In fact, we generally say, you may be suddenly enlightened, first take phosphorus and sulfur, unless the turning performance requirements of high materials, the general material does not require the inclusion of these two harmful impurity elements. Chromium, aluminum, silicon and rare earth elements can improve the oxidation resistance of heat-resistant steel. Chromium, molybdenum, tungsten, vanadium, titanium, niobium, cobalt, boron, rare earth, etc., can improve or improve the thermal strength of heat-resistant steel. Iron is the basic element of heat-resistant steel. The role of nickel and manganese is mainly to obtain austenitic structures. Now let's specifically introduce the role of the main alloying elements in heat-resistant steel.
Chromium (Cr), the element is the main element of high-temperature oxidation resistance and high-temperature corrosion resistance in heat-resistant steel, and can improve the thermal strength of heat-resistant steel. The high temperature corrosion resistance of heat-resistant steel has a certain relationship with the chromium content. Therefore, the chromium content of commonly used heat-resistant steel should not be less than 12%.
Nickel (Ni) is one of the important alloying elements in heat-resistant steel, which plays an irreplaceable role in heat-resistant stainless steel. In order for the steel to obtain a pure austenitic structure at room temperature, the nickel content is not less than 25%. However, when the steel contains other alloying elements, in order to obtain pure austenitic structure, the nickel content can be appropriately reduced. For example, when the carbon content of 0.1% in the steel is 18%, in order to obtain the pure austenitic structure of the steel, the nickel content is 8%, which is a typical 18-8 type austenitic heat-resistant stainless steel. When the steel contains other ferrithreiotic forming elements, in order to obtain pure austenitic structure, the nickel content will increase, if the nickel content is not increased, or the nickel content is reduced, there will be bidirectional structure, or unstable austenitic structure, cold processing may produce phase change (austenitic structure into martensitic structure).
Molybdenum (Mo), this elemental refractory metal, has a high melting point (2625 ° C). It has a better effect on improving the thermal strength of heat-resistant steel, and in fact, it is also helpful to corrosion resistance.
The role of cobalt (Co) in Austenitic heat-resistant steel is similar to the role of nickel, similarly, in the heat-resistant stainless steel bell appears more, adding cobalt in chromium-nickel Austenitic heat-resistant steel to improve the high temperature corrosion resistance of the steel is favorable. Cobalt is a rare and expensive metal and should be used sparingly.
Tungsten (W), like molybdenum, this element is also a refractory metal with a high melting point (3380 ° C). Adding tungsten can improve the thermal strength of the solid solution.
Vanadium (V) refractory metal, high melting point (1910℃) Vanadium is an effective element to improve the thermal strength of ferritic heat-resistant steel, vanadium is also used in Austenitic heat-resistant steel, but the content is generally between 0.3% and 0.5%.
Silicon (Si), in heat-resistant steel is a beneficial element to resist high temperature corrosion, at the same time, adding silicon to steel can also improve its performance at room temperature conditions. The silicon content in heat-resistant steel generally does not exceed 2%.
Aluminum (Al) is an important alloying element of oxidation resistance in heat-resistant steel, and the aluminum content in heat-resistant steel is generally not more than 6%.
Titanium (Ti), this element is a valuable alloy, it is one of the strong carbide forming elements, the purpose is to prevent indirect corrosion.
Niobium (Nb) is also a strong carbide forming element, and niobium carbides are very stable at high temperatures, only slightly less than titanium carbides. Because of its good thermal strength, niobium has been widely used in bulk alloy heat resistant steel and high alloy heat resistant steel. The niobium content in high alloy heat-resistant steel is generally 1% to 2%.
Boron (B) has a strong affinity with nitrogen (N) and oxygen (O), and a trace amount of boron (0.001%) in steel can be cultivated to improve its hardenability. In pearlite heat-resistant steel, trace boron can improve the high temperature strength of steel; Adding 0.025% boron to austenitic heat-resistant steel can improve its creep resistance, but the effect is opposite when the content of Peng is higher. Adding boron to strengthen grain boundaries is very important to enhance the durable strength of heat-resistant steel. Boron atoms are mainly distributed in the grain boundaries, so boron plays an important role in strengthening the grain boundaries.
Manganese (Mn) is a good deoxidizer and desulfurizer, it makes the ability of steel to form and stabilize austenitic structure is second only to nickel, to replace nickel with manganese heat resistant steel, has a wide range of uses. Although manganese can improve the instantaneous strength of steel at high temperature, it has no significant effect on the permanent strength and creep strength.
Carbon (C) is an indispensable element in steel. The strengthening effect of carbon in steel is closely related to the composition and structure of the carbide it forms, and its strengthening effect is also related to temperature. With the increase of temperature, the strengthening effect decreases due to the accumulation of carbides. The increase of carbon content in steel will reduce the plasticity and weldability of steel. Therefore, in addition to the steel with higher strength requirements, the carbon content in the general Austenitic heat-resistant steel is controlled in a low range.
The role of nitrogen (N) as alloying element in Austenitic heat-resistant steel is somewhat similar to that of carbon. Nitrogen content in chromium-nickel austenitic heat-resistant steel can improve the thermal strength of steel, and has almost no effect on brittleness. The reason may be due to the precipitation of dispersed nitrides. The role of each element in heat-resistant steel.
