Thread: A question about quenching media, and the science behind quenching

@ Vasilis:

“My new question; can we achieve maximum hardness with martempering? To my understanding, we can achieve high hardness while the piece of steel suffers the effects of crystalline changes to a lesser degree, so, good hardness, less damaged blades. But can we go above the, say 62 RC with that method? Again, for a simple steel, low alloy and close to 1% carbon (I'm using O2 steel, it's the cheapest available high quality blanks I can locally find. I'm not asking for this steel specifically but generally).


The simple answer to your first question is most likely No, for the reason eloquently explained here in Kevin’s second post (hypefreeblades forums • View topic - 01 Marquench?).

However if the steel has sufficiently hardenability that marquenching is appropriate, you should be able to get a HRC close enough (using the right quench medium) that it shouldn’t matter, as it would be as good as you could get with a full quench and temper.

FYI: The forum linked above is very informative even if it is not very active when compared to other forums, and reasonably knowledgably questions seem to get answered quickly and comprehensively.

Hardness is also affected by the amount of carbon in solution at the time of the quench, with the peak hardness occurring at the eutectoid. Just because your steel is hypereutectoid does not mean that all of the carbon needs to be in solution when you quench.

Yes it is certainly possible to go over 62.
I've made things in SC145 which is pure steel with 1.45% carbon.
Water quench that and the Rockwell C hardness is going to be 65 or so. Completely useless because it's also going to be brittle and chippy.
That's why it is tempered down anyway.

So Yamashita once showed me pics of a beautiful handmade kiridashi made from tamahagane. He said is was almost 67 HRc and basically defective, because at that hardness even he with his Japanese natural stones was unable to really put a solid edge on it that would survive actual use.

A Blacksmiths trick to cool steel real fast is to put a bottle of Dawn dish liquid in a gallon of water & a pound of salt also. This reduces the surface tension of the water & makes the water cling to the metal reducing the steam blanket around the steel. This will make high carbon steel very hard & can be used to harden mild steel a bit. When I was making railroad spike knives for the biker & buckskinner trade I would this process To get the blades a little harder. I may be off on the amounts of Dawn & salt but this is well known info. I have been out of smithing for a while & my memory sometimes is a little cloudy. LOL

Slawman

Originally Posted by Bruno

Yes it is certainly possible to go over 62.
I've made things in SC145 which is pure steel with 1.45% carbon.
Water quench that and the Rockwell C hardness is going to be 65 or so. Completely useless because it's also going to be brittle and chippy.
That's why it is tempered down anyway.

So Yamashita once showed me pics of a beautiful handmade kiridashi made from tamahagane. He said is was almost 67 HRc and basically defective, because at that hardness even he with his Japanese natural stones was unable to really put a solid edge on it that would survive actual use.

Thank you again gentlemen.

Bluesman, you are right about the amount of carbon in solution, I just didn't to go that deep into hardening but quenching otherwise nobody would answer with that many questions I have. Unless I'm wrong, hypereutectoid means more carbon than needed in a steel, like Bruno's CS145; cementite presence in the alloy, I think. For my case with O2, the carbide forming elements keep it eutectoid, or close to. I think.

Bruno,

That's my eventual goal, these "defective" creations that are more like cermet than steel.
Only, how did you, or the Japanese blacksmiths of these razors managed to reach such high hardness? Does the presence of "iron carbide"/cementite increase hardness that more, and, is its presence useful? Higher than about 1% carbon on plain steel usually considered unwanted even when toughness is not needed. Are the crystals small enough to be honed until a fine edge is obtained, or they remain big and when a part of them gets damaged they brake like tempered glass, or having problems with microchipping or any other negative aspects, toughness aside. Did it end up like cast iron or perfectly fine sharp (and fragile) edges that can be honed to a fine edge with a stone that works for these alloys, an edge that they can hold when shaving or filleting.
Water only was the trick? And, a kiridashi is a relatively safe type of instrument for failure rate because of its shape. On hollow razors how did they do it? And when they did, were they forging 100 razors to end up with a single piece that's undamaged and another 99 broken/warped or damaged anyway?

There is less than limited knowledge on metallurgy on internet, and on the university, the classes I visited the subjects were nothing more than introduction of the basics, again nothing that can help you theoretically, to make blades.

A few essays or something like that, that can be found but aside from the introduction, you have to buy them... I guess I'll have to become an apprentice of a bladesmith. Anyone interested for someone who doesn't look like a monkey and probably won't be warming their sandals, but can cook and will be helping in the forge? On the subject, for each answer I get, at least two new questions I have.

Also off topic, I'm reading about marquenching, it appears everyone uses salts (oil and molten metals aren't as suitable supposedly).
Nitrate salts! (I also researched into low melting point salts, these are the only ones that melt on that range of temperature).
That's extremely dangerous, if you have some carbon left on the blade or in the clay, or the gas from the forge is close by, or a piece of wood fells into them or you are smoking, or the oil is smoking... anyway, they are way too strong oxidizing agents by themselves, and they are at high temperature, liquid. I've played with them had some minor accidents as well, they are dangerous! You have a tank full of an oxidizing agent ready for something remotely reductant/reducer to explode. I wonder how I haven't heard about any accidents because of them and am glad about it, but be careful with them... is not enough, an accident can occur just by bad luck.

Originally Posted by Slawman

A Blacksmiths trick to cool steel real fast is to put a bottle of Dawn dish liquid in a gallon of water & a pound of salt also. This reduces the surface tension of the water & makes the water cling to the metal reducing the steam blanket around the steel. This will make high carbon steel very hard & can be used to harden mild steel a bit. When I was making railroad spike knives for the biker & buckskinner trade I would this process To get the blades a little harder. I may be off on the amounts of Dawn & salt but this is well known info. I have been out of smithing for a while & my memory sometimes is a little cloudy. LOL Slawman

Superquench solution has been discussed. And I specifically used 1030 steel as an example because that is the material track spikes are made from.

