A method for evaluating low-temperature toughness of ultra-high-strength steel parts

Abstract

The present application discloses a method for evaluating the low-temperature toughness of ultra-high-strength steel parts. The method for evaluating the low-temperature toughness of ultra-high-strength steel parts includes: obtaining the maximum deformation strain rate of the ultra-high-strength steel parts to be tested: performing a room temperature dynamic three-point bending test on the ultra-high-strength steel parts to be tested, thereby obtaining room temperature test results: performing a low-temperature dynamic three-point bending test on the ultra-high-strength steel parts to be tested, thereby obtaining low-temperature test results: evaluating the low-temperature toughness of the ultra-high-strength steel parts to be tested based on the room temperature test results and the low-temperature test results. The method for evaluating the low-temperature toughness of ultra-high-strength steel parts of the present application uses a dynamic three-point bending test method, which can simulate the high strain rate deformation conditions of the parts during a collision process, conduct dynamic three-point bending tests under room temperature and low-temperature environments, and evaluate the low-temperature toughness of the parts by comparing the test results.

Description

Technical Field

[0001] The present application relates to the technical field of ultra-high strength steel toughness detection, and in particular to a method for evaluating the low-temperature toughness of ultra-high strength steel parts. Background Art

[0002] With the increasing demand for lightweight and safety design of automobiles, the application of lightweight materials is becoming more and more extensive. Among them, the application of high-strength steel and ultra-high-strength steel is one of the important lightweight methods. Ultra-high-strength steel parts are increasingly used in automobile bodies, such as A / B pillars, front / rear bumper beams, door anti-collision beams, threshold beams and other safety parts. With the improvement of material strength, its potential low-temperature brittleness, that is, the problem of the material changing from toughness to brittleness in a low-temperature environment, cannot be ignored. If the part material undergoes a tough-to-brittle transition in the low-temperature use environment of the automobile, the collision safety of the automobile will be greatly reduced. The design and evaluation of automobile collision safety depends on CAE simulation analysis and real vehicle collision tests. However, simulation analysis cannot predict the deformation behavior of the whole vehicle and parts in a low-temperature environment. The real vehicle collision test also has no low-temperature environment requirements, so it is impossible to verify the safety performance of the parts in a low-temperature environment. Therefore, it is necessary to evaluate the low-temperature toughness of ultra-high-strength steel parts to predict the safety of the parts in the whole vehicle collision in a low-temperature environment, so as to support the application of materials and collision safety design.

[0003] The existing technology is to evaluate the low-temperature toughness of materials through the Charpy impact test method, but the test method is not suitable for thin plates, and the low-temperature impact of the material cannot well characterize the collision state of the parts on the whole vehicle, because the performance of the material is different from that of the processed parts, especially for hot-formed steel parts. The actual performance of the flat quenched material and the parts is quite different.

[0004] Therefore, it is hoped that a technical solution can be provided to solve or at least alleviate the above-mentioned deficiencies of the prior art. Summary of the invention

[0005] The object of the present invention is to provide a method for evaluating the low-temperature toughness of ultra-high strength steel parts to at least solve one of the above-mentioned technical problems.

[0006] One aspect of the present invention provides a method for evaluating the low-temperature toughness of an ultra-high-strength steel part, the method comprising:

[0007] Obtain the maximum deformation strain rate of the ultra-high strength steel part to be tested;

[0008] Performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result;

[0009] Performing a low-temperature dynamic three-point bending test on the ultra-high-strength steel part to be tested, thereby obtaining a low-temperature test result;

[0010] The low temperature toughness of the ultra-high strength steel part to be tested is evaluated based on the room temperature test results and the low temperature test results.

[0011] Optionally, before performing the room temperature dynamic three-point bending test, the method for evaluating low temperature toughness of ultra-high strength steel parts further comprises:

[0012] Design dynamic three-point bending test parameters;

[0013] The step of performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result, comprises:

[0014] Performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested according to the designed dynamic three-point bending test parameters, thereby obtaining a room temperature test result;

[0015] The step of performing a low temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a low temperature test result, comprises:

[0016] A low-temperature dynamic three-point bending test is performed on the ultra-high-strength steel part to be tested according to the designed dynamic three-point bending test parameters, so as to obtain a low-temperature test result.

