阅读说明：本技术 一种340MPa级含硼高强韧性热镀锌结构钢及其生产方法 (340 MPa-level boron-containing high-strength and high-toughness hot-dip galvanized structural steel and production method thereof ) 是由 王滕 柴立涛 杨平 赵云龙 李伟刚 孙霖 刘劼 孙镕强 张百勇 李超 何峰 于 2019-12-10 设计创作，主要内容包括：本发明提供了一种340MPa级含硼高强韧性热镀锌结构钢及其生产方法,基板成分：C：0.06％～0.12％,Si：≤0.06％,Mn：0.50％～1.10％,P：≤0.020％,S：≤0.020％,Als：0.020％～0.060％,B：0.0005％～0.0030％,Ti：0.010％～0.040％,Nb：0.010％～0.040％,N≤0.0020％,余量为Fe及不可避免的杂质。与现有技术相比,本发明通过对化学成分进行设计,对热轧工艺、酸轧压下率、镀锌退火温度及光整延伸率等进行控制,生产出表面质量优异的高强韧结构钢热镀锌产品,屈服强度≥340MPa,抗拉强度≥440MPa,延伸率A80≥20％。(The invention provides 340 MPa-grade boron-containing high-strength and high-toughness hot-dip galvanized structural steel and a production method thereof, wherein the substrate comprises the following components: c: 0.06% -0.12%, Si: less than or equal to 0.06 percent, Mn: 0.50% -1.10%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Als: 0.020% -0.060%, B: 0.0005% -0.0030%, Ti: 0.010% -0.040%, Nb: 0.010-0.040%, N is less than or equal to 0.0020%, and the balance is Fe and inevitable impurities. Compared with the prior art, the hot-dip galvanized product of the high-strength and high-toughness structural steel with excellent surface quality is produced by designing chemical components and controlling a hot rolling process, an acid rolling reduction rate, a galvanizing annealing temperature, a finishing elongation rate and the like, wherein the yield strength is more than or equal to 340MPa, the tensile strength is more than or equal to 440MPa, and the elongation A80 is more than or equal to 20%.)

1. The 340 MPa-grade boron-containing high-strength and high-toughness hot-dip galvanized structural steel is characterized in that a substrate of the 340 MPa-grade boron-containing high-strength and high-toughness hot-dip galvanized structural steel contains the following components in percentage by weight: c: 0.06% -0.12%, Si: less than or equal to 0.06 percent, Mn: 0.50% -1.10%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Als: 0.020% -0.060%, B: 0.0005% -0.0030%, Ti: 0.010% -0.040%, Nb: 0.010-0.040%, N is less than or equal to 0.0020%, and the balance is Fe and inevitable impurities.

2. The production method of the 340MPa grade boron-containing high-strength and high-toughness hot-dip galvanized structural steel is characterized by comprising the following steps of:

1) pretreating molten iron;

2) smelting in a converter;

3) an alloy fine tuning station;

4) refining in an LF furnace;

5) continuous casting;

6) discharging a casting blank;

7) hot rolling;

8) finish rolling;

9) coiling;

10) cold rolling;

11) continuous annealing;

12) hot-dip galvanizing;

13) and (6) finishing.

3. The production method according to claim 2, wherein in the step 5) of the continuous casting process, the target temperature of the tundish is controlled to be 15-40 ℃ above the liquidus temperature; setting the cooling water parameters of the crystallizer, wherein the flow rate of the cooling water on the wide surface of the crystallizer is 4500L/min-5000L/min, the flow velocity of a water gap is 6.0 m/s-7.0 m/s, and the casting blank drawing speed is 1.0 m/min-1.3 m/min.

4. The production method according to claim 2, wherein the tapping temperature of the cast slab in the step 6) is controlled to 1210 to 1250 ℃.

5. The production method according to claim 2, wherein the finishing temperature in the step 8) is controlled to be 850 ℃ to 920 ℃.

