A question about quenching media, and the science behind quenching

A question I have about quenching blades is, since water boils at 100C or so, and oils at 400-500C along with most waxes, when the steel, above critical temperature comes in contact with the quenching media, ("special quenchant", oil or water), that blade doesn't come in contact with the liquid but with it's vapor, not any liquid since that media is boiling at a lower temperature.
So, for that temperature range, between say 800 degrees C, and 400-500 degrees C, the heat transfer is a lot slower than below that temperature.
I've been searching for organic materials that don't boil at temperatures below 800C, but nothing that can be found easily seems to appear, and it makes sense.
On the other hand, there are some metal alloys (like Wood's alloy/"metal" and many other combinations) that are liquid at water's boiling temperature, boil at a higher temperature as well as not releasing fumes at critical temperatures for steels.
So, I've been thinking, has anyone used such an alloy for quenching, and if done correctly (for example, a big pot of water that boils, with a smaller in it that contains that alloy, in which you dip the piece of steel; the bigger the surface of the pot containing the alloy that comes in contact with the water, the faster the cooling rate, same with the volume of liquid alloy, and, metals are great heat conductors by their nature, so, it sounds excellent. Too good maybe to be working?) what happens to the steel, hardness and rate of unsuccessful attempts?

Has anyone tried it? I'm not referring to reaching hardening temperature using an alloy, nor tempering again, using some liquid alloy, the question is about quenching hot steel on low melting temperature alloys.

Overall, I expect, the quenched piece of steel will reach a temperature around 100C/212F faster than it would with any other media used. Also, because of specific gravity, a lot of pounds/kilos will be needed, and they are expensive, but again, liquids specifically for quenching are expensive too. (of course we are careful with the fumes anyway, as well as splashing etc etc)
If the metals were cheaper I wouldn't even ask and try it, but buying 20kg of them and being careful with lead/Thallium/Cadmium/Mercury is kind of important.
So I would appreciate your help on the question, as I imagine we could achieve higher hardness that way with the faster cooling rate and possibly obtain the bainite crystalline structure more easily. Or it would end up being a failure.
I've been searching on google for days and I didn't find anything serious.

Thank you for your time.

I believe “lead quenching” is used in the wire industry.

Liquid salt baths and liquid metal baths are also used for Marquenching/Martempering.

Your concern about the formation of a “vapour jacket” around the hot metal is well founded and a known problem.

That is why the hot metal should be continuously moved/agitated when quenching, as it insures that the metal remains in contact with the quench medium, as the vapour rises to the surface. Of course agitating the medium helps achieve the same result.

The search for quicker quench mediums in hopes of achieving more hardness may be misguided.

My understanding is that you only need to cool the steel just fast enough to get it through the transition zone in time, any faster does not give better results.
In fact going too fast leads to the dreaded “ping” and the breakage of the steel. By way of example if you take an oil hardening steel such as O1 and quench it in a fast medium such as water you will end up with lots of broken blades.

As for quenching speed, I don’t think there is anything faster than an agitated and saturated brine solution. Not to many steels can survive such a harsh quench, especially with the thin cross sections and stress prone shapes found in blades/razors.

Additional: This reasonable discussion (http://www.iforgeiron.com/topic/25457-quenching-medium/) is interesting and suggests that “super quench” (as outlined here http://magichammer.freeservers.com/robb_gunter.htm) is faster then brine.

You ask good questions Vasilis. And DrDalton has succinctly answered, and well. I'll buy you both a beer any time.

Lead baths are still used by Dovo if I watched that manufacturing video attentively. I think I recall Thiers Issard having a similar setup. Molten lead will get hot enough to austenitize the steel but it will work for martempering. It was probably the original martempering system. Unfortunately lead has a reputation for affecting children's intelligence and so has a reputation for being dangerous. As if a hot molten bath is not dangerous enough. Probably ecologically unsound too. The stuff is really depleted radioactive ore anyway.

The one item left off the list is a type of polymer. See here for examples, there have to be other suppliers. Quenchants My good friend Howard worked with polymer quenchants for a few years. The intention of this material was to have a water based solution act like water for a minimal critical period of time, then as the water vaporized, the blade would be coated with the polymer which slowed the quench and acted more like an oil. He may step in to correct this impression. It was messy and required particular attention to the dilution. That adds variables that all affect the results. Sometimes it's just hard enough to get from the right heat to the right cooler temperature without adding more stuff to think about.

