High-toughness microalloy structural steel and method for manufacturing same

Abstract

The application relates to the field of alloy structural steel, and particularly discloses a high-strength and high-toughness micro-alloy structural steel and a preparation method thereof; the preparation method comprises the following steps: S1: adding a refining agent into molten iron, refining and slagging; adding a modifier, and performing modification treatment; sequentially performing vacuum degassing, continuous casting and rolling to obtain a basic structural steel; S2: cleaning the basic structural steel, and electroplating to obtain a structural steel A with modified graphite deposited on the surface; S3: taking the structural steel A, performing high-temperature carburizing, low-temperature carburizing, diffusion, quenching and cooling and tempering to obtain the high-strength and high-toughness micro-alloy structural steel. The electroplating solution used in the electroplating in the S2 step comprises the following raw materials: 30-40 g / L of nickel sulfate hexahydrate, 5-15 g / L of nickel chloride hexahydrate, 5-10 g / L of zinc sulfate, 3.5-10.5 g / L of titanyl sulfate, 50-60 g / L of trisodium citrate, 5-10 g / L of an additive, 5-10 g / L of modified graphite, and the rest is water.

Description

Technical Field

[0001] The invention relates to the field of alloy structural steel, and particularly discloses high-strength and toughness microalloy structural steel and a preparation method thereof. Background Art

[0002] Microalloyed structural steels offer excellent performance and are widely used in bridges, high-rise buildings, power generation equipment, and various pipelines. The addition of small amounts of alloying elements to the steel matrix significantly improves performance. Microalloying within the steel matrix contributes to grain refinement, inclusion reduction, crack reduction, and improved hardenability. The appropriate alloying element type and content can be determined based on specific needs.

[0003] Carburizing the surface of microalloyed structural steel can further improve its strength, but the conventional carburizing process will lead to coarse grains, and the pre-carburizing step takes too long. The above problems will lead to a certain degree of decrease in the strength or toughness of microalloyed structural steel; therefore, it is of great significance to study a high-strength and toughness microalloyed structural steel and its preparation method. Summary of the Invention

[0004] The object of the present invention is to provide a high-strength and toughness microalloy structural steel and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing high-strength and high-toughness microalloy structural steel comprises the following steps:

[0006] S1: adding a refining agent to the molten iron, refining and slag removal; adding a modifier, modifying treatment; vacuum degassing, continuous casting, and rolling are carried out in sequence to obtain basic structural steel;

[0007] S2: The basic structural steel is cleaned and electroplated to obtain structural steel A with modified graphite deposited on the surface;

[0008] S3: Take structural steel A and perform high-temperature carburizing, low-temperature carburizing, diffusion, quenching and cooling, and tempering to obtain high-strength and toughness microalloy structural steel.

[0009] More optimally, step S1 specifically includes: taking molten iron; adding a refining agent of 1-2% of the mass of the molten iron at 1600-1700°C, stopping for 20-30 minutes, and then skimming the slag; adding a modifier of 1-2% of the mass of the molten iron, stopping for 20-30 minutes, and removing the slag; performing vacuum degassing, continuous casting (temperature: 1180-1220°C), and rolling (heating at 1200°C for 5-6 hours and then rolling to open the blank, pit cooling to 180°C after opening the blank, and then heating to 1180°C again, keeping warm for 5-6 hours, and rolling after the end of the insulation, the initial rolling temperature is 1100-1180°C, the final rolling temperature is 850-1000°C, and air cooling is performed after rolling) to obtain basic structural steel.

[0010] More preferably, the S1 step specifically comprises: taking the molten iron; adding a refining agent of 1% of the mass of the molten iron at 1600℃, stopping for 20 min, and then skimming the slag; adding a modifier of 1% of the mass of the molten iron, stopping for 25 min, and then removing the slag; vacuum degassing, continuous casting (temperature: 1220℃), and rolling (after heating at 1200℃ for 6h, rough rolling and blooming are performed, the billet is cooled to 180℃ after blooming, then heated to 1180℃ again, kept for 6h, and then rolled after the end of the keeping, with the initial rolling temperature being 1100℃ and the final rolling temperature being 950℃, and then air-cooled after rolling) to obtain the base structure steel.

[0011] More preferably, the molten iron comprises the following components in the following mass percentages: C: 0.7-0.85%, Si: 0.15-0.35%, Mn: 0.70-0.90%, P: ≤0.025%, S: ≤0.025%, Cr: 0.16-0.25%, V: 0.068-0.08%, Cu: ≤0.001%, Ni: ≤0.001%, Ti: ≤0.001%, and the rest being Fe and unavoidable impurities.

[0012] More preferably, the molten iron comprises the following components in the following mass percentages: C: 0.75%, Si: 0.2%, Mn: 0.75%, P: 0.005%, S: 0.015%, Cr: 0.22%, V: 0.071%, Cu: 0.001%, Ni: 0.001%, Ti: 0.001%, and the rest being Fe and unavoidable impurities.

[0013] More preferably, the cleaning process in the S2 step is as follows: the base structure steel is cleaned with water at 80℃ for 30s, immersed in 5% sulfuric acid for 10 min, and then cleaned with water again.

