Testing blades

[Lin Rhea]

I feel like I may have gotten off subject on the other thread. It's Dana's 01 Rockwell thread.
Guys,
I feel like there is a lot of misunderstandings about the grain growth and reduction of blade steels. I think it would be good to propose a small test to show the great difference of the two and how they affect the performance of a blade. This would require a forge or torch to do this. This test would only show the visible change of the steel's structure. Yes, you can see it easily.
   What do you think? I would want input and your experience in this regard. Thanks, Lin

[OconeeDan]

Lin, I would like to see this, as there is a lot that I could learn.
A very simple test I have done with unknown saw blade steel, just for kicks, I cut out a fairly large piece, but didn't go through the trouble of grinding into a blade.
I heat treated, quenched in oil.  Then put it in a vise and whacked it with a hammer.  It easily snapped off, showing a very fine grain structure.  
I then took the remaining piece left in the vise, and tempered it in an oven, about 400F for 2 cycles.
After the temper, I put it in the vise and couldn't hurt it at all with same hammer.  Hammer bounced off like a spring, the steel didn't even take a bend.  
Very unscientific, but proved to me the effect of a temper.
Heat treat makes it hard, temper makes it tough.
Dan

[Lin Rhea]

Yes Dan, that is what I'm talking about. But, to make the steel do more, you have to make sure that the grain structure has been reduced to a very small size. This will increase the flexibility of the steel and reduce the tendency to bend. flexibility and bend are , of course, two different things. When it flexes, it will come back to it's straightness. When it reaches it's maximum flexibility, it starts to take set, creating a bent blade. Grain reduction will contribute more than anything else to the flexibilty of a blade. Greater flexibility translates into less bent or broken blades. Lin

[kbaknife]

Lin, I saw a demon on grain growth one time that was a real eye opener!
I think it was Don Fogg.
Heated up an old file, which traditionally have a large percentage of carbon. heated it waaaaaaay too hot! Almost yellow.
Now, this would not be a bad heat for forging followed with the appropriate thermal cycling and normalizing which will REDUCE grain size, but he heated it up to this temp and quenched it in water! It got hard as glass!
Then, he broke the end off on the anvil and passed it around the room.
The broken end looked like gravel!
But you would NOT know that by seeing the outside of the blade. The only way to tell is to BREAK it!
Then, he took that same file, brought it up to the next full color change ABOVE non-magnetic and let it cool to a black heat (about 950 degress) three times, and the third time cooled all the way back to room temp.
Then, he heated the file once again, but ONLY to just above non-magnetic, about 1490, and quenched it again.
Again, it was just like glass.
Broke it.
The gain was so fine, that it looked like grey cream. Perfectly smooth.
The first one would have broken in use.
The second one, correctly tempered, would have made a good knife.
Here's one I did about a month ago.
I was having some kind of issue, so I decided to see what was going on.
This was a 5160 blade fully quenched to full hard and un-tempered.
1/3 stuck in  the vise. Being fully hard and untempered, I BARELY pulled it sideways and it broked in 2 places!
That's what it is SUPPOSED to do!!
If your blades do NOT break when un-tempered, then they're NOT hard.
The other picture is what fine grain looks like - like cream.
 
 

[Lin Rhea]

The test. I saw this done first by Joe Keeslar.

Take two pieces of the same steel and shape a round taper. From about 3/8" round to nearly a point in a distance of 3-4 inches.This should give you a cone shape on the end of the piece. They should be very close to the same shape and taper, to be fair.

Have oil for quenching ready and available.

The first test piece: heat well above what you would think is the critical temperature for that steel. The tip of the taper should be bright yellow or so but not shooting sparks. Do this one time and quench and set it aside.

Second test piece: Heat the piece to slightly above what you think is critical temp for the steel and let air cool. Heat again to same or slightly lower temp/color and, again, set it aside to air cool. Heat it for a third time, this time nailing the critical temperature as close as possible. Quench.

