Method for adding rare earth into low-alloy high-strength steel crystallizer

Abstract

The invention discloses a method for adding rare earth into a low-alloy high-strength steel crystallizer, which belongs to the technical field of application of rare earth in steel, and is mainly characterized in that rare earth is added in a manner of symmetrically feeding rare earth wires on two sides of a slab casting machine single-flow crystallizer by adopting a double-pipe wire feeder at a position which is 1 / 2 of the thickness and is 100mm away from a water gap in the width direction; the rare earth wires are 65% Ce-35% La mixed rare earth wires with the diameter being 2.5 mm and wrapped with iron sheets. According to the method for adding the rare earth into the low-alloy high-strength steel crystallizer, the liquid level of the crystallizer is stable in the whole wire feeding process, the storage amount of the rare earth in the steel is increased, water gap flocculation is avoided, the rare earth is evenly distributed on the whole section of a casting blank, the internal quality of the casting blank is improved, and reference can be provided for development of rare earth steel with the high storage amount of the rare earth.

Description

Technical Field

[0001] The invention belongs to the technical field of application of rare earth in steel, and in particular relates to a method for adding rare earth to a low-alloy high-strength steel crystallizer. Background Art

[0002] The effect of rare earth on the crystal structure of steel is mainly to make the grains finer and increase the equiaxed crystal ratio. The mechanism is that the rare earth compounds act as non-spontaneous cores of crystallization. The effect of rare earth on the crystal structure is mainly manifested in the refinement of the secondary dendrite spacing. The size of the secondary dendrite spacing will affect the micro-segregation, inclusions and looseness, thus affecting the mechanical properties. Rare earth elements form compounds with higher melting points in steel, which precipitate before the molten steel solidifies and are distributed in the molten steel as tiny particles. They act as heterogeneous nucleation centers, reduce the supercooling of the molten steel crystallization, and thus refine the solidification structure of the steel, reduce segregation, and achieve refinement of the solidification structure.

[0003] 1. The patent "A method for adding rare earth elements to wheel steel" adopts the electric furnace-LF-VD-continuous casting process, adding rare earths at the VD station to improve the castability of molten steel, reduce the size of inclusions in steel, and improve the ultra-detection quality of steel. The present invention adopts the converter-LF refining-continuous casting process, feeds cored rare earth wires into the continuous casting crystallizer, increases the rare earth inventory in the steel, avoids water inlet flocculence, and improves the internal quality of the ingot.

[0004] 2. The patent "A rare earth treatment method for low alloy wear-resistant steel" modifies the refined slag at the end of LF refining, and with the addition of rare earth iron alloy, the formation of large-sized high-melting point inclusions is suppressed, the nozzle agglomeration during the continuous casting process is avoided, and the wear resistance and corrosion resistance of the low alloy wear-resistant steel are significantly improved. The present invention adopts the converter-LF refining-continuous casting process, and core-clad rare earth wire is fed into the continuous casting crystallizer, which increases the rare earth stock in the steel, avoids nozzle flocculent flow, and improves the internal quality of the ingot.

[0005] 3. Patent "A rare earth treatment method for high-strength wheel steel" The rare earth treatment method with slag-metal coordinated control greatly improves the recovery rate of rare earth in high-strength wheel steel, refines the grains, and significantly improves the fatigue life of high-strength wheel steel. The present invention adopts the converter-LF refining-continuous casting process, feeds cored rare earth wire into the continuous casting crystallizer, increases the rare earth stock in the steel, avoids water inlet flocculence, and improves the internal quality of the ingot.

[0006] The novelty of the present invention lies in that a rare earth wire feeding process is adopted in the crystallizer, and core-clad rare earth wire is selected. The rare earth grade of the rare earth wire is 65% Ce-35% La, and the outside of the rare earth wire is coated with anti-oxidation iron scale. Because the core-clad rare earth wire can quickly and smoothly pass through the three-layer structure of the protective slag without rare earth oxidation, the influence on the modification of the protective slag is avoided, and therefore the selection of the crystallizer protective slag is not restricted. The amount of rare earth added can be increased, the rare earth recovery rate is high, and the rare earth stock in the steel is high. The normal pulling speed is adopted to avoid water inlet flocculence, and the production is stable and smooth. After feeding the rare earth wire, the segregation of the ingot composition is improved, the equiaxed crystal ratio of the ingot is increased, and the internal quality of the ingot is improved. Summary of the invention

[0007] The purpose of the present invention is to provide a method for adding rare earths to a low-alloy high-strength steel crystallizer. The liquid level in the crystallizer is stable during the entire wire feeding process, the rare earth inventory in the steel is increased, water inlet flocculence is avoided, the rare earths are distributed more evenly over the entire cross-section of the ingot, the internal quality of the ingot is improved, and the method can provide a reference for the development of rare earth steel with a high rare earth inventory.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention discloses a method for adding rare earth to a low alloy high strength steel crystallizer. The method comprises the following steps: adopting a double-tube wire feeder to symmetrically feed rare earth wires on both sides of a single-stream crystallizer of a slab caster. The rare earth wires are positioned at 1 / 2 of the thickness and 95-105 mm (preferably 100 mm) away from a water nozzle in the width direction. The rare earth wires are Φ2.5 mm iron-clad 65% Ce-35% La mixed rare earth wires.

