The welding performance of titanium products such as titanium plates and titanium rods has many remarkable characteristics. The physical and chemical features of titanium and titanium alloys dictate these welding characteristics.
1. The influence of gas and impurity pollution on welding performance At room temperature, titanium and titanium alloys are relatively stable. However, the test results show that during the welding process, the liquid droplet and molten pool metal have a strong effect of absorbing hydrogen, oxygen, and nitrogen, and in the solid state, these gases have already interacted with it. The ability of titanium and titanium alloys to absorb hydrogen, oxygen, and nitrogen also greatly increases as the temperature rises. At roughly 250°C, hydrogen starts to absorb, followed by oxygen at 400°C and nitrogen at 600°C. These gases After being absorbed, it will directly cause joint embrittlement, which is a very important factor affecting welding quality.
2. The problem of cracks in welded joints. When welding, the possibility of hot cracks in the joints is very small. This is because the content of impurities such as S, P, and C in titanium and titanium alloys is very small, and the eutectic with low melting points formed by S and P is not easy to appear. On the grain boundary, coupled with the narrow crystallization temperature range, the shrinkage of titanium and titanium alloys is small when solidified, and the weld metal will not produce hot cracks. During welding, cold cracks can appear in the heat-affected zone, which is characterized by cracks occurring hours or even longer after welding, so they are also called delayed cracks.
Pores in the weld When welding, porosity is a problem that is often encountered. The key element that causes pores to form is the impact of hydrogen. The fatigue strength of the joint is significantly impacted by the formation of pores in the metal used for the weld.
The main technological measures to avoid pores are:
1) The protective gas should be pure, and the purity should not be less than 99.99%.
2) Clean the surface of titanium coils, titanium plates, titanium rods, and other titanium products, and organic matter such as scale oil on the surface of welding wire.
3) Apply good gas protection to the molten pool, and control the flow and velocity of argon to avoid turbulent flow and affect the protective effect.
4) To enable bubble escape, properly choose the welding process parameters and lengthen the molten pool's residence duration.
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