Method for determining a high-performance and preheat-free welding process for steel for ocean engineering

Abstract

Provided is a method for determining a high-performance preheat-free welding process for steel for ocean engineering. 【Solution means】Steps of obtaining a first low-temperature cracking susceptibility index, a critical restraint distance and a critical restraint degree of a base metal test piece, obtaining the minimum diffusible hydrogen content of a welding material, and selecting an actual welding material based on the minimum diffusible hydrogen content; optimizing the carbon equivalent based on the low-temperature cracking susceptibility coefficient of the base metal test piece to obtain a new base metal; obtaining a second low-temperature cracking susceptibility index smaller than the first low-temperature cracking susceptibility index, and using the new base metal corresponding to this susceptibility index as the actual base metal; the time t required for the post-weld peak temperature of the actual welding material and the actual base metal at different welding heat inputs to cool to 100 °C 100 and the critical cooling time t of the welded joint cr are obtained, and t 100 and t cr The welding heat input when the difference is the largest is used as the actual welding heat input.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and specifically relates to a method for determining a high-performance preheating-free welding process for steel used in ocean engineering.

Background Art

[0002] When constructing ocean facilities in a specific sea area, the environmental temperature may reach -5 to 20 °C, and the problem of cold cracking in welding construction becomes very prominent. The hysteresis of cold cracking is particularly harmful and poses a great hidden danger to the safety of ocean engineering structures. Welding preheating can provide temperature and time conditions for the diffusion and escape of hydrogen, appropriately improve the structure, reduce the hardenability, and reduce the residual stress to a certain extent. Currently, for welding processes in a low-temperature environment, in order to eliminate the influence of cold cracking, it is necessary to perform pre-welding heat treatment. However, in a thick and complex structure, it is difficult to preheat the entire structure in actual production, or there are no pre-welding heat treatment conditions at the construction site facilities. In the conventional preheating-free welding process, measures are mainly taken to design an under-matching weld joint to reduce the tendency of cold cracking, but this causes the problem of reducing the load-bearing capacity of the joint.

[0003] Chinese Patent CN117778898A discloses a steel for high-performance marine engineering and its manufacturing method, which can achieve welding without preheating at room temperature. However, since it is necessary to manufacture a dedicated welding wire and dedicated steel materials to achieve welding without preheating, there are limitations in application and it cannot be applied to various welding scenarios. Many of the welding processes without preheating avoid the occurrence of low-temperature cracking in the welded joint by selecting and welding under-matching welding materials. Chinese Patent CN117226213A discloses an arc welding process for a steel for marine corrosion resistance with a yield strength of 420 MPa grade. In this patent, the welding parameters are continuously tried through orthogonal tests to obtain a process for realizing welding without preheating for the steel at room temperature, but it has the disadvantages of high cost, long test time, and low efficiency. In the prior art, the methods for realizing welding without preheating have poor versatility, and the welding process is often developed through a limited number of large-scale repeated trials and does not have a complete quantitative analysis theoretical system. Therefore, in order to meet the efficient manufacturing needs of large marine engineering facilities such as deep-water jacket platforms in extreme environments and improve the welding efficiency, it is urgent to obtain a method for realizing a high-performance welding process without preheating in a low-temperature environment for marine engineering steel of 420 MPa grade thick plate.

Summary of the Invention

[0004] In view of the deficiencies of the prior art, the object of the present invention is to provide a method for determining a high-performance welding process without preheating for steel for marine engineering, so as to solve the problems of low efficiency and poor versatility of the conventional welding process development method.

