Manufacturing method of 1200MPa cold-rolled ultra-high-strength steel tensile standard sample

Abstract

The invention discloses a manufacturing method of a 1200MPa cold-rolled ultrahigh-strength steel tensile standard sample, which comprises the following steps: 1) selecting cold-rolled high-strength steel as a raw material steel plate, and sequentially performing smelting, hot continuous rolling, acid pickling, cold continuous rolling and annealing processes to obtain an intermediate steel plate; 2) cutting off the edge part with unstable performance of the middle steel plate, and reserving the middle part with uniform and stable performance; 3) carrying out 0.1-0.2% plastic strain on the middle part of the reserved middle steel plate; 4) cutting into a strip sample to obtain a stretching standard sample; and (5) after heat preservation is conducted for a certain time at the aging temperature of 100-250 DEG C, accelerated aging treatment is conducted under the air cooling condition.

Description

Technical Field

[0001] The invention relates to a method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample, which is suitable for calibrating a tensile testing machine, predicting and determining the measurement uncertainty of a tensile test and for daily precision management in a laboratory, and belongs to the field of metallurgy and electronic technology. Background Art

[0002] The tensile performance test method is one of the internationally used standard methods for measuring the yield strength, tensile strength and elongation at break of metal materials. In engineering applications, tensile properties (yield strength, tensile strength, uniform elongation, elongation at break) are the main basis for the static strength design of structures. The tensile test is a mechanical performance test in which the tensile specimen is pulled to break at a specified tensile speed under the continuous action of static axial tensile force, and the force and elongation are continuously recorded during the stretching process to obtain its strength criterion and plasticity criterion. Reliable prediction and determination of the above tensile performance indicators are very important for both users and producers. However, in practice, there is no 1200MPa ultra-high strength tensile standard sample, and it is difficult to reliably predict and determine the measurement uncertainty of ultra-high strength steel tensile test.

[0003] At present, there are no publicly reported or recognized tensile standards for cold-rolled ultra-high strength steel with a strength grade of 1200MPa for tensile testing at home and abroad. Some research institutions at home and abroad have adopted various methods to manufacture some tensile standards with a strength grade below 500MPa. Among them, the most widely used method is to use dual-phase steel (ferrite and martensite) to manufacture tensile standards. The tensile standards made of dual-phase steel (ferrite and martensite) have a lower strength grade, usually less than 500MPa. According to the actual measurement results, among the above-mentioned mechanical performance indicators, it is difficult to accurately measure the yield strength of cold-rolled ultra-high strength steel with a strength grade of more than 1200MPa. At present, the four main reasons for the inaccurate measurement of the yield strength of cold-rolled ultra-high strength steel with a strength grade of more than 1200MPa have been found to be: 1. The specimen slips due to poor quality of the tooth surface of the clamp (see Figure 1 ), resulting in abnormal tensile curves in the pre-stretching section and the elastic section, and a large deviation in yield strength of about 43MPa. 2. Differences in the clamping and control technology of the extensometer blades cause abnormal tensile curves in the elastic section, which seriously affects the yield strength measurement value (see Figure 2), the yield strength deviation can reach 78MPa. 3. The selection method of the milling blade for milling the tensile specimen and the unreasonable cutting amount during the processing will also affect the yield strength measurement results. 4. The tensile speed will significantly affect the yield strength measurement results; although the tensile speed has an impact on various tensile performance indicators, the test results show that the yield strength of ultra-high strength steel, especially steel with a strength grade of 1200MPa or above, is more sensitive to the tensile control speed. The measurement error of the yield strength of ultra-high strength steel, especially the yield strength of steel with a strength grade of 1200MPa or above, has become a prominent problem when measuring the yield strength according to tensile standards such as GB / T228.1-2021, ISO6892-1-2019, ASTM E8 / E8M-22 and JIS Z2241:2011. Through the tensile performance comparison test of ultra-high strength steel, especially steel with a strength grade of 1200MPa or above, it can be seen from the test results that it is difficult to keep the yield strength index of ultra-high strength steel with a strength grade of 1200MPa or above consistent between different laboratories. From the perspective of tensile performance measurement accuracy control, the demand for ultra-high strength steel, especially for standard samples with strength grades above 1200MPa, is more urgent. However, due to the difficulty in production, although advanced steel mills at home and abroad manufacture and use tensile standards with strength grades below 500MPa to control tensile accuracy, there is no successful method to produce steel plate tensile standards with strength grades of 1200MPa so far. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned deficiencies in the prior art and provide a method for preparing a cold-rolled steel plate tensile standard sample with a strength grade of 1200 MPa.

