The heat treatment of high manganese steel castings is usually called water toughening treatment. In order to obtain high toughness, it must be water toughened to eliminate carbides in the structure. The carbon content in high manganese steel is generally about 13%, and the carbonization inside must be removed. It is necessary to heat high manganese steel to above 1000 degrees and then continue for a period of time to dissolve the carbides.
(1)Water toughness temperature
The water toughening temperature depends on the composition of high manganese steel, usually 1050~1100℃. The upper limit of water toughening temperature should be taken for high manganese steel with high carbon content or high alloy content, such as ZGMnl3 steel and GXl20Mnl7 steel. However, excessively high water toughening temperature will cause severe decarburization of the casting surface and cause the grains of high manganese steel to grow rapidly, affecting the performance of high manganese steel.
(2) Heating rate
High manganese steel has poorer thermal conductivity than ordinary carbon steel. High manganese steel castings have greater stress and are prone to cracking when heated. Therefore, the heating rate should be determined according to the wall thickness and shape of the casting. Generally, thin-walled simple castings can be heated at a faster rate; thick-walled castings should be heated slowly. In order to reduce the deformation or cracking of castings during the heating process, a process of preheating at around 650°C is often used in production to reduce the temperature difference between the inside and outside of thick-walled castings, make the temperature in the furnace uniform, and then quickly raise it to the water toughening temperature.
(3) Holding time
The holding time mainly depends on the wall thickness of the casting to ensure complete dissolution of carbides and homogenization of austenite in the cast structure. Usually the heat preservation time can be calculated based on the casting wall thickness of 25mm for 1 hour of heat preservation.
(4) Cooling time
The cooling process has a great influence on the specified performance indicators and organizational state of castings. During the water toughening treatment, the temperature of the casting before entering the water should be 950 degrees. Therefore, the time from the casting to the water entry should not exceed 2 minutes. The water temperature should be kept below 40 degrees. After the water toughening treatment, the casting can be tempered appropriately according to the requirements and complexity of the casting. , but the tempering temperature should not exceed 250 degrees.
Multipurpose trolley-type heat treatment furnace for toughening treatment of high manganese molten steel. When castings enter water, automatic tipping or hanging basket lifting quenching methods are commonly used. The former can easily cause deformation of large parts and thin-walled parts with complex shapes, and it is also difficult to take out the castings from the pool after quenching; the latter is easy to take out the castings after quenching, but the hanging basket consumes a lot of money.
