Cutting of high temperature alloy steel and stainless steel
There are some parts and components made of stainless steel and high-temperature alloy steel in coal mining machinery. These parts have certain difficulties in the processing process. Now we will discuss some issues.
1. Machinability of stainless steel
According to the metallographic structure, stainless steel is divided into three types: ferrite, martensite and austenite. The main component of ferritic and martensitic stainless steel is Cr, which is often used in the quenched, tempered or annealed state. The comprehensive mechanical properties are moderate, and the cutting process is generally not difficult. The composition of austenitic stainless steel is mainly Cr, Ni and other elements. After quenching, it has an austenitic structure with poor machinability, which is mainly manifested in:
The plasticity is large, the work hardening is very serious, and the built-up edge is prone to deteriorate the surface quality of the machined. The cutting force is about 25% higher than that of 45 steel. The degree of surface hardening and the depth of hardened layer are large. The thermal conductivity is small, only 1/3 of that of 45 steel, so it generates a lot of heat and is difficult to transmit, resulting in high cutting temperatures. The cutting temperature is high, the work hardening is serious, and the carbides in the steel form hard inclusions, and it is easy to cold weld with the tool, so the tool wears quickly.
2. Machinability of high temperature alloy steel
High-temperature alloy steel has three kinds of Fe-based, Ni-based, and Co-based according to its chemical composition, and contains many high melting point alloying elements, which form austenitic alloys with high purity and dense structure with other alloys. Some elements combine with non-metallic elements C, N, O, etc. to form high-hardness compounds with low specific gravity and high melting point. They can also form some tough and high-hardness intermetallic compounds. At the same time, some alloying elements enter the solid solution to strengthen the matrix. . After long-term aging, the superalloy can precipitate hard phases from the solid solution, further distorting the crystal lattice, which not only increases the plastic deformation resistance, but also increases the wear of the tool due to the existence of hard particles. The processing of high temperature alloy steel has the following characteristics:
High strength and strong resistance to plastic deformation, so the cutting force is great. The hardness is high, especially the high temperature hardness is higher than other metal materials, and it will be further hardened due to plastic deformation during processing. The thermal conductivity is small, only 1/3 to 1/4 of 45 steel. The high-hardness compounds in the alloy constitute hard points, which further aggravate tool wear. At medium and low cutting speeds, it is easy to cold weld with the tool. In the high temperature, the tool undergoes violent diffusion wear.
YT type cemented carbide tools are not suitable for processing austenitic stainless steel and high temperature alloy steel, because the Ti element in YT type cemented carbide is easy to interact with the Ti element in the workpiece material, resulting in cold welding, which is also aggravated at high temperatures In order to prevent diffusion wear, it is generally suitable to use YG, YH or YW cemented carbide. When processing austenitic stainless steel, a larger rake angle (generally g0=15-30°) and a medium cutting speed (v=50-80m/min) should be used. When processing high-temperature alloy steel, it is advisable to use a small rake angle (g0=0～10°) to increase the strength of the cutting edge and a low cutting speed (v=30～50m/min). Regardless of processing austenitic stainless steel or high-temperature alloy steel, the cutting depth and feed rate should be appropriately increased to avoid cutting edges and tool tips from scratching through the hardened layer. Extreme pressure cutting oil or extreme pressure emulsion should be used for the cutting fluid. It is widely used in the spring industry!