Sunday, December 18, 2011

Tech Talk No. 6: Titanium vs. Steel

I had no idea what I was getting myself into when I thought I'd write about Titanium vs Steel (316L stainless steel). I thought it would be easy and be done with within minutes. How wrong was I!! After weeks of on-and-off research, I could not find anything simple and definitive. Instead, I've found vastly conflicting reports, anywhere from information that titanium is three times stronger than steel, to something along the lines of "nothing is tougher than steel".

What I realised is that we need to narrow down exactly what we are asking when it comes to titanium vs steel in terms of usage for watch cases and bracelets. And it is also highly dependent on your definitions of certain words.

So, I will do my best to break it down for you here. Feel free to chime in on the comments below if I get anything wrong, or if you have anything to add!

Titanium crystal bar - from Wikipedia

Pretty much all the watch companies will use grade 5 titanium, but does anyone know what grade 5 really means? No, it doesn't mean it's the best grade. All it means is the most common titanium alloy used. Pure titanium is hard to come by. So next time use see a watch company saying "grade 5 titanium" you will know what that means.

Here's a little quick breakdown of the different grades of titanium

American Society for Testing and Materials (ASTM) defines a number of alloy standards with a numbering scheme for easy reference :
  • Grades 1-4 are unalloyed and considered commercially pure
  • Grade 5, also known as Ti6Al4V, Ti-6Al-4V or Ti 6-4, is the most commonly used alloy
  • Grade 6-38 are various other titanium alloys, all with slightly different chemical composition – for more detailed description please google titanium alloy grades and click on the first result.

Titanium is stronger than steel in terms of strength to weight ratio. That is, for the same weight, titanium is stronger than steel. (Ti is about 45% lighter than steel).  But in terms of watches, for the same model, the Ti version is almost always a lot lighter than steel, meaning the two will have approcimately equal 'strength'. Titanium, however, it is also more brittle, and harder to work with than steel. This doesn't mean that titanium won't scratch. It may not scratch as easily as steel, but it will scratch. And due to it being a harder metal to work with, the scratches will be a lot more difficult to polish out.

There are good points about titanium - it is non-magnetic, hypoallergenic, light and has a distinctive colour - in watches at least, it tend to be darker. It is also highly resistance to corrosion and chlorine, and especially in salt water.

Further, titanium's yield strength, tensile strength, and thermal conductivity are better than those of many steel, but not all. 

So what does that mean for you and your watch?

If your skin is highly sensitive, and you don't like having something heavy around your wrist but still need to tell the time from something that's not plastic, ceramic or a phone, swim everyday, and tend not to look after your watch all that much, then a titanium watch is for you! Or then again, maybe you just like the look of it…


1 comment:

initialjh said...

thanks for another useful tech talk!!! :)