Retained Austenite testing in Elmax

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Re: Retained Austenite testing in Elmax

Postby Robert C » Mon Jun 12, 2017 8:08 am

Yes ! Eta carbides need LN temperatures to form. They are very small and when they are forming the matrix is strained around the carbide .We can see this cohesion as the strain disrupts the electron beam .As a precipitate forms it has cohesion. At one point the precipitate gets to a size where the cohesion is lost .Cohesion is part of the strengthening of the metal !! This is seen on the hardness graph where the secondary bump flattens and then falls off ! So if we got to 900F with eta that will remove cohesion and most likely make other bad changes . Sub-zero [-100 F ] will make a big change in RA but below that only small changes .
So Decide for eta or secondary carbides but don't confuse the two. :?
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Re: Retained Austenite testing in Elmax

Postby Andre Grobler » Mon Jun 12, 2017 9:37 am

i want to maximize matrix strength, so small is good and it seems that eta carbide will add strain energy, which is OK, if not too much. definitely no more big carbides wanted than the primaries... grinding is a large enough chore already...


So thank you - i heat treat m390 for a friend and he asks for cryo and does the temper himself... my ovens don't do 500 dgc
Most of our's not to reason why, but to control heat or die... ;-)
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Re: Retained Austenite testing in Elmax

Postby Jozef S. » Mon Jun 12, 2017 5:37 pm

Robert, Is it true that the maximum strength peak at the high temper is where the most RA has been transformed
but matrix wasnt yet too softened where at the same time the cohesion between the secondary carbides and the matrix
is the highest ? Or better said such conjunction of these or more factors resulting in maximum strength.
Understood it correctly? I read a lot of research, I am not using LN (yet but I am planning to)
Knew something about ETA but never heard that is the bad idea to to have both types in the matrix.
Thank You for the information.

Andre, are You saying that elmax outperforms 14C28 in the kitchen for Your use ?
Never used 14C28 typically I work w AEB-L and RWL-34 both performing
a lot better at low angles than elmax for but again I dont do LN.
However no problem to get those steels to 62+ HRC giving already
a very decent edges at 10deg-15deg.
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Re: Retained Austenite testing in Elmax

Postby Robert C » Mon Jun 12, 2017 11:13 pm

Secondary carbides + eta together in the matrix ? Will the eta survive the 900F ? If you can, in typical HT of a tool steel, create new carbides with cohesion then destroy them in a relatively small temperature increase , what will happen going from 300 F to 900F with eta ??
Let's go back a moment . We HT to form martensite , a different crystal structure. That martensite is filled with lots of dislocations and a highly stressed matrix.. We temper to reduce those stresses . At lower temperature small carbides are formed and each carbide surrounded by a stressed matrix, the cohesion. Higher temperatures get more carbon to the carbide . Then the carbide reaches a size where cohesion is lost. Further changes in the matrix will end with usually, a spheroidized structure .
We have to play with those things to give us the best combination of properties.
While we talk about carbides alloys such as aluminum , while they don't have carbides have other precipitates which go by the same rules ! A look at the HT of some of the AL alloys is very interesting as they go through the formation of various precipitates to maximize properties.
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Re: Retained Austenite testing in Elmax

Postby Andre Grobler » Tue Jun 13, 2017 2:16 am

Yes, elmax does better than my limited experience with 14c28n both cryo'ed If rwl34 and aebl was easily and cost effectively obtained here, I would probably only use that.... I have a strip of aebl now and am playing with a rather large kitchen knife set...

Thanks Robert, things are falling into place now...

BTW according to Phil Wilson's review of M390 and his heat treat experiments, he mentioned that the secondary hardening curve moves to the cooler side once you cryo... could that be because you already "seeded" the matrix with eta carbides so the carbon in ra attaches to those seeded spots more easily ? Apparently this was feedback from Bohler on his queries...
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Re: Retained Austenite testing in Elmax

Postby Jozef S. » Tue Jun 13, 2017 6:27 am

Robert,
As I ve said, I read only very little about eta cabides and totally didnt realise,
that it will grow during the tempering at high temperature,
or will become a part of a bigger carbide that started to grow next to it,
or when a big carbide is present next to it, there will be not enough matrix to support both of them..
Is there any other factor than carbide size and volume involved related to cohesion you mentioned ?

