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Author Topic: Jominy Test  (Read 7729 times)
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Rex
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« on: June 26, 2007, 05:35:08 PM »

Hello,
Sorry it's been so long since I posted. Sometimes we can learn from things we do wrong.

Several months ago, we recieved a jominy sample from a European steel manufacterer to test. We did not know what grade it was, so we relied on the heat treating data they sent with the sample. We heat treated the jominy at 1600 degrees F as per their instructions and quenched. The jominy failed the hardness requirements. Upon giving this information to the company that sent it, they had us verify the chemistry. Guess what? 52100.

Upon learning this, we realized that they had given us the wrong austinitizing temp. It should have been quenched from 1550. We retested the sample, and it passed easily. It's interesting to note that, although the maximum hardness (the end closest to the quench) did not change, the hardness toward the end of the piece was four points higher. This simple test verifies the fact that...

1. You do not need to quench from a temp that is too high. Hot enough IS enough; more is not better. In this case, it was worse.
2. In this case, although it would take many more samples to verify, I feel that the results from the jominy test exhibited a more uniform grain size, due to the refinement of the double quench.

I will try to type in the entire test results so you can see the difference.

Thanks,
Rex    

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Ed Fowler
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« Reply #1 on: June 27, 2007, 07:26:02 AM »

In another post I describe how I discovered multiple quench by luck:
A simple inadvertent experiment that resulted in significant advances in knife performance.

Again another experiment undertaken by luck brings greater understanding of how multiple quench works, the qualities revealed in Rex's report are highly significant in our quest for our dream of Excalibur.

On the surface one would think that when we re-heat a hardened blade to critical temp we would be tempering the qualities of the first quench out and the second quench would be simply a duplication of the first.

Rex's experiment demonstrates that the grain refinement produced in the first quench remains through the second quench and influences the qualities of the steel in that The hardness penetrated further. I believe that when edge quenching blades the increased length of the hardened portion produces the martensite pyramid that we find inside of sectioned blades. The relationship and nature of the steel between this hardened cone and the outside of the blade is an opportunity for blade smiths to produce blades that are superior in qualities of toughness, strength and cut.

We are not the first to observe this phenomen, US Steel at one time had a patten on multiple quench hardening. I am absolutely certain that other blade and blacksmiths were cognizant of the this quality many years ago.

Again I thank Rex for his dedication and willingness to share his knowledge with us.
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Larrin
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« Reply #2 on: June 28, 2007, 06:19:11 AM »

There have been studies done in Germany on using an austenitizing temperature that is too high on the first quench and then the proper temperature on a second quench for a finer grain size. I'm sorry I don't have the actual study, I have only heard about it and I don't speak or read German.
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Ed Fowler
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« Reply #3 on: June 28, 2007, 06:35:18 AM »

I don't believe the higher temp was as significant as the cycle itself, still you have brought out another variable to work with.

The German steel industry has always been light years ahead of the pack. The most significant literature I have found always has many refferences in German.
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« Reply #4 on: June 29, 2007, 07:26:44 AM »

Again I wish to call attention to the significance of Rex's experiment, this is one of the milestones in the high endurance performance blade. I urge you to study the influence of the quenching cycles.
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Ed Fowler High Performance Knives
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« Reply #5 on: June 30, 2007, 03:37:24 PM »

  To quote Ed:
Rex's experiment demonstrates that the grain refinement produced in the first quench remains through the second quench and influences the qualities of the steel in that The hardness penetrated further.
         Ed, it has taken a little head scratching to see the reason this is so important. Chock it up to my not seeing the true relationship of grain refinement to hardness. Maybe ignorance is bliss. I never doubted the value of multiple quench because so many things are happening at different rates along the steel because of variances in heat transfer and grain structure. In my opinion, (and I think you will agree) each quench is bringing another part of the steel closer to the desired result. In theory the steel is exactly the same throughout, but like a loaf of bread it varies and needs a little kneading to reach consistency.
          Now we have evidence that goes even further. The steel seems to like its new state and maintains it while waiting for further improvement. You knew this and now have scientific evidence to support it.
          This news kinda threw us on the chat the other night and we didn't get into it. We will though. I have some dumb questions myself. But, I know you'll help us to better understand. I look forward to more photo-micrographs. Too, I hope this new information will help us to understand what happened to your friend's blade that blew out under test. Congratulations to you and Rex on a significant discovery. 
   Clay
   
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Harold Locke
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« Reply #6 on: June 30, 2007, 04:47:40 PM »

Please Ed or Others,

I have never come across the word Jominy what is the definition. I seems to me the power of 3.

