Energy-saving heat treatment of extension springs and application effects of heat treatment technology:
1. Energy-saving heat treatment for extension springs
Scientific production and energy management are the most potential factors for the effective use of energy. The establishment of a professional heat treatment plant to ensure full-load production and give full play to equipment capabilities is the choice of scientific management. In terms of heat treatment energy structure, priority is given to primary energy; waste heat and waste heat are fully utilized; processes with low energy consumption and short cycles are used instead of processes with long cycles and high energy consumption.
2. Less non-oxidizing heat treatment
By using protective atmosphere heating instead of oxidizing atmosphere heating to controllable atmosphere heating with precise control of carbon potential and nitrogen potential, the performance of 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 quality, reduce distortion and increase life.
3. Application effect of heat treatment technology of extension spring
(1) Expanded the scope of application of GCr15 steel
Generally, the effective wall thickness of the ferrule during quenching of GCr15 steel M is less than 12mm, but the effective wall thickness of the ferrule can be expanded to about 28mm due to the strong cooling ability of nitrate salt during BL quenching.
(2) Stable hardness and good uniformity
Because BL transformation is a slow process, generally GCr15 steel needs 4h, GCr18Mo steel needs 5h, the ferrule is isothermal in nitrate salt for a long time, and the surface core structure changes almost simultaneously, so the hardness is stable and the uniformity is good. Generally, GCr15 steel BL The hardness after quenching is 59～61HRC, and the uniformity is ≤1HRC. Unlike the larger ferrule wall thickness during quenching, problems such as low hardness, soft spots and poor uniformity will occur.
(3) Reduce quenching and grinding cracks
In the production of railway and rolling mill springs, 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 micro-cracks; while BL quenching, due to The toughness of the BL structure is much better than that of the M structure. At the same time, a compressive stress of -400～-500MPa is formed on the surface, which greatly reduces the tendency of quenching cracks; during grinding, the surface compressive stress offsets part of the grinding stress and makes the overall stress level Drop, greatly reducing the grinding cracks.