A method for producing alloyed galvanized sheet with a sheet width of ≥1800 mm

Abstract

A method for producing alloyed galvanized steel sheets with a width of 1800 mm or greater includes conventional hot rolling and hot-rolling to reduce the strip surface crown; pickling; cold rolling using five stands, with the group spacing refined and the cold rolling reduction controlled according to the finished product thickness; continuous annealing; galvanizing; alloying treatment; and skin-passing. This method not only produces strips with a width of 1800 mm or greater, but also offers a stable production process, with a qualified rate exceeding 80% from the current 50%; and a tensile strength of 280 MPa or greater, meeting user requirements.

Description

Technical Field

[0001] The invention relates to a method for producing an alloyed galvanized sheet, in particular to a method for producing an alloyed galvanized sheet with a sheet width of ≥1800 mm. Background Art

[0002] With the in-depth development of the automobile market, the market requirements for automobile steel have shown a trend of differentiation and diversification. In order to improve the material utilization rate of steel plates, meet the overall forming requirements of parts, and reduce the welding costs of the original tailor-welded plates, some users require cold-rolled plates with larger plate widths.

[0003] Galvanized alloy sheet offers excellent corrosion resistance, paintability, and resistance to stone and gravel impacts, making it suitable for automotive exterior panels. Ultra-wide galvanized alloy sheet is primarily used for large parts such as front and rear, side panels, and roof panels. Compared to conventional width materials, ultra-wide sheet significantly improves material utilization for large parts, reduces the use of laser-welded blanks, and lowers production costs and carbon emissions. The integrated formation of multiple components can improve vehicle safety.

[0004] Because the width of ultra-wide alloyed galvanized sheet exceeds 1800mm, it is easy for it to run away and scratch the furnace wall during production in the continuous annealing furnace, which can lead to strip breakage and shutdown. It usually takes more than 20 hours to deal with the strip breakage and shutdown accident, which seriously affects the production rhythm and causes huge losses to the company. Therefore, reducing the deviation of ultra-wide alloyed galvanized sheet can effectively improve the production efficiency of the unit, and the most important thing to control the deviation is to control the shape of the steel sheet. Secondly, ultra-wide alloyed galvanized sheet is mainly used for automotive covering parts, which have high requirements for the stamping performance and surface quality of the material. Usually, a high-temperature annealing process route is adopted. Therefore, ultra-wide strip steel can easily produce high-temperature thermal buckling in the continuous annealing furnace, which greatly affects the sheet passing and surface quality. The high sheet passing, high surface quality and high stamping performance requirements of the material have resulted in the inability of existing technologies to efficiently and stably manufacture ultra-wide alloyed galvanized sheet, and the production qualification rate is less than 50%.

[0005] Existing publicly available technologies only describe production, processing, or manufacturing methods for a specific steel grade, such as patent applications CN201210574442.8, CN202010095552.0, and CN201210205030.7. No effective cold rolling process control technology or technical solution for producing alloyed galvanized sheet with a width of 1800 mm or greater, good stability, and a high pass rate has been found domestically or internationally. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the existing technology and provide a method for producing alloyed galvanized sheets with a width of ≥1800mm, which not only has a strip width of ≥1800mm, but also has stable production, a qualified rate increased from the current 50% to more than 80%, performance meeting user needs, and a tensile strength of ≥280MPa.

[0007] Technical measures to achieve the above objectives:

[0008] A method for producing alloyed galvanized sheet with a sheet width of ≥1800 mm, comprising the following steps:

[0009] 1) Perform conventional hot rolling and hot-rolled plate surface convexity: the plate surface convexity value is controlled within 30 to 90 μm, wherein: when the thickness of the hot-rolled plate is ≤4.0 mm, the plate surface convexity value is controlled not to exceed 80 μm; when the thickness of the hot-rolled plate is greater than 4.0 to 6.0 mm, the plate surface convexity value is controlled not to exceed 90 μm;

[0010] 2) Pickling: control the acid tank temperature at 70-90°C;

[0011] The free acid concentration in the three acid tanks is controlled as follows:

[0012] The acid concentration in No. 1 acid tank shall not be less than 50g / l, that in No. 2 acid tank shall not be less than 80g / l, and that in No. 3 acid tank shall not be less than 140g / l; the pickling speed shall be controlled at no more than 180m / min;

