High manganese steel is an alloy steel containing more than 10% manganese. 1882 obtained high manganese steel with austenite structure for the first time, and 1883 British R.A.Hadfield obtained the patent of high manganese steel. High manganese steel can be divided into two types according to different uses: (1) wear-resistant steel. This steel contains manganese 10% ~ 15%, and the carbon content is relatively high, generally 0.90% ~ 1.50%, and most of them are above 1.0%. Its chemical composition is (%): c0.90 ~1.50mn10.0 ~15.0si0.30 ~1.05p ≤ 0.10. It is the most widely used high manganese steel and is often used in the production of high manganese steel. The as-cast structure of high manganese steel with the above composition is usually composed of austenite, carbide and pearlite, and sometimes contains a small amount of phosphorus crystals. When the amount of carbide is large, it often appears on the grain boundary in the form of a network. Therefore, high manganese steel with as-cast structure is brittle and cannot be used, so it needs solution treatment. The common heat treatment method is solution treatment, that is, the steel is heated to1050 ~1100℃, and the as-cast structure is eliminated by heat preservation to obtain single-phase austenite structure, and then quenched with water to keep this structure at room temperature. After heat treatment, the strength, plasticity and toughness of steel have been greatly improved, so this heat treatment method is often called water toughening treatment. The mechanical properties after heat treatment are σ B615 ~1275mpa σ 0.2340 ~ 470mpa ζ15% ~ 85% ψ15% ~ 45% akl96 ~ 294j/cm2 hb. When high manganese steel with austenite structure is subjected to impact load, the metal surface is plastically deformed. The result of deformation strengthening is that there is obvious work hardening phenomenon in the deformed layer, and the surface hardness is greatly improved. It can reach HB 300 ~ 400 under low impact load and HB 500 ~ 800 under high impact load. Under different impact loads, the depth of hardened layer can reach 10 ~ 20 mm, and the hardened layer has high hardness and can resist impact abrasive wear. High manganese steel has excellent wear resistance under the condition of strong impact abrasive wear, so it is often used to make wear-resistant parts in mining, building materials, thermal power and other mechanical equipment. Under the condition of low impact, because the work hardening effect is not obvious, high manganese steel can not give full play to the characteristics of the material. The brand and application range of high manganese steel commonly used in China are: ZGMN13-1(C1.10% ~1.50%), Using ZGMN13-2 (C1.00) ZGMN13-3 (C 0.90% ~1.30%), the manganese content of the above four steels is1/Kloc-0. In the process of cold deformation under impact load, steel is strengthened due to the large increase of dislocation density, dislocation transmission, dislocation plugging and the interaction between dislocation and solute atoms. This is an important reason for work hardening. Another important reason is that the stacking fault energy of high manganese austenite is low, which is easy to occur during deformation, thus creating conditions for the formation of ε martensite and deformation twins. In the deformation hardening layer of high manganese steel with conventional composition, high density dislocation, dislocation plugging and entanglement can often be seen. The appearance of ε martensite and deformation twins makes it difficult for steel to deform, especially the latter. All the above factors have greatly strengthened the hardened layer of high manganese steel and greatly improved its hardness. High manganese steel is very easy to work and harden, so it is difficult to work. Most of them are castings, and a few are forged. The castability of high manganese steel is better. The melting point of steel is low (about 14()()℃), the temperature range between liquid phase and solid phase of steel is small (about 50℃), the thermal conductivity of steel is low, and the molten steel has good fluidity and is easy to cast. The linear expansion coefficient of high manganese steel is 1.5 times that of pure iron and twice that of carbon steel, so the volume shrinkage and linear shrinkage are large during casting, and stress and cracks are easy to appear. In order to improve the properties of high manganese steel, many studies have been carried out in alloying, microalloying, carbon and manganese content adjustment and precipitation strengthening treatment, and they have been applied in production practice. The appearance of metastable austenitic manganese steel, compared with local high, can greatly reduce the content of carbon and manganese in steel and improve the deformation strengthening speed of steel, which is suitable for high, medium and low impact loads and is a new development of high manganese steel. (2) non-magnetic steel. The manganese content of this steel is more than 17%, and the carbon content is generally lower than 1.0%, which is often used to manufacture retaining rings in automobile industry. The density of this steel is 7.87 ~ 7.98g/cm3. Due to the high content of carbon and manganese, the thermal conductivity of steel is poor. The thermal conductivity is12.979 w/(m℃), which is about 1/3 of that of carbon steel. Because steel is austenitic and nonmagnetic, its magnetic permeability μ is 1.003 ~ 1.03 (h/m). [Edit this paragraph] Casting process of high manganese steel Under the condition of high energy impact, high manganese steel and ultra-high manganese steel castings have a wide range of applications. Many foundries lack the necessary knowledge about producing this kind of steel castings. The specific operation is briefly described for the reference of producers. High manganese steel with chemical composition of 1 is divided into five grades according to national standards, and the main difference is carbon content, ranging from 0.75%- 1.45%. Great influence and low carbon content. The manganese content is between11.0%-14.0%, and generally should not be lower than 13%. There is no national standard for ultra-high manganese steel, but the manganese content should be greater than 18%. Silicon content has a great influence on impact toughness, so the lower limit should be taken, and it is appropriate to not exceed 0.5%. Low phosphorus and sulfur is the most basic requirement. Because high manganese content naturally plays a role in desulfurization, reducing phosphorus is the most important thing, and try to reduce phosphorus below 0.07%. Chromium can improve the wear resistance, generally around 2.0%. The charge is determined by chemical composition. The main charges are high-quality carbon steel (or steel ingot), high-carbon ferromanganese, medium-carbon ferromanganese, high-carbon ferrochromium and high-manganese steel. It is especially reminded here that people think that as long as the chemical composition is suitable, more recycled materials can be used. This person is harmful. This is the reason for the poor quality of products in some factories. Not only high manganese steel and ultra-high manganese steel, but also all metal castings shall not use too much return charge, and the return charge shall not exceed 25%. Then, what should be done about the excess return fee? As long as waste products are minimized, there will be no surplus of recycled materials. 