The role of alloying elements(Chromium(Cr), Nickel(Ni), Molybdenum(Mo))
In order to make better and improve certain properties of steel and to achieve certain special properties. The elements that are intentionally added during the smelting process are called alloying elements. Commonly used alloying elements are chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, silicon, manganese, aluminum, copper, boron, rare earth, etc. Phosphorus, sulfur, nitrogen, etc. also act as alloys in some cases. Let us talk about some of them.
(1)Chromium(Cr)
Chromium can increase the hardenability of steel and has a secondary hardening effect, which can improve the hardness and wear resistance of carbon steel, so that the steel does not become brittle. When the content exceeds 12%, the steel has good high-temperature oxidation resistance and oxidation resistance, and also increases the thermal strength of the steel. Chromium is the main alloying element of stainless steel acid-resistant steel and heat-resistant steel.
Chromium can increase the strength and hardness of carbon steel in the rolling state, and reduce elongation and section shrinkage. When the chromium content exceeds 15%, the strength and hardness will decrease. Elongation and section shrinkage are correspondingly increased. Parts with chrome steel are easily ground to obtain high surface processing quality. The main role of chromium in quenching and tempering structure is to improve hardenability. After quenching and tempering, the steel has better comprehensive mechanical properties. It is also possible to form chromium-containing carbides in the carburized steel, thereby improving the wear resistance of the surface of the material.
Chromium-containing spring steel is not easily decarburized during heat treatment. Chromium can improve the wear resistance, hardness and red hardness of tool steel, and has good tempering stability. In electrothermal alloys, chromium can improve the oxidation resistance, electrical resistance and strength of the alloy.
(2)Nickel(Ni)
Nickel strengthens ferrite in steel and refines pearlite. The overall effect is to increase strength. The effect on plasticity is not significant. Generally speaking, for low carbon steel used in rolling, normalizing or annealing conditions without quenching and tempering treatment. A certain amount of nickel can increase the strength of the steel without significantly reducing its toughness. According to statistics, each increase of 1% nickel can increase the strength by 29.4Pa. As the nickel content increases, the yield of the steel increases faster than the tensile strength. Nickel increases the strength of steel. Damage to steel's toughness, plasticity, and other process properties is less affected than other alloying elements. For medium carbon steel, since the nickel reduces the pearlite transformation temperature, the pearlite is made fine. Since nickel reduces the carbon content of the eutectoids, the number of pearlites is larger than that of carbon steels of the same carbon content. The strength of the nickel-containing pearlitic ferritic steel is higher than that of the carbon steel of the same carbon content. On the other hand, if the strength of the steel is made the same, the carbon content of the nickel-containing steel can be appropriately lowered, so that the toughness and plasticity of the steel can be improved. Nickel can increase the resistance of steel to fatigue and reduce the sensitivity of steel to the gap. Nickel reduces the low-temperature brittle transition temperature of steel, which is of great importance for low-temperature steel. With 3.5% nickel-containing steel can be used at -100 °C, and nickel-containing 9% steel can work at -196 °C. Nickel does not increase the resistance of steel to creep, so it is generally not used as a strengthening element for heat-strength steel.
Iron-nickel alloy with high nickel content. The coefficient of linear expansion varies significantly with increasing or decreasing nickel content. With this feature, it is possible to design and produce precision alloys, bimetallic materials, etc. with an extremely low or constant coefficient of linear expansion. In addition, nickel is added to steel not only to resist acid, but also to alkali, and has resistance to the atmosphere and salt. Nickel is one of the important elements in stainless acid-resistant steel.
(3)Molybdenum(Mo)
Molybdenum improves hardenability and heat strength in steel, prevents temper brittleness, increases remanence and coercivity, and resists in certain media. In quenched and tempered steel, molybdenum can harden parts of larger sections and improve the tempering resistance or tempering stability of steel. Allows the part to temper at higher temperatures, thereby more effectively eliminating (or reducing) residual stress and increasing plasticity. In addition to the above effects, molybdenum in carburized steel. It also reduces the tendency of carbides to form a continuous network on the grain boundaries in the carburized layer. Reducing the retained austenite in the carburized layer relatively increases the wear resistance of the surface layer.
In forging steel, molybdenum also maintains a relatively stable hardness of steel and increases resistance to deformation, cracking and wear. In the stainless acid-resistant steel, molybdenum can further improve the corrosion resistance to organic acids, hydrogen peroxide, sulfuric acid, sulfurous acid, sulfates, acid dyes, bleaching powders and the like. In particular, the addition of molybdenum prevents the tendency of pitting corrosion caused by the presence of chloride ions. W12Cr4V4Mo high-speed steel containing about 1% molybdenum has wear resistance, tempering hardness and red hardness.
