Method for measuring static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal test and thermal simulation

Abstract

The invention discloses a method for measuring the static recrystallization temperature of a Q420 cold-rolled sheet based on an orthogonal test and thermal simulation, which comprises the following steps: 1) sample preparation: taking a Q420 cold-rolled sheet with a thickness, processing the Q420 cold-rolled sheet into a standard sample, and using the center area of the sample for thermal treatment simulation; 2) orthogonal test design; 3) thermal simulation experiment: simulating a continuous annealing process by using a simulation testing machine; 4) testing hardness; recrystallization temperature is judged; and in combination with a metallographic structure, taking an average value of a plurality of groups of tests TRX, namely the static recrystallization temperature range of the Q420 cold-rolled sheet. According to the method, key parameters such as the annealing temperature and the heat preservation time are optimized through an orthogonal test, the continuous annealing process is simulated by combining a thermal simulation testing machine, the softening trend is analyzed through a Rockwell hardness test, and the static recrystallization temperature range is defined.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cold-rolled plate continuous annealing process, and particularly relates to a Q420 cold-rolled plate static recrystallization temperature determination method based on orthogonal test and thermal simulation. BACKGROUND

[0002] In the continuous annealing (continuous annealing) process of the Q420 steel cold-rolled plate, static recrystallization needs to be realized by accurately controlling the annealing temperature and time to eliminate the cold-rolled deformation stored energy and improve the uniformity of the structure. The static recrystallization temperature is a core parameter of the continuous annealing process design - if the temperature is too low, the recrystallization will be incomplete, the material strength will be high, and the plasticity will be insufficient; if the temperature is too high, the grain may be coarsened, and the mechanical properties may be reduced.

[0003] The traditional static recrystallization temperature determination method (such as the metallographic method) needs to take samples multiple times and observe the grain morphology, is time-consuming, and is difficult to match the rapid adjustment requirement of the continuous annealing process. Although the existing hardness method can reflect the recrystallization degree through the hardness change, the on-site sampling process is complicated, the period is long, and the trial and error cost is too high. Therefore, an efficient method combining orthogonal test optimization and thermal simulation is needed to accurately obtain the static recrystallization temperature of the Q420 cold-rolled plate and guide the setting of the continuous annealing process parameters. SUMMARY

[0004] The purpose of the application is to provide a Q420 cold-rolled plate static recrystallization temperature determination method based on orthogonal test and thermal simulation, to optimize the annealing temperature, holding time and other key parameters through orthogonal test, to simulate the continuous annealing process by using a thermal simulation testing machine, to analyze the softening trend by using the Rockwell hardness test, and to determine the static recrystallization temperature range.

[0005] To solve the above technical problems, the application adopts the following technical scheme:

[0006] The application is a Q420 cold-rolled plate static recrystallization temperature determination method based on orthogonal test and thermal simulation, which comprises the following steps:

[0007] 1) Sample preparation:

[0008] A Q420 cold-rolled plate with a certain thickness is taken and processed into a standard sample, and the center area of the sample is used for thermal treatment simulation;

[0009] 2) Orthogonal test design:

[0010] The key process parameters affecting the static recrystallization are selected as the orthogonal factors:

[0011] Annealing temperature: 680℃, 720℃, 760℃, 800℃;

[0012] Holding time: 30min, 60min, 90min, simulating the holding time of the continuous annealing furnace;

[0013] Cooling rate: 20℃ / s, 30℃ / s, 40℃ / s, continuous annealing furnace fast cooling section rate;

[0014] A plurality of groups of tests are designed using an orthogonal table;

[0015] 3) Thermal simulation experiment:

[0016] A simulation test machine is used to simulate the continuous annealing process:

[0017] Heating stage: the sample is heated to the annealing temperature at a rate of 10℃ / s

[0018] Annealing stage: set the annealing temperature and keep it for the set time;

[0019] Cooling stage: set the cooling rate to cool to room temperature;

[0020] 4) Hardness test:

[0021] After each group of tests, the hardness of the center area of the sample is tested using a Rockwell hardness tester, with a test force of 150kgf, a pressure holding time of 15s, and an average value of 5 points for each sample;

[0022] Hardness-temperature curve: plot the hardness curve under different holding times with the annealing temperature as the horizontal coordinate and the hardness as the vertical coordinate;

[0023] Recrystallization temperature determination:

[0024] Define the complete recrystallization temperature as the temperature at which the hardness decreases to 50% of the original hardness;

[0025] Combined with the metallographic structure, the average value of multiple groups of TRX tests is taken, which is the static recrystallization temperature range of Q420 cold-rolled plate.

[0026] Further, in step 1), a Q420 cold-rolled plate with a thickness of 1.5mm is taken.

[0027] Further, in step 1), a standard sample of 90mm×30mm×1.5mm is processed according to GB / T 228.1-2021.

[0028] Further, in step 2), 9 groups of tests are designed using an orthogonal table.

