Testing edge holding and toughness on 52100

[Kevin]

Testing 52100 edge holding and blade tougness.


This is something I have been playing with and thought it may be interesting to post......I do not believe I am yet getting optimum performance, but I know I have improved somewhat from my earlier testing.....
If I have mentioned any of the theory that is not right, I would be obliged if you can correct me.
This is just one method of heat treating which works for me in my shop. It is not the ultimate or only way. I am still discovering and learning myself.





A few days ago, I experimented with heat treatment on 52100.
I have used this steel extensively for over a year now and have been happy with the performance, but I wanted to see if I could make any improvements.

I recently acquired an ‘Even heat’ oven, so now I can be much more precise with my temperatures, compared to relying on magnetic and color changes.

52100 has a carbon content around 1%.
Critical temperature of 52100 is usually between 1500 and 1550F, but I believe I am correct in thinking that only expect about .6% of this carbon to be dissolved into the martensite and the rest will stay as undissolved carbides (someone needs to pull me up on this if I have this wrong!).

My understanding suggests that if 52100 is heated to above critical, in this case 1850F, then more carbon may be dissolved. The disadvantages of this are that at higher temperatures, there may be rapid grain growth and the formation of brittle ‘plate’ martensite (‘lathe martensite is good, ‘plate’ is not so good’!).

From earlier tests, I know for a fact that if the steel is over heated, I can refine the grain either thru a process of triple normalizing , or even triple quenching (both I consider thermo cycling procedures).

I wanted to know if there was any potential to dissolve more carbon into the steel which would increase edge performance, without sacrificing the steels performance in other ways (becoming too brittle).

Earlier testing.

The first two test knives I made were fully hardened.
Convexed sharpen to a zero edge. I used 3/8th inch manila rope, cutting on a wooden bench. When a sharp knife cuts manila you can feel and hear it bite well into the rope. My intention was to continue to cut until I lost that bite as the edge became worn. I have done this tests many times with other knives, and around 80 cuts is what I considered a ball park figure of good performance (though I know this is exceeded by some makers).

Because I did not want the wooden bench to have much effect on the edge, cuts did not totally severe the rope, but a few loose threads were left hanging each time to protect against abrasion from the wooden bench.

Rather than the length of the blade dictate the cutting performance, I made a mark on the blade 1 inch in front of the ricasso. I would only cut within this 1 inch mark.

This first knife made a few days ago made over 600 cuts and continued to have that crisp cutting sound, biting its way thru the rope.

Picture of knife on its 600th cut.
http://www.coutelcutlery.com/600th%20cut.jpg


I then chopped a 2 x 4 which took some considerable time as the knife was small and light and had no handle. About 500 chops later the 2 x 4 was severed. I then sliced about 20 cuts in a cardboard box and went back to cutting the rope, thinking I may have tired the blade by now. The blade continued to cut just as aggressively and I stopped at another 100 cuts, making 700 cuts in total. It could have gone on and cut a lot more.

Picture of knife after all cutting tests wit items cut and chopped.
http://www.coutelcutlery.com/all%20materials%20cut.jpg



I wanted to snap the blade and look at the grain. I did the usual vice bend with a pipe, and it snapped very easily, maybe too easily. There appeared to be no flex at all. Was this the result of plate martensite,or did I not temper it long and high enough?
The grain looked super fine, a very pale gray color.

Picture of snapped blade showing grain..
http://www.coutelcutlery.com/snapped%20grain.jpg


I was amazed at the edge performance, but dismayed at the zero flex, so I knew I had to do more testing.

Second Tests.

I then forged two new knives from the same bar of 52100. Each knife was identical in shape, size and grind (convex grind to zero edge). About ¼ thick at the spine.

I also made two flat sectional test pieces which I would take thru the same heat treatment to test later.

Blade #2 and test piece #2 were over heated to 1850F then quenched.

Both blades and test pieces 1 and 2 were then normalized three times , then quenched three times.

Each was given identical tempering times and temperatures.

I invited fellow knife maker Kevin Brown and his son Bass to visit and help me with the tests.

The first thing we did was to test the hardness with Rockwell files. We each agreed it was between 55 and 60 Rc, nearer 60.

