Preparation process of low-alloy high-strength steel

Abstract

The invention relates to the technical field of material science and engineering, and discloses a low-alloy high-strength steel preparation process which comprises the following steps: step 1, molten iron pretreatment: firstly carrying out molten iron pretreatment; secondly, converter smelting is conducted, wherein high carbon catch and steel ladle deoxidation alloying are conducted; 3, LF refining, wherein narrow component control is carried out in the LF refining process; 4, continuous casting is conducted, specifically, continuous casting is conducted, and pouring is protected in the process; fifthly, rolling is conducted, specifically, after billet quenching is conducted, cooling and slow cooling are conducted; and 6, quality inspection is carried out, specifically, inspection is carried out one by one, appearance inspection and flaw detection are carried out, and the alloy components and the proportion range thereof are as follows: niobium 0.012%-0.014%; 0.33%-0.36% of cerium; 0.3%-0.5% of copper; through the operation process, the purity of the molten steel can be improved, the castability of continuous casting can be improved, it is ensured that the surface quality and the internal quality of a continuous casting billet meet the quality standard requirement, and through the combined action of an alloy formula, it can be ensured that the mechanical property of the billet meets the standard range and is stable.

Description

Technical Field

[0001] This invention relates to the fields of materials science and engineering technology, specifically to a process for preparing low-alloy high-strength steel. Background Technology

[0002] In the current field of materials science and engineering, the preparation of high-strength steel offers numerous advantages, including improved structural strength, reduced weight, and enhanced durability. However, despite these advantages, existing preparation techniques still have some shortcomings, which limit its potential for wider application. The main problems include high alloy costs, insufficient purity of molten steel, and performance instability.

[0003] To address these issues, alloy costs are reduced by optimizing chemical composition. Simultaneously, improvements to the continuous casting process ensure high purity of the molten steel and that the surface and internal quality of the continuously cast billets meet stringent quality standards. Furthermore, advancements in new technologies will focus on guaranteeing the stability of material properties, particularly ensuring that mechanical properties remain within and stable within standard ranges. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a process for preparing low-alloy high-strength steel, which has the advantages of low alloy cost, high steel purity, and stable performance, thus solving the problems of high alloy cost, insufficient steel purity, and unstable performance.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the present invention provides the following technical solution: a process for preparing low-alloy high-strength steel, comprising the following steps:

[0008] Step 1: Hot metal pretreatment: First, hot metal pretreatment is performed;

[0009] Step 2, Converter smelting: High-strength carbon extraction and ladle deoxidation alloying;

[0010] Step 3, LF Refining: Narrow component control is implemented during the LF refining process;

[0011] Step 4, Continuous Casting: Perform continuous casting and protect the pouring process during the process;

[0012] Step 5, Rolling: After quenching the steel billet, it is cooled and slowly cooled;

[0013] Step Six: Quality Inspection: Inspect each item individually, including visual inspection and flaw detection.

[0014] Preferably, the molten iron pretreatment process in step one is as follows:

[0015] S1.1 Desulfurization treatment: Before the molten iron enters the converter, the desulfurization temperature is set to 1600℃, and 0.5% lime powder by weight of molten iron is injected into the molten iron through the injection system for 5 minutes for desulfurization. The efficiency of the desulfurization treatment is determined to be over 90% by barium sulfate gravimetric method.

[0016] S1.2, Primary dephosphorization treatment: Add 1% of the synthetic slag by weight of the molten iron to the molten iron and carry out desulfurization treatment for 8 minutes at a temperature of 1400℃;

[0017] S1.3, Primary deoxidation treatment: Add 0.8% manganese ferromanganese by weight of the molten iron to the molten iron and carry out desulfurization treatment at a temperature of 1400℃ for 8 minutes;

[0018] S1.4 Impurity Removal: During the molten iron treatment process, an automatic slag removal operation is performed every 2 minutes. After the slag removal is completed, the molten iron is further purified through a filter.

