Titanium is not magnetic, with titanium construction of nuclear submarines do not have to worry about the magnetic mine attack. In 1947, people began to smelting titanium in the factory. That year, the output is only 2 tons. 1955 production surge to 20,000 tons. In 1972, the annual output reached 200,000 tons. Titanium hardness and steel almost, and its weight is almost only half of the same volume of steel, although slightly heavier than aluminum, its hardness is 2 times larger than aluminum. Now, in the universe rockets and missiles, a large number of titanium instead of steel. According to statistics, the current annual use of titanium in the world of titanium, has reached more than 1,000 tons. Very fine titanium powder, or rocket good fuel, so titanium known as the universe of metal, space metal. Titanium heat resistance is very good, the melting point of up to 1668 ℃. At room temperature, titanium can be safe and sound lying in a variety of strong acid and alkali solution. Even the most ferocious acid - aqua regia, it can not corrode it. Titanium is not afraid of the sea, it was a piece of titanium sink to the bottom of the sea, five years later to take a look, above the sticky many small animals and seabed plants, but there is no rust, still shining. Now, people began to use titanium to create a submarine - titanium submarine. Because titanium is very strong, can withstand high pressure, this submarine can be deep in the deep sea of 4500 meters.