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Edge Quench or Soft-back Draw?


B. Norris

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To give a little background on the question. I just ruined the heat treat on a seax today trying to soften the back enough to fit two narrow fullers on the blade. My water evaporated just enough that the cutting edge got too hot in one spot. I have been using a full quench because I am not setup for doing horizontal quenches but this experience has me wondering if I wouldn't be better off. I could save myself the time and expense of an additional step by just edge quenching to begin with. Of course maybe that would not have left the back of this thing soft enough to scrape my two grooves in. Just thought I would put this question to everyone on the forum and benefit from some different perspectives. So, how do you do this and why do you do it the way that you do?

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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I don;t, and think a better performing knife can be had by making the whole blade martensite, and tempering it properly. But if it is a question of scraping grooves in, that should be done before heat treat on the annealed or atleast normalised blade first. I think the best reason for edge quenching and differential heat treating are for a softer back to support a harder edge.

Edited by Sam Salvati

Let not the swords of good and free men be reforged into plowshares, but may they rest in a place of honor; ready, well oiled and God willing unused. For if the price of peace becomes licking the boots of tyrants, then "To Arms!" I say, and may the fortunes of war smile upon patriots

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I have gone to an edge quench almost entirely for my work. I full harden double edged blades, and sometimes small, light, thin blades, and all of my damascus. In the case of the damascus, I don't like the look of the transition line.

 

Before I started edge quenching pretty much all of the time, I had several test blades fail in the bend, and all of them because the core of the spine did not soften. Every one of the test blades showed a hard needle of material surrounded by soft steel. I do have to say that all of those failed blades were 5160, which is a deep hardening steel, and that might have something to do with it. Since that time I've gone to 10xx steels, and I like the results, though I am still working my way through a bunch of 5160.

 

I do three normalize steps after forging, and at least three more after grinding and as part of the heat treat. Then I bring the whole blade up to non-magnetic, soak it for a minute or two, then edge quench in a light mineral oil. I hold it in the oil, on a stop plate, until the spine goes black, then I do a quick check for streight, and drop the whole thing in the oil bath to cool down to ambient. Again, this is for 10xx and 5160 steel. After I do a quick check for hard with a file (though you can pretty much see and hear the difference) it goes into an oven for at least 3, two hour. temper cycles. The tempering temperature depends on the blade, hard use knives in 10xx go in at 425-450 F. Light duty blades and kitchen knives, at about 350-375 F.

 

After I have ground down close to the edge, then I do some chopping tests. None of the blades I have treated this way, including all of my JS piece, have ever chipped, cracked, or rolled over (knock on wood).

 

This is just what works for me, YMMV.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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transition line.

 

 

I do three normalize steps after forging, and at least three more after grinding and as part of the heat treat. Then I bring the whole blade up to non-magnetic, soak it for a minute or two, then edge quench in a light mineral oil. I hold it in the oil, on a stop plate, until the spine goes black, then I do a quick check for streight, and drop the whole thing in the oil bath to cool down to ambient. Again, this is for 10xx and 5160 steel. After I do a quick check for hard with a file (though you can pretty much see and hear the difference) it goes into an oven for at least 3, two hour. temper cycles. The tempering temperature depends on the blade, hard use knives in 10xx go in at 425-450 F. Light duty blades and kitchen knives, at about 350-375 F.

 

After I have ground down close to the edge, then I do some chopping tests. None of the blades I have treated this way, including all of my JS piece, have ever chipped, cracked, or rolled over (knock on wood).

 

This is just what works for me, YMMV.

 

Geoff

 

Do you only quench your edge quenched blades one time?

What temp did you temper your Performance knives - 5160 - that passed your "test"?

Edited by kbaknife
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It depends on the steel, but I like a full quench and then a soft-back draw for most things. If I edge-quench, I also only have the edge up to critical. This leaves the back at more or less normalized condition.

 

I will echo Sam though, scrape your fullers in before HT. You'll be a lot happier!

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I generally do just a single HT, I haven't seen anything that makes me think multiple HT's improves anything. When you HT you are converting austentite to martensite, so is there a benefit to converting it back and forth several times? At this point I don't think so, but it would be an interesting test to make.

