A kind of hot-rolled round steel and preparation method thereof

Abstract

The invention relates to a hot-rolled round steel and a preparation method thereof. After the steel billet is austenitized and heated, it is rolled in an assembly line in four steps: descaling and warming for the first time; reciprocating billet opening to obtain an intermediate billet; cutting before entering the continuous rolling mill, the middle billet is cut off before entering the continuous rolling mill, and is subjected to a second air cooling and waiting for temperature, so that the deformed austenite grains can be fully recrystallized, and at the same time, the carbonitrides of Nb and V can be fully Precipitation; continuous rolling and water penetration after rolling, the intermediate billet is rolled into round steel bars, and the final rolling temperature of the round steel is controlled to be higher than Ar3; after the completed round steel comes out of the continuous rolling mill, it is cooled by water to allow the structure to change from austenitic The unrecrystallized region of the solid body enters the pseudo-pearlite region, and quickly passes through the ferrite precipitation region to obtain as many fine-plate pearlite structures as possible; during the round steel sawing process, the surface temperature of the round steel rises due to the latent heat of phase transformation and the return temperature of the core Promote the precipitation of Nb and V carbonitrides that have not yet been precipitated, and the carbonitrides precipitated in this low temperature range are finer.

Description

technical field [0001] The present invention relates to a preparation method of hot-rolled round steel. Background technique [0002] Hot-rolled round steel for direct cutting is widely used to replace quenched and tempered steels such as 45, 40Cr, 42CrMo, etc., to produce injection molding machine tie rods, engineering vehicle oil cylinder piston rods and other various rod parts. Compared with traditional quenched and tempered steel, because the heat treatment link after rolling is omitted in the process, the production cycle is shorter and the production cost is lower, achieving the production goals of energy saving, cost reduction, emission reduction and efficiency improvement. However, this kind of round steel needs to control a lower finish rolling temperature to achieve grain refinement and obtain a higher strength and toughness match. Therefore, the temperature waiting during the rolling process is inevitable, resulting in a slow rolling rhythm and affecting productio...

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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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