High-frequency quenching with heating is widely used in industry to increase the hardness, strength, resistance to fatigue failure and wear resistance of parts. For this, it is necessary that the surface layer be uniform without cliffs at the places of the recesses, fillets, and shoulders.
However, quenching without breaking the quenched layer of the fillet is a significant difficulty. At the Kharkov Tractor Plant they developed a production method of hardening without breaking the hardened layer. A machine was created with an inductor and a magnetic core to concentrate the magnetic flux on the fillet.
The installation is powered by a generator of 100 kW 8000 Hz. For some parts, an optimal quenching mode was found. So, for the axis of the steering knuckle of the tractor DT-20 and the shaft of the rear axle of the tractor T-74 heating is carried out according to the mode: installation voltage 750 V; working 700 V, current 75-120 A, power 60-65 kW with an exposure time of 2.5-4 seconds. The hardening of the fist is carried out in the environment: a solution of glycerol (30-40%) and salt (15-20%) in water; tempering 220 ° C 90 min; for shaft cooling water through a sprayer. After quenching in this mode, the layer is located along the length of the fillet without breaking (see image).
Image1. Hardened axle of the knuckle of steel 38XC without a gap at the fillet.
The selected quenching medium, which provides a high cooling rate at 650–550 ° C and a decrease in the cooling rate at 300–200 ° C, made it possible to obtain a qualitative surface layer without cracks.
As shown by the results of the tests and operation, the fatigue strength of the axle of the steering knuckle after hardening increased by 2.4 times, and the rear axle shafts 2.2 times as compared with parts whose fillets did not have a hardened layer.
The introduction of quenching through the rear axle shaft fillet made it possible to replace the preliminary heat treatment, quenching and high tempering with normalization. This allowed us to simplify heat treatment, increase cutting speeds and reduce tool consumption.
When quenching with HDTV heating, the dimensions of the spline shafts change slightly. After quenching, the beating of the seat diameters and the diameters of the splines increases by about 0.1 m / m.
In slotted shafts, hardened by high-frequency heating with high-hardness splines, mating gears with internal splines can also be used with high hardness. Increasing the hardness of the mating parts led to a sharp increase in wear resistance and service life of parts and ensured their normal operation on machines with increased speeds.
The use of this method allows to increase the strength and durability of machine parts.
I. SH. LIGHT.
ISSN 0026-0819. “Metallurgy and heat treatment of metals”, № 8. 1968
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