If my memory serves me well enough, this was about the time we both were beginning to switch to using high and low temperature salt baths to achieve better results. The low temperature salts are hygroscopic and will draw water from ambient humidity. There will always be water available in them to boil and create a vapor jacket but for practical purposes this is minimal. I'm sure that the vapor jacket could be measured and could probably be shown to have an effect on quenching. But, according to John Verhoeven, hardening occurs at the speed of sound in the material. I am no longer fast enough to put a blade into the quenchant and pull it out fast enough to interrupt the quench to hardening process. I quit worrying about that.

I don't know that it would be practical to try when ultimately (the limiting factor for all razors is...) the hard blade then has to be tempered back from what is possible to achieve because the honemeisters begin to grumble about the blade eroding their stones. There is an upper limit to desirable hardness.

In the end, you want to achieve the correct austenitizing temperature and hold there for the recommended interval and then quench to below the "nose of the curve" on the isothermal transformation diagram for that steel and allow a faster or slower reduction in temperature in the lower temperature quench to achieve the phases between austenite and martensite as you desire. This will always be a simple mathematical relationship between time at temperature. Fast is needed if the nose of the curve requires it. Bainite needs more time and controlled temperature during that time.

A lot of decent blades have been made through history without any special equipment or attention to the modern metallurgical variables discussed here. There is no downside to years of quenching from a simple heat into a simple quench like oil or water. Whiskers won't complain if they are removed by a blade that is good enough, and honed well, versus the absolute best metallurgical performance known to modern science, and honed like crap.

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Originally Posted by DrDalton

I believe “lead quenching” is used in the wire industry.

Liquid salt baths and liquid metal baths are also used for Marquenching/Martempering.

Your concern about the formation of a “vapour jacket” around the hot metal is well founded and a known problem.

That is why the hot metal should be continuously moved/agitated when quenching, as it insures that the metal remains in contact with the quench medium, as the vapour rises to the surface. Of course agitating the medium helps achieve the same result.

The search for quicker quench mediums in hopes of achieving more hardness may be misguided.

My understanding is that you only need to cool the steel just fast enough to get it through the transition zone in time, any faster does not give better results.
In fact going too fast leads to the dreaded “ping” and the breakage of the steel. By way of example if you take an oil hardening steel such as O1 and quench it in a fast medium such as water you will end up with lots of broken blades.

As for quenching speed, I don’t think there is anything faster than an agitated and saturated brine solution. Not to many steels can survive such a harsh quench, especially with the thin cross sections and stress prone shapes found in blades/razors.

Additional: This reasonable discussion (Quenching Medium - Heat Treating, general discussion - I Forge Iron) is interesting and suggests that “super quench” (as outlined here Robb Gunter) is faster then brine.

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Thank you for your answer, you appear to know about the process.
I've read about marquenching and salt baths. What I'm wondering about is, metals are excellent heat conductors by their nature, so, wouldn't that result in a more uniform temperature drop to the piece of steel we'll be quenching, unlike oil/water/salts? If the piece of steel cools uniformly, no matter its speed, wouldn't that reduce greatly the formation of these cracks?
Theoretically, quenching in an alloy would be a smaller shock for the piece of steel; the liquid alloy will be a lot colder, but again, since it's an alloy, the heat transfer would be a lot faster, resulting in both a faster AND gentler quench for the whole piece. IF we achieve same or higher heat conductivity with that of iron (steel should be close to that) that would mean, we will be able to achieve maximum hardness with close to zero failure rate for our quenched edge no matter it's shape-size.

Does that make sense?

I would like to find a way to achieve hardness, for low alloy steel with carbon content close to 1%, of above 65 RC (like some Japanese razors that have showed a hardness rating of 67RC, how could they do that in an age where knowledge and technology was behind) and am searching for ways to do that. If I could reduce the failure rate, that would be a big bonus since grinding a blank, at least for me, takes days.

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Originally Posted by Vasilis

Theoretically, quenching in an alloy would be a smaller shock for the piece of steel; the liquid alloy will be a lot colder, but again, since it's an alloy, the heat transfer would be a lot faster, resulting in both a faster AND gentler quench for the whole piece.
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I would think that the most gentle quench would be as slow as you could go and still stay left of the nose and the formation of pearlite and bainite in the edge region. Faster than that does not result in higher hardness AFAIK. The depth of the hardness would be affected, but for razors this is not a concern IMO.

