Alloyed hot-dip galvanized steel plate with excellent machinability and manufacturing method thereof

Abstract

The invention discloses an alloyed hot-dip galvanized steel plate with excellent machinability, which comprises a steel substrate and an alloyed coating on the surface of the steel substrate, in the phase structure of the alloyed coating, the volume ratio of FeZn13 phase is less than or equal to 1%, and the sum of the volume ratio of Fe5Zn21 phase and the volume ratio of Fe3Zn10 phase is 0.5-2%. The invention further discloses a manufacturing method of the alloyed hot-dip galvanized steel plate. The manufacturing method comprises the following steps: smelting and casting; hot rolling; cold rolling; annealing is conducted; carrying out hot dipping in a zinc pot, wherein the temperature of the zinc pot is 450-480 DEG C; the heating rate of alloying treatment is controlled to be 30-40 DEG C / s, the heating temperature is controlled to be 480-560 DEG C, the heat preservation time is 10-30 s, and then the cooling rate of cooling is controlled to be 30-45 DEG C / s. The alloyed hot-dip galvanized steel plate prepared by the method has good surface sliding property and good pulverization resistance.

Description

Technical Field

[0001] The invention relates to a steel plate and a manufacturing method thereof, and in particular to a hot-dip galvanized steel plate and a manufacturing method thereof. Background Art

[0002] Compared with pure zinc hot-dip galvanized cold-rolled steel sheets, alloyed hot-dip galvanized cold-rolled steel sheets have better paintability, weldability and corrosion resistance, and their usage in the automotive field has gradually increased in recent years.

[0003] The alloying treatment of hot-dip galvanized steel sheet uses pure zinc hot-dip galvanized steel sheet as the initial material. The basic process is: the surface treated steel sheet is galvanized in a zinc pot and the thickness of the zinc layer is controlled by an air knife, and then diffusion annealing is performed in an alloying furnace above the zinc pot. Through the mutual diffusion of Fe and Zn, the zinc layer is transformed into a Fe-Zn alloy layer to obtain an alloy-coated steel sheet with a certain proportion of iron content. The zinc-iron alloy layer may contain ζ phase (FeZn 13 ),δ1 phase (FeZn 7 ), Γ1 phase (Fe 5 Zn 21 ), Γ phase (Fe 3 Zn 10 ).

[0004] Since automobile steel is required to have excellent stamping properties, the commonly used steel grades for automobiles are alloyed hot-dip galvanized IF steel and other steel grades with excellent formability. However, since the coating is prone to powdering or peeling under harsh stamping conditions, whether complex automobile parts can be stamped out requires good control of the coating phase structure of the steel plate.

[0005] In the alloyed coating phase structure, the ζ phase has a relatively low hardness and a large surface friction coefficient, which is not conducive to stamping and will also cause cracking of the steel plate during subsequent processing; while the Γ phase is the bonding layer between the coating and the substrate, and has a high hardness, but the thicker the Γ phase, the easier it is to cause the coating to powder. Generally speaking, for parts that are subjected to severe stamping, if a surface phase structure that is beneficial to stamping is required, the surface can be controlled to be dominated by the δ phase, with a small amount of the Γ phase and as little as possible of the ζ phase.

[0006] The existing technology for producing alloyed hot-dip galvanized products mainly controls the phase structure of the coating by controlling the alloying temperature. Among them, in order to obtain a lower surface friction coefficient, the niobium-titanium composite ultra-low carbon steel can adjust the alloying temperature to control the iron content of the coating to more than 10%. However, too high an iron content will lead to severe powdering of the coating during processing; at the same time, the iron content of the coating is high, and there is still a lot of ζ phase remaining on the surface of the coating, which will lead to poor powdering indicators of the coating and a high friction coefficient, thereby causing powdering of the coating on the processed parts, resulting in problems such as stamping or cracking of the processed parts, and cannot meet the requirements of punching parts. Therefore, taking into account both powdering of the coating and surface sliding properties (low friction coefficient) is a technical difficulty in alloyed hot-dip galvanized steel sheets. Summary of the invention

[0007] One of the purposes of the present invention is to provide an alloyed hot-dip galvanized steel sheet with excellent processability, which can have both good surface sliding properties and good anti-powdering properties, thereby solving the processing problems of steel sheet materials manufactured by the prior art.