[0019] Preferably, in step one, the high-temperature carbon extraction process involves setting the converter temperature to 1650°C and using an oxygen lance to blow 99% oxygen into the converter, with the oxygen supply intensity of the oxygen lance set to 3.0–4.5 standard meters per second. 3 / (ton·min), set the oxygen blowing time of the oxygen lance to 18-26min to make the final carbon content greater than 0.08%.

[0020] Preferably, in step one, the ladle deoxidation and alloying process is as follows: after oxygen blowing is completed, the ladle is subjected to secondary deoxidation treatment during the tapping process, and aluminum particles and calcium carbide in a ratio of 1:1 are added. At the same time, 0.86% of the mass of molten steel lime fluorite is added for pre-slag formation.

[0021] Preferably, in step three, the LF refining process involves: narrow composition control during the LF refining process; according to the composition requirements of the steel required by the manufacturer, alloying elements in the proportion of raw materials are added to the molten iron; the alloy composition is adjusted within a specified range; the melting temperature is controlled at 1460-1467℃; the tapping temperature is controlled at 1700-1720℃; and the ladle superheat is controlled between 15 and 25℃.

[0022] Preferably, the alloy composition and its proportion range are: niobium 0.012%-0.014%; cerium 0.33%-0.36%; copper 0.3%-0.5%; nickel 0.35%-0.39%.

[0023] Preferably, in step four, the process protection casting process is as follows: Q420 special protective slag is used for protective casting, the casting temperature is controlled at 1540-1570℃, the continuous casting speed is controlled between 1.0 and 1.3 m / min, the superheat is controlled between 20 and 30℃, electromagnetic stirring and dynamic light reduction technology are used, and casting begins after the above settings are completed, and finally a steel billet is formed.

[0024] Preferably, the billet quenching process in step five is as follows:

[0025] S2.1 Insulation treatment: Use an insulation cover to insulate the steel billet that has just come out of the continuous casting machine;

[0026] S2.2 Secondary descaling treatment: Descaling is performed on the heat-insulated steel billet. The descaling outlet pressure is set to ≥23MPa, the water flow rate of the high-pressure pump is set to 10-15L / min, and the dephosphorization time is set to 20-25min.

[0027] S2.3 Quenching treatment: Transfer the steel billet after secondary descaling to a quenching furnace at 700℃-800℃ and quench it for 30-40 minutes.

[0028] Preferably, the conditions for the quenching, cooling, and slow cooling process of the steel billet are as follows:

[0029] S3.1. Quickly transfer the quenched steel billet to water at 300℃-350℃, adjust the water ratio of the upper and lower nozzles to between 1.8 and 2.3, and control the cooling rate to be about 10℃-30℃ per second.

[0030] S3.2 At the same time, a clearance of 2-5cm should be reserved at the head and tail, and the billet should be slowly cooled after it is taken off the production line. The slow cooling temperature should be greater than 300℃.

[0031] S3.3 The steel billet after slow cooling must be stored in the warehouse for 24 hours before it can be put into the heating furnace for production.

[0032] Preferably, the visual inspection in step six includes: checking whether the surface of each billet sample is free of bubbles, scabs, folds and inclusions, and whether there are any visible cracks, shrinkage cavities and delamination; the flaw detection includes: performing flaw detection on each batch of billets, randomly selecting 2 billet samples from each batch, and conducting impact tests at room temperature, 0℃ or -20℃ according to the level requirements set by the manufacturer's engineers.

[0033] Compared with the prior art, the present invention provides a process for preparing low-alloy high-strength steel, which has the following beneficial effects:

[0034] 1. The high-carbon drawing process in step one of the preparation steps of this invention can ensure that the final carbon content of the steel billet is greater than 0.08%, and can guarantee successful furnace turning on the first attempt, avoiding over-oxidation of molten steel caused by re-blowing. The alloy composition and its proportion range are: niobium 0.012%-0.014%; cerium 0.33%-0.36%; copper 0.3%-0.5%; nickel 0.35%-0.39%. This range of alloy composition can reduce alloy costs. Finally, during the quenching process, the cooling rate is controlled at about 10℃-30℃ per second, which helps the steel billet to achieve martensitic or bainitic transformation, thereby avoiding cracking caused by excessively fast cooling or affecting the quenching effect by excessively slow cooling. Through the above operation process, the purity of molten steel can be improved, the castability of continuous casting can be improved, and the surface and internal quality of the continuously cast billet can be ensured to meet the quality standard requirements. Combined with the joint effect of the alloy formula, the mechanical properties of the steel billet can be guaranteed to meet the standard range and be stable. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the present invention; Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0037] Example 1