[0017] Optionally, obtaining the maximum deformation strain rate of the ultra-high strength steel part to be tested includes:

[0018] The maximum deformation strain rate of the ultra-high strength steel parts to be tested in the whole vehicle collision simulation analysis is extracted as the maximum strain rate used in the test.

[0019] Optionally, the obtaining and designing dynamic three-point bending test parameters includes:

[0020] Determine the span of the two supporting points of the ultra-high-strength steel part to be tested in the three-point bending test by referring to the assembly relationship of the ultra-high-strength steel part to be tested in the vehicle body;

[0021] A dynamic three-point bending test model is established, and the drop weight and the drop height of the drop hammer are obtained according to the maximum deformation strain rate of the ultra-high strength steel part to be tested.

[0022] Optionally, performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result includes:

[0023] Under room temperature conditions, a dynamic three-point bending test is performed on the ultra-high strength steel parts to be tested;

[0024] Obtain the load-displacement curve of the ultra-high strength steel part to be tested during three-point bending;

[0025] Extracting the maximum load according to the load-displacement curve and calculating the average load at room temperature;

[0026] According to the load-displacement curve, the area enclosed by the curve is calculated to record the energy value and calculate the average energy value at room temperature;

[0027] The crack length of the ultra-high strength steel part to be tested after the test is measured and the average value is calculated to obtain the average value of the room temperature crack.

[0028] Optionally, performing a low temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a low temperature test result includes:

[0029] The ultra-high strength steel parts to be tested are subjected to two dynamic three-point bending tests at temperatures lower than room temperature, wherein the dynamic three-point bending test at one temperature is called the first low-temperature bending test, and the other is called the second low-temperature bending test;

[0030] Obtain load-displacement curves of the ultra-high strength steel part to be tested in the three-point bending process in the first low-temperature bending test and the second low-temperature bending test, respectively, wherein the load-displacement curve obtained by the first low-temperature bending test is called the first low-temperature curve, and the other is called the second low-temperature curve;

[0031] Extracting the maximum load according to the first low temperature curve and calculating the first low temperature load average value;

[0032] Extract the maximum load according to the second low temperature curve and calculate the second low temperature load average value;

[0033] According to the first low temperature curve, calculate the area enclosed by the curve, record the energy value and calculate the first low temperature energy average value;

[0034] According to the second low temperature curve, the area enclosed by the curve is calculated to record the energy value and calculate the second low temperature energy average value;

[0035] Measuring the crack length of the ultra-high strength steel part to be tested after the first low temperature bending test and calculating the first low temperature crack average value;

[0036] The crack length of the ultra-high strength steel part to be tested after the second low temperature bending test is measured and the second low temperature crack average value is calculated.

[0037] Optionally, when conducting the dynamic three-point bending test at a temperature below room temperature, taking into account the temperature loss of the parts during the test, the temperature compensation is set to 2°C to 6°C lower than the test temperature, the time for the parts to be taken out of the temperature box and transferred to the test bench is less than 5s, and the time from the parts being taken out of the temperature box to the end of the test is less than 15s.

[0038] Optionally, the evaluating the low temperature toughness of the ultra-high strength steel part to be tested according to the room temperature test results and the low temperature test results includes:

[0039] Calculate the ratio of the first low-temperature load average value to the room-temperature load average value, which is called the first load ratio;

[0040] Calculate the ratio of the second low-temperature load average value to the room-temperature load average value, which is called the second load ratio;

[0041] Calculate the ratio of the first low-temperature energy average value to the room-temperature energy average value, which is called the first energy ratio;

[0042] Calculate the ratio of the second low temperature energy average value to the room temperature energy average value, which is called the second energy ratio;

[0043] Calculate the ratio of the first low-temperature crack average to the room-temperature crack average, which is called the first crack ratio;

[0044] Calculate the ratio of the second low-temperature crack average to the room-temperature crack average, which is called the second crack ratio;

[0045] The low-temperature toughness of the ultra-high-strength steel part to be tested is determined according to the obtained first load ratio, second load ratio, first energy ratio, second energy ratio, first crack ratio, and second crack ratio.