6. The production method according to claim 2, wherein the coiling temperature in step 9) is controlled to 560 ℃ to 620 ℃.

7. The production method according to claim 2, wherein the total reduction rate in the step 10) is controlled to 50% to 90%.

8. The production method according to claim 2, wherein the continuous annealing in step 11) is specifically: the atmosphere in the reducing furnace comprises the following components in percentage by volume: h₂: 5 to 10 percent of N, and the balance of N₂(ii) a The dew point in the furnace is controlled to be-20 to-50 ℃, and the soaking temperature is controlled to be 640 to 740 ℃.

9. The production method according to claim 2, wherein in the step 12) of hot dip coating, the temperature of the strip steel entering the zinc pot is controlled as follows: 450-485 ℃, and the temperature of zinc liquid is as follows: 455-465 ℃.

10. The production method according to claim 2, wherein the finishing in step 13) is specifically: the finishing elongation is controlled to be 0.5-2.0%.

Technical Field

The invention belongs to the technical field of metal material processing and steel plate hot dip coating processing, and particularly relates to 340 MPa-level boron-containing high-strength and high-toughness hot dip galvanized structural steel and a production method thereof.

Background

In recent years, with the development of the world economy, particularly the development of automobiles, household appliances and the construction industry, the demand of galvanized steel strips is greatly increased, and the market demand is very considerable. In the great steel production countries such as the United states and the Japan, the proportion of the hot-dip galvanized steel sheet in the steel is up to 13-35%. The hot galvanizing is the most common, most economical and most effective anti-corrosion method for steel, and the continuous hot galvanizing has the advantages of mature technology, stable process, low production cost, excellent coating performance, long service life and the like, and is widely applied to national economic basic industries such as the building industry, the household appliance industry, the electromechanical industry, the automobile manufacturing industry and the like. Important development directions for modern automobile structures, performance and technology are weight reduction, energy saving, emission reduction and safety improvement. The weight of the automobile and the energy consumption are in a linear relationship. According to statistics, the fuel consumption can be reduced by 0.6-1.0% when the weight of the automobile is reduced by 1%. One way of reducing the weight of the automobile is to reduce the thickness of the material for the automobile body, improve the strength of the material and ensure the reliability of the finished piece. The requirements of reducing the weight and the cost of the user are met.

The following brief analysis is made on the production method and the technical current situation of the domestic structural steel which is disclosed in the prior art:

the method for producing 390-500Mpa structural grade galvanized products by controlling annealing temperature, which is CN 102676759A, explains the production of S390GD and S450GD products by adjusting the chemical components of C, Si, Mn, P, S and Als and combining the control of annealing temperature. The Mn content is low, and the annealing temperature is 560-620 ℃. The patent mainly depends on incomplete annealing to realize the improvement of strength, and the product has poor plasticity and poor forming performance.

Chinese patent No. CN 102094149A, "a niobium-containing high-strength hot-dip galvanized steel sheet and a production method thereof", the chemical components of the patent are as follows: c: 0.03-0.1%, Si: less than or equal to 0.05 percent, Mn: 0.5-0.9%, P: less than or equal to 0.025 percent, S: less than or equal to 0.015 percent, N: less than or equal to 0.005 percent, Ti: less than or equal to 0.005 percent, Nb: 0.03-0.06%, Al: 0.01 to 0.08 percent, and the balance of Fe and inevitable impurities. The patent is strengthened by adding Nb alloy, and the cost is higher.

An economical high-plasticity 360 MPa-level structural steel plate with Chinese patent number CN 108914008A and a manufacturing method thereof, the chemical components are as follows: 0.13 to 0.18%, Mn: 1.0-1.6%, Si: 0.20-0.50%, P: less than or equal to 0.025 percent, S: less than or equal to 0.010 percent, Ti: 0.020-0.050%, Als: not less than 0.015%, N: the alloy is not more than 0.005 percent, and the balance of Fe and inevitable impurity elements, thereby realizing the production of products with yield strength not less than 360MPa, tensile strength not less than 500MPa and elongation not less than 30 percent.

