1 Take reasonable heat treatment
1.1 quenching treatment
After the liner is cast, it is quenched. The heating furnace is heated to above 500 ° C, the liner is placed in the furnace, and when heated to 650-680 ° C, the liner is kept warm, and the holding time is as long as possible. Studies have shown that high manganese steel at 650 ~ 680 ° C temperature, the longer the holding time, the more the brittle phase dissolves, not only can reduce the occurrence of casting cracks, but also reduce the brittle phase, reduce the internal and external temperature difference, reduce thermal stress and tissue stress , thereby reducing the tendency of casting cracks and improving the plasticity of the lining.
After the completion of the heat preservation, the temperature is raised to a quenching temperature of 1060 to 1090 ° C at a heating rate of 250 to 400 ° C / h, and the temperature is maintained for 2.5 to 3 hours. The purpose of quenching is to eliminate carbides in the as-cast microstructure and to obtain a single austenitic structure. The presence of carbides in high manganese steel reduces the strength of the liner and causes the liner to become brittle, causing the liner to crack. However, the holding time cannot be long. Castings are prone to decarburization, demanganization and oxidation at high temperatures for a long period of time, forming martensite structure and increasing the sensitivity of cracks.
1.2 aging treatment
After the quenched liner is heated to 300-350 ° C, it is kept for 6-8 h, and then cooled with the furnace. After such treatment, the high plasticity resistance of the high manganese steel can be enhanced, and the erosion wear resistance and fracture resistance can be improved.
2 pay attention to the details of the installation
2.1 The gap between the linings should be secure
During the installation process, the mill liners often have gaps between each other. The presence of the gaps may cause the liners to oscillate, cut the bolts, or damage the liner. Therefore, the steel plate of 16Mn material can be used for plugging and welding. The thickness of the steel plate can be determined according to the size of the gap between the lining plates, and then the steel plate is processed by machining means.
2.2 Oxygen-acetylene flame cutting liner should not be used during installation
The lining plate may have an improper size of the lining during installation, and the acetylene flame cutter may not be used for cutting. Because the liner is cut with an oxygen-acetylene flame cutter, the temperature of the cutting portion will reach about 400 ° C. This temperature is equivalent to tempering the liner. During the subsequent cooling process, carbides are deposited along the crystal lattice. The crystal grain size of the grain boundary is coarse, and at the same time, the liner has a large brittleness, and the fracture phenomenon is likely to occur during use.
Our approach is: grinding the poorly lining plate for grinding; for larger linings, can not be used, can replace the smaller lining, and then use the sew method to solve.
3 Improve the liner
3.1 Adding Cr and Mo elements to high manganese steel
We have improved the lining material, added some elements such as cr and Mo to the high manganese steel, and adopted low temperature insulation and high temperature quenching heat treatment method. The experimental result is to improve the wear resistance by about 30%. Practice has proved that the chrome-plated high-manganese steel liner formed by microalloying is superior to pure high-manganese steel in strength and toughness under the condition that the carbide is completely dissolved, especially the yield limit is more obvious, and it is preventive lining. The main method of plate fracture.
3.2 lining thickness increase
In the production, we found that the wearer end liner wear is more serious. In order to realize the synchronous replacement of several liners, the replacement frequency and the number of mill stops are effectively reduced, and the thickness of the end liner is thickened under the condition that the simplified liner is unchanged. From the analysis of the wear state, the center of the end lining plate is seriously worn, and the edge portion is worn lightly, so we design the end lining plate to have a slanted shape in the thickness direction, the edge is thin, and the center is thick. This design achieves wear effects such as various linings.