[0014] More preferably, the specific process of electroplating in the S2 step is as follows: the temperature is controlled to be 50-60℃, the pH is controlled to be 7-8, the current density is controlled to be 4-6A / dm 3 , electroplating in the electroplating solution for 10-15 min;

[0015] The electroplating solution comprises the following raw materials: nickel sulfate hexahydrate 30-40g / L, nickel chloride hexahydrate 5-15g / L, zinc sulfate 5-10g / L, titanyl sulfate 3.5-10.5g / L, trisodium citrate 50-60g / L, 5-10g / L additive, 5-10g / L modified graphite, and the rest being water.

[0016] More preferably, the preparation of the modified graphite comprises the following steps: step one: taking epoxy silane coupling agent, di(hydroxyethyl)methyl dodecyl ammonium chloride, 3-amino-5-fluoropyridine, and DMSO, heating to 130-140℃, stirring for 4-6h, and then removing the solvent to obtain the modifier A;

[0017] Step 2: Take nanographite, ethanol, and water, add modifier A, stir at 40-50°C for 5-6 hours, filter, and dry to obtain modified graphite;

[0018] The modifier A comprises the following raw materials, calculated by mass: 10 to 15 parts of epoxy silane coupling agent, 5 to 8 parts of di(hydroxyethyl)methyl dodecyl ammonium chloride, 2 to 4 parts of 3-amino-5-fluoropyridine, and 150 to 200 parts of DMSO;

[0019] The modified graphite comprises the following raw materials, calculated by mass: 10 to 15 parts of nanographite, 40 to 60 parts of ethanol, 40 to 60 parts of water, and 3 to 5 parts of modifier A.

[0020] More optimally, the preparation of the additive includes the following steps: Step 1: taking portions of hyperbranched polyacrylic acid, citrate, 6-hydroxy-2-pyridinecarboxylic acid, stannous isooctanoate, and p-toluenesulfonic acid monohydrate, mixing them evenly, heating to 130-140° C. and stirring for 1-2 hours, heating to 150-160° C. and stirring for 4-6 hours, cooling to 130-140° C., adding an epoxy silane coupling agent, stirring for 4-6 hours, and removing the solvent to obtain a modifier B;

[0021] Step 2: Take molybdenum disulfide, ethanol, and water, add modifier B, and stir at 40-50°C for 5-6 hours to obtain an additive;

[0022] The modifier B comprises the following raw materials, calculated by mass: 15 to 20 parts of hyperbranched polyacrylic acid, 4 to 6 parts of citrate, 1 to 3 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.1 to 0.2 parts of stannous isooctanoate, 0.04 to 0.05 parts of p-toluenesulfonic acid monohydrate, and 10 to 15 parts of epoxy silane coupling agent;

[0023] The additive comprises the following raw materials, calculated by mass: 5 to 10 parts of molybdenum disulfide, 40 to 60 parts of ethanol, 40 to 60 parts of water, and 8 to 12 parts of modifier B.

[0024] More optimally, in step S2, the specific process of high-temperature carburizing is: temperature of 900-950°C, carbon potential of 1.1, and time of 3-4h; the specific process of low-temperature carburizing is: temperature of 800-850°C, carbon potential of 1.1, and time of 2-3h; the specific process of diffusion is: temperature of 800-850°C, carbon potential of 0.8, and time of 1-2h.

[0025] More optimally, the refining agent includes the following raw materials, by mass percentage: 80-90% CaO, 10-20% Al2O3; the modifier includes the following raw materials, by mass percentage: 50-60% rare earth ferrosilicon, 20-30% modified ferrosilicon, 10-20% silicon-calcium alloy, 5-10% trace elements; the trace elements include the following raw materials, by mass percentage: 40% Zr, 25% Cu, 15% Sb, 15% Bi and 5% B.

[0026] More optimally, the refining agent includes the following raw materials, by mass percentage: 85% CaO, 15% Al2O3.

[0027] More optimally, the preparation of the modified ferrosilicon includes the following steps: mixing titanium carbide powder and nickel-based powder in a mass ratio of (1-2):1 to obtain a mixture; and depositing the mixture on the surface of ferrosilicon by plasma transferred arc welding to obtain modified ferrosilicon.

[0028] More optimally, the preparation of the modified ferrosilicon includes the following steps: mixing titanium carbide powder and nickel-based powder in a mass ratio of 2:1 to obtain a mixture; depositing the mixture on the surface of ferrosilicon by plasma transferred arc welding to obtain modified ferrosilicon; the nickel-based powder is METCOCLAD 625 powder (Ni21Cr9Mo4Nb) from Oerlikon Metco; the deposition equipment is a STARWELD 400A with an EXCALIBUR welding torch, and the deposition parameters are: 2L / minAr central airflow, 2L / minAr powder airflow, 12L / minAr shielding airflow, voltage 29V, current 145A, and deposition time 0.2s.