[0005] To achieve the above object, according to the present invention, there is provided a method for determining a high-performance welding process without preheating for steel for marine engineering, including the following S1 to S6: S1: Obtain the first low-temperature cracking susceptibility index required for welding without preheating at a specific temperature, S2: The critical restraint distance L of the base metal test piece at the specific temperature cr and the critical restraint degree R crObtain, based on the first low-temperature cracking susceptibility index, the minimum diffusible hydrogen content [H] of the welding consumable required for welding without preheating cr Obtain [H] cr Based on this, select the actual welding consumable, S3: Optimize the carbon equivalent according to the low-temperature cracking susceptibility coefficient of the base metal test piece to obtain a new base metal, S4: Based on the minimum diffusible hydrogen content [H] cr , the critical restraint degree R cr and the low-temperature cracking susceptibility coefficient of the new base metal, obtain the second low-temperature cracking susceptibility index corresponding to the new base metal, S5: Determination of the actual base metal: If the second low-temperature cracking susceptibility index is smaller than the first low-temperature cracking susceptibility index, use the new base metal corresponding to the second low-temperature cracking susceptibility index as the actual base metal. If the second low-temperature cracking susceptibility index is greater than or equal to the first low-temperature cracking susceptibility index, repeat steps S3 - S5 until the second low-temperature cracking susceptibility index is lower than the first low-temperature cracking susceptibility index, S6: Obtain the time t required for the post-weld peak temperature of the actual welding consumable and the actual base metal under different welding heat inputs to cool to 100°C, 100 Based on t 100 obtain the critical cooling time t of the welded joint, cr Based on t 100 and t cr A method is provided in which the welding heat input E corresponding to the maximum difference between them is used as the actual welding heat input.

[0006] In the present invention, the adjustment of the base metal chemical composition, the diffusible hydrogen content of the welding consumable, and the influence of the welding heat input on the low-temperature cracking of the welded joint are comprehensively considered. A complete quantitative analysis theory system is used to realize the development of a welding process without preheating for steel materials such as marine engineering steel of 420 MPa grade thick plates under various low-temperature environments. The development process is simple, has high versatility for the environment, and a welding process without preheating can be obtained in various temperature environments. The welded joint obtained by actual welding using the obtained welding process has excellent performance.

[0007] Furthermore, in step S6, a double-ellipsoid heat source model is selected, and the heat input during welding is changed by varying the magnitude of the welding current. The double-ellipsoid heat source model has the advantages of high simulation accuracy, high flexibility, high efficiency, a wide range of applications, and can be applied to various welding process types.

[0008] Furthermore, when the welding current gradually increases within the range of 140 A to 190 A, the stability of the molten pool increases, and arc drift and instability due to insufficient current are reduced. If the welding current is less than 140 A, there is a problem that the welded part cannot be completely melted. If the welding current exceeds 190 A, defects such as welding undercut and melting may occur.

[0009] Furthermore, the welding current sequentially increases with a gradient value of 5 A

[0010] Furthermore, in step S2, the critical restraint distance L cr and the critical restraint degree R cr are obtained through a rigid restraint welding crack test. The test equipment is pre-cooled to a specific temperature before the test, and the environmental humidity is the same during each rigid restraint welding crack test.

[0011] Furthermore, in step S2, the welding end of the base metal test piece is processed into an inclined Y groove, and the angle of the groove is 60° or less.

[0012] Furthermore, the root distance between the welding ends of the base metal test piece is 1 mm to 2 mm.

[0013] Furthermore, in step S2, the minimum diffusible hydrogen content is obtained by gas chromatography. The inner diameter of the column used is 4 mm or more. When obtaining the minimum diffusible hydrogen content by gas chromatography, the carrier gas is argon gas with a concentration of 99.9% or more, and the flow rate of the argon gas carrier gas is 20 ml / min to 40 ml / min. By setting this flow rate range, the separation efficiency and analysis speed of the welding test piece in the column are increased.

[0014] Furthermore, after step S6, an inclined Y-groove weld crack test is performed using the actual welding material, actual base material, and actual heat input obtained in steps S1 - S6. During the inclined Y-groove weld crack test, double-sided welding is employed for the restraint welding part.

[0015] Furthermore, in the inclined Y-groove weld crack test, the angular deformation of the actual base material is controlled within 5°.

