Ultrahigh-strength steel cold-rolled material constitutive hardening model construction method
By combining simulated rolling and mechanical property testing, a power-law constitutive hardening model was constructed, which solved the problem of inaccurate matching of rolling force and tension in the cold rolling process of ultra-high strength steel. This achieved stability and consistency in the production process, shortened the R&D cycle, and improved product quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANSTEEL BEIJING RES INST CO LTD
- Filing Date
- 2026-01-07
- Publication Date
- 2026-05-01
AI Technical Summary
The existing technology for cold rolling ultra-high strength steel lacks an accurate material constitutive hardening model, which leads to problems such as sudden changes in rolling force, inaccurate tension matching, unreasonable rolling pass arrangement for thin-gauge products, and poor plate shape. Reliance on operational experience results in high safety risks, high costs, and slow research and development.
By combining simulated rolling with mechanical property determination, a power function constitutive hardening model was constructed. A two-roll hydraulic cold rolling mill and a universal tensile testing machine were used for linear fitting and data processing to establish a model σ=Kεⁿ, which is used to accurately characterize the hardening behavior of materials.
It improves the accuracy of predicting material hardening behavior and production stability, reduces the risk of tape breakage, shortens the R&D cycle, reduces reliance on operational experience, and improves product quality and production consistency.
Smart Images
Figure CN121963906A_ABST
Abstract
Description
A method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials Technical Field
[0001] This invention relates to the field of high-strength steel production technology, and in particular to a method for constructing a constitutive hardening model for ultra-high-strength cold-rolled steel materials. Background Technology
[0002] In recent years, with increasingly stringent requirements from the automotive industry regarding energy conservation, environmental protection, and collision safety, 980MPa grade and above ultra-high strength steel (UHSS) has experienced rapid development and widespread application due to its significant advantages in achieving automotive lightweighting. Currently, leading steel companies both domestically and internationally are primarily focusing on product composition design, process improvement, and research into the impact of key processes on material microstructure and properties in the research and development and production of ultra-high strength steel.
[0003] However, systematic research on the cold rolling process of ultra-high strength steel remains insufficient, especially in the early stages of new material development, where accurate constitutive hardening models are often lacking. This leads to common problems in actual cold rolling production, such as abrupt changes in rolling force during continuous cold rolling, inaccurate matching of rolling force and tension for new products, unreasonable arrangement of rolling passes for thin-gauge products, and poor strip shape of cold-hardened steel. Current production processes rely heavily on operator experience, resulting in high safety risks, high trial-and-error costs, and severely hindering the development speed and industrialization of new ultra-high strength steel products.
[0004] In actual production, whether using continuous acid rolling or single-stand rolling, the core technical challenges lie in optimizing the matching of rolling force and tension, as well as the rational distribution of reduction rate. Furthermore, single-stand rolling of ultra-thin gigapascal grade ultra-high-strength steel (below 1.0 mm) also involves optimizing the number of rolling passes. With the accelerating pace of product iteration and upgrading in ultra-high-strength steel, from the perspective of cold rolling process control, there is an urgent need to establish accurate constitutive hardening models for new or novel compositional systems of ultra-high-strength steel. Summary of the Invention
[0005] The purpose of this invention is to provide a method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials. By combining simulated rolling with mechanical property measurement, it achieves accurate characterization of the material's hardening behavior. The constructed power-law hardening model exhibits high fitting accuracy. This invention effectively solves the problem of excessive reliance on experience and manual intervention in the current research and production of ultra-high strength steel. It is widely applicable to material modeling of various ultra-high strength steels, including dual-phase steel, multiphase steel, reinforced formable dual-phase steel, and martensitic steel with a strength of 980 MPa and above. The established model can be directly applied to the secondary control system of the cold rolling process, providing reliable material data support for achieving precise matching of rolling force and tension, optimizing reduction rate distribution, and improving production stability and product quality.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing a constitutive hardening model for ultra-high strength steel cold-rolled materials, comprising: S1, sample processing: cutting the hot-rolled ultra-high strength steel base material to be tested into rectangular sheets; the sheet dimensions are: length 200mm–210mm, width 100mm–110mm, and thickness 2.5mm–3.0mm; S2, simulated rolling: using a two-roll hydraulic cold rolling mill to perform a series of cold rollings on the rectangular sheets at different reduction rates to obtain cold-hardened steel strips corresponding one-to-one with each reduction rate; S3, mechanical property determination: cutting tensile samples from each cold-hardened steel strip. And determine its yield strength; S4, Data processing and plotting: Take the natural logarithm of each reduction rate (ε) and its corresponding average yield strength (σ), and plot a two-dimensional line graph with ln(ε) as the X-axis data and ln(σ) as the Y-axis data; S5, Linear fitting: Perform linear fitting on the two-dimensional line graph to obtain the corresponding linear equation, the expression of which is as follows: y=kx+b①; In equation ①: y represents the logarithmic value of the yield strength; k represents the slope of the linear fitting; x represents the logarithmic value of the reduction rate; b represents the intercept of the linear fitting; S6, Model construction: Convert the linear equation into a power function form, the expression of which is as follows: σ=Kε n ②; In equation ②: K represents the strengthening coefficient, in MPa; ε represents the reduction ratio; σ represents the yield strength, in MPa; n represents the strengthening index; the strengthening index n is equal to the slope k of the linear equation, and the strengthening coefficient K is calculated by the equation b=ln(K).