[0029] Compared with the prior art, the present invention has the following beneficial effects: after slag removal is completed, a modifier is added to further refine the grains. The modifier contains modified ferrosilicon, i.e., ferrosilicon with titanium carbide powder deposited on the surface and nickel-based powder. Ferrosilicon is an alloy modifier that can improve the mechanical properties of basic structural steel, but the overall effect is not good. Titanium carbide is enriched at the grain boundaries, acting as a pinning agent and increasing the strength and toughness of the basic structural steel. However, due to its small size, it easily accumulates into agglomerates, reducing its effectiveness. Therefore, titanium carbide is deposited on the surface of ferrosilicon and then added, which effectively improves the strength and toughness of the basic structural steel. Moreover, after the grains are refined, it facilitates the subsequent carburizing step.

[0030] Electroplating on the surface of basic structural steel not only improves the corrosion resistance of the basic structural steel, but also serves as a transition layer, which is conducive to improving the uniformity of the carburized layer during the subsequent carburizing step. The modified graphite distributed in the plating layer can serve as the growth core of carbides in the subsequent step, improving the nucleation rate and helping to obtain fine and uniform carbide particles. This eliminates the need for low-temperature carburizing to form pre-existing carbide particles during carburizing, and allows direct high-temperature carburizing, thereby improving carburizing efficiency.

[0031] Modifier A is used to improve the dispersion of graphite in the electroplating solution. The molecular planarity of the pyridine structure in 3-amino-5-fluoropyridine in Modifier A facilitates the orderly adsorption of the coating on the surface of carbon nanotubes, while fluorine acts as a lubricant, helping to obtain a smooth coating. The cationic structure of di(hydroxyethyl)methyldodecylammonium chloride effectively improves the dispersion of graphite.

[0032] An additive is also added to the electroplating solution. The additive is molybdenum disulfide modified with modifier B. Molybdenum disulfide itself has good lubricity, and its addition helps improve the performance of the coating. Modifier B includes hyperbranched polyacrylic acid, citrate, and 6-hydroxy-2-pyridinecarboxylic acid. Hyperbranched polyacrylic acid can improve the dispersibility of molybdenum disulfide. Citrate and 6-hydroxy-2-pyridinecarboxylic acid have an auxiliary complexing effect and can also serve as brighteners and leveling agents for electroplating, contributing to the uniformity of the coating. In summary, the additive helps form a smooth and uniform coating and also helps disperse the modified graphite, which has a positive effect on the subsequent carburizing step.

[0033] Carburizing treatment can further improve the surface hardness of structural steel A and maintain good toughness inside it. However, conventional carburizing processes have problems such as coarse grains that affect performance, and the pre-carburizing step is too long. Due to the presence of modified graphite on the surface of structural steel A, the present invention can directly perform high-temperature carburizing. After high-temperature carburizing, the temperature is lowered to perform low-temperature carburizing, further refining the carbides and reducing the stress in the carburized layer, thereby obtaining a uniform carburized layer. DETAILED DESCRIPTION

[0034] The following describes preferred implementations of the present invention. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. It will be apparent to those skilled in the art that all other implementations derived without inventive effort, without departing from the principles of the present invention, are within the scope of protection of the present invention.

[0035] The following parts are by mass unless otherwise specified;

[0036] Example 1: S1: adding a refining agent to molten iron, refining and skimming; adding a modifier, modifying the molten iron; vacuum degassing, continuous casting, and rolling are sequentially performed to obtain basic structural steel;

[0037] The modifier comprises the following raw materials, in percentage by mass: 55% rare earth ferrosilicon, 25% modified ferrosilicon, 12% calcium silicon alloy, and 8% trace elements;

[0038] S2: Cleaning and electroplating the basic structural steel to obtain structural steel A;

[0039] The specific process of electroplating is as follows: temperature is 55℃, pH=8, constant current DC current density is 5A / dm 3 , electroplating in the plating solution for 12 minutes;

[0040] The electroplating solution includes the following ingredients: 35 g / L nickel sulfate hexahydrate, 10 g / L nickel chloride hexahydrate, 6 g / L zinc sulfate, 5 g / L titanyl sulfate, 55 g / L trisodium citrate, 8 g / L additives, 10 g / L modified graphite, and the remainder is water;

[0041] The modified graphite preparation method comprises the following steps: (1) taking 12 parts of an epoxy silane coupling agent, 6 parts of di(hydroxyethyl)methyldodecylammonium chloride, 3 parts of 3-amino-5-fluoropyridine, and 200 parts of DMSO, heating the mixture to 140° C., stirring the mixture for 5 hours, and removing the solvent to obtain a modifier A;

[0042] (2) Take 12 parts of nanographite, 60 parts of ethanol, and 60 parts of water, add 4 parts of modifier A, stir at 50°C for 6 hours, filter, and dry to obtain modified graphite;

[0043] The preparation method of the additive comprises the following steps: (1) taking 18 parts of hyperbranched polyacrylic acid, 5 parts of citrate, 2 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.2 parts of stannous isooctanoate, and 0.04 parts of p-toluenesulfonic acid monohydrate, mixing them uniformly, heating them to 130° C. and stirring them for 1 hour, heating them to 160° C. and stirring them for 5 hours, cooling them to 140° C., adding 12 parts of epoxy silane coupling agent, stirring them for 5 hours, and removing the solvent to obtain a modifier B;

[0044] (2) Take 8 parts of molybdenum disulfide, 60 parts of ethanol, and 60 parts of water, add 10 parts of modifier B, and stir at 50° C. for 5 hours to obtain an additive;

[0045] S3: Take structural steel A and perform carburizing: high temperature carburizing: 950℃, carbon potential 1.1, carburizing for 4h, then cooling in oil at 100℃; low temperature carburizing: 800℃, carbon potential 1.1, carburizing for 3h, cooling in oil at 100℃; low carbon potential diffusion: 800℃, carbon potential 0.8, diffusion for 1h, quenching and cooling in oil at 100℃; tempering at 180℃ for 3h to obtain high strength and toughness microalloy structural steel.