[0046] Optionally, the room temperature is 15°C to 25°C;

[0047] The temperature in the first low temperature bending test is -20°C;

[0048] The temperature in the second low-temperature bending test was -40°C.

[0049] Optionally, the ultra-high strength steel part to be tested is a thin plate-shaped ultra-high strength steel part for automobiles.

[0050] Beneficial Effects

[0051] The method for evaluating the low-temperature toughness of ultra-high-strength steel parts in this application uses a dynamic three-point bending test method, which can simulate the high strain rate deformation conditions of parts during a collision, conduct dynamic three-point bending tests at room temperature and low temperature environments, and evaluate the low-temperature toughness of parts by comparing the test results. The method of this application can simply, effectively and cost-effectively predict the collision safety of ultra-high-strength steel parts in low-temperature environments, provide a reference for the application of ultra-high-strength steel and collision safety design, and has important engineering practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a flow chart of a method for evaluating low-temperature toughness of ultra-high-strength steel parts according to an embodiment of the present application.

[0053] Figure 2 It is a schematic diagram of the test device structure in the dynamic three-point bending test.

[0054] Figure 3 It is a schematic diagram of the load-displacement curve in the dynamic three-point bending test.

[0055] Figure 4 It is a schematic diagram of the structure of the ultra-high-strength steel part to be tested after a dynamic three-point bending test. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical scheme and advantages of the implementation of this application clearer, the technical scheme in the embodiment of this application will be described in more detail below in conjunction with the drawings in the embodiment of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of this application, not all of them. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be construed as limitations on this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The embodiments of this application are described in detail below in conjunction with the drawings.

[0057] Figure 1 It is a flow chart of a method for evaluating low-temperature toughness of ultra-high-strength steel parts according to an embodiment of the present application.

[0058] like Figure 1 The low temperature toughness evaluation methods for ultra-high strength steel parts shown include:

[0059] Step 1: Obtain the maximum deformation strain rate of the ultra-high strength steel part to be tested;

[0060] Step 2: performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result;

[0061] Step 3: performing a low temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a low temperature test result;

[0062] Step 4: Evaluate the low-temperature toughness of the ultra-high-strength steel part to be tested based on the room temperature test results and the low-temperature test results.

[0063] The method for evaluating the low-temperature toughness of ultra-high-strength steel parts in this application uses a dynamic three-point bending test method, which can simulate the high strain rate deformation conditions of parts during a collision, conduct dynamic three-point bending tests at room temperature and low temperature environments, and evaluate the low-temperature toughness of parts by comparing the test results. The method of this application can simply, effectively and cost-effectively predict the collision safety of ultra-high-strength steel parts in low-temperature environments, provide a reference for the application of ultra-high-strength steel and collision safety design, and has important engineering practical significance.

[0064] It is understandable that the order of step 2 and step 3 of the present application can be set as needed, and changing the order will not affect the method of the present application.

[0065] In this embodiment, before performing the room temperature dynamic three-point bending test, the low temperature toughness evaluation method of the ultra-high strength steel part further includes:

[0066] Design dynamic three-point bending test parameters;

[0067] The room temperature dynamic three-point bending test is performed on the ultra-high strength steel parts to obtain the following room temperature test results:

[0068] Performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested according to the designed dynamic three-point bending test parameters, thereby obtaining a room temperature test result;

[0069] The step of performing a low temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a low temperature test result, comprises:

[0070] A low-temperature dynamic three-point bending test is performed on the ultra-high-strength steel part to be tested according to the designed dynamic three-point bending test parameters, so as to obtain a low-temperature test result.

[0071] In this embodiment, obtaining the maximum deformation strain rate of the ultra-high strength steel part to be tested includes:

[0072] The maximum deformation strain rate of the ultra-high strength steel parts to be tested in the whole vehicle collision simulation analysis is extracted as the maximum strain rate used in the test.