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Originally Posted by bluesman7

I would think that the most gentle quench would be as slow as you could go and still stay left of the nose and the formation of pearlite and bainite in the edge region. Faster than that does not result in higher hardness AFAIK. The depth of the hardness would be affected, but for razors this is not a concern IMO.

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By gentle, I mean the whole piece of steel would contain the same concentration of martensite/ferrite/perlite/bainite and any other formation. The damage on quench happens because the size of the martensitic crystals is different from the ones on ferrite/perlite; the one expands, the other stays the same in the end, and, on the weakest part of the blade/place where that formation was the harshest, a crack is formed.
I think, the thermal conductivity is something really important aspect to that. Lead has about 35W/(m.K) and 1095 has 48 or so, where water has 0.591 BUT is faster quenchant. I think.

Mike, once again thank you for your answer. On the Dovo video I remember that they were heating the razors on an alloy, lead as you said, but I thought they were quenching them in oil as the surface tension or viscosity was lower that that of any liquid metal, or so I remember observing, but I won't find it strange if I'm wrong.
So, blacksmiths do think about wear resistance of their blades, and try not to reach the highest point. I would have never think about it, always striving for the highest possible.

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Originally Posted by Vasilis

By gentle, I mean the whole piece of steel would contain the same concentration of martensite/ferrite/perlite/bainite and any other formation. The damage on quench happens because the size of the martensitic crystals is different from the ones on ferrite/perlite; the one expands, the other stays the same in the end, and, on the weakest part of the blade/place where that formation was the harshest, a crack is formed.
I think, the thermal conductivity is something really important aspect to that. Lead has about 35W/(m.K) and 1095 has 48 or so, where water has 0.591 BUT is faster quenchant. I think.

Mike, once again thank you for your answer. On the Dovo video I remember that they were heating the razors on an alloy, lead as you said, but I thought they were quenching them in oil as the surface tension or viscosity was lower that that of any liquid metal, or so I remember observing, but I won't find it strange if I'm wrong.
So, blacksmiths do think about wear resistance of their blades, and try not to reach the highest point. I would have never think about it, always striving for the highest possible.

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In martempering, martensite does not start forming until the piece is removed from the quench medium with the idea that the steel moves slowly through the Ms to Mf temperatures resulting in a more uniform rate though out the piece. According to Verhoeven the susceptibility to quench cracking depends strongly on the cooling rate through the Ms-Mf range.

Maybe we are talking about different types of cracking.

I returned to the Dovo video and they are using molten lead to austenitize the blades and quench in oil. The oil is probably warmed and that means marquenching.

The shock to the steel is reduced when you reduce the required drop in temperature to the least amount needed to achieve hardness. A drop from 800C to 200C is much less severe than a drop from 800C to 50C. Even so all the dynamic movement in the crystalline structure is going to occur at the speed of sound. Any stressors induced by temperature or the shape (e.g. avoid sharp corners and avoid large grain crystals - more fracture potentials) mean that the shock waves from transformation all work within the dimensions of the blade. Quenching also reduces grain size which translates into a collapse in dimension and movement of the steel. That movement is another factor in potential stressors that induce cracking.

Blade preparation includes grain size uniformity before heat treatment and the least amount of thermal shock to the material during heat treatment.

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Originally Posted by Vasilis

By gentle, I mean the whole piece of steel would contain the same concentration of martensite/ferrite/perlite/bainite and any other formation. The damage on quench happens because the size of the martensitic crystals is different from the ones on ferrite/perlite; the one expands, the other stays the same in the end, and, on the weakest part of the blade/place where that formation was the harshest, a crack is formed.

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More or less, with some debate, this is true. Watch: https://www.youtube.com/watch?v=viqrOAG13Q0 This is a much larger blade than a razor but the same forces are at work. There is a lot of movement happening in a very short time, eh? I have seen similar smiles in razors of only four inches length.

Re: minor alloys with sometimes major effects. A low-hardenability steel, e.g. only iron and carbon, may not completely form martensite as the section thickness can determine how fast or slowly the steel will cool. The edge can get hard but the spine may not harden as much because in the half second it takes to cool, it's not fast enough to form martensite and falls back through to pearlite.