[0005] The technical problem to be solved by the present invention can be implemented through the following technical solutions.

[0006] A method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample comprises the following steps:

[0007] 1) In terms of weight percentage, a cold-rolled high-strength steel having a carbon content of 0.15-0.35%, a silicon content of 0.10-0.40%, a manganese content of 1.3-1.8%, a phosphorus content of ≤0.012%, a sulfur content of ≤0.002%, an aluminum content of 0.010-0.030%, a boron content of 0.001-0.003%, a titanium content of 0.02-0.05%, and a niobium content of 0.01-0.03% is selected as the raw steel plate, and smelting (deep desulfurization, converter + refining), hot rolling (hot rolling heating After reaching 1230-1280°C, the final rolling temperature is 900-950°C, and the steel plate is rapidly cooled after rolling at a cooling rate of 30-60°C / s, and coiled at 520-620°C), pickling, cold continuous rolling (35-60% reduction rate), and annealing process (820-850°C insulation, insulation time 80-160s, cooling to 720-750°C at a cooling rate of 6-15°C / s, cooling to below 250°C by water cooling, and then tempering at 200-300°C for 100-300s) to obtain the intermediate steel plate;

[0008] 2) Cut off the unstable edge of the middle steel plate (5-10% of the width of the whole plate on the left and right sides respectively), and keep the middle part with uniform and stable performance (the left and right sides are cut off to leave the middle part);

[0009] 3) Performing a plastic strain of 0.1-0.2% on the middle part of the retained middle steel plate;

[0010] 4) Then, cut into long strips to obtain the tensile standard sample;

[0011] 5) Finally, after keeping the aging temperature at 100-250°C for a certain period of time, accelerated aging treatment is carried out under air cooling conditions.

[0012] The present invention adopts the above technical solution, wherein the key is to select a suitable material as the raw steel plate. If the carbon content of the raw steel plate is too low, the yield strength and tensile strength of the ultra-high strength steel tensile standard sample produced may be low; if the carbon content is too high, it may cause chemical composition segregation, thereby deteriorating the uniformity of the ultra-high strength steel tensile standard sample produced in batches, and also make the stress aging effect of the standard sample too large, especially the yield strength index will change with time, increasing the uncertainty of the standard sample. Among them, in terms of weight percentage, it is preferred to select cold-rolled high-strength steel with a carbon content of 0.18-0.25%, a silicon content of 0.13-0.18%, a manganese content of 1.4-1.6%, a phosphorus content of ≤0.010%, a sulfur content of ≤0.001%, an aluminum content of 0.01-0.02%, a boron content of 0.001-0.002%, a titanium content of 0.025-0.40%, and a niobium content of 0.01-0.02% as the raw steel plate.

[0013] In addition, step 3) subjecting the middle portion of the retained middle steel plate to a plastic strain of 0.1%-0.2% creates conditions for the middle portion of the retained middle steel plate to have stable yield strength and tensile strength. Step 5) uses a relatively low temperature aging process, the key is to ensure that the mass-produced ultra-high strength steel standard samples can be aged under uniform temperature conditions, thereby eliminating internal stress and reducing the uncertainty in the measurement of the yield strength of ultra-high strength steel.

[0014] In order to make the performance of the produced tensile standard sample better, in the further improvement of the method for producing the tensile standard sample with ultra-high strength steel described in the present invention, in the step 1), during the hot rolling, pickling, cold rolling and annealing processes of the raw steel plate, the hot rolling temperature, curling temperature, cold rolling annealing temperature and flattening curve are measured in real time, and in step 2), the middle steel plate with the smallest fluctuation in the hot rolling final rolling temperature curve is selected to cut off the two sides.

[0015] In order to ensure that the produced ultra-high strength steel tensile standard can be stored for a long time under appropriate storage conditions without being affected by rust, thereby creating conditions for mass production and use, the raw steel plate in step 1) is a pure zinc hot-dip galvanized steel plate, or a process of pure zinc hot-dip galvanizing the raw steel plate is added in step 1).

