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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Dive Knives - Titanium vs. Stainless Steel
I am after recommendations on which way to go regarding the purchase of a dive knife. Tossing up between Titanium or SS (variants various) I have come across Underwater Kinetics "Hydralloy" SS. They state it is a combination of 420 and 316 giving the strength of 420 but the corrosion resistance of 316, to what degree I don't know.
Cost is one factor but not that bad.
Is Titanium's tensile strength greater than SS and can therefore put up with more use as a lever, or is it the other way around?
Edge holding is another consideration.
- Rockingham, Western Australia
2003
Geoff,
I can't imagine anyone outside of a fantasy gamer or a yuppie with more cash than sense wanting a knife made of titanium :-)
The most common grade, 6% Al- 4 V- balance Ti, a.k.a. 6-4, or Grade 5, won't hold an edge, even in the highest strength heat treatment. Even the beta titanium alloys, the highest strength ones, will only get to mid 40's on the Rockwell C hardness scale. Compare that to 420 which easily makes it to 50+ HRC, or 440C at 60+. I did a quick search of "titanium knives" on Google and most of the offerings were stainless steel coated with PVD titanium nitride (a worthy combination) or a titanium carbide powder metallurgy product (also reasonable). But straight titanium alloy? Wrong material for the job.
Regarding strength, titanium alloys will be between 316 and heat treated 420. I'm unfamiliar with Hydralloy, though I can think of several stainless grades that might fill those claims, so they're likely reasonable.
Lee Gearhart
metallurgist - E. Aurora, New York
2003
I've read letter number 22859 wherein an individual ask about a titanium knife and Mr. Lee Gearhart responds and says not right material for the job. Wrong, along with some of the other things stated in his answer letter. Mr. Gearhart I'm neither a fantasy gamer or a yuppie with more money than sense. By pointed headed academic croissant munching internationalist New York elites I'm what ya'll would deem a redneck. In truth I'm just an individual that enjoys hunting and fishing in south Louisiana which means high humidity and salt water marshes.
I also like owning and using the highest quality tools I can purchase. I recently purchased a Mission MPF, folding knife constructed entirely out of Beta C titanium heat treated and is rockwell tested to 45-47. No longer do I have worry about leaving a knife on the boat or on the pier and overnight have to worry about it starting to rust or just having a knife starting to rust over a relatively short period of time to the excessive humidity we live/work/play in constantly.
While this knife doesn't hold an edge as well as a knife with a steel blade, it is by far and away the most superior knife on the planet and in all other categories of testing would run gigantic circles around any steel knife placed in competition against it. Put it away wet either fresh or salt water, bloody, etc, it doesn't matter its impervious to the elements, which cannot be said of steel even of the new "super" steels such as ATS 34, CPMS30V, etc and coatings just chip or eventually fail. Furthermore, beta c titanium can be heat treated in excess of 45-47 rockwell, I recently ran across a small remaining batch of beta c ti that was 55 rockwell c and was left over from a military project. It was a 50 - 60 lb lot of the material left over from one 50,000 lb run. They haven't made another batch due to cost and other economic issues, but it can and has been done. I'm sure given the current commodity situation coupled with the requirements of globalization and advancing technologies that another run of this high rockwell beta c will be made again in the near term future. Anyway enough of trying to educate the "expert", hell why I am even asking you a question. I'll get my info somewhere else.
- Lafayette, Louisiana
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Ed. note: Sorry, that you found Lee's posting offensive, Michael! If you like your knife and it's vital to you, that's great! To be clear, Lee never claimed to be "the expert", but some of us appreciate his warning that titanium folding knives can cost $395+ and still not hold an edge, as you've agreed.
People have personalities, and when someone answers hundreds upon hundreds of questions as Lee has so generously done for so many years, that kind of thing will happen every once in a while. Please work to keep your postings polite! Unlike countless public forums ruined by flaming, this site has survived 18 years and 59,000 threads ... and we credit it largely to so many great readers who bite their tongue, count to ten, and work very hard to be civil.
I'm still trying to get a simple explanation about the abilities of the various materials. Both men deserve credit for writing in and attempting to educate the rest of us. Both struck me as standing a chance of being mislabeled as arrogant, dogmatic, or needlessly rude. And worse yet neither simply said this is best for this and that is best for that. Price is an individual decision. If either of you or anyone else would like to help with a less Cerebral materials evaluation than the original explanations I would appreciate it. Make it simple, as you type; assume I know nothing about anything. If the truth be known your assumption will not be far from the truth until I ingest your input. Thanks.
Mike Powerstinkerer - Mount Dora, Florida
2007
January 9, 2008
Hi Guys,
I caught this link searching for other Ti data.
Not sure if available, but with the correct heat treatment and surface engineering, a Ti dive knife sounds an excellent, though somewhat expensive proposition.
With the correct spec of ti and the correct heat treatment, even without shotpeening, a ti knife would be totally corrosion free, and, just like a spring, be difficult to break as a lever.
(Repeated spring cycles would require shotpeening, which would be damaged by resharpening - however, in my experience, should be fine even without shotpeening and with receiving inexact HT temps / times to well over 5,000 flex cycles)
As for holding an edge, what do you want to cut?
Rope, wood, etc no problems.
I certainly wouldn't envisage any issues in self defense against a sea animal.
As for cutting against metals etc, I would probably opt for steel / coated steel, but any edge will dull quickly if used / abused.
Some people sharpen knives after every use anyway, and this is probably the answer - buy a titanium knife and just keep it sharp.
(Diamond whetstones usually give an excellent edge with only a few strokes, and are extremely easy to carry - small and flat - maybe carry it with the knife)
Hope this helps,
Thanks, Andy
- Belfast, Northern Ireland
November 25, 2008
A good option to consider are the knifes produced by Emerson in the USA. These blades are titanium and are between C57 and C59 on the Rockwell scale.