[0013] 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product:

[0014] When the finished product thickness is 0.6mm<0.7mm, the thickness of the hot-rolled raw material is selected to be 2.7~≤2.9mm, and the total cold-rolling reduction is controlled at 74~79%;

[0015] When the finished product thickness is 0.7mm<0.8mm, the thickness of the hot-rolled raw material is selected to be 2.9~≤3.1mm, and the total cold-rolling reduction is controlled at 72%~77%;

[0016] When the thickness of the finished product is 0.8mm<0.9mm, the thickness of the hot-rolled raw material is selected to be 3.4~≤3.6mm, and the total cold-rolling reduction is controlled at 74~78%;

[0017] When the finished product thickness is 0.9mm<1.0mm, the hot rolling raw material thickness is selected to be 3.7~≤3.9mm, and the total cold rolling reduction is controlled at 73%~77%;

[0018] When the finished product thickness is 1.0mm<1.2mm, the thickness of the hot-rolled raw material is selected to be 3.9~≤4.1mm, and the total cold-rolling reduction is controlled at 69~76%;

[0019] When the finished product thickness is 1.2mm<1.4mm, the hot rolling raw material thickness is selected to be 4.6~≤4.8mm, and the total cold rolling reduction is controlled at 70~75%;

[0020] When the finished product thickness is 1.4mm<1.6mm, the thickness of the hot-rolled raw material is selected to be 5.4~≤5.6mm, and the total cold-rolling reduction is controlled at 70~75%;

[0021] When the finished product thickness is 1.6mm<≤2.0mm, the hot rolling raw material thickness is selected to be 6.4~≤6.6mm, and the total cold rolling reduction is controlled at 69~75%;

[0022] And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g;

[0023] The crown of the working rolls of each stand is controlled to be 20-40 μm for the 1st to 4th stands, and no more than 10 μm for the 5th stand. The inclination value of the 5th stand is also controlled to be no more than 300 μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤4 kN. The surface reflectivity of the exiting steel plate is controlled to be no less than 70%.

[0024] 4) Continuous annealing: Before annealing the galvannealed steel sheets with a width of ≥1800mm after cold rolling, first arrange 2-3 rolls of DX51 plain carbon steel coils with a width greater than the width of the galvannealed steel sheets to be annealed, and the width greater than the width is not less than 5mm; DX51 steel and galvannealed steel sheets are annealed at the same temperature and speed, and then the galvannealed steel sheets with a width of ≥1800mm are continuously annealed;

[0025] Each process operation is carried out as follows:

[0026] The annealing temperature of each section is controlled as follows:

[0027] The annealing temperature in the soaking section is 825-835°C;

[0028] The temperature of the rapid cooling section is 475-495°C;

[0029] The temperature of the equalization section is 460-470°C;

[0030] Control the annealing speed of each section above to be between 80 and 100 m / min;

[0031] Control the tension of each segment:

[0032] The tension of the heating section is controlled at 4~8KN;

[0033] The tension in the soaking section is controlled at 3~7KN;

[0034] The tension of the cooling section is controlled at 6~10KN;

[0035] 5) Carry out galvanizing and control the temperature of the zinc solution at 450-470°C;

[0036] 6) Perform alloying treatment, control the alloying treatment temperature at 495-525°C, and simultaneously turn on the burner-type edge heating device to heat the edge of the strip;

[0037] 7) Perform skin pass and replace new working rollers before producing ultra-wide alloyed galvanized sheets. The skin pass elongation is controlled at 0.4-0.7%.

[0038] Furthermore: during continuous annealing, when the unit has an abnormality and needs to be decelerated, the heating furnace adopts a step-by-step deceleration method, that is, the speed is reduced step by step, and the single deceleration does not exceed 5m / min.