[0046] Example 2: S1: adding a refining agent to molten iron, refining and skimming; adding a modifier, modifying the molten iron; and sequentially performing vacuum degassing, continuous casting, and rolling to obtain basic structural steel;

[0047] The modifier comprises the following raw materials, in percentage by mass: 55% rare earth ferrosilicon, 25% modified ferrosilicon, 12% calcium silicon alloy, and 8% trace elements;

[0048] S2: Cleaning and electroplating the basic structural steel to obtain structural steel A;

[0049] The specific process of electroplating: temperature is 55℃, pH=8, constant current direct current density is 5A / dm 3 , and electroplating in the electroplating solution for 12 min;

[0050] The electroplating solution comprises the following components: 40 g / L of nickel sulfate hexahydrate, 5 g / L of nickel chloride hexahydrate, 5 g / L of zinc sulfate, 10.5 g / L of titanyl sulfate, 60 g / L of trisodium citrate, 10 g / L of an additive, 6 g / L of modified graphite, and the rest is water;

[0051] The preparation method of the modified graphite is as follows: (1) 10 parts of epoxy silane coupling agent, 5 parts of di(hydroxyethyl)methyl dodecyl ammonium chloride, 2 parts of 3-amino-5-fluoropyridine, and 150 parts of DMSO are taken, and the temperature is raised to 130℃, and stirred for 6 h, and the solvent is removed to obtain a modifier A;

[0052] (2) 10 parts of nano-graphite, 40 parts of ethanol, and 40 parts of water are taken, 3 parts of the modifier A is added, and stirred at 50℃ for 6 h, and filtered and dried to obtain the modified graphite;

[0053] The preparation method of the additive is as follows: (1) 15 parts of hyperbranched polyacrylic acid, 4 parts of citric acid ester, 1 part of 6-hydroxy-2-pyridine carboxylic acid, 0.1 part of isooctanoic acid stannous, and 0.04 part of p-toluene sulfonic acid monohydrate are taken, and uniformly mixed, and the temperature is raised to 130℃ and stirred for 1 h, and the temperature is raised to 160℃ and stirred for 4 h, and the temperature is lowered to 130℃, and 10 parts of epoxy silane coupling agent is added, and stirred for 6 h, and the solvent is removed to obtain a modifier B;

[0054] (2) 5 parts of molybdenum disulfide, 40 parts of ethanol, and 40 parts of water are taken, 8 parts of the modifier B is added, and stirred at 50℃ for 5 h to obtain the additive;

[0055] S3: the structural steel A is taken, carburized: high-temperature carburization: 900℃, carbon potential 1.1, carburized for 4 h, and then cooled in oil at 100℃; low-temperature carburization: 850℃, carbon potential 1.1, carburized for 3 h, and then cooled in oil at 100℃; low-carbon potential diffusion: 800℃, carbon potential 0.8, diffused for 2 h, and then quenched and cooled in oil at 100℃; tempered at 180℃ for 3 h to obtain a high-strength and high-toughness micro-alloy structural steel.

[0056] Example 3: S1: a refining agent is added to molten iron, and slag is refined; a modifier is added for modification treatment; vacuum degassing, continuous casting, and rolling are sequentially performed to obtain a base structural steel;

[0057] The modifier comprises the following raw materials in percentage by mass: 55% of rare earth ferrosilicon, 25% of modified ferrosilicon, 12% of silicon-calcium alloy, and 8% of trace elements;

[0058] S2: the base structural steel is cleaned, and electroplated to obtain the structural steel A;

[0059] The specific process of electroplating is as follows: temperature is 55℃, pH=8, constant current DC current density is 5A / dm 3 , electroplating in the plating solution for 12 minutes;

[0060] The electroplating solution includes the following ingredients: 30 g / L nickel sulfate hexahydrate, 15 g / L nickel chloride hexahydrate, 10 g / L zinc sulfate, 3.5 g / L titanyl sulfate, 50 g / L trisodium citrate, 5 g / L additives, 10 g / L modified graphite, and the remainder is water;

[0061] The modified graphite preparation method comprises the following steps: (1) taking 15 parts of an epoxy silane coupling agent, 8 parts of di(hydroxyethyl)methyldodecylammonium chloride, 4 parts of 3-amino-5-fluoropyridine, and 200 parts of DMSO, heating the mixture to 140° C., stirring the mixture for 6 hours, and removing the solvent to obtain a modifier A;