[0016] The technical means of the present invention have the following beneficial effects compared with the prior art. (1) In the present invention, in view of the fact that the conventional welding process without preheating is only applicable to the room temperature environment, a method for developing a welding process without preheating in a low temperature environment is provided. This method efficiently develops a high-performance welding process without preheating for various types of marine engineering steels in various low temperature environments by means of a complete quantitative analysis theoretical system. Specifically, a low temperature crack susceptibility index capable of realizing welding without preheating at a specific temperature is obtained, the critical restraint degree is measured by a restraint weld crack test with adjustable rigidity, the carbon equivalent of the base material, the diffusible hydrogen content of the welding material, and the actual restraint state of the welded joint are fully considered, the low temperature crack susceptibility of the marine engineering steel during welding is quantitatively evaluated, and then the welding material is optimized by restricting the diffusible hydrogen content of the welding material, and the base material is optimized based on the low temperature crack susceptibility coefficient related to the composition of the base material, so that the chemical composition of the base material, the diffusible hydrogen content of the welding material, and the restraint degree of the welded joint can meet the low temperature crack susceptibility index for realizing welding without preheating. Furthermore, numerical simulation calculations are performed on the butt welded joints at different heat inputs, and the optimum heat input is selected based on the determination formula of the critical cooling time t cr of the low alloy high strength steel.

[0017] (2) In the present invention, by comprehensively considering the effects of the base metal chemical composition, the diffusible hydrogen content of the welding material, and the welding heat input on the low-temperature cracking of the welded joint, the development of a welding process without preheating for steel materials such as 420 MPa grade marine engineering steel for thick plates under various low-temperature environments is realized by the above complete quantitative analysis theory system. The development process of the welding process is relatively simple, there is no need to conduct orthogonal tests, the acquisition method has higher applicability to various welding environments, and in actual welding, welding can be carried out using a welding material with matching strength (equivalent strength), and the comprehensive performance of the welded joint is better.

[0018] (3) In the present invention, when simulating with different welding heat inputs, a current gradient is provided to change the welding heat input, and the welding current is gradually increased within the range of 140 A to 190 A, so that the stability of the molten pool is increased, and the arc drift and instability due to insufficient current are reduced. When the welding current is less than 140 A, there is a problem that the welded part cannot be completely melted. When the welding current exceeds 190 A, defects such as welding undercut and melting drop may occur.

[0019] (4) In the present invention, the argon gas used in gas chromatography has a large relative molecular weight and a small thermal conductivity coefficient, so that the purity of the sample, the accuracy of the analysis result, the stability of the baseline, and the sensitivity of the measuring instrument in the analysis process are ensured. Within the planned flow rate range, the separation efficiency and analysis speed of the welding sample in a column of 4 mm or more are higher.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

[0021] In all the drawings, the same elements or structures are denoted by the same reference numerals. 1 - movable end, 2 - test welding part, 3 - fixed end.

Best Mode for Carrying Out the Invention

[0022] In order to more clearly illustrate the object, technical means and advantages of the present invention, the present invention will be described in more detail below with reference to the drawings and embodiments. It should be noted that the specific embodiments described in this specification are only for interpreting the present invention and do not limit the present invention.

[0023] The term "and / or" in this specification is used to describe the relationship between related objects, and there may be three types of relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In this specification, the symbol " / " indicates that there is an "or" relationship between related objects. For example, A / B indicates A or B.

[0024] The terms "first", "second", etc. in this specification and the claims are for distinguishing different objects and not for explaining a specific order of the objects. For example, the first response message and the second response message are used to distinguish different response messages and not a specific order for describing the response messages.

[0025] In the embodiments of the present invention, terms such as "exemplary" or "for example" are used for the purpose of example, illustration or explanation. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present invention should not be construed as being more preferred or superior to other embodiments or designs. Specifically speaking, the use of terms such as "exemplary" or "for example" is intended to specifically present related concepts.

[0026] In the description of the embodiments of the present invention, unless otherwise specified, the meaning of "a plurality" refers to two or more. For example, a plurality of processing units refers to two or more processing units, and a plurality of elements refers to two or more elements, etc.

[0027] Example 1 This example provides a method for determining a high-performance preheat-free welding process for steel used in ocean engineering. As shown in FIG. 1, this method includes the following steps. S1: Obtain the first low-temperature cracking susceptibility index required for preheat-free welding at a specific temperature. Specifically, based on the ambient temperature T0, according to the following preheat temperature determination formula, the low-temperature cracking susceptibility index P w for realizing preheat-free welding in a low-temperature environment is obtained.

