Ask A Knifemaker: The Truth About Blade Steels

[Editor’s Note: William Woods is our resident knifemaker and author of our series “Ask A Knifemaker.”]

The Truth About Blade Steels

What is the soul of any knife? What defines a blade as a knife? Sure, boxcutters do many knife related tasks, but are they knives or simply edged tools? I would argue that the importance of any knife style and design lies in its heart and soul. The steel.

Hello, my name is William Woods and I am a knife maker . . .

Since The Truth About Knives is just taking its first steps this week, Chris Dumm and I thought we would start things off properly and start a discussion about blade steel. Now enough of the introductions: let’s talk blades!

The single most asked question is always, “What is the best steel for a knife?” Well, like all simple questions the answer is far from direct and concise. Choosing the steel that fits your needs is kind of like picking a car. Can you tow a horse trailer with a Porsche? Sure. Will it perform terribly and eventually fail? Yes, yes it will. The most common complaint that leads many to bad-mouth a certain alloy of steel is to try and force one type of knife to perform tasks it is ill suited to.

Three things determine the “performance” of any cutting blade. Blade geometry (the style and shape of a knife), alloy (the particular mix of steel), and the heat treatment (the process used to harden the alloy). In this article we will be discussing steel alloys and their performance characteristics.

Corrosion

OK, so the big first distinction most people are familiar with are “stainless” and “carbon” steel. These are slight misnomers, considering that stainless steel is only stain “resistant” and ALL steel has carbon in it. [Ed: if it didn’t, it wouldn’t be steel.] Semantics aside, it is generally accepted that to be considered “stainless” a steel alloy must contain 13% chromium. Now here is where it gets complicated. There are hundreds of steel alloys that are suitable for making knife blades and the individual composition of those alloys mean they can contain anywhere from 0% to 25% chromium. Great, let’s add a bunch of chromium and make the most super-duper stainless blade ever! Right? Hold on: unfortunately metallurgy is insanely complex, and the more chromium you add the worse the steel gets at important things like staying sharp and cutting things.

The point is that blade steel metallurgy is a delicate balancing act. Every alloy is made to balance corrosion resistance, edge holding, machining, wear resistance, and toughness. There is no magical unicorn horn steel that can live in salt water, slice paper all day, and cut down trees in its down time. It doesn’t exist.

Since we are talking about corrosion, let’s say you asked me for recommendations of corrosion resistant steels. I would say the most popular and highest performing stainless steels on the market today are 440C, CPM-S30V, 154-CM, 12C27, AUS-8. In no particular order these stainless steels offer superior stain fighting powers and will hold an edge if properly maintained.

Toughness

So we have covered what puts the “stainless”  in stainless steel. Let’s talk toughness. Toughness is a very particular metric. Specifically it means the ability of a material to absorb energy and plastically deform without fracturing. Knives that break are blades that have been pushed beyond the limit of that alloy’s (and heat treatment) capability. Many many elements contribute to the toughness of an alloy but commonly manganese, molybdenum, nickel, and silicon are used to control the hardness/toughness of an alloy. Toughness is typically a one way street. The tougher the steel the worse is holds an edge and vice versa.

Typically really tough knives made for extreme tasks like chopping, prying, and hammering are made with equally suited alloys. Some are very simple like the good ol KA-BAR. KA-BAR’s are made with 1095 steel which is essentially iron, .95% carbon, and .4% manganese. Tough, holds an edge, re-sharpens easily. All the things you want in a combat/survival blade. Like all things though technology has advanced the metallurgy field and more companies are releasing “super steels” with complex compositions and precise heat treating specs.

The king of the hill these days for tough steel alloys is probably CPM-3V. It’s expensive, semi-stainless (only 7.5% chromium), and practically bomb proof. I’ve personally cut dozens of card board boxes and then chopped down a 8” tree trunk into kindling and still been able to shave my arm. Amazing stuff, but leave it in a hunting bag in the back of a truck for a few hot and humid Georgia summer days and hello pitted rust! It is just not designed to resist moisture without constant oiling and maintenance.

So for the tough alloys we have discussed 1095 and CPM-3V. Is that it? Hell no! 5160, D2, INFI, SR-101, and CPM-S35VN are all great tough steels. Each alloy has its place and usefulness. They all have great toughness but many have varying degrees of wear resistance with brings us to…

Edge Holding

Here is the most subjective part of any blade steel. Wear resistance or edge holding is difficult to measure as a metric. Most end users measure the time it takes for a knife to go dull. This can be misleading since on a microscopic level there are at least 4 different types of edge failure but that is a different topic for a different day. The old stand by tests of slicing paper and shaving hair are reasonably good metrics for testing sharpness so let’s stick with those.