Now, take the first test piece and lay just the very tip over the anvil edge and lightly strike down with a hammer till you can break off the tip. Wear glasses for this. I would predict that the tip will break very easily , it being quite brittle. Set it aside.

Take the second piece and do the same, but notice some things. First strike it the same as with the first test piece and if it dont break hit a little harder and even harder till it breaks.

Now take both pieces and hold them near each other and closely examine the visible grain structure of the steel where you broke it.

What do you see? If you have pictures, that would be great. Lin

[Lin Rhea]

You were posting while I was typing Karl. Exactly right. You cant see what's inside, but you can control it by reducing the grain structure by thermocycling. I would encourage anyone who has never done this to see it for themselves. Lin

[kbaknife]

Here is a piece of the file that I used for that Commerative File knife I made a few weeks ago.
I just heated it up hot - REALLY HOT to ensure grain growth - and quenched in fast oil.
Notice the difference between this one and the photos above.
This is coarse and grainy looking like the first example you gave above with the cone. It broke VERY easily!
 

[tippit]

That's exactly what Greg Neely did at the ABS Great Smokey MT Blade Symposium.  That was how the symposium started...you can bet I paid attend to what these Master Smiths did from that point on  :eek:  At the end of the symposium, I was even trying to wear the same socks & shirts they had on  

Those 3 days changed my whole concept on bladesmithing...All for the Better!  tippit

[tippit]

After going back and reading the Rockwell Hardness topic by Dana, another interesting point made by Dr James Babson on heat treating was how to tell Rockwell Hardness on a quenched blade to make sure you actually hardened it.  

By using a slightly dull file:

1) If the file skates over the edge and doesn't bite in at all--> R greater than 60

2) file skates more than cuts--> R 59-60

3) file skates & cuts the same--> R 58-59

4) file cuts well--> R less than 58

So now you know 2 things:

1) Your blade is either hard or not.

2) Your blade was at or above critical temperature at quench if it is hard.

Final point:

Getting a hard blade is easy by just heating it above critical temperature and quick cooling...But getting a hard blade with small grain structure is a matter of quenching right at or near critical temperature without over heating the steel.  This is where the file test can really help you out.  If you know you are not over heating and very close to critical, you may occasionlly NOT get the blade hard.  

So I'm very aware now of my blade not getting too hot after I've forged and ground it.  I now watch my color in a darkened shop to see shadows in the steel from that point on so I know I'm not too hot on any annealing or normalising before quench.  

Now when I quench, the file tells me that it hardened.  But because I'm at the low end on critical, the file will tell me if I was too cautious and didn't harden the blade.  Hope that makes some sense...tippit

[tippit]

2nd Final Point    

For me anyway having a proper heat treated blade is what knife making is all about.  The blade can be beautiful like all our JS & MS makers can accomplish or it can be the ugliest looking excuse for a knife...BUT if that blade has a proper heat treat, it will give you great service with holding an edge and flexibility to with stand normal abuse.

Thanks Lin & Karl for this topic...tippit

[Lin Rhea]

 Getting a hard blade is easy by just heating it above critical temperature and quick cooling...But getting a hard blade with small grain structure is a matter of quenching right at or near critical temperature without over heating the steel.

Jeff, Yes, but I have been concerned that some of the new makers who are just getting into heat treating their blades might be missing the importance of thermocycling. This is whether they are forging or grinding from saw blades. Cycling the temperature up to or slightly above critical and allowing the blade to cool in air
( I prefer three times )is what reduces the grain, making the steel much, much more suitable for blades. After all a lot of the steels that we use is spring steel. Think about what heat treat is used in actually making the spring a spring. I bet grain reduction is a big step in producing a spring. When we are making a knife from spring steel, we are making a spring of sorts, even though it's straight, that has within it two or more different levels of hardness running somewhat prallel down the blade. It's still amazing to me. Lin