 

The "test" I'm talking about is the ABS performance test. 1) Cut through a piece of free hanging 1 inch manila rope. 2) Chop through a 2 x 4 twice, without damage to the blade. 3) Shave hair at the end of the chopping test. 4) Take a 90 degree bend without breaking. All of this in a blade not more than 2 inches wide, not more than 10 inches from tip handle, not more than 15 inches overall length.

 

I have had 5160 blades successfully perform this test, I tempered them at 375-400 F. However, 5160 is a deep hardening steel. If you quench 1/4 inch of the blade, I've found that you get as much as 1/2 inch of hard steel. I have also found that the oil temperature is critical. At one point I forged and HT'ed 5 test blades all in a row, in the same oil, with a torch draw. The oil started out at ambient, call it mid 60's F. The first blade failed due to a handling problem, I dropped it in the bath, full hardening it. It broke at about 80 degrees of bend. Blades 2 -4 all passed the bend, though blade # 4 cracked (which should have been a warning to me), blade #5 had the most comfy handle on it, so I used it for the actual test. It failed at about 85 degrees. We took the broken end, polished it and etched it. You could see a spike of hard steel up into the spine. I went home and did the same to each of the remaining blades. In each case I found that the hard edge went deeper through the sequence (as the oil got hotter and hotter) even though each blade used the same oil, and the same stop plate. I also found a spike of unconverted martensite at the core of every blade.

 

This led me to discard the torch draw method, in favor of an edge quench of a shallow hardening steel. I don't like the way a torch draw works for me, I find it difficult to get the core of a blade hot enough to effect a change in state, while not altering the edge hardness.

 

I also think if I am just bringing the blade up to critical (which means the edge is critical but the thicker parts are lagging just a bit) that the spine is going through a normalize cycle while the edge is hardening. The softness of the spine should not be affected.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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I will echo Sam though, scrape your fullers in before HT. You'll be a lot happier!

 

At this point that is what will happen since I have them both in there now and have to reharden the edge after overheating it trying to get the back drawn. The seax is long and thin, 10 inches of blade less than 1 inch wide at the narrowest part. I used some 5160 that I had leftover from taking the Introduction to Bladesmithing Class last year.

 

When I took the class the instructors (Burt Gaston and Greg Neely) had half the class edge quench and half the class do a soft-back draw. I was in the half of the class that did the soft-back draw. There was some discussion about which method produces a better knife. Both instructors felt that the blades with the backs drawn were more likely to crack during the bending portion of the test. My test knife did not crack but, I did a total of 4 draws on the back of that blade. I also tempered it three times, one cycle of which went the better part of a day because I forgot it in the oven.

 

This particular seax I was trying out the "Groovemaster 2000" (thanks Alan!) I wanted to put two narrow grooves in, the first about 1/8 of an inch from the back, the other about 3/8's of an inch. I softened the back and scraped the first groove in without a problem. When I got to the second groove, even though that area showed oxidation colors that would have left it dead soft, it was so hard it dulled my scraper. Well, I did a second draw, after making another grooving tool, and used less water to get the color further down on the blade. This time I managed to get the colors too far down but, despite this, when I put the second groove in there were still spots on the blade that were somewhat hard. This despite portions of the edge being noticeably softer.

 

I have primarily been doing full quenches because all my equipment is outside, in a shed, and I need to have a lid on my quenching oil to keep bugs, children and dogs out of it. Not to mention putting out oil fires by smothering the fire with the lid. The first thing I found that would work was an old 9 gallon milk can. I am begining to think I should come up with some kind of setup to do edge quenches however. Mostly because the draw on the back seems to be a lot of extra work that can easily undo much previous work. I also wonder about how good a job it actually does after my experiences with scraping the fullers in.

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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A good cheap quick setup for oil quenching edges owuld be a nice TURKEY PAN from the grocery store.

Let not the swords of good and free men be reforged into plowshares, but may they rest in a place of honor; ready, well oiled and God willing unused. For if the price of peace becomes licking the boots of tyrants, then "To Arms!" I say, and may the fortunes of war smile upon patriots

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Ah, sorry. I use a light mineral oil. I get it in gallon jugs at my local feed store as "Veterinary grade mineral oil". It's low stink, high flash temp, leaves little scale, and it's pretty cheap, about $12USD a gallon. It's fast enough to give me a bit of hammon in 10xx steels. Faster than motor oil or brake fluid, and without all the smoke and scale, not as fast as water.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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I prefer the whole blade hardened and the back tempered. I switched when I saw that differentially hadened blade don't brake easily after the bend, but bend far more easily than a 100% martensite blade. I think that outside the ABS test, you really don't need to bend a blade; once you ruin its straightness, you ruined the blade, imho.