Picture of two test knives and test pieces .

http://216.46.248.210/pixc/coutel/pre-test.jpg


We took in turns cutting the 3/8inch diameter manila rope. I made the first 100 cuts and Kevin the next and so on. By about 360 cuts on knife # 2, we noticed the performance had dropped slightly than when we first started, but it was still happily crunching thru the rope with no sign of wear enough for us to stop.
Knife #1 seemed to show the same signs at about 250 cuts, but continued to bite thru the rope. They both just needed a bit more pressure to cut. These knives did not have handles and we also needed to take into account our fatigue!

Picture of Kevin making his 100 cuts.
http://216.46.248.210/pixc/coutel/cutting.jpg


Both blades hit the 600 cut mark,…. both would still bite crisply into the rope, but not as easy as the first couple hundred cuts…..but we both agreed that they could keep on cutting if we had the stamina..neither blades started to slide on the rope, a sign of wear….It was a very hot day, and we stopped, besides , we were running out of rope (cut about 40 feet in length)

We both commented that there was hardly any noticeable difference in the cutting ability of the two blades, BUT, if we had to choose, we both felt that blade #2 had a bit more bite left in the edge than knife #1…but it was marginal.

Both edges still felt sharp to the touch, but would not shave hair, unlike when they were first sharpened (hair popping with no effort). I decided to test the ease at which they could be sharpened.
I have a leather strop in my shop and used this to strop the edge three time per side. The edge had recovered sufficiently that it would easily shave hair again.

Next, I wanted to flex test them to see how they performed. Both blades had been given three edge quenches, using a limiter plate in the oil, so were quenched at identical depths.

Both blades were very tough and needed a preacher bar to assist in bending. With a lot of effort, I managed to bend blade #1 to 90 degrees with no edge damage seen. It stayed bent.

Picture of blade #1 being bent..
http://216.46.248.210/pixc/coutel/bending.jpg


Knife #2 (the blade that was over heated) bent to 90 then snapped.

Picture of blade #1 bent at 90 degrees with no visible damage to the edge.
http://216.46.248.210/pixc/coutel/90-bend.jpg


I wanted blade #1 to be taken to failure point. It was bent multiple times back and forth, about 10 times before it suffered fatigue and snapped very coarsely.

Looking at the grain, a distinct line could be seen at the hardness zone, above the zone the grain looked courser.
Neither grain was as fine as the blade I snapped a few days before which was fully hardened (complete thermocycles)…..but nonetheless, the grain was not what I would consider course. Blade #1 only snapped after constant fatiguing, and the shear effect could be seen in the grain (the blade was also so hot to the touch from fatigue that it could not be held without gloves).

So far, blade #1 seemed to be tougher than blade two, but it could be argued that blade #2 may have marginaly held a slightly better edge.

I decided to test the two test pieces that underwent the same heat treatment. I placed them in the vice and used a 4 pound sledge hammer in an attempt to snap them. I must have struck test piece #1 20 times, it bent slightly but I could not get it to snap!!
Test piece #2 (the one that was over heated) took just one heavy strike to snap it.

Picture of both knives after snapping . The blade and test piece on the left side is blade #2, the one that was pre heated and quenched to 1850 F , then subsequently thermo cycled and hardened at 1550F. The test piece given identical heat treatment failed on the first blow with the hammer.
The blade on the right is blade #1, thios only snapped after multiple bends back and forth which fatigued the steel.The Test piece to the right side could not be snapped even with multiple blows with a 4#hammer, though it bent slightly.
http://216.46.248.210/pixc/coutel/pieces.jpg




Results.

For me, these tests appear to confirm (at this time anyway) that overheating the steel over and above critical temperature somehow made the steel more brittle, even though I could refine the grain .
Although not conclusive, it appears that overheating the blade in theory may dissolve more carbon and may have given a slightly better edge holding performance, but I feel this performance was not enough to justify a trade off in blade toughness.

[Colin KC]

Great testing Kev, scientific & good conclusion

[narsil]

Excellent post, you certanly don't mess about when you test your baldes do you ? I must say that your disciplened approach to this subject has been a great inspiration to me, thanks very much You've taught me a lot about testing, quality and forging in general, probably more than anybody else in fact.

[RHGraham]

IF you heat 52100 to 1550F and hold, most if not all of the carbon available will go into solution, and you'll still have a signifcant amount of plate martensite forming in the quench.

