[saberience]

I mean, I'm no materials scientist but one google tells me that Titanium is AS strong as steel but much less dense. I just browsed through the top 10 Google results and everyone states that titanium is roughly equal to steel in strength but with various other benefits. So your comment is definitely off-base somewhere, you make it seem like steel is much stronger, which clearly isn't the case.

[petertodd]

Read this for starters: https://www.thomasnet.com/articles/metals-metal-products/ste...

"When comparing the tensile yield strengths of titanium and steel, an interesting fact occurs; steel is by-and-large stronger than titanium."

Many people confuse this issue, because they're actually talking about measures of strength/weight ratios, on which titanium does really well. But if you are size limited rather than weight limited, steel is often a better material than titanium even when cost is no object.

[saberience]

Every source says that titanium is as strong as the most commonly used steel. Sure if you're going for lesser used alloys of steel you may as well compare to lesser used alloys of titanium. Or just compare iron with titanium, as that's really comparing one element with another, and is the "fair" comparison.

And anyway, your original comment suggested someone was totally in the wrong for thinking a 4mm titanium plate was strong, which is obviously incorrect. 4mmm of titanium plate is clearly going to be really strong and resistant. They wouldn't make plane engines from it if it wasn't.

[petertodd]

> They wouldn't make plane engines from it if it wasn't.

...but they don't! Jet engines can only use titanium for certain low pressure, low temperature, sections. The high temperature parts are made from nickle/iron-based superalloys. And aluminum still gets significant usage, because for many geometries an aluminum part has a better strength/weight ratio.

Like I said, titanium is strong. But it's not magic. Stronger than any aluminum alloy, weaker than commonly used steel alloys. Hitting a 4mm plate of titanium with a hammer just isn't a very special experience. I've done it.

Hitting a 4mm tool steel plate definitely can be a special experience. Because it's so strong and hard that you could easily cause the thing to shatter, sending sharp shards in unpredictable directions...

[MeImCounting]

No the parent is correct. Steel is by and large stronger than titanium of the same size. Pray tell what is this "most commonly used alloy of steel"? Because just fyi different steel alloys are used for different applications just like different titanium alloys are also used for different applications.

Titanium has excellent strength to weight properties compared to steel. A 4mm titanium plate would absolutely be dented by common shop hammers. This doesnt mean that "titanium isnt strong" it just means they have different material properties.

[scythe]

Steel has a range of strengths. The "most commonly used steel" is probably just mild steel and yeah Ti-6Al-4V is going to be the rough equal of mild steel on strength broadly assessed. But a high strength steel alloy will be three times that strong, and titanium can only be pushed so far.

[SV_BubbleTime]

I would use “cold roll” instead of “mild steel”.

But otherwise, yea irrc… Grade5 Ti (6AL4V) is approx equal to ultimate tensile of 303 stainless (extremely common) at 50% the weight.

BUT… Ti doesn’t even get close to 600 steels (like Inconel) or even common 17-4PH, etc.

[petertodd]

Exactly.

Indeed, if your design goal is strictly "don't get dented when hit by a hammer", the "strongest" material could easily be a good synthetic rubber!

[MeImCounting]

For most non-architectural design goals striking the right balance of toughness strength and hardness is generally what you want correct? I would imagine for building a bridge you care much more about elasticity and creep strength.

[petertodd]

Also fatigue resistance.

Bicycle design is a good example of where this matters: steel has a significant fatigue limit, and can endure cyclic stresses below that limit indefinitely. Aluminum has no fatigue limit, so any flexing is inevitably eating away at fatigue life. Thus aluminum bike frames have to be made much stronger and stiffer than otherwise necessary, to avoid bikes breaking unexpectedly due to fatigue. And that in turn means that aluminum bike frames don't have as much of a weight advantage over steel as you'd expect.

[nullc]

Titanium is quite expensive. I don't know if it makes sense to compare it to mild steel and not compare it to fancier steel selections which are still much less expensive than titanium and also much easier to work.

AR500 has a HRC of 47, modulus of 220 GPa, and tensile strength of 1740 MPa. Ti-6Al-4V is 37, 113.8 GPa, and 880 MPa respectively. The AR500 costs less than half as much as the Ti, and is much easier to work (though obviously working will degrade the properties).

The titanium is super really light, however... so the choice of material will depend on how relatively important weight is vs size and how simple your geometry is such that the added difficulty in working with Ti doesn't add problems.

Obviously there are also other grades of Ti too, but I think the comparison generally holds: If you don't care about weight/mass there is a steel selection which will be stronger, cheaper, and easier to form.

