40Cr steel smelting process based on synergistic effect of C deoxidation and rare earth

Abstract

The invention discloses a 40Cr steel smelting process based on a synergistic effect of C deoxidation and rare earth. The 40Cr steel smelting process comprises the following steps: S1, after converter smelting, carrying out oxygen determination; s2, converter tapping; s3, carbon pre-deoxidation; s4, refining slag modification; s5, deoxidizing rare earth; and S6, carrying out secondary alloying. Aiming at a deoxidization method adopting deoxidization alloy in a 40Cr steel smelting process in the traditional industry and an existing deoxidization method adopting carbon powder deoxidization, the invention provides a method combining the clean deoxidization capability of carbon powder deoxidization and the deep deoxidization capability of rare earth, and the method is simple in process, high in operability and low in cost. The problem that in the background technology, the control difficulty of inclusions is large is solved.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, and particularly relates to a 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements. Background Technology

[0002] 40Cr steel is a widely used alloy structural steel with excellent comprehensive properties, mainly used in the manufacture of mechanical parts, such as those for automobiles, tractors, machine tools, mining, and petrochemical machinery. Effectively controlling the oxygen content and inclusion morphology in the steel is crucial in determining the final product's mechanical properties (especially fatigue strength and impact toughness) and machinability. Currently, Al deoxidation is mainly used in the smelting of 40Cr steel both domestically and internationally. However, this process has a series of significant technical challenges and limitations in practical applications, directly affecting the steel's purity, mechanical properties, machinability, and product stability, primarily manifested in the following ways:

[0003] The main deoxidation products of aluminum are solid Al2O3 inclusions with high melting points (approximately 2050℃). These Al2O3 inclusions aggregate in molten steel into clusters or strings, and are large in size, irregular in shape, and high in hardness. During subsequent casting and solidification processes, they are difficult to float to the surface and be removed completely, leaving a large amount of residue in the steel and significantly deteriorating the purity of the steel.

[0004] In Al deoxidized steel, sulfur (S) typically exists as elongated or chain-like MnS inclusions. These MnS inclusions extend along the deformation direction during hot working (rolling, forging) of the steel. The extended MnS not only significantly ruptures the matrix, becoming fatigue crack initiation points, but also severely degrades the steel's mechanical properties (anisotropy) such as transverse impact toughness, reduction of area, and fatigue strength, making it difficult to meet the stringent comprehensive performance requirements of high-end 40Cr components (such as high-strength connecting rods and gear shafts).

[0005] To ensure effective deoxidation, excessive aluminum is typically added, resulting in a high content of acid-soluble aluminum (Als) in the steel. High Al content increases the viscosity of the molten steel, hindering the flotation of inclusions. Under certain conditions, excessive Al may promote the precipitation of AlN, negatively impacting the steel's toughness and aging properties. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a method that combines the clean deoxidation capabilities of carbon powder deoxidation with the deep deoxidation capabilities of rare earth elements, targeting the traditional deoxidation alloy used in the 40Cr steel smelting process and the existing deoxidation method using carbon powder. This method is simple in process, highly operable, and solves the problem of difficulty in controlling inclusions in the prior art.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements, comprising the following steps:

[0009] S1. Oxygen determination after converter smelting;

[0010] S2. Converter tapping;

[0011] S3. Carbon pre-deoxidation;

[0012] S4. Upgrading of refining slag;

[0013] S5. Rare earth deoxidation;

[0014] S6. Secondary alloying;

[0015] In step S3, carbon powder is added starting when 1 / 4 of the steel has been tapped and ending when 3 / 4 of the steel has been tapped.

[0016] In step S4, rare earth alloys are added for deep deoxidation; the amount of rare earth alloys added is 0.3kg-2kg / t steel.

[0017] In step S6, after the rare earth alloy is added, carbon powder, silicon manganese, aluminum blocks, and high-carbon ferrochrome alloying material are added sequentially according to the steel composition requirements to complete the alloying operation of the steel. The amount of carbon powder added is 0.3~0.5 kg / t steel, the amount of silicon manganese alloy added is 5-7 kg / t steel, the amount of aluminum blocks added is 0.6~0.7 kg / t steel, and the amount of high-carbon ferrochrome added is 14-15 kg / t steel.

[0018] Furthermore, in step S1, before tapping steel from the converter, an oxygen analyzer is used to measure the oxygen content.

[0019] Furthermore, in step S2, once the composition meets the requirements, the steel tapping operation begins, with a tapping time of 3-8 minutes and a tapping temperature of 1630-1650℃.