[0016] In order to further improve the performance indicators of the ultra-high strength steel tensile standard sample and obtain a standard sample with good uniformity of yield strength and tensile strength, in the step 5), it should be ensured that the length direction of the cut small steel plate is parallel to the rolling direction of the steel plate.

[0017] Through the above-mentioned production method, tensile standard samples of ultra-high strength steel with a strength grade of 1200MPa can be mass-produced, and the tensile standard samples have good uniformity and small standard deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It shows the normal tensile curve and the abnormal tensile curve caused by the slip of the specimen due to the poor quality of the tooth surface of the clamp. Figure 1 a is the normal stretching curve, Figure 1 b is the abnormal stretching curve;

[0019] Figure 2 The diagram shows the normal tensile curve and the abnormal tensile curve caused by the clamping and control problems of the extensometer blade; Figure 2 a is the normal stretching curve, Figure 2 b is the abnormal stretching curve;

[0020] Figure 3 It is a schematic diagram of the final rolling temperature curve;

[0021] Figure 4 Schematic diagram of cutting the middle steel plate.

[0022] In the figure: 1, middle steel plate; 20, edge; 25, middle part; 30, stretched blank sample. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0024] The present invention provides a method for preparing a steel plate tensile standard sample with a strength grade of 1200 MPa, which comprises the following steps:

[0025] 1. In terms of weight percentage, cold-rolled high-strength steel with a carbon content of 0.18-0.25%, a silicon content of 0.13-0.18%, a manganese content of 1.4-1.6%, a phosphorus content of ≤0.010%, a sulfur content of ≤0.001%, an aluminum content of 0.01-0.02%, a boron content of 0.001-0.002%, a titanium content of 0.025-0.40%, and a niobium content of 0.01-0.02% is selected as the raw steel plate.

[0026] The intermediate steel plate is obtained by sequentially performing smelting (deep desulfurization, converter + refining), hot rolling (hot rolling is heated to 1230-1280℃ and then the final rolling temperature is 900-950℃, rapid cooling after rolling, cooling rate is 30-60℃ / s, cooling to 520-620℃ for coiling), pickling, cold rolling (35-60% reduction rate), annealing process (820-850℃ insulation, insulation time is 80-160s, cooling to 720-750℃ at a cooling rate of 6-15℃ / s, cooling to below 250℃ by water cooling, and then tempering at 200-300℃ for 100-300s); wherein, in the process of hot rolling, pickling, cold rolling and annealing of the raw steel plate, the hot rolling temperature, coiling temperature, cold rolling annealing temperature and flatness curve are measured in real time.

[0027] In this step, cold-rolled high-strength steel with the above-mentioned component content is selected as the raw steel plate, which can avoid component segregation caused by recrystallization and obtain high yield strength and tensile strength. Moreover, after aging treatment, the tensile properties do not change significantly with time.

[0028] 2. Select the hot rolling final rolling temperature curve with small fluctuation (corresponding to Figure 3 The middle steel plate 1 of the AB segment in the figure is cut off from the unstable edge 20, and the middle part 25 with uniform and stable performance is retained, such as Figure 4 shown.

[0029] The side portion of the present invention comprises two parts, the left side portion and the right side portion, each of which is 5-10% of the entire board width; the middle portion refers to the portion remaining after the left side portion and the right side portion are removed.

[0030] 3. The middle portion 25 of the retained middle steel plate 1 is subjected to a plastic strain of 0.1%-0.2%. The role of the plastic strain is to create conditions for the middle portion of the retained middle steel plate to have stable yield strength and tensile strength.

[0031] 4. Then, the middle portion 25 of the retained middle steel plate 1 is cut into a tensile blank sample 30 to obtain an ultra-high strength steel tensile standard sample. When cutting, it should be ensured that the length direction of the cut tensile blank sample 30 is parallel to the rolling direction of the steel plate, as shown in FIG. Figure 4 The advantage of this is that the performance indicators of the tensile standard can be improved so as to obtain stable yield strength and tensile strength indicators.

[0032] 5. Finally, at an aging temperature of 100-250℃, keep warm for a certain period of time and then perform accelerated aging treatment under air cooling conditions; the key to using a lower temperature aging process here is to ensure that the standard samples produced in large quantities can be aged under uniform temperature conditions, thereby reducing the measurement uncertainty of high yield strength and tensile strength. The aging time here is shortened as the aging temperature increases. For example, when the aging temperature is 100℃, the aging time is 24 hours. When the aging temperature is 250±2℃, the aging time is 40±2 minutes.

