Hot-rolled round steel and preparation method thereof

Abstract

The invention relates to hot-rolled round steel and a preparation method thereof. After a steel billet is austenitized and heated, assembly line type rolling is carried out in four steps that descaling and first-time temperature holding are carried out; reciprocating cogging is carried out to obtain an intermediate square billet; head cutting and temperature holding before continuous rolling are carried out, specifically, the intermediate square billet is subjected to head cutting before entering a continuous mill, and secondary air cooling temperature holding is carried out, so that deformedaustenite grains are fully recrystallized, and meanwhile, carbonitrides of Nb and V are fully precipitated; continuous rolling and water passing after rolling are carried out, specifically, the intermediate square billet is rolled into a round steel bar, and the finish rolling temperature of the round steel is controlled to be higher than A<r>3; and the rolled round steel is taken out of the continuous mill and then cooled by passing through water, the structure enters a pseudo-pearlite area from an austenite non-recrystallization area, and the round steel rapidly passes through a ferrite precipitation interval to obtain as many fine lamellar pearlite structures as possible. In the round steel sawing process, due to phase change latent heat and core temperature return of the round steel, surface temperature returns to promote the carbonitrides of the Nb and the V which are not precipitated in time to be precipitated, and carbonitride grains precipitated in the low-temperature intervalare finer.

Description

technical field [0001] The invention relates to a method for preparing hot-rolled round steel. Background technique [0002] Hot-rolled round steel for direct cutting is widely used to replace 45, 40Cr, 42CrMo and other quenched and tempered steels to produce injection molding machine tie rods, engineering vehicle cylinder piston rods and other various rod parts. Compared with traditional quenched and tempered steel, because the heat treatment after rolling is omitted in the process, the production cycle is shorter and the production cost is lower, so as to achieve the production goals of energy saving, cost reduction, emission reduction and efficiency increase. However, this type of round steel needs to be controlled at a lower final rolling temperature to achieve grain refinement and higher strength and toughness matching. Therefore, the waiting temperature during the rolling process is inevitable, resulting in a slow rolling rhythm and affecting production. efficiency, t...

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Problems solved by technology

[0007] Patent application CN 201711100874 discloses a non-quenched and tempered steel and its preparation method, the non-quenched and tempered steel of the invention, by weight percentage, C: 0.46-0.55%, Si: 0.20-0.60%, Mn: 1.20-1.60% , Cr: 0.00-0.30%, Al: 0.010-0.030%, Ni: 0.10-0.30%, Cu: 0.00-0.20%, P: 0.000-0.030%, S: 0.020-0.050%, V: 0.050-0.250%, Nb: 0.020-0.050%, Ti: 0.010-0.030%, B: 0.0005-0.0030, N: 0.012-0.020%, the balance is Fe, the patent application product contains higher alloys Mn, V, Nb, Ti, B , the cost of materials is high, and it needs to be finished at 780-850°C for final rolling, and the production efficiency is low

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