[0007] In S1, the length direction of the rectangular sheet is the original rolling direction of the hot-rolled base material. Before simulating rolling, an angle grinder is used to remove burrs from the edge of the sample to prevent damage to the roll surface during the rolling process.
[0008] In S2, the reduction rate (ε) used in the simulated rolling ranges from 5% to 65%, and the interval between adjacent reduction rates is 5%. By calculating the target thickness corresponding to different reduction rates, cold-hardened steel strip samples with different reduction rates are obtained by reciprocating rolling.
[0009] In S3, longitudinal tensile specimens with a gauge length of 50 mm are cut from the central region (along the rolling direction) of each cold-hardened steel strip sample obtained in step S2 using wire cutting method; at least 3 tensile specimens are cut from the rolling direction of the cold-hardened steel strip corresponding to each reduction rate for mechanical property determination, and the average yield strength is taken as the yield strength index corresponding to that reduction rate.
[0010] Linear fitting in S5 and plotting in S4 were performed using data processing software.
[0011] Compared with existing technologies, the beneficial effects of this invention are as follows: 1. Based on the idea of combining physical experiments and mathematical modeling, a constitutive model is established through a systematic process of "simulated rolling + mechanical property measurement + double logarithmic linear fitting". Data processing and linear regression are performed using software such as Origin to obtain a power function hardening model of the form σ=Kεⁿ, as shown in Table 2. The established model shows excellent fitting accuracy in both 980MPa and 1180MPa grade ultra-high strength steels (Pearson correlation coefficients reach 0.96853 and 0.99695 respectively, and adjusted variances reach 0.9324 respectively). 2. The model has clear statistical support (0.99335), significantly improving the accuracy and reliability of predicting material hardening behavior; 2. The entire modeling process has clear steps and uses conventional equipment, requiring only a standard two-roll cold rolling mill, universal tensile testing machine, wire cutting machine, and general data processing software. The entire process from sample preparation to model output is highly standardized, making it easy to reproduce and promote in different laboratories or production units. It provides a practical technical path for rapidly establishing proprietary constitutive models for high-strength steels with different composition systems in different steel mills; 3. The established constitutive hardening model can be directly output. The secondary control system of the cold rolling production line serves as a key material parameter for setting and optimizing process parameters such as rolling force, tension, and reduction rate. The model accurately reflects the work hardening law of the material as the reduction rate changes, helping to solve common problems in the cold rolling process of ultra-high strength steel, such as sudden changes in rolling force, inaccurate tension matching, and excessive rolling passes for thin-gauge products. This improves the stability of the rolling process, reduces the risk of strip breakage, and fully utilizes the unit's capacity. 4. Traditional ultra-high strength steel development relies on production line trial rolling and experience adjustments, which are costly, time-consuming, and risky. This invention can be completed in the laboratory stage during the early stages of new product development. The systematic evaluation and modeling of the hardening properties of materials significantly reduces reliance on industrial trials, shortens the R&D cycle, reduces material loss and energy consumption caused by repeated debugging, and accelerates the industrialization process of new products; 5. By providing a high-precision material constitutive model, this invention helps to realize the transformation of the ultra-high strength steel cold rolling process from "experience-driven" to "model-driven", reducing excessive reliance on the personal experience of operators, improving the consistency and controllability of the production process, and providing cold-hardened steel strip raw materials with more stable shape and performance for subsequent continuous annealing, hot-dip galvanizing and other processes, ultimately improving product quality and market competitiveness. Attached Figure Description
[0012] Figure 1 is a linear fitting diagram of the 1980MPa grade ultra-high strength steel in Example 1.
