A low-cost semi-annealed low-carbon steel thick-coated zinc-aluminum-magnesium alloy and a preparation method thereof

Abstract

The application relates to the metallurgical technical field, in particular to a low-cost semi-annealed low-carbon steel thick zinc-aluminum-magnesium alloy coating and a preparation method thereof. The chemical components of a base material are as follows in percentage by weight: C: 0.01-0.08%, Si: less than or equal to 0.030%, Mn: 0.15-0.26%, P: 0.015-0.026%, S: less than or equal to 0.010%, Al: 0.02-0.06%, Ti: less than or equal to 0.3000%, and the rest is Fe and inevitable impurities. The chemical components of a plating solution for preparing the coating are as follows in percentage by weight: Al: 9-11%, Mg: 2.8-3.1%, rare earth elements: less than or equal to 0.1%, Si: 0.1-0.2%, and the rest is Zn and inevitable impurities. The application controls the residual stress of the strip steel through a low-carbon steel low-temperature semi-annealing process, improves the substrate strength by using the organizational genetic mechanism of work hardening and grain distortion, and realizes the synergistic optimization of the corrosion resistance of the coating and the mechanical properties of the substrate by combining the multi-element diffusion kinetics control technology of the zinc-aluminum-magnesium coating.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, and particularly relates to a low-cost semi-annealed low-carbon steel thick zinc-aluminum-magnesium alloy coating and a preparation method thereof. BACKGROUND

[0002] With the urgent demand of modern industry for lightweight, corrosion resistance and high-strength materials, low-carbon steel has become an important choice for basic materials due to its low cost, easy processing and wide applicability. However, low-carbon steel is prone to corrosion in harsh environments (such as marine, hot and humid, industrial pollution, etc.), which seriously restricts its service life and safety. Traditional corrosion protection methods mainly rely on hot-dip galvanizing or hot-dip zinc-aluminum-magnesium alloy coating technology to prolong the service life of the material through the sacrificial anode effect and physical barrier effect. However, the existing technology still has many problems such as high cost, complex process, performance imbalance, environmental pressure, etc.

[0003] As known, semi-annealed steel has a serious grain distortion in the processing process, and has a banded crystal fiber structure. In the zinc plating process, there is a certain metallurgical reaction between the zinc liquid and the base body of the strip steel. Due to the interaction of grain and internal dislocation, the dislocation ring is seriously accumulated, which usually causes the penetration of zinc atoms and forms a local potential difference. Once the surface is scratched during subsequent processing and use, serious intergranular corrosion will occur, which will cause deterioration during subsequent deformation. In addition, since the grain boundary provides a fast channel for atomic diffusion, excessive iron atoms will react with zinc atoms in the zinc liquid to form burst phase organizations, which will adhere to the coating substrate, causing uneven nucleation of the coating and abnormal crystallization on the surface, affecting the quality of the plate. Therefore, how to perfectly combine the semi-annealed base material with the zinc-aluminum-magnesium coating has become a technical problem.

[0004] In addition, the zinc-aluminum-magnesium product not only increases the price due to the addition of alloy elements such as magnesium and aluminum in the alloy coating, but also has defects such as cracks and peeling due to the mismatch between the elongation of low-carbon steel and the thick coating. In addition, the base material of semi-annealed low-carbon steel has poor compatibility with the coating, resulting in insufficient bonding force. The traditional process cannot balance the comprehensive performance of the coating corrosion resistance, adhesion and toughness.

[0005] To solve the above problems, the industry urgently needs to develop a low-cost, high-performance and environmentally friendly thick coating preparation technology. The specific requirements include low-cost alloy design, semi-annealed base material adaptation, thick coating quality control, performance synergistic regulation, etc. SUMMARY

[0006] The application provides a low-cost semi-annealed low-carbon steel thick plated zinc-aluminum-magnesium alloy and a preparation method thereof, proposes a low-cost, high-performance and process-controllable synergistic preparation and performance regulation method, eliminates the product quality problems of uneven surface, abnormal crystallization, insufficient elongation and easy zinc stripping of the traditional semi-annealed steel material plated layer, and meets the market orientation of cost reduction and the demand of diversified application scenarios.

[0007] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0008] A low-cost semi-annealed low-carbon steel thick plated zinc-aluminum-magnesium alloy comprises a base material and a plated layer formed on the base material, and the chemical composition of the base material is as follows in terms of percentage by weight: C: 0.01-0.08%, Si≤0.030%, Mn: 0.15-0.26%, P: 0.015-0.026%, S≤0.010%, Als: 0.02-0.06%, Ti≤0.3000%, and the rest is Fe and inevitable impurities.

