Titanium is a metallic chemical element with the chemical symbol Ti and atomic number 22, and is located in Period 4, Group IVB of the Periodic Table of Chemical Elements. It was discovered by Gregor in 1791. It is a silvery-white transition metal characterized by its light weight, high strength, metallic luster, and resistance to wet chlorine corrosion. However, titanium cannot be used in dry chlorine gas, even if the temperature of 0 ℃ below the dry chlorine gas, will undergo a violent chemical reaction, the generation of titanium tetrachloride, and then decomposed to generate titanium dichloride, and even burning. Titanium remains reliably stable in chlorine gas only when the water content in it is higher than 0.5%.
Titanium is considered a rare metal due to the fact that in nature its presence is dispersed and difficult to extract. However, it is relatively abundant, ranking tenth among all elements. The main ores of titanium are ilmenite and rutile, which are widely distributed in the earth's crust and lithosphere.
Titanium (Ti)
1, titanium can improve the thermal strength of steel, improve the creep resistance of steel and high temperature enduring strength.
2, can improve the stability of steel in high temperature and high pressure hydrogen. So that the stability of steel in high pressure to hydrogen up to 600 ℃ or more, in pearlite low alloy steel, titanium can prevent molybdenum steel at high temperatures in the graphitization phenomenon. Therefore, titanium is one of the important alloying elements in the heat-strengthened steel used for boiler high-temperature components.
Titanium and nitrogen, oxygen, carbon have a strong affinity, is a good deoxidizing degassing agent and fixation of nitrogen, carbon effective elements. Titanium and carbon compounds (TiC) combining force is extremely strong, high stability, only heated to more than 1000 ℃ will slowly dissolve into the solid solution of iron, TiC particles have to prevent the steel grain growth coarsening effect. Titanium is one of the strong ferrite-forming elements, so that the austenite phase region is narrowed. Titanium in solid solution improves the hardenability of steel, while the presence of TiC particles reduces the hardenability of steel. At a certain value of titanium content, precipitation hardening can occur due to diffuse precipitation of TiFe2.
The effect of titanium on the mechanical properties of steel. When titanium exists in solid solution in ferrite, its strengthening effect is higher than that of aluminum, manganese, nickel, molybdenum, etc., followed by beryllium, phosphorus, copper, silicon. The effect of titanium on the mechanical properties of steel depends on the form in which it exists, the ratio of Ti to C content, and the heat treatment method. The mass fraction of titanium between 0.03% and 0.1% can make the yield strength increased, but when the ratio of Ti and C content more than 4, its strength and toughness decreased sharply. Titanium increases the enduring strength and creep resistance. Titanium has an improved effect on the toughness of steel, especially the low temperature impact toughness.
The effect of titanium on the physical, chemical and process properties of steel. Improves the stability of steel at high temperatures, high pressures and in hydrogen. Titanium improves the corrosion resistance of stainless and acid-resistant steels, especially the resistance to intergranular corrosion. In low carbon steel, when the ratio of Ti and C content reaches 4.5 or more, it has good resistance to stress corrosion and alkali embrittlement due to the fact that oxygen, nitrogen and carbon are all fixed. Adding titanium to steel with a chromium mass fraction of 4%-6% improves the oxidation resistance of steel at high temperatures. The addition of titanium to steel can promote the formation of nitriding layer, and can more quickly obtain the required surface hardness. Titanium-containing steels are known as 'fast nitriding steels' and can be used to make high-precision screws. Improves weldability of low carbon manganese steel and high alloy stainless sodium.
Titanium can be considered as an alloying element when its mass fraction exceeds 0.025%. Titanium as an alloying element is widely used in common low alloy steel, alloy structural steel, alloy tool steel, high-speed tool steel, stainless and acid-resistant steel, heat-resistant and non-skinning steel, permanent magnet alloy and cast steel. Titanium has been used as a variety of advanced materials, and has become an important strategic material, accounting for more than half of the use in the aerospace industry, such as aerospace vehicles, power machinery and so on.