Mourir pour des idées, c'est bien beau mais lesquelles?

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I prefer the whole blade hardened and the back tempered. I switched when I saw that differentially hadened blade don't brake easily after the bend, but bend far more easily than a 100% martensite blade. I think that outside the ABS test, you really don't need to bend a blade; once you ruin its straightness, you ruined the blade, imho.

 

 

 

See I am with you Guiseppe, when talking blades swords or knives, i'd rather have a blade of complete martensite and bend and not stay bent. As you say, how often in a knife's working life do you need to bend it to 90 degrees then back again? What's everyone saying, knives aren't screwdrivers nor pry bars. But then again a blade should perform it's best at being a blade, cutting and stuff, so with the enhanced performance of havbing a soft back support a harder edge is a good thing also.

Edited by Sam Salvati

Let not the swords of good and free men be reforged into plowshares, but may they rest in a place of honor; ready, well oiled and God willing unused. For if the price of peace becomes licking the boots of tyrants, then "To Arms!" I say, and may the fortunes of war smile upon patriots

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What I have use to edge quench is a roasting pan filled with my version of Goddard's Goop. Its a mixture of pan drippings, vegetable oil, old candles, and a little parrafin. At room temperature it's hard in the pan and it's easy to transport and store. I like to take a piece of scrap steel and melt a chanel in the goop before I quench my blade.

 

Sam, Giuseppe, I agree with you guys about what is needed to make a quality blade, heat treating wise. If you need a knife get a knife; if you need a pry bar get a pry bar. I visited a knifemakers web page once and that person pretty much said the same thing as he was discussing the warrantee that he offered. He actually had one customer return a blade because he damaged it driving it into a tree trunk and using it as a step to get up into his tree stand. A knife, especially something like a camp knife, should be able to take a little twisting and prying but there is a limit as to what one can rationally expect a knife to do. Exceed that and it becomes abuse. Sort of like using a knife to rearrange the coals in a fire and then getting mad that it won't hold an edge any more.

 

Doug Lester

HELP...I'm a twenty year old trapped in the body of an old man!!!

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I prefer A completely hardened blade, and then draw the back to a spring temper, usually Blue. Yes, I have occasionally ruined a heat treat. The last time by pulling the blade out of the tray of water to soon and the heat in the spine ran down to the edge in one spot. I do the draw with the edge in a tray of water about 1" deep, depending on the width of the blade. I don't like a totally soft spine, the knife will bend to easily. with a springy back I think its a lot harder to actually bend the blade. Just my thoughts, and worth about what it cost you.

 

Tony G

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I do a full quench, temper, then draw the spine to a spring temper with a torch using a method I saw demostrated at the ABS Mid-America Hammer-In last year. James Rodebaugh did a JS Test blade start to finish and tested using this method, I'd like to give credit to the person he credited but I don't remimber who that was. He did an edge quench on the test blade, tempered in toaster oven multiple times, then draw temper the spine multiple times. He took a cake pan full of sand and mixed water till thoroughly saturated but no standing water. He set the blade in the sand with the edge buried as deep as he wanted to protect, molded the sand up arround the tip and dug it out a little under the tang. Played the torch up and down the spine and tang to draw to desired temper. I used to always over-heat the tip or cutting edge next to the riccasso trying to do this in a pan of water. I haven't over heated any since switching to this method plus the sand holds the blade in position and I don't have to fumble with vise-grips or pliers while doing this.

Steve

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I do a full quench, temper, then draw the spine to a spring temper with a torch using a method I saw demostrated at the ABS Mid-America Hammer-In last year. James Rodebaugh did a JS Test blade start to finish and tested using this method, I'd like to give credit to the person he credited but I don't remimber who that was. He did an edge quench on the test blade, tempered in toaster oven multiple times, then draw temper the spine multiple times. He took a cake pan full of sand and mixed water till thoroughly saturated but no standing water. He set the blade in the sand with the edge buried as deep as he wanted to protect, molded the sand up arround the tip and dug it out a little under the tang. Played the torch up and down the spine and tang to draw to desired temper. I used to always over-heat the tip or cutting edge next to the riccasso trying to do this in a pan of water. I haven't over heated any since switching to this method plus the sand holds the blade in position and I don't have to fumble with vise-grips or pliers while doing this.