Equation

[0028] S2: Obtain the critical restraint distance L cr and the critical restraint degree R cr of the base metal test piece at a specific temperature, obtain the minimum diffusible hydrogen content [H] of the welding material required for preheat-free welding based on the first low-temperature cracking susceptibility index, and select the actual welding material based on [H]. cr cr

[0029] Specifically, design and process a special inclined Y-groove test piece, and perform a rigid restraint welding crack test at a predetermined ambient temperature to obtain the critical restraint distance L cr and the critical restraint degree R cr corresponding to the cases where cracks occur and do not occur in the test piece.

[0030] ​​In the rigid restraint welding crack test, the type of welding method selected is consistent with the welding process to be developed. In this embodiment, various welding processes such as shielded metal arc welding (SMAW), flux-cored wire gas shielded welding, and gas metal arc welding can be developed. Also, the type of welding consumable is consistent with the welding method, for example, the welding rod, flux-cored wire, solid wire, etc. corresponding to each welding method. The type of shielding gas can be determined according to the welding consumable obtained. The size of the test weld and the shape of the groove use a bevel Y-groove. To ensure the accuracy of the results, it is necessary to pre-cool the test equipment to a specific temperature before the test.

[0031] Furthermore, the environmental humidity during each rigid restraint welding crack test is the same.

[0032] In this embodiment, the welding parameters of the rigid restraint welding crack test are designed as follows. 1. In shielded metal arc welding, a 4.0 mm welding rod is used, the welding current is 170 A, and the welding speed is 150 mm / min. 2. In gas metal arc welding, a 1.2 mm welding wire is used. When CO2 is used as the shielding gas, the welding current is 200 A and the welding speed is 190 mm / min. When a mixed gas of 80% Ar and 20% CO2 is used as the shielding gas, the welding current is 270 A and the welding speed is 400 mm / min. 3. In flux-cored wire gas shielded welding, the welding current is 280 A and the welding speed is 350 mm / min.

[0033] The selected restraint distance starts from 1.60 mm. In the rigid restraint welding crack test, when cracks occur on the surface or cross-section of the test weld, the restraint distance is increased, and when there are no cracks on the surface and cross-section, the restraint distance is decreased. In this embodiment, the finally measured critical restraint distance was 50 mm.

[0034] After that, based on the following high-strength steel welding low-temperature cracking susceptibility index formula, the minimum diffusible hydrogen content [H] in the weld metal that can achieve welding without preheating is measured by the method for measuring diffusible hydrogen in weld metal described in "Method for Measuring Diffusible Hydrogen in Weld Metal (GB / T 3965-2012)". cr is obtained.

Number

[0035] In this example, the minimum diffusible hydrogen content is obtained by gas chromatography. The inner diameter of the column used is 4 mm or more, for example, 4 mm, 4.6 mm, 5 mm, etc. If it is less than 4 mm, it is difficult to achieve the optimal separation efficiency.

[0036] In this example, when obtaining the minimum diffusible hydrogen content by gas chromatography, the concentration of the carrier gas is argon gas of 99.9% or more, and the flow rate of the carrier gas of argon gas is 20 ml / min.

[0037] In this example, based on the obtained actual welding material, the optimized actual base material, and the optimal welding heat input E obtained at S5, an inclined Y-groove welding cracking test is performed at low temperature to verify whether low-temperature cracking occurs in the welded joint when welding without preheating is achieved by the preferred welding material, the optimized base material, and the selected welding heat input.

[0038] In other preferred examples, the flow rate of the carrier gas of argon gas is 20 ml / min to 40 ml / min, for example, 20 ml / min, 25 ml / min, 30 ml / min, 35 ml / min, 40 ml / min, or any flow rate value between any two of the above-mentioned values.​

[0039] S: Optimize the carbon equivalent of the base metal test piece multiple times according to the low-temperature cracking susceptibility coefficient of the base metal test piece to obtain various new base metals with different components.

[0040] The base metal test piece used in this example is EH420 steel for marine engineering. Its chemical composition is shown in Table 1. The low-temperature cracking susceptibility coefficient P of the steel material cm is 0.159.

