STRENGTHENING METHOD OF FASTENERS FROM LOW-CARBON STEEL Russian patent published in 2014 - IPC C21D8/06 C21D9/00 B21C37/04 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, and namely to methods for obtaining high-strength and high-viscosity fasteners of any structural parameters with and without a thread. The method for obtaining fasteners from low-carbon alloyed steel of 15Kh3G3MFT type involves hot plastic deformation of an ingot of low-carbon steel so that a rod is obtained with further cooling in the air, heat treatment at temperatures of complete austenisation with accelerated cooling, cold plastic deformation using die blocks, and upsetting. In order to perform martensitic hardening, accelerated cooling is performed in the air from temperature of hot plastic deformation. After accelerated cooling in the air is completed, cold plastic deformation is performed with degrees of 55-60% by a method of radial forging with strikers arranged uniformly around the rod and forming at closure an inner surface of a conical profile, thus forming a detachable die block, and a rod of the specified diameter of the workpiece of the fastener is obtained. After that, heat treatment is performed by accelerated heating for hardening with austenisation at the temperature of 850-1000°C by charging the workpiece into a hot furnace with air atmosphere; then, accelerated cooling is performed so that a structural state of packet nanomartensite is obtained simultaneously with upsetting of the workpiece in austenitic state so that a head for bolts is obtained or without any upsetting so that the specified structural parameters of a fastener are obtained.

EFFECT: invention provides simultaneous improvement of a set of mechanical properties (strength, reliability and relaxation resistance) of fasteners; enlargement of a field of use of systemic low-carbon alloyed steels.

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