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  #1  
Old 10-14-2012, 08:03 AM
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AUBE AUBE is offline
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An example of why testing is a good idea.

Recently I picked up some steels I've never used before, from a supplier I've never used before. After getting the heat treat info, I started some testing on them. Unfortunately I wasn't planning on posting the testing online so I didn't take pics of each step.

I did some tests with oil hardening it, air hardening, and water hardening. I had the literature on what the heat treat schedule should be, but I like to play around and try different things.

Well after doing various non destructive tests (rope cutting, wood carving, pounding the blade into wood and torquing it out sideways, etc) I started with destructive...hammering it through brass rods, followed by iron wire, followed by half hard steel.

The oil and water hardened blades performed as well as expected.

Next I clamped the blades in the vice and bent them. These blades were fairly narrow, with steep grinds, through hardened, and short blades...so they didn't fair as well as they would have if they were a bit wider, with shallower angles, differential hardening, and a longer blade to distribute the force across.

The water hardened blade bent to about 50ish degrees and snapped.

Now from this test I learned the water quench was too severe...that at least 1 microcrack had formed. I had sharpened the blades and polished it several times when testing and examined it under a magnifying glass and I could not spot the crack until it snapped.

The second thing of interest I found was this steel plate is actually a 2 part laminate. If you look at the pics you will see a line running the length of the spine...this is where the 2 layers began to come apart from a combination of water quenching and the bend test.

The oil hardened steel bent to over 90degrees before snapping, and never showed any signs of delamination, nor stress cracks.

If I hadn't done the bend test I may have come to the conclusion "the water hardened blade got slightly harder, but not brittle, and performed slightly better than the oil hardened" which was true...the edge never chipped and it did cut better...right up til the crack was found. If I had followed the ht schedule and oil hardened the blade, I wouldn't have found it was a laminate sheet.


(click the pics to open larger ones, then you can zoom in from there. The crack can be seen as the rusty colored portion of the cross section near the edge)
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Old 10-14-2012, 08:33 AM
Doug Lester Doug Lester is offline
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I couldn't agree more on the need to test the knife making process by deliberately making knives that will be tested to destruction. Without that testing we are just going by theory on how the blades will function. Considering how plate steel is produced, I question your conclusion that it bar was made from two plates laminated together. Most of it is done by continuous pour and then rolled out. My best guess is that it was a defect in the bar that caused it to crack with the harsher water quench. I had a bar of 1095 once that had a cold shut running through it where for some reason the steel evidently folded over on itself in one spot and was pressed down into the steel.

Doug


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Old 10-14-2012, 08:56 AM
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Originally Posted by Doug Lester View Post
Considering how plate steel is produced, I question your conclusion that it bar was made from two plates laminated together. Most of it is done by continuous pour and then rolled out. My best guess is that it was a defect in the bar that caused it to crack with the harsher water quench.

Doug
That is possible. I have broken 2 of the water quenched knives so far. They were cut from a 12"x12" plate I bought. Each one was from opposite sides of the plate. So if its a flaw, it would be a wide one. But then with being run through rolling mills a flaw that started thick could be stretched out pretty long.

I've run into a fair amount of inclusions but this is the first time I've had something break in a perfectly straight line like this. I was a bit surprised.

I have at least 1 more piece left from the water quench that I haven't broken yet..but that piece was cut from between the other 2 pieces so I suspect it has the same flaw. I will be breaking the oil quenched blades into small piece and seeing if they also want to crack along the same line. So far I've done 2 breaks on the oil quench, and neither seemed to...but 2 pieces is a pretty small test pool.

Next time I go to the steel place I might pick up another piece cut from a different sheet and see if it has the same flaw running the length of it.
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Old 10-14-2012, 09:00 AM
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Actually on further thought a rolling mill would lengthen the flaw, but not widen it much at all. I've never really looked into how plates are made....do they also use a hydraulic press which would widen the area as well as lengthen it? Or change directions 90 degrees between rolling it through a rolling mill?
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Old 10-14-2012, 09:03 AM
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Ray Rogers Ray Rogers is offline
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You did good there, Jason. I agree with Doug on the lamination idea though. I've had blades split lengthwise when the HT didn't match the steel's requirements. It's fairly rare, I suppose, but it happens. In one case, my blade cracked a little right away after the quench and the crack continued to grow considerably larger over the next few hours while the blade sat on my work bench ...