[0009] The chemical composition of the plating solution for preparing the plated layer is as follows in terms of percentage by weight: Al: 9-11%, Mg: 2.8-3.1%, rare earth elements≤0.1%, Si: 0.1-0.2%, and the rest is Zn and inevitable impurities.

[0010] Further, the thickness of the plated layer is 275-300 g / m 2 .

[0011] A preparation method of a low-cost semi-annealed low-carbon steel thick plated zinc-aluminum-magnesium alloy, the preparation method comprises the following process:

[0012] hot metal pretreatment→ converter smelting→ secondary refining→ continuous casting→ heating→ 1700 / 2300 rolling→ controlled cooling→ coiling→ one cold pickling and cold rolling→ one cold continuous annealing and galvanizing→ post-plating treatment→ coiling→ sampling→ inspection.

[0013] Further, the one cold continuous annealing adopts a three-stage temperature rising process, the initial temperature is raised to 485-495 DEG C at a rate of 6-8 DEG C / s, and then the temperature is raised to 555-565 DEG C at a rate of 12-16 DEG C / s in two stages.

[0014] Further, the post-plating cooling in the post-plating treatment process adopts a three-stage variable temperature cooling process, the air knife distance is 15-25 mm, the air knife pressure is 80-100 mbar, the cooling stage in the post-plating treatment process comprises an air cooling stage and a water cooling stage, the cooling rate of the air cooling stage is 40-50 DEG C / s, and the cooling rate of the water cooling stage is kept at 55-65 DEG C / s.

[0015] Compared with the prior art, the application has the following beneficial effects:

[0016] 1) The present application realizes partial recrystallization of the surface layer of the strip steel by reasonable temperature control and cooling process of the strip steel substrate, combined with the special heat transfer mode of direct-fired heating method, through multi-stage controllable heating, so that the surface layer of the strip steel is remelted, the intergranular corrosion is inhibited, the adhesion of the plated layer and the elongation are improved, the dislocation pile-up is closed to form a rapid diffusion channel, the diffusion of iron atoms in the matrix is slowed down, the probability of hard and brittle iron-zinc burst structure is reduced, the grain size of the burst structure is reduced, so that the surface quality is improved, and the iron-aluminum phase combination efficiency is higher than that of iron-zinc phase, combined with the multi-stage plated layer cooling process, the iron-aluminum inhibition layer is formed, the combination of the matrix and the plated layer is thin, the adhesion of the plated layer is improved, the non-uniform nucleation of the plated layer is inhibited, and the plated layer surface is more beautiful;

[0017] 2) It can be suitable for production of different sizes and plated layer thickness, and the plated layer thickness can reach 300 g / m 2 Double-sided, optimizing the plated layer structure, refining the grain size, eliminating the product quality problems of uneven surface of traditional semi-annealed steel plated layer, abnormal crystallization, insufficient elongation and easy dezincification, while meeting the market orientation of cost reduction, stabilizing the mechanical properties of the substrate while maintaining high mechanical strength of the substrate, realizing the win-win of quality and price;

[0018] 3) The residual stress of the strip steel is adjusted by low-carbon steel low-temperature semi-annealing process, the strength of the matrix is improved by using the organizational genetic mechanism of work hardening and grain distortion, and the corrosion resistance of the plated layer and the mechanical properties of the matrix are synergistically optimized by combining the multi-element diffusion dynamics control technology of zinc-aluminum-magnesium plated layer;

[0019] 4) The accurate temperature control process of the annealing section and the cooling section realizes the organic combination of the zinc-aluminum-magnesium plated layer and the semi-annealed low-carbon steel, which not only ensures the controllable cost of the product, but also improves the mechanical properties and plated layer quality of the product, realizes the preparation method of semi-annealed low-carbon steel thick plated zinc-aluminum-magnesium alloy with low cost, high performance and controllable process, and meets the needs of diversified application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the annealing temperature curve schematic diagram of the continuous annealing section according to the embodiment of the present application.

[0021] Figure 2 is the post-plating cooling temperature curve schematic diagram according to the embodiment of the present application. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described below in combination with the drawings:

[0023] The application discloses a low-cost semi-annealed low-carbon steel thick-plated zinc-aluminum-magnesium alloy, which comprises a base material and a plated layer formed on the base material. 2 ;

[0024] The base material is designed as follows: Fe as a base body, and other chemical components are added in the following weight percentage: C: 0.01-0.08%, Si≤0.030%, Mn: 0.15-0.26%, P: 0.015-0.026%, S≤0.010%, Als: 0.02-0.06%, Ti≤0.3000% and the like.

