Commercially Pure Titanium contains 98-99.5% titanium. The small additions of oxygen, nitrogen, carbon, and iron improve strength. CP alloys have the best weldability of titanium grades. This is due to their combination excellent corrosion resistance, good ductility and excellent weldability.
The most common CP grades are Grades 1, 2, 3 and 4. The difference between these is how much oxygen and iron are alloyed in them. Grade 1 is the most pure and also the weakest. Keep in mind that the mechanical properties increase with the grade number. Grades with more oxygen and iron have higher strength but lower ductility and weldability.
When welding CP Titanium, you should use a filler that is one or two PSI strength grades lower than the parent metal. The weld dilution with the base metal will increase in the strength of the weld metal.
Alpha alloys typically contain aluminum, tin, and trace amounts of oxygen, nitrogen, and carbon. Also, they have medium strength compared to other titanium alloys. Also, they have reasonably good ductility and excellent mechanical properties at cryogenic temperatures. Lastly, they are very weldable and are always welded in the annealed condition.
Alpha alloys do not respond to heat treatment. However, they can be strengthened by cold working. Alongside the CP Titanium grades, Alpha alloys possess the highest corrosion resistance of the Titanium groups.
As the name indicates, Alpha-Beta alloys of Titanium contain both crystal structures. They are formed by the addition less than 6% aluminium and varying amounts of the Beta forming elements. These include vanadium, chromium and molybdenum.
These alloys have medium to low strength compared to the other Titanium grades. Unlike CP and Alpha alloys, which can only be strengthened by cold work, Alpha-Beta alloys are heat treatable. Therefore, these grades can undergo machining while the material is still ductile. Then they can be heat treated to further strengthen the material.
Alpha-Beta alloys are generally weldable. However, their weldability is dependent on the amount of Beta present. The higher the Beta elements, the lower the weldability of titanium grades. Also, the higher the Beta elements, the more brittle the welds become. High-Beta grades are very strong and rarely welded.
Alpha-Beta alloys can be welded with various filler metals. It is common to use filler metal of an equivalent grade, especially for the lower alloyed materials. Another option is one grade lower to ensure good weld strength and ductility.
Beta alloys are the smallest group of titanium alloys. They are high strength, low weight, and highly corrosion resistant. Beta alloys are fully heat treatable, possess good hardenability, and are generally weldable.
Beta alloys are slightly denser than other titanium alloys. But, they have the highest strength and good creep resistance. These grades are welded in the annealed or solution heat treated condition. When welded, the joint has a low strength but is ductile. Next, they are cold-worked, then solution treated and aged. This increases strength but avoids embrittlement.
These alloys are welded using filler wire of matching composition. However, when welding higher strength titanium alloys, fillers of a lower strength are sometimes used to maintain weld metal ductility.