(1)Chromium(Cr)
Chromium can increase the hardenability of steel and has a secondary hardening effect, which can improve the hardness and wear resistance of carbon steel, so that the steel does not become brittle. When the content exceeds 12%, the steel has good high-temperature oxidation resistance and oxidation resistance, and also increases the thermal strength of the steel. Chromium is the main alloying element of stainless steel acid-resistant steel and heat-resistant steel.
Chromium can increase the strength and hardness of carbon steel in the rolling state, and reduce elongation and section shrinkage. When the chromium content exceeds 15%, the strength and hardness will decrease. Elongation and section shrinkage are correspondingly increased. Parts with chrome steel are easily ground to obtain high surface processing quality. The main role of chromium in quenching and tempering structure is to improve hardenability. After quenching and tempering, the steel has better comprehensive mechanical properties. It is also possible to form chromium-containing carbides in the carburized steel, thereby improving the wear resistance of the surface of the material.
Chromium-containing spring steel is not easily decarburized during heat treatment. Chromium can improve the wear resistance, hardness and red hardness of tool steel, and has good tempering stability. In electrothermal alloys, chromium can improve the oxidation resistance, electrical resistance and strength of the alloy.
Nickel strengthens ferrite in steel and refines pearlite. The overall effect is to increase strength. The effect on plasticity is not significant. Generally speaking, for low carbon steel used in rolling, normalizing or annealing conditions without quenching and tempering treatment. A certain amount of nickel can increase the strength of the steel without significantly reducing its toughness. According to statistics, each increase of 1% nickel can increase the strength by 29.4Pa. As the nickel content increases, the yield of the steel increases faster than the tensile strength. Nickel increases the strength of steel. Damage to steel's toughness, plasticity, and other process properties is less affected than other alloying elements. For medium carbon steel, since the nickel reduces the pearlite transformation temperature, the pearlite is made fine. Since nickel reduces the carbon content of the eutectoids, the number of pearlites is larger than that of carbon steels of the same carbon content. The strength of the nickel-containing pearlitic ferritic steel is higher than that of the carbon steel of the same carbon content. On the other hand, if the strength of the steel is made the same, the carbon content of the nickel-containing steel can be appropriately lowered, so that the toughness and plasticity of the steel can be improved. Nickel can increase the resistance of steel to fatigue and reduce the sensitivity of steel to the gap. Nickel reduces the low-temperature brittle transition temperature of steel, which is of great importance for low-temperature steel. With 3.5% nickel-containing steel can be used at -100 °C, and nickel-containing 9% steel can work at -196 °C. Nickel does not increase the resistance of steel to creep, so it is generally not used as a strengthening element for heat-strength steel.
Iron-nickel alloy with high nickel content. The coefficient of linear expansion varies significantly with increasing or decreasing nickel content. With this feature, it is possible to design and produce precision alloys, bimetallic materials, etc. with an extremely low or constant coefficient of linear expansion. In addition, nickel is added to steel not only to resist acid, but also to alkali, and has resistance to the atmosphere and salt. Nickel is one of the important elements in stainless acid-resistant steel.
(3)Molybdenum(Mo)
Molybdenum improves hardenability and heat strength in steel, prevents temper brittleness, increases remanence and coercivity, and resists in certain media. In quenched and tempered steel, molybdenum can harden parts of larger sections and improve the tempering resistance or tempering stability of steel. Allows the part to temper at higher temperatures, thereby more effectively eliminating (or reducing) residual stress and increasing plasticity. In addition to the above effects, molybdenum in carburized steel. It also reduces the tendency of carbides to form a continuous network on the grain boundaries in the carburized layer. Reducing the retained austenite in the carburized layer relatively increases the wear resistance of the surface layer.
In forging steel, molybdenum also maintains a relatively stable hardness of steel and increases resistance to deformation, cracking and wear. In the stainless acid-resistant steel, molybdenum can further improve the corrosion resistance to organic acids, hydrogen peroxide, sulfuric acid, sulfurous acid, sulfates, acid dyes, bleaching powders and the like. In particular, the addition of molybdenum prevents the tendency of pitting corrosion caused by the presence of chloride ions. W12Cr4V4Mo high-speed steel containing about 1% molybdenum has wear resistance, tempering hardness and red hardness.
Comments
Post a Comment