[0038] Please see Figure 1 A process for preparing low-alloy high-strength steel includes the following steps:

[0039] Step 1: Pretreatment of molten iron: First, pretreatment of molten iron is carried out to remove impurities and improve its chemical composition;

[0040] Step 2, Converter smelting: High-strength carbon extraction and ladle deoxidation alloying;

[0041] Step 3, LF Refining: Narrow component control is implemented during the LF refining process;

[0042] Step 4, Continuous Casting: Perform continuous casting and protect the pouring process during the process;

[0043] Step 5, Rolling: After quenching the steel billet, it is cooled and slowly cooled;

[0044] Step Six: Quality Inspection: Inspect each item individually, including visual inspection and flaw detection.

[0045] Specifically, the pretreatment process of molten iron in step one is as follows:

[0046] S1.1 Desulfurization treatment: Before the molten iron enters the converter, the desulfurization temperature is set to 1600℃, and 0.5% lime powder by weight of the molten iron is injected into the molten iron through the injection system for 5 minutes for desulfurization. The spray gun is inserted deep into the molten iron, and the lime powder is evenly sprayed below the surface of the molten iron by the drive of the carrier gas to ensure that the lime powder is in full contact with the molten iron. The efficiency of the desulfurization treatment is determined to be over 90% by the barium sulfate gravimetric method to meet the requirements of low sulfur content for subsequent refining and continuous casting.

[0047] S1.2 Primary dephosphorization treatment: Add 1% of the synthetic slag by weight of the molten iron to the molten iron and carry out desulfurization treatment at a temperature of 1400℃ for 8 minutes to promote the removal of phosphorus (P) and improve the dephosphorization efficiency.

[0048] S1.3, Primary deoxidation treatment: Add 0.8% manganese ferromanganese by weight of the molten iron to the molten iron and carry out desulfurization treatment at a temperature of 1400℃ for 8 minutes to reduce the oxygen content in the molten iron.

[0049] S1.4 Impurity Removal: During the molten iron treatment process, an automatic slag removal operation is performed every 2 minutes to remove impurities and oxides floating on the surface of the molten iron. After the slag removal is completed, the molten iron is further purified by a filter to remove small inclusions and non-metallic impurities.

[0050] Specifically, in step one, the high-temperature carbon extraction process involves setting the converter temperature to 1650℃ and using an oxygen lance to blow 99% concentrated oxygen into the converter. The oxygen supply intensity of the oxygen lance is set to 3.0–4.5 standard meters per second. 3 / (ton·min), set the oxygen blowing time of the oxygen lance to 18-26min to make the final carbon content greater than 0.08%, so as to ensure successful furnace turning on the first time and avoid over-oxidation of molten steel caused by supplementary blowing.

[0051] Specifically, in step one, the ladle deoxidation and alloying process involves the following steps: After oxygen blowing, the ladle undergoes a secondary deoxidation process during tapping, with aluminum granules and calcium carbide added in a 1:1 ratio to diffuse deoxidation and reduce inclusion contamination. Simultaneously, 0.86% of the steel mass of lime-fluorite is added for pre-slag formation, creating favorable conditions for subsequent LF refining.

[0052] Specifically, in step three, the LF refining process involves narrow composition control. Based on the manufacturer's required steel composition, alloying elements in the specified proportions are added to the molten iron. The alloy composition is adjusted within a defined range to regulate the chemical composition of the molten iron, thereby reducing alloy consumption and minimizing performance instability caused by composition fluctuations. Strict control is maintained over the tapping temperature, keeping the melting temperature between 1460-1467℃ and the tapping temperature between 1700-1720℃. Furthermore, the ladle superheat is controlled between 15 and 25℃ to ensure the stability of the continuous casting process and the quality of the cast billet.