[0073] Specifically, the maximum deformation strain rate of the parts in the whole vehicle collision simulation analysis is extracted through LS-Dyna software as the maximum strain rate used in the test.

[0074] In this embodiment, obtaining the design dynamic three-point bending test parameters includes:

[0075] The span of the two supporting points of the ultra-high-strength steel part to be tested in the three-point bending test is determined with reference to the assembly relationship of the ultra-high-strength steel part to be tested in the vehicle body, that is, the minimum distance between the welding points of the two ends of the ultra-high-strength steel part to be tested and the matching part;

[0076] A dynamic three-point bending test model is established, and the drop weight and the drop height of the drop hammer are obtained according to the maximum deformation strain rate of the ultra-high strength steel part to be tested.

[0077] Specifically, the span L0 of the two supporting points of the part in the three-point bending test is determined with reference to the assembly relationship of the part on the vehicle body;

[0078] A dynamic three-point bending test model was established in the LS-Dyna software. The drop weight W and the drop height h of the drop weight were analyzed and designed according to the maximum deformation strain rate of the parts determined in step one.

[0079] In this embodiment, a room temperature dynamic three-point bending test is performed on the ultra-high strength steel part to be tested, so as to obtain the room temperature test results including:

[0080] Under room temperature conditions, a dynamic three-point bending test is performed on the ultra-high strength steel parts to be tested;

[0081] Obtain the load-displacement curve of the ultra-high strength steel part to be tested during three-point bending;

[0082] Extracting the maximum load according to the load-displacement curve and calculating the average load at room temperature;

[0083] According to the load-displacement curve, the area enclosed by the curve is calculated to record the energy value and calculate the average energy value at room temperature;

[0084] The crack length of the ultra-high strength steel part to be tested after the test is measured and the average value is calculated to obtain the average value of the room temperature crack.

[0085] In this embodiment, a low temperature dynamic three-point bending test is performed on the ultra-high strength steel part to be tested, so as to obtain the low temperature test results including:

[0086] The ultra-high strength steel parts to be tested are subjected to two dynamic three-point bending tests at temperatures lower than room temperature, wherein the dynamic three-point bending test at one temperature is called the first low-temperature bending test, and the other is called the second low-temperature bending test;

[0087] Obtain load-displacement curves of the ultra-high strength steel part to be tested in the three-point bending process in the first low-temperature bending test and the second low-temperature bending test, respectively, wherein the load-displacement curve obtained by the first low-temperature bending test is called the first low-temperature curve, and the other is called the second low-temperature curve;

[0088] Extracting the maximum load according to the first low temperature curve and calculating the first low temperature load average value;

[0089] Extract the maximum load according to the second low temperature curve and calculate the second low temperature load average value;

[0090] According to the first low temperature curve, calculate the area enclosed by the curve, record the energy value and calculate the first low temperature energy average value;

[0091] According to the second low temperature curve, the area enclosed by the curve is calculated to record the energy value and calculate the second low temperature energy average value;

[0092] Measuring the crack length of the ultra-high strength steel part to be tested after the first low temperature bending test and calculating the first low temperature crack average value;

[0093] The crack length of the ultra-high strength steel part to be tested after the second low temperature bending test is measured and the second low temperature crack average value is calculated.

[0094] In this embodiment, when performing the dynamic three-point bending test at a temperature below room temperature, the temperature compensation is set to 2° C. to 6° C., the part transfer time is less than 5 seconds, and the test completion time is less than 15 seconds.

[0095] In this embodiment, the low temperature toughness evaluation of the ultra-high strength steel part to be tested according to the room temperature test results and the low temperature test results includes:

[0096] Calculate the ratio of the first low-temperature load average value to the room-temperature load average value, which is called the first load ratio;

[0097] Calculate the ratio of the second low temperature energy average value to the room temperature load average value, which is called the second load ratio;

[0098] Calculate the ratio of the first low-temperature energy average value to the room-temperature energy average value, which is called the first energy ratio;

[0099] Calculate the ratio of the second low temperature energy average value to the room temperature energy average value, which is called the second energy ratio;

[0100] Calculate the ratio of the first low-temperature crack average to the room-temperature crack average, which is called the first crack ratio;

[0101] Calculate the ratio of the second low-temperature crack average to the room-temperature crack average, which is called the second crack ratio;

[0102] The low-temperature toughness of the ultra-high-strength steel part to be tested is determined according to the obtained first load ratio, second load ratio, first energy ratio, second energy ratio, first crack ratio, and second crack ratio.