[0033] Through the above-mentioned production method, ultra-high strength steel tensile standard samples with stable yield strength and tensile strength can be mass-produced, and the ultra-high strength tensile standard samples have good uniformity and small standard deviation. This will be explained through specific embodiments below:

[0034] Example 1

[0035] In terms of weight percentage, a cold-rolled high-strength steel with a carbon content of 0.20%, a silicon content of 0.15%, a manganese content of 1.5%, a phosphorus content of 0.008%, a sulfur content of 0.001%, an aluminum content of 0.015%, a brass content of 0.002%, a titanium content of 0.035%, and a niobium content of 0.015% is selected as a raw steel plate, smelted in a converter, and a slab with a width of 1200 mm is obtained by continuous casting. The segregation zone is less than 200 mm from the edge of the slab after detection. An intermediate steel plate with a width of 1100 mm is obtained by hot rolling, pickling, cold rolling, and annealing. During the above process, the hot rolling temperature, the curling temperature, the cold rolling annealing temperature, and the smoothing rate curve are measured in real time. Then, among the intermediate steel plates obtained, the intermediate steel plate with a small fluctuation in the hot rolling final rolling temperature curve is selected, and 120 mm of each of its two sides are cut off, and the middle part of the intermediate steel plate with uniform mechanical properties is retained. The middle part of the retained middle steel plate is further subjected to 0.2% plastic deformation. After plastic deformation, it is cut into tensile blank samples. 250 tensile blank samples are produced in batches. When cutting, the length of the cut tensile blank samples should be ensured to be parallel to the rolling direction of the steel plate. Finally, the 250 tensile blank samples are subjected to aging treatment at 100°C for 24 hours, so that a tensile standard sample with stable yield strength, tensile strength and elongation at break is obtained. The obtained ultra-high strength tensile specimens are compared and tested on three different types of tensile machines. The standard deviation of yield strength caused by the non-uniformity of the standard sample is calculated to be 2.75MPa (the original standard deviation of yield strength is 8.4MPa); the standard deviation of tensile strength is 2.76MPa (the original standard deviation of tensile strength is 5.9MPa); the standard deviation of elongation at break is 0.32% (the original standard deviation of elongation at break is 0.4%) (data are shown in Tables 1 and 2 below).

[0036] Table 1:

[0037]

[0038] Table 2 is the statistical summary data of three testing equipment for the tensile properties of ultra-high-strength steel of a certain company from May 2020 to September 2021.

[0039] Table 2:

[0040]

[0041] Example 2

[0042] In terms of weight percentage, cold-rolled high-strength steel with a carbon content of 0.18%, a silicon content of 0.21%, a manganese content of 1.55%, a phosphorus content of 0.001%, a sulfur content of 0.001%, an aluminum content of 0.018%, a brass content of 0.0014%, a titanium content of 0.037%, and a niobium content of 0.013% is selected as the raw steel plate, and is smelted in a converter and continuously cast to obtain a slab with a width of 1200 mm. It is detected that the segregation zone is less than 200 mm from the edge of the slab. An intermediate steel plate with a width of 1100 mm is obtained through hot rolling, pickling, cold rolling, and annealing processes, and then 120 mm of each side is cut off to retain the middle part of the intermediate steel plate with uniform mechanical properties. The middle part of the retained middle steel plate is further subjected to 0.2% plastic deformation. After plastic deformation, it is subjected to aging treatment at 250°C for 40 minutes. After aging treatment, it is cut into 250 small steel plates to obtain a batch of stable tensile standard samples of yield strength, tensile strength and elongation at break. When cutting, it should be ensured that the length direction of the cut small steel plates is parallel to the rolling direction of the steel plates. The samples are measured on 3 stretching machines, and the standard deviations of yield strength are calculated to be 2.50-3.39MPa (the original standard deviation of yield strength is within 7.24-9.16MPa); the standard deviations of tensile strength are 2.81-3.13MPa (the original standard deviation of tensile strength is within 5.58-6.40MPa); the standard deviations of elongation at break are 0.24-0.36% (the original standard deviation of elongation at break is within 0.27-0.55%) (data are shown in Tables 3 and 4 below).