I have found that the best angle for sharpening is a 25 degree angle, This way you hold an edge longer and it will shave the hairs off your arm.
Titanium should also offer you virtually complete resistance to corrosion and is practically impossible to break.
- South Africa
Thanks, Andrew. I went to emersonknives.com. Although the blade is made of titanium, Emerson says it "is not hard like knife steel and will not hold an edge", so "We then bond a layer of tantalum carbide micro- crystals onto the backside of the cutting edge. These crystals are ultra hard and sharp, acting as thousands of tiny saw teeth along the edge."
My understanding is that titanium is strong, light, flexible, and corrosion resistant, but it won't hold a sharp edge as well as steel. Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 25, 2008
Lee is right though. The cost of a Ti knife is high. Stainless holds an edge better and a knife needs to stay sharp as long as possible. I have been using a Buck Nemo since 1968. It resists rust but any that forms on the surface of the blade is easily removed with polishing compound.
Dean Carpenter- Woodstock, Georgia
January 11, 2009
Mr. Lee Gearhart, two things; there seems to be two flaws in your argument about titanium and its alloys not being suitable for sword making.First, although it is true that titanium alloys cannot be heat treated to a hardness level that of steel for swordmaking, unless I am wrong, a nitride coating-Ti,N on both,titanium and it's alloys would increase the level of hardness high enough that the difference would be made up since Ti. nitride has a hardness of 85 on the Rockwell C hardness scale. Second, in another source I read, part of it said that there is a balance between toughness and hardness, and that a Rockwell C rating of mid 30ties to 40ties would be sufficient.
Rex Darling- Marina del Rey California
March 23, 2009
Just my honest opinion to this, no degree to back up my statements but if you research it you'll also see what I've found for myself...
don't buy steel nor titanium if your looking for a dive knife that will not corrode nor hardly ever if ever dull. the knife you are searching for is in my mind no comparison a ceramic knife. you won't find a knife stronger nor more versatile than ceramic. In fact the U.S. Navy Seals use these for the reasons alone. If they're good enough for our armed forces, I'm definitely impressed at throwing my money that way. it's a little more expensive but easily found under a hundred dollars depending on what style your looking for.
- Marion, Ohio
May 25, 2009
May 9, 2010
1.Cheap stainless gets blunt and rusts I have some.
2.440c is a little better but still gets blunt.i believe it was tempered. surface was electro treated grey in color.
3.ceramic knife I bought, had to use diamond sharpener but still gets blunt even faster than 440c
4. the best blade so far for me is a AUS-8 cryogenic tempered and was made in china folding knife, if only I could get 8 inches of this. It rusts but its OK
5. will buy titanium full tang blade in future
people sacrifice cutting edge for anti rust properties too easily.
You could electroplate a high carbon blade with silver if you like but a good cutting edge is by far my preference
But still want to buy 1 titanium from mission-knife just to see for myself
if anyone knows where to buy AUS-8 billets please post
Such pleasures are unavailable in south Africa
- cape town, western province, south africa
I have had many SS dive knives and finally got tired of chasing rust before every dive excursion. I now have a Titanium knife and don't worry about rust. If I was a commercial diver I might think differently, but for a recreational diver, I feel there is are only two alternatives - a real cheap SS knife to discard after each excursion or titanium.
Louis Weiner- Huntsville, Alabama US
September 24, 2010
I've done a fair amount of materials research and testing with different alloys of steel and titanium, and the by far strongest material for its weight, as far as a knife goes, is titanium. It is extremely corrosion resistant and has a very high tensile strength. On average, titanium is stronger than most unworked steels (as steel is cold worked, such as shot peened, cold-rolled, cold-forged etc. it becomes harder due to strain hardening). However, some of the higher quality carbon steels and stainless steels (440) will hold a MUCH better edge have a higher tensile strength. So I guess the answer to your question is what do you want to use it for? If you are a scuba diver and you don't need a knife sharp enough to perform surgery, but need high corrosion resistance, titanium would be a good choice. On the other hand if you're a fan of a super sharp knife that can be easily kept sharp, go with some form of low carbon steel or a good stainless.
Hope this helped, if you want more info on different metals go to MATWEB.com.
- Tuscaloosa, Alabama USA
April 24, 2011
There are many wonderful theories here. Nice job.
From the point of view of a SCUBA dive boat captain and spearfisherman, I would like to give this practical advice. I have owned many knives (Buck, SOG, Camillus, West Marine, Myerchin, etc) and watched my crew and other divers with their knives and the only knife for me is a Spyderco H1.
Titanium dive knives will not rust, even if you NEVER wash them. However, they are not as strong as steel. I have bent my Ti dive knife in the bony head of a large amberjack. If you are not abusing your Ti knife like I do, you'll have no problems. There are plenty of Ti dive knives available and reasonably cheap. Stick with the big name brands (ScubaPro, Cressi, etc)
My favorite blade is any H1 knife from SpyderCo. They cost $55-$70. I found one in the ocean with barnacles on it and NO RUST! Amazing. They are scary sharp and strong. I've tried to make mine rust, but they just won't. They don't bend as easy, either. I did break the tip of one knife as I was using it as a pry bar. Seriously.
Dive boat captain - miami beach
July 20, 2012
Dear reviewer,
I've come across a gold colored, heavy type of knife which has black, removable tarnish and looks as if some spots of rust/pitting have occurred. This knife is a diver's knife for the navy and my guess would be bronze yet you have mentioned bronze and copper does not rust, so these would be good choices for a knife to be used under water. The metal is also non-magnetic, so what would you classify this type of metal to be?
- Marshalltown, Iowa
July 25, 2012
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