Method for controlling mechanical property stability of cold-rolled galvanized high-strength steel sheet

Abstract

The application discloses a mechanical property stability control method of a cold-rolled galvanized high-strength steel plate, which comprises the following steps: determining whether the content of a main component variable in the current cold-rolled galvanized high-strength steel plate is located in a set content interval; if the detection result is no, adjusting a main process parameter so that the mechanical property of the cold-rolled galvanized high-strength steel plate reaches a target requirement; and if the detection result is yes, the main process variable is at a target value; when the content of the main component variable in the cold-rolled galvanized high-strength steel plate is in the set content interval and the main process variable is at the target value, the mechanical property of the cold-rolled galvanized high-strength steel plate meets the target value. Through component grading and process joint debugging mechanism, the application optimizes the mechanical property fluctuation of a process-sensitive cold-rolled galvanized high-strength steel product, avoids large performance fluctuation between batches, and provides a downstream customer with a mechanical property stable product.

Description

Technical Field

[0001] This invention belongs to the field of cold-rolled strip galvanizing technology, and more specifically, this invention relates to a method for stable control of the mechanical properties of cold-rolled galvanized high-strength steel sheets. Background Technology

[0002] With the continuous improvement of automotive energy conservation, environmental protection, and safety regulations, the application of galvanized high-strength steel sheets and strips in automotive body-in-white is gradually increasing, and market demand is widespread. Galvanized high-strength steel typically uses different proportions of elements such as C, Si, Al, Mn, Cr, Mo, Nb, and Ti to obtain products with specific mechanical property ranges. The production process involves five major steps: steelmaking, continuous casting, hot rolling, cold rolling, and annealing / hot-dip galvanizing. Due to the large variety of alloys, high content, and complex production processes, it exhibits high element sensitivity and is affected by multiple process factors, resulting in large batch-to-batch variations in mechanical properties. This is detrimental to the stable manufacturing of downstream parts suppliers. Furthermore, the narrow range control of C and Mn elements during steelmaking is difficult, hindering stable batch production by steel mills.

[0003] Patent application number CN201911243425.4 discloses a method for adjusting process parameters based on the mechanical properties of cold-rolled galvanized strip steel. The method uses a nonlinear fitting method to design the galvanizing process parameters of cold-rolled strip steel, and then continuously verifies and tests to optimize the process parameters in order to achieve the mechanical properties of galvanized high-strength steel sheets. In actual production, the composition of molten steel fluctuates, which leads to uncontrollable fluctuations in the mechanical properties of the produced cold-rolled galvanized high-strength steel sheets. When the composition exceeds the set range, the probability of not meeting the product performance requirements also increases significantly. Summary of the Invention

[0004] This invention provides a method for stabilizing the mechanical properties of cold-rolled galvanized high-strength steel sheets, aiming to stabilize the mechanical properties of cold-rolled galvanized high-strength steel sheets within a target range.

[0005] This invention is achieved by providing a method for stable control of the mechanical properties of cold-rolled galvanized high-strength steel sheets, the method comprising the following steps:

[0006] Determine whether the content of the main component variable in the current cold-rolled galvanized high-strength steel sheet is within the set content range. If the test result is negative, adjust the main process parameters to make the mechanical properties of the cold-rolled galvanized high-strength steel sheet meet the target requirements. If the test result is positive, the main process variable is at the target value.

[0007] When the content of the main component variable in cold-rolled galvanized high-strength steel sheet is within the set content range and the main process variable is at the target value, the mechanical properties of cold-rolled galvanized high-strength steel sheet meet the target value.

[0008] Furthermore, the specific method for determining the principal component variables is as follows:

[0009] Determine the mechanical properties of cold-rolled galvanized high-strength steel sheets;

[0010] Determine the influence coefficient of each component variable on each mechanical property. The component variable with the larger influence coefficient is the principal component variable corresponding to the mechanical property.

[0011] Furthermore, the specific method for calculating the influence coefficient is as follows:

[0012] By fitting historical production data, the linear relationship between each component variable Xc and each mechanical property Yi is obtained: Yi = k * Xc, and the slope k is the influence coefficient of component variable Xc on mechanical property Yi.

[0013] Furthermore, the specific method for determining the main set content range is as follows:

[0014] The mechanical properties of cold-rolled galvanized high-strength steel sheets were determined under different principal component variables.

[0015] The range of principal component variables whose content values ​​meet the target mechanical properties is the set content range of the corresponding principal component variables.

