure out...you and Murray both are having great success with this method it makes me wonder if there is any reason I'm doing it any other way. If I can get my forge to hold a constant temp I will make 2 test blades. One with a soak and one without and try and see if there is any significant difference

-Jeff


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Yes.
I am convinced that soak times "add up".
When 'soaking' at a specific temp, for the most part, what we're seeking is an evenly dispersed dissolving of alloy. Like Stacy said, the more alloy = the longer soak.
I often think of alloy in steel like the ingredients in a cake mix. The more ingredients, the more you have to stir it and cook it.
When I'm austenizing my blade in the forge, I am in and out repeatedly checking colors and watching closely what's going on. It often takes a loooooong time for the steel to get up to temp. Once there, soak time begins and the alloy really begins to dissolve and equalize. My main focus is to no get too hot too long, so I pull it out to avoid over heating.
This may only be a few seconds, and then back in.
A little more soak time.
Do this repeatedly and it adds up.
Just avoid over heating.
This method works well with the lower alloy steels. It doesn't take much.
And working with hamons is a not-so-difficult learning process when you can put the heat where you want it.

 
Also how heavily spheroidized the steel is will determine if a soak is needed. Most of the time our steels are fine spheroidized annealed. This alone requires a short soak to put the carbon in solution. If you have a hypereutectoid steel, like O1, Blue 2, CFV, then the soak is needed not only to break up the spheroidized carbides, but also to help put the excess carbon in solution. The heavier the spheroidizing, the more alloying, the longer the soak.

The way I understand, if the steel is in a fine pearlite state (after thermal cycles air cool only), the soak can be shortened (spheroidized carbides have been broken up already...hopefully...especially with a normalizing). However, if you're dealing with hypereutectoids, and fine pearlite, the soak is still needed because of the excess carbon and alloying.

Carbon in solution is temp driven way more than time, so if your temp is high, shorten the soak time. If you're sticking to 1475F, use soak.
 
The Verhoeven PDF is instrumental in learning about this. Different elements move at different rates and the rates change at different temperatures. The structure of the steel, such as speroidized, course or fine, the type of pearlite, all effect the rate of diffusion of these elements. This is why some of us normalize, thermal cycle, spheroidized, then heat treat even if doing stock removal. We eliminate many variables by having a consistent structure to start from.
 
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