Bainite-based high-strength steel and CTS performance improving method thereof

Abstract

The invention relates to the technical field of high-strength steel welding, and discloses bainite-based high-strength steel and a CTS performance improving method thereof.The bainite-based high-strength steel comprises the steps that spot welding process parameters are set, and welding is conducted; the spot welding process is a three-section spot welding process; wherein the electrode pressure ranges from 4.5 kN to 5.5 kN; according to the technological parameters of the first-section type spot welding, the welding time ranges from 200 ms to 230 ms, the welding current ranges from 2.5 kA to 3.5 kA, and the cooling time ranges from 100 ms to 200 ms; according to the technological parameters of the second-stage spot welding, the welding time ranges from 400 ms to 520 ms, the welding current ranges from 7.0 kA to 12.0 kA, and the cooling time ranges from 500 ms to 800 ms; according to the technological parameters of the three-section type spot welding, the welding time ranges from 200 ms to 300 ms, and the welding current ranges from 3.5 kA to 6.5 kA. A three-section spot welding process is adopted, the effect of improving the CTS performance of a spot-welded joint is achieved, and the spot welding problem of bainite-based high-strength steel is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-strength steel welding, and particularly to a bainite-based high-strength steel and a method for improving its CTS performance. Background Art

[0002] In the automotive industry, spot welding is the most widely used welding method. However, the high alloy element content in high-strength steel has a great impact on its weldability, and the spot welding performance of high-strength steel has become one of the factors restricting its development.

[0003] For the performance of high-strength steel solder joints, the tensile strength of the solder joints is an important index, which is usually evaluated by TSS (tensile shear strength) and CTS (cross tensile strength). TSS refers to the anti-tensile shear force measured by applying a tensile load in the shear direction of the solder joint, and CTS refers to the cross tensile force measured by applying a tensile load in the peeling direction of the solder joint. The measurement methods are specified in JIS Z 3136 and JIS Z 3137 standards.

[0004] The patent document with the application publication number CN112247332A discloses "a resistance spot welding method for ultra-high-strength hot-formed steel plates". This invention welds ultra-high-strength hot-formed steel plates with a carbon content ≥ 0.33 wt% and a tensile strength ≥ 1800 MPa, and adopts a four-stage spot welding process to achieve the purpose of improving the CTS strength. The material in this method is hot-formed steel, and its structure is martensite, which is quite different from the present invention in terms of material, and the specific process is also significantly different.

[0005] The patent document with the application publication number CN108136535A discloses a "spot welding joint and spot welding method". This invention provides a spot welding joint and its welding method that can obtain high CTS even when including more than 1 high-strength steel plate. At least 1 of the multiple steel plates used is a high-strength steel plate with a tensile strength of 750 MPa to 2500 MPa. By controlling the heat input, the effect of regulating the structure is achieved, and thus the CTS strength is improved, but the spot welding process is not described.

[0006] The patent document with the application publication number CN112338334A discloses a "resistance spot welding joint of aluminum materials". This invention is a resistance spot welding joint of aluminum materials with a weld nugget shape capable of reducing the CTS strength deviation, and a resistance spot welding joint of aluminum materials formed by overlapping multiple aluminum materials for resistance spot welding. By regulating the pores of the spot welding joint, the effect of improving the CTS performance is achieved, and the material and process are quite different from the present invention. Summary of the Invention

[0007] The object of the present invention is to provide a method for improving the CTS performance of bainite-based high-strength steel. The CTS (cross tensile strength) performance is an index used in materials science and engineering to evaluate the strength performance of the spot weld joints of materials under tensile loads. The larger the CTS, the stronger the tensile capacity of the material or joint in the direction perpendicular to the joint surface, indicating better safety performance of the solder joints and a more stable overall structure. The present invention adopts a three-stage spot welding process to achieve the effect of improving the CTS performance of the spot weld joints, which has great popularization and application value in the automotive manufacturing industry. To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a method for improving the CTS performance of bainite-based high-strength steel, and the method includes the following steps:

[0009] Set the spot welding process parameters and perform welding; the spot welding process is a three-stage spot welding process; wherein,

[0010] The electrode pressure of the three-stage spot welding process is 4.5 - 5.5 kN;

[0011] The process parameters of the first-stage spot welding process include: welding time 200 - 230 ms, welding current 2.5 - 3.5 kA, cooling time 100 - 200 ms;

[0012] The process parameters of the second-stage spot welding process include: welding time 400 - 520 ms, welding current 7.0 - 12.0 kA, cooling time 500 - 800 ms;

[0013] The process parameters of the third-stage spot welding process include: welding time 200 - 300 ms, welding current 3.5 - 6.5 kA.

