Common titanium alloys are made by reduction. For example; cuprotitanium (rutile with copper added is reduced), ferrocarbon titanium (ilmenite reduced with coke in an electric furnace), and manganotitanium (rutile with manganese or manganese oxides) are reduced.[22] 2TiFeO3 + 7Cl2 + 6C (900 °C) → 2TiCl4 + 2FeCl3 + 6CO TiCl4 + 2Mg (1100 °C) → 2MgCl2 + Ti About 50 grades of titanium and titanium alloys are designated and currently used, although only a couple of dozen are readily available commercially.The ASTM International recognizes 31 Grades of titanium metal and alloys, of which Grades 1 through 4 are commercially pure (unalloyed). These four are distinguished by their varying degrees of tensile strength, as a function of oxygen content, with Grade 1 being the most ductile (lowest tensile strength with an oxygen content of 0.18%), and Grade 4 the least (highest tensile strength with an oxygen content of 0.40%) The remaining grades are alloys, each designed for specific purposes, be it ductility, strength, hardness, electrical resistivity, creep resistance, resistance to corrosion from specific media, or a combination thereof. The grades covered by ASTM and other alloys are also produced to meet Aerospace and Military specifications (SAE-AMS, MIL-T)], ISO standards, and country-specific specifications, as well as proprietary end-user specifications for aerospace, military, medical and industrial applications. In terms of fabrication, all welding of titanium must be done in an inert atmosphere of argon or helium in order to shield it from contamination with atmospheric gases such as oxygen, nitrogen or hydrogen. Contamination will cause a variety of conditions, such as embrittlement, which will reduce the integrity of the assembly welds and lead to joint failure. Commercially pure flat product (sheet, plate) can be formed readily, but processing must take into account the fact that the metal has a 'memory' and tends to spring back. This is especially true of certain high-strength alloys.The metal can be machined using the same equipment and via the same processes as stainless steel.