[0103] In this embodiment, the room temperature is 15°C to 25°C;

[0104] The temperature in the first low temperature bending test is -20°C;

[0105] The temperature in the second low-temperature bending test was -40°C.

[0106] In this embodiment, the ultra-high-strength steel parts are thin-plate ultra-high-strength steel parts for automobiles, for example, ultra-high-strength steel parts such as door anti-collision beams, A / B pillars, and door sill beams.

[0107] In this embodiment, a dynamic three-point bending test method is applied to carry out a dynamic three-point bending test at room temperature and low temperature environment respectively to simulate the dynamic deformation process of parts during a car collision. By comparing the maximum load and energy value or the crack length of the parts during the deformation process, the low-temperature toughness of the parts is evaluated, thereby predicting the collision safety of the parts in a low-temperature environment.

[0108] In this embodiment, the tensile strength of the mechanical performance index of the ultra-high strength steel parts to be tested ranges from 1300 to 2100 MPa;

[0109] In this embodiment, when the dynamic three-point bending test is performed, the number of test pieces is 3;

[0110] In this embodiment, a dynamic three-point bending test is performed at two temperatures T1 and T2, and the number of test pieces is 3 at each temperature;

[0111] The present application is further described in detail below by way of examples. It should be understood that the examples do not constitute any limitation to the present application.

[0112] See also Figures 1 to 4 The method for evaluating low temperature toughness of ultra-high strength steel parts described in this embodiment includes the following steps:

[0113] Step 1: Select the door anti-collision beam as the ultra-high strength steel part to be tested. The material is hot-formed steel with a tensile strength greater than 1800 MPa. Use LS-Dyna software to extract the maximum deformation strain rate of the part in the collision simulation analysis, which is about 50 / s.

[0114] See also Figure 2 , Step 2: Design dynamic three-point bending test parameters:

[0115] The first step is to determine the span L0 = 800 mm between the two supporting points of the part in the three-point bending test with reference to the assembly position of the door anti-collision beam in the front door assembly;

[0116] The second step is to establish a dynamic three-point bending test model in LS-Dyna software, analyze it according to the maximum deformation strain rate of 50 / s, design the weight of the drop weight to be 175kg, and the drop height of the drop weight to be h=1200mm;

[0117] Step 3: Dynamic three-point bending test at room temperature:

[0118] In the first step, a dynamic three-point bending test was performed on the three ultra-high-strength steel parts to be tested;

[0119] See also Figure 3,The second step is to obtain the load-displacement curve of the ultra-high strength steel part to be tested during the three-point bending process, extract the average value F0 of the maximum load, calculate the area enclosed by the curve and record the energy value E0;

[0120] See also Figure 4 , the third step is to measure the crack length of the ultra-high strength steel parts to be tested after the test and calculate the average value L c0 ;

[0121] The test data are shown in Table 1;

[0122] Step 4: Low temperature dynamic three-point bending test:

[0123] In the first step, the ultra-high strength steel parts to be tested are subjected to dynamic three-point bending tests at -20°C and -40°C, respectively, with temperature compensation of 2°C and 5°C, that is, the actual temperature of the temperature box is set to -22°C and -45°C, respectively. The time for taking the parts out of the temperature box and transferring them to the test bench is less than 5s, and the time from taking the parts out of the temperature box to the end of the test is completed within 15s. Each temperature test is carried out 3 times;

[0124] The second step is to obtain the load-displacement curve of the part during three-point bending, extract the maximum load and calculate the average values ​​F1 and F2, calculate the area enclosed by the curve, record the energy value and calculate the average values ​​E1 and E2;

[0125] The third step is to measure the crack length of the parts after the test and calculate the average value L c1 , L c2 ;

[0126] The test data are shown in Table 1;