In the method for manufacturing the hot rolled steel plate of the low-alloy structural steel with the Chinese patent No. CN 103447295A, alloy elements such as Ti, Nb and V are not added, and the production of the high-strength hot rolled steel plate is realized mainly by adjusting chemical elements such as C, Si, Mn, P, S and Als, a rolling process and the like. The low-alloy structural steel is a steel comprising, in weight percent, 0.12 to 0.18% of C, 0.10 to 0.30% of Si, 0.70 to 1.00% of Mn, 0.015 to 0.040% of Als, 0.030% or less of S, and 0.030% or less of P. The steel plate in the patent has high Si content, and the product has poor platability in the galvanizing procedure.

Chinese patent No. CN 103627951A, "high-toughness boron-containing carbon structural steel plate coil and production method thereof", contains carbon less than or equal to 0.30%, silicon: less than or equal to 0.50 percent, manganese: less than or equal to 1.70 percent, phosphorus: less than or equal to 0.035%, sulfur: less than or equal to 0.035%, aluminum: 0.015-0.050% and 8-50 ppm of boron, and the balance of iron and trace impurities. The following elements may or may not be added according to different special performance requirements: niobium: less than or equal to 0.050 percent; vanadium: less than or equal to 0.050 percent; titanium: less than or equal to 0.020%; nickel: less than or equal to 0.40 percent; chromium is less than or equal to 0.50 percent; copper: less than or equal to 0.40 percent. The steel plate has wide chemical component range, low coiling temperature (650-500 ℃) and hot rolling structure.

Chinese patent No. CN 103509996A entitled "high strength carbon manganese structural steel with 400MPa level tensile strength and manufacturing method thereof" comprises the following chemical components in percentage by weight: carbon: 0.10-0.20%, silicon is less than or equal to 0.30%, manganese is less than or equal to 0.40%, and aluminum: 0.010-0.030 percent of phosphorus, less than or equal to 0.02 percent of sulfur, less than or equal to 0.015 percent of sulfur, and the balance of Fe and inevitable impurity elements. The yield strength is 250-280 MPa, the tensile strength is more than or equal to 400MPa, and the elongation is more than or equal to 32%. The product in this patent has a low yield strength and is the hood exit path.

Chinese patent No. CN 103882292A, "a production method of cold-rolled carbon structural steel", wherein the chemical components of the carbon structural steel are 0.06-0.10% by mass of C; 1.2 to 1.5 percent of Mn; si, less than or equal to 0.06 percent; p is less than or equal to 0.030 percent; s, less than or equal to 0.010 percent; 0.02-0.06% of Als; 0.0020-0.0050% of N; the balance being Fe. The process route is continuous annealing, an overaging section is added, the process is different from a galvanizing process, and the yield strength of the product is low and is about 180 MPa.

The economic low-yield-ratio structural steel and the manufacturing method thereof in Chinese patent No. CN 105506507A are characterized in that the chemical components by mass percent are as follows: c: 0.005-0.02%, Si: 0.30-0.50%, Mn: 1.50% -1.80%, Nb: 0.02-0.04%, Ti: 0.005-0.030%, Cr: 0.10% -0.30%, Ni: 0.10% -0.20%, Als: 0.010-0.070%, and the balance of Fe and inevitable impurities; the tensile strength of the steel plate is more than or equal to 600MPa, and the yield ratio is less than or equal to 0.75. The patent adds a large amount of alloy elements, and the cost is high.