[0014] Furthermore, the method further includes the following steps:

[0015] Cut the bainite-based high-strength steel into CTS specimens;

[0016] Vertically lap two of the CTS specimens and place them between the spot welding electrodes.

[0017] Furthermore, the electrode is a chromium zirconium copper spherical electrode with an end face diameter of 6.0 - 8.0 mm.

[0018] Furthermore, the method further includes the following steps:

[0019] Use a tensile testing machine to detect the CTS performance of the CTS specimens after welding.

[0020] Furthermore, the detection speed of the tensile testing machine is 0.1 - 0.5 mm / s.

[0021] The present invention also provides a bainite-based high-strength steel. In terms of mass percentage, the chemical composition and content of the bainite-based high-strength steel include:

[0022] C: 0.14% - 0.23%, Si: 0.90% - 1.55%, Mn: 1.50% - 2.80%, Als: 0.01% - 0.15%, Cr: 0.08% - 0.70%, Nb+Ti: 0.02 - 0.20%, P≤0.009%, S≤0.009%, N≤0.0065%, and the remaining elements are Fe and inevitable impurities.

[0023] Furthermore, in terms of mass percentage, the chemical composition and content of the bainite-based high-strength steel include:

[0024] C: 0.20%, Si: 1.34%, Mn: 1.78%, Als: 0.08%, Cr: 0.48%, Nb+Ti: 0.12%, P: 0.005%, S: 0.006%, N: 0.004%, and the remaining elements are Fe and inevitable impurities.

[0025] Furthermore, the microstructure of the bainite-based high-strength steel consists of 70% - 90% bainite, 5% - 10% martensite, and 2% - 8% retained austenite.

[0026] Furthermore, the microstructure of the bainite-based high-strength steel consists of 87% bainite, 8% martensite, and 5% retained austenite.

[0027] Furthermore, the yield strength of the bainite-based high-strength steel is 860 - 930 MPa, the tensile strength is 1180 - 1250 MPa, the elongation at break A 50 value is 15% - 24%, the hole expansion rate is 26% - 37%, and the CTS strength is 7.0 - 13.0 kN.

[0028] Technical effects and advantages of the present invention:

[0029] 1. In the three-stage spot welding process of the present invention, the welding time of each stage is relatively long. Increasing the welding time of each stage can effectively eliminate the shrinkage cavity defect of the spot welding joint, promote the diffusion of the composition in the fusion zone, and eliminate segregation.

[0030] 2. The cooling time in the second-stage spot welding process of the present invention is relatively long. Increasing the cooling time of the second-stage process can effectively eliminate the tensile stress brought to the fusion zone when the electrode relaxes, reduce the tissue stress between the lath martensites in the fusion zone, and thus improve the CTS performance of the spot welding joint.

[0031] 3. The present invention solves the spot welding problem of the bainite-based high-strength steel from the perspective of the spot welding process, which is of great significance for the popularization and application of the product.

[0032] Other features and advantages of the present invention will be described in the following specification, and, in part, will be apparent from the specification or learned by practicing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structure pointed out in the specification and the drawings. Brief Description of the Drawings

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 Microstructure diagram of the bainite-based high-strength steel provided by the present invention;

[0035] Figure 2 Flowchart of a method for improving the CTS performance of a bainite-based high-strength steel provided by the present invention. Detailed Description of the Embodiments

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0037] The flowchart shown in the drawings is only an exemplary illustration and does not necessarily include all steps. For example, some steps can be decomposed, while some steps can be combined or partially combined. Therefore, the actual execution order may change according to the actual situation.