[0008] In order to achieve the above object, the present invention provides an alloyed hot-dip galvanized steel sheet with excellent processability, which comprises a steel substrate and an alloyed coating on the surface of the steel substrate, wherein the phase structure of the alloyed coating is FeZn 13 The volume ratio of the phase is ≤1%, Fe 5 Zn 21 Phase and Fe 3 Zn 10 The sum of the volume proportions of the phases is: 0.5% to 2%.

[0009] Furthermore, in the alloyed hot-dip galvanized steel sheet of the present invention, the steel substrate contains Fe and inevitable impurity elements, and the steel substrate also contains the following chemical elements in the following mass percentages:

[0010] C: 0.0015% to 0.003%, Si: 0.03 to 0.1%, Mn: 0.1% to 0.8%, P: 0.01 to 0.03%, Ti: 0.01 to 0.04%, Nb: 0.005 to 0.02%, 0<N≤0.004%.

[0011] Furthermore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage of each chemical element of the steel substrate is:

[0012] C: 0.0015%~0.003%, Si: 0.03~0.1%, Mn: 0.1%~0.8%, P: 0.01~0.03%, Ti: 0.01~0.04%, Nb: 0.005~0.02%, 0<N≤0.004%; the balance is Fe and unavoidable impurity elements.

[0013] In the present invention, the inevitable impurity element is mainly S, and it is desirable that the content thereof is as low as possible.

[0014] In the alloyed hot-dip galvanized steel sheet of the present invention, the design principles of the chemical elements of the steel substrate are as follows:

[0015] C: In the alloyed hot-dip galvanized steel sheet described in the present invention, carbon is an interstitial solid solution element, which can improve the strength of the material and hinder recrystallization. At the same time, carbon can hinder the alloying diffusion of the coating. However, too much carbon is not conducive to the formation of stamping texture. When there is excessive free interstitial carbon in the material, the processability will deteriorate. In order to reduce such problems, a certain amount of alloying elements for fixing carbon must be added to the material. The more carbon elements are added, the more alloying elements are added, which will lead to the deterioration of the r-value performance of the material, which is not conducive to the processing performance and increases the cost. At the same time, too low a carbon content in the material will lead to rapid alloying of grain boundaries. In the present invention, in order to avoid the explosive phase structure of the ultra-low carbon steel coating with titanium, the resulting strip defects on the surface of the coating, and the excessive alloying leading to Fe 3 Zn 10 and Fe 5 Zn 21 Therefore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage content of C in the steel substrate can be controlled between 0.0015% and 0.003%.

[0016] Si: In the alloyed hot-dip galvanized steel sheet described in the present invention, silicon can strengthen the material. Adding a certain amount of silicon to ultra-low carbon steel IF steel can improve the bonding performance of the hot-dip galvanized IF steel coating and improve the anti-powdering property of the coating. For the steel sheet and coating to which silicon and phosphorus are added in combination, the zinc element in the steel coating containing silicon can easily penetrate into the grain boundary, which can improve the bonding strength of the coating. Adding silicon to the steel sheet can delay the alloying process of the coating, thereby reducing the propagation of coating cracks in the coating, and thus can reduce the amount of coating powdering and peeling. However, excessive silicon in the steel sheet has an adverse effect on the plating property of the hot-dip coating on the surface of the steel sheet, and is also prone to produce the defect of red iron oxide scale during hot rolling. Therefore, in the alloyed hot-dip galvanized steel sheet described in the present invention, the mass percentage content of Si in the steel substrate can be controlled between 0.03 and 0.10%.