[0062] (2) Take 15 parts of nanographite, 60 parts of ethanol, and 60 parts of water, add 5 parts of modifier A, stir at 50°C for 5 hours, filter, and dry to obtain modified graphite;

[0063] The preparation method of the additive comprises the following steps: (1) taking 20 parts of hyperbranched polyacrylic acid, 6 parts of citrate, 3 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.2 parts of stannous isooctanoate, and 0.05 parts of p-toluenesulfonic acid monohydrate, mixing them uniformly, heating them to 130° C. and stirring them for 2 hours, heating them to 160° C. and stirring them for 4 hours, cooling them to 140° C., adding 10 parts of epoxy silane coupling agent, stirring them for 5 hours, and removing the solvent to obtain a modifier B;

[0064] (2) Take 10 parts of molybdenum disulfide, 60 parts of ethanol, and 60 parts of water, add 12 parts of modifier B, and stir at 50° C. for 6 hours to obtain an additive;

[0065] S3: Take structural steel A and perform carburizing: high temperature carburizing: 950℃, carbon potential 1.1, carburizing for 4h, then cooling in oil at 100℃; low temperature carburizing: 800℃, carbon potential 1.1, carburizing for 2h, cooling in oil at 100℃; low carbon potential diffusion: 800℃, carbon potential 0.8, diffusion for 2h, quenching and cooling in oil at 100℃; tempering at 180℃ for 3h to obtain high strength and toughness microalloy structural steel.

[0066] Comparative Example 1 (nanographite is used instead of modified graphite, and the remaining steps are the same as those in Example 1): S1: adding a refining agent to molten iron and refining and skimming; adding a modifier and performing a modification treatment; vacuum degassing, continuous casting, and rolling are sequentially performed to obtain basic structural steel;

[0067] The modifier comprises the following raw materials, in percentage by mass: 55% rare earth ferrosilicon, 25% modified ferrosilicon, 12% calcium silicon alloy, and 8% trace elements;

[0068] S2: Cleaning and electroplating the basic structural steel to obtain structural steel A;

[0069] The specific process of electroplating is as follows: temperature is 55℃, pH=8, constant current DC current density is 5A / dm 3 , electroplating in the plating solution for 12 minutes;

[0070] The electroplating solution includes the following ingredients: 35 g / L nickel sulfate hexahydrate, 10 g / L nickel chloride hexahydrate, 6 g / L zinc sulfate, 5 g / L titanyl sulfate, 55 g / L trisodium citrate, 8 g / L additives, 10 g / L nanographite, and the remainder is water;

[0071] The preparation method of the additive comprises the following steps: (1) taking 18 parts of hyperbranched polyacrylic acid, 5 parts of citrate, 2 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.2 parts of stannous isooctanoate, and 0.04 parts of p-toluenesulfonic acid monohydrate, mixing them uniformly, heating them to 130° C. and stirring them for 1 hour, heating them to 160° C. and stirring them for 5 hours, cooling them to 140° C., adding 12 parts of epoxy silane coupling agent, stirring them for 5 hours, and removing the solvent to obtain a modifier B;

[0072] (2) Take 8 parts of molybdenum disulfide, 60 parts of ethanol, and 60 parts of water, add 10 parts of modifier B, and stir at 50° C. for 5 hours to obtain an additive;

[0073] S3: Take structural steel A and perform carburizing: high temperature carburizing: 950℃, carbon potential 1.1, carburizing for 4h, then cooling in oil at 100℃; low temperature carburizing: 800℃, carbon potential 1.1, carburizing for 3h, cooling in oil at 100℃; low carbon potential diffusion: 800℃, carbon potential 0.8, diffusion for 1h, quenching and cooling in oil at 100℃; tempering at 180℃ for 3h to obtain high strength and toughness microalloy structural steel.

[0074] Comparative Example 2 (the preparation method of the additive is changed, and the remaining steps are the same as those of Example 1): S1: adding a refining agent to molten iron, refining and skimming; adding a modifier, and performing a modification treatment; vacuum degassing, continuous casting, and rolling are sequentially performed to obtain basic structural steel;

[0075] The modifier comprises the following raw materials, in percentage by mass: 55% rare earth ferrosilicon, 25% modified ferrosilicon, 12% calcium silicon alloy, and 8% trace elements;

[0076] S2: Cleaning and electroplating the basic structural steel to obtain structural steel A;

[0077] The specific process of electroplating is as follows: temperature is 55℃, pH=8, constant current DC current density is 5A / dm 3 , electroplating in the plating solution for 12 minutes;

[0078] The electroplating solution includes the following ingredients: 35 g / L nickel sulfate hexahydrate, 10 g / L nickel chloride hexahydrate, 6 g / L zinc sulfate, 5 g / L titanyl sulfate, 55 g / L trisodium citrate, 8 g / L additives, 10 g / L modified graphite, and the remainder is water;

[0079] The modified graphite preparation method comprises the following steps: (1) taking 12 parts of an epoxy silane coupling agent, 6 parts of di(hydroxyethyl)methyldodecylammonium chloride, 3 parts of 3-amino-5-fluoropyridine, and 200 parts of DMSO, heating the mixture to 140° C., stirring the mixture for 5 hours, and removing the solvent to obtain a modifier A;