[0127] Table 1 Maximum load, energy value and crack length of dynamic three-point bending test of door anti-collision beam

[0128]

[0129] Step 5: Evaluation of low temperature toughness of parts:

[0130] The first step is to calculate the maximum load ratios a1 = F1 / F0, a2 = F2 / F0 at low temperatures of -20°C, -40°C and room temperature, the energy value ratios b1 = E1 / E0, b2 = E2 / E0, and the crack length ratios c1 = L c1 / L c0 、c2=L c2 / L c0 , data are shown in Table 2;

[0131] In the second step, the target values ​​of evaluation indicators a1 and b1 were set to 0.85, and the target values ​​of a2 and b2 were set to 0.70. The calculated values ​​were all higher than the target values, and the part was evaluated as ductile fracture without obvious low-temperature brittleness. The target values ​​of evaluation indicators c1 and c2 were set to 1.15 and 1.30 respectively. The calculated values ​​were all lower than the target values, and the part was evaluated as ductile fracture without obvious low-temperature brittleness.

[0132] Table 2 Calculated values ​​and target values ​​of evaluation indicators

[0133] Evaluation indicators <![CDATA[a1]]> <![CDATA[a2]]> <![CDATA[b1]]> <![CDATA[b2]]> <![CDATA[c1]]> <![CDATA[c2]]> Calculated Value 0.89 0.79 0.86 0.72 1.09 1.18 Target value 0.85 0.70 0.85 0.70 1.15 1.30

[0134] By comparing and evaluating the maximum load, energy values ​​and crack length of ultra-high-strength steel door anti-collision beams obtained by dynamic three-point bending tests at room temperature and low temperature environments, it is concluded that the door anti-collision beam parts have good toughness in low temperature environments, which can effectively predict that the safety performance of the door anti-collision beam parts will not be significantly reduced due to the low temperature environment during a vehicle collision.

[0135] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. A method for evaluating low temperature toughness of ultra-high strength steel parts, characterized in that: The method for evaluating low temperature toughness of ultra-high strength steel parts comprises: Obtain the maximum deformation strain rate of the ultra-high strength steel part to be tested; Performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result; Performing a low-temperature dynamic three-point bending test on the ultra-high-strength steel part to be tested, thereby obtaining a low-temperature test result; Performing low temperature toughness evaluation on the ultra-high strength steel part to be tested according to the room temperature test results and the low temperature test results; Before performing a room temperature dynamic three-point bending test, the method for evaluating low temperature toughness of ultra-high strength steel parts further comprises: Design dynamic three-point bending test parameters; The step of performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result, comprises: Performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested according to the designed dynamic three-point bending test parameters, thereby obtaining a room temperature test result; The step of performing a low temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a low temperature test result, comprises: Performing a low-temperature dynamic three-point bending test on the ultra-high-strength steel part to be tested according to the designed dynamic three-point bending test parameters, thereby obtaining a low-temperature test result; The method of obtaining the maximum deformation strain rate of the ultra-high strength steel part to be tested includes: Extract the maximum deformation strain rate of the ultra-high strength steel parts to be tested in the whole vehicle collision simulation analysis as the maximum strain rate used in the test; The acquisition and design of dynamic three-point bending test parameters includes: Determine the span of the two supporting points of the ultra-high-strength steel part to be tested in the three-point bending test by referring to the assembly relationship of the ultra-high-strength steel part to be tested in the vehicle body; A dynamic three-point bending test model is established, and the drop weight and the drop height of the drop hammer are obtained according to the maximum deformation strain rate of the ultra-high strength steel part to be tested; The step of performing a room temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a room temperature test result, comprises: Under room temperature conditions, a dynamic three-point bending test is performed on the ultra-high strength steel parts to be tested; Obtain the load-displacement curve of the ultra-high strength steel part to be tested during three-point bending; Extracting the maximum load according to the load-displacement curve and calculating the average load at room temperature; According to the load-displacement curve, the area enclosed by the curve is calculated to record the energy value and calculate the average energy value at room temperature; The crack length of the ultra-high strength steel part to be tested is measured after the test and the average value is calculated to obtain the average value of the crack at room temperature; wherein, The low temperature toughness of parts is evaluated by the following method: The first step is to calculate the maximum load ratios a1 and a2, energy value ratios b1 and b2, and crack length ratios c1 and c2 at low temperatures of -20°C and -40°C and room temperature respectively; In the second step, target values ​​of evaluation indicators a1 and b1, and target values ​​of a2 and b2 are set. If the calculated values ​​are all higher than the target values, the part is evaluated as ductile fracture without obvious low-temperature brittleness. Target values ​​of evaluation indicators c1 and c2 are set. If the calculated values ​​are all lower than the target values, the part is evaluated as ductile fracture without obvious low-temperature brittleness.