[0017] Mn: In the alloyed hot-dip galvanized steel sheet of the present invention, manganese is a strengthening element of the material. Adding a certain amount of manganese to the material can improve the strength. At the same time, manganese can delay the alloying process of the hot-dip galvanized coating, thereby improving the anti-powdering property of the coating. However, when the content of Mn is too high, it will be detrimental to the product quality. Therefore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage content of Mn in the steel substrate can be controlled between 0.10% and 0.80%.

[0018] P: In the alloyed hot-dip galvanized steel sheet of the present invention, the addition of phosphorus to the steel can inhibit explosive organizational reactions during grain boundary segregation, inhibit Fe-Zn alloying reactions in the coating, and inhibit Fe 3 Zn 10 growth, and also reduce FeZn 13 Phase density and FeZn 13 The phase grains are coarse, thereby improving the anti-powdering property of the coating and reducing the surface friction coefficient of the coating. Therefore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage content of P in the steel substrate can be controlled between 0.01 and 0.030%.

[0019] Ti: In the alloyed hot-dip galvanized steel sheet described in the present invention, the titanium element can combine with carbon and nitrogen atoms in the steel to form compounds, thereby purifying the material and improving the r value of the material. When the titanium content is too low, it cannot fix nitrogen and part of the carbon, which is not conducive to the stamping processing of the material. When the titanium content is too high, excess titanium will be produced, resulting in explosive phase structure of the coating, which is not conducive to the surface quality of the coating. At the same time, excess titanium can easily promote Fe 3 Zn 10 and Fe 5 Zn 21 phase growth, excessive Fe 3 Zn 10 and Fe 5 Zn 21 Therefore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage content of Ti in the steel substrate can be controlled between 0.01 and 0.04%.

[0020] Nb: In the alloyed hot-dip galvanized steel sheet of the present invention, niobium combines with carbon atoms in the steel to form compounds. NbC in the steel is partially decomposed during the recrystallization annealing process after cold rolling, and a trace amount of solid solution carbon is generated in the grain boundary, which can hinder the rapid zinc and iron diffusion at the grain boundary and hinder the alloying process of the coating, thereby inhibiting the Fe 3 Zn 10 and Fe 5 Zn 21 Therefore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage content of Nb in the steel substrate can be controlled between 0.005 and 0.02%.

[0021] N: In the alloyed hot-dip galvanized steel sheet of the present invention, nitrogen is an interstitial solid solution element. In ultra-low carbon steel containing titanium, nitrogen combines with titanium in the steel to form TiN. When the nitrogen content is too high, too much effective titanium will be consumed. Therefore, in the alloyed hot-dip galvanized steel sheet of the present invention, the mass percentage content of N in the steel substrate can be controlled to 0<N≤0.004%.

[0022] Furthermore, in the alloyed hot-dip galvanized steel sheet of the present invention, the chemical elements of the steel substrate also satisfy at least one of the following formulas:

[0023] Ti≤4C+0.03×Mn+0.2×P+3.42×N;

[0024] 0.0002≤Ti×Nb≤0.0003;

[0025] In the formula, substitute the value before the percentage sign of each element's mass percentage.

[0026] Furthermore, in the alloyed hot-dip galvanized steel sheet described in the present invention, the V-bend powdering width is ≤3.5 mm, and the friction coefficient μ is ≤0.21.

[0027] Furthermore, in the alloyed hot-dip galvanized steel sheet described in the present invention, its r value is ≥1.6.

[0028] Accordingly, another object of the present invention is to provide an alloyed hot-dip galvanized steel sheet having good stamping performance, wherein the FeZn in the phase structure of the hot-dip galvanized coating is 13 ≤1%, 0.5%≤Fe 5 Zn 21 +Fe 3 Zn 10 ≤2%, so that the hot-dip galvanized steel sheet can have both good surface sliding properties and good anti-powdering properties.

[0029] In order to achieve the above object, the present invention provides a method for manufacturing an alloyed hot-dip galvanized steel sheet, comprising the steps of:

[0030] smelting and casting;

[0031] Hot rolling;

[0032] Cold rolling;

[0033] annealing;

[0034] Enter the zinc pot for hot dip plating: the temperature of the zinc pot is 450-480℃;

[0035] Alloying treatment: The heating rate of the alloying treatment is controlled at 30-40°C / s, the heating temperature is controlled at 480-560°C, the holding time is 10-30s, and then the cooling rate is controlled at 30-45°C / s.

