METHOD FOR MANUFACTURING HIGH-STRENGTH FASTENERS FROM ALLOY STEEL WITHOUT SPHEROIDIZING ANNEALING Russian patent published in 2024 - IPC C21D8/06 C22C38/22 C22C38/24 

FIELD: metallurgy.

SUBSTANCE: invention relates namely to the methods for manufacturing high-strength fasteners and other critical products from alloy steel for transport, construction, mining and other types of equipment using cold die forging. The method includes steel smelting, hot rolling to produce round steel, pickling, calibration of round steel, production of fasteners using cold die forging, followed by austenitization, hardening and tempering. Steel is smelted having a chemical composition containing, in wt.%: carbon (C) 0.30-0.35, silicon (Si) 0.17-0.37, manganese (Mn) 0.60-0.90, aluminium (Al) 0.020-0.050, molybdenum (Mo) 0.20-0.30, vanadium (V) 0.10-0.18, nitrogen (N)≤0.010, chromium (Cr) 0.40-0.60, nickel (Ni)≤0.30, copper (Cu)≤0.06, phosphorus (P)≤0.010, sulfur (S)≤0.005, the rest is iron and inevitable impurities. Hot rolling is carried out according to a regime that ensures the production of at least 50% spheroidized pearlite in the structure of round steel in the complete absence of hardening structures of bainite and martensite. After hot rolling, the round steel is coiled into coils at a temperature of 760-800°C with a cooling rate of 0.005-0.02°S/s with obtaining a tensile strength of rolled products of no more than 650-700 MPa without spheroidizing annealing. Austenization of fasteners is carried out by holding at a temperature of 880-900°C in a nitrogen-hydrogen gas mixture, followed by quenching in oil and tempering, the temperature of which is determined based on the target indicators of the tensile strength of manufactured fasteners according to the expression T_tempering = -0.767×σ_B+(1485÷1515)°C, where σ_B is the target indicator of the tensile strength of manufactured fasteners.

EFFECT: manufactured fasteners have a high endurance limit.

1 cl, 8 tbl