[0043] Table 3:

[0044]

[0045] Table 4 is the original statistical summary data of each test equipment on the tensile properties of ultra-high strength steel from May 2020 to September 2021.

[0046] Table 4:

[0047]

[0048] Example 3

[0049] This embodiment is specifically used to illustrate the beneficial effects of the present invention through test data.

[0050] Compared with the prior art, the method for preparing the steel plate tensile standard sample with a strength grade of 1200MPa described in the present invention replaces the existing technology of manufacturing the tensile standard sample with a strength grade of only 800Mpa dual-phase steel, thereby solving the defect that there is currently no tensile standard sample with a strength grade of 1200MPa. From the data analysis of Tables 1 and 2, the difference (extreme difference) and standard deviation between the standard sample data are very small, reflecting that the tensile standard sample prepared by the method for preparing the steel plate tensile standard sample with a strength grade of 1200MPa described in the present invention has good uniformity.

[0051] Therefore, it is concluded that the method for producing a steel plate tensile standard sample with a strength grade of 1200 MPa described in the present invention can be used to mass produce ultra-high strength tensile standard samples, and the tensile standard samples have good uniformity.

Claims

1. A method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard, characterized in that: Use the following steps: 1) Select cold-rolled high-strength steel as the raw steel plate, and carry out smelting, hot rolling, pickling, cold rolling and annealing processes in sequence to obtain the intermediate steel plate; 2) Cut off the unstable edge of the middle steel plate and keep the middle part with uniform and stable performance; 3) Performing a plastic strain of 0.1-0.2% on the middle part of the retained middle steel plate; 4) Cut into long strips to obtain tensile standard samples; 5) After keeping the aging temperature at 100-250℃ for a certain period of time, carry out accelerated aging treatment under air cooling conditions.

2. The method for preparing the 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: In terms of weight percentage, the raw steel plate has a carbon content of 0.15-0.35%, a silicon content of 0.10-0.40%, a manganese content of 1.3-1.8%, a phosphorus content of ≤0.012%, a sulfur content of ≤0.002%, an aluminum content of 0.010-0.030%, a boron content of 0.001-0.003%, a titanium content of 0.02-0.05%, and a niobium content of 0.01-0.03%.

3. The method for preparing the 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: In terms of weight percentage, the raw steel plate has a carbon content of 0.18-0.25%, a silicon content of 0.13-0.18%, a manganese content of 1.4-1.6%, a phosphorus content of ≤0.010%, a sulfur content of ≤0.001%, an aluminum content of 0.01-0.02%, a boron content of 0.001-0.002%, a titanium content of 0.025-0.40%, and a niobium content of 0.01-0.02%.

4. The method for preparing the 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: The raw steel plate is a pure zinc hot-dip galvanized steel plate.

5. The method for preparing the 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: Step 1) also includes a step of subjecting the raw steel plate to a pure zinc hot-dip galvanizing process.

6. The method for preparing the 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: In step 1), the hot rolling process includes: After hot rolling and heating to 1230-1280℃, the final rolling temperature is 900-950℃, and the rolling is rapidly cooled at a cooling rate of 30-60℃ / s, and coiled when cooled to between 520-620℃; The reduction rate of the cold rolling is 35-60%; The annealing process includes: keeping at 820-850°C for 80-160s, cooling to 720-750°C at a cooling rate of 6-15°C / s, cooling to below 250°C by water cooling, and then tempering at 200-300°C for 100-300s.

7. The method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1 or 6, characterized in that: Step 1) also includes the step of measuring the hot rolling temperature, curling temperature, cold rolling annealing temperature and flattening rate curve in real time.

8. The method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: In step 4), the middle part of the retained middle steel plate is cut into a tensile blank sample to obtain an ultra-high strength steel tensile standard sample; during cutting, ensure that the length direction of the cut tensile blank sample 30 is parallel to the rolling direction of the steel plate.

9. The method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: In step 5), the aging treatment time is shortened as the aging temperature increases.

10. The method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: In step 2), the middle steel plate with small fluctuation in the hot rolling final rolling temperature curve is selected to cut off the two sides.

11. The method for preparing a 1200MPa cold-rolled ultra-high strength steel tensile standard sample according to claim 1, characterized in that: The edges with unstable performance include a left edge and a right edge, and each of the two side edges is 5-10% of the board width; the middle part is the middle part left after cutting off the two side edges.

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