[0080] (2) Take 12 parts of nanographite, 60 parts of ethanol, and 60 parts of water, add 4 parts of modifier A, stir at 50°C for 6 hours, filter, and dry to obtain modified graphite;

[0081] The preparation method of the additive is as follows: (1) taking 2 parts of 6-hydroxy-2-pyridinecarboxylic acid and 2 parts of epoxy silane coupling agent, stirring for 5 hours, and removing the solvent to obtain modifier B;

[0082] (2) Take 8 parts of molybdenum disulfide, 60 parts of ethanol, and 60 parts of water, add 10 parts of modifier B, and stir at 50° C. for 5 hours to obtain an additive;

[0083] S3: Take structural steel A and perform carburizing: high temperature carburizing: 950℃, carbon potential 1.1, carburizing for 4h, then cooling in oil at 100℃; low temperature carburizing: 800℃, carbon potential 1.1, carburizing for 3h, cooling in oil at 100℃; low carbon potential diffusion: 800℃, carbon potential 0.8, diffusion for 1h, quenching and cooling in oil at 100℃; tempering at 180℃ for 3h to obtain high strength and toughness microalloy structural steel.

[0084] Comparative Example 3 (modifier A is used instead of modified graphite, and the remaining steps are the same as those in Example 1): S1: adding a refining agent to molten iron and refining and skimming; adding a modifier and performing a modification treatment; vacuum degassing, continuous casting, and rolling are sequentially performed to obtain basic structural steel;

[0085] The modifier comprises the following raw materials, in percentage by mass: 55% rare earth ferrosilicon, 25% modified ferrosilicon, 12% calcium silicon alloy, and 8% trace elements;

[0086] S2: Cleaning and electroplating the basic structural steel to obtain structural steel A;

[0087] The specific process of electroplating is as follows: temperature is 55℃, pH=8, constant current DC current density is 5A / dm 3 , electroplating in the plating solution for 12 minutes;

[0088] The electroplating solution includes the following ingredients: 35 g / L nickel sulfate hexahydrate, 10 g / L nickel chloride hexahydrate, 6 g / L zinc sulfate, 5 g / L titanyl sulfate, 55 g / L trisodium citrate, 8 g / L additives, 10 g / L modifier A, and the remainder is water;

[0089] The preparation method of the modifier A is as follows: 12 parts of an epoxy silane coupling agent, 6 parts of di(hydroxyethyl)methyldodecylammonium chloride, 3 parts of 3-amino-5-fluoropyridine, and 200 parts of DMSO are taken, heated to 140° C., stirred for 5 hours, and the solvent is removed to obtain the modifier A;

[0090] The preparation method of the additive comprises the following steps: (1) taking 18 parts of hyperbranched polyacrylic acid, 5 parts of citrate, 2 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.2 parts of stannous isooctanoate, and 0.04 parts of p-toluenesulfonic acid monohydrate, mixing them uniformly, heating them to 130° C. and stirring them for 1 hour, heating them to 160° C. and stirring them for 5 hours, cooling them to 140° C., adding 12 parts of epoxy silane coupling agent, stirring them for 5 hours, and removing the solvent to obtain a modifier B;

[0091] (2) Take 8 parts of molybdenum disulfide, 60 parts of ethanol, and 60 parts of water, add 10 parts of modifier B, and stir at 50° C. for 5 hours to obtain an additive;

[0092] S3: Take structural steel A and perform carburizing: high temperature carburizing: 950℃, carbon potential 1.1, carburizing for 4h, then cooling in oil at 100℃; low temperature carburizing: 800℃, carbon potential 1.1, carburizing for 3h, cooling in oil at 100℃; low carbon potential diffusion: 800℃, carbon potential 0.8, diffusion for 1h, quenching and cooling in oil at 100℃; tempering at 180℃ for 3h to obtain high strength and toughness microalloy structural steel.

[0093] Comparative Example 4 (the raw material of the modifier is changed, and the remaining steps are the same as those of Example 1): S1: adding a refining agent to molten iron, refining and skimming; adding a modifier, and performing a modification treatment; vacuum degassing, continuous casting, and rolling are sequentially performed to obtain basic structural steel;

[0094] The modifier comprises the following raw materials, by mass percentage: 40% rare earth ferrosilicon, 20% ferrosilicon, 20% titanium carbide, 12% silicon calcium alloy, and 8% trace elements;

[0095] S2: Cleaning and electroplating the basic structural steel to obtain structural steel A;

[0096] The specific process of electroplating is as follows: temperature is 55℃, pH=8, constant current DC current density is 5A / dm 3 , electroplating in the plating solution for 12 minutes;

[0097] The electroplating solution includes the following ingredients: 35 g / L nickel sulfate hexahydrate, 10 g / L nickel chloride hexahydrate, 6 g / L zinc sulfate, 5 g / L titanyl sulfate, 55 g / L trisodium citrate, 8 g / L additives, 10 g / L modified graphite, and the remainder is water;

