Gr2 Titanium Welding Quality Of What Factors

Gr2 titanium welding is an important process in the manufacturing process of table equipment. There are many welding methods, according to the design structure of titanium equipment or components and specific application conditions, choose the appropriate welding method.
The principle of selecting welding methods is to ensure the quality of welded joints, high productivity, simple operation, low cost, always focus on quality. It is necessary to fully understand the various factors affecting the quality of welding in order to achieve the purpose of ensuring the quality of welded joints.

Titanium welding

The effect of gas impurities on the welding performance of the metal

Titanium has a high degree of chemical activity, and oxygen and nitrogen in the air has a very high affinity. When the temperature is low, titanium and oxygen interaction, the formation of a layer of dense oxide film, its thickness increases with the temperature, in 600 degrees Celsius or more, titanium began to absorb oxygen, and oxygen dissolved in titanium. When the temperature rises again, the activity of titanium increases dramatically and reacts violently with oxygen to form titanium oxide. Titanium begins to absorb hydrogen above 300°C and nitrogen above 700°C. As titanium is contaminated with oxygen and nitrogen, titanium's strength and hardness increase while plasticity decreases. Oxygen has a greater effect than nitrogen.

A hydrogen mass fraction of 0.01% to 0.05% in titanium causes a sharp decrease in the impact toughness of the weld metal, while the plasticity decreases less. This implies hydride-induced embrittlement. Hydrogen is also a source of porosity in the weld. During the welding process, the molten pool acts as a mini metallurgical furnace and the molten metal comes into contact with the air. If appropriate protective measures are not taken, the molten metal and air are isolated, oxygen, nitrogen, hydrogen and other gaseous elements are incorporated into the titanium, forming brittle oxides and nitrides, the plasticity of the weld metal decreases, the tensile strength rises, and in severe cases cracks, and the plasticity equals 0.

Titanium

The effect of other impurities on the performance of the weld metal

Other impurities are impurities that may be incorporated into the pool in addition to gas impurities. Its source may be the welding operation environment is not clean, welders wearing dirty gloves after contact with oil left behind the weldment, welding before scrubbing the joint with cotton gauze may leave cotton wool, welding production environment and steel welding to produce a mixture of rust, wet and other organic substances. These contaminants decompose oxygen, hydrogen, nitrogen, carbon and other elements under the high temperature of the arc, dissolved in dissolved titanium. When the amount of these elements exceeds the titanium solubility, titanium dioxide, titanium hydride, titanium nitride, titanium carbide and other compounds are formed. Through melt pool crystallization, these compounds enter the lattice of titanium and form deformed outer regions, thereby altering the mechanical properties of titanium.

Small amounts of trace elements are incorporated into titanium, if not exceeding the permissible range is still possible and sometimes desired. However, it is not allowed to exceed the content of impurity elements, especially organic impurities, harmful. This is because these impurity elements make the mechanical properties of titanium welds deteriorate, corrosion resistance is reduced, but also the source of cold air porosity.

Organizational changes in the weld metal and joint heat-affected zone

Titanium is a metal with an isotropic transformation. In 886 ° C began to occur when the organization of the solid-state transformation. 886 ° C below the crystal structure for the dense row of hexagonal structure, become α titanium; higher than 886 ° C when the α structure of the titanium transformed into a body-centered cubic structure of β titanium. This transformation process is completed in the melt pool from liquid to solid instant. The difference in the length of this instant has an effect on the crystallization form of the melt pool, the longer the instant the more conducive to the growth of columnar crystals. As titanium has a high melting point (1668 ° C), heat capacity and poor thermal conductivity and other characteristics, so the weld received welding line energy size and weld forced cooling of the good and bad influence, the cold wind is at high temperatures in the stagnation of the moment there is a difference. Moment slightly longer, for the molten pool crystallization columnar crystal growth and expansion of the joint heat-affected zone to provide conditions. This is one of the main reasons for the decrease in plasticity of welded joints. The tensile strength port of the joint usually occurs in the heat affected zone of the weld. In order to minimize this adverse effect, titanium welding should be performed using a soft welding specification, i.e., a smaller welding line energy and a faster cooling rate should be used.

Porosity is a common and unavoidable defect in titanium coil seam.

Porosity is a common process defect in titanium welding. Porosity generation mechanism is: welding process into the liquid metal gas through diffusion, dissolution, nucleation, growth and other processes and the formation of gas bubbles. Due to the molten pool of solidification and crystallization rate is very fast, the growth of bubbles can not escape from the liquid metal in time in the form of gas holes remain in the solid metal. Brewing pores of hydrogen and carbon monoxide and other gases are mainly produced by organic contaminants of the crystal arc heat effect. Sometimes welding before the weldments and welding consumables to do a full cleaning, cleaning, varnish protection is also ideal, but the cold wind still have pores. This indicates that the important source of contamination is not completely removed. Practice has shown that there is an important source of porosity that is often overlooked, and that is moisture in the air. A comparative experiment proved this. Welding in two environments that do not pass air humidity: one case is welding in a rainy weather environment with a relative humidity of 90% or more, and the other is welding in a sunny and clear weather environment with a humidity of less than 40%. Other pre-welding cleaning, cleaning and welding operations are the same. The presence of porosity in titanium welds in rainy weather with high air humidity was both numerous and large, while no porosity was seen in the welds in the case of low air humidity. This also indicates that the generation of porosity is related to air humidity.