A production method of boron-containing structural steel of Chinese patent No. CN 102080179A comprises the following chemical components in percentage by weight: 0.08 to 0.20, Si: 0.10 to 0.30%, Mn: 0.80-1.50%, P: less than or equal to 0.010 percent, S: less than or equal to 0.010 percent, B: 0.0008 to 0.0030 percent, and the balance of Fe and inevitable impurities. The obtained boron-added structural steel mainly comprises ferrite, bainite and a small amount of pearlite. The product in the patent is a hot rolled steel plate, and has high Si content, poor surface quality, no control on N content and poor thermoplasticity.

Chinese patent No. CN 103911544A "Low cost Thick Specification Low alloy structural Steel and its production method", wherein the weight percentages of the components are: c: 0.17-0.20%, Si: 0.15-0.30%, Mn: 0.35-0.55%, P is less than or equal to 0.025%, S is less than or equal to 0.01%, N is less than or equal to 0.008%, and the balance is Fe and inevitable impurities. The patent has lower Mn content range, improves the strength by adding Si, and is not suitable for the production of a galvanizing procedure.

Regarding the existing structural steel patents, mainly: (1) the strength of the steel sheet is improved by adding single Ti or single Nb, and the formability of the product is deviated. (2) The Si content in part of structural steel is high, and the surface quality of the product cannot meet the surface requirement of the galvanized steel sheet. (3) The C, Mn-reinforced structural steel alone has high anisotropy and poor plasticity.

Disclosure of Invention

The invention aims to provide 340 MPa-level boron-containing high-strength and high-toughness hot-dip galvanized structural steel and a production method thereof.

The specific technical scheme of the invention is as follows:

the 340 MPa-grade boron-containing high-strength and high-toughness hot-dip galvanized structural steel comprises the following components in percentage by weight: c: 0.06% -0.12%, Si: less than or equal to 0.06 percent, Mn: 0.50% -1.10%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Als: 0.020% -0.060%, B: 0.0005% -0.0030%, Ti: 0.010% -0.040%, Nb: 0.010-0.040%, N is less than or equal to 0.0020%, and the balance is Fe and inevitable impurities.

Preferably, C0.07% to 0.10%, Si: less than or equal to 0.06 percent, Mn: 0.50% -1.10%, P: not more than 0.020%, not more than 0.010% of S), Als: 0.020% -0.060%, B0.0005% -0.0010%, Ti: 0.010% -0.040%, Nb: 0.010-0.040%, N is less than or equal to 0.0020%, and the balance is Fe and inevitable impurities.

The invention provides a production method of 340 MPa-level boron-containing high-strength and high-toughness hot-dip galvanized structural steel, which comprises the following steps of:

1) pretreating molten iron;

2) smelting in a converter;

3) an alloy fine tuning station;

4) refining in an LF furnace;

5) continuous casting;

6) discharging a casting blank;

7) hot rolling;

8) finish rolling;

9) coiling;

10) cold rolling;

11) continuous annealing;

12) hot-dip galvanizing;

13) and (6) finishing.

In the step 1), molten iron is pretreated, and front slag skimming and rear slag skimming are required.

In the step 2), no pig iron or slag steel is added in the converter smelting; self-circulation steel scrap tapping is adopted, converter dephosphorization is enhanced, and slag blocking operation is enhanced; lime is added in the tapping process, and deoxidation is not carried out.

And 3) modifying the ladle top slag by the alloy fine tuning station.

Refining in the LF furnace in the step 4) to ensure that the weak stirring time before and after wire feeding is not less than 11 minutes;

in the continuous casting process of the step 5), the target temperature of the tundish is controlled to be 15-40 ℃ above the liquidus temperature; setting the cooling water parameters of the crystallizer, wherein the flow rate of the cooling water on the wide surface of the crystallizer is 4500L/min-5000L/min, the flow velocity of a water gap is 6.0 m/s-7.0 m/s, and the casting blank drawing speed is 1.0 m/min-1.3 m/min.

And 5) in the continuous casting process, setting the cooling water parameters of the crystallizer to achieve the purpose of reducing the cracks of the casting blank.

And 6), controlling the discharging temperature of the casting blank to be 1210-1250 ℃.