[0053] Specifically, the alloy composition and its proportion range are: niobium 0.012%–0.014%; cerium 0.33%–0.36%; copper 0.3%–0.5%; nickel 0.35%–0.39%.

[0054] Specifically, in step four, the process protection during casting is as follows: Q420 special protective slag is used for protective casting, the casting temperature is controlled at 1540-1570℃ to prevent secondary oxidation of molten steel during casting, the continuous casting speed is controlled between 1.0 and 1.3 m / min, the superheat is controlled between 20 and 30℃, the liquid level in the intermediate mold and the liquid level in the crystallizer are kept stable, and electromagnetic stirring and dynamic light reduction technology are used to reduce the segregation of the billet center and prevent slag entrapment, internal cracks and porosity quality problems. After the above settings are completed, casting begins, and finally a steel billet is produced.

[0055] Specifically, the billet quenching process in step five:

[0056] S2.1 Insulation treatment: The steel billet that has just come out of the continuous casting machine is insulated with an insulation cover in order to maintain the high temperature of the steel billet and prevent the temperature from dropping too quickly.

[0057] S2.2 Secondary descaling treatment: The heat-insulated steel billet is descaled. The descaling outlet pressure is set to ≥23MPa, the water flow rate of the high-pressure pump is set to 10-15L / min, and the dephosphorization time is set to 20-25min. This high-pressure water flow can effectively impact the surface of the steel billet and remove iron oxide scale.

[0058] S2.3 Quenching treatment: After secondary descaling, the steel billet is transferred to a quenching furnace at 700℃-800℃ and quenched for 30-40 minutes to cause phase transformation in the internal structure of the steel billet, thereby improving the mechanical properties of the steel.

[0059] Specifically, the conditions for the quenching, cooling, and slow cooling process of the steel billet are as follows:

[0060] S3.1. Quickly transfer the quenched steel billet to water at 300℃-350℃, adjust the water ratio of the upper and lower nozzles to between 1.8 and 2.3, and control the cooling rate to about 10℃-30℃ per second to achieve martensitic or bainitic transformation, thereby avoiding cracking due to excessively fast cooling or affecting the quenching effect due to excessively slow cooling.

[0061] S3.2 At the same time, a clearance of 2-5cm is reserved at the head and tail. This length can minimize the temperature difference between the head and tail and allow the billet to be slowly cooled after it is removed from the production line. The slow cooling temperature is greater than 300℃ to prevent cracks and other defects caused by internal stress.

[0062] S3.3 After slow cooling, the steel billet must be stored in the warehouse for 24 hours before it can be put into the heating furnace for production, in order to ensure that its internal structure is uniform and stable.

[0063] Specifically, step six, visual inspection, includes: inspecting each billet individually: checking the surface of each billet sample for defects such as bubbles, scabs, folds, and inclusions, as well as for visible cracks, shrinkage cavities, and delamination; and flaw detection, which includes: performing flaw detection on each batch of billets, randomly selecting two billet samples from each batch, and conducting impact tests at room temperature, 0℃, or -20℃ according to the level requirements set by the manufacturer's engineers to ensure that the comprehensive mechanical properties of the material meet the standards.

[0064] Comparative Example 1

[0065] The high-temperature carbon extraction process in step one of Example 1 is modified as follows: the converter temperature is set to 1500℃, and 99% oxygen is blown into the converter using an oxygen lance, with the oxygen supply intensity of the oxygen lance set to 1.5–2.0 standard meters per second. 3 / (ton·min), set the oxygen lance blowing time to 30-50min to make the final carbon content greater than 0.08%, and keep other steps unchanged.

[0066] The manufacturer determined that the carbon content of the final steel billet produced in Comparative Example 1 was 0.067%.

