Why Titanium Cracks Occur Often?
Welding characteristics of titanium products: Titanium equipment is easily oxidized, nitrided and embrittled.
1. At 400 ° C, a large amount of hydrogen is absorbed. Hydrogen is one of the most harmful elements of titanium, which can reduce the plasticity and toughness of titanium, leading to brittle fracture. When cooling down, hydrogen does not come out to produce pores, therefore, titanium is generally required the content of the material is less than 0.01% to 0.15%. If the base material contains a large amount of hydrogen, it should be dehydrogenated in advance.
2. Titanium will be abruptly combined with oxygen and nitrogen at 600 °C to form TiO2 and TiN (very hard), which will reduce the plasticity and toughness of the welded joint and cause porosity and crack defects.
3. When heated to above 800 ° C, TiO 2 is dissolved in titanium and diffused deep into the internal structure of the metal titanium to form an intermediate brittle layer of 0.01 to 0.08 mm thick. The higher the temperature, the longer the time, the more severe the oxidation and nitridation, and the plasticity of the welded joint drops sharply. It is required that the oxygen content in titanium is less than 0.1% to 0.15%, and titanium is also extremely easy to form brittle carbides with carbon, which reduces plasticity and weldability.
4. High melting point, 1608 ~ 1725 ° C, large heat capacity, poor thermal conductivity, welded joints are easy to overheat, coarse grains, especially β titanium alloy, the plastic joint of the welded joint is the most obvious decline, if the workpiece is structurally rigid, the role of welding stress It can also cause cracks.
5. Titanium may have cold cracks under the action of hydrogen and residual stress, and the hydrogen content in the welded joint must be strictly controlled. Once titanium is contaminated with iron ions, it becomes brittle, which is one of the important reasons for causing cracks in the titanium material of titanium equipment such as titanium reactors.