3 normalizing cycles
3 temepers and quenches, Makes your blades 300% or more of what they can be. Of course there are other important variables.

Do I have this right? Or is the double quench the most signifcant gain?

And I belive that stock reductionists should be adopting this NTQ pattern. I still don't think I have convinced my heat treater that this is the way to go yet.

I was going to by a paragon or evenheat oven seeing that I couldn't pull off the Willow bow seminar. Being laid off I have had to go into full survival mode and conserve all rescourses so that's out of the question now. I am lucky that I was paid so well I do have a fairly high unemployment check but not enough to put in savings like I was I can still put over a hundred a month away. Most importantly I am able to put more time in the knife shop and the Big D is close to completion it has taken over a year and a half. Wew!



Thank You Gentlemen

Harold Locke
« Last Edit: June 30, 2007, 05:36:55 PM by Harold Locke » Logged
Larrin
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« Reply #7 on: June 30, 2007, 09:43:40 PM »

Jominy is simply a test of hardenability, the test is described in the Verhoeven book.
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Harold Locke
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« Reply #8 on: July 01, 2007, 05:14:06 AM »

Thanks Larrin,

I'll run into the word I'm sure.

Harold Locke
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Ed Fowler
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« Reply #9 on: July 01, 2007, 07:09:43 PM »

The Jominy test  end quench test uses a 1 inch diameter bar, 3 or 4 iches long, quenched at one end only by a strong stream of cold water applied for 3 minutes. The rest of the bar does not come in contact with the water. The quenched end cools at a fast rate while the other end cools at a slower air-cooling rate.
This information courtesy of the Metalurgical Staff of the
Battelle Memorial Institute. in the book  "Steel and its Heat Treatment"

Sorry to take so long answering your question, been real busy! Thanks for filling in Larrin
« Last Edit: July 01, 2007, 07:16:11 PM by Ed Fowler » Logged

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ChrisAnders
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« Reply #10 on: November 10, 2014, 10:24:13 AM »

I had heard about this before on this board and wanted to read the test and retest for myself.  So in an exercise that takes thread resurrection to new levels, I had a few questions.  I see Rex doesn't post much, and realize a lot of this may be too long ago to remember, but any information would be beneficial.

Do we know that the grains actually got smaller with the 2nd quench?  If so, were they appreciably smaller than normal for this type of bar, or did they just get reduced from the slightly larger grains from the slightly higher (1600 F-1650 F) austenizing temperature used initially?  Grain size has a significant effect on hardenability, with smaller grains causing lower hardenability.  Does anyone know what grain size was expected in the bar initially?

There are a few mechanisms/causes that could possibly explain the difference from the first to the second quench.  Was any work/testing done to rule any out vs. confirm any others?

Does anyone know what condition the bar was in before the initial test?  (annealed, hot rolled, as forged, etc?)

Ed (Fowler) often states the distribution of grain sizes is important, though here Rex postulates the uniformity of grain size is important.  These principles seem to be at odds.  Any thoughts on how both could be working at the same time?
« Last Edit: November 11, 2014, 07:40:49 AM by ChrisAnders » Logged
Ed Fowler
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« Reply #11 on: November 11, 2014, 09:16:53 AM »

Rex in totally swamped at work, I miss his input greatly. Next summer he is planing to visit the Willow Bow and wants to work with us. Until then it looks like we will have to wait. In the meantime Rex continues to learn and we will all benefit.