2. The method for evaluating low temperature toughness of ultra-high strength steel parts according to claim 1, characterized in that: The step of performing a low temperature dynamic three-point bending test on the ultra-high strength steel part to be tested, thereby obtaining a low temperature test result, comprises: The ultra-high strength steel parts to be tested are subjected to two dynamic three-point bending tests at temperatures lower than room temperature, wherein the dynamic three-point bending test at one temperature is called the first low-temperature bending test, and the other is called the second low-temperature bending test; Obtain load-displacement curves of the ultra-high strength steel part to be tested in the three-point bending process in the first low-temperature bending test and the second low-temperature bending test, respectively, wherein the load-displacement curve obtained by the first low-temperature bending test is called the first low-temperature curve, and the other is called the second low-temperature curve; Extracting the maximum load according to the first low temperature curve and calculating the first low temperature load average value; Extract the maximum load according to the second low temperature curve and calculate the second low temperature load average value; According to the first low temperature curve, calculate the area enclosed by the curve, record the energy value and calculate the first low temperature energy average value; According to the second low temperature curve, the area enclosed by the curve is calculated to record the energy value and calculate the second low temperature energy average value; Measuring the crack length of the ultra-high strength steel part to be tested after the first low temperature bending test and calculating the first low temperature crack average value; The crack length of the ultra-high strength steel part to be tested after the second low temperature bending test is measured and the second low temperature crack average value is calculated.

3. The method for evaluating low temperature toughness of ultra-high strength steel parts according to claim 2, characterized in that: When conducting the dynamic three-point bending test at a temperature below room temperature, taking into account the temperature loss of the parts during the test, the temperature compensation is set to 2°C to 6°C lower than the test temperature. The time it takes to remove the parts from the temperature box and transfer them to the test bench is less than 5s, and the time it takes to remove the parts from the temperature box to the end of the test is less than 15s.

4. The method for evaluating low temperature toughness of ultra-high strength steel parts according to claim 3, characterized in that: The low temperature toughness evaluation of the ultra-high strength steel part to be tested according to the room temperature test results and the low temperature test results comprises: Calculate the ratio of the first low-temperature load average value to the room-temperature load average value, which is called the first load ratio; Calculate the ratio of the second low-temperature load average value to the room-temperature load average value, which is called the second load ratio; Calculate the ratio of the first low-temperature energy average value to the room-temperature energy average value, which is called the first energy ratio; Calculate the ratio of the second low temperature energy average value to the room temperature energy average value, which is called the second energy ratio; Calculate the ratio of the first low-temperature crack average to the room-temperature crack average, which is called the first crack ratio; Calculate the ratio of the second low-temperature crack average to the room-temperature crack average, which is called the second crack ratio; The low-temperature toughness of the ultra-high-strength steel part to be tested is determined according to the obtained first load ratio, second load ratio, first energy ratio, second energy ratio, first crack ratio, and second crack ratio.

5. The method for evaluating low temperature toughness of ultra-high strength steel parts according to claim 4, characterized in that: The room temperature is 15°C to 25°C; The temperature in the first low temperature bending test is -20°C; The temperature in the second low-temperature bending test was -40°C.

6. The method for evaluating low temperature toughness of ultra-high strength steel parts according to any one of claims 1 to 5, characterized in that: The ultra-high strength steel part to be tested is a thin plate-shaped ultra-high strength steel part for automobiles.

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