Method for reducing grade of B-type inclusions in steel for weather-proof bolt

Abstract

The invention discloses a method for reducing the grade of B-type inclusions in steel for a weather-proof bolt. The method comprises the following steps: controlling the oxygen content of molten steel in an electric furnace to be less than or equal to 800ppm; steel grit aluminum is used as a precipitation deoxidizing agent and an Al increasing agent; the Alt component is controlled within the range of 0.06%-0.07% through Al wire feeding operation, and aluminum is not increased in subsequent refining; the refining period is controlled to be smaller than or equal to 45 min, and the VD period is controlled to be smaller than or equal to 25 min; the molten steel subjected to VD is subjected to calcium treatment, and the Ca content in the molten steel is controlled to range from 0.015% to 0.025%; and the molten steel subjected to calcium treatment is subjected to soft blowing, the soft blowing time is controlled to be larger than or equal to 15 min, and the soft blowing flow is controlled to be 30-50 NL / min. According to the invention, the control level of the inclusions of the steel for the weather-resistant bolt can be reduced from the original B-type coarse system 1.0 level and fine system 0.5 level to the B-type coarse system 0.5 level and fine system 0 level, the product quality and the processing performance are obviously improved, the use of coatings in the application scene is effectively reduced, the energy and materials consumed by later maintenance are reduced, and the full life operation cycle of equipment is prolonged.

Description

Technical Field

[0001] The invention relates to a method for reducing the level of Class B inclusions in weathering bolt steel, belonging to the technical field of steel smelting. Background Art

[0002] A certain weathering bolt steel is smelted using the EAF-LF-VD-CCM process and processed through the following steps: ingot casting - hot rolling - spheroidizing annealing - wire rod descaling - cold drawing - cold heading - threading - heat treatment. Because fine-grained materials have a higher proportion of grain boundaries, grain boundary sliding and dislocation movement are more uniform, which helps disperse stress concentration during plastic deformation, thereby improving the material's ductility and reducing cracking tendency. Fine-grained materials experience a faster increase in dislocation density during deformation, resulting in a significant work hardening effect, which helps to homogenize deformation and avoid fracture caused by localized excessive deformation. Therefore, the aluminum content in the ingot must be strictly controlled during the smelting process for weathering bolt steel to refine the grain size and improve heading performance.

[0003] Due to the strong reducing properties of Al, during the Al smelting and control process, Al easily reacts with oxides in steel and oxygen in the air to form Class B inclusions. Class B inclusions have high hardness and poor plasticity, and are weakly bonded to the metal matrix. When the material is subjected to stress, they easily become the source of cracks, resulting in brittle fracture of the material. When the Class B inclusions exceed the standard, the tensile strength, impact toughness and ductility of the material cannot be guaranteed. In particular, during rolling, drawing or heat treatment, hard and brittle Class B inclusions may hinder the uniform deformation of the material, resulting in surface cracking or internal defects. Other studies have shown that for weather-resistant metal materials, the difference in electrode potential between Class B inclusions and the metal matrix may form micro-batteries, accelerating local corrosion (such as pitting corrosion and intergranular corrosion). In particular, in humid, high-temperature or corrosive media, corrosion near the inclusions will further trigger crack propagation. During the actual smelting process, Al shows a trend of continuous oxidation and reduction. In order to ensure the Al composition control requirements, multiple Al replenishment operations are adopted in the refining process, which is not conducive to the full floating of Al2O3 inclusions. There is a risk of exceeding the level of Class B inclusions, and the product quality cannot be stably guaranteed.

[0004] In summary, finding a method to achieve stable control of the Al content in steel, eliminate the need for later aluminum addition, and promote the full agglomeration, floating, and deformation transformation of Al2O3 particles in steel is the key to ensuring the quality and performance of weather-resistant bolt steel. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for reducing the level of Class B inclusions in weathering bolt steel, thereby improving the Al control stability of the finished product and reducing the level of Class B inclusions in weathering bolt steel, thereby improving product quality.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A method for reducing the level of Class B inclusions in weathering bolt steel, the method comprising:

[0008] During the electric furnace smelting process, the oxygen content of the electric furnace steel liquid is controlled to be within the range of ≤800ppm to reduce the Al loss during steel tapping; after the electric furnace steel is tapped, steel sand aluminum is used as a precipitated deoxidizer and Al increasing agent; after the ladle arrives at the refining, the actual Al content is measured, and the Alt component is controlled within the range of 0.06%-0.07% by feeding the Al line operation, and no aluminum is added in the subsequent refining; the refining LF and VD treatment cycles are controlled to be within ≤45 minutes and the VD cycle is controlled to be within ≤25 minutes to prevent serious Al loss during the process; the steel liquid after the VD is treated with calcium to control the Ca content in the steel liquid to between 0.015% and 0.025%; the steel liquid after the calcium treatment is soft-blown, the soft-blowing time is controlled to be ≥15 minutes, and the soft-blowing flow rate is controlled to be 30-50NL / min to promote the full floating of Al2O3 inclusions in the steel liquid.

