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/*728*90 created on 2018/5/16*/ var cpro_id = "u3440131"; Home>Bearing knowledge>Effect of permanent impurities on steel function Effect of common impurities on steel function
In the actual use of steel; in addition to rich in iron, carbon and alloying elements; during the exercise; inevitably bring some impurities (such as manganese, silicon, sulfur, phosphorus, non-metallic impurities and some gases; such as Nitrogen, hydrogen, oxygen, etc.) These impurities have a great influence on the quality of steel. /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';
1. When manganese manganese is present as an impurity in steel; it is usually less than 0.8%. It comes from pig iron as a steelmaking material and ferrite as a deoxidizer. Manganese has good deoxidation ability; it can also form MnS with sulfur to eliminate sulfur. The harmful effects. Most of these reaction products are removed from the slag; small parts remain in the steel to become non-metallic inclusions. In addition, manganese can be dissolved in ferrite at room temperature; it has a certain strengthening effect on steel. Soluble in cementite; constitute alloy cementite. But manganese exists as a few impurities; it has no obvious effect on the function of steel.
2. Silicon silicon is present as an impurity in steel; usually less than 0.4%, it also comes from pig iron and deoxidizer. Silicon can be dissolved in ferrite at room temperature; it has a certain strengthening effect on steel. But silicon as a minority impurity When it exists; it has no obvious effect on the function of steel.
3. Sulfur and sulfur are impurities brought into the steel by pig iron and fuel. In the solid state; the solubility of sulfur in iron is extremely high and the shape of FeS is present in steel. Because of the plasticity of FeS; the brittleness of steel with more sulfur More serious; FeS and Fe can form a low melting point (985 ° C) eutectic; scattered on the austenite grain boundary. When the steel is heated to about 1200 ° C for hot pressure processing; The crystal has melted; the intergranular connection is damaged; the steel is cracked along the grain boundary during processing; this appearance is called hot brittleness. In order to eliminate the harmful effects of sulfur; it is necessary to add manganese in the steel. Manganese and sulfur are preferred. Forming a high melting point (1620 ° C) of manganese sulfide; and dispersed in the grain in the grain; it has a certain portability at high temperatures; then avoiding the hot brittleness; sulfides to the wrong metal inclusions; will reduce the mechanical function of the steel; And in the rolling process to form a hot-processed fiber arrangement. Therefore; under normal conditions; sulfur is a harmful impurity. In the steel to strictly limit the sulfur content. But the sulfur content of the steel; can constitute more MnS; In the cutting process; MnS can act as chip breaking; can improve the cutting of steel Workability; sulfur which is the positive side.
4. Phosphorus and phosphorus are brought into the steel by the pig iron; under normal conditions; the phosphorus in the steel can be completely dissolved in the ferrite. Phosphorus has a strong solid solution strengthening effect; the strength and hardness of the steel are added; but the plasticity and the resistance are obvious. Declining. This embrittlement appearance is more severe at low temperatures; it is called cold brittleness. It is usually expected that the cold-brittle transition temperature is lower than the working temperature of the workpiece; avoiding cold and brittleness. Phosphorus is in the crystallization process; Segregation; causing high phosphorus content in local areas; leading to an increase in cold-brittle transition temperature; then cold and brittle. Cold brittleness is severely harmful to structural members operating in cold regions and other low temperature conditions; in addition; segregation of phosphorus It also makes the steel form a strip arrangement after hot rolling. Therefore, under normal conditions, phosphorus is also a harmful impurity. The phosphorus content should also be strictly controlled in the steel. However, when the phosphorus content is large, the brittleness is large; Steel and improved machinability in terms of machinability are advantageous.
5. Non-metallic inclusions in the steelmaking process; a small number of slag, refractory materials and reverberation products during exercise can enter the molten steel; constitute non-metallic inclusions such as oxides, sulfides, silicates, nitrides, etc. They will drop steel Mechanical function; especially the plasticity, resistance and fatigue limit. When severe, the steel will be cracked during hot working and heat treatment or it will be brittle when used. Non-metallic inclusions also promote the arrangement of steel and hot-worked fibers. Arrangement; make the data anisotropic. Severe; transverse plasticity is only half of the longitudinal direction; and the impact resistance is greatly reduced. Therefore; for important applications of steel (such as rolling bearing steel, spring steel, etc.) to see non-metal The number, shape, size and dispersion of inclusions. In addition; steel is touched with air throughout the exercise; therefore, some gases are absorbed in the molten steel; such as nitrogen, oxygen, hydrogen, etc. Will have adverse effects.
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Effect of common impurities on steel function
Source: China Bearing Network Time: 2017-12-22