I. Introduction <br> According to statistics, China's annual consumption of wear-resistant metal material above about 300 tons, of which only consumes lining metallurgical and mining amounted to 10 million tons. At present, China and other types of mining beneficiation mill mountain mill and other processing equipment used in the lining of wearing parts are generally used ZGMn 13 high-manganese steel. Such consumables are subject to certain impact and abrasive wear during use, so the material should have good anti-wear properties and certain impact toughness. ZGMn13 austenitic high manganese steel has high impact toughness (ak up to 200J/cm 2 ), and the original hardness does not exceed HB230. However, under high impact load, the working surface layer can produce hardening effect, and its surface hardness can reach HRC42. -48, while the center still maintains excellent toughness. However, if the impact energy is insufficient during service, the surface impact hardening effect of austenitic high manganese steel cannot be fully produced. If the surface of high manganese steel does not reach high hardness, the workpiece will wear quickly. At the same time, the yield limit of high manganese steel (δ0.2) ) is low (about 350Mpa or so), and it is prone to plastic deformation during use, especially in the early stage. There is also the grinding media and the liner between the ball (e.g., ball) matching a hardness, the hardness of the grinding media generally should be higher than the hardness should be about HRC3 plate, but many factories use low-chromium cast iron, high chromium cast iron The hardness of the grinding ball is much higher than that of the high manganese steel plate. The above-mentioned shortcomings of high manganese steel under low impact load often lead to more toughness of the workpiece and insufficient wear resistance, fast wear failure, and severe deformation, resulting in short life of the workpiece. Entry Level Trombone,Plastic Trombone,Colorful Trombone,Trombone For Beginners ZhengOu Musical Instruments Co.,LTD , https://www.zomusical.com
The eutectic carbide of Cr>11% high-chromium white cast iron is hexagonal M7C3, and the hardness of (CrFe)7C3 is HRM501200-1800, which is eutectic carbide Fe 3 C 3 (HRV50840-1100) than ordinary white cast iron. High, while solidification (CrFe) 7C3 is an isolated phase, and austenite is a continuous phase, so the toughness is much better than ordinary white cast iron, so it is the material of choice for abrasive wear and cutting wear resistance. It is widely used in foreign countries, and is mainly used for large and medium-sized wear parts such as lining plates, hammer heads, grinding balls, and slurry pump over-current parts in medium and low impact load conditions. A series of studies on the wear mechanism, fracture mechanism, fracture toughness (K1c value) and crack propagation mechanism of high chromium cast iron have been carried out at home and abroad. The results show that the high chromium cast iron can adjust the size and shape of the carbide, the amount of secondary carbide and Dispersion and matrix structure (martens, austenite, sorbite) to adjust performance and meet working requirements. In recent years, domestic related units have also carried out research on high-chromium cast iron linings, and their wear resistance can reach more than twice that of high-manganese steel under the same working conditions. However, the toughness of these materials is still low (10×10×55mm unnotched specimen impact value ≤7.3J/cm 2 ) and contains alloying elements such as molybdenum and copper , and the production cost is high. Therefore, this type of high chromium cast iron still needs further improvement and improvement.
Second, the composition design of high chromium cast iron 1. The main role of carbon and chromium carbon and chromium is to ensure the amount and shape of carbide in cast iron. As the amount of C increases, the number of carbides increases. With the increase of Cr/C ratio, the morphology of eutectic carbides undergoes a process of continuous network-like→sheet-like continuous reduction of eutectic carbide crystals. The type undergoes a process of change from M 3 C→M 3 C+M 7 C 3 →M 7 C 3 . It is pointed out that when the eutectic carbide is unchanged and the Cr/C is 6.6~7.1, the same crack initiation ability of the same chrome cast iron is the strongest. According to these principles, the amount of C should be set to 3.1 to 3.6%, and the amount of Cr should be 20 to 25%. Cr in the matrix also increases the hardenability of the material.
2. The role of nickel is to increase the hardenability of high chromium cast iron, inhibit the transformation of austenite matrix to pearlite, and promote the formation of martensite.