Most blade steel alloys hardness is measured on the Rockwell C scale (from now on referred to as the RC). Most knives will register anywhere from 54-65 RC depending on alloy and heat treatment. Wear resistance refers to a blade’s edge holding capabilities. Some alloys can support finer thinner edges and will cut more easily. Some alloys take a “toothy” edge and consequently have nano-serrations that make excellent slicers but are poor for push cutting. So what chemically is making these alloys so hard? Well principally adding carbon increases wear resistance but vanadium and tungsten are commonly added to boost wear resistance. The basic principle is the formation of carbides during the heat treatment process to increase the hardenability.

So you can see getting a knife to be sharp and stay sharp is really a balance of the ability to take an edge and the strength to hold it. This is where the industry has really gone crazy in the last 20 years. Since higher and higher RC hardness steels have always been possible the issue was toughness. There is little use for a sharp brittle knife. Kershaw, Spyderco, and Benchmade have all been selling these super steels that boast never ending sharpness. ZDP-189, CPM-M4, S110V, and the current champ REX 121 (with an insane RC of 72) are all extremely hard steels that will outlast a more pedestrian alloy by 3 or 4 times before sharpening.

BUT…there always is a tradeoff. Sharpening a blade made of these exotic alloys is difficult. Quality sharpening stones are required and it is NOT for beginners. Coupled with the extra brittleness and general exotic nature makes knives made from these alloys more suited to very specific tasks. This also leads me to…

Cost

When customers are shopping for knives there usually is a limit. What’s the best knife for under $25/50/100/500? Well the moment you step outside the boundaries of “standard” industry steel and start shopping for more performance oriented alloys the prices start to rise. As a knife maker when I buy steel in bulk I pay by the pound. By weight a more common “mid range” stainless steel like 440C will cost 3-4X less than a more exotic alloy like CPM S30V. Add in the extra costs associated with machining, grinding, and heat treating exotic steels and you have a much more expensive knife.

It all comes down to perceived value. Is it worth it to you? Do you need a Spyderco Endura 4 with a ZDP-189 blade for $170 or would the VG-10 version for $100 be more than enough? These are questions every collector or enthusiast must make for themselves. I can say definitively though that when you have a knife you truly love in a steel that performs just as well you have something special. It is an intangible feeling of having the pinnacle of what science and design are capable of doing together in one package.

There are very few areas in our lives where we can honestly attain the absolute “best”. I will never be able to afford a Ferrari. I will never own an island or date a super model, or even own the finest 1911 man could want. But I can for $7-800 own one of the planet’s best knives, an elite group of people. That is the attraction of exotic super steels.

Country Of Origin

Now for every “What is the best _?” question comes “Hey check out my knife! I got it on Ebay / China / Pakistan / truck stop / flea market!” This is the moment when your unknowledgeable friend will attempt to impress you with their newly acquired stabbing implement. Hey, we were all 11 years old once so try and let them down easily.

Unfortunately, cheap and downright dangerous knock-off knives have been flooding the market for decades. The majority of which are made in China, Pakistan, or Indonesia. Now I will not say that a cheap import knife can’t cut well. I have been surprised 2 or 3 times in my life by a cheap Chinese knife. I have also been wildly unimpressed by HUNDREDS of crappy import knives. Many of these designs are so alluring because they 100% rip off designs from actual makers and manufacturers. (Anybody who collects Extrema Ratio or Rick Hinderer knives feels my pain) In many cases there are more fakes floating around than actual original knives, leading to some serious confusion.

“China pot steel” and “Pakistani car bumper” knives are also quite dangerous. Folding knife locks fail, blades snap, and they go dull faster than a knife fight in a phone booth. Honestly good knives can be had starting at $20. There is no reason to start diving in the “Bucket O’ Knives” at your local gas station.

Conclusion

We started this discussion by examining the question, “What is the best steel for a knife?” As you can see that is quite the loaded question. The only way to answer it is to ask some questions. What performance do you want from the knife? Will this knife be exposed to moisture? Will you be performing hard use tasks with the knife? What is your budget? These are some of the relevant questions that must be answered before a responsible answer can be made.

Well thanks for listening to me ramble on about steel. I hope you learned something or at the least weren’t terribly bored. I hope to post more of these articles in the future. If you want more please let us know in the comments. I will do my best to answer any questions you have in the comments as well.

This entry was posted in Ask A Knifemaker and tagged , . Bookmark the permalink.

42 Responses to Ask A Knifemaker: The Truth About Blade Steels

  1. H. Clay Aalders says:

    Thanks William. I am a noob on the metallurgy front. I am looking forward to learning from someone who makes a living in the field.