Your concepts of what it is doing are dead on but I'd suggest adjusting the temps a little, that's all.

try this;

Normalize;
heat to 1550F and hold for around 3 minutes, remove and allow to drop below critical,
Back in at 1525 for around 6 minutes, remove and allow to drop below critical,
Back in at 1500 for around 9 minutes, and quench in oil down to 120f, and back in the oven for a 1hour soak at 1250F.

File, girnd, drill, whatever.

Harden;

try 1450 for 10 minute soak and quench, oil or maybe marquench, whatever turns your crank, and temper at 475-500F for 30 minutes to an hour.

You should have lathe martensite and a large amount of secondary carbides, fairly high toughness and great edge-holding, as well as a fine grain and a very fine edge.

"Blacksmith method"
Norm;
heat to non-mag and then what you think is another heat range, up to around 1550F, quench in oil till all the reds are gone, immediately back into the fire;
Heat again to non mag, try not to get quite as hot as last time, quench in oil as before, back into the fire,
Last time heat just to non mag and a TINY bit above if you can, qiench in oil, then back into the fire and heat it slowly to a dull red, around 1200F, and hold it as long as you can , allow it to cool.

grind, file, drill etc...

Heat to just non-mag and try to hold it right there for a good long soak, try not to get hotter than that if you can, or if you are doing it all by eye, you want to bring it up slow and gentle in the dark and watch for the blade carefully; the blade will be a nice salmon red colour, and if you are carefull and are getting the heat nice and even, at some point a brighter flare of colur, a brighter orangy-red, will appear along the edge... you want to stop adding heat but simply allow that flare to envelop the whole blade.
Hold it there for awhile, then quench it.

It should accomplish much the same thing as above.

Give it a try.

[patro]

I don't know all about this subject and your explanations are great. I was to post a question relate to that subject.

I make blade for wodden plane. I was given a piece of HCHC and make this blade. I was told that this steel was M52.

Blade for wodden plane and the steel use.

I normalise, profile, polish, harden red-ti straw with Oxi-Ac,and quenche in oil, temper in oven in glass bead or 2 hours at 400.

My problem is the the steel does not hold it's cutting edge at all.

I don't have this problem if I use 1/8 steel from old 18" round saw used in wood mill. Nor with O1

Is this because that M52 steel can't be harden this way.
I presume more that it is beacause I am new to this. Any help is appreciate.


I also need to fin in this site informations about sharpening and polishing blades. Your's are just great.

I also discover here Damascus steel.
Is there a good article describing what is the process to make such a beautiful blade. I am dreaming of making some like that.

Regards

[coreysmith]

Great test protocols. I tried to break a lot of 52100 in my shop as well, and found it very tough to break. The edge quench worked very well, and the file wouldn't touch the as hardened edge. As mostly an 01 guy (which is the most forgiving steel ever) I must admit I don't stray too far. I've just renormalised and straightened 3 times a chunk of W1 which will not stay straight. I also remember a lot of early problems getting 5160 and L6 to respond perfectly everytime. Good old 01 though, so hard to beat. I'd say if the grain looks good, in your first test, it probably is, and perhaps the tempering cycle is in question. Your second set of results sound much more like what I encountered with 52100. And of course, some great makers swear by it.

[Samurai Stu]

I have also forged and used 52100. It is an amazing steel and when heat treated correctly can out perform most other steels. I'm sure most of you know but ed Fowler is the master of 52100. I saw his DVD on the subject and he get over a thousand cuts and can perform a 180deg flex 18 times. Google him and his method. There is a wealth of info out there.

[FGYT]

oooo h will read later im jsut going over to 52100 steel and am playing with HT including bainite

[Englishrose222]

Interesting, total dedication

[jdm61]

Kevin Cashen played around a bit with some 52100 recently. He austenized it in high temp salts at 1475F which is still below the saturation point and quenched in 11-13 second oil. He said that he was able to get the very fine grain, nice little carbides and an as quenched hardness as high as 67RC!!! He also said that 52100 is actually one of the carbon steels that you can play around with quite a bit as opposed to others like L6 or A2 where you basically get the toughness, etc that the chemistry of the steel will give you. Of course, the well known caveat is the 52100 is NOT an "easy" or "beginner" steel. It can be a tad finicky if you don't treat it right.