Steve

 

 

Steve,

I'll have to try this method, sounds cool.

 

Tony G

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I think quite highly of Mr. Rodebaugh both as a knife maker, and as person. Having said that, I have to take exception with the HT method as described.

 

1) When you bring the blade up to critical, then let it cool in ambient air below 900F, you have done a normalize cycle, which should result in an austentitic piece of steel.

 

2) When you bring the blade up to critical, then quench the edge, while letting the spine cool in ambient air below 900F, you should have a martensitic edge with an austentitic spine.

 

3) An oven draw, say at 400F, relieves uneven stresses in the blade set up by the quench, and converts partly transformed martensite back into one of the less hard states, perlite, cementite, banite, or austentite.

 

What does the torch draw get you? If you could get the spine up to critical again, you have austentite, which is the dead soft spine people in this thread have said they don't like. If you are not exceeding the oven draw temperature, then you've gone through an extra step to no purpose.

 

Have I missed something?

 

Color of blade Temp in Fahrenheit

 

Pale Yellow 300

Bright Yellow 350

Light Straw 400

Dark Straw 425

Brown 450

Purple 475

Violet 500

Dark Blue 525

 

The oxide colors achieved by heating steel are a guide to the temperature, but not an absolute measure. They can be changed (at least I think this is true) by other factors. As an added problem, what I call Purple, you might see as Violet, and in fact there are a bunch of colors between Purple and Violet. OTOH, a properly calibrated oven should give you predictable results every time.

 

I agree that owners should not stress a knife to the extent that test referred to above does. But people do dumb stuff. My experience is that you can't tell the difference in normal use between a full hard, torch draw knife, and an edge hard, oven drawn knife. Presumably, the Japanese swordsmiths liked a soft spine, hard edge for a reason. Perhaps, when your life depended on it, a bent sword was better than a broken one.

 

I use the process I have described because it works for me, in my shop, with my equipment. If you can show me one that give better results, I'll start using that one. The point is to make the best blades (whatever that means to you) we can.

 

Apologies if I have come off as strident or as lecturing, I come from a long line teachers, and other folks with strong opinions.

 

Geoff

 

 

Bright Blue

550

 

Gray

575

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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Reading through the responses to this post, it has become obvious that I asked a vague question about a subject that people have strong feelings about. The point has been made that this is a cutting instrument, not a prybar, and that a knife with a softer back may bend too easily in use. Conversely, people are going to abuse our work and judge its quality in so doing. Should our work fail too easily, not only will it reflect poorly on just ourselves, it will reflect poorly on handmade knives as a whole. Why spend the extra money when a $20 knife from Wal-Mart will stand up just as well?

 

We are all individuals here, with different methods and different expectations of what our knives should do. My intention is not to start a thread about whose methods are better. I would much rather learn from the rest of you practitioners of this craft. The saying "there is more than one way to skin a cat" applies here and sometimes our different methods will have nearly identical results. The back of a knife can be drawn back so that it is springy and stiff but, an edge quench can also control the stifness of a blade simply by hardening more or less of it. I should have asked "for this size blade, in this style, in this steel, and with these fullers."

 

Obviously, the intended use of the blade will dictate some of its properties. A sword is not a camp knife and neither is a hunter. The techniques that we use should provide the optimum for a given use. To my way of thinking a sword needs to not break and will benefit from an edge quench, or clay treatment, if applicable. A small hunting knife is just not going to see the stresses that a sword is expected to endure and a full quench and temper will probably yield the best properties for such a knife. The middle ground seems to be where there is the greatest variation in technique and this is what I am interested in hearing about.

 

I do a full quench, temper, then draw the spine to a spring temper with a torch using a method I saw demostrated at the ABS Mid-America Hammer-In last year. James Rodebaugh did a JS Test blade start to finish and tested using this method, I'd like to give credit to the person he credited but I don't remimber who that was. He did an edge quench on the test blade, tempered in toaster oven multiple times, then draw temper the spine multiple times. He took a cake pan full of sand and mixed water till thoroughly saturated but no standing water. He set the blade in the sand with the edge buried as deep as he wanted to protect, molded the sand up arround the tip and dug it out a little under the tang. Played the torch up and down the spine and tang to draw to desired temper. I used to always over-heat the tip or cutting edge next to the riccasso trying to do this in a pan of water. I haven't over heated any since switching to this method plus the sand holds the blade in position and I don't have to fumble with vise-grips or pliers while doing this.

