What does blade toughness really mean?

Ive
jsarche said:
I'm in the market for a new fixed blade and have been doing my due diligence on steel types but haven't been able to come up with an answer to this question: What does steel toughness mean in practical terms? I've seen lots of graphs and tables comparing the relative toughness of various types of steel, but nothing to tell me what those numbers or bar graphs really mean in the real world.

Here's an example of my confusion. Some tables and graphs I've seen say CPM 3V can be up to three or four times as tough as CPM 154, for example, depending on the heat treating. Does that mean batonning or other striking-type tasks should be avoided - or done only very lightly - with CPM 154? Does it mean I could confidently cut copper wire or other softer metals with a 3V blade? I'd love to hear about some practical translations of these toughness comparisons.

I've watched what seems like a gajillion YouTube videos showing a wide range of steel types being tested doing tasks like those and it helps, but I want a knife that will last me for many years and still be able to take anything I can throw at it.

For the record, I'm torn between a Benchmade Bushcrafter 162 and a Survive!Knives GSO 4.7 -- if it's ever available again in CPM 3V. The GSO is available right now in CPM 154, but those relative toughness charts have kind of turned me off of CPM 154. I don't worry about corrosion resistance because I live in a semi-arid climate and take good care of my gear. I would expect to be doing some general bushcraft-type activities with the knife, including batonning.

I tried searching this forum and others for answers to questions like this, but have had no luck, so I apologize if I'm not using the right search terms and missing a whole bunch of conversations.

Thanks for reading.
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I was on the same quest for several years, and the conclusion I have reached is that Elmax, Z-Wear, 3V, INFI, and Cruwear are among the best steels that met the requirements of what I looking for in my higher-end one tool options. My knife of choice for a general survival knife is the TRC Apocalypse in Elmax.

Unlike some others on here, I feel that corrosion resistance and edge retention should be of a higher consideration in a prolonged survival situation rather than how easily it can be sharpened. Just because a knife is harder to sharpen doesn't mean that it can't be sharpened; it just means that it may require a little more effort. Furthermore, corrosion resistance facilitates edge retention, because rust dulls blades. I've owned several quality high carbon blades such as the Essee-5, the BK-2, the Mora Garberg carbon, and others. All of them have been in the field with me and put through the motions. I've had oiled 1095 break out in rust that covered nearly the entire blade from one night of sitting in the open atop my pack. To me, that is problematic because it means your edge is constantly dulling and alot of energy goes into field maintenance from constantly sharpening and Cleaning.

From all of my experience with knives in the field and from having owned many, I can recommend the following knives as knives that meet the standard of being life-long, tough, reliable, and performance effective in accordance with what you seek:

TRC Apocalypse
Miller Brothers M-8
Benchmade Bushcrafter
Bark River Bravo 1
Fallkniven A1 Pro or A1x
Winkler Field Knife
 
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IDK, for me, toughness means forgivable.

Can I use and abuse the knife without it failing (obviously) and with it being relatively easily restored to where it was before I used and abused it. In that regard, a steel that is readily re-sharpened, not prone to chipping and malleable enough to not catastrophically fail is "tough."

Though so called Super Steels may hold and edge loner (and be harder to sharpen) and be more corrosion resistant, for me, in my definition of "tough" I think of relatively think stock 1095 with some added Chromium and Vanadium; IOW, the Becker BK2.

Just my two cents.
 
Material toughness is a measure of resistance to fracture.

Resistance to fracture is also a function of geometry and loading, so knowing the toughness of the material will only get you so far.

Impact test data is useful when comparing knives that have similar geometry and will be loaded in the same way, but use different steels.
 
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jsarche said:
I'm in the market for a new fixed blade and have been doing my due diligence on steel types but haven't been able to come up with an answer to this question: What does steel toughness mean in practical terms? I've seen lots of graphs and tables comparing the relative toughness of various types of steel, but nothing to tell me what those numbers or bar graphs really mean in the real world.