[0039] Function and mechanism of the main process in the present invention

[0040] The present invention controls the plate convexity of the hot-rolled raw material. The good plate shape mainly comes from a good hot-rolled raw material profile and the proportional extension of the strip in the width direction during the cold rolling process. The hot-rolled raw material profile has the most direct impact on the plate shape. The cold-rolled strip outlet convexity depends on the hot-rolled raw material convexity and the mill roll gap convexity. The difference between the two determines the size of the strip wave shape. In the plate shape control of ultra-wide alloyed galvanized sheet, because the plate width reaches the limit of the mill roll length, conventional plate shape control methods such as bending rolls and stringing rolls cannot achieve the best plate shape control effect. Therefore, appropriate hot-rolled raw material convexity can reduce the intermediate extension degree of strip rolling and improve the strip shape. Through a large number of production results, it was found that when the hot-rolled raw material thickness of ultra-wide alloyed galvanized sheet is ≤4.0mm, the plate convexity value is 30-80μm; when the hot-rolled raw material thickness of ultra-wide alloyed galvanized sheet is >4.0 to 6mm, the plate convexity value is 30-90μm, and the cold-rolled plate shape control is better.

[0041] The present invention controls the acid tank temperature at 70-90° C., the free acid concentrations in the three acid tanks, acid tank No. 1 not less than 50 g / l, acid tank No. 2 not less than 80 g / l, and acid tank No. 3 not less than 140 g / l, and the pickling speed is controlled below 180 m / min, in order to avoid over-pickling and under-pickling of the steel coil and improve the surface quality of the product.

[0042] The purpose of this invention is to control the emulsion temperature between 45°C and 60°C, and to maintain a saponification value of no less than 170KOH / g, in order to control the shape of the ultra-wide alloyed galvanized sheet, reduce residual oil and iron on the coil surface, and improve product surface quality. Furthermore, a surface reflectivity of ≥70% is required for the exported steel sheet to ensure quality in subsequent processes.

[0043] The reason why the present invention refines the group spacing during cold rolling is that, especially for ultra-wide alloyed galvanized sheets with a finished thickness of less than 1.0 mm, the total reduction rate is controlled by grouping every 0.1 mm of finished product thickness. When the width exceeds 1800 mm, the increase in deformation will cause a sharp increase in the rolling force of the rolling mill, which greatly affects the effect of bending and shifting rolls on the plate shape. At the same time, it poses an extreme challenge to the cooling of the rolling mill, causing the rolling mill motor to overheat, which is even more detrimental to the stable control of the plate shape. As the rolling amount increases, the plate shape deteriorates further. Therefore, the deformation amount, that is, the total reduction rate, is controlled, especially for ultra-wide alloyed galvanized sheets with a thickness of less than 1.0 mm, and the total reduction rate is controlled below 80%.

[0044] The present invention controls the crown of the work rolls of stands 1-5 to 20-40 μm, and the crown of the work rolls of stand 5 to no more than 10 μm. The inclination of stand 5 is also controlled to below 300 μm, ensuring that the absolute tension difference between the two sides of the strip at the mill exit is ≤4 kN. Reducing the tension difference between the two sides of the strip improves strip shape quality, especially in the width direction, and significantly reduces the risk of strip deviation in the hot-dip galvanizing line.

[0045] The present invention uses 2-3 rolls of DX51 plain carbon steel because the width of the DX51 steel needs to be greater than the width of the ultra-wide galvannealed sheet. The lead stock needs to be adjusted to the production process of ultra-wide galvannealed sheet in advance. To ensure smooth passage of the ultra-wide galvannealed sheet into the annealing furnace, minimize temperature differences between the strip and the furnace rollers along the length, and reduce thermal stress differences across the strip width, a certain amount of lead stock is placed on the hot rollers before production to minimize strip buckling and deviation.

[0046] The present invention controls the annealing temperature in different process sections, with the soaking section at 825-835°C, the cooling section at 465-485°C, and the equalization section at 460-470°C. This is mainly to improve the deep drawing performance of the material. Therefore, high-temperature annealing is required in the soaking section. Properly lowering the cooling section temperature helps reduce the temperature difference between the strip and the furnace rollers, thereby reducing the risk of cold buckling.

[0047] The present invention controls the annealing speed to 80-100 m / min. To reduce the impact of the furnace roller profile on wide strip, the annealing furnace operating speed needs to be increased. However, increased speed can easily cause the strip to deviate, and in severe cases, break, while low annealing speeds can easily cause intermittent strip buckling in the heating section. During production, when an abnormality occurs in the unit and the speed needs to be reduced, to prevent strip buckling, the heating furnace adopts a stepped speed reduction method, that is, the speed is reduced step by step, and a single speed reduction should not exceed 50 m / min.