3. The role of tungsten is to refine grains, increase hardness, and increase wear resistance.
4. The high-efficiency rare earth composite modifier has the functions of deoxidation and desulfurization, thereby suppressing the segregation of inclusions at the grain boundary and improving the grain boundary condition; in addition, carbonization is caused by the segregation of rare earth elements and adsorption in the direction of preferred growth of carbides. The growth of the object is suppressed, so that it becomes uniform and isolated, and other metamorphic elements can form dispersed carbon and nitrogen compounds, preventing grain growth and refining the grains. The above effects of the rare earth composite modifier not only improve the microstructure of the material, but also significantly improve the hardness of the material, particularly the impact toughness. The addition amount of the high-efficiency rare earth composite modifier is preferably 0.2 to 0.5%. [next]
 Third, the organization and performance of high chromium cast iron 1. As-cast microstructure: Sorbite + eutectic carbide and strip-shaped block-shaped carbide.
Hardness: HRC 48.6, 49.3, 46.0, 49.4, 51.7. Average hardness: HRC49.
2. Heat treated state
After heat treatment of "normalizing air cooling + tempering air cooling", the hardness is HRC60.5 on average, and the metallographic structure is martensite + eutectic carbide + strip-like block-shaped carbide.
Fourth, the lining castings trial production 1. Melting process smelting in 500kg acid medium frequency electric furnace
(1) Firstly add scrap steel and pig iron into the 500kg acid medium frequency electric furnace, and then add ferrochrome, tungsten iron and nickel to adjust the molten iron composition.
(2) Add ferromanganese and ferrosilicon in 5~10 minutes before tapping.
(3) adding 0.05% pure aluminum deoxidation iron before about 2 minutes.
(4) The temperature of molten iron is controlled at around 1460~1500 °C.
(5) Injecting 1.4kg high-efficiency rare earth composite modifier into the bag for inoculation.
(6) Sprinkle an appropriate amount of thermal insulation slag into the bag and calm it for about 5 minutes.
(7) The pouring temperature of molten iron is controlled at around 1360~1400 °C.
2. The molding core molding process uses organic ester water glass sand process ingredients: lower box sand and core sand: raw sand (40/70 mesh) 100% + water glass 5% (accounting for the original sand weight) + organic ester 12% (accounting for Water glass weight) + EZK type disintegrating agent 2.5% (accounting for the original sand weight).
Upper box sand: raw sand 100% + water glass 4.5% (accounting for the original sand weight) + organic ester 12% (accounting for water glass weight) without adding a broken agent.
Sand mixing process: mixing the original sand and crushing agent for 1 minute → adding organic ester for 2~3 minutes → adding water glass for 1~2 minutes → sanding sand can be used for 25~30 minutes.
Demoulding time: 0.5~1.5 hours.
The coating uses an alcohol-based zircon powder coating, which requires sufficient agitation, evenly brushing twice, taking up the fire and drying quickly. The riser adopts a floating bead insulation set. The cast surface of the trial production has good surface quality and no casting defects.
3. After the heat treatment process is cleaned, the heat treatment is performed. The heat treatment is carried out in a trolley type electric resistance furnace, and the heat treatment process is "normalizing air cooling + tempering air cooling". The hardness of the casting after heat treatment is HRC60.5 on average, and the impact toughness is as high as 8. J/cm 2 (10×10×55 mm unnotched specimen).
   V. Installation test The lining installation test of the trial production was carried out in a ф3.6×4m wet ball mill with a productivity of 115 T/h in Jinshandian Iron Mine of Wuhan Iron and Steel Co., Ltd. The iron ore hardness of the iron ore was F=7-8. The new high-chromium cast iron liner is installed at the same time as the high manganese steel (ZGMn13) liner. The test began on July 4, 2001, after using 5081 hours to treat 606,720 tons of iron, the quality of the new low-alloy steel liner and the high-manganese steel liner under the same working conditions were compared. It can be seen that the wear resistance of high chromium cast iron liner is 2.6 times that of high manganese steel (ZGMn13) liner.
The boot was checked and there was no crack in the liner. This shows that the toughness of this high chromium cast iron liner can meet the requirements of the mill.
VI. Conclusion <br>The new high-toughness and high-chromium cast iron liner (KmTBCr20NiWRe) does not contain expensive molybdenum and copper. It adopts the main effect rare earth composite modifier and more chromium suitable for China's resource characteristics, and its hardness reaches HRC60 or above. The impact toughness is more than 8J/cm 2 and the wear resistance is 2.6 times that of the ZGMn13 high manganese liner.