[0036] In the manufacturing method of the present invention, when the steel plate enters the zinc pot, an aluminum barrier layer will quickly form on the ferrite interface to inhibit the diffusion of iron. The aluminum barrier layer hinders the zinc-iron alloy reaction and can inhibit the diffusion of Fe. 3 Zn 10 The zinc pot temperature is controlled at 450-480℃ to achieve this purpose.

[0037] Furthermore, in the alloying step of the manufacturing method of the present invention, FeZn 13 The phase is formed by alloying below 470℃, so it is necessary to limit the alloying of galvanized steel sheets to below 470℃. At the same time, the alloying temperature should be appropriately adjusted according to the alloy content in the steel sheet. The higher the alloy content in the steel sheet, the higher the alloying temperature of the coating should be required to ensure that the FeZn coating 13 Under the condition of the same alloy content in steel plate, excessively high heating temperature will lead to over-alloying of the coating, Fe 3 Zn 10 and Fe 5 Zn 21 Will overgrow, in order to ensure the coating phase structure target 0.5% ≤ Fe 5 Zn 21 +Fe 3 Zn 10 ≤2%, so the heating temperature of the steel plate coating alloying temperature is controlled between 480 and 560°C, and the holding time is controlled between 10 and 30 seconds. 13 Phase, Fe 3 Zn 10 and Fe 5 Zn 21 The growth of FeZn 13 Phase, Fe 3 Zn 10 and Fe 5 Zn 21 The less, so the heating rate of the steel plate is controlled at 30-40℃ / s, and the cooling rate is controlled at 30-45℃ / s.

[0038] Furthermore, in the hot rolling step of the method for manufacturing alloyed hot-dip galvanized steel sheet described in the present invention, the hot rolling heating temperature is 1120-1200°C; and the coiling temperature is controlled at 600°C-700°C.

[0039] In the hot rolling step, in order to reduce the decomposition and dissolution of carbides into the material, the hot rolling heating temperature can be low temperature heating. Too high a heating temperature is not good for the material processing performance and will also cause problems with the surface quality of the steel plate. Therefore, the hot rolling heating temperature can be controlled between 1120 and 1200 ° C; the hot rolling final rolling temperature is between Ar 3 Above the temperature, but too high will cause quality problems of surface oxide scale pressing in.

[0040] In addition, the coiling temperature also has a certain influence on the performance of the steel plate and the surface of the coating. When the coiling temperature is too low, it will be detrimental to the mechanical properties of the steel plate, and when the coiling temperature is too high, it will be detrimental to the alloying of the coating. Therefore, in order to take into account the performance and surface of the material, the coiling temperature can be controlled at 600℃~700℃.

[0041] Furthermore, in the cold rolling step of the method for manufacturing the alloyed hot-dip galvanized steel sheet described in the present invention, the cold rolling deformation is controlled to be greater than 70%.

[0042] In the cold rolling step, in order to further reduce the thickness of the hot rolled steel coil to the required cold rolling thickness, and also to transform the material grains into fibrous structures to facilitate the recrystallization of the material, the recrystallization temperature can be reduced with the increase of the deformation amount under an appropriate deformation amount, thereby improving the annealing effect and the r value. Therefore, in the preferred embodiment of the present invention, the cold rolling deformation amount can be controlled to be greater than 70%.

[0043] Furthermore, in the annealing step of the method for manufacturing alloyed hot-dip galvanized steel sheet described in the present invention, the annealing temperature is controlled at 750-820°C.

[0044] In order to improve the workability of cold rolled steel coils, continuous annealing is required. In order to ensure that the rolled material can be fully recrystallized, annealing requires high temperature annealing. Since the annealing temperature has a great influence on the material properties, if the annealing temperature is too low, the material cannot be recrystallized, which will lead to the deterioration of the material's ductility and r value. Therefore, the annealing temperature can be controlled between 750 and 820 °C.