[0041] Table 1: Composition of EH420 Steel for Marine Engineering (wt%)

Table 1

[0042] When adjusting the chemical composition of the base metal test piece, first reduce the contents of Mn and Si elements. Adjust the content of Mn element by 0.01% each time and the content of Si element by 0.005% each time. If necessary, sequentially reduce the contents of C, Cu, and Cr elements, and the adjustment gradient each time is 0.001%. When adjusting the chemical composition of the steel material, it is necessary to consider the mechanical properties, crystal grain size, and the contents of ferrite, pearlite, and bainite structures of the steel material, and select the chemical composition of the steel material with the best performance while the mechanical properties reach the standard. Finally, the selected base metal component only needs to meet the low-temperature cracking susceptibility index without preheating under a predetermined low-temperature environment. Since the specific optimization method is a prior art, the description is omitted here.

[0043] S4: The minimum diffusible hydrogen content [H] cr , the critical restraint degree R cr and based on the low-temperature cracking susceptibility coefficient of the new base metal, obtain the second low-temperature cracking susceptibility index corresponding to the new base metal.

[0044] S5: Determination of the actual base material: When the second low-temperature cracking susceptibility index is smaller than the first low-temperature cracking susceptibility index, the new base material corresponding to the second low-temperature cracking susceptibility index is taken as the actual base material. When the second low-temperature cracking susceptibility index is equal to or greater than the first low-temperature cracking susceptibility index, steps S3 - S5 are repeated until the second low-temperature cracking susceptibility index becomes smaller than the first low-temperature cracking susceptibility index.

[0045] S6: Obtain the time t required for the post-weld peak temperature of the actual welding material and the actual base material at different welding heat inputs to cool to 100°C. 100 Based on t 100 obtain the critical cooling time t cr of the welded joint, and take the welding heat input E corresponding to the maximum difference between t 100 and t cr as the actual welding heat input.

[0046] Specifically, numerical simulation calculations are performed on the butt welded joints at different welding heat inputs E. The welding heat source during numerical simulation uses a double-ellipsoid heat source model, and the welding heat input is changed by varying the magnitude of the welding current. In particular, the current of the shielded arc welding increases from 140A, increasing by 5A each time until it reaches 190A. As a result, there are a total of 10 groups of welding heat inputs. In other preferred embodiments, more welding heat inputs can be obtained by reducing the increase gradient. For example, the gradient value can be 2A, 4A, etc.

[0047] Select the center of the welded part at the intermediate stage where the welding condition of the welded joint is stable under different welding heat inputs of each group as the measurement node for temperature measurement, define the node temperature as a variable of time, extract the simulated thermal cycle curve of the node, and calculate the time t 100 required for cooling from the peak temperature to 100°C. Then, analyze the time t 100 required for cooling from the post-weld peak temperature to 100°C, and after optimizing the welding heat input E and the components, the P cm of the actual base material, the diffusible hydrogen content [H] of the weld metal of the actually selected welding material, and the critical restraint degree R cr are substituted into the determination formula of the critical cooling time t cr for low alloy high-strength steel, and t 100 - tcr Take the welding heat input E corresponding to the case when it is maximum as the actual welding heat input.

Number

[0048] In the formula, t cr is the critical cooling time, P cm is the low-temperature cracking susceptibility coefficient, [H] is the diffusible hydrogen content in the weld metal of the selected welding material, E is the selected welding heat input, R cr is the critical restraint degree, ΔR is the additional restraint degree with local preheating. Here, since a welding process without preheating is used, ΔR = 0.

[0049] In other preferred embodiments, the Y-groove angle of the base metal test piece is 60° or less, the root gap of the welded end of the base metal test piece is 1 mm to 2 mm, and the quality of the welded part after welding is ensured.

[0050] In this embodiment, the test piece dedicated to the rigid restraint welding crack test, the test piece of the inclined Y-groove welding crack test, and the welding material all need to be subjected to pre-welding treatment. For example, use a grinder or wire brush to grind the groove to remove rust, remove burrs, remove oil stains on the groove surface of the test piece by alcohol or acetone, dry the welding material at a predetermined temperature according to the usage instructions, keep it warm and wait.