    • Well I don’t know about “Master”. We are all constantly learning and there are always more knowledgeable and experienced makers out there. I am glad I have been able to learn from my mentors and pass on what little knowledge I have retained over the years.

  2. Matt in FL says:

    Thanks for the post. I learned enough to have some idea of what I don’t know.

  3. Kaliope says:

    Fantastic post, I really enjoyed it. I think I’ve found another site to visit constantly.

  4. Adam says:

    So what is your opinion of the San Mai 3 blades? I know nothing about blades.

    • San Mai steel is three layers forge welded together. Usually the outer two layers are a stainless softer steel and the inner layer is a harder tool steel. San Mai is fantastic when made properly. You really get the best of both worlds. Unfortunately it’s wicked expensive.

  5. SubZ says:

    Very nice write up. I worked as a heat treater in my youth (25+years ago). At that time, we had about 30-4″ binders with alloy specs, can only imagine it would be double that today.

    Current edc uses 8Cr14MoV. I know it’s a Chinese steel, but been very impressed so far. Did I just get a “good one”?

    • 8CR14MOV is a Chinese steel comparable to Japanese AUS8. By all accounts its a good “value” steel. My best guess is that you would have to move up to a CPM-154CM alloy before you noticed any difference in edge holding or corrosion resistance. 8CR14MOV is a good “bang for your buck.”

  6. Nate says:

    Good article. I often find that VG-10 is everything I want in a steel. Good corrosion resistance, gets really sharp, keeps an edge well (going on 3 weeks without sharpening), and fairly cheap.

    • Jeff S. says:

      Yeah VG-10 is a great steel. I almost feel like it’s hard to screw up sharpening VG-10. It takes a mirror polish very fast and stays sharp for a quite a while.

      But lately I’ve been keeping my Spyderco Paramilitary 2 on me. The CPM-S30V does stand up a lot longer. I’ve gone months without sharpening it and it’s still really sharp. Now I don’t put it through a lot of hard use but cutting through plastic packaging and cardboard does take it’s toll on an edge. This blade keeps on cutting though.

  7. dave says:

    Great article Will, very informative for someone who only has the barest clue in metallurgy. I have a question though, is there any way I can verify a blade’s steel short of taking it to a spectrometer? I bought a handmade fixed blade knife from a gun showe months ago, and its pretty well put together. The thing is, the guy who sold it to me (I will presume he was the maker, he spoke like he was) said it was made from D2 tool steel. So far I can tell that it is certainly harder and retains an edge better (and is a bit harder to sharpen) than my 440C and 440A knives (haven’t compared it to my 1095 nives). Any way I can verify this is actually D2? I mean I love the knife, but it would be nice to know for sure.

    • Unfortunately it is quite difficult to authenticate different alloys of steel especially if they are similar in chromium content. D2 is classified as a semi-stainless because of its 11.5% chromium content. Theoretically your 440C blades with 17% should be more corrosion resistant BUT in the real world the quality of finish can determine resistance. A perfect mirror polished D2 MAY out perform a bead blasted satin 440C knife. Either way D2 will be significantly harder and hold an edge longer.

  8. dave says:

    Also, just out of curiosity, would you care to speculate as to why we haven’t been able to recreate legit Damascus steel? Also, how do you think/theorize they made it back in the day? I’ve just heard some of the myths about Damascus steel and I was curious what an expert thought.

    • I purposely left all pattern welded steels out of this article for reasons of clarity. Frankly I feel I could write a book on the origins of Damascus/Wootz steel. It has been a fascination of mine for several years now. I will be sure to write up an article soon on the subject.

      • dave says:

        Thnaks for the responses. Yeah, Damascus steel is one of those fascinating lost art. Until we do know for sure though, I’ll cling to my theory of siren’s tears and dragon’s blood being used in the hardening process to create the carbon nanotubes ;) Oh and if you ever do write that book, I will be one of the first people in line to read it.

  9. janitor says:

    well broken down….

  10. Chris Dumm says:

    I’m sure that Damascus steel will get its own post here someday; its the metallurgical equivalent of ‘what was Greek fire?’ or ‘what happened to Jimmy Hoffa?’

  11. David says:

    William (do you ever go by Will?) – my thinking is that a big advantage of common types of steel over exotic ones is they are predictable in how they will handle stress and wear especially over time. The maintenance and use curves are already established and one already knows what he is getting. I think the fact that iron based alloys are almost exlusively used is due (in part) to the fact that steel is more well known in terms of how to forge, handle, maintain, etc. Working with bronze, titanium, etc. is not as well known and the tooling for it is not as readily available.