[tippit]

Lin, You teach this stuff.  As in all my passions, from a young man playing tennis, to shooting a bow, and on to forging blades...If only I had started out with a series of instruction like ABS gives on bladesmithing, that learning curve could have been made into a straight line.  My hat is off to ya'll...my new Southern Aiken, SC draw    tippit

[Doug Campbell]

Great stuff guys, I've been a little concerned of some of our new guys myself but it's all part of the learning curve I guess. I used to be amazed at guys bending knives as every time I tried it I wound up with multiple pieces. My problem back then was not thermo-cycling and the subsequent grain structure. After I figured that little jewel out and differential heat treating it changed everything. I've got a blade on the bench now that has cut rope, chopped 2X4s, shaved hair and been bent 180º, 18 times so far without breaking.

One thing that helped me with over heating was keeping magnets stuck anywhere I was heating steel and constantly checking "critical" temp. I'd hate to have to get by without my pyromoters now though...  

Nice Southern drawl there Doc  

[Kevin Evans]

Great Stuff Guys!!!!      

[Montauks]

Yes, great thread, thank you.

Gene

[Lin Rhea]

From my testing I learned that the reduction of grain size adds toughness, even to the fully hardened steel.

The real benifits show up after the draw back (tempering) and the knife is complete and in hard use. This is when it shows whether or not it has guts.

Any of you guys that hav'nt already done it thinking about trying this test? Just curious. Lin

[Kevin Evans]

I am thinking about trying some of this stuff Lin,but really don't know if I should without proper instructions of what I,m looking at.
Going to school in Dec.,may just wait and learn more then.
I mostly do everything you guys talk about in these threads.Lin what can you tell me about that little black knife you have of mine?

[OconeeDan]

OK, I tried this again yesterday.  Used O1 steel, and what I think is an accurate digital controller on an oven.
Heated to 1475 for about 30 min, quenched in 125 degree trans fluid.  I did this with 2 pieces of steel for testing (not ground to blade shape, just 1/8" bar stock).
First piece, put in vise and tapped with small 8oz hammer.  It snapped easily, like glass.  Grain structure was very fine.  So small you almost can't see it.  Good.
Next piece, I tempered, two times for an hour at 400 degrees.
Put in vise and smacked with hammer.  No break.  I hit it progressively harder and it finally broke but it took a hard smack.  So it is much tougher.
BUT, is it tough enough?  Should it have not broken or did several hard smacks with hammer cause enough shock to break about anything?
No photos needed, both steels had fine grain like those that Karl posted.
Dan

[Lin Rhea]

Kevin,
       This test is simply to witness the difference that you as a maker has over the steel on the granular level. Also the profound effect this has on it's performance. It's very visible, but that's just what you can see.  
By the way, I used your knife Satuday, but have never carried it in the woods yet. It's doing great though.

Kevin and Dan,
       Be sure and test two pieces of the same steel. The only difference being your actions toward one over the other. In other words treat one the proper way as if you were treating a blade. The other, get careless, letting the heat get too high, no thermocycling to achieve good grain reduction, etc. Dan I think this point is very important or I would not harp on it. The test I've been speaking of did not include drawing one back at this point. Both pieces are fully hardened. Just to compare the grain structure of the two peices after one was properly thermocycled and the other one not properly thermocycled. Apples for apples. Then go all the way and make two test blades, one using all the proper methods, the other not.

When you see for yourself what this does you will be amazed. I encourage you to do this complete process.  Lin

[DANA HOLMAN]

I would like to say thanks to lin, karl, jeff for all the info. that they shared, for all the new guys like me.
i thought i was making some good knife's, but sounds like i have a lot to learn about knife's.
i have made about 15 knives and hope none of them fail in the field,
hope this helps the newbe's, i know it's help me.
i have a peice of 01 steel that i'm going to do a test on and will let you know i fine.
dana