[0016] Furthermore, the specific method for determining the main process variables is as follows:

[0017] Determine the mechanical properties of cold-rolled galvanized high-strength steel sheets, namely, control the yield and tensile strength;

[0018] Determine the influence coefficient of each process variable on each mechanical property. The process variable with the larger influence coefficient is the main process variable for the corresponding mechanical property.

[0019] Furthermore, the specific methods for adjusting the main process variables are as follows:

[0020] The graded value CMn is calculated based on the main component content value in the current cold-rolled galvanized high-strength steel sheet. The current adjustment scheme is determined based on the graded value range in which the graded value is located. The adjustment scheme is a combination of the amplitude adjustment of the corresponding main process variables.

[0021] The adjustment schemes include: adjustment scheme 1 for adjusting low tensile strength and adjustment scheme 2 for adjusting high yield strength.

[0022] Furthermore, the mechanical properties were characterized by controlling the yield strength and tensile strength.

[0023] Furthermore, the specific process for determining the corresponding tiered value ranges for the adjustment scheme is as follows:

[0024] The expression for determining the grading value CMn is based on the numerical relationship between the influence coefficients of each principal component variable;

[0025] Determine adjustment scheme 1 and adjustment scheme 2, and measure the adjustment amount of yield strength and tensile strength under adjustment scheme 1 and adjustment scheme 2;

[0026] Based on the adjustment amount of the yield strength mentioned above, the adjustment range 1 of the corresponding principal component variable content is determined, and at the same time, the adjustment range 2 of the corresponding principal component variable content is determined based on the adjustment amount of the tensile strength.

[0027] Based on adjustment range 1 and adjustment range 2, determine the range of values ​​CMn for adjustment scheme 1 and adjustment scheme 2.

[0028] Furthermore, the adjustment of the main process variables in the adjustment scheme satisfies the following principles:

[0029] (1) The adjustment range of yield strength and tensile strength should be as large as possible;

[0030] (2) Under the condition of satisfying (1), select the adjustment range of the main process parameters that can respond quickly in actual production.

[0031] This invention optimizes the mechanical properties of cold-rolled galvanized high-strength steel products that are sensitive to composition and process through composition grading and process coordination mechanisms, thereby avoiding large performance fluctuations between batches and providing downstream customers with products with stable mechanical properties. Attached Figure Description

[0032] Figure 1 A flowchart illustrating the method for stabilizing the mechanical properties of cold-rolled galvanized high-strength steel sheets provided in this embodiment of the invention;

[0033] Figure 2 The mechanical properties comparison diagram of 800MPa grade cold-rolled galvanized DP800 provided in the embodiments of the present invention is shown, where (a) is the yield strength and (b) is the tensile strength. Detailed Implementation

[0034] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0035] Figure 1 The flowchart of the method for stabilizing the mechanical properties of cold-rolled galvanized high-strength steel sheets provided in this embodiment of the invention is shown. The method specifically includes the following steps:

[0036] Determine whether the content of the main component variable in the current cold-rolled galvanized high-strength steel sheet is within the set content range. If the test result is negative, adjust the main process parameters so that the mechanical properties of the cold-rolled galvanized high-strength steel sheet meet the target requirements. If the test result is positive, there is no need to adjust the main process variable, that is, the main process variable is at the target value.

[0037] When the content of the main component variable in cold-rolled galvanized high-strength steel sheet is within the set content range and the main process variable is at the target value, the mechanical properties of cold-rolled galvanized high-strength steel sheet meet the target value.

[0038] In this embodiment of the invention, the method for determining the principal component variables is as follows:

[0039] Determine the mechanical properties of cold-rolled galvanized high-strength steel sheets;

[0040] Determine the influence coefficients of each component variable on each mechanical property, and then determine the principal component variables that have the greatest impact on each mechanical property.

[0041] The specific calculation method for the influence coefficient of each component variable on each mechanical property is as follows: Based on historical production data, a linear relationship Yi = k*Xc between each component variable Xc and each mechanical property Yi is obtained, where the slope value is the influence coefficient of component variable Xc on mechanical property Yi.

[0042] In this embodiment of the invention, the method for determining the set content range of the principal component variable is as follows:

[0043] The mechanical properties of cold-rolled galvanized high-strength steel sheets were determined under different principal component variables. The range of principal component variable contents corresponding to the mechanical properties that meet the target requirements is the set content range of the corresponding principal component variable.