[0020] Furthermore, in step S3, to avoid the molten steel from boiling due to excessive carbon powder addition speed and excessive single addition amount, the carbon powder is added in small amounts multiple times, and the entire addition process is carried out with argon bottom blowing operation.

[0021] Furthermore, in step S3, the carbon powder added under normal pressure removes the oxygen content to 100 ppm. The method for calculating the amount of carbon added is as follows:

[0022]

[0023] Among them W steel [O] represents the converter steel output. 出钢wt.% is the oxygen content in the steel at the time of tapping, and k is the carbon powder addition coefficient for deoxidation, with a value ranging from 1 to 12.

[0024] Furthermore, in step S4, after the addition of carbon powder in step S3, 3-6 kg of quicklime and 2-5 kg ​​of refining slag are added per ton of steel to form a refining slag with good fluidity, which promotes the flotation and removal of inclusions.

[0025] Furthermore, in step S4, the amount of rare earth alloy added, W RE The calculation formula is as follows:

[0026]

[0027] Among them W steel M represents the amount of molten steel. RE M represents the relative atomic mass of rare earth elements. O denoted as the relative atomic mass of oxygen, a is the rare earth content in the rare earth alloy, ranging from 5% to 50%, and b is the rare earth alloy addition coefficient for deoxidation, ranging from 1 to 15.

[0028] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0029] Using carbon (C) as the main deoxidizer, its deoxidation product is gaseous CO, which can directly escape from the molten steel into the furnace gas without leaving any solid inclusions in the molten steel. This fundamentally avoids the formation of large, hard inclusions such as Al2O3, significantly improves the purity of the molten steel, and significantly reduces the oxide inclusion rating.

[0030] In the favorable low-oxygen potential environment created by carbon deoxidation, rare earth (RE) elements are introduced for deep deoxidation and desulfurization. Rare earth elements have a strong affinity for the trace amounts of oxygen and sulfur remaining in steel, forming fine, dispersed, high-melting-point, and non-deformable rare earth inclusions such as RE₂O₂S, RE₂O₃, or rare earth sulfur oxides. These rare earth compounds maintain a spherical or near-spherical shape during hot working, effectively solving the problem of MnS elongation, significantly improving the transverse properties and isotropy of the steel, and enhancing key mechanical properties such as impact toughness and fatigue strength.

[0031] This avoids the addition of excessive aluminum, reducing the potential risks associated with high AlN precipitation. It can meet the performance requirements of high-purity 40Cr steel. Detailed Implementation

[0032] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention addresses the problems of harmful oxide inclusions generated by traditional deoxidation, the difficulty in achieving low oxygen content levels with atmospheric pressure carbon deoxidation, and the inefficient utilization of rare earth resources. It proposes a method to improve the cleanliness of molten steel through the synergistic effect of carbon deoxidation and rare earth elements.

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] Example 1

[0036] This embodiment describes an industrial application for producing 40Cr steel, using a 150t top-and-bottom blown converter for smelting. The process route is converter → LF refining → continuous casting, including the following steps:

[0037] S1. Oxygen content at the converter endpoint was determined using an oxygen analyzer, with an oxygen content of 631 × 10⁻⁶. -6 ;

[0038] S2. Converter tapping volume of molten steel: 149.3t;

[0039] S3. Based on the oxygen determination results, the amount of carbon powder added was calculated to be 321.8 kg. After adding the carbon powder, the oxygen content of the molten steel was 103 × 10⁻⁶ kg. -6 The carbon content is 0.179%.

[0040] S4. Refining slag is modified by adding 631 kg of quicklime and 483 kg of refining synthetic slag. After tapping, the ladle car is driven into the LF station.

[0041] S5. After the molten steel reaches the LF station, bottom blowing and temperature adjustment are performed. 133 kg of calcium carbide, 112 kg of silicon carbide, and 54 kg of aluminum granules are added to create white slag. Then, a rare earth alloy containing 30% Ce is added for deoxidation, at a rate of 693 kg. After bottom blowing until inclusions have fully floated to the surface, 75 kg of carbon powder, 2.19 t of high-carbon ferrochrome, 831 kg of silicon manganese, and 105 kg of aluminum blocks are added through the alloy hopper for alloying. Once the molten steel composition is correct, it is soft-blown for 15 minutes before being cast on the platform.

[0042] The oxygen content measured from the sample taken from the middle package was 18 × 10⁻⁶. -6 The number density of inclusions is 6.97 / mm. 2 More than 75% of the inclusions have an equivalent diameter of less than 3 μm.