[0038] The terms "first", "second", etc. in the specification, claims and drawings of the present application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here.

[0039] In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or sub-modules does not necessarily have to be limited to those clearly listed steps or sub-modules, but may include other steps or sub-modules not clearly listed or inherent to these processes, methods, products or devices.

[0040] To solve the deficiencies of the prior art, the present invention discloses a bainite-based high-strength steel. In terms of mass percentage content, its chemical composition and content include: C: 0.14% - 0.23%, Si: 0.90% - 1.55%, Mn: 1.50% - 2.80%, Als (acid-soluble aluminum content in the steel): 0.01% - 0.15%, Cr: 0.08% - 0.70%, Nb + Ti: 0.02 - 0.20%, P ≤ 0.009%, S ≤ 0.009%, N ≤ 0.0065%, and the remaining elements are Fe and inevitable impurities. Preferably, the chemical composition and content include: C: 0.20%, Si: 1.34%, Mn: 1.78%, Als: 0.08%, Cr: 0.48%, Nb + Ti: 0.12%, P: 0.005%, S: 0.006%, N: 0.004%, and the remaining elements are Fe and inevitable impurities.

[0041] The above bainite-based high-strength steel is obtained through smelting process, continuous casting process, hot rolling process, pickling and cold rolling process, and continuous annealing process. Figure 1 This is the micrograph of the bainite-based high-strength steel of the present invention, as Figure 1 shown, its microstructure is composed of 70% - 90% bainite, 5% - 10% martensite, and 2% - 8% retained austenite. Preferably, it is composed of 87% bainite, 8% martensite, and 5% retained austenite.

[0042] The yield strength of the described bainite-based high-strength steel is 860 - 930 MPa, the tensile strength is 1180 - 1250 MPa, the elongation rate A 50 value is 15% - 24%, and the hole expansion rate is 26% - 37%. Preferably, the yield strength is 886 MPa, the tensile strength is 1220 MPa, and the elongation rate A 50 value is 18.5%, and the hole expansion rate is 32.2%.

[0043] When the described bainite-based high-strength steel adopts a one-stage spot welding process, the maximum CTS strength is 5.68 kN without spattering. To improve its CTS performance, the present invention also discloses a method for improving the CTS strength of the bainite-based high-strength steel, that is, adopting a three-stage spot welding process with a large welding time. Figure 2 This is the flow chart of the method for improving the CTS performance of the bainite-based high-strength steel provided by the present invention, as Figure 2 shown, the specific method includes the following steps:

[0044] Step S1: Select a bainite-based high-strength steel with a predetermined composition and cut it into a CTS specimen of 50×150 mm.

[0045] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium zirconium copper spherical electrodes with an end face diameter of 6.0 - 8.0 mm, preferably 6.0 mm;

[0046] Step S3: Set the spot welding process parameters and perform welding;

[0047] In step S3 of the present invention, the spot welding process is a three - stage spot welding process; further, the electrode pressure of the three - stage spot welding process is 4.5 - 5.5 kN; among them,

[0048] The parameters of the first - stage spot welding process include: welding time 200 - 230 ms, welding current 2.5 - 3.5 kA, cooling time 100 - 200 ms; the function of the first - stage spot welding process is to eliminate surface gaps and surface oxides, avoid excessive local heating and spatter caused by too large contact resistance, stabilize the contact resistance, reduce deformation, and initially form a fusion nucleus;

[0049] The parameters of the second - stage spot welding process include: welding time 400 - 520 ms, welding current 7.0 - 12.0 kA, cooling time 500 - 800 ms; the function of the second - stage spot welding process is to promote the growth of the fusion nucleus. The relatively long time in this stage is to control the growth rate of the fusion nucleus, eliminate shrinkage holes and crack defects caused by too large a growth rate of the fusion nucleus, promote the diffusion of the composition in the fusion nucleus area, and eliminate segregation. The relatively large welding current is to enable the fusion nucleus to obtain sufficient energy to ensure its growth to a certain size, thereby increasing the cross - sectional area of the spot weld joint and further improving the mechanical properties of the spot weld joint. The relatively long cooling time is to cool the fusion nucleus under slow conditions, eliminate the tensile stress brought to the fusion nucleus area when the electrode relaxes, reduce the tissue stress between the lath martensites in the fusion nucleus area, and thus improve the CTS performance of the spot weld joint;