3 Melting What is emphasized here is the order of feeding. Whether smelting in intermediate frequency furnace or electric arc furnace, carbon steel is always smelted first, and various precious alloy materials such as ferromanganese are put into the furnace several times, and a small amount of precious elements are added at last to reduce the burning loss. The block should be as small as possible, preferably 50-80 mm After melting, when the furnace temperature reaches 1580- 1600℃, aluminum wire, calcium silicon alloy or SiC can be used for deoxidation, dehydrogenation and denitrification. The deoxidizer must be pressed deep into the furnace. At this time, the metal liquid level is tightly covered with covering agent to isolate the outside air. Calm down for a period of time, so that oxides and inclusions have enough time to float. But many enterprises just spread aluminum wires and even aluminium scrap on the metal surface without covering it, which is a waste! At the same time, the contents of manganese and carbon are adjusted in time with medium carbon ferromanganese. Before the molten steel is tapped, the ladle must be baked above 400℃. Modified with trace elements such as ferrovanadium, ferrotitanium and rare earth. It is a necessary means to refine primary crystallization, and its influence on product performance is very important. 4 burden and modeling materials should be expanded to distinguish the properties of steel and lining. Manganese steel is alkaline, and the furnace lining is of course magnesium oxide. Tamping furnace lining shall be carried out in turn, and transposition operation shall be repeated. The lining material should not be too thick, about 80 cm at a time, and it should be baked at low temperature for a long time after tamping. In order to improve the production efficiency, the author suggests to use the forming crucible (Shenyang Lide Factory and Hengfeng Factory both sell finished products), which can be put into production without 1 hour, and the forming crucible is of great benefit to prevent the furnace from penetrating. Of course, the length of furnace sequence is related to the operator. Many operators, like shot put, throw the burden into the furnace from three or four meters away, which is unsafe and detrimental to the furnace sequence. They want to preheat the furnace charge next to the furnace mouth, then slowly put it next to the furnace mouth with clips, and then slowly put it along the furnace wall with clips. Modeling materials and coatings should also conform to the properties of molten metal, or ZTE materials (such as chromite and brown corundum, etc. ) it should be used. If you want to obtain a refined aggregate, it is correct to use chromite with large heat storage capacity, especially in EPC foundry, which will overcome the shortcomings of slow heat dissipation. 5 Casting process design Manganese steel is characterized by large solidification shrinkage and poor heat dissipation. Accordingly, the shrinkage of castings in process design is 2.5%-2.7%, and the longer the casting growth time, the higher the upper limit should be. The concession between molding sand and sand core must be good. The gating system is on. A plurality of dispersed internal sprues are introduced from the thin wall of the casting, and they are flat and wide trumpet-shaped, and the cross-sectional area near the casting is larger than that associated with transverse sprues, so that molten metal can be injected into the mold quickly and smoothly, and the temperature difference in the whole mold can be prevented from being too large. The diameter of the riser is larger than that of the hot spot, close to the hot spot, and the height is 2.5-3.0 times of the diameter. It is necessary to use hot risers or even pouring risers to make enough high-temperature molten metal to make up for the vacancy of castings during solidification and shrinkage. Put the sprue and riser in a high place (there are 5-8 sand boxes. ) is also correct. When pouring, pour as soon as possible at low temperature. Once solidified, loosen the sand box in time. Smart designers are always good at using chilled iron, including inner chilled iron and outer chilled iron, which not only refines the primary crystal, eliminates shrinkage cavities and pores, but also improves the process yield. Of course, the appropriate dosage and specifications should be considered. The inner cooling iron should be clean and easy to melt, and the dosage should be less. The functional relationship between the three-dimensional size of the external cooling iron and the three-dimensional size of the cooled object is 0.6-0.7 times. Too small won't do, too big will cause the casting to crack. Castings should be placed in the mold for a long time until the temperature is lower than 200℃ before unpacking. 6 heat treatment heat treatment cracking is caused by excessive temperature rise in the low temperature stage. Therefore, the correct operation is below 350℃, the heating rate is 750℃, the casting is in a plastic state, and the temperature can be raised quickly. When the temperature reaches 1050℃, the holding time is determined according to the casting thickness, and then it is increased to above 1 100℃. Leave room for the furnace to cool down and enter the water as soon as possible. At high temperature, the temperature rise is too slow, the holding time is too short, and the time interval between discharging and water inflow is too long (should not be >: 0.5 minutes), which all affect the casting quality. Inlet water temperature should be
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