The development process of heat treatment (1) clean heat treatment Heat treatment of wastewater, waste gas, waste production of salt, dust, noise and the electromagnetic radiation will cause pollution to the environment. To solve the pollution problems of heat treatment, clean heat treatment (or green heat treatment) is the direction of the development of heat treatment technology in developed countries. In order to reduce SO2, CO, CO2, dust and cinder emissions, has been basically put an end to the use of coal as fuel, the use of heavy oil is less, the majority of diesel oil, natural gas is still the most ideal fuel.
Combustion has reached a high degree of furnace waste heat utilization ratio, strict control ensures the premise of reasonable combustion combustion optimization and air burner structure, make NOX and CO decreased to the minimum; the use of gas carburizing, carbonitriding and vacuum heat treatment technology to replace the salt bath treatment to reduce the waste salt and water CN- toxic pollution of water sources; the synthesis of water-soluble quenching oil instead of part of quenching oil, using biodegradable vegetable oil instead of part of mineral oil to reduce oil pollution.
(2) precision heat treatment Precision heat treatment has two meanings: one is according to the requirements, parts of the use of materials, structure size, using the knowledge of physical metallurgy and advanced computer simulation and detection technology, optimization of process parameters, to achieve maximum performance or desired exerts the potential of materials; on the other hand is fully guarantee the stability of the optimization process product quality, implementation of the dispersion is very small (or zero) and heat treatment distortion is zero.
(3) energy saving heat treatment Scientific production and energy management is the most potential factor energy efficiency, the establishment of professional heat treatment plant in order to ensure the full load production, make full use of the equipment ability is the choice of scientific management. In the energy structure of heat treatment, give priority to primary energy; make full use of waste heat, waste heat; the technology of low energy consumption, short cycle instead of long cycle, high energy consumption of the process.
(4) less or non oxidation heat treatment By the use of protective atmosphere heating alternative oxidative atmosphere heating to precise control of carbon potential, potential of nitrogen controlled atmosphere heating parts, can improve the performance of heat treatment, heat treatment defects such as decarburization, crack greatly reduced after heat treatment, machining allowance to reduce, increase rate and machining efficiency of utilization of material. Heating in vacuum gas quenching, vacuum or low pressure carburizing, nitriding, nitrocarburizing and boronizing can significantly improve the quality, reduce the distortion, and increased life expectancy.
Effect of heat treatment technology (1) expand the application range of GCr15 steel, GCr15 steel M general quenching ring effective wall thickness below 12mm, but the BL quenching due to nitrate cooling ability, if the mixing, series, water and other measures, effective wall thickness of ring can be extended to about 28 mm. (2) stable hardness, good uniformity Because the BL change is a slow process, generally GCr15 to 4h steel, GCr18Mo steel 5h, ring isothermal long time in nitrate in surface, change heart tissue were almost at the same time, so the stable hardness, good uniformity, general BL GCr15 steel quenched hardness uniformity in 59~61HRC, ≤ 1 HRC, not like quenching when the ring wall thickness slightly larger problems of low hardness, soft point, poor uniformity. (3) reduce the quenching, grinding cracks In the production of railway, rolling mill bearing ferrule, because of large size, heavy weight, oil quenching M brittleness, in order to obtain high hardness after quenching often adopt strong cooling measures, resulting in the quenching crack quenching; while BL, because the BL tissue than M toughness is much better, while the surface form up to -400~-500MPa compressive stress, which greatly reduces the quenching cracking tendency; the grinding surface compressive stress to offset a portion of the grinding stress, so that the overall stress levels down, greatly reducing the grinding crack.
(4) to prolong the life of bearing To withstand the impact load of railway, rolling bearings, the M quenching when used after the main failure modes are: assembly sleeve cracking, affected by the impact of external flange off block, the inner ring fragmentation in the use process, and the isothermal quenching bearing because of good toughness, surface stress, not on the assembly sleeve cracking in the process of using, or outer flange off block, the inner sleeve fracture tendency is greatly reduced, and can reduce the roller edge stress concentration. Therefore, isothermal quenching ratio increase the average life and reliability of M after quenching.