[0044] In this embodiment of the invention, the method for determining the main process variables is as follows:

[0045] The mechanical properties of cold-rolled galvanized high-strength steel sheets are determined, namely, the yield strength and tensile strength are controlled; the influence coefficients of each process variable Xg on each mechanical property are determined, and then the main process variable Xg that has the greatest impact on each mechanical property is determined. The calculation method of the influence coefficient of the process variable on the mechanical property is the same as the calculation method of the influence coefficient of the composition variable on the mechanical property.

[0046] In this embodiment of the invention, the method for adjusting the main process variables is as follows:

[0047] The graded value CMn is calculated based on the current main component content values ​​in cold-rolled galvanized high-strength steel sheets. The current adjustment scheme is determined based on the graded value range in which it falls.

[0048] The adjustment schemes include: Adjustment Scheme 1 for adjusting low tensile strength and Adjustment Scheme 2 for adjusting high yield strength. The specific process for determining the corresponding value ranges for the adjustment schemes is as follows:

[0049] The expression for determining the grading value CMn is based on the numerical relationship between the influence coefficients of each principal component variable;

[0050] Determine adjustment scheme 1 and adjustment scheme 2, and measure the adjustment amount of yield strength and tensile strength under adjustment scheme 1 and adjustment scheme 2;

[0051] The adjustment amount of the main process parameters in the adjustment scheme shall meet the following principles: (1) The adjustment amount of yield strength and tensile strength shall be as large as possible; (2) Under the condition of satisfying (1), the adjustment range of the main process parameters that can respond quickly in actual production shall be selected.

[0052] Based on the adjustment amount of the yield strength mentioned above, the adjustment range 1 of the corresponding principal component variable content is determined, and at the same time, the adjustment range 2 of the corresponding principal component variable content is determined based on the adjustment amount of the tensile strength.

[0053] Based on adjustment range 1 and adjustment range 2, determine the range of values ​​CMn for adjustment scheme 1 and adjustment scheme 2.

[0054] This example is a production example of 800MPa grade cold-rolled galvanized duplex steel. Table 1 shows the corresponding grade and mechanical property requirements (i.e. target mechanical properties). The key control is that the yield strength and tensile strength meet the target requirements.

[0055] Table 1 Target Requirements for Mechanical Properties of 800MPa Grade Cold-Rolled Galvanized Duplex Steel

[0056] Brand Yield strength, MPa Tensile strength, MPa Elongation, % HC420 / 780DPD 420～550 ≥780 ≥14.0

[0057] The influence coefficients of component variable Xc and process variable Xg on mechanical properties were determined by fitting historical production data, as shown in Table 2.

[0058] Table 2. Correspondence between performance Y and influencing variables.

[0059]

[0060] In the component variable Xc, the contents of C and Mn are high-priority component variables, i.e., principal component variables. The influence of principal component variables on mechanical properties such as yield strength and tensile strength is shown in Table 3.

[0061] Table 3. Effects of C and Mn content on yield and tensile strength

[0062]

[0063] Based on the adjustable range of the process variable Xg, the adjustable range for low tensile strength and high yield strength is determined to be +22MPa and -19MPa, respectively.

[0064] Table 4 Risk Prevention and Adjustment Plan

[0065] Mechanical performance risk Adjustment Plan Mechanical property adjustment boundary Low tensile strength Adjustment scheme 1: Heat spreader temperature -20℃, rapid cooling temperature +10℃ +22MPa High yield strength Adjustment scheme 2: rapid cooling temperature -30℃, finishing -0.1%. -19MPa

[0066] The adjustment boundary for the process variable Xg is approximately 20 MPa, and the normal detection error is 15 MPa. To facilitate system identification, a CMn value grading system is established (CMn = 10 * C + Mn). If CMn < 2.86 or > 3.08, surplus material is used to prevent defective products and products with poor formability from reaching end customers. If 2.86 ≤ CMn ≤ 2.90, adjustment scheme 1 is triggered to increase tensile strength. If 2.90 < CMn < 3.04, normal process production continues. If 3.04 ≤ CMn ≤ 3.08, adjustment scheme 2 is triggered to reduce yield strength.

[0067] The method of this invention has been successfully applied to cold-rolled galvanized high-strength steel sheet and strip products. Industrial production verification shows that the method achieves good improvement results. Figure 2 The graph shows a comparison of yield strength and tensile strength of mechanical properties before and after the application of the method, with 1293 and 1812 samples respectively before and after the method application. For the high risk of yield strength, the mean yield strength decreased from 499.5 MPa to 488.5 MPa, and the standard deviation narrowed from 23.84 MPa to 17.97 MPa; for the low risk of tensile strength, the mean tensile strength increased from 814.5 MPa to 819.3 MPa, and the standard deviation increased from 23.55 MPa to 16.60 MPa.