Steve

 

Thank you Steve for a new trick to add to my bag. I will have to try this method and see how I like it. I built myself a stand to hold the edge underwater but, the method you described seems so much more controllable. Especially for knives that have curved edges. I am always amazed at how good a job the water does at keeping the steel cool. Getting any color to show, nevermind getting it close to the edge, has been a real struggle for me. I have ended up taking my burner for my forge (a Shorty Burner from Hybridburners) and using it to heat the backs for my draw. Using it I can get the colors to run down to within about 3/8" from the waterline. With the sand/water mix I imagine that a plumbers torch is sufficient for a heat source as it probably does not leach the heat from a blade at the same rate as sitting in a straight tub of water will. What is your heat source when you do this? Is a plumbers torch adequate?

 

1) When you bring the blade up to critical, then let it cool in ambient air below 900F, you have done a normalize cycle, which should result in an austentitic piece of steel.

 

2) When you bring the blade up to critical, then quench the edge, while letting the spine cool in ambient air below 900F, you should have a martensitic edge with an austentitic spine.

 

3) An oven draw, say at 400F, relieves uneven stresses in the blade set up by the quench, and converts partly transformed martensite back into one of the less hard states, perlite, cementite, banite, or austentite.

 

What does the torch draw get you? If you could get the spine up to critical again, you have austentite, which is the dead soft spine people in this thread have said they don't like. If you are not exceeding the oven draw temperature, then you've gone through an extra step to no purpose.

 

Have I missed something?

 

Definition of Austenite from Wikipedia:

Austenite (or gamma phase iron) is a metallic non-magnetic solid solution of iron and an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K (about 727 °C); other alloys of steel have different eutectoid temperatures. It is named after Sir William Chandler Roberts-Austen (1843-1902). Its face-centred cubic (FCC) structure has more open space than the body-centered cubic structure, allowing it to hold a higher proportion of carbon in solution.

As the austenite cools, it often transforms into a mixture of ferrite and cementite as the dissolved carbon falls out of solution. Depending on alloy composition and rate of cooling, pearlite may form. If the rate of cooling is very fast, the alloy may experience a slight lattice distortion known as martensitic transformation, instead of transforming into a mixture. In this industrially very important case the carbon is not allowed to blend out in the remaining melt due to the cooling speed, but are captured inside the FCC-structure of austenite, creating tension in the crystal when the alloy cools down. The result is hard martensite. The rate of cooling determines the relative proportions of these materials and therefore the mechanical properties (e.g. hardness, tensile strength) of the steel. Quenching (to induce martensitic transformation), followed by tempering will transform some of the brittle martensite into bainite. If a low-hardenability steel is quenched, a significant amount of austenite will be retained in the microstructure. (I believe these two sentences to be erroneous but, I leave it to better minds than mine to correct)

The addition of certain alloying elements, such as manganese and nickel, can stabilize the austenitic structure, facilitating heat-treatment of low-alloy steels. In the extreme case of austenitic stainless steel, much higher alloy content makes this structure stable even at room temperature. On the other hand, such elements as silicon, molybdenum, and chromium tend to de-stabilize austenite, raising the eutectoid temperature.

In many magnetic alloys, the Curie point, the temperature at which magnetic materials cease to behave magnetically, occurs at nearly the same temperature as the austenite transformation. This behavior is attributed to the paramagnetic nature of austenite, while both martensite and ferrite are strongly ferromagnetic.

A blacksmith causes phase changes in the iron-carbon system in order to control the material's mechanical properties, often using the annealing, quenching, and tempering processes. In this context, the color of light emitted by the workpiece is an approximate gauge of temperature, with the transition from red to orange corresponding to the formation of austenite in medium- and high-carbon steel.

Maximum carbon solubility in austenite is 2.03% C at 1420 K (1147 °C).

 

1) When you bring the blade up to critical, then let it cool in ambient air below 900F, you have done a normalize cycle. The steel has absorbed carbon from the grain boundaries as it shifts to a Face Centered Cubic structure (uses 6 carbon atoms) from a Body Centered Cubic structure (uses 1 carbon atom) and than redeposited the carbon as it cools. This process reduces residual stresses in the steel and prepares the steel to form a fine grain structure when it is hardened. I am still kind of fuzzy on exactly how this works, perhaps some of the resident steel gurus will explain.

