Vanadium has a strong affinity with carbon, ammonia, and oxygen, and forms corresponding stable compounds with them. Vanadium exists mainly in the form of carbides in steel. Its main function is to refine the structure and grains of steel and reduce the strength and toughness of steel. When dissolved into solid solution at high temperature, the hardenability is increased; conversely, when it exists in the form of carbide, the hardenability is decreased. Vanadium increases the tempering stability of quenched steel and produces a secondary hardening effect. The vanadium content in steel, except for high-speed tool steel, is generally not greater than 0.5%.
Vanadium can refine the grains in ordinary low-carbon alloy steel, improve the strength, yield ratio and low-temperature characteristics after normalizing, and improve the welding performance of the steel.
Vanadium is often used in combination with elements such as manganese, chromium, molybdenum and tungsten in structural steel because it will reduce the hardenability under general heat treatment conditions. Vanadium in quenched and tempered steel mainly improves the strength and yield ratio of the steel, refines the grains, and reduces overheating sensitivity. Because it can refine the grains in carburized steel, the steel can be quenched directly after carburizing without the need for secondary quenching.
Vanadium in spring steel and bearing steel can increase the strength and yield ratio, especially increase the proportional limit and elastic limit, reduce decarburization sensitivity during heat treatment, thereby improving surface quality. Pentachromium-containing vanadium bearing steel has high carbonization dispersion and good performance.
Vanadium refines the grains in tool steel, reduces overheat sensitivity, increases tempering stability and wear resistance, thereby extending the service life of the tool.
Titanium has a strong affinity with nitrogen, oxygen, and carbon, and has a stronger affinity with sulfur than iron. Therefore, it is a good deoxygenating degassing agent and an effective element in fixing nitrogen and carbon. Although titanium is a strong carbide-forming element, it does not combine with other elements to form composite compounds. Titanium carbide has strong binding force, stability, and is not easy to decompose. In steel, it can only be slowly dissolved into solid solution when heated to above 1000°C. Before being dissolved, titanium carbide particles can prevent grain growth. Since the affinity between titanium and carbon is much greater than the affinity between chromium and carbon, titanium is commonly used in stainless steel to fix the carbon in it to eliminate the depletion of chromium at the grain boundaries, thereby eliminating or reducing intergranular corrosion of steel.
Titanium is also one of the strong ferrite-forming elements, which strongly increases the A1 and A3 temperatures of steel. Titanium can improve plasticity and toughness in ordinary low alloy steel. Because titanium fixes nitrogen and sulfur and forms titanium carbide, it increases the strength of the steel. After normalizing, the grains are refined and carbides are precipitated to form, which can significantly improve the plasticity and impact toughness of the steel. Titanium-containing alloy structural steel has good mechanical properties and process properties, but its main disadvantage is slightly poor hardenability. .
Titanium with about 5 times the carbon content is usually added to high-chromium stainless steel, which can not only improve the corrosion resistance (mainly resistance to intergranular corrosion) and toughness of the steel; it can also prevent and improve the grain growth tendency of the steel at high temperatures. Welding properties of steel.
