A method for improving the strength of hot-rolled low-carbon steel

Abstract

The invention discloses a method for improving the strength of hot-rolled low-carbon steel, comprising the steps of: (1) sieving titanium carbide powder, washing, and obtaining a washed powder; (2) plating a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea to obtain a primary plating powder; (3) plating a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine to obtain a secondary plating powder; (4) carbonizing the surface to obtain a partially carbonized surface powder; (5) melting low-carbon steel into molten steel, adding the partially carbonized surface powder, and casting into a steel ingot; rolling, cooling, and obtaining the hot-rolled low-carbon steel. The method of the invention can significantly improve the yield strength of low-carbon steel, so that the low-carbon steel has more excellent mechanical properties and is suitable for applications with higher strength requirements.

Description

Technical Field

[0001] The invention relates to the technical field of low-carbon steel processing, and in particular to a method for improving the strength of hot-rolled low-carbon steel. Background Art

[0002] Grain refinement and second phase strengthening are powerful means to improve the comprehensive mechanical properties of steel. The dispersed and fine second phase particles in the steel pin the movement of austenite grain boundaries, which plays a role in improving the strength of steel. Due to the process characteristics of hot-rolled low-carbon steel high-temperature forming, the application of traditional controlled rolling technology is severely limited, and the production process lacks effective online organizational control methods, which often results in coarse phase transformation organizations. With the help of metallurgical technology, this problem is expected to be improved. By pinning the grain boundaries and inducing nucleation through the second phase, and coordinating controlled cooling technology to refine the high-temperature hot-rolled organization, the organizational control of low-carbon steel products can be achieved. Summary of the invention

[0003] To this end, the present invention provides a method for improving the strength of hot-rolled low-carbon steel, the steps comprising:

[0004] (1) titanium carbide powder is passed through a 1500 mesh sieve, and the sieved powder is collected. The sieved powder is immersed in an acetone solution, and cleaned for more than 10 minutes under an ultrasonic environment, and then the solid-liquid separation is performed, and the solid phase is dried to obtain the cleaned powder;

[0005] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, immersing the cleaned powder in the primary plating solution, heating the powder in a water bath to 60±3° C., maintaining the temperature for plating for more than 90 minutes, then separating the solid from the liquid, washing the solid phase with deionized water for more than 3 times, and drying the solid phase at 60° C. for more than 30 minutes to obtain a primary plating powder;

[0006] (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; immersing the primary plating powder in the secondary plating solution, heating the solution to 40±3° C. in a water bath, and plating the powder at this temperature for more than 120 min, then separating the solid from the liquid, washing the solid phase with deionized water for more than 3 times, and drying the solution at 60° C. for more than 30 min to obtain a secondary plating powder;

[0007] (4) placing the secondary plated powder on the cathode plate of a plasma nitriding furnace, and performing glow plasma carbonization in a methane and hydrogen mixed atmosphere at an internal furnace pressure of 400 Pa, a voltage of 700 to 750 V, and a temperature set to 400 to 420° C. for carbonization for 5 to 6 hours to obtain a partially carbonized powder on the surface;

[0008] (5) Melting low carbon steel into molten steel by using a vacuum induction heating furnace, and then stirring the molten steel. During the stirring process, the partially carbonized surface powder is added to the molten steel. After adding the materials, stirring is continued for 2 minutes, and then the molten steel is immediately cast into a steel ingot; heating the steel ingot to 1250° C. and keeping the temperature for 30 minutes, and then rolling the steel ingot from 100 mm to 30 mm through 7 rolling passes, with a final rolling temperature of 1060° C. After hot rolling, the steel ingot is cooled to 600° C. at a rate of 20° C. / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel.

[0009] Furthermore, in the step (1), the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W and the frequency is 40 kHz.

[0010] Furthermore, in the step (2), the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite and thiourea are: iridium chloride 0.5-0.6 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 2-4 g / L, thiourea 0.5 mg / L, and the solvent is water; the mass ratio of the cleaned powder immersed in the primary plating solution is cleaned powder: primary plating solution = 1:500.