Add manganese in a small amount and the same blade will through harden. The material composition will affect heat treatment performance as well.

I will just stick this out there...I do not quench in brine. I see no reason to do so using a well-prepared known alloy of steel and do not recommend it unless you like to gamble on how many blades you will get to survive this violent process. It's just not needed but persists in the Mythology of How Things Should Really Be Done. I can identify a very limited set of conditions that might require brine. Mostly they are unknown steels from the junkyard that won't harden using normal techniques.

And, Rob Gunther's Superquench is a soap solution that addresses the surface tension. It will leave a hardened thin skin on even low carbon steels. The first honing will remove anything good about using this on a cheap steel to achieve a quick result. It's best to use known materials of good quality and good heat treatment rituals.

I've been interrupting my quench at somewhere around 450 F (a SWAG and a 480 degree temp stick) The last time I did this I was thinking that the steel, in theory, should still be austenite at this point. So directly out of the quench I checked the steel with a magnet and low and behold it was non-magnetic despite being almost a 1000 degrees below the curie temperature. Ain't science great!

Just an interesting side note, mildly related to the topic.

But you are taking observations and learning from them. I am fascinated by the fact that so many "good" blades have been made without the makers having the benefits of the education available to us. Humans are keen observers and learn from their mistakes.

Right, and your mention of ritual is/was a part of this human learning. Trying to repeat what has worked before as accurately as possible. An audience member at a talk, that I attended, about Japanese swords suggested that a lot of the ritual and prayer during the sword making was related to the timing of different operations during the forging.

To my understanding, aside from inclusions and cracks in steel, the reason blades get damaged on quenching isn't the reduction on size of the martensite crystals, while a millimeter next to it a different form of iron-carbon combination exists, like ferrite, that doesn't change shape? Steel gets literary stretched or pressed, until it snaps. Is there some other serious reason a blade breaks on quenching?
What I'm purposing is to have the whole blade, or cubic centimeter/inch to drop its temperature uniformly whether it's the edge or center (of course, the center will be a bit harder since it's further away). The liquid alloy will get hotter as you dip the blade, ending up a few degrees colder than the steel in an instant.
This liquid alloy won't work like water, a polymer or salt or NaOH and any other combination but like the outer layer of a few molecules from a piece of steel that is being quenched since the heat transfer will be similar. Theoretically, the temperature difference between the hot blade and finished-tempered blade will not matter because of that heat transfer.

The same way heat travels inside the hot piece of steel that gets colder will also be transferred out of it is what I'm saying reducing the chance for failure.
So, a fast cooling rate between Ms and Mf won't matter since it will be happening to the whole blade, and, from the center of it, to the outer layer, there will be no deformation, aside from the one because it got cold. After that, increasing the volume of the alloy, the surface of the pot with the other pot that contains water or leaving it to cool down by itself as simple as posible is up to the blacksmith-scientist.

@ Vasilis:

“If the piece of steel cools uniformly, no matter its speed, wouldn't that reduce greatly the formation of these cracks?”

“To my understanding, aside from inclusions and cracks in steel, the reason blades get damaged on quenching isn't the reduction on size of the martensite crystals, while a millimeter next to it a different form of iron-carbon combination exists, like ferrite, that doesn't change shape? Steel gets literary stretched or pressed, until it snaps."

You are right, the cracks form due to the stress of the surface of the piece cooling faster than the centre of the piece, not due to (in most part) there being slightly different rates of cooling at different parts of the surface (due to the formation of vapor jacket, which with good technique can be considered negligible anyway).

There is no way possible (when quenching austenite straight to martensite) of dropping the temperature at the surface and in the centre of the piece at the same rate (the physics of heat transfer in steel does not allow for that). Different cooling rates means different structures present in the steel (which have different shapes/densities) which results in stress. Faster cooling rates (i.e. faster quench mediums) exacerbates the differences and leads to increased failure.

