A Goliath of Strength? Or just a Goliath?
Titanium has been known for its high strength and low density. "The strength-to-weight ratios for titanium-based alloys are superior to almost all other metals," states Reactive Alloy Manufacturing of Sweet Home, Oregon.
Is Titanium stronger than steel, then? If the word "weight" is disregarded, many may conclude that titanium is indeed stronger due to its "superior strength-to-weight" ratio. However, except where weight is an issue such as in aircraft parts, steel is in most cases still a structurally superior material. In most applications, weight is somewhat less important than other factors. In knives, you want the material to be hardenable, so that it can hold an edge and cut. If the material you choose can't be hardened, then it doesn't matter what its other properties are like. For example, like titanium, aluminum also has a better strength-to-weight ratio than steel, but you certainly don't want a knife made out of aluminum! Aluminum and titanium are simply not the right materials for the purpose.
As mentioned above, where these materials are of use are in applications where weight is paramount and other properties are less important. But forgetting this for a moment, here's an example using some average values for titanium alloys and high carbon steels: A steel when hardened to RC 60 has tensile yield strength of 1,500 units/cross-sectional area (there are other more appropriate measures of strength for swords/knives, but we'll stick to tensile strength as an example), it also weighs 7,800 units per volume; an alpha-titanium alloy can be hardened to RC 40 and has yield strength of 850 units/cross-sectional-area and it weighs 4,500 units per volume. So, for a given volume of material at the hardnesses mentioned, the titanium is about half as strong and twice as light as the steel.
So you see that in order to have the same strength, the titanium bar must be made much larger in cross section than the steel, but because of its good strength-to-weight ratio, the much larger titanium bar would still lighter than the steel bar. Or, in other words, if the bars were exactly the same size, the titanium bar would be much weaker than the steel!! Ti alloys have superior strength/weight, but nobody said anything about strength/size!!
To illustrate graphically:
You also see from the example numbers that at knife hardnesses, the strength-to-weight ratio of the steel when hardened to RC 60 is actually a bit better than that of the Ti alloy! This is a fact often omitted by the comparisons: the strength-to-weight ratios are calculated based on materials at structural hardness (e.g. steel at RC 30-40 used as I-beams) rather than at knife hardness (RC 50-60) - strength of materials is greater at higher hardnesses, so in fact, when used for knives, steels can in fact have a similar strength/weight ratio to Ti alloys! If we redid this example with a lower carbon steel at RC 35-40, then the Ti alloy would look much better (approx 3 or 4 times better; aluminum is about 2 times better) in comparison.
What are the implications for cutlery? Well, it means that although Ti compares favorably to steel in an I-beam, this isn't true when you start hardening the steel for use in cutlery: let's take a sword for example. If you made a typical broadsword in steel, its blade would be between 1"-1.5" wide, 1/4"-3/8" thick and about 2-3 feet long. Now, if we ignore the fact that Ti alloys don't hold an edge for now, to make a Ti blade that is as strong as the steel, you'd need to make the cross section about twice the area, so you'd end up with something about 1/2-3/4" thick and 1-3/4"-2" wide! Such a blade would look more like a 2x4 than a sword!! On the other hand, the blade would be lighter than the equivalent steel blade.. Here's what I'm talking about.
Look at this from another point of view: if you have two blades made out of the exact shape and size, one of tempered steel, and one of titanium, the steel blade would in this case be stronger and because of it higher hardness, would likely cut the titanium sword in half, but the titanium sword would weigh but a small fraction of the weight of the steel blade. Titanium's only advantage here is low weight. Essentially, it's a glorified version of aluminum.
Now there are Beta-titanium alloys available which have yield strengths that are as good or better than that of steel, but the majority still suffer from a lack of hardenability. There are a few of this class of alloys that can be hardened to RC 50, but these materials have less flexibility than steel, so use in sword-lengths is probably not feasible, and at the current time, the cost of such materials is so high as to be prohibitive.