[0011] Furthermore, in the step (3), the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 8-10 g / L, cerium nitrate 2-3 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, L-lysine 1.5 g / L, and the solvent is water; the mass ratio of the primary plating powder immersed in the secondary plating solution is primary plating powder: secondary plating solution = 1:500.

[0012] Furthermore, in step (4), the volume ratio of the methane and hydrogen mixture is methane:hydrogen=1:100.

[0013] Furthermore, in the step (5), the mass ratio of the partially carburized surface powder added to the molten steel is the partially carburized surface powder: molten steel = 0.6-0.9:100.

[0014] The beneficial effects of the present invention are as follows: the method of the present invention can significantly improve the yield strength of low carbon steel, so that the low carbon steel has more excellent mechanical properties and is suitable for applications with higher strength requirements. This is mainly because the added surface partially carburized powder, on the one hand, acts as a non-uniform nucleation site, improves the nucleation rate of the material, and has a certain effect of refining the grains. On the other hand, the addition of the surface partially carburized powder as a second phase reinforcement can significantly improve the overall strength of the material. The present invention first forms an activated surface layer on the surface of the second phase powder by plating once, and then forms a partial carbonized structure on the surface of the second phase powder through a secondary plating and carbonization process, thereby improving the wettability and bonding of the second phase powder and the low carbon steel matrix, making the two-phase interface bond more fully and firmly, reducing the defect rate, making it difficult for the material to produce microcracks when subjected to stress, and significantly improving the mechanical strength of the material. At the same time, the surface of the second phase powder that has been plated and carbonized is more likely to form crystal nuclei, promote the nucleation process, and refine the grains. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the embodiments.

[0016] Example 1

[0017] A method for improving the strength of hot-rolled low-carbon steel, comprising:

[0018] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0019] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, wherein the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea are: iridium chloride 0.5 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 2 g / L, thiourea 0.5 mg / L, and the solvent is water; soaking the cleaned powder in the primary plating solution, wherein the mass ratio of the cleaned powder soaked in the primary plating solution is cleaned powder: primary plating solution = 1:500; heating in a water bath to 60±3° C., keeping the temperature for plating for 90 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a primary plating powder;

[0020] (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 8 g / L, cerium nitrate 2 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, and L-lysine 1.5 g / L, and the solvent is water; immersing the primary plating powder in the secondary plating solution, the mass ratio of the primary plating powder immersed in the secondary plating solution being primary plating powder: secondary plating solution = 1:500; heating in a water bath to 40±3° C., keeping the temperature for plating for 120 min, then separating the solid and liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a secondary plating powder;

[0021] (4) Placing the secondary plated powder on the cathode plate of a plasma nitriding furnace, and subjecting the powder to glow plasma carbonization in a methane and hydrogen mixed atmosphere at a furnace internal pressure of 400 Pa, a voltage of 750 V, and a methane:hydrogen mixed atmosphere, wherein the methane:hydrogen mixed atmosphere has a volume ratio of methane:hydrogen = 1:100; the temperature is set at 420° C., and the carbonization is performed for 5 h to obtain a partially carbonized powder on the surface;

[0022] (5) The Q345D low carbon steel is heated to 1570° C. in a vacuum induction heating furnace to melt into molten steel, and then the molten steel is stirred. During the stirring process, the surface partially carburized powder is added to the molten steel, and the mass ratio of the surface partially carburized powder added to the molten steel is surface partially carburized powder: molten steel = 0.6:100; stirring is continued for 2 minutes after the addition, and then immediately cast into a steel ingot; the steel ingot is heated to 1250° C. and kept warm for 30 minutes, and then rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature is 1060° C., and after hot rolling, it is cooled to 600° C. at 20° C. / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel.