[0009] As a preferred solution, the addition amount of the steel grit aluminum as a precipitation deoxidizer and Al-increasing agent is 4.1-4.7 kg / t.

[0010] Beneficial effects: Compared with the existing technology, the present invention solves the problem that it is difficult to effectively control the levels of Al and Class B inclusions in weathering bolt steel. The inclusion control level of weathering bolt steel can be reduced from the original Class B fine system level 1.0 and coarse system level 0.5 to Class B fine system level 0.5 and coarse system level 0. The product quality and processing performance are significantly improved, the use of coatings in its application scenarios is effectively reduced, the energy and materials consumed in later maintenance are reduced, and the full life cycle of the equipment is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the visual field of Class B inclusions in rolled steel (φ20) for weathering bolts before process improvement;

[0012] Figure 2 This is the field of view of Class B inclusions in rolled steel (φ20) for weather-resistant bolts after process improvement. DETAILED DESCRIPTION

[0013] The present invention will be described in detail below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments and examples are for illustrating the present invention, rather than for limiting the present invention.

[0014] Example 1: A method for reducing the level of Class B inclusions in weathering bolt steel, comprising the following process steps:

[0015] 1. Control the oxygen content of steel tapping from electric furnace

[0016] The oxygen content of steel tapped from the electric furnace is controlled at ≤800ppm to reduce Al loss during tapping.

[0017] 2. Steel grit aluminum precipitation deoxidation and Al addition are used in electric furnace tapping

[0018] After the steel is tapped from the electric furnace, steel sand aluminum is used as a precipitation deoxidizer and Al-increasing agent, and the addition amount is controlled at 4.1-4.7kg / t.

[0019] 3. Primary control of Al in the refining process

[0020] The actual Al content of the ladle is measured after refining, and the Al content is controlled within the range of 0.060%-0.070% by feeding the Al wire. No aluminum is added in subsequent refining.

[0021] 4. Control the refining LF and VD smelting cycle

[0022] Control the refining cycle within ≤45min and the VD cycle within ≤25min to prevent serious Al loss in the process.

[0023] 5. Control the calcium treatment intensity of molten steel

[0024] The VD-finished molten steel is subjected to calcium treatment. After the calcium treatment, the Ca content in the molten steel is controlled between 0.015% and 0.025%.

[0025] 6. Ensure the soft blowing time of molten steel

[0026] The molten steel after VD is treated with calcium, the soft blowing time is controlled to be ≥15min, and the soft blowing flow rate is controlled to be 30-50NL / min to promote the full floating of Al2O3 inclusions in the molten steel.

[0027] By adopting the process of the present invention, the control level of Class B inclusions (Class B fine system 1.0 level, coarse system 0.5 level) in weathering bolt steel rolled material (φ20) can be changed from the original Class B fine system 1.0 level, coarse system 0.5 level (such as Figure 1 As shown) down to Class B fine system 0.5 level, coarse system 0 level (as shown) Figure 2 As shown in Figure 2, product quality and processing performance are significantly improved.

[0028] Throughout the specification, unless otherwise specified, the terms used herein are to be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. If there is a conflict, this specification takes precedence. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention, etc., can be purchased from the market or can be prepared by existing methods.

Claims

1. A method for reducing the level of Class B inclusions in weathering bolt steel, characterized by: The method comprises the following steps: during electric furnace smelting, controlling the oxygen content of electric furnace steel liquid within a range of 800 ppm or less to reduce Al loss during steel tapping; using steel grit aluminum as a precipitation deoxidizer and Al increasing agent after steel tapping; measuring the actual Al content of the ladle after refining, controlling the Al component within a range of 0.06%-0.07% by feeding an Al line, and not increasing Al in subsequent refining; controlling the refining and VD smelting cycles, controlling the refining cycle within 45 minutes or less, and the VD cycle within 25 minutes or less to prevent severe Al loss during the process; performing calcium treatment on the steel liquid after VD treatment to control the Ca content in the steel liquid to between 0.015% and 0.025%; and performing soft blowing on the steel liquid after calcium treatment, controlling the soft blowing time to be 15 minutes or more, and the soft blowing flow rate to be 30-50 NL / min, to promote sufficient floating of Al2O3 inclusions in the steel liquid.

2. The method for reducing the level of Class B inclusions in weathering bolt steel according to claim 1, characterized in that: The addition amount of the steel grit aluminum as a precipitation deoxidizer and Al increasing agent is 4.1-4.7 kg / t.

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