Step 7), the hot rolling is specifically as follows: and (4) continuously rolling by using six frames, and carrying out high-pressure descaling at a primary inlet and a secondary outlet.

And 8) controlling the finishing temperature to be 850-920 ℃.

Step 9), the coiling temperature is controlled to be 560-620 ℃.

As the B element is added into the steel, the B element preferentially forms a coarse BN strengthening phase with N, the formation of AlN is prevented, the pinning effect of AlN on a crystal boundary is weakened, ferrite grains are coarsened, the yield strength is reduced, and the preset strength is realized through a hot rolling process.

The total reduction rate in the step 10) is controlled to be 50-90% and has great influence on subsequent recovery recrystallization of the product and the forming performance of the finished product, when the reduction rate is low, the r value is reduced, and the forming performance is deteriorated;

furthermore, in order to effectively remove impurities such as rolling oil, iron powder and the like on the surface of the cold-rolled steel plate strip steel so that the strip steel enters an annealing furnace with a clean surface, the concentration of degreasing fluid in an alkaline washing tank of a strip steel cleaning section is as follows: 1-2% at 70-90 deg.C; the concentration of the degreasing solution in the electrolytic cleaning tank is as follows: 3-8% and the temperature is 70-90 ℃.

The continuous annealing in the step 11) is specifically as follows: the atmosphere in the reducing furnace comprises the following components in percentage by volume: h₂: 5 to 10 percent of N, and the balance of N₂(ii) a The dew point in the furnace is controlled to be-20 to-50 ℃, and the soaking temperature is controlled to be 640 to 740 ℃.

Step 12) in the hot dip coating process, controlling the temperature of the strip steel in a zinc pot as follows: 450-485 ℃, and the temperature of zinc liquid is as follows: 455-465 ℃; the mass percentage of the total aluminum in the hot galvanizing liquid is controlled to be 0.17-0.25%, and the balance is Zn, unavoidable Fe and other impurities. And adjusting according to the thickness of the strip steel.

The polishing in the step 13) is specifically as follows: the galvanized steel sheet is finished under a finishing machine, and the finishing elongation is controlled to be 0.5-2.0%.

The chemical components of the invention are mainly based on the following principles:

carbon (C): c is the most economical and effective solid-solution strengthening element for improving strength, and the content of C increases, the formed pearlite increases, and the strength increases, but the plasticity and formability of the steel decrease, and the weldability is not good. Comprehensively, the control range of the percentage content of C in the invention is 0.06% -0.12%.

Manganese (Mn) belongs to an alloy element capable of expanding the range of a gamma phase region, a continuous solid solution is not formed in an Fe-Mn system in a solid state, the diffusion of manganese in α iron and gamma iron is far more difficult than the diffusion of carbon, but the Mn content is too high, the Mn segregation degree of a casting blank is increased in the continuous casting process, a pearlite or bainite banded structure is easily formed at the central part of the thickness of a steel plate, and the plasticity, the welding performance and the fatigue performance are not good.

Silicon (Si): the silicon in the steel can block the growth of the alloy layer, the thickness of the alloy layer can be greatly reduced, the silicon content in the steel is improved, and the hardness of the alloy layer can be reduced. However, the content of Si in the steel sheet is too high, and oxides are easily generated on the surface of the steel sheet, so that the wettability of the steel sheet is reduced, and the defect of poor plating is easily generated. The percentage content control range of Si in the invention is less than or equal to 0.06 percent.

Phosphorus (P): phosphorus is an element effective for strengthening steel, but when the amount of phosphorus added exceeds 0.050%, the surface oxide layer (scale) formed by hot rolling peels off too much, resulting in deterioration of the surface after plating. The percentage content control range of P in the invention is less than or equal to 0.020%.

Sulfur (S): s is a harmful element in general. The present invention controls the S percentage content of steel grade to be less than 0.020% because the S content is generally required to be as low as possible, which causes hot shortness of steel, reduces ductility and toughness of steel, and causes cracks during forging and rolling.

