Niobium-nitrogen-containing micro-alloyed HRB 400 E steel bar and production method thereof

Abstract

The invention provided a niobium-nitrogen-containing micro-alloyed HRB 400 E steel bar and a production method thereof. The method is characterized in that the precipitation strengthening effect of niobium and nitrogen on the steel bar is utilized, parts of solid solution strengthening element manganese and silicon are replaced, parts or all of micro-alloyed element vanadium are replaced, and meanwhile, microalloying treatment is carried out on the steel bar by means of cheap nitrogen element, and the precipitation strengthening effect of the micro niobium and nitrogen are exerted. The steel bar is characterized in that Rel is 435-490 MPa, Rm is 590-650 MPa, A is 24%-35%, Rm / Rel 1.30-1.42, A<gt> is 11.5%-19%, the cold bending yield is 100%, and Ceq is less than or equal to 0.48%. Accordingto the steel bar and the method, the production cost is reduced by 30-80 yuan / ton compared with the production cost of a traditional method, three-month natural aging is performed, the fluctuation value of Rel and Rm is less than 10 MPa, the welding performance is good, and meanwhile, the performance index of the obtained steel bar is far more than GB / T 1499.2-2018 standard requirement.

Description

technical field [0001] The invention relates to a niobium-nitrogen microalloyed steel bar and a production process thereof, in particular to a niobium-containing and nitrogen microalloyed HRB400E steel bar and a production process thereof. Background technique [0002] Recently, HRB400MPa steel bars have three major production processes: [0003] The first category is the carbon-manganese steel system composition design mainly based on 20MnSi, using manganese and silicon-based iron alloys for manganese and silicon alloying, air-cooling process for steel bars after rolling, and vanadium-iron or vanadium-nitrogen alloys for vanadium microalloying Niobium microalloying, or using niobium-iron alloy alone for niobium microalloying, or using niobium and vanadium alone for composite alloying, generally its main components are controlled between [Mn] 1.2wt% -1.6wt%, [Si] at 0.40wt% -0.80wt%, [C] is between 0.17wt%-0.25wt%, [V] is controlled between 0.030wt%-0.05wt% or [Nb] is contr...

AI Technical Summary

Problems solved by technology

However, this method has the following problems: ① the content of silicon, manganese and carbon is high, and higher vanadium or niobium or vanadium-niobium composite alloy needs to be added, and the cost of the alloy increases; ② element segregation is easy to occur during solidification and cooling; ③ carbon If the equivalent is too high, the welding performance is poor; ④ yield is not obvious and mixed crystals are prone to occur; ⑤ no yield platform and brittle fracture are prone to occur when niobium microalloying is used alone; Billet cracks, square off and other quality defects, and even steel breakout accidents;

This method is still in the stage of industrial experimentation and promotion, and the disadvantages of this method are: 1. It is necessary to greatly increase the rolling capacity of the rolling mill, greatly increase equipment investment and renovate the old rolling mill to bring a substantial increase in fixed asset investment; 2. The steel bars produced cannot Welding with conventional technology, otherwise the welded area will grow due to the grain growth, resulting in a significant decrease in the strength of the steel bar in the heat-affected zone; ③The ratio of the steel bar strength to yield ratio (Rm / Rel) ≥ 1.25 is less than 95%, and the shock resistance of the steel bar is reduced;

[0005] The third category is to control the composition at or below the lower limit, and use little or no vanadium or niobium, adopt pre-piercing water cooling between intermediate rolling and finishing rolling and post-rolling water-piercing forced cooling, alloy The composition can also be greatly reduced. This method is currently widely used, but it conflicts with national standards, especially the new national standards implemented in 2018. For example, there are conflicts in the structure of steel bars, and even have adverse effects on the performance of steel bars. At the same time, there are The following defects: ① need to increase water-piercing equipment, increasing investment and operating costs; ② large fluctuations in the performance of steel bars, after natural aging, the performance of steel bars fluctuates greatly; ③ poor welding performance; ④ easy corrosion of steel bars, which seriously affects the appearance of steel bars There are adverse effects; ⑤The structure of the surface of the steel bar is inconsistent with that of the core, the difference between the surface hardness and the hardness of the core is relatively large, and the surface is prone to tempered martensite and tempered sorbite, and the structure of steel bars exceeding the national standard is ferrite + pearlescent The basic requirements of the body; ⑥Reinforcement Rm / Rel≥1.25, the qualified rate is below 90%, and the seismic resistance of the reinforcement is reduced;