Andre,
The case with Phil Wilson can be that he mostly uses high carbide volume steels and tries to get max wear resistance.
He makes some compromises in terms of corrosion resistance and blade flexibility but wear resistance probably
is the main objective for him. Perhaps his grinds are thin behind the edge, according to what I ve seen
he does not use very low edge angles. So as long the knife cuts long enough at 30deg was fine for him.

Please anyone, correct me if I was wrong at anything :)
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Re: Retained Austenite testing in Elmax

Postby Andre Grobler » Tue Jun 13, 2017 8:28 am

Jozef i think you are right... his heat treat seems very well considered.
Most of our's not to reason why, but to control heat or die... ;-)
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Re: Retained Austenite testing in Elmax

Postby Robert C » Tue Jun 13, 2017 1:24 pm

I had a problem with Bohler a few years ago as their website didn't do much as far as explaining eta carbides ! Obviously we both learned a few things since then . They can't be all bad as my FLZ rifle made in the '30s still keeps the woodchuck [marmot ] population in check -- with it's Bohler barrel !! :D
Do you have a source for the bohler info ??
Once you deplete the matrix of carbon you won't grow the carbide or increase the cohesion. Bohler may very well be right about the eta influence on secondary carbides .
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Re: Retained Austenite testing in Elmax

Postby Andre Grobler » Tue Jun 13, 2017 2:00 pm

Haha!

I just guessed that that might be the reason - i sent you an email with the testimonial... but actually i can't find a link to it anymore... so for completeness sake i will post a quote from it here... Kevin if this goes to far...

so it does seem that he opted on these for low temper in the end, unfortunately no information on the why...