[0023] Example 2

[0024] A method for improving the strength of hot-rolled low-carbon steel, comprising:

[0025] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0026] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, wherein the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea are: iridium chloride 0.5 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 3 g / L, thiourea 0.5 mg / L, and the solvent is water; soaking the cleaned powder in the primary plating solution, wherein the mass ratio of the cleaned powder soaked in the primary plating solution is cleaned powder: primary plating solution = 1:500; heating in a water bath to 60±3° C., keeping the temperature for plating for 90 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a primary plating powder;

[0027] (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 9 g / L, cerium nitrate 2 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, and L-lysine 1.5 g / L, and the solvent is water; immersing the primary plating powder in the secondary plating solution, the mass ratio of the primary plating powder immersed in the secondary plating solution being primary plating powder: secondary plating solution = 1:500; heating in a water bath to 40±3° C., keeping the temperature for plating for 120 min, then separating the solid and liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a secondary plating powder;

[0028] (4) Placing the secondary plated powder on the cathode plate of a plasma nitriding furnace, and subjecting the powder to glow plasma carbonization in a methane and hydrogen mixed atmosphere at a furnace internal pressure of 400 Pa, a voltage of 750 V, and a methane:hydrogen mixed atmosphere, wherein the methane:hydrogen mixed atmosphere has a volume ratio of methane:hydrogen = 1:100; the temperature is set at 420° C., and the carbonization is performed for 5 h to obtain a partially carbonized powder on the surface;

[0029] (5) The Q345D low carbon steel is heated to 1570° C. in a vacuum induction heating furnace to melt into molten steel, and then the molten steel is stirred. During the stirring process, the partially carburized surface powder is added to the molten steel, and the mass ratio of the partially carburized surface powder to the molten steel is 0.7:100. After adding the materials, the stirring is continued for 2 minutes, and then the steel ingot is immediately cast into a steel ingot; the steel ingot is heated to 1250° C. and kept warm for 30 minutes, and then the steel ingot is rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature is 1060° C., and after hot rolling, it is cooled to 600° C. at 20° C. / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel.

[0030] Example 3

[0031] A method for improving the strength of hot-rolled low-carbon steel, comprising:

[0032] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0033] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, wherein the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea are: iridium chloride 0.6 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 3 g / L, thiourea 0.5 mg / L, and the solvent is water; soaking the cleaned powder in the primary plating solution, wherein the mass ratio of the cleaned powder soaked in the primary plating solution is cleaned powder: primary plating solution = 1:500; heating in a water bath to 60±3° C., keeping the temperature for plating for 90 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a primary plating powder;

[0034] (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 9 g / L, cerium nitrate 3 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, and L-lysine 1.5 g / L, and the solvent is water; immersing the primary plating powder in the secondary plating solution, the mass ratio of the primary plating powder immersed in the secondary plating solution being primary plating powder: secondary plating solution = 1:500; heating in a water bath to 40±3° C., keeping the temperature for plating for 120 min, then separating the solid and liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a secondary plating powder;

[0035] (4) Placing the secondary plated powder on the cathode plate of a plasma nitriding furnace, and subjecting the powder to glow plasma carbonization in a methane and hydrogen mixed atmosphere at a furnace internal pressure of 400 Pa, a voltage of 750 V, and a methane:hydrogen mixed atmosphere, wherein the methane:hydrogen mixed atmosphere has a volume ratio of methane:hydrogen = 1:100; the temperature is set at 420° C., and the carbonization is performed for 5 h to obtain a partially carbonized powder on the surface;

[0036] (5) The Q345D low carbon steel is heated to 1570° C. in a vacuum induction heating furnace to melt into molten steel, and then the molten steel is stirred. During the stirring process, the partially carburized surface powder is added to the molten steel, and the mass ratio of the partially carburized surface powder to the molten steel is the partially carburized surface powder: molten steel = 0.8:100; the stirring is continued for 2 minutes after the addition, and then the steel is immediately cast into a steel ingot; the steel ingot is heated to 1250° C. and kept warm for 30 minutes, and then the steel ingot is rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature is 1060° C., and after hot rolling, it is cooled to 600° C. at 20° C. / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel.

