flexiblity of tempered O1

bikermikearchery

bikermikearchery

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Jan 18, 2007
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I broke a test piece of O1 today. This was hardened and triple tempered at 400F With a poorboy cryo. the piece was 1/10" thick and 1.5 wide. It took a good whack with a 4lbs hammer to break it. the grain looked very fine But what surprised me was there was no bending before it broke.
When I have tried this test with 1095, and various junk yard steels the blades bent quite aways before breaking. The O1 sprung a bit on the first whack, so I hauled off and really hit it and it snapped clean. I was wondering if I have over soaked at to high of a temp? I kind of like a bit of flex in the steel.
 
Hardening from too high a temperature will cause large brittle grains.Flexibility is a function of thickness not hardness. I wonder if the 1095 was heat treated properly ??
 
Mike,
Hitting the blade with a hammer isn't going to tell you much of anything. If I hit a diamond with a hammer ( and I have ) it will break. That doesn't tell me that the diamond wasn't hard, just that it can be broken.

The test for toughness and flexibility is to put about 1/3 of the blade in a vise. Grasp the handle/tang with leather gloved hands. SLOWLY bend the blade with even pressure. The feel of the resistance, the amount of bend, and at what point it breaks will tell you a lot about the blades geometry, HT, and that particular steels abilities.
For more flex, use spring steels, like 1095, 1084, and 5160.
Stacy
 
Thanks all for the reply. Still have much to consider on this.

mete, Thats why I'm doing this test. I have made many fillet knives out of old saw blades and 1/16" 1095 and they were great. I started using only new steel and made some fillet knives out of 1/6" O1 and they are very stiff. Edge holding seams to be the same but stiff.


Stacy, It was a very small test piece. I tried using a crescent wrench to bend it and pulled the screws out of my work bench. :)

My experience has been that a well tempered piece of steel will flex to a certain point and return. Flex past that point and take a set, and slightly past that point it will fail.

The piece I tested seamed to be sturdy but stiff. For a country-boys analogy on grain size coarse looks like gravel and broken glass, med looks like granulated sugar, and fine looks like sifted flower. The test piece looked like sifted flower. A small fine grain. I was not unhappy with the grain. I was just surprised at the crispness of the failure.

I made a lot of knives "farmer stile" over the years and never had any problems:rolleyes: Then I got an injury that put me house bound for a year so I started learning and have had nothing but problems sense then:grumpy:

Thanks for the help, Mike
 
Mike, it may have been a bit on the hard side and thus have reduced toughness compared to lower hardnesses. The tempering chart I've got on hand from an old Heat Treaters Guide has a 400F temper for O-1 yielding a HRc@62-63.
Not saying that source is the final word. Newer charts may reflect different values.
 
fitzo said:
Mike, it may have been a bit on the hard side and thus have reduced toughness compared to lower hardnesses. The tempering chart I've got on hand from an old Heat Treaters Guide has a 400F temper for O-1 yielding a HRc@62-63.
Not saying that source is the final word. Newer charts may reflect different values.
Click to expand...

i had seen it being lower RC at that temper (i think the chart i saw was expecting 2 1 or 2 hour soaks and cools)but the first blade i made i snapped pretty easily after i tempered it and the second one i think did feel kind of brittle

-matt
 
fitzo said:
Mike, it may have been a bit on the hard side and thus have reduced toughness compared to lower hardnesses. The tempering chart I've got on hand from an old Heat Treaters Guide has a 400F temper for O-1 yielding a HRc@62-63.
Not saying that source is the final word. Newer charts may reflect different values.
Click to expand...

The raper on the steel has 400f for 1 hr yielding a RWC of 58 to 60. But you have given me a thought that my thermometer may be wrong.

Thanks Mike
 
FYI.

If memory serves me (and it seldom does) O1 has an embrittlement tempering range that should be avoided. I'm thinking around 500-700.

Edit to add:

It appears it is 400-500, 62-59 HRC

That sucks....
 
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The bad news is that the TME range of O1 is around 400F-500F making it almost unavoidable for knives, the good news is that instead of a dip in impact toughness there is only a plateu, or leveled off flat line in toughess gain.

We are really discussing several properties here that bladesmiths often have a hard time seperating and coming to grips with. Hitting with a hammer has nothing to do with flexibility (as mete pointed out neither does heat treatment). Ductility and when the metal will yield a little before breaking also has nothing to do with impact toughness from being hit with a hammer. Sudden loading like this can however make a normally ductile material behave as though it were brittle. So if you are looking for a blade that will bend when pulled on too hard, the hammer test is not a fair method of getting an idea of this.

Strength is resistance to deformation, the blade that took more force to break and did it withough bending first is by definition the stronger blade. Tempering the blade back until it bends a little first only increases ductility so that is will bend quicker. I can however give you some increase in impact toughness, but at the expense of edge holding- edges like strength! But in the 21st century we have the option of using an alloy that has the same impact toughness at a much higher hardness, with heat treatment alone we must choose or compromise, but with alloying we can have our cake and eat it too:).
 
So this begs the question, does anyone have a chart/table of impact resistance versus hardness for O-1?
 
fitzo said:
So this begs the question, does anyone have a chart/table of impact resistance versus hardness for O-1?
Click to expand...

I've got one from Timken in Adobe format- I could email it to those interested but haven't got it hosted online anywhere. (And I think Timken must have took them off their page or something, 'cause I sure can't find 'em anymore.)

It's unnotched Izod, and they don't seem to show the embrittlement region, leading me to wonder how the graph was extrapolated. It just shows hardness going down at a 45 degree angle, while toughness pretty much goes up at a 45, forming a nearly perfect X. By the way, it also does show a 400 degree temper resulting in a hardness around 62 Rc.
 
fitzo said:
So this begs the question, does anyone have a chart/table of impact resistance versus hardness for O-1?
Click to expand...


o1impact.jpg
 
Thanks, Kevin. Interesting chart. I see now why a "minimum temper of 350F" is recommended in the literature. :) This suggests an excellent range of tempering choices to tailor the hardness to the intended purpose without loss of toughness.

Possum, I would indeed appreciate having that Timken data. My email is fitzo1at ameritech dot net
Thank you!
 
Thank you, mete. There's a lot of interesting stuff in that pdf.
 
The documents I'm referring to were the spec sheets for each individual steel, which I can't find back anywhere. If anyone else has stumbed across 'em, hope you'll let us know. They contained much more details than their general Metallurgy booklet. Email sent, Fitzo.
 
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