[0098] The modified graphite preparation method comprises the following steps: (1) taking 12 parts of an epoxy silane coupling agent, 6 parts of di(hydroxyethyl)methyldodecylammonium chloride, 3 parts of 3-amino-5-fluoropyridine, and 200 parts of DMSO, heating the mixture to 140° C., stirring the mixture for 5 hours, and removing the solvent to obtain a modifier A;

[0099] (2) Take 12 parts of nanographite, 60 parts of ethanol, and 60 parts of water, add 4 parts of modifier A, stir at 50°C for 6 hours, filter, and dry to obtain modified graphite;

[0100] The preparation method of the additive comprises the following steps: (1) taking 18 parts of hyperbranched polyacrylic acid, 5 parts of citrate, 2 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.2 parts of stannous isooctanoate, and 0.04 parts of p-toluenesulfonic acid monohydrate, mixing them uniformly, heating them to 130° C. and stirring them for 1 hour, heating them to 160° C. and stirring them for 5 hours, cooling them to 140° C., adding 12 parts of epoxy silane coupling agent, stirring them for 5 hours, and removing the solvent to obtain a modifier B;

[0101] (2) Take 8 parts of molybdenum disulfide, 60 parts of ethanol, and 60 parts of water, add 10 parts of modifier B, and stir at 50° C. for 5 hours to obtain an additive;

[0102] S3: Take structural steel A and perform carburizing: high temperature carburizing: 950℃, carbon potential 1.1, carburizing for 4h, then cooling in oil at 100℃; low temperature carburizing: 800℃, carbon potential 1.1, carburizing for 3h, cooling in oil at 100℃; low carbon potential diffusion: 800℃, carbon potential 0.8, diffusion for 1h, quenching and cooling in oil at 100℃; tempering at 180℃ for 3h to obtain high strength and toughness microalloy structural steel.

[0103] In the above examples, the test methods used are conventional methods unless otherwise specified; the raw materials used are commercially available unless otherwise specified, and the sources of the raw materials are as follows: nickel sulfate hexahydrate (CAS: 10101-97-0); nickel chloride hexahydrate (W00416, Wuhan Jiye Sheng); zinc sulfate (S22124, Shanghai Yuanye); titanyl sulfate (S41632, Shanghai Yuanye); trisodium citrate (S67462, Shanghai Yuanye); epoxy silane coupling agent (KH560, S15029, Shanghai Yuanye); di(hydroxyethyl)methyldodecylammonium chloride (Y17642, Shanghai Yuanye); 3-amino-5-fluoropyridine (CAS: 210169-05-4); DMSO (CAS: 67-68-5); nanographite (40 nm, Kramar); ethanol (C AS: 64-17-5); hyperbranched polyacrylic acid (H20-star-PAA, Xi'an Ruixi Biotechnology Co., Ltd.); citrate ester (B20912, Shanghai Yuanye); rare earth ferrosilicon (rare earth 17%-37%, Si 35%-46%, Mn 5%-8%, Ca 5%-8%, Ti 6%, the rest is iron; Anyang Jinsheng Metallurgical Materials Co., Ltd.); ferrosilicon (FeSi75-C, Beijing Jingang); silicon calcium alloy (Ca content 30%); 6-hydroxy-2-pyridinecarboxylic acid (CAS: 19621-92-2); stannous isooctanoate (S3252, Sigma-Aldrich); p-toluenesulfonic acid monohydrate (CAS: 6192-52-5); molybdenum disulfide (S30491, Shanghai Yuanye); titanium carbide powder (TIC1235, Yumu New Materials Co., Ltd.).

[0104] Experiment: Take the high-strength and toughness microalloy structural steel prepared in Examples 1 to 3 and Comparative Examples 1 to 4; (1) Use a 430SVD Vickers hardness tester to measure the Vickers hardness at 1 cm, with a load of 200 g; (2) Use a JB-30B drop hammer impact tester to conduct an impact test, with the impact specimen size being 10×10×55 mm; Specific data are shown in the table below;

[0105]

[0106] Conclusion: According to Comparative Example 1, nanographite is used instead of modified graphite. Due to the poor dispersibility of nanographite in the electroplating solution, the nanographite is unevenly distributed in the coating, which affects carburization and significantly reduces the performance; Comparative Example 2 changes the additive preparation method. Due to the change in the coating state, the performance is not as good as the embodiment; Comparative Example 3 uses modifier A instead of modified graphite, that is, no nanographite is introduced, which has a greater impact on the carburizing process and significantly reduces the performance; Comparative Example 4 changes the raw material of the modifier, and the performance is reduced, which shows the importance of a suitable modifier; In summary, the microalloyed structural steel prepared by the present invention has the characteristics of high strength and high toughness.

