The hottest titanium and titanium alloy welding I

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Welding of titanium and titanium alloys (I)

Abstract This paper expounds the material characteristics and weldability of titanium and titanium alloys, and carries out weldability tests in view of the welding defects of titanium and titanium alloys, such as oxidation, cracks, pores and so on. Through the continuous exploration of titanium and titanium alloy welding process specifications and the reasonable analysis of the problems in the test process, the characteristics and operation essentials of titanium and titanium alloy welding process can be summarized. 1、 Classification and characteristics of titanium and titanium

there are three kinds of domestic industrial pure titanium: TA1, TA2 and TA3. The difference is that the content of impurities containing hydrogen, oxygen and nitrogen is different. These impurities strengthen the industrial pure titanium, but the plasticity is significantly reduced. Although the strength of industrial pure titanium is not high, it has excellent plasticity and toughness, especially good low-temperature impact toughness; At the same time, it has good corrosion resistance. Therefore, this kind of material is mostly used in chemical industry, petroleum industry, etc. in fact, it is mostly used in working conditions below 350 ℃

according to the room temperature microstructure of titanium alloys in annealing state, titanium alloys can be divided into three types:

α Type titanium alloy( α+β) Titanium alloy and β Type titanium alloy

α Ti AI alloys of TA4, TA5 and TA6 and ti+ai+sn alloys of TA7 and ta8 are widely used. The strength of this alloy can reach 931n/mm2 at room temperature, and it has stable performance and good weldability at high temperature (below 500 ℃)

β The application amount of type a titanium alloy is less in China, and its application scope needs to be further expanded. 2、 Weldability of titanium and titanium alloys

the weldability of titanium and titanium alloys has many remarkable characteristics, which are determined by the physical and chemical properties of titanium and titanium alloys

1. Influence of gas and impurity pollution on welding performance

titanium and titanium alloys are relatively stable at room temperature. However, according to the test table, during the welding process, the liquid droplet and molten pool metal have strong chemical resistance to absorb hydrogen, oxygen and nitrogen, and these gases have interacted with them in the solid state. With the increase of temperature, the ability of titanium and titanium alloys to absorb hydrogen, oxygen and nitrogen also increases significantly. It starts to absorb hydrogen at about 250 ℃, oxygen at 400 ℃ and nitrogen at 600 ℃. After these gases are absorbed, they will directly cause the embrittlement of welded joints, which is a very important factor affecting the welding quality

(1) hydrogen is the most serious factor affecting the mechanical properties of titanium among the gas impurities. The change of hydrogen content in the weld has the most significant effect on the impact properties of the weld, which is mainly due to the increase of flake or needle TiH2 precipitated in the weld with the increase of hydrogen bomb content in the weld. The strength of TiH2 is very low, so the effect of sheet or needle guard hih2 is exemplified by notch, combined with impact 2 The performance of the lever transmission system is significantly reduced; The effect of the change of hydrogen content in the weld on the increase of strength and the decrease of plasticity is not obvious from time to time

(2) the influence of oxygen on titanium α Phase sum β All of them have high melting degree and can form interstitial solid phase. The crystal wound of titanium is seriously distorted, which improves the hardness and strength of titanium and titanium alloy, but significantly reduces the plasticity. In order to ensure the performance of the welding joint, in addition to strictly preventing the main oxidation of the weld and welding according to the heat affected zone during the welding process, the oxygen content in the base metal and welding wire should also be limited

(3) effect of nitrogen at high temperatures above 700 ℃, nitrogen and titanium react violently to form brittle titanium nitride (RIN), and the lattice deflection caused by the formation of interstitial solid solution between nitrogen and titanium is more serious than that caused by the amount of oxygen. Therefore, nitrogen is more significant than oxygen in improving the tensile strength and hardness of industrial pure titanium welds and reducing the plastic properties of welds

(4) the influence of carbon carbon is also a common impurity in titanium and titanium alloys. The experiment shows that when the carbon content is 0.13% of electrolytic aluminum supply and modification, the carbon depth is α In titanium, the weld strength limit is increased and the plasticity is decreased, but the effect of oxygen and nitrogen is not as strong. However, when the carbon content of the weld is further increased, the weld appears like tic, and its number increases with the increase of carbon content, which makes the weld plasticity drop sharply, and cracks are easy to appear under the action of welding stress. Therefore, the carbon content of titanium and titanium alloy base metal communicated through the serial port (COM port) on the back of the accounting machine is not more than 0.1%, and the carbon content of weld joint is not more than that of base metal

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