"Bohler- Uddeholm Corporation (BUC) Blade Steels
This year I was fortunate to receive some steel samples from BUC. These grades are: Bohler
M390 Microclean, Bohler K294 Microclean (A11), Uddeholm Elmax and Bohler N690.
All of these steels except N690 are made with the 3rd generation particle metallurgy process.
My experience shows that this yields a very fine clean structure. I have heat treated and
completed knives with all of them to date. For more information on designs and some photos
see www.seamountknifeworks.com
General workability
M390, ELMAX and K294 are very well annealed and drilling, milling and rough grinding are
pretty much the same as the other Particle steels we are familiar with. The steel is furnished in
plate that is cut into strips (bars) for knife making blanks. Several thicknesses are available but
the samples I worked with were .145 to .150 inch. Rolled thickness seems very uniform.
Profiling and rough grinding was done with Norton SG (hogger) belts in 50 and 60 grit. Prior to
heat treat, I grind to an edge thickness of about 0.030 and finish with 150 grit to minimize
warpage during heat treat. I did detect some stress in M390 while removing the outer layer on
the surface grinder. The solution is to take small cuts (.002 inch) and alternate sides and keep it
wet with coolant and it will settle down in a couple passes per side. This is typical of other very
high alloy steels since they are very difficult to roll into thin sheets. ELMAX, N690 and K294 did
not exhibit this characteristic. All of these steels are very sensitive to tempering. Changes as
little as 20 degrees F can make one point RC hardness difference.
M390 Microclean
Carbon 1.9, Chromium 20, Molybdenum 1, Vanadium 4, Tungsten 0.60
Heat-treating this grade took a couple of tries before I got what I wanted. My target hardness
was 61 HRC but I missed this by quite a bit on the first attempt. With some help from BUC and
some thermocouple calibration in my furnace, the final success came with the following recipe.
Preheat at 1550 ⁰F, Ramp to 2120 ⁰F, hold 30 min and a rapid forced air quench down to room
temperature. The as quenched hardness was 62-63 HRC. A four hour subzero in Liquid Nitrogen
gave 63. Three tempers at 400 ⁰F for one hour yielded a final hardness of 61. It is possible to
push the final hardness up to 62 for enhanced wear resistance if torqueing, twisting and impact
loads like chopping are avoided. Note: The data sheet shows a tempering hardness bump at
about 1000 ⁰F. but on the first attempt, I missed the peak and actually got about 58 as a
finished hardness. In general the lower temperature range on these high alloy grades gives
maximum corrosion resistance and slightly better toughness. For this reason I settled on the
lower temperature range as the best overall procedure for this grade. According to the BUC
metallurgist I consulted with the subzero moves the high temper hardness peak to the left of
the curve. This is probably why I missed the peak on the first try.
I did some rope cutting and whittling on fir to get a feel for wear resistance and strength of the
edge. I used 3/4 inch diameter rope and cut with my standard test procedure. Again, see the
Seamount web site for more information on the rope cutting test procedure. In short, if a blade
will make about 150 cuts on the 3/4 rope with less than 20 pounds on the scale and still have
good bite, then I judge this blade to be good for a big game hunting knife. This knife is about
0.010 inch behind the cutting edge and was sharpened on a Norton Silicon Carbide (Crystalon)
medium stone. Edge burr was removed with a loaded strop. I got the 150 cuts just fine and it
was starting to slide a bit at about 180 cuts. I stropped the edge again and it was back to the
original sharpness. This is very good cutting performance. I whittled on fir and twisted the
blade out of the cut so it makes a kind of popping, scrunching sound. There was no edge
chipping but some slight deformation. This is exactly how it should perform.
I carried this knife on a recent fishing trip to Baja. It was used for gill bleeding on fish and
general boat use on two outings on the sea of Cortez. The sea has a high salt content and the
weather was 80 ambient. There was no evident corrosion at all even though the knife was not
rinsed in fresh water until the end of the day.
Overall, this steel is a very good choice for an all-around hunting, utility, salt-water carry knife.
The steel is nice to work, very clean with very fine grain. Based on just three blades and limited
field-testing I would judge this steel to be one of the best available for this type of knife. I think
also it would make an excellent kitchen knife based on the wear, corrosion resistance and
toughness.
K 294 (A11)
Carbon 2.0, Chromium 5.2, Molybdenum 1.3, Vanadium 9.7
The best way to describe this grade is to say that this is the BUC version of CPM 10V.
Since I am very familiar with heat treating the CPM version the first heat treat trial on this one
was successful. Aim hardness was 63-64 HRC. Preheat at 1540 ⁰F, ramp to 2140 ⁰F and hold for
30 minutes. With a forced air cool down to room temperature the as quenched hardness was
65 HRC. Direct immersion in liquid Nitrogen and a hold for 2 hours did not increase the 65
hardness. Three tempers at 1000 ⁰F for 2 hours yielded a final hardness of 63 HRC.
The finish grind on this steel after heat treat is to say the least a challenge. The 10% Vanadium
is there for wear resistance and it shows up during the finish process. There is some Sulfur
added to this grade for ease of machining and I would say it helps. Drilling and milling are fine
