Steel and Titanium are very different, but I don’t think you can actually engrave either one with a 45W laser.
Steel is a fairly good conductor of heat, and you need to get it very hot before it changes color at all. This means that a relatively small input like the laser spot is going to have a hard time making a localized change in appearance.
Ti is a lousy heat conductor and it oxidizes very rapidly at elevated temperatures to produce an layer of TiO2. When this layer is thin it shows brilliant interference colors, and generally looks awesome. I am not sure, but I think the Glowforge folks are saying that you can “mark” Ti with the laser, basically drawing on it with a line of colored oxide. The colors are very heat sensitive, and I bet you can adjust them by varying the laser time and focus. Having made a lot of lot of Titanium jewelry back in the late '80s when it was cool, I look forward to experimenting with this!