[0045] The alloyed hot-dip galvanized steel sheet and the method for manufacturing the same according to the present invention have the following advantages and beneficial effects:

[0046] The alloyed hot-dip galvanized steel sheet of the present invention has a specific chemical composition and process design, and the FeZn in the phase structure of the hot-dip galvanized coating is 13 ≤1%, 0.5%≤Fe 5 Zn 21 +Fe 3 Zn 10 ≤2%, alloyed hot-dip galvanized steel sheet with good stamping forming performance can be obtained.

[0047] In the alloyed hot-dip galvanized steel sheet of the present invention, FeZn 13 The surface friction coefficient is relatively low, which can reduce the cracking of alloyed hot-dip galvanized steel sheets during stamping and forming. At the same time, the Fe coating of the product of the present invention is 3 Zn 10 and Fe 5 Zn 21 Less, not easy to cause coating powdering, coating powdering width is narrow, so the coating is not easy to powder or peel off.

[0048] The alloyed hot-dip galvanized steel sheet described in the present invention has good surface sliding properties, good anti-powdering properties and good peeling properties, and solves the processing problems of steel sheet materials manufactured by the prior art. DETAILED DESCRIPTION

[0049] The alloyed hot-dip galvanized steel sheet with excellent processability and the method for manufacturing the same described in the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0050] Examples 1-6 and Comparative Examples 1-3

[0051] The alloyed hot-dip galvanized steel sheets of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3 of the present invention are prepared by the following steps:

[0052] (1) Smelting and casting to obtain corresponding slabs. Table 1 lists the chemical composition ratios of various embodiments and comparative examples.

[0053] (2) Hot rolling: The hot rolling heating temperature is 1120~1200℃; the coiling temperature is controlled at 600℃~700℃.

[0054] (3) Cold rolling: Control the cold rolling deformation to be greater than 70%.

[0055] (4) Annealing: The annealing temperature can be controlled between 750℃ and 820℃.

[0056] (5) Entering the zinc pot for hot dip plating: the temperature entering the zinc pot is controlled at 450-480℃.

[0057] (6) Alloying treatment: the heating rate is controlled at 30-40°C / s, the heating temperature is controlled at 480-560°C, the holding time is 10-30s, and the cooling rate is controlled at 30-45°C / s.

[0058] It should be noted that, in the present invention, the chemical composition design and related manufacturing processes used in the alloyed hot-dip galvanized steel sheets of Examples 1-6 all meet the specification requirements designed by the present invention. Accordingly, the chemical composition design and related manufacturing processes used in the comparative steel sheets of Comparative Examples 1-3 all have process parameters that do not meet the design requirements of the present invention.

[0059] Table 1 lists the mass percentages of various chemical elements in the alloyed hot-dip galvanized steel sheets of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3.

[0060] Table 1. (wt%, the balance is Fe and other inevitable impurities)

[0061]

[0062] Accordingly, Table 2 lists the specific process parameters of the alloyed hot-dip galvanized steel sheets of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3 in the above process steps (1)-(6).

[0063] Table 2.

[0064]

[0065] The alloyed hot-dip galvanized steel sheets of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3 were sampled respectively, and the coating phase structure of each example and comparative example was observed by scanning electron microscopy (SEM), and the composition of the coating phase was analyzed by EDS. The test results are listed in Table 3.

[0066] In addition, the alloyed hot-dip galvanized steel sheets of Examples 1-6 and the comparative steel sheets of Comparative Examples 1-3 were sampled, respectively, and subjected to V-bend powdering width detection, friction coefficient detection and r-value detection. The detection results are also listed in Table 3 below.

[0067] Among them, the V-bend powdering width detection method is: the sample is bent 60°, then peeled off with tape, and the width of the black powder on the tape is measured.