[0043] Example 2

[0044] This embodiment describes an industrial application for producing 40Cr steel, using a 200t top-and-bottom blown converter. The process route is converter → LF refining → continuous casting, including the following steps:

[0045] S1. Oxygen content at the converter endpoint was determined using an oxygen analyzer, with an oxygen content of 628 × 10⁻⁶. -6 ;

[0046] S2. Converter tapping volume of molten steel: 198.5t;

[0047] S3. Based on the oxygen determination results, the amount of carbon powder added was calculated to be 420.8 kg. After adding the carbon powder, the oxygen content of the molten steel was 101 × 10⁻⁶ kg. -6 The carbon content is 0.182%.

[0048] S4. Refining slag is modified by adding 835 kg of quicklime and 640 kg of refining synthetic slag. After tapping, the ladle car is driven into the LF station.

[0049] S5. After the molten steel reaches the LF station, bottom blowing and temperature adjustment are performed. 179 kg of calcium carbide, 149 kg of silicon carbide, and 70 kg of aluminum granules are added to create white slag. Then, a rare earth alloy containing 30% Ce is added for deoxidation, at a rate of 920 kg. After bottom blowing until inclusions have fully floated to the surface, 101 kg of carbon powder, 2.95 t of high-carbon ferrochrome, 1100 kg of silicon manganese, and 139 kg of aluminum blocks are added through the alloy hopper for alloying. Once the molten steel composition is correct, it is soft-blown for 15 minutes before being cast on the platform.

[0050] The oxygen content measured from the sample taken from the middle package was 17 × 10⁻⁶. -6 The number density of inclusions is 6.92 inclusions / mm. 2 More than 79% of the inclusions have an equivalent diameter of less than 3 μm.

[0051] Comparative Example 1

[0052] This embodiment describes an industrial application of producing 40Cr steel using Al deoxidation. A 150t top-and-bottom blown converter is used for smelting, and the process route is converter → LF refining → continuous casting, including the following steps:

[0053] S1. Oxygen content at the converter endpoint was determined using an oxygen analyzer, with an oxygen content of 594 × 10⁻⁶. -6 ;

[0054] S2. Converter tapping volume of molten steel: 146.8t;

[0055] S3 was deoxidized and alloyed by adding 142g of aluminum blocks;

[0056] S4. Refining slag is modified by adding 642 kg of quicklime and 491 kg of refining synthetic slag. After tapping, the ladle car is driven into the LF station.

[0057] S5. After the molten steel reaches the LF station, bottom blowing and temperature adjustment are performed. 136 kg of calcium carbide, 109 kg of silicon carbide, and 58 kg of aluminum granules are added to create white slag. After bottom blowing until the inclusions have fully floated to the surface, 99 kg of carbon powder, 2.3 t of high-carbon ferrochrome, and 842 kg of silicon manganese are added through the alloy hopper for alloying. After the molten steel composition is aligned, it is soft-blown for 15 minutes before being poured onto the casting platform.

[0058] The oxygen content measured from the sample taken from the middle package was 24 × 10⁻⁶.-6 The number density of inclusions is 9.41 inclusions / mm. 2 55% of the inclusions have an equivalent diameter of less than 3 μm.

[0059] Comparative Example 2

[0060] This embodiment describes an industrial application of producing 40Cr steel using Al deoxidation. A 200t top-and-bottom blown converter is used for smelting, and the process route is converter → LF refining → continuous casting, including the following steps:

[0061] S1. Oxygen content at the converter endpoint was determined using an oxygen analyzer, with an oxygen content of 596 × 10⁻⁶. -6 ;

[0062] S2. Converter tapping volume of molten steel: 196.3t;

[0063] S3 was deoxidized and alloyed by adding 191 kg of aluminum blocks;

[0064] S4. Refining slag is modified by adding 855 kg of quicklime and 659 kg of refining synthetic slag. After tapping, the ladle car is driven into the LF station.

[0065] S5. After the molten steel reaches the LF station, bottom blowing and temperature adjustment are performed. 183 kg of calcium carbide, 149 kg of silicon carbide, and 68 kg of aluminum granules are added to create white slag. After bottom blowing until inclusions have fully floated to the surface, 131 kg of carbon powder, 3.12 t of high-carbon ferrochrome, and 1130 kg of silicon-manganese are added through the alloy hopper for alloying. Once the molten steel composition is correct, it is soft-blown for 15 minutes before being poured onto the casting platform.