Originally Posted by Vasilis

Thank you again gentlemen. Bluesman, you are right about the amount of carbon in solution, I just didn't to go that deep into hardening but quenching otherwise nobody would answer with that many questions I have. Unless I'm wrong, hypereutectoid means more carbon than needed in a steel, like Bruno's CS145; cementite presence in the alloy, I think. For my case with O2, the carbide forming elements keep it eutectoid, or close to. I think.

Depending on the source, eutectoid is defined somewhere between 0.74 and 0.85 percent carbon in a plain carbon steel. I have used the upper limit over time with predictable results. Carbon, major and minor alloying elements, time and temperature, the list of potential effects by all the variables continues to grow. Most people think blacksmiths are simple. Not so long ago they were akin to wizards because of what they had observed in their shops over a lifetime.

... Only, how did you, or the Japanese blacksmiths of these razors managed to reach such high hardness? Does the presence of "iron carbide"/cementite increase hardness that more, and, is its presence useful? Higher than about 1% carbon on plain steel usually considered unwanted even when toughness is not needed.

Tamahagane, as smelted, is between 1.4-1.6% carbon. By the time the smith is finished with orogshigane (blade steel) the carbon content will drop to about 0.6% carbon in a sword for example. A ten pound billet reduced to about 3 pounds of steel refined by fire. The intention is to reduce the carbon content. A tool maker (entirely different craft/guild in Japan) may have a different process goal and all smiths have likely experimented or played with their materials testing the limits of performance regardless.

... Are the crystals small enough to be honed until a fine edge is obtained, or they remain big and when a part of them gets damaged they brake like tempered glass, or having problems with microchipping or any other negative aspects, toughness aside. Did it end up like cast iron or perfectly fine sharp (and fragile) edges that can be honed to a fine edge with a stone that works for these alloys, an edge that they can hold when shaving or filleting.

This is why grain structure is a subject to be understood. Some refine grain with a hammer, some refine grain by thermal cycling. It's all what you learn how to do.

... Water only was the trick? And, a kiridashi is a relatively safe type of instrument for failure rate because of its shape. On hollow razors how did they do it? And when they did, were they forging 100 razors to end up with a single piece that's undamaged and another 99 broken/warped or damaged anyway?

We don't know for certain, but water is routinely used as a quenchant. More than other smithing cultures. They are used to it and know how to get the most from it. Traditionally made kiridashi will have a wrought iron body and a small piece of high carbon steel welded on as a tooth. There will be a little carbon lost to the wrought iron during welding due to carbon migration, then water quenched and tempered. Without knowing what the smith did/used, it's hard to be accurate responding.

... There is less than limited knowledge on metallurgy on internet, and on the university, the classes I visited the subjects were nothing more than introduction of the basics, again nothing that can help you theoretically, to make blades.

Well, blades are evil you know. Especially razors. Knives will eventually repeat history and the only sharp object in a village will be chained to a post in the town square. No self respecting liberal university would tolerate the study of such things. Verhoeven and the rest like him were anachronisms and his was an Agricultural and Mechanical University.

... A few essays or something like that, that can be found but aside from the introduction, you have to buy them... I guess I'll have to become an apprentice of a bladesmith. Anyone interested for someone who doesn't look like a monkey and probably won't be warming their sandals, but can cook and will be helping in the forge? On the subject, for each answer I get, at least two new questions I have.

You have arrived at the suggestion I would have made. You already have the disease of steel, now you are destined to have to associate with those who also have it. Eventually we will all be rounded up and herded into confinement and be happy in each other's company. You will learn more in a working shop even if you are making tongs or bolts and nails than you can imagine. If the smith knows nothing about knives, he will eventually send you to someone just to get rid of you and your pestering questions. I know a guy that happened to.

... Also off topic, I'm reading about marquenching, it appears everyone uses salts (oil and molten metals aren't as suitable supposedly).
Nitrate salts! (I also researched into low melting point salts, these are the only ones that melt on that range of temperature).
That's extremely dangerous, if you have some carbon left on the blade or in the clay, or the gas from the forge is close by, or a piece of wood fells into them or you are smoking, or the oil is smoking... anyway, they are way too strong oxidizing agents by themselves, and they are at high temperature, liquid. I've played with them had some minor accidents as well, they are dangerous! You have a tank full of an oxidizing agent ready for something remotely reductant/reducer to explode. I wonder how I haven't heard about any accidents because of them and am glad about it, but be careful with them... is not enough, an accident can occur just by bad luck.

Ah, more to learn. No they are not that dangerous except from the perspective of someone who has never worked with them. I use a non-nitrate salt (mainly sodium and potassium chlorides, I can even flush it down the sewer according to the MSDS) for high temperature, easily 800C or higher. There have been accidents and thankfully only happened once that I am aware of. The most common is a loose drop of water finding its way into the top of the molten volcano of high temperature salts. That's exciting, but it's only a steam explosion not due to the salts themselves. The low temperature nitrate salts are not nearly so dangerous except they are hot enough to burn flesh. I have the marks to prove that.

http://www.parkthermal.com/Technical...lt%20Baths.pdf

I hope this helps.

When I started doing a "stress relief" at around 1200F after all forging and rough grirding, my warpage went down to almost zero and the tiny bit that might show up could be corrected easily by hand with an insulated glove out of the quench. .

Originally Posted by Bruno

Great discussion btw.
My experience is that warp is caused most commonly by not enough normalisation or not holding the blade straight during the quench so one side cools faster.

Also gently quenching instead of ramming it in as fast as possible seems to work for me