METHOD FOR PRODUCING FROM CONTINUOUSLY CAST ROLLED BAR WITH SPHEROIDAL STRUCTURE OF LOW-CARBON STEEL FOR COLD BULK PRESSING OF HIGH-STRENGTH FASTENING PARTS OF COMPOUND SHAPE Russian patent published in 2004 - IPC

FIELD: metallurgy, in particular, production of high-strength fastening parts of specifically compound shape.

SUBSTANCE: method involves melting steel in electric furnace, said steel containing, wt%: carbon 0.27-0.32; manganese 0.30-0.65; silicon 0.01-0.17; sulfur 0.005-0.020; chromium 0.01-0.25; niobium 0.005-0.02; calcium 0.001-0.010; iron the balance, with ratios of 12/C-Mn/0.03≥20; Ca/S2≥.0650 being met; providing processing beyond furnace and continuous pouring of steel while protecting metal flow with argon; providing hot rolling of continuous bar at hot rolling initial temperature of 900-950⁰C and hot rolling final temperature of 740-850⁰C at deformation extent of at least 20% in final passes; providing cold gauging deformation at deformation extent of 20-25% and spheroidizing annealing including high-speed inductive heating in intercritical temperature range of cold deformed metal, with following controlled cooling within temperature range of 650-730⁰C at cooling rate of 0.5-1.0⁰C/min and further cooling in thermal chamber at temperature of 100-200⁰C. Microalloying of steel with niobium inhibits recrystallization process at temperature of 1,000-1,100⁰C and provides for fine-grained structure of austenite favorable for steel spheroidization process.

EFFECT: provision for producing of rolled bars having structure enabling advantageous conditions for cold bulk pressing of compound shape fastening parts and improved workability characteristics of steel.

3 cl, 1 ex