If you do care a lot about weight, an aluminum alloy often comes out the winner unless you just don't care much about costs or have fatigue concerns.

[AlotOfReading]

Steel's strength varies by orders of magnitude depending on the alloy and heat treatment. It's an incredibly flexible family of materials. Some members of that family are far stronger than anything in the titanium family, e.g. 4340 steel has a nominal yield strength of >1800 MPa, compared to <1300 MPa for Ti 10-2-3.

[saberience]

We're not talking about exotic and expensive varieties of steel though. We're just talking about "general" or common steel and comparing it to unalloyed "common"/"general" titanium. Remember, Steel is itself an alloy, Titanium is an element.

If you start comparing Titanium alloys to Steel then the comparison gets even harder. Titanium alloys are in general stronger than steel as well as much lighter and more corrosion resistant.

[petertodd]

> We're not talking about exotic and expensive varieties of steel though.

4340 steel isn't exotic. It's one of the most commonly used grades of steel out there, and it's much cheaper than titanium. There are steels out there with significant stronger yield strengths too. Meanwhile the highest yield strength of any Ti alloy is <1300MPa.

Titanium is still a really great material in certain applications. But it's not magic. You have to use it intelligently in the right application to get a benefit from it.

[bch]

The family of materials we call steel is so fantastic, it almost a shame it’s so ubiquitous that we take it for granted. If it were invented today the front page of HN would be loaded with stories of this miracle material.

[panick21_]

The newest generation most advanced spaceships are made from steel, see Starship.

When you go to both maximum cold (cryo fuel), and you go to maximum (reentry heat) then steel is amazing.

Aluminum would turn to butter on reentry, it would require a massive amount of heat shielding. Titanium alloys would have same issue.

Titanium alloy also become to brittle in deep cryo.

So steel beats everything in this demanding application. Its amazing.

[MeImCounting]

Pure elemental titanium has much less desirable material properties than various titanium alloys which are what you encounter most commonly. It is very uncommon to encounter elemental titanium outside of a chemistry lab.

[metal_am]

Grade 1 is still pretty common for ultralight backpacking items like pots and pans due to its ductility.

[MeImCounting]

Thats cool! I didnt know there were specific common applications where grade 1 would be desirable compared to the stronger alloys available.

[scythe]

IIRC you can buy titanium foil that you can just make stuff out of at home.

[cwillu]

So called “mild steel” would be far more accurately called “iron”, the carbon content is insignificant.

[dreamcompiler]

The carbon content of mild steel is low but not insignificant. Pure wrought iron [0] is a dream to forge and it has a huge grain structure. It's more ductile than mild steel but it's also not as hardenable or tough as mild steel [1]. That little bit of carbon in mild steel makes a big difference.

[0] I mean real wrought iron -- the almost 100% elemental stuff -- like the Eiffel tower is made of. This is practically unobtainable today. The "wrought iron" you commonly see for sale nowadays is always mild steel. And "cast iron" is actually very high carbon steel, not iron. Cast iron so high in carbon that it's brittle and cannot be forged or easily welded.

[1] It's a myth that mild steel cannot be hardened. With a proper wetting agent added to the quench, you can harden it significantly.

[jacquesm]

Wrought iron and mild steel are more or less functionally equivalent. One other reason why cast iron is so brittle is because it contains quite a bit of silicon.

[ClumsyPilot]

> We're not talking about exotic and expensive...

> "general" or common steel and "common"/"general" titanium

Why would you compare 'trash-quality' steel vs exotic and expensive material like Titanium?

That does not make any sence.

[scythe]

Wikipedia:

>4340 steel is an ultra-high strength steel

https://en.wikipedia.org/wiki/4340_steel

The alloy composition calls for 0.2-0.3% molybdenum and expects accuracy to within a few per mille for ten elements. Moly is considered so important that there are entire towns in the United States established to mine it to secure the military supply chain.

[justinator]

Is this true? From the Wikipedia article, the two mines that produce molybdenum as the main product are the two in CO, Henderson and Climax. They have no towns associated with them. Climax is near Leadville, but Leadville existed as a mining town before molybdenum was being mined at any scale. The other mine isn't close to any town that has more than a trailer park of people.

The others mine molybdenum as a byproduct of copper. I guess you could say the Bagdad mine has a company town, but it wasn't made to secure the military supply chain 140 year ago.

[rowanG077]

There are definitely steels that lose out to grade 5 Titanium. There are also steels that beat all Titanium grades. It's not so simple to say steel is stronger then Titanium. Some steels are stronger then titanium. Some Titanium grades are stronger then Some steels.