[0025] The plating solution for preparing the plated layer is designed as follows: Zn as a base body, and other chemical components are added in the following weight percentage: Al: 9-11%, Mg: 2.8-3.1%, rare earth elements≤0.1%, Si: 0.1-0.2%; wherein the rare earth elements include lanthanum, cerium, indium and the like, the content ratio of magnesium and aluminum can improve the corrosion resistance of the plated layer, the rare earth elements can refine the plated layer grains, and the silicon can inhibit the aggregation of brittle phases such as Zn-Al-Mg ternary eutectic compounds.

[0026] A preparation method of the low-cost semi-annealed low-carbon steel thick-plated zinc-aluminum-magnesium alloy comprises the following process steps:

[0027] hot metal pretreatment, converter smelting, secondary refining, continuous casting, heating, 1700 / 2300 rolling, controlled cooling, coiling, one-cold pickling and cold rolling, one-cold continuous annealing and zinc plating, post-plating treatment, coiling, sampling and inspection.

[0028] The one-cold continuous annealing adopts a three-stage temperature rising process, in which the temperature is raised to 487℃ at a speed of 6℃ / s in the initial stage, and then raised to 556℃ at a speed of 14℃ / s and 12℃ / s in the two subsequent stages.

[0029] The post-plating cooling process adopts a three-stage variable-temperature cooling process, in which a 15mm air knife distance, 80mbar air knife pressure and the latent heat release of the strip steel are combined to realize a low cooling rate, so as to eliminate the stress between the plated layer and the base body structure, the cooling rate in the air cooling stage is 40℃ / s, the cooling rate in the water cooling stage is kept at 55℃ / s, so as to realize the elimination of the influence of the latent heat release of the strip steel, refine the plated layer structure and optimize the plated layer structure, and finally pass through the water cooling stage to reduce the residual stress of the plated layer, quickly solidify the structure and improve the adhesion of the plated layer structure.

[0030] The following examples are implemented on the premise of the technical scheme of the application, and detailed implementation modes and specific operation processes are given, but the protection scope of the application is not limited to the following examples. The methods used in the following examples are all conventional methods unless otherwise specified.

[0031] Example 1:

[0032] Base material composition: Fe as the base, other chemical components are added as follows in percentage by weight: 0.03% C, 0.010% Si, 0.18% Mn, 0.020% P, 0.010% S, 0.05% Als, 0.27% Ti, and the like.

[0033] Plating solution composition design: Zn as the base, Al content is controlled at 9.8wt%, Mg content is reduced to 2.8wt%, and trace rare earth elements such as lanthanum, cerium, indium, and the like are added, total content ≤0.1wt%, Si: 0.13wt%, reasonable Mg / Al content ratio can improve the corrosion resistance of the coating, rare earth elements refine the coating grain, and Si suppresses the generation of brittle phases such as Zn-Al-Mg ternary eutectic compounds.

[0034] Continuous annealing process adopts a three-stage temperature rising process, as shown in Figure 1 , first, heat up at 7°C / s to eliminate stress to 490°C, then heat up at 16°C / s and 12°C / s in two stages to 560°C, high hydrogen (20%) reduction process is used to eliminate the surface oxide layer and improve the adhesion of the coating, then cool down at 20°C / s to 480°C to ensure the strength of the base material, and then enter the zinc pot after a short slow cooling to 468°C.

[0035] Post-plating cooling process adopts a three-stage variable temperature cooling process, as shown in Figure 2 , the first stage is to realize a reasonable cooling rate of 18°C / s by using the air knife distance of 17mm, air knife pressure of 85mbar, air knife angle of -1.5°, and the latent heat release of the strip to eliminate the stress between the coating and the base material organization, and the cooling rate is increased to 46°C / s in the air cooling stage to eliminate the influence of the latent heat release of the strip, refine the coating organization grain, and optimize the coating organization structure, and finally pass through the water cooling stage to reduce the residual stress of the coating, quickly solidify the organization, and improve the adhesion of the coating organization.

[0036] Example 2:

[0037] Base material composition: Fe as the base, other chemical components are added as follows in percentage by weight: 0.05% C, 0.010% Si, 0.22% Mn, 0.021% P, 0.011% S, 0.05% Als, 0.27% Ti, and the like.

[0038] Plating solution composition design: Zn as the base, Al content is controlled at 10.4wt%, Mg content is reduced to 2.9wt%, and trace rare earth elements such as lanthanum, cerium, indium, and the like are added, total content ≤0.1wt%, Si: 0.15wt%, reasonable Mg / Al content ratio can improve the corrosion resistance of the coating, rare earth elements refine the coating grain, and Si suppresses the generation of brittle phases such as Zn-Al-Mg ternary eutectic compounds.