Marquenching is the solution you are looking for, as it insures that the entire piece is at the same temperature before it is cooled (relatively slowly) through the martensite transition zone. Therefore giving you your desired “uniform cooling”. Obviously there will still be a temperature gradient across the piece as it cools through the martensite transition zone, but as the cooling rate is so slow (i.e. in ambient air) the gradient can be considered negligible


“I would like to find a way to achieve hardness, for low alloy steel with carbon content close to 1%, of above 65 RC (like some Japanese razors that have showed a hardness rating of 67RC, how could they do that in an age where knowledge and technology was behind) and am searching for ways to do that. If I could reduce the failure rate, that would be a big bonus since grinding a blank, at least for me, takes days.”

Try marquenching, alternatively:
More uniform grinding and the elimination of stress risers in the blank will also help, the former takes years of practice and the latter is a matter of simple design (and may be helped by doing more of the grinding post heat treatment so that the quenched blank is thicker and less intricate).
Quenching spine first may also help

However, blade failure is an occupational hazard for smiths using water as a quenching medium, and water is necessary (when quenching straight from austenite to martensite) to get low alloy/plain carbon steel razors to their maximum hardness (when using forms relevant to blades/razors). I recall seeing a YouTube video of the Iwasaki workshop that showed a pile of razor blanks that had failed during heat treatment.

@ Mike Blue:

“I will just stick this out there...I do not quench in brine. I see no reason to do so using a well-prepared known alloy of steel and do not recommend it unless you like to gamble on how many blades you will get to survive this violent process. It's just not needed but persists in the Mythology of How Things Should Really Be Done. I can identify a very limited set of conditions that might require brine. Mostly they are unknown steels from the junkyard that won't harden using normal techniques.”

I agree (and I imagine anyone who understands metallurgy would do likewise) that brine is unnecessary for any steel when used in forms appropriate to razor/knife blade. However, Tim Zowadas post (http://straightrazorpalace.com/forge...elf-today.html) beautifully exemplifies a further set of (very limited) conditions where brine is appropriate.

“And, Rob Gunther's Superquench is a soap solution that addresses the surface tension. It will leave a hardened thin skin on even low carbon steels. The first honing will remove anything good about using this on a cheap steel to achieve a quick result. It's best to use known materials of good quality and good heat treatment rituals.”

I found Superquech an interesting phenomenon that allows some hardening of “unhardenable” steel (an alternative to case hardening if you will), but you are wise in advising that it cannot in any way replace a good heat treatment of a “hardenable” steel”.

@ Vasilis:

“If I could reduce the failure rate, that would be a big bonus since grinding a blank, at least for me, takes days.”

The laminar construction and/or differential hardening techniques used (initially) by Japanese smiths may also help. By hardening only the cutting edge, the rest of the blank works as a stable support matrix during the quench to prevent (or at less lessen) the stress of hardening cracking the blade.

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Originally Posted by bluesman7

I've been interrupting my quench at somewhere around 450 F (a SWAG and a 480 degree temp stick) The last time I did this I was thinking that the steel, in theory, should still be austenite at this point. So directly out of the quench I checked the steel with a magnet and low and behold it was non-magnetic despite being almost a 1000 degrees below the curie temperature. Ain't science great!

Just an interesting side note, mildly related to the topic.

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While normalizing my last batch of 1095 blades, I did what you are talking about: Played with temps and magnet, cool stuff!

On my phone so short answer.
Laminating with lower carbon steel makes it harder not easier to keep things straight because both sides will not be identical. Additionally the piece may just tear each other in half lengthwise if the core hardens and then the sided contract strongly.

Also uniform cooling is all but impossible on a razor with less than 1/16 edge and 1/4 spine

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

Gentlemen, you are right.
I was trying to figure out a way to quench a piece while trying to achieve same thermal conductivity of that liquid alloy with the piece of steel being quenched, but I forgot that you have to "force" martensite out of austenite. Without martempering, that's a paradox.
I thought that thermal conductivity was a key for that. Only, you have to go beyond that and drop temperature more violently than steel's own thermal conductivity so that "carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities" for the formation of martensite. It sounds so obvious now that it was way too simple to "achieve maximum hardness with close to zero shock on the piece of steel while losing energy" to be true, laws of phisics don't allow it, martempering aside, again. But playing with the rate the temperature drops could help achieving something that again belongs to the category of martempering.

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).
Is it possible to achieve higher hardness than the 60-62? Submerging blades in liquid Nitrogen and other fancy ways to reach subzero temperatures before or between cycles of tempering sounds bothersome for half a degree RC to do them.
(I remember reading an old chemistry book 20 years ago, elementary school probably, 1960-70 university book, where it was written that with ice and enough CaCl2 you can drop the temperature to below 60 degrees C).

