Increase of spring service life
For large shock load of the railway, mill spring, by M after quenching is used as the main failure form of the assembly sleeve cracking, by the impact of external flange block, inner ring fragmentation process, and isothermal quenching spring due to the impact toughness, surface compressive stress, the assembly sleeve cracking still, in the process of using coat rib block, inner sleeve fragmentation tendency is greatly reduced, which can reduce the roller edge stress concentration. Therefore, the average life and reliability of the quenching after austempering are higher than that of M quenching.
The manufacture of spring steel by root forming can be divided into two types: cold forming and thermoforming (also known as reinforced after forming and after forming).
1. Heat treatment of cold forming spring steel
The manufacturer of the compression spring tells you that for small springs, such as helical spring or spring steel strip with a diameter less than 8 mm, it can be formed after heat treatment or cold modification, that is, cold drawing and cold roll forming. The cold drawn steel wire has a high strength, which is obtained by using the cold drawn deformation of the steel to produce the hardened steel. The cold drawn spring steel wire can be divided into three kinds according to its strengthening process.
(1) the torsion spring manufacturers prompt you to lead patenting is the first cold drawn steel wire rod to a certain size, when heated to Ac3+80~100 after austenitizing, 450~550 in lead bath in isothermal quenching has been fine pearlite and then repeatedly drawn to the desired diameter. By adjusting the carbon content of steel and the cold drawn variable (the type variable can reach 85~90%), the high strength and certain plastic spring steel wire. The lead wire is actually a process of quenching deformation of heat treatment, that is to change the pearlite deformation, the strength of steel wire is about 3000MPa.
(2) cold drawn steel wire. This wire is mainly to strengthen through the cold deformation, but with lead quenching cold drawn steel wire, it is in the cold drawing process into the middle of a 680 degree between the spheroidizing annealing and improve the plasticity, the wire drawing continued to the final desired size, the intensity ratio of lead quenching low strength cold drawn steel wire.
(3) quenched and tempered steel wire: this kind of steel wire is cold drawn to the final size, and then quenched and tempered by medium temperature and tempered at the middle temperature, and finally formed by cold coil. The disadvantage of this kind of strengthening is that the process is more complex, and the strength of the steel wire is lower than that of the lead quenched and cold drawn steel wire.
The steel wire strengthened by the above three methods must add a low temperature tempering process after cold roll forming. The tempering temperature of the steel wire is 250~300 and the tempering time is 1 hours. The special-shaped spring manufacturers suggest that the purpose of low temperature tempering is to eliminate stress, stabilize the size, and improve the elastic limit. That has been hardening steel wire in cold roll forming after the elastic limit is not high in practice, this is because the cold roll forming is the change of wrong number, and because the Bauschinger effect caused by the initial plastic deformation resistance decreased. Therefore, the cold coil must be tempered at a low temperature after the cold roll forming, which has resulted in the multi change process and the increase of the elastic limit.
Two. Heat treatment of thermoforming spring
The tensile spring prompts you to hot forming spring is generally the quenching and thermal forming together, which is slightly higher than the heating temperature of quenching temperature, heating coil after molding, and then use the residual heat quenching, the tempering of 350~450, so as to obtain troostite tissue. This is a kind of deformation heat treatment process, which can effectively improve the elastic limit and fatigue life. In general, this method is used for large plate springs on the car. The neutral spiral spring can also be formed under cold and then quenched and tempered.
Dongguan precision spring factory indicates that you should pay three points at the cost of spring heat treatment in order to give full play to the performance potential of spring steel.
(1) the spring steel is mostly silicon manganese steel, and silicon can promote the decarburization, and manganese can promote the grain growth. The fatigue strength of the surface decarburization and grain growth is greatly reduced, so the heating temperature, the heating time and the heating medium should be selected and controlled. Such as the rapid heating of the salt furnace and the heating under the condition of protective atmosphere. After quenching, it should be tempered as soon as possible in order to prevent the delayed fracture.
(2) the tempering temperature is generally 350~450 degrees. If the surface condition of steel is good (such as grinding), tempering with low limit temperature should be chosen. Otherwise, the upper limit temperature can be tempered, so as to improve the toughness and reduce the sensitivity of surface defects.
(3) the silicon content of spring steel is high, and the steel is easily graphitized during the process of retreating, which must be paid attention to. The content of graphite is required to be checked when the general steel enters the factory.