Improve the pre-heat treatment process
Quenching process improvement
Due to the influence of the spring support distortion snares on subsequent welding, it must be kept in nitrate salt at 160℃ for 3-5 minutes, and then air-cooled graded quenching process. The stress and distortion after quenching are small, and the hardness is 58-60HRC.
After oil quenching, the surface of the spring support appears salty, which is not easy to clean, and is easy to rust in long-term storage. It is not easy to weld during the next process of spot welding. To solve this problem, the workpiece is quenched and tempered before the next use of spot welding , Perform sand blast cleaning on the principal support, make the surface of the part clean, easy to spot welding, and meet the technical requirements of the workpiece.
The production and development status of this material at home and abroad
Through experiments, the 65mn steel circular saw blade is pre-carburized with the teeth to increase the carbon and nitrogen content, and then subjected to conventional heat treatment to improve the tempering stability of the teeth, thereby increasing the hardness and wear resistance of the teeth. Improve the service life of circular saw blades.
65mn steel circular saw blades are widely used in metallurgy, steel rolling, machinery, building materials and other industrial fields for high-speed cutting of various types of steel, steel pipes and steel bars. A carbonitriding method is carried out in advance through the teeth to achieve the purpose of improving the service life of the saw blade.
After the 65Mn saw blade has just been pre-infiltrated, a continuous hypereutectoid layer with a depth of about 0.7-1.0mm is formed along the tooth row, and the outermost layer is a white ribbon carbonitriding layer with a thickness of 5-10um. The inner side contains a large amount of granular carbonitride layer. After quenching and tempering, the metallographic structure of the tooth is uniform tempered troostite and a large number of dispersed granular carbonitrides, while the base structure is only tempered troostite .
65Mn steel is a medium carbon steel, and its tempering stability is poor. In order to meet the strength and toughness of the saw blade substrate, the hardness of the saw blade will be significantly reduced from HRC60 above to HRC44-50 after the implementation of medium temperature tempering (300-400℃). Before quenching, pre-carbonitriding treatment on the teeth of the saw blade can make the teeth enter the surface to obtain eutectoid carbon and a certain number of nitrogen atoms. After quenching, a large number of dispersed particles will be formed. Carbon and nitrogen compounds, and at the same time, a large amount of carbon and nitrogen elements dissolved in the matrix will significantly reduce the martensite transformation point of the steel, thereby obtaining more retained austenite. Such a structure is then tempered at medium temperature and exists in large amounts. The carbonitrides can hinder the decomposition of martensite and the accumulation of precipitated carbides. At the same time, due to the catalysis of carbon and nitrogen atoms, more retained austenite has the ability to further transform into secondary martensite. Therefore, the pre-infiltration treatment significantly improves the tempering stability of 65Mn steel, that is, at the same tempering temperature, the 65Mn steel circular saw blade with pre-infiltration treatment can maintain a higher tempering hardness than the non-pre-infiltration saw blade. Improve the wear resistance of the teeth.
In a domestic steel pipe factory, a batch cutting of cold drawn seamless steel pipes was carried out on the machine. The cut steel pipes were smooth and free of burrs and deformation. The statistical results proved that the average service life of the pre-permeated saw blades was significantly higher than that of the conventional heat treated saw blades. .
The 65Mn steel circular saw blade is pre-carbonitrided before quenching, which can significantly improve its tempering stability. The teeth of the saw blade after medium temperature tempering can obtain a large amount of granular carbonitride and uniform tempered troostite Its hardness is HRC5～8 higher than that of conventional heat-treated saw blades, and its wear resistance is doubled, while maintaining the strength and toughness of the matrix. The experimental production and application prove that the pre-infiltration treatment can effectively increase the service life of the 65Mn steel circular saw blade.
Market development prospects of this material
65Mn is one of the materials for making various leaf springs and wire springs. It is used in vehicles, trams, trains and other transportation vehicles. It is also widely used in the manufacture of meters, furniture, and children’s toys. This kind of steel has very good fatigue strength, excellent elasticity, and quite good plasticity and hardness. Because of the low price of this steel, the future of this material is bright, and it will be widely used now and in the future.
The surface treatment of 65Mn can be shot peening treatment, which is a work hardening treatment, thereby improving the strength and corrosion resistance. This work hardening can cause residual compressive stress, which can not only prevent stress corrosion cracking SCC , And it can also improve the fatigue strength. If the vortex jet is used, the same effect can be obtained, because the vortex impact around the vortex jet can strengthen the material, and the fatigue strength can also be improved. The vortex jet causes the residual compressive stress on the surface of the material to strengthen For metallic materials, this is better than shot peening. Therefore, both methods can improve the strength and corrosion resistance.
The surface quality of the spring has a great influence on the service life, and decarburization can cause stress concentration and reduce the fatigue strength of the spring. For decarburization, controlled atmosphere heat treatment or vacuum heat treatment can be used to prevent decarburization.