Titanium?
 

It seems as though there are framebuilders who are familiar with various types of steel tubing, and with titanium tubings, and they often seem to lean strongly toward steel. Does anyone know what it is about titanium that makes some people steer away from it and toward steel instead?

$$ + more complex welding setup.

Also, titanium is about half as stiff (modulus of elasticity) as steel. Ti also has half the density of steel, so the stiffness to weight ratio of the two materials is about the same. This means that to keep a frame from being too flexible, the wall of a tube of titanium has to be thicker than a tube of steel, so much of the weight advantage of Ti in having a lower density than steel is lost.

Most importantly, a Ti weld can be compromised and result in a broken frame if the welding process isn't carefully done (harder to do than steel and more time consuming it appears). Read the below article as a great primer on all materials being used today. It's an older article, but still has salient features worth remembering: http://www.63xc.com/scotn/metal.htm

A blurb from that article about Ti: "It's also difficult -- or, at least, different -- to weld or machine. A Ti builder can't cut corners. Without meticulous procedures, he risks contaminated welds, and catastrophic failures. At the recent Cactus Cup race, I came around a corner on the course to find a guy whose titanium bike had just lost its head tube. A quick inspection revealed my suspicion: a contaminated weld. Machining titanium is either a dream or a nightmare, depending on your procedure. If you use the proper speeds and feeds, and the right cutting tools, it will machine beautifully -- but it may be unsuited to mass production."

Please, let's not spread misconceptions here. Ti is not exponentially more difficult to fabricate than a high end air hardening steel. The only reason the fabrication costs are higher is because you have to do double pass welds, which essentially double your weld labour portion of the build. High quality steel is still backpurged like Ti, the tubes are still a real bugger to cut (Although not impossible once you have it down), and the same level of cleanliness is required to do a good job.

If companies 'lean toward steel', it probably has more to do with cost or marketing or just pure personal preference than anything else. The raw materials for Ti are four times higher than that of steel, and steel is probably a more versatile material in terms of tubesets available, types of braze-ons etc.