Practice of using lost foam casting to produce high manganese steel lining plates for crushers

Crushers are widely used in industries such as mining, metallurgy, machinery, coal, building materials, and chemical engineering. The lining plate is an important wear-resistant part of the crusher, which mainly bears impact force and wear during service. Its performance and service life directly affect the crushing efficiency, service life, and production cost of the crusher. Wear resistance and impact resistance are the main technical and economic indicators for measuring the lining plate. High manganese steel is commonly used in the production of crusher liners. High manganese steel castings undergo work hardening when subjected to strong impact or extrusion forces, greatly increasing their hardness, forming a hard surface and high toughness interior, producing a wear-resistant surface layer, and maintaining excellent impact toughness. They can withstand large impact loads without damage and have good wear resistance. Therefore, they are often used in the manufacture of wear-resistant parts.    

However, high manganese steel cannot exert work hardening performance under non strong impact load conditions, resulting in excess toughness but insufficient strength, and mechanical properties and wear resistance cannot meet the requirements. Therefore, targeted optimization of alloy chemical composition design and heat treatment are needed to achieve the desired performance. This study investigated the chemical composition, melting, casting, and heat treatment of high manganese steel alloys to produce high-quality high manganese steel liners, while ensuring high hardness and toughness, and improving the wear resistance of crusher liners.

Alloying and modification treatment are one of the main methods to improve the wear resistance of high manganese steel. By adding alloying elements such as Cr, Si, Mo, V, Ti to high manganese steel and modifying it, dispersed carbide particles can be obtained on its austenite matrix to improve the wear resistance of the material. The formation of carbide particles with a second phase strengthening mechanism through alloying and the use of alloying elements to strengthen the austenite matrix to enhance its deformation hardening ability are effective ways to improve the wear resistance of high manganese steel. The reasonable combination of Mn, Cr, and Si in high manganese steel lining plate improves the hardenability of the material, reduces the transformation temperature of martensite, and refines the grain size. In addition, adding a small amount of Mo, Cu, and rare earth elements for microalloying and composite modification treatment purified the molten steel, effectively refined the as cast structure, and dispersed carbides in the matrix.

The melting of high manganese steel is carried out in an alkaline medium frequency induction furnace. During the melting process, stirring of the molten metal should be avoided as much as possible to reduce the oxidation of the furnace charge. The smelting process includes stages such as melting period, steel alloying and composition adjustment, final deoxidation, and deterioration treatment. The material blocks added in the later stage of smelting should not be too large and should be dried to a certain temperature. The feeding sequence is: scrap steel, pig iron → nickel plate, chromium iron, molybdenum iron → silicon iron, manganese iron → rare earth silicon iron → aluminum deoxidation → modification treatment. The thermal conductivity of high manganese steel alloy in casting process is only 1/5-1/4 of that of carbon steel, with poor thermal conductivity, slow solidification, and large shrinkage. It is prone to hot cracking and cold cracking during casting. The free shrinkage is 2.4% -3.6%, with a larger linear shrinkage and a higher solidification shrinkage rate than carbon steel. It has a greater sensitivity to cracking and is prone to cracking during casting solidification. Lost foam casting is selected, foam models are bonded to form model clusters, refractory materials are brushed and dried, sand is buried and vibrated, and poured under negative pressure. Generally, internal cooling iron is not provided, and external cooling iron is used at the hot junction to facilitate simultaneous or sequential solidification of the metal. The pouring system is designed as a semi closed type, with the transverse runner located on the longest side of the upper box casting. Multiple internal runners are set up in the lower box, evenly distributed in a flat trumpet shape. The cross-sectional shape is designed to be thin and wide enough to facilitate breaking but not hinder shrinkage. Place the sand box at a 5-10 ° angle to the ground during pouring. For the convenience of cleaning the riser, insulation risers with cutting blades are used. High manganese steel has good fluidity and strong filling ability when poured at a temperature of 1500-1540 ℃. During pouring, follow the principle of low-temperature rapid pouring and use a slow, fast, and slow operation method. The casting is cooled in the box for 8-16 hours, and the box is opened when the temperature drops below 200 ℃. The heat treatment process adopts a "quenching+tempering" heat treatment process based on the chemical composition, as cast microstructure, performance requirements, and operating conditions of the lining plate. After repeated experiments, the optimal heat treatment process was obtained: slowly raise the temperature at a rate of ≤ 100 ℃/h; Keep at around 700 ℃ for 1-1.5 hours, and maintain at 30-50 ℃ above Ac3 for 2-4 hours; Quenching under forced air cooling conditions, slowly cooling to below 150 ℃ when the temperature drops to about 400 ℃; Timely temper, keep at 250-400 ℃ for 2-4 hours, and cool in the furnace to room temperature. Strict control of quenching temperature, holding time, and cooling rate is required during operation, especially the holding time of the lower bainite transformation zone temperature.