[0013] Figure 2 is a linear fitting diagram of the 180MPa grade ultra-high strength steel in Example 21.
[0014] Figure 3 is a flowchart of the constitutive hardening model construction method for ultra-high strength cold-rolled steel materials. Detailed Implementation
[0015] The present invention will now be described in detail with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.
[0016] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.
[0017] Example 1 takes the hot-rolled base material corresponding to 2.5mm thick 980MPa grade cold-rolled dual-phase steel from a steel plant as an example to illustrate the implementation process of the present invention. See Figure 3. It includes: Step 1, sample processing: The hot-rolled base material is processed into several rectangular sheets with dimensions of 200mm (length) * 100mm (width) * 2.5mm (thickness). The length direction is the rolling direction. Before rolling, the burrs on the edge of the sample are removed to avoid damaging the rolls.
[0018] Step 2, Simulated Rolling: A two-roll cold rolling mill was used, with the rolling speed controlled at 10 m / min. The reduction rate was set from 5% to 65%, and simulated rolling was performed at 5% intervals. The rolling was calculated and rolled to the corresponding target thickness to obtain cold-hardened steel strips with different reduction rates. The specific thickness and the average yield strength measured subsequently are shown in the "Example 1" column of Table 1.
[0019] Step 3, Performance determination: Cut three tensile specimens from each chilled steel strip, determine the yield strength, and record the average value of the results in Table 1.
[0020] Step 4, Data Processing and Fitting: After taking the natural logarithm of the reduction rate ε and yield strength σ, a two-dimensional line graph is plotted (see Figure 1). Linear fitting is performed to obtain the equation: y = 0.10408x + 7.12733.
[0021] Step 5, Model Establishment: From the fitted equation, we know that the slope k = 0.10408 and the intercept b = 7.12733.
[0022] Enhancement index n=k=0.10408; Enhancement coefficient K=e b =e 7.12733≈1245.55; therefore, the constructed constitutive hardening model is: σ=1245.55ε 0.10408 Step 6, Model Validation: The statistical indicators of the model's fitting accuracy are shown in Table 2 (Example 1). The high Pearson correlation coefficient (PCCS=0.96853) and adjusted variance (R-sq(adjusted)=0.93242) indicate that the model has high fitting accuracy and can be used to guide the cold rolling production control of this grade of steel.
[0023] Example 2 This example uses a hot-rolled base material corresponding to a 3.0mm thick 1180MPa grade cold-rolled dual-phase steel from a steel plant as an example to further illustrate the applicability of this method.
[0024] Step 1, Sample Processing: Process the hot-rolled base material into several rectangular sheets with dimensions of 210mm (length) * 110mm (width) * 3.0mm (thickness), with the length direction being the rolling direction. Remove burrs from the edges before rolling.
[0025] Step 2, Simulated Rolling: A two-roll cold rolling mill was used, with the rolling speed controlled at 10 m / min. The reduction rate was set from 5% to 65%, and simulated rolling was performed at 5% intervals to obtain cold-hardened steel strips with different reduction rates. Specific thicknesses and subsequently measured average yield strengths are shown in the "Example 2" column of Table 1.
[0026] Step 3, Performance determination: Cut three tensile specimens from each chilled steel strip, determine the yield strength, and record the average value of the results in Table 1.
[0027] Step 4, Data Processing and Fitting: After taking the natural logarithm of the reduction rate ε and yield strength σ, a two-dimensional line graph is plotted (see Figure 2). Linear fitting is performed to obtain the equation: y = 0.06791x + 7.21738.
[0028] Step 5, Model Establishment: From the fitted equation, we know that the slope k = 0.06791 and the intercept b = 7.21738.
[0029] Enhancement index n=k=0.06791; Enhancement coefficient K=e b =e 7.21738 ≈1362.91; therefore, the constructed constitutive hardening model is: σ=1362.91ε 0.06791 Step 6, Model Validation: The statistical indicators of the model's fitting accuracy are shown in Table 2 (Example 2). The extremely high Pearson correlation coefficient (PCCS=0.99695) and adjusted variance (R-sq(adjusted)=0.99335) indicate that the model has extremely high fitting accuracy and can be effectively applied to the cold rolling process control of this higher strength grade steel.
