Who made titanium?
Titanium is a product of chemical industry/metallurgy; titanium is extracted from two minerals: ilmenite and rutile.
A titanium is a metal which looks like steel with high quality surface finish. But the difference between steel and titanium is its weight. An object made of titanium is lighter than that made of steel having same volume. The second difference is corrosion. Titanium is less prone to corrosion than steel.
We have several variables here. Titanium can be made in various thicknesses, and bullets can be made in various calibers. Some bullets will bounce off some titanium armor. Also, you should understand that titanium is not stronger than steel. The usefulness of titanium is that it has a better strength to weight ration than steel. But if weight is no object, as in a tank, you would want to use steel armor, not titanium.