 

2) When you bring the blade up to critical, then quench the edge, while letting the spine cool in ambient air below 900F, you should have a martensitic edge with a spine made up of a mixture of alpha iron and perlite.

 

3) An oven draw, say at 400F, relieves uneven stresses in the blade set up by the quench, and converts martensite into tempered martensite. The spine stays a mixture of alpha iron and perlite. Okay gurus. Is this part right?

 

4) A full quench, followed by tempering in an oven (x3,) and then a soft back draw (x3,) should yield an edge of martensite tempered to one hardness with a spine of martensite tempered ever softer towards the back. The softness of the spine can be controlled by the degree to which the martensite is tempered. The point of doing this is to have a spine softer than the oven temper but, springier than an edge quench.

 

I generally do just a single HT, I haven't seen anything that makes me think multiple HT's improves anything. When you HT you are converting austentite to martensite, so is there a benefit to converting it back and forth several times? At this point I don't think so, but it would be an interesting test to make.

 

What is your heat source for hardening? The quys working digitaly controlled salt pots or electric ovens will not gain much from multiple hardening cycles. Those of us heat treating by eye out of an atmospheric forge can use it to reduce grain size from overheating caused by lack of good controls. Help! Steel gurus. I cannot quite seem to explain this one well enough to be of any use. Something about the carbides pinning the grains, keeping them from growing.

Edited by B. Norris

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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It all depends. On the prior condition, the prior grain size, the accuracy of your eye or equipment, and every other variable in the equation.

 

There can indeed be benfits from many cycles, even if you do have salt and good controls, bu again, it depends. There are good things and bad things about hard edge/soft back, hard edge/springy back, and all even temper throughout. No one condition satistfies everyones requirements. There is no "best for everything". There can be "best" for a specific thing, sometimes, and even then it can depend an awful lot on what you want, and your point of view and pre-conceived notions.

 

There can be no one answer to any of these questions.

 

Read books, then get to the shop and make stuff. And experiment and break things, and pay attention to the resluts you get with the setup you have. And keep notes, it makes it easier to remember when you start getting some gray hair. :)

 

Our species has existed most of it's time here on the mudball with stone tools, then with simple bronze, copper, and iron. And now we are all woriied about that last 0.1% performance that most of cannot distinguish because they all work so well now, if the steel is half decent, and the heat treatment not downright poor.

 

Use the best information and technology you can get your mitts on, and check things out for yourself. Think for yourself.

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If you substitute "pearlitic" for "austenitic" in Geoff's post, it makes more metallurgic sense, pearlite being what austenite decomposes into at room temperature, and I agree with the question he is posing - if you didn't harden the spine, there is not an obvious reason to temper it, especially if you have already done a stress relief to the entire blade.

:huh:

Jomsvikingar Raða Ja!

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If you substitute "pearlitic" for "austenitic" in Geoff's post, it makes more metallurgic sense, pearlite being what austenite decomposes into at room temperature, and I agree with the question he is posing - if you didn't harden the spine, there is not an obvious reason to temper it, especially if you have already done a stress relief to the entire blade.

 

Jeff. Whoops I read this " Depending on alloy composition and rate of cooling, pearlite may form." and missed the phase diagram on that page. I have edited my post. By temper it do you mean do a draw on the back with a torch? You are right, if you do not harden the spine there is no obvious reason to temper it.

 

Use the best information and technology you can get your mitts on, and check things out for yourself. Think for yourself.

 

You are right on with this Howard. I should keep better notes on what I do as well.

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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Thanks guys, all kinds of new information in the last couple of posts. I feel like I need to hard copy this one for future reference.

 

Geoff

"The worst day smithing is better than the best day working for someone else."

 

I said that.

 

If a thing is worth doing, it is worth doing badly.

- - -G. K. Chesterton

 

So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy.

 

Grant Sarver

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Maybe I should start a new post, but my question does relate to this subject.

How long does steel have to be tempered for the temper to 'stick'? I've been told that anything less than an hour in the oven is not enough time, yet if I bring the edge too hot for 2 or 3 seconds grinding I'm told I have to re-harden the blade...

 

Which is it? How long a soak do the steels we bladesmiths use need to temper the martensite? How long would it be nessisary to heat the back of the blade in a soft-back draw in order for it to have any effect?