[0010] Furthermore, the process route of the low alloy high strength steel includes: blast furnace - KR desulfurization - converter - LF refining - slab continuous casting.

[0011] Further, the process conditions are as follows:

[0012] The molten iron is treated with KR desulfurization, and the sulfur content of the molten iron entering the converter is ≤0.020%; the final tapping temperature of the converter is ≥1620℃, and ferroaluminum, ferrosilicon and ferromanganese are added during the converter tapping process for deoxidation and alloying; the LF furnace carries out slag making, deoxidation and desulfurization, and ferromanganese and ferrosilicon alloy are added to adjust the composition of the molten steel. After the LF furnace treatment, calcium treatment is carried out, and the soft blowing time after the calcium treatment is completed is ≥8min; the continuous casting superheat is 15-30℃, and the pulling speed range is 1.0-1.6m / min.

[0013] Furthermore, the low alloy high strength steel is low alloy high strength steel Q355B.

[0014] Furthermore, the cross section of the ingot is 2040 mm×230 mm, and the fixed length is 8.1 m.

[0015] Furthermore, the continuous casting superheat is 23°C and the casting speed range is 1.05m / min.

[0016] Furthermore, the crystallizer was fed with 50ppm rare earth wire, the billet drawing speed was 1.0m / min, and the crystallizer wire feeding speed was 2.8m / min.

[0017] Furthermore, the crystallizer was fed with 150ppm rare earth wire, the ingot drawing speed was 1.0m / min, and the crystallizer wire feeding speed was 8.3m / min.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] The present invention uses core-clad rare earth wire and adopts a crystallizer wire feeding process. The casting speed is normal, the protective slag is not denatured, and the crystallizer liquid level is stable. The amount of rare earth added can be increased, the water inlet floccules can be avoided, the rare earth recovery rate is high, the rare earth stock in the steel is high, and the rare earth is evenly distributed in the cross section of the casting. Rare earth can serve as a nucleation core in the steel, refine the crystal structure of the steel, increase the equiaxed crystal rate, and improve the internal quality of the casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Figure 1 Schematic diagram of feeding rare earth wire to the crystallizer. DETAILED DESCRIPTION

[0022] A method for adding rare earth to a low-alloy high-strength steel crystallizer is used. An industrial test of feeding rare earth wire to a crystallizer is carried out on a 2-machine 2-strand slab continuous casting machine. A 65% Ce-35% La mixed rare earth wire with a diameter of 2.5 mm and an outer iron sheet is fed into a single-strand crystallizer. The wire feeding process maintains a normal billet drawing speed, the protective slag process does not change, the crystallizer liquid level is stable, and the production is stable and smooth.

[0023] 1. Process route

[0024] Blast furnace—KR desulfurization—converter—LF refining—slab continuous casting.

[0025] 2. Chemical composition

[0026] Chemical composition of steel grade / %

[0027] Steel Type C Si Mn P S Q355B ≤0.24 ≤0.55 ≤1.60 ≤0.035 ≤0.035

[0028] 3. Process conditions

[0029] The molten iron is treated by KR desulfurization, and the sulfur content of the molten iron entering the converter is ≤0.020%. The final tapping temperature of the converter is ≥1620℃, and aluminum iron, ferrosilicon and ferromanganese are added during the converter tapping process for deoxidation and alloying. The LF furnace is used for slag making, deoxidation and desulfurization, and ferromanganese, ferrosilicon and other alloys are added to adjust the composition of the molten steel. After the LF furnace treatment, calcium treatment is carried out, and the soft blowing time after calcium treatment is completed is ≥8min. The continuous casting superheat is 15~30℃, and the pulling speed range is 1.0~1.6m / min.

[0030] 4. Wire feeding parameters

[0031] The commonly used calculation formula for feeding rare earth wire is: The rare earth wire is a Φ2.5mm iron-covered 65% Ce-35% La mixed rare earth wire, which is fed symmetrically on both sides of the single-stream crystallizer of the slab caster using a double-tube wire feeder. The wire is positioned at 1 / 2 of the thickness and 95-105mm away from the water nozzle in the width direction.