[0050] The parameters of the third - stage spot welding process include: welding time 200 - 300 ms, welding current 3.5 - 6.5 kA; the function of the third - stage spot welding process is to perform tempering treatment on the fusion nucleus. The purpose is to improve the microstructure, transform martensite into tempered martensite or bainite with better toughness, reduce residual stress, reduce crack tendency, improve the toughness of the spot weld joint, and improve the dynamic load performance of the joint.

[0051] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.1 - 0.5 mm / s, preferably 0.2 mm / s.

[0052] The following further illustrates the technical solutions of the present application with specific examples and comparative examples.

[0053] Example 1:

[0054] Example 1 of the present invention provides a method for improving the CTS strength of a bainite-based high-strength steel, and the method includes the following steps:

[0055] Step S1: Select a bainite-based high-strength steel with a predetermined composition and cut it into a CTS specimen of 50×150 mm;

[0056] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium-zirconium-copper spherical electrodes with an end face diameter of 6.0 mm;

[0057] Step S3: Set the spot welding process parameters and perform welding;

[0058] In step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 4.5 kN; among them,

[0059] The parameters of the first-stage spot welding process include: welding time 230 ms, welding current 2.5 kA, and cooling time 100 ms;

[0060] The parameters of the second-stage spot welding process include: welding time 520 ms, welding current 7.0 kA, and cooling time 600 ms;

[0061] The parameters of the third-stage spot welding process include: welding time 300 ms, welding current 3.5 kA.

[0062] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 7.88 kN, the second test result is 7.72 kN, the third test result is 7.83 kN, and the average value of the three test results is 7.81 kN.

[0063] Example 2:

[0064] Example 2 of the present invention provides a method for improving the CTS strength of a bainite-based high-strength steel, and the method includes the following steps:

[0065] Step S1: Select a bainite-based high-strength steel with a predetermined composition and cut it into a CTS specimen of 50×150 mm;

[0066] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium-zirconium-copper spherical electrodes with an end face diameter of 6.0 mm;

[0067] Step S3: Set the spot welding process parameters and perform welding;

[0068] In step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 5.0 kN; among them,

[0069] The process parameters of the first-stage spot welding include: welding time 210 ms, welding current 3.0 kA, and cooling time 150 ms;

[0070] The process parameters of the second-stage spot welding include: welding time 440 ms, welding current 8.0 kA, and cooling time 800 ms;

[0071] The process parameters of the third-stage spot welding include: welding time 260 ms, welding current 5.0 kA.

[0072] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 8.35 kN, the second test result is 8.51 kN, the third test result is 8.45 kN, and the average value of the three test results is 8.44 kN.

[0073] Example 3:

[0074] Example 3 of the present invention provides a method for improving the CTS strength of bainite-based high-strength steel, and the method includes the following steps:

[0075] Step S1: Select bainite-based high-strength steel with a predetermined composition and cut it into CTS specimens of 50×150 mm;

[0076] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium zirconium copper spherical electrodes with an end face diameter of 6.0 mm;

[0077] Step S3: Set the spot welding process parameters and perform welding;

[0078] In step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 5.5 kN; among them,

[0079] The process parameters of the first-stage spot welding include: welding time 200 ms, welding current 3.5 kA, and cooling time 200 ms;

[0080] The process parameters of the second-stage spot welding include: welding time 400 ms, welding current 10.0 kA, and cooling time 500 ms;

[0081] The process parameters of the third-stage spot welding include: welding time 200 ms, welding current 6.5 kA.

[0082] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 9.24 kN, the second test result is 9.15 kN, the third test result is 9.18 kN, and the average value of the three test results is 9.19 kN.