[0048] The present invention controls the tension in each process section primarily to control deviation and buckling of ultra-wide strip and to reduce fluctuations in the strip flow. In the heating section, as the strip enters a higher temperature from a lower temperature, the internal stress in the strip is released, making it prone to deviation. Ultra-wide alloyed galvanized sheet with poor shape or a large tension difference between the two sides of the strip will further aggravate the strip's deviation. Therefore, the tension in the heating section needs to be increased and controlled at 4 to 8 kN. In the soaking section, as the strip temperature reaches above 825°C and the steel is relatively soft, ultra-wide strip is prone to buckling. Therefore, the tension needs to be lowered, controlled at 3 to 7 kN. In the cooling section, lowering the cooling temperature helps reduce the temperature difference between the strip and the furnace rollers, which can reduce the risk of buckling. However, the temperature reduction is achieved through the cooling bellows, which have high wind speeds and can easily cause the strip to shake and cause scratches. Ultra-wide strip shakes more, causing more serious scratches. Therefore, the tension needs to be higher, controlled at 6 to 10 kN.

[0049] The alloying treatment temperature in this invention is controlled between 495°C and 525°C to ensure that the Fe element diffuses into the zinc coating to an appropriate level, resulting in excellent powdering resistance and weldability for the ultra-wide alloyed sheet. Simultaneously, the burner-type edge heating device heats the edges of the strip, making the alloying coating of the ultra-wide sheet more uniform and improving powdering resistance.

[0050] The reason for replacing the working rolls before producing ultra-wide alloyed galvannealed sheets is to ensure that the edges of the ultra-wide sheets do not have color differences. The skin-finishing elongation is controlled at 0.4-0.7% to ensure high surface quality and mechanical properties of the finished product.

[0051] Compared with the prior art, the present invention not only has a strip width of ≥1800mm, but also has a stable production process, a qualified rate increased from the current 50% to over 80%, a tensile strength of ≥280MPa, and performance that meets user needs. DETAILED DESCRIPTION

[0052] The present invention is described in detail below:

[0053] Table 1 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0054] Table 2 is a table of performance test results of various embodiments of the present invention and comparative examples.

[0055] Each embodiment of the present invention is produced according to the following steps

[0056] 1) Perform conventional hot rolling and hot-rolled plate surface convexity: the plate surface convexity value is controlled within 30 to 90 μm, wherein: when the thickness of the hot-rolled plate is ≤4.0 mm, the plate surface convexity value is controlled not to exceed 80 μm; when the thickness of the hot-rolled plate is greater than 4.0 to 6.0 mm, the plate surface convexity value is controlled not to exceed 90 μm;

[0057] 2) Pickling: control the acid tank temperature at 70-90°C;

[0058] The free acid concentration in the three acid tanks is controlled as follows:

[0059] The acid concentration in No. 1 acid tank shall not be less than 50g / l, that in No. 2 acid tank shall not be less than 80g / l, and that in No. 3 acid tank shall not be less than 140g / l; the pickling speed shall be controlled at no more than 180m / min;

[0060] 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product:

[0061] When the thickness of the finished product is 0.6mm<≤0.7mm, the thickness of the hot-rolled raw material is selected to be 2.7~≤2.9mm, and the total cold-rolling reduction is controlled at 74~79%;

[0062] When the finished product thickness is 0.7mm<0.8mm, the thickness of the hot-rolled raw material is selected to be 2.9~≤3.1mm, and the total cold-rolling reduction is controlled at 72%~77%;

[0063] When the thickness of the finished product is 0.8mm<0.9mm, the thickness of the hot-rolled raw material is selected to be 3.4~≤3.6mm, and the total cold-rolling reduction is controlled at 74~78%;

[0064] When the finished product thickness is 0.9mm<1.0mm, the thickness of the hot-rolled raw material is selected to be 3.7~≤3.9mm, and the total cold-rolling reduction is controlled at 73%~77%;

[0065] When the finished product thickness is 1.0mm<1.2mm, the thickness of the hot-rolled raw material is selected to be 3.9~≤4.1mm, and the total cold-rolling reduction is controlled at 69~76%;