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Old 10-14-2012, 10:47 AM
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Originally Posted by Ray Rogers View Post
You did good there, Jason. I agree with Doug on the lamination idea though. I've had blades split lengthwise when the HT didn't match the steel's requirements. It's fairly rare, I suppose, but it happens. In one case, my blade cracked a little right away after the quench and the crack continued to grow considerably larger over the next few hours while the blade sat on my work bench ...
Thanks Ray.

What Doug said does make sense. I was a bit baffled why they would laminate 2 sheets. It didn't seem like an efficient method...but then I;ve seen other things in business that aren't the height of efficiency.

I've cracked a bunch of blades (the joys of experimenting with hamons and water quenches) but this is my first that ran lengthwise down the spine, it was an interesting experience.

I should have mentioned this is a lower carbon steel than most blades....think along the lines of 4140. Which explains the decent flex test results from a less than optimal blade shape. I'm thinking of offering some breaching axes so I'm looking for tough. The 5160 I can get locally isn't wide enough, so I'm testing some other options available locally.

I was a bit surprised by this steel actually.... with a .4% carbon level I was expecting tough but not that good in edge retention. While it didn't cut as well as something like 1095, it actually was better than I expected. It's softer than I'd prefer so I'm going to bump up the quench oil tempt a bit, and lower the tempering temp from 425 to 400 and see what happens.
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Old 10-14-2012, 10:57 AM
metal99 metal99 is offline
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Pretty interesting AUBE I did some destruction seating on some 1095 blades that I messed up the grinds. (Free hand grinding with no file guide!) the ricasso's didn't match up very well so I hardened them and destroyed them. That's when I found out the 1095 I had didn't through harden in my canola oil.

What kind of steel were you testing?
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Old 10-14-2012, 11:06 AM
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What Ray said about cracks continuing to grow over a few hours remided me of a time at work when I had a piece of A2 tool steel heat treated. I am a die maker/designer and this particular block was a die component about 2 x 6 x 10 in size. It had very little macining done to it and had no sharp corners. When it came back from ht I put it up on the auto wet surface grinder and did a min clean up top and bottom. When I finished, I noticed a couple of surface cracks. After about an hour or so there were surface cracks all over the top and bottom of the block and after a few hours the cracks got so bad that you can feel the height differeces. We had to scrap the piece and never found the exact cause. Our steel supplier gave us a new piece, we remachined the block and Ht company did the heat treat for free so we all lost. My guess without getting the steel tested is that the ht company did not temper properly. I'm just very curious. Thanks.
Anyway, I agree testing a blade you make is not only a great idea but even necessary but what is really accomplished by not using a non specified heat treating process on any given known steel. Wouldn't it b like taking A2(Air cooled) and tossing it in water to see what happens. This is just a question. I am probably thinking like a die maker and not a die maker. Is there any steels out there that benefit by wondering from recomended ht specs when making knife blades?
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Old 10-14-2012, 11:17 AM
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Originally Posted by metal99 View Post
Pretty interesting AUBE I did some destruction seating on some 1095 blades that I messed up the grinds. (Free hand grinding with no file guide!) the ricasso's didn't match up very well so I hardened them and destroyed them. That's when I found out the 1095 I had didn't through harden in my canola oil.

What kind of steel were you testing?
Thats what I usually do with my scrap blades. Its better to possibly learn a little something about them then to just toss them in the trash.