    • Sure call me Will! Even exotic alloys like REX 121 or Inconel are not typically designed for the consumer knife market from the ground up. Many are designed as tooling steels for very specific industry use. Crucible Industries for example pioneered the CPM process and the resulting alloys are so extremely thoroughly tested that there are no surprises. If properly heat treated exotic alloys will perform very consistently. Frankly because of their cost and the fact that only smaller sized runs are produced the quality control checks are higher than common cutlery steel like 420/440A/B/C.

      Most cutlery is iron/steel based because of hardness. Very very very few alloys can achieve the balance of hardness/toughness needed to make a usable knife. Titanium won’t harden enough, nickle can hold an edge, straight iron rusts, the more exotic metal elements are either too rare/expensive or extremely hazardous to our health. Ceramic is the only other widely used knife material and in my opinion waaaay to brittle for any duties outside the kitchen.

      Your right about tooling though. Machining titanium or Inconel is a religious experience. Many of the non-ferrous material work harden the moment and force or heat is applied making manufacturing expensive and time consuming.

  12. Don says:

    Nice article…as a metallurgist I enjoyed it…

  13. Joe says:

    Loved the article!! Thank you so much. I’m completely ignorant about this stuff and found the article fascinating. One of my favorite knives is a Spyderco with CPM-M4 steel so I found it especially interesting learning more about it. Again, thank you very much!

  14. Colin says:

    “I will never be able to afford a Ferrari. I will never own an island or date a super model, or even own the finest 1911 man could want. But I can for $7-800 own one of the planet’s best knives, an elite group of people.”

    Stop giving me excuses!

  15. gerald brennan says:

    Thank you. So succinct and well-written.

  16. Chaz says:

    … not designed to resist moisture without constant oiling and maintenance

    Would CLR products advertised for firearms (Froglube et al) be effective, practical on these knives?

    • CLR would works just as well as WD-40 or any other penetrating and protecting oil. I usually use Froglube to lubricate the internal parts of folders like pivots, ball detents, and roller bearings.

      • Froglube Rocks! I use it on the moving parts of my fly tying vise , my folding knives, and all of my firearms. I am hoping RF will let me do a formal review of Froglube at TTAG some day.

  17. DrewN says:

    Will, I notice on your chef’s knife pictured below you have decided on a full bolster instead of a “Cordon Bleu” style with a full length edge (which is my preference). Is this just a stylistic choice or do you find it has other advantages?

    • I can do either. In this case the customer has a certain style of chopping that had her hand choked up on the blade with the terminating edge contacting her knuckles. It was requested that the edge have a “safety zone” located there. This particular knife was also unique in the fact that it was hollow ground on very thin stock. Most of my customers request thicker stock and full flat grinds.

  18. frankgon4 says:

    Any information on EN-31 steel?

  19. R. Hemke says:

    This past Christmas I purcharsed a Emmersson “Horseman” folder for each of our boys then one for myself. When I took them into get names engraved it surprised me to learn the blades were tungston? I have since been informed to keep a edge on tungston you need a stone with diamonds embedded. I ask Emmerson if they could reccommend something but have gotten no response? So if anyone has any knowledge on this subject any and all input would be helpful?

    • J- says:

      Many of the “affordable” Emerson knives are made of 154CM. If you got the black option, the knife is coated in a 1-3 micron thick tungsten containing composite: W-DLC, Cerakote, WC PVD, etc. This is a pain to etch with an engraving tool, but the edge itself will be of the underlying stainless steel. A high quality sharpener should work just fine. DMT makes good diamond sharpening stones, but a white crock stick (Alumina) will be alright too.

  20. john says:

    Hey William nice input so 3v is stronger then zdp-189 right?

  21. Ghoul says:

    Hi Will
    thanks for your post which I find very informative
    I guess that the CPM M4 and the M390 are among the exotic alloys ? my question is when you say difficult to maintain (in terms of sharpness ) does it mean that you can’t do so with something like a Smith’s pocket sharpener?

  22. Gerald Bell says:

    What is a good place to find reasonably priced cpm metals in a variety of sizes?

  23. Jag says:

    3V steel will corrode if not cared for but will never develop “pitted” rust. Watch and believe: http://www.youtube.com/watch?v=bNo2YUe-mbQ

  24. HuckleCat says:

    William – thanks for a great article. I like how you explained the Alphabet Soup of steels – grouped by attribute and identifying the leading steels in each group.

  25. Pingback: App Review: Zvisoft Knife Steel Composition Chart | The Truth About Knives

  26. Pingback: Housekeeping/Question of the Day: How did you first find TTAK? | The Truth About Knives

  27. Paul says:

    We’ll I found this article enjoyable , as with all the YouTube video cutting tests with jdavis , price seems to be the equalizer. Keep up the great work

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>