[0107] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the spirit and principles of the present invention and within the technical scope disclosed in this application should be included in the scope of protection of this application. The embodiments and features of the embodiments of this application can be combined with each other unless there is a conflict. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A method for preparing high-strength and high-toughness microalloyed structural steel, characterized by: The following steps are involved: S1: Add refining agent to molten iron, refine and skim slag; add modifier and perform modification treatment; Vacuum degassing, continuous casting and rolling are carried out in sequence to obtain basic structural steel; S2: The basic structural steel is cleaned and electroplated to obtain structural steel A with modified graphite deposited on the surface; S3: Take structural steel A and perform high-temperature carburizing, low-temperature carburizing, diffusion, quenching and cooling, and tempering in sequence to obtain high-strength and toughness microalloy structural steel; Among them, in the step S2, the specific process of the electroplating is: controlling the temperature to 50~60℃, pH=7~8, and current density to 4~6A / dm 3 , electroplating in the electroplating solution for 10~15min; The electroplating solution comprises the following raw materials: 30-40 g / L nickel sulfate hexahydrate, 5-15 g / L nickel chloride hexahydrate, 5-10 g / L zinc sulfate, 3.5-10.5 g / L titanyl sulfate, 50-60 g / L trisodium citrate, 5-10 g / L additives, 5-10 g / L modified graphite, and the remainder is water; The preparation of the modified graphite includes the following steps: step 1: taking an epoxy silane coupling agent, di(hydroxyethyl)methyl dodecyl ammonium chloride, 3-amino-5-fluoropyridine, and DMSO, heating to 130-140° C., stirring for 4-6 hours, and removing the solvent to obtain a modifier A; step 2: taking nanographite, ethanol, and water, adding the modifier A, stirring at 40-50° C. for 5-6 hours, filtering, and drying to obtain the modified graphite; the modifier A includes the following raw materials, calculated by mass: 10-15 parts of an epoxy silane coupling agent, 5-8 parts of di(hydroxyethyl)methyl dodecyl ammonium chloride, 2-4 parts of 3-amino-5-fluoropyridine, and 150-200 parts of DMSO; The modified graphite comprises the following raw materials, calculated by weight: 10-15 parts of nanographite, 40-60 parts of ethanol, 40-60 parts of water, and 3-5 parts of modifier A; The preparation of the additive includes the following steps: step 1: taking parts of hyperbranched polyacrylic acid, citric acid ester, 6-hydroxy-2-pyridinecarboxylic acid, stannous isooctanoate, and p-toluenesulfonic acid monohydrate, mixing them evenly, heating them to 130-140° C. and stirring them for 1-2 hours, heating them to 150-160° C. and stirring them for 4-6 hours, cooling them to 130-140° C., adding an epoxy silane coupling agent, stirring them for 4-6 hours, and removing the solvent to obtain a modifier B; step 2: taking molybdenum disulfide, ethanol, and water, adding the modifier B, and stirring them at 40-50° C. for 5-6 hours to obtain the additive; the modifier B includes the following raw materials, calculated by mass: 15-20 parts of hyperbranched polyacrylic acid, 4-6 parts of citric acid ester, 1-3 parts of 6-hydroxy-2-pyridinecarboxylic acid, 0.1-0.2 parts of stannous isooctanoate, 0.04-0.05 parts of p-toluenesulfonic acid monohydrate, and 10-15 parts of an epoxy silane coupling agent; The additive comprises the following raw materials, calculated by mass: 5 to 10 parts of molybdenum disulfide, 40 to 60 parts of ethanol, 40 to 60 parts of water, and 8 to 12 parts of modifier B; Among them, in step S3, the specific process of the high-temperature carburizing is: temperature 900~950℃, carbon potential 1.1, time 3~4h; the specific process of the low-temperature carburizing is: temperature 800~850℃, carbon potential 1.1, time 2~3h; the specific process of the diffusion is: temperature 800~850℃, carbon potential 0.8, time 1~2h; The refining agent includes the following raw materials, by mass percentage: 80-90% CaO, 10-20% Al2O3; the modifier includes the following raw materials, by mass percentage: 50-60% rare earth ferrosilicon, 20-30% modified ferrosilicon, 10-20% silicon-calcium alloy, 5-10% trace elements; the trace elements include the following raw materials, by mass percentage: 40% Zr, 25% Cu, 15% Sb, 15% Bi and 5% B.

2. The method for preparing a high-strength and toughness microalloyed structural steel according to claim 1, characterized in that: The molten iron includes the following components in percentage by mass: C: 0.7-0.85%, Si: 0.15-0.35%, Mn: 0.70-0.90%, P: ≤0.025%, S: ≤0.025%, Cr: 0.16-0.25%, V: 0.068-0.08%, Cu: ≤0.001%, Ni: ≤0.001%, Ti: ≤0.001%, and the rest is Fe and unavoidable impurities.

3. The method for preparing a high-strength and toughness microalloyed structural steel according to claim 1, characterized in that: The addition amount of the refining agent and the modifier is 1-2% of the mass of the molten iron respectively.

4. The method for preparing a high-strength and toughness microalloyed structural steel according to claim 1, characterized in that: The preparation of the modified ferrosilicon comprises the following steps: Titanium carbide powder and nickel-based powder are mixed in a mass ratio of (1-2):1 to obtain a mixture; the mixture is deposited on the surface of ferrosilicon by plasma transferred arc welding to obtain modified ferrosilicon.

5. High-strength and toughness microalloyed structural steel prepared according to the method for preparing high-strength and toughness microalloyed structural steel according to any one of claims 1 to 4.

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