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Comment by MeImCounting | Hacker News Reader

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.

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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.

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.

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!

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.

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.

Right now, top quality steel bike frames at the minimum bike weight allowed by the UCI are stronger than top quality carbon fibre bike frames of the same weight. Aluminum frames of the same weight would not be considered usable probably... (Pro cyclists would still use carbon fibre bikes because they can be made more aerodynamic).

That’s with a minimum weight imposed. Doesn’t change the fact that aluminum and titanium alloys generally have better strength-to-weight ratios than steel.

And fork is made out of steel (or carbon) even on aluminium bikes

For a rigid road bike aluminum can definitely be made stronger and lighter, even though what you wrote about fatigue limit is technically true. People like steel because they feel it’s more comfortable to ride. For mountain bikes, you will find almost zero steel bikes. Here the stiffness and lightness of aluminum (and carbon fiber at the high end) is almost universally preferred.

One advantage that adds to the potential lightness of aluminum and carbon fiber bike frames is manufacturing method. Aluminum is cheap to machine and hydroform into efficient shapes, and carbon fiber can also be layed up into efficient shapes.

> For a rigid road bike aluminum can definitely be made stronger and lighter,

Absolutely. What I meant was that while an aluminum bike frame can be lighter than steel, it's not as much lighter than steel than you'd expect. Steel bike frames tend to be only ~15% heavier than aluminum, not 50%.

Personally I bought a steel road because the difference in weight vs the aluminum alternative was small enough that I decided to go with the bike that looked nicer, and would last longer. Besides, I could use to lose a lot more weight than any bike ever could...

> I could use to lose a lot more weight than any bike ever could...

Get a child trailer and load it up with groceries or cement! i tried it, the results are.. Surprising

> For mountain bikes, you will find almost zero steel bikes

Surly makes (only) steel mountain bikes, and I think there are approx. a... there's a lot of them out there. One reason is that they are inexpensive (relatively) and take a lot of abuse.

https://surlybikes.com/bikes/trail

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