but grinding and finish is still at the very high end of effort for a knife blade steel.
Sharpened the same way and with the cutting procedure above on M390 yielded over 240 cuts
before any smoothing of the edge could be detected. This grade also responds well to a loaded
strop and a few strokes put it back to shaving sharp. The same whittling test on Fir showed
some very fine yielding at the thin edge. If pushed very hard (abused in my mind) and at this
high hardness it is possible to get some fine chipping as well. CPM 10V and now this grade are
my standards that I compare all other to for wear resistance and edge holding. I like this
version; it has very fine grain and is clean and reasonable to work with. I have not done any
corrosion resistance tests yet, just one blade completed, but a hunter utility blade is going to
require care in cleaning and drying before storing to insure it stays corrosion free. It comes
down to the right steel for the application. I would take the M390 fishing and use the K294 for
the tough big game skinning and dressing tasks. Wild pigs are the greatest challenge for a
hunting knife and I cannot wait to try K294 on my next pig hunt.
Elmax
1.7 carbon, 18 chromium, 3.0 vanadium, 1.0 Molybdenum
If you are used to working with CPM S30V this one will be familiar. Pretty much the same heat
treat process as for M390 will work but in general I got the same final hardness using lower
austentizing temperatures. On the first knife with this steel I did a finish grind with a 220 belt
and went direct to a ‘Scotch Brite’ fine belt. This finish is pleasing and is fine enough to make a
good working knife. Initial cutting tests show ELMAX to be in the same category as CPM S30V at
the same hardness. It is capable of an extremely sharp edge due to the fine structure. I have
seen some Charpy toughness tests done by Bohler–Uddeholm that show ELMAX dynamic
toughness to exceed several other steel grades used for custom knives. This good toughness
can be used to advantage by increasing the hardness up a couple of points (to 62 HRC) and still
be left with an edge that will resist chipping and have good strength to resist rolling. I think the
best application for this grade is all around using knives, kitchen knives and fillet knives. Cost
per pound is lower than M390 and if both are heat treated at the same hardness ELMAX only
gives up about 20% in edge holding. If sharpening is convenient then this difference would be
hard to detect in actual use.
N690
1.1 Carbon, 17.3 Chromium, 1.1 Molybdenum, 1.5 Cobalt
This one was a pleasant surprise. It kind of looks like 440C based on the chemistry but acts very
different in use. The addition of Cobalt and Molybdenum change the character it seems.
Custom makers do not have access to VG10 which has a closer chemistry. VG10 is a very
popular all around steel, so it is fortunate to now have a similar grade to work with. It responds
nicely to the initial austentizing cycle by providing up to 63 HRC with a forced air quench. After
the cryo cycle it is then possible to temper down to 60/61 on a temperature range of 375-400 F.
At this hardness it has very good edge strength and will limit rolling on a thin edge with hard
use. The grain structure is visible in the initial grinding and it looks like D2 or 154 CM with the
visible carbide strings. This is not a particle based steel and the larger grain size contributes to
very aggressive cutting personality. When sharpened on a medium Silicon carbide or diamond
stone it will cut abrasive materials like cardboard and rope very nicely. The corrosion resistance
is excellent due to the large chromium content so I think this grade will make a very versatile all
around use knife. I have done a couple fillet knives with N690 and have tested it on rope and
cutting fir. At 60 HRC and a very thin edge I did not detect any chipping but some incipient
rolling. This shows good ductility and means the heat treat is close to optimum. Next test will
be a check out filleting some large salmon or halibut. I just have to take some time off making
knives and get to the ocean. This steel has been used by many European production and
custom makers for years and it is obvious why it is one of the standby steels over there.
Another nice factor is that N690 is very reasonable priced compared to other commonly used
blade steels.
The heat treat results outlined above were done in my shop with my furnace, hardness tester
and tempering furnace. Calibrations in other set ups may vary and results can be different
depending on user techniques. In general I found the information on the BUC data sheets for
these grades to be very good for knife blade type applications.
I cut manila rope to get an idea of edge retention and toughness and to predict performance
in the field. My results can vary from test to test, depending on the rope thickness, humidity
and batch of rope. Other’s testing will get different results (number of cuts etc.) using a
different batch of rope, scale and slicing techniques. The CATRA test eliminates more variables
but I find in general that my method will parallel the CATRA results pretty close with large
differences (+/- 20%) clearly showing up.
PhilWilson
Seamount Knife Works
www.seamountknifeworks.com
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Re: Retained Austenite testing in Elmax

Postby Robert C » Tue Jun 13, 2017 4:22 pm

Thanks ! I like those field tests more than the formal ones. I had seen his website , good info .Some updates are needed.
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