Welding Of Industrial Pure Titanium TA2

                       Welding of industrial pure titanium TA2

preface

Industrial pure titanium TA2, standard sheet No.: GB/T3621-2007 (titanium and titanium alloy sheet for to 350 DEG C part, although the intensity is low, but due to the good ductility, excellent corrosion resistance, especially good low-temperature impact properties and good weldability, it as a kind of emerging and future development of nonferrous metal materials, gradually in the petroleum chemical industry get more and more widely used.

2 TA2 basic characteristics and welding characteristics

2.1 physical properties

Pure titanium TA2 in annealing state tensile strength value is low, the physical properties is high melting point, poor thermal conductivity, heat capacity, density is lower than iron. In addition, it has the characteristics of high resistivity, small linear expansion coefficient and so on.

High melting point, poor thermal conductivity, easy to produce large grain size in the weld and near seam area, which causes the decrease of the plasticity and toughness of the weld, so the welding heat input should be strictly controlled.

2.2 chemical properties

Active chemical properties of titanium and susceptible to gaseous impurities pollution caused by welding joint embrittlement. With the increase of temperature, titanium absorption capacity for oxygen, nitrogen and hydrogen is gradually rising, heating temperature of 250 DEG to hydrogen absorption and 400 DEG C to absorb oxygen and 600 DEG C to absorb nitrogen, such as pure titanium in welding process due to improper protection, causing the weld excess contains elements of these gases, on the one hand, the weld is easy to form pores and other defects, on the other hand is bound to cause weld strength is increased, the plastic a serious decline in the weld brittle. Therefore, oxygen, nitrogen, hydrogen is a harmful element of titanium, so the weld pool and temperature of the weld and heat affected zone (including the back of the weld pool) must be protected when welding. In addition carbon elements of base metal and weld performance also significantly affected, increasing carbon content, plasticity decreased significantly, China under the technical conditions, industrial pure titanium and titanium alloy base material containing carbon content should not exceed 0.1% weld containing carbon content should not exceed base metal carbon content.

3 TA2 welding process

3.1 welding methods

Has been analyzed in the previous, the properties of titanium is very active, using ordinary manual arc welding and other welding methods are not applicable to the welding of titanium material, the application of the most should be tungsten argon arc welding.

3.2 preparation before welding

Before welding the workpiece near the surface, especially the butt end must be carefully mechanical cleaning, and then scrub with acetone or alcohol, the same wire must be used before the use of acetone.

3.3 welding materials

According to the chemical composition of the base metal and the parent metal, the purity of argon should not be less than 99.99%.

3.4 key points of welding process

Welding heat input is not too large, prevent weld coarse grain resulted in a decline in performance of the weld, welding in the process of strengthening the protection measures, in more than 400 DEG C molten pool at the back of the weld and heat affected zone, both the application of drag cover for argon protection, the back weld should also be using the same measures. The layer temperature is as low as possible, it is best to stay the first layer of weld cooling to below 70 degrees Celsius, and then the next layer of weld to prevent overheating. The welding torch swing as small as possible to prevent the molten pool from argon. During the welding process, attention should be paid to the change of the color of the welded joint.


4 welding procedure qualification test

4.1 preparation before trial

According to the procurement of materials and the requirements of welding procedure qualification test, using 8mm TA2 plate test, filling materials used and quality as the base material of wire ERTA2ELI diameter 3mm wire with NB/T47018.7-2011 for the bearing pressure equipment welding material ordering technical conditions "part 7.


4.2 welding process parameters and requirements

Before welding with acetone cleaning groove on both sides of 50mm range within the oil and dirt, to ensure the assembly gaps and unfitness of butt, wire with acetone to clean grease, welding nozzle gas flow rate of 15 ~20L/min, dorsal drag cover argon flow 20~25L/min, welding is completed after pulling cover flow protection 20~25L/min, welding process control layer between the temperature is less than or equal to 70 DEG C, welding process parameters see table.

4.3 nondestructive testing

100%RT after welding, in compliance with JB/T4730.2-2005, grade I qualified.

4.4 physical and chemical test

After 2 tensile tests and 4 bending tests, the welded joint is in accordance with the requirements of the relevant standards.

5 concluding remarks

TA2 plate has good welding properties, using tungsten electrode argon arc welding, select the appropriate specification, in the case of reliable protection, can be satisfied with the quality of welded joints.