The quality of heat treatment is directly related to the quality of subsequent processing, which ultimately affects the performance and life of the parts.The heat treatment quality control of bearing parts is the most strict in the whole mechanical industry.Bearing heat treatment has made great progress in the past 20 years.Research on heat treatment technology and application technology;Development of new heat treatment equipment and related technologies....
The development of heat treatment
(1) Cleaning heat treatment
The waste water, waste gas, waste salt, dust, noise and electromagnetic radiation produced by heat treatment will pollute the environment.It is one of the developing directions of heat treatment technology in developed countries to solve the environmental pollution problem of heat treatment and implement clean heat treatment (or green heat treatment).For reducing SO2, CO, CO2 emissions, dust and coal cinder, have put an end to coal as fuel, fewer and fewer in the use of heavy oil, diesel oil in the majority of natural gas is still the most ideal fuel.The waste heat utilization of the combustion furnace has reached a high degree, and the optimization of burner structure and strict control of air-fuel ratio ensure reasonable combustion, so as to reduce NOX and CO to the minimum.The use of gas carburizing, carbon and nitrogen co-carburizing and vacuum heat treatment technology instead of salt bath treatment to reduce the pollution of waste salt and cn-containing toxic substances to water sources;Water soluble synthetic quenching oil was used instead of some quenching oil, and biodegradable vegetable oil was used instead of some mineral oil to reduce oil pollution.
(2) Precision heat treatment
Precision heat treatment have two meanings: on the one hand, is based on the use requirements of the parts, material, structure, size and the use of physical metallurgy knowledge and advanced computer simulation and testing technology, optimization of process parameters, to achieve the required performance or maximize the potential of materials;On the other hand, the stability of the optimized process is fully guaranteed, and the product quality dispersion is small (or zero) and the heat treatment distortion is zero.
(3) Energy-saving heat treatment
Scientific production and energy management are the most potential factors for energy efficient utilization. It is the choice of scientific management to establish a professional heat treatment plant to ensure full capacity production and give full play to equipment capacity.In heat treatment energy structure, primary energy is preferred.Make full use of waste heat and waste heat;The technology with low energy consumption and short cycle is adopted to replace the technology with long cycle and high energy consumption.
(4) Less non-oxidation heat treatment
By adopting protective atmosphere heating instead of oxidizing atmosphere heating to the precise control of carbon potential, nitrogen potential controlled atmosphere heating, parts performance was improved after heat treatment, heat treatment defects such as decarburization and cracks decrease greatly, finish machining allowance reduced after heat treatment, improve the utilization rate of material and machining efficiency.Vacuum heating quenching, vacuum or low pressure carburizing, nitriding, nitrogen carburizing and boronizing can improve quality, reduce distortion and improve life.
Application effect of heat treatment technology
(1) Expanded the application scope of GCr15 steel
M generally GCr15 steel quenching ring effective wall thickness under 12 mm, but the BL quenching by nitrate cooling ability is strong, if use the measures, such as stirring, string move, add water ring effective wall thickness can be expanded to about 28 mm.
(2) Stable hardness and good uniformity
The BL change is a slow process, generally GCr15 steel 4 h, GCr18Mo steel need 5 h, ring in long isothermal nitrate, on the surface of the core organization transformation almost simultaneously, so the hardness of stability, uniformity, good general BL GCr15 steel after quenching hardness in 59 ~ 61 HRC, uniformity of 1 or less HRC, unlike M quenching ring wall thickness slightly bigger when there is low hardness, soft point, poor uniformity.
(3) Reduce quenching and grinding cracks
In railway, rolling mill bearing production, because the ring size, weight, oil quenching M the organization brittleness is big, in order to obtain high hardness after quenching is often strong cooling measures, as a result, quenching cracks;When BL is quenched, because BL tissues are much more ductile than M tissues, and the pressure stress up to -400 ~ -500mpa is formed on the surface, which greatly reduces the tendency of quenching cracks.In the grinding process, the surface pressure stress counteracts part of the grinding stress, which reduces the overall stress level and greatly reduces the grinding crack.
(4) The service life of the bearing is improved
To withstand large impact load of railroad, rolling mill bearings, etc., after M quenching when using main failure forms is: inner sleeve cracking when assembling, use in the process of impact outer ring, inner ring fracture, falling guard and isothermal quenching bearing with good impact toughness, surface compressive stress, whatever the assembly inner sleeve craze, or using Chinese and foreign set of guard metal shed and inner sleeve fracture tendency is greatly reduced, and can reduce the edge stress concentration of roller.Therefore, the average life and reliability are improved after isothermal quenching compared with that after M quenching.
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