[0066] The oxygen content measured from the sample taken from the middle package was 24 × 10⁻⁶. -6 The number density of inclusions is 9.41 inclusions / mm. 2 55% of the inclusions have an equivalent diameter of less than 3 μm.

[0067] (4) The oxygen content measured from the sample taken from the middle package was 27 × 10⁻⁶. -6 The number density of inclusions is 8.73 / mm. 2 71% of the inclusions have an equivalent diameter of less than 3 μm.

[0068] The embodiments 1 and 2 of this invention have achieved significant application results in the industrial production of 40Cr steel. After converter smelting, the oxygen content of the molten steel is effectively reduced through the synergistic effect of carbon deoxidation and rare earth elements. The oxygen content in embodiments 1 and 2 is reduced to 18 × 10⁻⁶. -6 and 17×10 -6 The oxygen content of comparative examples 1 and 2 was 24 × 10⁻⁶. -6 and 27×10 -6The inclusion density was significantly higher than expected. Meanwhile, the present invention significantly reduced the inclusion number density; the inclusion number densities in Examples 1 and 2 were 6.97 inclusions / mm² and 6.92 inclusions / mm², respectively, far lower than the 9.41 inclusions / mm² and 8.73 inclusions / mm² of the comparative examples. The inclusion size was also greatly reduced; in Examples 1 and 2, over 75% and 79% of the inclusions had an equivalent diameter of less than 3 μm, respectively, compared to 55% and 71% in Comparative Examples 1 and 2. This indicates that the present invention effectively improves the cleanliness of molten steel, overcomes the shortcomings of traditional deoxidation processes, and achieves efficient utilization of rare earth resources, which is of great significance for the production of high-quality steel.

[0069] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements, characterized in that: Includes the following steps: S1. Oxygen determination after converter smelting; S2. Converter tapping; S3. Carbon pre-deoxidation; S4. Upgrading of refining slag; S5. Rare earth deoxidation; S6. Secondary alloying; In step S3, carbon powder is added starting when 1 / 4 of the steel has been tapped and ending when 3 / 4 of the steel has been tapped. In step S4, rare earth alloys are added for deep deoxidation; the amount of rare earth alloys added is 0.3kg-2kg / t steel. In step S6, after the rare earth alloy is added, carbon powder, silicon manganese, aluminum blocks, and high-carbon ferrochrome alloying material are added sequentially according to the steel composition requirements to complete the alloying operation of the steel. The amount of carbon powder added is 0.3~0.5 kg / t steel, the amount of silicon manganese alloy added is 5-7 kg / t steel, the amount of aluminum blocks added is 0.6~0.7 kg / t steel, and the amount of high-carbon ferrochrome added is 14-15 kg / t steel.

2. The 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements according to claim 1, characterized in that: In step S1, before tapping steel from the converter, an oxygen analyzer is used to measure the oxygen content.

3. The 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements according to claim 1, characterized in that: In step S2, once the composition meets the requirements, the steel tapping operation begins, with a tapping time of 3-8 minutes and a tapping temperature of 1630-1650℃.

4. The 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements according to claim 1, characterized in that: In step S3, to avoid the molten steel from boiling due to excessive carbon powder addition speed and excessive single addition, the carbon powder is added in small amounts multiple times, and the entire addition process is carried out with argon bottom blowing.

5. The 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements according to claim 1, characterized in that: In step S3, the carbon powder added under normal pressure removes the oxygen content to 100 ppm. The method for calculating the amount of carbon added is as follows: Among them W steel [O] represents the converter steel output. 出钢wt.% is the oxygen content in the steel at the time of tapping, and k is the carbon powder addition coefficient for deoxidation, with a value ranging from 1 to 12.

6. The 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements according to claim 1, characterized in that: In step S4, after the addition of carbon powder in step S3, 3-6 kg of quicklime and 2-5 kg ​​of refining slag are added per ton of steel to form a refining slag with good fluidity, which promotes the flotation and removal of inclusions.

7. The 40Cr steel smelting process based on the synergistic effect of C deoxidation and rare earth elements according to claim 1, characterized in that: In step S4, the amount of rare earth alloy added is W RE The calculation formula is as follows: Among them W steel M represents the amount of molten steel. RE M represents the relative atomic mass of rare earth elements. O denoted as the relative atomic mass of oxygen, a is the rare earth content in the rare earth alloy, ranging from 5% to 50%, and b is the rare earth alloy addition coefficient for deoxidation, ranging from 1 to 15.

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