Titanium and titanium alloy welding:
Titanium and titanium alloy has excellent corrosion resistance, oxidation resistance, neutral and in chloride medium, its corrosion resistance is superior to steel, sometimes even for common austenitic stainless steel 1Cr18Ni9Ti 10 times. Industrial pure titanium with good plasticity, but lower strength, good low-temperature performance, the linear expansion coefficient and thermal conductivity is small, it is not difficult to weld. Titanium alloy than strength, but also has good toughness and weldability in aerospace industry, the most widely used. Titanium and titanium alloy in our current standards in their annealing are organized into a titanium alloys, titanium alloys andα + βtitanium alloy three categories, respectively TA, TB and TC. In the petrochemical industry in the pressure vessel, the brand is TA2 this kind of industrial pure titanium using are.
1 titanium and titanium alloy welding characteristics
①impurities contamination induced embrittlement
Titanium is an active element, especially in the welding high temperature very easy to absorb nitrogen, hydrogen, oxygen, and thus make the weld hardness, strength increases, plasticity, ductility decreases, cause embrittlement. Carbon will and titanium on the formation of hard and brittle TiC, easy to cause crack. Therefore, titanium and titanium alloy welding must be protected effectively, prevent air pollution or other factors. So the titanium and titanium alloy welding can not be used in gas welding or arc welding method, it can not meet the quality requirements for welding joints, generally only use argon protection or under vacuum welding.
The welding joint plasticity declined due to phase transition
Commonly used industrial pure titanium alloy welding forα, due to poor heat conduction, heat capacity of small titanium, high temperature and long residence time, the cooling speed is slow, easy to form coarse crystalline; if the use of accelerated cooling, and is easy to produce the acicularαorganization, also can make the plastic drop.
③the welding crack
Titanium alloy welding the welding hot crack probability minimal, only when the wire or parent material quality problem is hot crack. Cold crack is caused by hydrogen titanium alloy welding should pay attention to preventing, welding pool and low temperature zone in a base material of hydrogen to the heat affected zone caused by the diffusion, heat affected zone of hydrogen content is increased, resulting in heat affected zone appeared delayed crack.
Titanium and titanium alloy welding porosity is one of the most common welding defects. Welding wire or the base material surface is not clean or argon impure will cause to generate pores, therefore the protection gas argon purity requirements in 99.99% above, wire and workpiece surface to pickling, water washing and drying.
2 titanium and titanium alloy tungsten argon arc welding
Titanium and titanium alloy welding using is the largest tungsten argon arc welding for thick workpiece, may also be used in TIG welding, for the strict technical requirements of aerospace industry in a number of important equipment often also adopts the vacuum electron beam welding.
Selection of welding wire. Welding wire selection should be made in normal welding technology in welding seam condition after the tensile strength of not less than the parent material in the annealed state standard tensile strength limit, post weld state of plastic and corrosion resistant performance of not less than the parent material or annealed condition and parent material, weld of good performance, can meet the needs of titanium container manufacturing and use requirements.
Welding wire of nitrogen, oxygen, hydrogen, carbon, iron and other impurities elements content of the standard limit value should be greatly lower than that of the base metal impurity elements in the content of the standard limit value. Do not allow the parent material on CD as welding wire, must use the JB/T 4745-2002 ” titanium welded vessel ” in Appendix D of titanium wire wire used for container. Impurity element content not higher than JB/T 4745-2002 in Appendix D of the other standard wire can also be used. Parent material grade and recommended by wire grade table are listed in table 10-8.