O1 hardened below 50HRC, possible?

H

Heli00

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Oct 19, 2017
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Hi,


I’m working on a throwing knife prototype, but only had O1 on hand in the thickness I wanted, 1/4”.

So I finished shape grinding it and now to HT. Planning to soak it at 1475F for about 15-20 min, then quench in canola oil heated at 130F.

Please correct if you see anything wrong with the HT regiment above.

I would like to achieve about 50 HRC after the temper, or even a bit lower, BUT everywhere I looked, it is mentioned that tempering temperature is up to 400F.

My question please, can I go with a higher temp in tempering, in order to achieve a lower final HRC?

I do plan later on on using 5160 instead of O1.

Thanks in advance,
Constantin
 
Here's the tempering chart from Alpha Knife Supply. You will need to temper up around 700F.
k5wTM6c.png
 
It probably won't hurt to start at 500°F, but for what you want two 700°F tempers would have been better.
I don't think TME will be an issue with O-1 and 700°.
 
TME= Tempered Martensite Embrittlement for those not in the know.
 
A.McPherson said:
TME= Tempered Martensite Embrittlement for those not in the know.
Click to expand...
Just to make sure I understand, the more time spent on tempering, leads to more embrittlement?

So getting to the target hardness in the minimum time, is the most desirable, correct?

Thanks again,
 
Heli00 said:
Just to make sure I understand, the more time spent on tempering, leads to more embrittlement?
Click to expand...
No, it's a temperature range where tempering results in both lower hardness and toughness. Toughness will continue to increase once you pass through that range.
Here is a chart stolen from Larrin Thomas (https://knifesteelnerds.com/2018/04/23/what-happens-during-tempering-of-steel/). Lower force (y axis) is more brittle
L6-steel-toughness.jpg


The exact region varies depending on alloy. As Stacy said 700f would be better for what you're doing, although if it's just a prototype it's not too critical
 
As you see from the chart, O-1/L-6 will not be affected by the TME range if tempered at 700°F.

I think folks make too much of TME for knives because it sounds scarry. STD - ALS - HPV - TME ... sound like something I don't ever want!!!
Yes, there is a dip in hardness and toughness ... but it is a minor dip, not a catastrophic nose-dive. The area that has any noticeable effect is 450-525°F for O-1. The toughness drop is only a minor amount - 15%. It reverses and gains almost double the toughness by 700°F.

For knives I used these HT specs for O-1. (I haven't used it in a while, though.)
Austenitize at 1475°F for 15 minutes
Quench in 130°F medium speed oil (AAA).
Temper IMEDIATELY at 400°F for one hour ... twice.
 
Stacy E. Apelt - Bladesmith said:
As you see from the chart, O-1/L-6 will not be affected by the TME range if tempered at 700°F.

I think folks make too much of TME for knives because it sounds scarry. STD - ALS - HPV - TME ... sound like something I don't ever want!!!
Yes, there is a dip in hardness and toughness ... but it is a minor dip, not a catastrophic nose-dive. The area that has any noticeable effect is 450-525°F for O-1. The toughness drop is only a minor amount - 15%. It reverses and gains almost double the toughness by 700°F.

For knives I used these HT specs for O-1. (I haven't used it in a while, though.)
Austenitize at 1475°F for 15 minutes
Quench in 130°F medium speed oil (AAA).
Temper IMEDIATELY at 400°F for one hour ... twice.
Click to expand...
lol, yeah, I wouldn’t want to catch one of these either.

So I’ve done one temper at 500F and will follow up with another at 700F. Unfortunately it was too late by the time I saw your previous response.

I’ll measure the HRC in between.

By the way, what are the negatives on toughness, that the 500F temper brings to the table. I always thought if the second temper is at a higher temp than the previous one, it will overwrite it. Are some of the changes to the steel structure that occurred at 500F, not being “erased” by the second, higher temp temper?

Thanks again,
 
The only concern would be a bit of TME from the 500° temper. It would probably all be reversed in the 700°. As I said and te chart shows, it isn't a likely concern.
 
In the first temper at 500F, I got about 57-57.5 HRC, austenized at 1475F, which shows about what expected based on the alphaknifesupply chart for O1.

Going for the second temper at 725F, hoping to get not higher than 50 HRC.
 
So, at 725F I got about 51HRC, pretty close to what I was hoping for. Keep in mind, this is on my own oven.

Thanks again to all of you,
Constantin
 
O1 with that hardness drop by tempering is not a good choice for throwing knives. They are soft and ful of secondary carbides. Bend easily, but when straightening it looses more than half of the strength. 55-57HRC would endure much longer. O1 generally is not for throwing knives. 5160 is a good choice, but also mid or upper 50'HRC. If you want lower, go for bainite.
Issue with throwing knives are vibrations. Imagine that every material has endurance in wiggling. 5160 has it like 50x more than O1. Whenever you hear the zzzing, it has wiggled a hundred times. Soft steels with a lot of carbides will break fast.
 
JoeBusic said:
O1 with that hardness drop by tempering is not a good choice for throwing knives. They are soft and ful of secondary carbides. Bend easily, but when straightening it looses more than half of the strength. 55-57HRC would endure much longer. O1 generally is not for throwing knives. 5160 is a good choice, but also mid or upper 50'HRC. If you want lower, go for bainite.
Issue with throwing knives are vibrations. Imagine that every material has endurance in wiggling. 5160 has it like 50x more than O1. Whenever you hear the zzzing, it has wiggled a hundred times. Soft steels with a lot of carbides will break fast.
Click to expand...
I agree O1 is not a good choice, it was what I had on hand in 1/4” and only used it for a prototype.
I’m going to create a new tread do discuss what steel would be a good choice and at what hardness.
I’d like to get some recommendations. Thank you.
 
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