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Originally Posted by Vasilis

Gentlemen, you are right.
I was trying to figure out a way to quench a piece while trying to achieve same thermal conductivity of that liquid alloy with the piece of steel being quenched, but I forgot that you have to "force" martensite out of austenite. Without martempering, that's a paradox.
I thought that thermal conductivity was a key for that. Only, you have to go beyond that and drop temperature more violently than steel's own thermal conductivity so that "carbon atoms do not have time to diffuse out of the crystal structure in large enough quantities" for the formation of martensite. It sounds so obvious now that it was way too simple to "achieve maximum hardness with close to zero shock on the piece of steel while losing energy" to be true, laws of phisics don't allow it, martempering aside, again. But playing with the rate the temperature drops could help achieving something that again belongs to the category of martempering.

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I would encourage you to continue to think about the problem. As often happens, breakthroughs occur because the status quo argues that nothing new is left to be discovered. On the other hand, you want to get shop work done and the methods that are available do have a track record of some success. And sometimes you will run the experiment knowing it's not likely to succeed because you're bored or you just have to pee on the electric fence for yourself.

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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).
Is it possible to achieve higher hardness than the 60-62? Submerging blades in liquid Nitrogen and other fancy ways to reach subzero temperatures before or between cycles of tempering sounds bothersome for half a degree RC to do them.
(I remember reading an old chemistry book 20 years ago, elementary school probably, 1960-70 university book, where it was written that with ice and enough CaCl2 you can drop the temperature to below 60 degrees C).

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I am going to suggest another course of reading. Find the isothermal transformation diagrams about the particular steel (they each have one if they are common steels or the steel supplier should have one for each that they sell) and read, study, then test the variables. Each of these diagrams has large sample size so the numbers are really pretty valid and reliable. The curves shown will give you predictable information about the correct temperatures and times necessary to achieve the hardness value you desire. If that hardness number is not on the diagram, it's probably not possible for that steel, at least under the conditions specified. Example: 1030 (a simple carbon steel) will not achieve greater than Rc45 under normal conditions of heat treatment. That is as-quenched hardness. Tempering it will reduce the max Rc. You could use a Superquench to achieve a harder "skin" but it's not very deep and the parent material is not Rc45. Such quenchants were not tested developing the diagrams. Most of that benefit would be abraded away honing anyway.

About liquid nitrogen: The people selling the equipment to process steels with this stuff are the ones who produce the research into it's benefits. I see that as a conflict of interest. There are steels that benefit, notably high-alloy steels, e.g. stain resistant types, that often produce retained austenite (RA) when HT'd. Ordinary carbon steels, if HT'd correctly, do not produce enough RA to benefit practically from such treatments. There may be a statistical proof of change (see conflict problem above) but that does not translate into an economic benefit to the smith/maker or the customer (your point about bothersome). John Verhoeven's book specifically mentions LN treatments in the chapters on stainless steels. No where in the chapters on carbon steels do you read about LN or cold treatments during HT processes.

Quenching a hot billet into a liquid nitrogen bath could be very exciting for the operator. There was a How It's Made show that was produced about razors that showed very briefly a thin strip of steel for multiblade plastic razors emerging from the induction heater to austenitize the steel and being immediately quenched between two LN frozen metal dies. That's the way to do it correctly. The currently sold products for home shops require heat then quench then a lower temperature soak/exposure rather than an immediate quench to low temperature. It takes more time added to the product and additional expense in equipment. LN evaporates and must be replaced more frequently than oil or water. Quenching in oil might flare up a bit, water hisses, neither is nearly as exciting as LN expanding trying to absorb all that heat. I also think the idea of a vapor jacket would be even more dramatic a problem with condensed gasses like LN. The thermal shock of that large a temperature drop given all that has been said before, might leave you with a handful of fractured pieces of steel. Your original concern was to quench without so much shock.

It's a good thought problem.

@ 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

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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.

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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? :p 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.

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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

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

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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.

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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.

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... 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.

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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.

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... 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.

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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.

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... 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?

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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.

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... 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.

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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.

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... 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? :p On the subject, for each answer I get, at least two new questions I have.

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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.

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... 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.

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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. .

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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

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