[0032] 5. Ingot quality inspection

[0033] After wire feeding is completed, low-magnification samples are cut from the blank ingot and the ingot fed with rare earth wire respectively, and cold acid low-magnification rating is performed on the low-magnification samples to inspect the internal quality of the ingot.

[0034] Application examples:

[0035] The steel grade is Q355B, and the process route is blast furnace-KR desulfurization-converter-LF refining-slab continuous casting. The molten iron is treated with KR desulfurization, and the sulfur content of the molten iron entering the converter is 0.018%. The final tapping temperature of the converter is 1625℃, and aluminum iron, ferrosilicon and ferromanganese are added during the converter tapping process for deoxidation and alloying. The LF furnace is used for slag making, deoxidation and desulfurization, and alloys such as ferromanganese and ferrosilicon are added to adjust the composition of the molten steel. After the LF furnace treatment, calcium treatment is carried out, and the soft blowing time after calcium treatment is 9min. The cross-section of the ingot is 2040mm×230mm, the fixed length is 8.1m, the continuous casting overheat is 23℃, and the pulling speed range is 1.05m / min.

[0036] After wire feeding is completed, low-magnification samples are cut from the blank ingot and the rare earth ingot fed with rare earth wire respectively, and cold acid low-magnification rating is performed on the low-magnification samples to inspect the internal quality of the ingot.

[0037] The chemical composition of the test heat is as follows:

[0038] Chemical composition / %

[0039] Steel Type C Si Mn P S Q355B 0.17 0.14 0.54 0.014 0.005

[0040] Under the same molten steel condition, two different rare earth addition tests were carried out in a single-strand crystallizer, with rare earth feed amounts of 50ppm and 150ppm, and two complete fixed-length billets were tested respectively. The implementation method is as follows:

[0041] Case 1:

[0042] The crystallizer is fed with 50ppm rare earth wire. The casting speed is 1.0m / min, and the crystallizer wire feeding speed is 2.8m / min. During the wire feeding process, the crystallizer liquid level is stable, there is no flocculent flow at the water outlet, and the production is stable and smooth.

[0043] Case 2:

[0044] The crystallizer is fed with 150ppm rare earth wire. The casting speed is 1.0m / min, and the crystallizer wire feeding speed is 8.3m / min. During the wire feeding process, the crystallizer liquid level is stable, there is no flocculent flow at the water outlet, and the production is stable and smooth.

[0045] The results of low-power inspection of the ingot are as follows:

[0046]

[0047] After rare earth is added by the method of the present invention, the rating results of the center segregation, center crack and triangular crack of the rare earth casting billet are respectively reduced by 0.5 level compared with the blank casting billet, indicating that the rare earth in the steel can refine the grains and improve the internal quality of the casting billet under this method.

[0048] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for adding rare earth to a low alloy high strength steel crystallizer, characterized in that: A double-tube wire feeder is used to symmetrically feed rare earth wires on both sides of the single-stream crystallizer of the slab caster, at 1 / 2 of the thickness and 95-105mm away from the water nozzle in the width direction; the rare earth wire is a Φ2.5mm iron-clad 65% Ce-35% La mixed rare earth wire.

2. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 1, characterized in that: Furthermore, the process route of low alloy high strength steel includes: blast furnace - KR desulfurization - converter - LF refining - slab continuous casting.

3. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 2, characterized in that: The process conditions are as follows: The molten iron is treated with KR desulfurization, and the sulfur content of the molten iron entering the converter is ≤0.020%; the final tapping temperature of the converter is ≥1620℃, and ferroaluminum, ferrosilicon and ferromanganese are added during the converter tapping process for deoxidation and alloying; the LF furnace carries out slag making, deoxidation and desulfurization, and ferromanganese and ferrosilicon alloy are added to adjust the composition of the molten steel. After the LF furnace treatment, calcium treatment is carried out, and the soft blowing time after the calcium treatment is completed is ≥8min; the continuous casting superheat is 15-30℃, and the pulling speed range is 1.0-1.6m / min.

4. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 1, characterized in that: The low alloy high strength steel is low alloy high strength steel Q355B.

5. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 3, characterized in that: The cross section of the ingot is 2040mm×230mm, and the fixed length is 8.1m.

6. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 3, characterized in that: The continuous casting superheat is 23℃ and the casting speed range is 1.05m / min.

7. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 1, characterized in that: The crystallizer is fed with 50ppm rare earth wire, the billet drawing speed is 1.0m / min, and the crystallizer wire feeding speed is 2.8m / min.

8. The method for adding rare earth to a low alloy high strength steel crystallizer according to claim 1, characterized in that: The crystallizer is fed with 150ppm rare earth wire, the billet drawing speed is 1.0m / min, and the crystallizer wire feeding speed is 8.3m / min.

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