[0037] Example 4

[0038] A method for improving the strength of hot-rolled low-carbon steel, comprising:

[0039] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0040] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, wherein the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea are: iridium chloride 0.6 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 4 g / L, thiourea 0.5 mg / L, and the solvent is water; soaking the cleaned powder in the primary plating solution, wherein the mass ratio of the cleaned powder soaked in the primary plating solution is cleaned powder: primary plating solution = 1:500; heating in a water bath to 60±3° C., keeping the temperature for plating for 90 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a primary plating powder;

[0041] (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 10 g / L, cerium nitrate 3 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, L-lysine 1.5 g / L, and the solvent is water; immersing the primary plating powder in the secondary plating solution, the mass ratio of the primary plating powder immersed in the secondary plating solution being primary plating powder: secondary plating solution = 1:500; heating in a water bath to 40±3° C., keeping the temperature for plating for 120 min, then separating the solid and liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a secondary plating powder;

[0042] (4) Placing the secondary plated powder on the cathode plate of a plasma nitriding furnace, and subjecting the powder to glow plasma carbonization in a methane and hydrogen mixed atmosphere at a furnace internal pressure of 400 Pa, a voltage of 750 V, and a methane:hydrogen mixed atmosphere, wherein the methane:hydrogen mixed atmosphere has a volume ratio of methane:hydrogen = 1:100; the temperature is set at 420° C., and the carbonization is performed for 5 h to obtain a partially carbonized powder on the surface;

[0043] (5) The Q345D low carbon steel is heated to 1570° C. in a vacuum induction heating furnace to melt into molten steel, and then the molten steel is stirred. During the stirring process, the surface partially carburized powder is added to the molten steel, and the mass ratio of the surface partially carburized powder to the molten steel is surface partially carburized powder: molten steel = 0.9:100; stirring is continued for 2 minutes after the addition, and then immediately cast into a steel ingot; the steel ingot is heated to 1250° C. and kept warm for 30 minutes, and then rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature is 1060° C., and after hot rolling, it is cooled to 600° C. at 20° C. / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel.

[0044] Comparative Example 1

[0045] A method for comparison includes the following steps:

[0046] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0047] (2) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a plating solution; the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 9 g / L, cerium nitrate 3 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, and L-lysine 1.5 g / L, and the solvent is water; immersing the cleaned powder in the plating solution, the mass ratio of the cleaned powder to the plating solution being cleaned powder: plating solution = 1:500; heating in a water bath to 40±3° C., keeping the temperature for 120 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a plating powder;

[0048] (3) Placing the plated powder on the cathode plate of a plasma nitriding furnace, and subjecting the powder to glow plasma carbonization in a methane and hydrogen mixed atmosphere at a furnace internal pressure of 400 Pa, a voltage of 750 V, and a methane:hydrogen mixed atmosphere, wherein the methane:hydrogen mixed atmosphere has a volume ratio of methane:hydrogen = 1:100; the temperature is set at 420° C., and the carbonization is performed for 5 h to obtain a partially carbonized powder on the surface;

[0049] (4) The Q345D low carbon steel was heated to 1570°C in a vacuum induction heating furnace to melt into molten steel, and then the molten steel was stirred. During the stirring process, the surface partially carburized powder was added to the molten steel, and the mass ratio of the surface partially carburized powder to the molten steel was surface partially carburized powder: molten steel = 0.8:100; the stirring was continued for 2 minutes after the addition, and then it was immediately cast into a steel ingot; the steel ingot was heated to 1250°C and kept warm for 30 minutes, and then the steel ingot was rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature was 1060°C, and after hot rolling, it was cooled to 600°C at 20°C / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel of this comparative example.

[0050] Comparative Example 2

[0051] A method for comparison includes the following steps:

[0052] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0053] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a plating solution, wherein the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea are: iridium chloride 0.6 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 3 g / L, thiourea 0.5 mg / L, and the solvent is water; immersing the cleaned powder in the plating solution, wherein the mass ratio of the cleaned powder to the plating solution is cleaned powder: plating solution = 1:500; heating in a water bath to 60±3° C., keeping the temperature for 90 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a plating powder;

[0054] (3) Placing the plated powder on the cathode plate of a plasma nitriding furnace, and subjecting the powder to glow plasma carbonization in a methane and hydrogen mixed atmosphere at a furnace internal pressure of 400 Pa, a voltage of 750 V, and a methane:hydrogen mixed atmosphere, wherein the methane:hydrogen mixed atmosphere has a volume ratio of methane:hydrogen = 1:100; the temperature is set at 420° C., and the carbonization is performed for 5 h to obtain a partially carbonized powder on the surface;

[0055] (4) The Q345D low carbon steel was heated to 1570°C in a vacuum induction heating furnace to melt into molten steel, and then the molten steel was stirred. During the stirring process, the surface partially carburized powder was added to the molten steel, and the mass ratio of the surface partially carburized powder to the molten steel was surface partially carburized powder: molten steel = 0.8:100; the stirring was continued for 2 minutes after the addition, and then it was immediately cast into a steel ingot; the steel ingot was heated to 1250°C and kept warm for 30 minutes, and then the steel ingot was rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature was 1060°C, and after hot rolling, it was cooled to 600°C at 20°C / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel of this comparative example.