 

It has occured to me to stop messing with this differntial hardening/tempering bit and just make them all composite blades so I can have complete control over the properties in each area of the blade... no, please don't mention carbon migration...

George Ezell, bladesmith

" How much useful knowledge is lost by the scattered forms in which it is ushered to the world! How many solitary students spend half their lives in making discoveries which had been perfected a century before their time, for want of a condensed exhibition of what is known."
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How long does steel have to be tempered for the temper to 'stick'? I've been told that anything less than an hour in the oven is not enough time, yet if I bring the edge too hot for 2 or 3 seconds grinding I'm told I have to re-harden the blade...

 

Which is it? How long a soak do the steels we bladesmiths use need to temper the martensite?

 

This is a very good question. As Mr. Clark pointed out we are searching for the last 0.1% of performance from our steels. The industry standard for tempering is something like one hour per inch of thickness. Knives can be tempered for one fifteen minute cycle and they will be tempered. However, is there anything more that can be done to give it that extra something that guarantees that your customers will not have one of your blades break on them? Even if they abuse the knife? Who wants one of your knives to break in someone elses hands? There are practical reasons behind the standard of three, one hour, tempering cycles.

 

For the steel to harden it has to go from red hot to below about 800F very quickly, for 1095 you have something around 0.5 seconds. Sometimes when steel is hardened all of the martensite that can form does not. Perhaps it did not cool quite as quickly as ideal, whatever the case, there is retained austenite. In other words some percentage of the steel has the potential to become martensite but, it has not completed the transformation. It sits there, as retained austenite, until something causes it to finish the conversion to martensite. This something is either time or temperature. Steel that was hardened years ago can have retained austenite that slowly converts to martensite and makes the steel more brittle because the new martensite is untempered. The tempering cycle itself can trigger a transformation of this retained austenite to martensite. Some steels are alloyed highly enough that they do not finish the transformation to martensite at room temperature. They have to be cooled below room temperature. Many of the stainless steels used by knifemakers finish the transformation to martensite right around room temp.

 

One way to prevent this is to quench the steel well enough that there is no retained austenite. That is the Perfect World solution. The other approach is to use multiple tempering cycles to temper any fresh martensite that is triggered by the previous temper cycle. Longer tempering cycles is another solution. The best blade I can turn out is one that is hardened to the best of my abilities and then tempered for three, long, cycles. I have too much time into making my knives to do less then my best with the heat treatment. I am using mostly simple steels, 10xx, 5160, 6150, and the occaisional file and coil spring. If I were to use any of the stainless steels like: S30, BG42, 154CM, or 440C. I would consider a cryogenic treatment after the first temper cycle, along with, an extra temper cycle and longer cycles.

 

How long would it be nessisary to heat the back of the blade in a soft-back draw in order for it to have any effect?

 

Again, the standard is three draws on the back to whatever temper you wish it to be. On the seax that inspired this post there were still hard spots after two draws.

“All work is empty save when there is love, for work is love made visible.” Kahlil Gibran

"It is easier to fight for one's principles than to live up to them." - Alfred Adler

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The other approach is to use multiple tempering cycles to temper any fresh martensite that is triggered by the previous temper cycle. Longer tempering cycles is another solution. The best blade I can turn out is one that is hardened to the best of my abilities and then tempered for three, long, cycles. I have too much time into making my knives to do less then my best with the heat treatment. I am using mostly simple steels, 10xx, 5160, 6150, and the occaisional file and coil spring. If I were to use any of the stainless steels like: S30, BG42, 154CM, or 440C. I would consider a cryogenic treatment after the first temper cycle, along with, an extra temper cycle and longer cycles.

 

Thank you for the reply, Mr. Norris. That did clear a few things up. For the record, I do 3-2 hour tempers (in the oven, I edge-quench normally) simply because I am a firm believer in overkill, I don't believe it is possible to temper for too long (or too many times), and it gives time to work on that cursed dagger I may or may not finish in the next ten years... I will have to give the soft-back draw some more thought and testing because I'm lately becoming more and more displeased with my current methods.

George Ezell, bladesmith

" How much useful knowledge is lost by the scattered forms in which it is ushered to the world! How many solitary students spend half their lives in making discoveries which had been perfected a century before their time, for want of a condensed exhibition of what is known."
Buffon


view some of my work

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