[0067] Comparative Example 2

[0068] The alloy composition and its proportion range in Example 1 were changed to: niobium 0.018%-0.020%; cerium 0.19%-0.26%; copper 0.23%-0.25%; nickel 0.60%-0.69%, while other steps and compositions remained unchanged.

[0069] The manufacturer estimated that the low-alloy cost of the final steel billet product made from Comparative Example 2 was 110% of the low-alloy cost of Example 1.

[0070] Comparative Example 3

[0071] In Example 1, step S3.1 is modified as follows: the quenched steel billet is quickly transferred to water at 100℃-120℃, the water ratio between the upper and lower nozzles is adjusted to between 1.1 and 1.3, and the cooling rate is controlled at about 3℃-5℃ per second. Other steps remain unchanged.

[0072] The manufacturer determined that the mechanical properties of the final steel billet produced from Comparative Example 3 exceeded the standard range by 1%.

[0073] The carbon content and mechanical properties of the steel billets produced in Example 1 and Comparative Examples 1-3, along with the manufacturers' estimated costs of low-alloy steel and total raw materials, are statistically analyzed in a table as follows:

[0074]

[0075] The above table summarizes Example 1 and Comparative Examples 1-3:

[0076] Carbon content: Examples 1 and Comparative Examples 2 and 3 maintained the same carbon content (0.08%), while the carbon content of Comparative Example 1 was slightly lower (0.067%), indicating that the change in the high-pulling carbon operating conditions in Comparative Example 1 could lead to a decrease in carbon content.

[0077] Mechanical properties: The mechanical properties of Example 1 and Comparative Examples 1 and 2 all meet the standard and do not exceed the standard range. However, the mechanical properties of Comparative Example 3 exceed the standard range by 1%, which is due to improper adjustment of the cooling rate during the quenching process.

[0078] Low alloy cost: The low alloy cost of Example 1 is the lowest, while the cost of Comparative Example 2 is the highest, reaching 110% of that of Example 1, indicating that changing the alloy composition and its proportion will affect the cost.

[0079] Total raw material cost: Example 1 and Comparative Examples 1 and 2 maintained the same total raw material cost, while the cost of Comparative Example 3 was slightly higher, at 110% of that of Example 1, due to the cost increase caused by the adjustment of the quenching process in Comparative Example 3.

[0080] The advantages are: the high-carbon drawing process in step one of the preparation steps of this invention can ensure that the final carbon content of the steel billet is greater than 0.08%, and can guarantee successful furnace turning on the first attempt, avoiding over-oxidation of molten steel caused by re-blowing. The alloy composition and its proportion range are: niobium 0.012%-0.014%; cerium 0.33%-0.36%; copper 0.3%-0.5%; nickel 0.35%-0.39%. This range of alloy composition can reduce alloy costs. Finally, during the quenching process, the cooling rate is controlled at about 10℃-30℃ per second, which helps the steel billet to achieve martensitic or bainitic transformation, thereby avoiding cracking caused by excessively fast cooling or affecting the quenching effect by excessively slow cooling. Through the above operation process, the purity of molten steel can be improved, the castability of continuous casting can be improved, and the surface and internal quality of the continuously cast billet can be ensured to meet the quality standard requirements. The combined effect of the above measures ensures that the mechanical properties of the steel billet meet the standard range and are stable.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing low-alloy high-strength steel, characterized in that, Includes the following steps: Step 1: Hot metal pretreatment: First, hot metal pretreatment is performed; Step 2, Converter smelting: High-strength carbon extraction and ladle deoxidation alloying; Step 3, LF Refining: Narrow component control is implemented during the LF refining process; Step 4, Continuous Casting: Perform continuous casting and protect the pouring process during the process; Step 5, Rolling: After quenching the steel billet, it is cooled and slowly cooled; Step Six: Quality Inspection: Inspect each item individually, including visual inspection and flaw detection.

2. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: The process of molten iron pretreatment in step one is as follows: S1.1 Desulfurization treatment: Before the molten iron enters the converter, the desulfurization temperature is set to 1600℃, and 0.5% lime powder by weight of molten iron is injected into the molten iron through the injection system for 5 minutes for desulfurization. The efficiency of the desulfurization treatment is determined to be over 90% by barium sulfate gravimetric method. S1.2, Primary dephosphorization treatment: Add 1% of the synthetic slag by weight of the molten iron to the molten iron and carry out desulfurization treatment for 8 minutes at a temperature of 1400℃; S1.3, Primary deoxidation treatment: Add 0.8% manganese ferromanganese by weight of the molten iron to the molten iron and carry out desulfurization treatment at a temperature of 1400℃ for 8 minutes; S1.4 Impurity Removal: During the molten iron treatment process, an automatic slag removal operation is performed every 2 minutes. After the slag removal is completed, the molten iron is further purified through a filter.

3. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: In step one, the high-temperature carbon extraction process involves setting the converter temperature to 1650℃ and using an oxygen lance to blow 99% oxygen into the converter. The oxygen supply intensity of the oxygen lance is set to 3.0–4.5 standard meters per second. 3 / (ton·min), set the oxygen blowing time of the oxygen lance to 18-26min to make the final carbon content greater than 0.08%.

4. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: In step one, the ladle deoxidation and alloying process is as follows: after oxygen blowing, the ladle is subjected to secondary deoxidation treatment during the tapping process, and aluminum particles and calcium carbide in a 1:1 ratio are added. At the same time, lime fluorite with a mass of 0.86% of the molten steel is added for pre-slag formation.

5. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: In step three, the LF refining process involves narrow composition control. According to the steel composition requirements of the manufacturer, alloying elements in the proportion of raw materials are added to the molten iron. The alloy composition is adjusted within a specified range to control the melting temperature at 1460-1467℃, the tapping temperature at 1700-1720℃, and the ladle superheat at 15-25℃.

6. The process for preparing low-alloy high-strength steel according to claim 5, characterized in that: The alloy composition and its proportion range are: niobium 0.012%–0.014%; cerium 0.33%–0.36%; copper 0.3%–0.5%; nickel 0.35%–0.39%.

7. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: In step four, the process protection casting process is as follows: Q420 special protective slag is used for protective casting, the casting temperature is controlled at 1540-1570℃, the continuous casting speed is controlled between 1.0 and 1.3 m / min, the superheat is controlled between 20 and 30℃, electromagnetic stirring and dynamic light pressure technology are used, and casting begins after the above settings are completed, and finally a steel billet is formed.

8. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: The billet quenching process in step five: S2.1 Insulation treatment: Use an insulation cover to insulate the steel billet that has just come out of the continuous casting machine; S2.2 Secondary descaling treatment: Descaling is performed on the heat-insulated steel billet. The descaling outlet pressure is set to ≥23MPa, the water flow rate of the high-pressure pump is set to 10-15L / min, and the dephosphorization time is set to 20-25min. S2.3 Quenching treatment: Transfer the steel billet after secondary descaling to a quenching furnace at 700℃-800℃ and quench it for 30-40 minutes.

9. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: The conditions for the quenching, cooling, and slow cooling process of the steel billet are as follows: S3.

1. Quickly transfer the quenched steel billet to water at 300℃-350℃, adjust the water ratio of the upper and lower nozzles to between 1.8 and 2.3, and control the cooling rate to be about 10℃-30℃ per second. S3.2 At the same time, a clearance of 2-5cm should be reserved at the head and tail, and the billet should be slowly cooled after it is taken off the production line. The slow cooling temperature should be greater than 300℃. S3.3 The steel billet after slow cooling must be stored in the warehouse for 24 hours before it can be put into the heating furnace for production.

10. The process for preparing low-alloy high-strength steel according to claim 1, characterized in that: The visual inspection in step six includes: checking whether the surface of each billet sample is free of bubbles, scabs, folds and inclusions, and whether there are any visible cracks, shrinkage cavities and delamination; the flaw detection includes: performing flaw detection on each batch of billets, randomly selecting 2 billet samples from each batch, and conducting impact tests at room temperature, 0℃ or -20℃ according to the level requirements set by the manufacturer's engineers.

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