[0056] Comparative Example 3

[0057] A method for comparison includes the following steps:

[0058] (1) Passing titanium carbide powder through a 1500 mesh sieve, collecting the sieved powder, soaking the sieved powder in an acetone solution, and washing it under an ultrasonic environment for 10 minutes, wherein the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W, and the frequency is 40 kHz; then solid-liquid separation is performed, and the solid phase is dried at 60° C. to remove residual acetone, thereby obtaining a washed powder;

[0059] (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, wherein the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea are: iridium chloride 0.6 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 3 g / L, thiourea 0.5 mg / L, and the solvent is water; soaking the cleaned powder in the primary plating solution, wherein the mass ratio of the cleaned powder soaked in the primary plating solution is cleaned powder: primary plating solution = 1:500; heating in a water bath to 60±3° C., keeping the temperature for plating for 90 min, then separating the solid and the liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a primary plating powder;

[0060] (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 9 g / L, cerium nitrate 3 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, and L-lysine 1.5 g / L, and the solvent is water; immersing the primary plating powder in the secondary plating solution, the mass ratio of the primary plating powder immersed in the secondary plating solution being primary plating powder: secondary plating solution = 1:500; heating in a water bath to 40±3° C., keeping the temperature for plating for 120 min, then separating the solid and liquid, washing the solid phase with deionized water for 3 times, and drying at 60° C. for 30 min to obtain a secondary plating powder;

[0061] (4) The Q345D low carbon steel was heated to 1570°C in a vacuum induction heating furnace to melt into molten steel, and then the molten steel was stirred. During the stirring process, the secondary plating powder was added to the molten steel, and the mass ratio of the secondary plating powder added to the molten steel was secondary plating powder: molten steel = 0.8:100; stirring was continued for 2 minutes after the addition, and then immediately cast into a steel ingot; the steel ingot was heated to 1250°C and kept warm for 30 minutes, and then rolled from 100 mm to 30 mm through 7 rolling passes, the final rolling temperature was 1060°C, and after hot rolling, it was cooled to 600°C at 20°C / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel of this comparative example.

[0062] Example 5

[0063] The yield strength of the hot-rolled low-carbon steel prepared by the methods described in the above embodiments and comparative examples was tested in exactly the same manner in accordance with the requirements of standard GB / T228.1-2021, and the results are shown in Table 1.

[0064] As shown in Table 1, the yield strength of low carbon steel can be significantly improved by the method of the present invention, so that low carbon steel has more excellent mechanical properties and is suitable for applications with higher strength requirements. This is mainly because the added surface partially carburized powder, on the one hand, acts as a non-uniform nucleation point, improves the material nucleation rate, and has a certain effect of refining grains. On the other hand, the addition of the surface partially carburized powder as a second phase reinforcement can significantly improve the strength of the material as a whole. The present invention first forms an activated surface layer on the surface of the second phase powder by plating once, and then forms a partial carbonized structure on the surface of the second phase powder through a secondary plating and carbonization process, improves the wettability and bonding of the second phase powder and the low carbon steel matrix, makes the two-phase interface bond more fully and firmly, reduces the defect rate, makes it difficult to produce microcracks when the material is stressed, and significantly improves the mechanical strength of the material. At the same time, the surface of the second phase powder that has been plated and carbonized is more likely to form crystal nuclei, promote the nucleation process, and refine the grains.