[0068] Friction coefficient detection method: Use a ball friction tester to simulate the surface friction state of the metal steel plate during the stamping process. After the ball returns to the steel plate for multiple times, the friction coefficient of the tested sample is collected and analyzed.

[0069] R-value detection method: GB / T 5027 (Determination of plastic strain ratio (r-value) of metal sheets and strips) is used for detection.

[0070] Table 3.

[0071]

[0072]

[0073] Note: The r values ​​in Table 3 are three-way means.

[0074] As can be seen from Table 3, in the alloyed hot-dip galvanized steel sheets of Examples 1 to 6 of the present invention, FeZn 13 Phase, Fe 5 Zn 21 Phase and Fe 3 Zn 10 The V-bend powdering width is ≤3.5 mm, and the friction coefficient μ is ≤0.21, which are significantly lower than those of comparative examples 1 to 3. In addition, it can be seen from Table 3 that r of embodiments 1 to 6 of the present invention is ≥1.6.

[0075] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0076] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. An alloying hot-dip galvanized steel sheet with excellent processability, which comprises a steel substrate and an alloying coating on the surface of the steel substrate. Characterized in that, In the phase structure of the alloying coating, FeZn 13 phase has a volume ratio of ≤ 1%, Fe 5 Zn 21 phase and Fe 3 Zn 10 phase have a combined volume ratio of: 0.5% - 2%.

2. The alloying hot-dip galvanized steel sheet according to claim 1, wherein the steel substrate contains Fe and inevitable impurity elements. Characterized in that, The steel substrate further contains the following chemical elements with the mass percentages as follows: C: 0.0015% - 0.003%, Si: 0.03 - 0.1%, Mn: 0.1% - 0.8%, P: 0.01 - 0.03%, Ti: 0.01 - 0.04%, Nb: 0.005 - 0.02%, 0 < N ≤ 0.004%.

3. The alloying hot-dip galvanized steel sheet according to claim 2. Characterized in that, The mass percentages of the chemical elements of the steel substrate are: C: 0.0015% - 0.003%, Si: 0.03 - 0.1%, Mn: 0.1% - 0.8%, P: 0.01 - 0.03%, Ti: 0.01 - 0.04%, Nb: 0.005 - 0.02%, 0 < N ≤ 0.004%; the balance is Fe and inevitable impurity elements.

4. The alloying hot-dip galvanized steel sheet according to claim 1 or 2. Characterized in that, The chemical elements of the steel substrate further satisfy at least one of the following formulas: Ti ≤ 4C + 0.03×Mn + 0.2×P + 3.42×N, 0.0002 ≤ Ti×Nb ≤ 0.0003; In the formulas, each element is substituted with the value before the percentage sign of its mass percentage.

5. The alloying hot-dip galvanized steel sheet according to claim 1 or 2. Characterized in that, Its V-bend powdering width ≤ 3.5 mm, and its friction coefficient μ ≤ 0.

21.

6. The alloying hot-dip galvanized steel sheet according to claim 1 or 2. Characterized in that, Its r value ≥ 1.

6.

7. The manufacturing method of the alloying hot-dip galvanized steel sheet according to any one of claims 1 - 6. Characterized in that, It includes the steps of: Smelting and casting; Hot rolling; Cold rolling; Annealing; Entering the zinc pot for hot-dip galvanizing: the temperature entering the zinc pot is 450 - 480 °C; Alloying treatment: the heating rate of the alloying treatment is controlled at 30 - 40 °C / s, the heating temperature is controlled at 480 - 560 °C, the holding time is 10 - 30 s, and then the cooling rate during cooling is controlled at 30 - 45 °C / s.

8. The manufacturing method according to claim 7. Characterized in that, In the hot rolling step, the hot rolling heating temperature is 1120 - 1200 °C; the coiling temperature is controlled at 600 °C - 700 °C.

9. The manufacturing method according to claim 7. Characterized in that, In the cold rolling step, the cold rolling deformation amount is controlled to be greater than 70%.

10. The manufacturing method according to claim 7. Characterized in that, In the annealing step, the annealing temperature is controlled at 750 - 820 °C.

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