Heat treatment development history

(1) Cleaning heat treatment

Wastewater, waste gas, waste salt, dust, noise and electromagnetic radiation formed by heat treatment will cause environmental pollution. To solve the environmental pollution problem of heat treatment, the implementation of clean heat treatment (or green heat treatment) is one of the development directions of heat treatment technology in developed countries. In order to reduce the emissions of SO ₂ , CO, CO ₂ , dust and cinder, coal has been basically eliminated as a fuel, and the use of heavy oil is becoming less and less. Most of the light oil is used, and natural gas is still the most ideal fuel.

The waste heat utilization of the combustion furnace has reached a high level. The optimization of the burner structure and the strict control of the air-fuel ratio ensure that NOX and CO are reduced to a minimum under the premise of reasonable combustion; gas carburizing and carbonitriding are used. The vacuum heat treatment technology replaces the salt bath treatment to reduce the pollution of waste water and CN-toxic substances to the water source; the water-soluble synthetic quenching oil is used to replace part of the quenching oil, and the biodegradable vegetable oil is used to replace part of the mineral oil to reduce oil pollution.

(2) Precision heat treatment

Precision heat treatment has two meanings: on the one hand, based on the use requirements of the parts, materials, structural dimensions, the use of physical metallurgical knowledge and advanced computer simulation and detection technology, optimize process parameters, achieve the required performance or maximize the material The potential; on the other hand, it is sufficient to ensure the stability of the optimized process, to achieve a small dispersion of product quality (or zero) and heat treatment distortion to zero.

(3) Energy-saving heat treatment

Scientific production and energy management are the most promising factors for the effective use of energy. It is a scientific management choice to establish a professional heat treatment plant to ensure full-load production and full use of equipment capabilities. In the heat treatment energy structure, priority is given to primary energy; waste heat and waste heat are fully utilized; and processes with low energy consumption and short cycle are used to replace processes with long cycle and high energy consumption.

(4) Less oxidation heat treatment

Heating by a protective atmosphere heating instead of an oxidizing atmosphere to precisely control the carbon potential and nitrogen potential, the performance of the parts after heat treatment is improved, heat treatment defects such as decarburization, cracks, etc. are greatly reduced, and the finishing allowance after heat treatment is reduced. Improve material utilization and machining efficiency. Vacuum heating, gas quenching, vacuum or low pressure carburizing, nitriding, nitrocarburizing and boronizing can significantly improve the quality, reduce distortion and improve life.

Heat treatment technology application effect

(1) Expanded the application range of GCr15 steel.

Generally, the effective wall thickness of the ferrule of GCr15 steel is less than 12mm when quenching. However, due to the strong cooling ability of nitrate salt during BL quenching, the effective wall thickness of the ferrule can be expanded to about 28 mm if measures such as stirring, series moving, and water addition are adopted.

(2) Stable hardness and good uniformity

Since the BL transition is a slow process, generally GCr15 steel takes 4h, GCr18Mo steel takes 5h, the ferrule is isothermally long in the nitrate salt, and the surface core structure transition is almost simultaneous, so the hardness is stable and uniform, and the general GCr15 steel BL After quenching, the hardness is 59-61HRC, and the uniformity is ≤1HRC. Unlike the wall thickness of the ferrule when quenching, the hardness is low, the soft point and the uniformity are poor.

(3) reduce quenching and grinding cracks

In the production of railway and rolling mill bearings, due to the large size and heavy weight of the ferrule, the M structure is brittle during oil quenching. In order to obtain high hardness after quenching, strong cooling measures are often taken, resulting in quenching microcracks; The BL structure is much better than the M structure, and the surface is formed with compressive stress of up to -400 ~ -500MPa, which greatly reduces the tendency of quenching crack; the surface compressive stress compensates for part of the grinding stress during the grinding process, so that the overall stress level The drop greatly reduces the grinding crack.

(4) Increased bearing life

For railways, rolling mill bearings, etc. subjected to large impact loads, the main failure modes after M quenching are: inner casing cracking during assembly, the outer ring is broken by the impact outer ring, the inner ring is broken, and the austempered bearing is broken during use. Due to the good impact toughness and surface compressive stress, no matter whether the inner sleeve is cracked during assembly or during use, the outer edge of the outer casing is greatly reduced, and the edge stress concentration of the roller can be reduced. Therefore, the average life and reliability after quenching after M quenching are improved.