[0065] Table 1

[0066] Experimental Group Yield strength(MPa) Example 1 437 Example 2 446 Example 3 459 Example 4 453 Comparative Example 1 382 Comparative Example 2 418 Comparative Example 3 395

[0067] The technical solution provided by the present invention is introduced in detail above. For those skilled in the art, according to the concept of the embodiments of the present invention, there may be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for improving the strength of hot-rolled low-carbon steel, characterized in that the steps include: (1) titanium carbide powder is passed through a 1500 mesh sieve, and the sieved powder is collected. The sieved powder is immersed in an acetone solution, and cleaned for more than 10 minutes under an ultrasonic environment, and then the solid-liquid separation is performed, and the solid phase is dried to obtain the cleaned powder; (2) preparing a composite solution of iridium chloride, ethylenediamine, sodium hypophosphite, and thiourea as a primary plating solution, immersing the cleaned powder in the primary plating solution, heating the powder in a water bath to 60±3° C., maintaining the temperature for plating for more than 90 minutes, then separating the solid from the liquid, washing the solid phase with deionized water for more than 3 times, and drying the solid phase at 60° C. for more than 30 minutes to obtain a primary plating powder; (3) preparing a composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine as a secondary plating solution; immersing the primary plating powder in the secondary plating solution, heating the solution to 40±3° C. in a water bath, and plating the powder at this temperature for more than 120 min, then separating the solid from the liquid, washing the solid phase with deionized water for more than 3 times, and drying the solution at 60° C. for more than 30 min to obtain a secondary plating powder; (4) placing the secondary plated powder on the cathode plate of a plasma nitriding furnace, and performing glow plasma carbonization in a methane and hydrogen mixed atmosphere at an internal furnace pressure of 400 Pa, a voltage of 700 to 750 V, and a temperature set to 400 to 420° C. for carbonization for 5 to 6 hours to obtain a partially carbonized powder on the surface; (5) Melting low carbon steel into molten steel by using a vacuum induction heating furnace, and then stirring the molten steel. During the stirring process, the partially carbonized surface powder is added to the molten steel. After adding the materials, stirring is continued for 2 minutes, and then the molten steel is immediately cast into a steel ingot; heating the steel ingot to 1250° C. and keeping the temperature for 30 minutes, and then rolling the steel ingot from 100 mm to 30 mm through 7 rolling passes, with a final rolling temperature of 1060° C. After hot rolling, the steel ingot is cooled to 600° C. at a rate of 20° C. / s, and then air-cooled to room temperature to obtain the hot-rolled low carbon steel.

2. A method for improving the strength of hot-rolled low-carbon steel according to claim 1, characterized in that: In the step (1), the mass ratio of the sieved powder soaked in the acetone solution is sieved powder: acetone = 1:200; the ultrasonic power is 300 W and the frequency is 40 kHz.

3. A method for improving the strength of hot-rolled low-carbon steel according to claim 1, characterized in that: In the step (2), the concentrations of the components in the composite solution of iridium chloride, ethylenediamine, sodium hypophosphite and thiourea are: iridium chloride 0.5-0.6 g / L, ethylenediamine 5 mL / L, sodium hypophosphite 2-4 g / L, thiourea 0.5 mg / L, and the solvent is water; the mass ratio of the cleaned powder immersed in the primary plating solution is cleaned powder: primary plating solution = 1:

500.

4. A method for improving the strength of hot-rolled low-carbon steel according to claim 1, characterized in that: In the step (3), the concentrations of the components in the composite aqueous solution of nickel dichloride, cerium nitrate, citric acid, L-malic acid, dimethylamine borane, ethylene glycol, and L-lysine are: nickel dichloride 8-10 g / L, cerium nitrate 2-3 g / L, citric acid 1.5 g / L, L-malic acid 1 g / L, dimethylamine borane 8 g / L, ethylene glycol 2 g / L, L-lysine 1.5 g / L, and the solvent is water; the mass ratio of the primary plating powder immersed in the secondary plating solution is primary plating powder: Secondary plating solution = 1:

500.

5. A method for improving the strength of hot-rolled low-carbon steel according to claim 1, characterized in that: In the step (4), the volume ratio of the methane and hydrogen mixture is methane:hydrogen=1:

100.

6. A method for improving the strength of hot-rolled low-carbon steel according to claim 1, characterized in that: In the step (5), the mass ratio of the partially carbonized surface powder added to the molten steel is: Molten steel = 0.6~0.9:100.