Aluminum (Al): al is used as a main deoxidizer, and meanwhile, aluminum also has a certain effect on grain refinement. Aluminum has the disadvantage of affecting the hot workability, weldability and machinability of the steel. The percentage content of Als is controlled to be 0.020-0.060%.

Nitrogen (N): n can improve the strength, low-temperature toughness and weldability of steel and increase aging sensitivity. The invention controls the N percentage content of the steel grade below 0.0020 percent.

Boron (B): the trace boron has the partial aggregation function on austenite grain boundaries, can inhibit the nucleation of ferrite, enables the C curve to move to the right, and inhibits the transformation of pearlite. The action mechanism is as follows: boron is partially aggregated in austenite crystal boundary, so that the crystal boundary energy is reduced and the position of preferential nucleation of ferrite is reduced; boron reduces the self diffusion coefficient of iron on the grain boundary, and reduces the nucleation speed of ferrite; after being partially gathered in a grain boundary, boron occupies a preferential nucleation position; fine boride is formed along grain boundaries and is coherent and adherent to the matrix, making it difficult for ferrite to nucleate at the interface between boride and matrix. The boron added into the steel has the function of preventing phosphorus from segregating at the grain boundary, thereby improving the secondary processing brittleness resistance of the steel. Therefore, the content is limited to the range of 0.0005% to 0.0030%.

Titanium (Ti): ti is a strong deoxidizer in steel. It can make the internal structure of steel compact, refine grain force, raise strength of steel and improve welding property. The invention controls the control range of the percentage content of Ti to be 0.010 percent to 0.040 percent.

Niobium (Nb): nb can refine grains, reduce the overheating sensitivity and the tempering brittleness of steel, improve the strength and improve the welding performance. The percentage content control range of Nb is controlled to be 0.010-0.040 percent.

The invention has the following functions of hot rolling, annealing temperature and finishing elongation:

on one hand, the deformation resistance is increased, the work hardening effect is enhanced, the hot rolling deformation energy storage is increased, the quantity of dislocation, deformation band, substructure and two-phase particles generated in the hot deformation structure is increased, on the other hand, the Ar3 is increased, the static recovery process from finishing rolling to the beginning of the gamma → α phase transformation is relatively shortened, and the rate of reducing the crystal defects is reduced.

The yield strength tends to decrease with increasing annealing temperature, which is related to the fact that increasing annealing temperature promotes growth and coarsening during the recrystallization of crystal grains, while the tensile strength is substantially unchanged with the change of annealing temperature. The high annealing temperature is beneficial to obtaining higher elongation and n and r values, and is beneficial to the stamping forming performance of the material. The annealing temperature is designed to be 640-740 ℃.

As the percent elongation of the finish increases, the yield strength increases. From the rule, the finishing elongation is improved by 0.1 percent, and the yield strength is improved by about 2.5 MPa. The invention controls the finishing elongation rate to be 0.5-2.0%.

Compared with the prior art, the hot-dip galvanized product of the high-strength and high-toughness structural steel with excellent surface quality is produced by designing chemical components and controlling a hot rolling process, an acid rolling reduction rate, a galvanizing annealing temperature, a finishing elongation rate and the like, wherein the yield strength is more than or equal to 340MPa, the tensile strength is more than or equal to 440MPa, and the elongation A80 is more than or equal to 20%.

Drawings

FIG. 1 shows the metallographic structure of a hot-dip galvanized steel sheet produced in example 1 of the present invention;

FIG. 2 shows the metallographic structure of a hot-dip galvanized steel sheet produced in comparative example 1;

FIG. 3 is the results of the secondary processing brittleness test at-40 ℃ of example 1;

FIG. 4 shows the results of the secondary work brittleness test at-40 ℃ of comparative example 1.

Detailed Description