[0039] The continuous annealing process adopts a three-stage temperature rising process, first rising at 6°C / s to eliminate stress to 488°C, then rising at 16°C / s and 12°C / s in two stages to 560°C for short-term insulation of 2s and using high hydrogen (20%) reduction process to eliminate the surface oxide layer and improve the coating adhesion, then cooling at 18°C / s to 478°C to ensure the strength of the substrate, and then short-term slow cooling to 466°C into the zinc pot.

[0040] The post-plating cooling process adopts a three-stage variable temperature cooling process, the first stage uses air knife distance of 19mm, air knife pressure of 92mbar, air knife angle of -1.0° after coming out of the zinc pot at 465°C, and cooperates with the release of strip latent heat to achieve a low cooling rate of 8°C / s to eliminate the stress between the coating and the substrate structure, the air cooling stage increases the cooling rate to 40°C / s to eliminate the influence of strip latent heat release, refine the coating structure and optimize the coating structure, and finally passes through the water cooling stage to reduce the residual stress of the coating, quickly solidify the structure and improve the adhesion of the coating structure.

[0041] Example 3:

[0042] The substrate composition is: Fe as the matrix, and other chemical components are added in the following weight percentages: 0.04% C, 0.010% Si, 0.21% Mn, 0.021% P, 0.010% S, 0.05% Als, 0.27% Ti, etc. to form the matrix.

[0043] The plating solution composition design is: Zn as the matrix, Al content controlled at 10.1wt%, Mg content reduced to 3.1wt%, and trace amounts of rare earth elements such as lanthanum, cerium, indium, etc. added with total content ≤0.1wt%, silicon Si: 0.12wt%, reasonable Mg / Al content ratio can improve the corrosion resistance of the coating, rare earth elements refine the coating grains, and silicon suppresses the aggregation of brittle phases such as Zn-Al-Mg ternary eutectic compounds.

[0044] The continuous annealing process adopts a three-stage temperature rising process, first rising at 6°C / s to eliminate stress to 488°C, then rising at 16°C / s and 12°C / s in two stages to 560°C for short-term insulation of 2s and using high hydrogen (20%) reduction process to eliminate the surface oxide layer and improve the coating adhesion, then cooling at 18°C / s to 478°C to ensure the strength of the substrate, and then short-term slow cooling to 466°C into the zinc pot.

[0045] The post-plating cooling process adopts a three-stage variable temperature cooling process. In the first stage, after the strip leaves the zinc pot at 465℃, the air knife distance is 23mm, the air knife pressure is 95mbar, the air knife angle is 0°, and the strip latent heat is released to achieve a low cooling rate of 8℃ / s, so as to eliminate the stress between the coating and the substrate structure. In the air cooling stage, the cooling rate is increased to 50℃ / s to eliminate the influence of the strip latent heat release, refine the coating structure, and optimize the coating structure. Finally, the water cooling stage is used to reduce the residual stress of the coating, quickly solidify the structure, and improve the adhesion of the coating structure.

Claims

1. A low cost semi-annealed state low carbon steel thick coated zinc-aluminum-magnesium alloy characterized in that, The chemical composition of the substrate is as follows: C: 0.01-0.08%, Si: ≤0.030%, Mn: 0.15-0.26%, P: 0.015-0.026%, S: ≤0.010%, Al: 0.02-0.06%, Ti: ≤0.3000%, and the rest is Fe and inevitable impurities; The chemical composition of the plating solution for preparing the plating layer is as follows: Al: 9-11%, Mg: 2.8-3.1%, rare earth elements: ≤0.1%, Si: 0.1-0.2%, and the rest is Zn and inevitable impurities; The preparation method of the low-cost semi-annealed thick zinc-aluminum-magnesium alloy coating on low-carbon steel comprises the following processes: hot metal pretreatment, converter smelting, secondary refining, continuous casting, heating, 1700 / 2300 rolling, controlled cooling, coiling, one-cold pickling and cold rolling, one-cold continuous annealing and galvanizing, post-galvanizing treatment, coiling, sampling, and inspection; The one-cold continuous annealing adopts a three-stage temperature rising process, in which the temperature is raised to 485-495 ℃ at a rate of 6-8 ℃ / s, and then heated to 555-565 ℃ at a rate of 12-16 ℃ / s in two stages; The post-galvanizing cooling adopts a three-stage variable-temperature cooling process, with an air knife distance of 15-25 mm and an air knife pressure of 80-100 mbar; the cooling stage in the post-galvanizing treatment process comprises an air cooling stage and a water cooling stage, the cooling rate of the air cooling stage is 40-50 ℃ / s, and the cooling rate of the water cooling stage is maintained at 55-65 ℃ / s.

2. A low cost semi-annealed low carbon steel thick coated zinc-aluminum-magnesium alloy as claimed in claim 1, wherein, The plating layer thickness is 275-300 g / m on both sides 2 .

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