1. machinability of high manganese steel
1, Severe work hardening: During the cutting process of high manganese steel, due to large plastic deformation, the austenite structure is transformed into fine-grained martensite structure, resulting in serious hardening phenomenon. The hardness before processing is generally HB 200 ~ 220, the surface hardness after processing can reach HB 450 ~ 550, and the depth of hardened layer is 0. 1 ~ 0.3 mm, which is several times higher than that of 45 steel. Severe work hardening will increase cutting force, aggravate tool wear, and easily lead to the collapse and damage of tool edge.
2. High cutting temperature: Due to the high cutting power, much heat is generated, and the thermal conductivity of high manganese steel is lower than that of stainless steel, which is only 1/4 of medium carbon steel, so the cutting zone temperature is very high. When the cutting speed VC
3, chip breaking is difficult: the toughness of high manganese steel is 8 times that of 45 steel, and the chip is not easy to warp and break during cutting.
4. The dimensional accuracy is not easy to control: the linear expansion coefficient of high manganese steel is similar to that of brass, and local thermal deformation will occur at higher cutting temperature, so the dimensional accuracy is not easy to control. When cutting high manganese steel, rough machining should be carried out first, and then finish machining should be carried out after the workpiece is cooled to ensure the dimensional accuracy of the workpiece.
Second, the characteristics of various tool materials when cutting high manganese steel
High manganese steel is a kind of difficult-to-machine material, which requires high cutting tool materials. Generally speaking, materials are required to have high red hardness, good wear resistance, high strength, toughness and thermal conductivity.
1, high-speed steel is a kind of high-alloy tool steel, which can withstand the cutting temperature of 500~600C C. At present, it is basically incompetent to process high manganese steel, and it is generally used to make non-standard bits.
2. When machining high manganese steel with cemented carbide tool, it is generally used for machining small parts (CBN tool brand with nonmetallic binder is more suitable for large high manganese steel parts). According to statistics, when the processing time of high manganese steel parts is less than 5 minutes, cemented carbide tools can be selected, YG series brands with good impact toughness can be used for rough machining, and YW series can be used for finishing.
3. Characteristics of ceramic materials: high hardness (9 1~94HRA), good wear resistance and high heat resistance (>; 1200), allowing a higher cutting speed, but it is fragile and easy to collapse when cutting.
4. Characteristics of cubic boron nitride (CBN) material: high hardness (7300~9000HV), high heat resistance (1300~ 1500 degrees), good wear resistance, higher chemical stability than diamond, low affinity with iron group metals, good cutting performance and high brittleness. At this time, CBN tools with excellent impact toughness can be selected. Because this nonmetallic bond CBN tool has excellent toughness and wear resistance, it can be competent for rough machining and finish machining of high manganese steel.