Here's an example of my confusion. Some tables and graphs I've seen say CPM 3V can be up to three or four times as tough as CPM 154, for example, depending on the heat treating. Does that mean batonning or other striking-type tasks should be avoided - or done only very lightly - with CPM 154? Does it mean I could confidently cut copper wire or other softer metals with a 3V blade? I'd love to hear about some practical translations of these toughness comparisons.

I've watched what seems like a gajillion YouTube videos showing a wide range of steel types being tested doing tasks like those and it helps, but I want a knife that will last me for many years and still be able to take anything I can throw at it.

For the record, I'm torn between a Benchmade Bushcrafter 162 and a Survive!Knives GSO 4.7 -- if it's ever available again in CPM 3V. The GSO is available right now in CPM 154, but those relative toughness charts have kind of turned me off of CPM 154. I don't worry about corrosion resistance because I live in a semi-arid climate and take good care of my gear. I would expect to be doing some general bushcraft-type activities with the knife, including batonning.

I tried searching this forum and others for answers to questions like this, but have had no luck, so I apologize if I'm not using the right search terms and missing a whole bunch of conversations.

Thanks for reading.
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Basically, it means that if you have 2 blades that are similar in geometry, the tougher steel can take more punishment before failing (Blades snapping, chipping, shattering, edge rolling, etc).

In general, you shouldn't abuse stainless steels because the chromium in them, makes the steel more brittle. That is price for corrosion resistance in the older stainless steels.

Here's a guy that actually had some experience with Survive!Knives GSO 4.7 in 3V and 154. He likes the 154 CPM blade better than the 3V.

After using 3V, 20CV, and CPM-154....Also handles, Micro Textured and Not

I thought it might be helpful to share my experience with Survive!'s current steels and handle materials: Survive!'s 20CV has been impressive. The edge holding is amazing and it's been tough enough for everything I've used it for. It is very difficult to sharpen if allowed to dull too much...
www.bladeforums.com www.bladeforums.com
 
Cobalt said:
Toughness becomes more important with size. On a smaller knife, toughness is not as critical. How much batoning can you do with a 4.5" blade? not much. Same goes for chopping. So either steel will work in that case.

But to answer your question. Toughness measured is for a square steel sample with either a c-notch or a v-notch cut into it. A hammer looking arm hits the sample causing fracture. The force of that fracture is measured and that gives the steels resistance to the fracture or toughness. There are many ways to overcome lack of toughness. Blade, geometry, edge geometry, lowering hardness etc. All these can make the perceived toughness very high. So 154cm isn't as tough as 3V but with the right geometry and hardness it can be tough enough for most tasks you will need it to do and it has better corrosion resistance.
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I know what toughness means but it is still hard to describe in common words. The Charpy test measures the energy that the sample absorbs during failure, steel samples absorb energy by being ductile. If the steel fractures immediately then there is very little energy absorbed. If the steel bends some amount then fractures, it absorbs more energy. I've seen samples that were ductile enough to deform to the point of coming out of the machine without fracturing. So while the test measures energy absorbed, this is roughly equivalent to ductility. A knife blade with ductility will bend without breaking, the edge would roll without chipping, that kind of thing. Another thing that is measured is the steel's notch-sensitivity meaning when will it fracture if there are stress concentrations in the sample. So take a steel of medium strength but it has low notch sensitivity- you stress the blade and the blade bends, or it reaches the theoretical strength of the steel and fractures. Now take a strong steel with high notch sensitivity- you stress the blade and it may fail at the point where the blade necks down for the guard, or it may fail at one of the handle rivets, and fail at a stress that is far lower than the theoretical strength of the steel. So if you are going to beat on a knife you want a steel with good toughness. Blades always involve a tradeoff- usually the combination of steel chemistry and heat treat will dictate the point that separates hardness and toughness. Change chemistry and heat treat and you move this point one way or the other. Refine the chemistry and heat treat, i.e. make a super steel, and you can raise one side of the performance without lowering the other, but there will still be a tradeoff. So you have to define how the blade will be used and what characteristics are important, then pick a steel to match. Now beyond all of this, you can also change the geometry of the blade to improve its slicing ability or its toughness so pay attention to that too.
 