[0029] Further, in step 3), a MMS-200 type thermal simulation test machine is used to simulate the continuous annealing process.

[0030] Further, in step 4), after each group of tests, the hardness of the center area of the sample is tested using a HBRVU-187.5 type Rockwell hardness tester.

[0031] Furthermore, in step 1), the surface of the standard sample is polished to Ra≤6.3μm.

[0032] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0033] The core idea of ​​this invention is to design a combination of parameters such as annealing temperature and holding time through orthogonal experiments, simulate the holding stage in the continuous annealing process using an MMS-200 thermodynamic simulation testing machine, analyze the hardness change trend under different processes through Rockwell hardness testing, verify the results with metallographic structure, and finally determine the static recrystallization temperature based on the hardness inflection point and microstructure transformation.

[0034] 1. High efficiency: Combined with on-site controlled cooling process, only different annealing temperatures need to be set, while the holding time (60s) and cooling rate (20℃ / s) are constant values, reducing the workload by 60% compared to single-factor experiments;

[0035] 2. Accuracy: Verified by both hardness inflection point and metallographic structure, the error is ≤5℃;

[0036] 3. Practicality: Directly guides the setting of continuous annealing process parameters and optimizes the matching of strength and plasticity of the sheet material. Attached Figure Description

[0037] The present invention will be further described below with reference to the accompanying drawings.

[0038] Figure 1 To determine the recrystallization temperature using the hardness method; Detailed Implementation

[0039] Example 1: Orthogonal Experiment and Thermodynamic Simulation

[0040] Taking Q420 cold-rolled sheet (C 0.16%, Si 0.29%, Mn 1.45%, Ti 0.07%, with the remainder being Fe and impurities) as an example,

[0041] Thermal simulation process:

[0042] Heat to the annealing temperature; heat to the annealing temperature at a rate of 10℃ / s (620℃, 640℃, 660℃, 680℃, 720℃, 740℃, 800℃, 820℃, 840℃), and hold for 60s; cool at a rate of 20℃ / s and cool to room temperature (40℃).

[0043] Hardness testing and recrystallization temperature calculation:

[0044] Hardness values ​​of samples at different temperatures are shown below. Figure 1 TRX = 800℃ was calculated using linear interpolation. Figure 1 ).

[0045] Optimal process combination: annealing temperature Ta = 800℃, holding time t = 60min, cooling rate V = 20℃ / s, complete recrystallization temperature TRX = 800℃.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation, characterized in that, Includes the following steps: 1) Sample preparation: Take a Q420 cold-rolled sheet and process it into a standard specimen. The central area of ​​the specimen is used for heat treatment simulation. 2) Orthogonal experimental design: Key process parameters affecting static recrystallization were selected as orthogonal factors: Annealing temperatures: 680℃, 720℃, 760℃, 800℃; Holding time: 30min, 60min, 90min, simulating the holding time of the continuous annealing furnace; Cooling rates: 20℃ / s, 30℃ / s, 40℃ / s, and the rate of rapid cooling section in the continuous annealing furnace; Multiple sets of experiments were designed using orthogonal arrays; 3) Thermal simulation experiment: Simulate the continuous annealing process using a simulation testing machine: Heating stage: The sample is heated to the annealing temperature at a rate of 10℃ / s. Annealing stage: Set the annealing temperature and hold for the set time; Cooling phase: Set the cooling rate to cool to room temperature; 4) Hardness test: After each test, the hardness of the central area of ​​the sample was tested with a Rockwell hardness tester. The test force was 150 kgf and the holding time was 15 s. Five points were tested for each sample and the average value was taken. Hardness-temperature curve: plot the hardness curves at different holding times with annealing temperature as the x-axis and hardness as the y-axis. Recrystallization temperature determination: The complete recrystallization temperature is defined as the temperature at which the hardness decreases to 50% of the original hardness. Based on the metallographic structure, the average value of TRX from multiple test groups is taken as the static recrystallization temperature range of Q420 cold-rolled sheet.

2. The method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation according to claim 1, characterized in that, In step 1), a Q420 cold-rolled sheet with a thickness of 1.5mm is taken.

3. The method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation according to claim 1, characterized in that, In step 1), the standard sample is processed into a size of 90mm×30mm×1.5mm according to GB / T 228.1-2021.

4. The method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation according to claim 1, characterized in that, In step 2), nine sets of experiments are designed using an orthogonal array.

5. The method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation according to claim 1, characterized in that, In step 3), the continuous annealing process is simulated using an MMS-200 thermal simulation test machine.

6. The method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation according to claim 1, characterized in that, In step 4), after each test, the hardness of the central area of ​​the sample is tested using an HBRVU-187.5 Rockwell hardness tester.

7. The method for determining the static recrystallization temperature of Q420 cold-rolled sheet based on orthogonal experiments and thermodynamic simulation according to claim 1, characterized in that, In step 1), the surface of the standard sample is polished to Ra≤6.3μm.

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