[0066] When the finished product thickness is 1.2mm<1.4mm, the hot rolling raw material thickness is selected to be 4.6~≤4.8mm, and the total cold rolling reduction is controlled at 70~75%;

[0067] When the finished product thickness is 1.4mm<1.6mm, the thickness of the hot-rolled raw material is selected to be 5.4~≤5.6mm, and the total cold-rolling reduction is controlled at 70~75%;

[0068] When the finished product thickness is 1.6mm<≤2.0mm, the hot rolling raw material thickness is selected to be 6.4~≤6.6mm, and the total cold rolling reduction is controlled at 69~75%;

[0069] And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g;

[0070] The crown of the working rolls of each stand is controlled to be 20-40 μm for the 1st to 4th stands, and no more than 10 μm for the 5th stand. The inclination value of the 5th stand is also controlled to be no more than 300 μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤4 kN. The surface reflectivity of the exiting steel plate is controlled to be no less than 70%.

[0071] 4) Continuous annealing: Before annealing the galvannealed steel sheets with a width of ≥1800mm after cold rolling, first arrange 2-3 rolls of DX51 plain carbon steel coils with a width greater than the width of the galvannealed steel sheets to be annealed, and the width greater than the width is not less than 5mm; DX51 steel and galvannealed steel sheets are annealed at the same temperature and speed, and then the galvannealed steel sheets with a width of ≥1800mm are continuously annealed;

[0072] Each process operation is carried out as follows:

[0073] The annealing temperature of each section is controlled as follows:

[0074] The annealing temperature in the soaking section is 825-835°C;

[0075] The temperature of the rapid cooling section is 475-495°C;

[0076] The temperature of the equalization section is 460-470°C;

[0077] Control the annealing speed of each section above to be between 80 and 100 m / min;

[0078] Control the tension of each segment:

[0079] The tension of the heating section is controlled at 4~8KN;

[0080] The tension in the soaking section is controlled at 3~7KN;

[0081] The tension of the cooling section is controlled at 6~10KN;

[0082] 5) Carry out galvanizing and control the temperature of the zinc solution at 450-470°C;

[0083] 6) Perform alloying treatment, control the alloying treatment temperature at 495-525°C, and simultaneously turn on the burner-type edge heating device to heat the edge of the strip;

[0084] 7) Perform skin pass and replace new working rollers before producing ultra-wide alloyed galvanized sheets. The skin pass elongation is controlled at 0.4-0.7%.

[0085] Table 1 List of main process parameters of various embodiments of the present invention and comparative examples

[0086]

[0087] Table 1

[0088]

[0089]

[0090] Table 2 Performance test results of various embodiments of the present invention and comparative examples

[0091]

[0092] As can be seen from Table 2, Examples 1-8, the ultra-wide alloyed galvanized sheets within the scope of the claims of the present invention, can not only be smoothly and high-quality plate-passed and produced, but also meet the requirements for surface quality and mechanical properties. The performance indicators meet the technical indicators of DX56D+ZF steel, and the 60° V-bend (rating) test results are all level 1. The products do not show obvious powdering and falling off during the stamping process of the corresponding parts. The qualified rate of the overall products of Examples 1-8 reaches 85%. Comparative Example 1: Due to the large difference in the tension of the strip at the exit of the rolling mill, the strip deviates in the annealing furnace. The unit takes emergency deceleration measures, resulting in surface quality defects such as severe scratches on the surface of the strip. Comparative Example 2: Due to the excessively high heating temperature, the strip is subjected to thermal buckling. In order to prevent the thermal buckling from worsening and causing the strip to break, the unit takes emergency deceleration measures and simultaneously reduces the tension of each section in the heating furnace. The tension is reduced, which easily causes the strip to vibrate more in the furnace, aggravating the occurrence of quality problems such as scratches on the strip, further resulting in a low qualified rate of the product.