[0083] Example 4:

[0084] Example 4 of the present invention provides a method for improving the CTS strength of a bainite-based high-strength steel, and the method includes the following steps:

[0085] Step S1: Select a bainite-based high-strength steel with a predetermined composition and cut it into a CTS specimen of 50×150 mm;

[0086] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium-zirconium-copper spherical electrodes with an end face diameter of 6.0 mm;

[0087] Step S3: Set spot welding process parameters and perform welding;

[0088] In step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 5.2 kN; among them,

[0089] The parameters of the first-stage spot welding process include: welding time 220 ms, welding current 3.3 kA, and cooling time 180 ms;

[0090] The parameters of the second-stage spot welding process include: welding time 480 ms, welding current 11.0 kA, and cooling time 700 ms;

[0091] The parameters of the third-stage spot welding process include: welding time 280 ms, welding current 5.5 kA.

[0092] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 11.38 kN, the second test result is 11.26 kN, the third test result is 11.29 kN, and the average value of the three test results is 11.31 kN.

[0093] Example 5:

[0094] Example 5 of the present invention provides a method for improving the CTS strength of a bainite-based high-strength steel, and the method includes the following steps:

[0095] Step S1: Select a bainite-based high-strength steel with a predetermined composition and cut it into a CTS specimen of 50×150 mm;

[0096] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium-zirconium-copper spherical electrodes with an end face diameter of 6.0 mm;

[0097] Step S3: Set spot welding process parameters and perform welding;

[0098] In step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 4.8 kN; among them,

[0099] The parameters of the first-stage spot welding process include: welding time 220 ms, welding current 3.4 kA, cooling time 200 ms;

[0100] The parameters of the second-stage spot welding process include: welding time 500 ms, welding current 12.0 kA, cooling time 750 ms;

[0101] The parameters of the third-stage spot welding process include: welding time 290 ms, welding current 6.0 kA.

[0102] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 12.20 kN, the second test result is 12.35 kN, the third test result is 12.28 kN, and the average value of the three test results is 12.27 kN.

[0103] Comparative example 1:

[0104] Comparative example 1 of the present invention provides a method for improving the CTS strength of bainite-based high-strength steel, and the method includes the following steps:

[0105] Step S1: Select bainite-based high-strength steel with a predetermined composition and cut it into CTS specimens of 50×150 mm;

[0106] Step S2: Vertically lap two CTS specimens and place them between the spot welding electrodes. The electrodes are chromium-zirconium-copper spherical electrodes with an end face diameter of 6.0 mm;

[0107] Step S3: Set the spot welding process parameters and perform welding;

[0108] In step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 5.5 kN; among them,

[0109] The parameters of the first-stage spot welding process include: welding time 180 ms, welding current 3.5 kA, cooling time 80 ms;

[0110] The parameters of the second-stage spot welding process include: welding time 350 ms, welding current 5.0 kA, cooling time 400 ms;

[0111] The parameters of the third-stage spot welding process include: welding time 100 ms, welding current 2.0 kA.

[0112] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 5.38 kN, the second test result is 5.35 kN, the third test result is 5.24 kN, and the average of the three test results is 5.32 kN.

[0113] Comparative Example 2:

[0114] Comparative Example 2 of the present invention provides a method for improving the CTS strength of bainite-based high-strength steel. The method includes the following steps:

[0115] Step S1: Select bainite-based high-strength steel with a predetermined composition and cut it into CTS specimens of 50×150 mm.

[0116] Step S2: Vertically lap two CTS specimens and place them between spot welding electrodes. The electrodes are chromium zirconium copper spherical electrodes with an end face diameter of 6.0 mm.

[0117] Step S3: Set the spot welding process parameters and perform welding.

[0118] In Step S3 of the present invention, the spot welding process is a three-stage spot welding process; further, the electrode pressure of the three-stage spot welding process is 6.0 kN; among them,

[0119] The parameters of the first-stage spot welding process include: welding time 240 ms, welding current 3.5 kA, cooling time 220 ms;

[0120] The parameters of the second-stage spot welding process include: welding time 300 ms, welding current 12.5 kA, cooling time 300 ms;

[0121] The parameters of the third-stage spot welding process include: welding time 350 ms, welding current 6.0 kA.

