500 MPa level high-nitrogen composite microalloyed steel bar and production method thereof

Abstract

The invention relates to a 500 MPa level high-nitrogen composite microalloyed steel bar and a production method thereof. The 500 MPa level high-nitrogen composite microalloyed steel bar comprises thefollowing chemical components of, by mass, 0.18-0.25 parts of C, 0.40-0.80 parts of Si, 1.30-1.60 parts of Mn, less than or equal to 0.045 parts of P, less than or equal to 0.045 parts of S, 0.020-0.040 parts of V, 0.010-0.040 parts of Nb, 0.010-0.040 parts of Ti, 0.0090-0.0150 parts of N, and the balance iron and unavoidable impurity elements. In the production method, after the continuous casting process is completed, a continuous casting billet is heated to 1130-1250 DEG C and subjected to heat preservation for 90-150 minutes, and then cooled to 1020-1120 DEG C for rolling; after the rolling, water cooling is carried out with the water pressure being 0.1-0.5 MPa and the temperature of an upper cooling bed being controlled at 920-1010 DEG C; and the steel bar is naturally cooled after entering the cooling bed, so that the high-nitrogen composite microalloyed steel bar is obtained. The mechanical properties of the steel bar meet the requirements of the national standard, the production cost is low and a production process is simple and easy to implement.

Description

technical field [0001] The invention relates to a steel bar and a production method thereof, in particular to a 500MPa grade high-nitrogen composite microalloyed steel bar and a production method thereof. Background technique [0002] Steel bar is the most widely used steel type with mature technology, which can be produced by almost all iron and steel enterprises. With the formulation and implementation of the new national standard "Steel for Reinforced Concrete—GB / T1499.2" in 2018, since the standard requires that rings different from the internal contrast are not allowed to appear on the periphery of the cross-section of the steel bar, the water-penetrating steel bar is limited to a certain extent. Production, a large number of steel mills began to adopt the traditional vanadium micro-alloy process; at the same time, with the strengthening of national environmental protection, the supply of vanadium alloy resources is tight, and the price of vanadium alloys has risen shar...

AI Technical Summary

Problems solved by technology

With the formulation and implementation of the new national standard "Steel for Reinforced Concrete—GB / T1499.2" in 2018, since the standard requires that rings different from the internal contrast are not allowed to appear on the periphery of the cross-section of the steel bar, the water-penetrating steel bar is limited to a certain extent. Production, a large number of steel mills began to adopt the traditional vanadium micro-alloy process; at the same time, with the strengthening of national environmental protection, the supply of vanadium alloy resources is tight, and the price of vanadium alloys has risen sharply due to various reasons, resulting in the traditional micro-vanadium or vanadium-nitrogen The production cost of alloying process steel bar is greatly increased

[0003] In order to reduce production costs, the microalloying elements mainly used in 500Mpa level steel bar production plants are V, V-N, V-Nb composite, and V-Ti composite, among which the high content of vanadium leads to high production costs; Patent Publication No. CN102703813 A The patent application disclosed a "vanadium-titanium composite micro-alloyed steel bar and its production method", which involves 500Mpa grade steel bar mainly adopts vanadium-titanium composite micro-alloyed, although the content of vanadium in its composition is low, it reduces to a certain extent Production cost, but the high titanium content is 0.05-0.12wt%. High titanium content leads to coarse precipitation of TiN particles, which cannot play the role of pinning austenite grain boundaries and makes the castability of molten steel worse, which is easy to cause production In addition, the final rolling temperature is low at 800-860°C, and it is difficult for ordinary rolling mills to meet the requirements of the process conditions, and the production is difficult

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