[0093] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A method for producing alloyed galvanized sheet with a sheet width of ≥1800 mm, characterized in that Here are the steps: 1) Perform conventional hot rolling and hot rolled plate surface crown: the plate surface crown value is controlled within 30-90 μm, wherein: when the thickness of the hot rolled plate is ≤4.0 mm, the plate surface crown value is controlled not to exceed 80 μm; when the thickness of the hot rolled plate is greater than 4.0 to 6.0 mm, the plate surface crown value is controlled not to exceed 90 μm; 2) Pickling: Control the acid tank temperature at 70-90°C; The free acid concentration in the three acid tanks is controlled as follows: The acid concentration in No. 1 acid tank shall not be less than 50g / l, that in No. 2 acid tank shall not be less than 80g / l, and that in No. 3 acid tank shall not be less than 140g / l; the pickling speed shall be controlled at no more than 180m / min; 3) Use five stands for cold rolling, refine the group spacing and control the cold rolling reduction rate according to the thickness of the finished product: When the finished product thickness is 0.6mm<≤0.7mm, the hot-rolled raw material thickness is selected to be 2.7~≤2.9mm, and the total cold-rolling reduction is controlled at 74~79%; When the finished product thickness is 0.7mm<≤0.8mm, the hot-rolled raw material thickness is selected to be 2.9~≤3.1mm, and the total cold-rolling reduction is controlled at 72~77%; When the finished product thickness is 0.8mm<≤0.9mm, the hot-rolled raw material thickness is selected to be 3.4~≤3.6mm, and the total cold-rolling reduction is controlled at 74~78%; When the finished product thickness is 0.9mm<1.0mm, the thickness of the hot-rolled raw material should be 3.7~≤3.9mm, and the total cold-rolling reduction should be controlled at 73%~77%. When the finished product thickness is 1.0mm<1.2mm, the hot-rolled raw material thickness is selected to be 3.9~≤4.1mm, and the total cold-rolling reduction is controlled at 69~76%; When the finished product thickness is 1.2mm<1.4mm, the hot-rolled raw material thickness is selected to be 4.6~≤4.8mm, and the total cold-rolling reduction is controlled at 70.21%~75%; When the finished product thickness is 1.4mm<1.6mm, the thickness of the hot-rolled raw material should be 5.4~≤5.6mm, and the total cold-rolling reduction should be controlled at 70~75%; When the finished product thickness is 1.6mm<≤2.0mm, the hot-rolled raw material thickness is selected to be 6.4~≤6.6mm, and the total cold-rolling reduction is controlled at 69~75%; And control the emulsion temperature at 45-60°C, and the saponification value is not less than 170KOH / g; The crown of the working rolls of each stand is controlled to be 20-40μm for the 1st to 4th stands, and no more than 10μm for the 5th stand. The inclination value of the 5th stand is also controlled to be no more than 300μm. The absolute value of the tension difference on both sides of the strip at the mill exit is ≤4KN. The surface reflectivity of the exiting steel plate is controlled to be no less than 70%. 4) Continuous annealing: Before annealing the galvannealed steel sheets with a width of ≥1800mm after cold rolling, first arrange 2-3 rolls of DX51 plain carbon steel coils with a width greater than the width of the galvannealed steel sheets to be annealed, and the width greater than the width is not less than 5mm; DX51 steel and galvannealed steel sheets adopt the same temperature and speed, and then continuously anneal the galvannealed steel sheets with a width of ≥1800mm; Each process operation is carried out as follows: The annealing temperature of each section is controlled as follows: The annealing temperature in the soaking section is 832-835°C; The temperature of the rapid cooling section is 475-495°C; The temperature of the equalization section is 460-470°C; Control the annealing speed of each section above to be between 80 and 88 m / min; Control the tension of each segment: The tension of the heating section is controlled at 4~8KN; The tension in the soaking section is controlled at 3~7KN; The tension of the cooling section is controlled at 6~10KN; 5) Carry out galvanizing and control the temperature of the zinc solution at 450-458°C; 6) Perform alloying treatment, control the alloying treatment temperature at 495-525°C, and simultaneously turn on the burner-type edge heating device to heat the edge of the strip; 7) Perform skin-passing and replace new working rollers before producing ultra-wide alloyed galvanized sheets. The skin-passing elongation should be controlled at 0.4-0.5%.

2. The method for producing an alloyed galvannealed sheet with a sheet width of ≥1800 mm according to claim 1, wherein: During continuous annealing, when the unit has an abnormality and needs to be slowed down, the heating furnace adopts a step-by-step speed reduction method, that is, the speed is reduced step by step, and the single speed reduction does not exceed 5m / min.

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