[0122] Step S4: Use a tensile testing machine to detect the CTS performance at a speed of 0.2 mm / s. The first test result is 5.96 kN, the second test result is 5.74 kN, the third test result is 5.82 kN, and the average of the three test results is 5.84 kN.

[0123] The spot welding processes and CTS performance test results of the examples and comparative examples of the present invention are summarized in Table 1-4 below. From the results, it can be seen that the present invention adopts a three-stage spot welding process, in which the welding time in each stage process is relatively large, the cooling time in the second-stage process is relatively large, and the cooling time does not need to be set in the third-stage process, and the highest CTS performance is increased by nearly 2 times.

[0124] Table 1 Spot welding process of the example

[0125]

[0126] Table 2 CTS performance of the examples

[0127]

[0128] Table 3 Resistance spot welding process of the comparative examples

[0129]

[0130] Table 4 CTS performance of the comparative examples

[0131]

[0132]

[0133] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the CTS performance of bainite-based high-strength steel, characterized in that: The method comprises the following steps: Set the spot welding process parameters and perform welding; the spot welding process is a three-stage spot welding process; wherein, The electrode pressure of the three-stage spot welding process is 4.5-5.5 kN; The first stage spot welding process parameters include: welding time 200-230ms, welding current 2.5-3.5kA, cooling time 100-200ms; The second stage spot welding process parameters include: welding time 400-520ms, welding current 7.0-12.0kA, cooling time 500-800ms; The third-stage spot welding process parameters include: welding time 200-300ms, welding current 3.5-6.5kA.

2. The method for improving the CTS performance of bainite-based high-strength steel according to claim 1, characterized in that: The method further comprises the steps of: The bainite-based high-strength steel was cut into CTS specimens; Two CTS specimens were overlapped vertically and placed between spot welding electrodes.

3. The method for improving the CTS performance of bainite-based high-strength steel according to claim 2, characterized in that: The electrode is a chromium-zirconium-copper spherical electrode with an end face diameter of 6.0 to 8.0 mm.

4. The method for improving the CTS performance of bainite-based high-strength steel according to claim 1, characterized in that: The method further comprises the steps of: The CTS properties of the CTS specimens after welding were tested using a tensile testing machine.

5. The method for improving the CTS performance of bainite-based high-strength steel according to claim 4, characterized in that: The detection speed of the tensile testing machine is 0.1-0.5 mm / s.

6. A bainite-based high-strength steel, wherein the CTS performance thereof is improved by the method according to any one of claims 1 to 5, characterized in that, in terms of mass percentage, the chemical composition and content of the bainite-based high-strength steel include: C: 0.14%~0.23%, Si: 0.90%~1.55%, Mn: 1.50%~2.80%, Als: 0.01%~0.15%, Cr: 0.08%~0.70%, Nb+Ti: 0.02~0.20%, P≤0.009%, S≤0.009%, N≤0.0065%, and the remaining elements are Fe and unavoidable impurities.

7. The bainite-based high-strength steel according to claim 6, characterized in that: The chemical composition and content of the bainite-based high-strength steel include, in terms of mass percentage: C: 0.20%, Si: 1.34%, Mn: 1.78%, Als: 0.08%, Cr: 0.48%, Nb+Ti: 0.12%, P: 0.005%, S: 0.006%, N: 0.004%, and the remaining elements are Fe and inevitable impurities.

8. The bainite-based high-strength steel according to claim 6, characterized in that: The microstructure of the bainite-based high-strength steel consists of 70% to 90% bainite, 5% to 10% martensite and 2% to 8% residual austenite.

9. The bainite-based high-strength steel according to claim 7, characterized in that: The microstructure of the bainite-based high-strength steel consists of 87% bainite, 8% martensite and 5% retained austenite.

10. The bainite-based high-strength steel according to claim 6, characterized in that: The yield strength of the bainite-based high-strength steel is 860-930 MPa, the tensile strength is 1180-1250 MPa, and the elongation A 50 The value is 15%~24%, the hole expansion rate is 26%~37%, and the CTS strength is 7.0~13.0kN.

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