Well, I dunno. 3V is great stuff although I haven't (yet) used my Benchmade Puukko 200 to hammer through the shinbone of a mastodon. But I think my Kabar Mark 1 might do just as well (1095 cro van/Carbon V). In the real word, most of today's super steels and even conventional steels are plenty tough.
 
jsarche said:
Thank you all for your input. How about if I phrase it a little differently: are there certain tasks you just wouldn't tackle with certain steels? For example, would you avoid batonning or chopping with a particular steel, all other things like geometry and heat treatment being equal?
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Any increase in hardness ,alloy content, or carbide size will reduce toughness.
Toughness being the ability for the material to deform, flex or dent, without chipping or cracking.
Very broadly, most steels with more than .6 to .8 carbon content will continue to increase hardness at the expense of toughness.
Very broadly again, anything with enough chromium ,12% or so,to be stainless will not like to bend, these steels usually fracture before taking a permanent deformation, at rockwells above the low fifties.
 
A have heard stories about the old Ka Bar knives that were given in WW2 and Korean war to marines. Opening crates, digging, etc. What steel were they made from and what steel today?
 
jsarche said:
Thank you all for your input. How about if I phrase it a little differently: are there certain tasks you just wouldn't tackle with certain steels? For example, would you avoid batonning or chopping with a particular steel, all other things like geometry and heat treatment being equal?
Click to expand...
Don’t confuse steel chemistry with performance. While some steels can help performance, it is really a combination of all of the factors that go into the design of the knife. One of my local makers the late Tom Enos, specialized in making knives out of 440C. It was a material he first learned about when he was a young engineer working on the Apollo Saturn V engines. He made all kinds of choppers out of the stuff and they worked well, but his knives were designed to take advantage of that material. Lots of other makers have learned to optimize other steel type. So it is not so much the steel, but the makers ability to get the most out of it, that will determine the result.

n2s
 
Guy K. Seiferd started SurviveKnives back in Gettysburg , PA. He demonstrated the toughness of his 3V 1/8" thick blades by driving a knife into a tree with a sledge-hammer and standing on the horizontal knife and bouncing on it. He drove it into another tree trunk (vertical blade) ,next to a steep drop-off, put a rope on the handle, and lowered himself down a cliff 20 feet or so. Also used the 5-lb sledge on live, thick tree limbs...4" DIAM limbs to hack them off the tree with his knives. AFAIK, his blades were 1/8" thick and always 3v back when nobody heard of 3V. These were great videos.
I know the company now has a bad rep, but I've always loved his knives.
 
jbmonkey said:
5 year old thread....but best part of it being brought back to life was seeing Matt brought back. sure miss him. thanks for that part......
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Yeah! I started reading, but didn't take notice of the dates until In saw the post from Charlie Mike.:)
 
I'm no blade steel expert but, from what I've read, blade "toughness" is a measure of how "durable" the blade is.

That is, how difficult it is to chip, break or fracture the blade and, also from what I've read, there is an inverse relationship between toughness and the degree of edge retention & ease of sharpening (both of which are indicators of "hardness)."

Toughness, ease of sharpening and edge retention are 3 out of the 4 main factors usually used to judge/compare blade steels. The 4th is corrosion resistance.

Again from what I've read, if you are looking for a knife w/a blade steel that has extreme toughness and a balance of the other characteristics, 3V or 4V seem to be the best choice at this time.

For a "balance of ALL 4 of these characteristics (probably w/more availability and at a lower price), knives using S30/S35VN would be a good choice with the nod going to Elmax or CTS-XHP if edge retention (and LC200N if corrosion resistance) is of greater importance.

Here's a link to a useful (to me) comparison of the differences between major steel types prepared by BHQ: Best Knife Steel Guide.

For a more technical approach that analyzes many more steel types, you should also consider the info posted by @Larsen on the Knife Steel Nerds Blog regarding his "Testing of the Edge Retention of 48 Knife Steels" here and the related BF thread here.
 
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