[0068] The present invention has been described by way of example. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for controlling the mechanical properties of a cold-rolled galvanized high-strength steel sheet, characterized in that, The method comprises the following steps: Determine whether the content of the main component variable in the current cold-rolled galvanized high-strength steel plate is within the set content interval. If the detection result is no, adjust the main process parameter to make the mechanical properties of the cold-rolled galvanized high-strength steel plate meet the target requirements. If the detection result is yes, the main process variable is at the target value; When the content of the main component variable in the cold-rolled galvanized high-strength steel plate is within the set content interval and the main process variable is at the target value, the mechanical properties of the cold-rolled galvanized high-strength steel plate meet the target value; The determination method of the main process variable is as follows: Determine the mechanical properties of the cold-rolled galvanized high-strength steel plate, i.e. control the yield and tensile strength; Determine the influence coefficient of each process variable on each mechanical property. The process variable with a large influence coefficient is the main process variable corresponding to the mechanical property. The adjustment method of the main process variable is as follows: Based on the content value of the main component in the current cold-rolled galvanized high-strength steel plate, calculate the grading value CMn. Based on the grading value interval where the grading value is located, determine the current adjustment scheme, which is the combination of the adjustment amplitude of the corresponding main process variable. The adjustment scheme includes adjustment scheme 1 for low tensile strength adjustment and adjustment scheme 2 for high yield strength adjustment.

2. The method of claim 1, wherein the cold-rolled galvanized high-strength steel sheet is a steel sheet having a tensile strength of 590 MPa or more. The determination method of the main component variable is as follows: Determine the mechanical properties of the cold-rolled galvanized high-strength steel plate; Determine the influence coefficient of each component variable on each mechanical property. The component variable with a large influence coefficient is the main component variable corresponding to the mechanical property.

3. The method of claim 2, wherein the mechanical properties of the cold-rolled galvanized high-strength steel sheet are stably controlled by controlling the amount of the alloying element added to the molten steel. The calculation method of the influence coefficient is as follows: Fit the historical production data to obtain the linear relationship between each component variable Xc and each mechanical property Yi, Yi=k*Xc. The slope k is the influence coefficient of the component variable Xc on the mechanical property Yi.

4. The method of claim 3, wherein the mechanical properties of the cold-rolled galvanized high-strength steel sheet are stably controlled by controlling the amount of the alloying element added to the molten steel. The determination method of the main set content interval is as follows: Determine the mechanical property value of the cold-rolled galvanized high-strength steel plate under different contents of the main component variable; The content value interval of the main component variable corresponding to the mechanical property meeting the target requirements is the set content interval of the corresponding main component variable.

5. The method of claim 1, wherein the cold-rolled galvanized high-strength steel sheet is a steel sheet having a tensile strength of 590 MPa or more and a yield strength of 340 MPa or more. The mechanical property is represented by controlling the yield and tensile strength.

6. The method of claim 5, wherein the mechanical properties of the cold-rolled galvanized high-strength steel sheet are stably controlled by controlling the amount of the alloying element added to the molten steel. The determination process of the grading value interval corresponding to the adjustment scheme is as follows: Determine the expression of the grading value CMn based on the numerical relationship between the influence coefficients of each main component variable; Determine adjustment scheme 1 and adjustment scheme 2, and determine the yield strength and tensile strength adjustment amount under adjustment scheme 1 and adjustment scheme 2; Based on the above yield strength adjustment amount, determine the adjustment range 1 of the content of the corresponding main component variable, and based on the tensile strength adjustment amount, determine the adjustment range 2 of the content of the corresponding main component variable; Based on the adjustment range 1 and the adjustment range 2, determine the grading value CMn value range of adjustment scheme 1 and adjustment scheme 2.

7. The method for stabilizing the mechanical properties of cold-rolled galvanized high-strength steel sheets as described in claim 6, characterized in that, The adjustment amplitude of the main process variable in the adjustment scheme meets the following principles: (1) The adjustment amount of the yield strength and the tensile strength should be as large as possible; (2) Under the condition of meeting (1), select the adjustment amplitude of the main process parameter that can quickly respond in actual production.

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