Rex told me that when they receive a sample of steel to test the first thing they do is give it  a soak at above critical and let it cool down slowly to eliminate any variables that may influence their tests. As I remember it us usually a 1,700 f. soak for two hours and allowed to cool down slowly. The soak temp may vary for different steels.

There are many who claim that you have to take blades over critical and soak when hardening, Rex found this was not necessary. His statement that enough is enough is highly significant.

Their experiment revealed that 50 degrees over critical was not beneficial is music to my ears, I had forgotten all about this experiment and thank you for bringing it back to life.

I continue to watch what the magnet tells me very carefully.

 I have a huge file of correspondence with Rex and plan to review it this winter. Most if the information is already recorded in this forum.
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« Reply #12 on: November 11, 2014, 01:02:49 PM »

Rex in totally swamped at work, I miss his input greatly. Next summer he is planing to visit the Willow Bow and wants to work with us. Until then it looks like we will have to wait. In the meantime Rex continues to learn and we will all benefit.

Rex told me that when they receive a sample of steel to test the first thing they do is give it  a soak at above critical and let it cool down slowly to eliminate any variables that may influence their tests. As I remember it us usually a 1,700 f. soak for two hours and allowed to cool down slowly. The soak temp may vary for different steels.

There are many who claim that you have to take blades over critical and soak when hardening, Rex found this was not necessary. His statement that enough is enough is highly significant.

Their experiment revealed that 50 degrees over critical was not beneficial is music to my ears, I had forgotten all about this experiment and thank you for bringing it back to life.

I continue to watch what the magnet tells me very carefully.

 I have a huge file of correspondence with Rex and plan to review it this winter. Most if the information is already recorded in this forum.

More power to you Ed. 
like awaking a sleeping Giant ( kinda )   Grin
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ChrisAnders
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« Reply #13 on: November 11, 2014, 06:42:47 PM »

Based on the information in this thread, I don't think any solid conclusions can really be drawn about multiple quenching.  We don't really know if the grain size was smaller than usual.  I can say with certainty that the grain structure was not uniform when the hardness testing was done.  A 1700?F soak for 2 hours seems like it would have significant effects on it's own.  A question that comes to mind is would the sample have passed as it was recieved from the maker, without the 1700 F soak?   Would the sample have passed if it had been hardened from 1550 F on the first try?  What about all the samples that harden properly on the first try?  This sample seems notable because it was an exception.  I am making the assumption that Rex's lab does Jominy testing regularly, and this was not an out of the ordinary thing for them to do.  In any event, even Rex said more samples would be needed to verify what was happening. 

Something to note is that there are several temperatures that are significant.  First is the Curie temperature.  This is the point where steel becomes nonmagnetic, and is around 1400-1425 F.  It varies slightly and some alloying elements affect it.  The second temperature is the lower critical temperature.  This is the temperature where the change to austenite begins.  This temperature ranges from 1350-1400+.  It is increased or decreased by various elements.  The third temperature is the actual hardening temperature.  This is the recommended hardening temperature from the stel maker and is not fixed.  This point is critical.  The hardening temperature varies for the same steel, depending on the intended use of the steel.  Overshooting the hardening temperature for a given application and soaking the steel has not been something that is recommended that I have seen. 
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Ed Fowler
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« Reply #14 on: November 12, 2014, 10:34:52 AM »

Rex works in the largest privately owned lab in the US, they do testing 24 hours a day 7 days a week.

When steel comes from the rolling mill it is stacked to cool. Bars in the center naturally cool at a different rate than bars on the outside. That is but one example why two samples of steel are different. By soaking at 1,700 f. this is one variable in the samples they receive that is negated.

To really stretch the crystal ego of traditional science; My "theory" - I note that steel that I have worked down from large bars (high rate of reduction) drops through the allotropic phase change at different rates from the first to the last. Forging becomes easier after each thermal cycle from the large bar to the final blade. Judging by color, I feel many factors in addition to chemistry contribute to temperature differences, for all three phases you mentioned. Would love to be able to measure them.!

The long soaks are usually discussed by blade smiths who do not test blades. By long soaks I mean over 1 minute.

Interesting thoughts Chris, thanks.
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