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Crusher parts manufacturer and solution service provider since 1985.
The Influence of Chemical Composition on the Microstructure and Performance of High Manganese Steel.
The chemical composition of high manganese steel affects its microstructure and mechanical properties when it is different. In the following, we will specifically introduce the basic composition and the influence of certain alloying elements on the microstructure and performance of high manganese steel.
1. Influence of Basic Composition on the Microstructure and Performance of High Manganese Steel.
1.1 Carbon
1.2 Manganese
1.3 Silicon
1.4 Sulfur
1.5 Phosphorus
1.1 Carbon
Carbon is one of the main elements constituting high manganese steel. Carbon can stabilize austenite in the alloy. When rapidly cooled, carbon can maintain austenite as a single-phase structure at room temperature. Increasing the carbon content enhances the solid solution strengthening effect of carbon, thereby improving the hardness, strength, and wear resistance of high manganese steel. If the carbon content continues to increase, the amount of carbides in the cast structure of high manganese steel will increase, and most of the carbides can be dissolved into austenite. However, due to the difference in molar volume between carbides and austenite, there will be very small void defects in the solid-solution treated high manganese steel, which leads to a decrease in density and has a certain impact on the performance of high manganese steel. If water toughened, the remaining carbides in the austenite of high manganese steel will be more, and these carbides may distribute along the grain boundaries, greatly reducing the toughness of high manganese steel.
1.2 Manganese
Manganese is the main component of high manganese steel. It has a significant impact on the expansion of the γ phase range, the stability of the austenite structure, and the reduction of the Ms point. Manganese can keep the austenite structure of high manganese steel stable at room temperature. In addition to being dissolved in austenite, manganese also exists in (Mn, Fe)C type carbides. If the manganese content increases, the strength and impact toughness of high manganese steel will be improved because manganese has the effect of increasing intergranular binding force. If the manganese content is too high, it will cause a decrease in thermal conductivity of the steel and the occurrence of transgranular structure, severely affecting the mechanical and mechanical properties of high manganese steel, etc. To obtain ideal mechanical properties, when the carbon content is in the range of 0.9% to 1.5%, we usually control the manganese content within the range of 11% to 14%. The manganese content is mostly determined by the casting structure and working conditions of the casting. For large sections and complex structures, the manganese content should be relatively higher, and if the casting is used for intense impact, the manganese content should also be higher.
1.3 Silicon
Silicon is usually introduced as a deoxidizer, and it has the effect of strengthening the solid solution and increasing the yield strength. However, it closes the γ phase range and promotes graphitization. When the silicon content exceeds 0.6%, it will lead to the production of coarse grains in high manganese steel and reduce the solubility of carbon in austenite, which promotes the precipitation of carbides in the grain boundaries. This not only reduces the wear resistance and toughness of the steel but also increases the tendency of thermal cracking. Therefore, we usually control the silicon content within the range of 0.3% to 0.6%. However, in certain special cases, such as when good flowability of molten steel is required, we should increase the silicon content to improve the condition of the grain boundaries.
1.4 Sulfur
In high manganese steel, due to the presence of sulfur with manganese, manganese sulfide is formed, and manganese sulfide can enter the slag. In production, if sulfur is less than 0.02%, it can fully meet the standard requirements.
1.5 Phosphorus
Phosphorus has very low solubility in austenite and usually forms eutectic phosphides with iron and manganese, which precipitate in the grain boundaries. Phosphorus and the formation of phosphides easily cause thermal cracking of castings, reduce the mechanical properties of castings, and damage the wear resistance. In severe cases, fractures may occur during work. For example, if high manganese steel with a phosphorus content of 0.12% is used to make the lining plate of a cone crusher, its service life is often only half of that of high manganese steel with a phosphorus content of 0.038%. In addition, phosphorus promotes the segregation of manganese and carbon elements, so the phosphorus content should be minimized. We usually control the phosphorus content within the range of ≤0.07% to 0.09%, and for some important parts, it should be controlled within P < 0.06%.
2. Influence of Alloying Elements on the Microstructure and Performance of High Manganese Steel
2.1 Chromium
2.2 Molybdenum
2.1 Chromium
Chromium is currently used more in high manganese steel. After water toughening, most of the chromium will dissolve into the austenite of high manganese steel, improving the stability of high manganese steel and accelerating the precipitation of carbides during cooling. After solid-solution, chromium can improve the yield strength of the steel, reduce the elongation and impact toughness of the steel. If chromium is increased during casting, the precipitation of carbides will also accelerate, and usually, a continuous network distribution will occur at the grain boundaries. When reheating, it is relatively difficult for chromium to dissolve into austenite, so it is not easy to obtain a single-phase austenite. In this case, the heating temperature of water toughening should be increased by 30℃ to 50°C based on standard high manganese steel. High manganese steel with added chromium has improved wear resistance when facing strong impact wear, so it can be used for lining walls, hammer heads, bucket teeth, etc. However, it does not significantly improve the wear resistance when facing non-strong impact abrasive wear.
2.2 Molybdenum
Molybdenum is widely used internationally and has gradually been adopted in China. Molybdenum has a strong bond with iron, and the size and diffusion rate of aluminum atoms are small. When it is solidified in cast high manganese steel with added molybdenum, the precipitation of carbides will be reduced, and the network-like distribution on the grain boundaries will no longer appear. Molybdenum can also slow down the precipitation rate of needle-like carbides in steel and lower their precipitation temperature. All of these are beneficial for improving the plasticity and strength of high manganese steel in the cast state and can effectively compensate for the shortcomings caused by the addition of chromium. Therefore, it is very beneficial to add molybdenum to high manganese steel with added chromium.
After water toughening, molybdenum will solid-solution in the austenite, delaying the decomposition of austenite, and can also be precipitated by precipitation strengthening to promote the precipitation of dispersed carbides in the austenite, thereby improving the wear resistance of high manganese steel.
Conclusion
Finally, we introduce the influence of several other alloying elements on the microstructure and performance of high manganese steel. First is vanadium, which has the effect of refining the microstructure of high manganese steel, improving the yield strength, original hardness, and wear resistance of the steel. Second is titanium, which can eliminate columnar crystals in high manganese steel and has a good effect on improving the wear resistance and mechanical properties of the steel. Lastly, rare earth elements have the function of purifying molten steel, reducing the quantity and size of inclusions, refining the cast structure, reducing columnar crystals, improving the fluidity of molten steel, reducing the tendency of cold cracking and thermal cracking of the steel, improving the work hardening capacity of the steel, and improving the process performance of high manganese steel.
Crusher parts manufacturer and solution service provider since 1985.