[0030] Table 1 shows the thickness and yield strength of ultra-high strength steel under simulated rolling at different reduction rates in each embodiment. Table 2 shows the statistical indicators of the fitting accuracy of the constitutive hardening model of ultra-high strength steel in each embodiment. This invention is based on the idea of combining physical experiments and mathematical modeling. It establishes a constitutive model through a systematic process of "simulated rolling + mechanical property measurement + double logarithmic linear fitting," and uses software such as Origin for data processing and linear regression to obtain a model of the form σ = The power function hardening model of Kεⁿ, as shown in Table 2, demonstrates excellent fitting accuracy in both 980MPa and 1180MPa grade ultra-high strength steels (Pearson correlation coefficients of 0.96853 and 0.99695, respectively, and adjusted variances of 0.93242 and 0.99335, respectively). The model has clear statistical support, significantly improving the accuracy and reliability of predicting material hardening behavior. The entire modeling process is clearly defined and uses conventional equipment, requiring only a standard two-roll cold rolling mill, universal tensile testing machine, wire cutting machine, and general data processing software. The entire process, from sample preparation to model output, is highly standardized, making it easy to reproduce and promote in different laboratories or production units. This provides a practical technical path for rapidly establishing proprietary constitutive models for high-strength steels with different composition systems in different steel mills. The established constitutive hardening model can be directly input into the secondary control system of the cold rolling production line as a key material parameter for setting and optimizing process parameters such as rolling force, tension, and reduction rate. The model accurately reflects… This invention elucidates the work hardening characteristics of materials with varying reduction rates, helping to solve common problems in the cold rolling of ultra-high strength steel, such as sudden changes in rolling force, inaccurate tension matching, and excessive rolling passes for thin-gauge products. This improves rolling process stability, reduces strip breakage risk, and fully utilizes mill capacity. Traditional ultra-high strength steel development relies on production line trial rolling and experience-based adjustments, resulting in high costs, long cycles, and significant risks. This invention allows for a systematic evaluation and model building of material hardening characteristics in the laboratory stage during the early stages of new product development, significantly reducing reliance on industrial trials, shortening the R&D cycle, reducing material loss and energy consumption due to repeated adjustments, and accelerating the industrialization of new products. By providing a high-precision material constitutive model, this invention helps shift the ultra-high strength steel cold rolling process from "experience-driven" to "model-driven," reducing excessive reliance on individual operator experience, improving the consistency and controllability of the production process, and providing cold-hardened steel strip raw materials with more stable shape and performance for subsequent continuous annealing, hot-dip galvanizing, and other processes, ultimately improving product quality and market competitiveness.
Claims
1. A method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials, characterized in that, include: S1. Sample processing: The hot-rolled base material of the ultra-high strength steel to be tested is sheared and processed into rectangular sheets; S2. Simulated rolling: The rectangular sheets are subjected to a series of cold rolling with different reduction rates to obtain chilled hard steel strips corresponding to each reduction rate; S3. Mechanical property determination: Tensile specimens are cut from each chilled hard steel strip and their yield strength is determined. S4. Data Processing and Plotting: Take the natural logarithm of each reduction rate (ε) and its corresponding average yield strength (σ), and plot a two-dimensional line graph with ln(ε) as the X-axis and ln(σ) as the Y-axis. S5. Linear Fitting: Perform linear fitting on the two-dimensional line graph to obtain the corresponding linear equation, expressed as follows: y=kx+b①; In equation ①: y represents the logarithmic value of the yield strength; k represents the slope of the linear fit; x represents the logarithmic value of the reduction rate; b represents the intercept of the linear fit. S6. Model Construction: Convert the linear equation into a power function form, expressed as follows: σ=Kε n ②; In equation ②: K represents the strengthening coefficient, in MPa; ε represents the reduction ratio; σ represents the yield strength, in MPa; n represents the strengthening index; the strengthening index n is equal to the slope k of the linear equation, and the strengthening coefficient K is calculated by the equation b=ln(K).
2. The method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials according to claim 1, characterized in that, In S1, the length direction of the rectangular sheet is the rolling direction of the hot-rolled base material, simulating the removal of burrs on the edge of the sample before rolling.
3. The method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials according to claim 1, characterized in that, In S2, the reduction rate (ε) used in the simulated rolling ranges from 5% to 65%, and the interval between adjacent reduction rates is 5%. Cold-hardened steel strips with different reduction rates are obtained by reciprocating rolling.
4. The method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials according to claim 1, characterized in that, In S3, at least three tensile specimens are cut from the rolling direction of the cold-hardened steel strip corresponding to each reduction rate for mechanical property determination, and the average yield strength is taken as the yield strength index corresponding to that reduction rate.
5. The method for constructing a constitutive hardening model for ultra-high strength cold-rolled steel materials according to claim 1, characterized in that, Linear fitting in S5 and plotting in S4 were performed using data processing software.