I can't recall the name of the steel offhand. It was along the lines of Xl41. I had never heard of it, nor can I find info online. The steel supplier did have the alloy composition on hand along with the ht schedule. As soon as I find my piece of paper with the info on it, or I get back to the supplier I'll let you know. Supposedly its from Singapore...but for all I know its made in China then shipped to Singapore before being shipped here. The composition was very close to 4140.
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Old 10-14-2012, 11:22 AM
Doug Lester Doug Lester is offline
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AUBE, from what I've understand from reading on the subject is that continuous pour is the most common method of forming steel plates. The molten steel is poured into a hopper that has a port in the bottom that is cooled with water. That allow the steel to come out in a continuous ribbon of molten steel within a semi-molten jacket. That is fed down onto a track of rollers that goes from almost vertical and curves to horizontal. There is also a water spray at this point to cool the steel ribbon rapidly to form austinite. The ribbon is then cut into plates with cutters that move at the same speed as the ribbon of steel to give a square cut. A this point, from an illustration in the book, it looks like the steel is several inches thick and still glowing hot. From there the plates are sent off to other sections of the factory for other cutting and rolling operations. There are other methods of production, however.

Doug


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Old 10-14-2012, 11:29 AM
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Originally Posted by Icho View Post
Anyway, I agree testing a blade you make is not only a great idea but even necessary but what is really accomplished by not using a non specified heat treating process on any given known steel. Wouldn't it b like taking A2(Air cooled) and tossing it in water to see what happens. This is just a question. I am probably thinking like a die maker and not a die maker. Is there any steels out there that benefit by wondering from recomended ht specs when making knife blades?
One problem with ht schedules is they are typically for larger cross sections than us knifemakers use. What may work on a 1" thick cross section may not work on a .030" edge, etc. Also the schedule may call for "oil quench" but at what speed? Various oils quench at different speeds..and also the temp of the oil can change things a bit.

I've used some oil quench steel that cracked in a fast oil but worked fine in a slower oil quench. I used slower oil on this steel, and I think it could benefit from a faster quench.

Being a steel I never worked before I wanted to test its limits..thus the water quench. It would be disappointing to make a few hundred pieces using the proscribed oil quench only to later find out I could have gained a bit more hardness without much in the way of negative effects by using water. In this case it didn't turn out that way, but now I know.

Mainly I just like to experiment. I was pretty darn sure the air hardening wouldn't get the results I wanted (springy, but not brittle) but it didn't (very little spring to it) but it was easy enough to cut a chunk off and try.

It cost me maybe $5 in materials and 30mins to grind the blades....I consider it a cheap learning experience...a lot less than I paid for college.
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Old 10-14-2012, 11:32 AM
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Originally Posted by Doug Lester View Post
AUBE, from what I've understand from reading on the subject is that continuous pour is the most common method of forming steel plates. The molten steel is poured into a hopper that has a port in the bottom that is cooled with water. That allow the steel to come out in a continuous ribbon of molten steel within a semi-molten jacket. That is fed down onto a track of rollers that goes from almost vertical and curves to horizontal. There is also a water spray at this point to cool the steel ribbon rapidly to form austinite. The ribbon is then cut into plates with cutters that move at the same speed as the ribbon of steel to give a square cut. A this point, from an illustration in the book, it looks like the steel is several inches thick and still glowing hot. From there the plates are sent off to other sections of the factory for other cutting and rolling operations. There are other methods of production, however.

Doug
Thanks for the explanation Doug. Sometime in the next few weeks I will pick up another piece cut from a different sheet and see if it does the same thing. Its got my curiosity up.
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Old 10-14-2012, 12:04 PM
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Hey thanks for the info. Experimenting keeps us thinking and learning which in the end I guess keeps us going at it. Some great info.
I may even check out YouTube for vids on making and rolling steel plates.
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Old 10-16-2012, 02:51 AM
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What kind of steel were you testing?
I was mistaken, the stuff in this thread was actually 4140. The other sheet is the oddball steel called "XL41" thats supposed to be from Singapore.

The alloy content is pretty much identical except the XL41 says .4-.45% carbon instead of .38-.43% listed for the 4140. I'm thinking the XL41 is just rebranded 4140.

So far they have tested about the same although the 2 pieces from XL41 didn't do that odd crack forming straight down the spine. Other than that I can't tell a difference.
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