[0051] Example 2 In this embodiment, the method steps for obtaining the welding process are the same as steps S1 - S5 of Example 1 and include the following steps. S1: Obtain the first low-temperature cracking susceptibility index required for welding without preheating at a specific temperature. S2: Obtain the critical restraint distance L cr and the critical restraint degree R cr of the base metal test piece at a specific temperature, obtain the minimum diffusible hydrogen content [H] of the welding material required for welding without preheating based on the first low-temperature cracking susceptibility index, and select the actual welding material based on [H]. cr [H] cr S3: Optimize the carbon equivalent according to the low-temperature cracking susceptibility coefficient of the base metal test piece to obtain a new base metal after component change. S4: Minimum diffusible hydrogen content [H] cr , critical restraint degree R cr and obtain the second low-temperature cracking susceptibility index corresponding to the new base metal based on the minimum diffusible hydrogen content [H], critical restraint degree R and low-temperature cracking susceptibility coefficient of the new base metal. S5: Determination of the actual base metal: When the second low-temperature cracking susceptibility index is smaller than the first low-temperature cracking susceptibility index, the new base metal corresponding to the second low-temperature cracking susceptibility index is used as the actual base metal. When the second low-temperature cracking susceptibility index is greater than or equal to the first low-temperature cracking susceptibility index, repeat steps S3 - S5 until the second low-temperature cracking susceptibility index is smaller than the first low-temperature cracking susceptibility index. S6: Obtain the time t required to cool the actual weld metal and the actual base metal from the post-weld peak temperature to 100°C under different welding input heats 100 , and obtain the critical cooling time t of the welded joint based on t 100 , and take the welding input heat E corresponding to the maximum difference between t cr and t 100 as the actual welding input heat. cr When the difference is the largest.

[0052] In this embodiment, the specific environmental temperature is set to -10°C. When obtaining the welding process, as shown in FIG. 2, as the welding test piece in the rigid restraint welding crack test, EH420 steel for marine engineering is selected. The thickness t is 40 mm, which is the standard specification of the steel for marine engineering (the structure is shown in FIG. 2). An inclined Y-groove is made at its welding end, the groove angle is 60°, and the root gap is 1 mm - 2 mm during welding, for example, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, or any value between the above two gap values. In this embodiment, it is 1.5 mm. After obtaining the welding process, select EH420 steel for marine engineering as the test piece for the inclined Y-groove welding crack test. The thickness is 40 mm, and the size and groove form are processed according to the test piece size described in the national standard CB / T 4364 (Method for Inclined Y-Groove Welding Crack Test).

[0053] When not preheated before welding, the minimum welding low-temperature cracking sensitivity coefficient obtained based on formula (1) in Example 1, at which no welding low-temperature cracking occurs, is 0.2653.

[0054] The welding machine, auxiliary equipment, and test pieces used in the rigid restraint welding crack test and the inclined Y-groove welding crack test are placed in a low-temperature environment of -10°C 4 hours before the start of the test, and a dedicated device (for example, a humidifying device) is used to ensure that the environmental humidity for each welding test is consistent.

[0055] In step S2, a rigid restraint welding crack test is performed using a conventional rigid-adjustable restraint welding joint crack test device. The inclined Y-groove dedicated test piece is attached to the rigid-adjustable restraint welding joint crack test device. As shown in Figure 3, by adjusting the movable end 1, the adjustable restraint distance W between the movable end 1 and the fixed end 3 can be changed. During welding, it is strictly ensured that the set restraint distance does not change, a restraint load is applied to the test piece, and the restraint stress maintains the load for 48 hours. Then, continue to adjust the adjustable restraint distance W (that is, the degree of restraint) of the test piece shown in Figure 3, repeat the above test at least 3 groups, and obtain the critical restraint stress corresponding to the case where cracks occur and do not occur in the test weld part 2. According to formula (4) and formula (5), the critical restraint stress σ cr is converted to the critical degree of restraint R cr (The critical degree of restraint is also obtained by this method in Example 1).

Number

[0056] In the formula, m is the restraint stress conversion coefficient, a is the linear expansion coefficient, h w is the height of the weld part, η is the welding heat efficiency, E is the heat input for welding, C v is the volumetric specific heat, l w is the average width of the weld part.

[0057] In this embodiment, the diffusible hydrogen content in the weld metal of different welding materials is measured by gas chromatography. For each group of tests, it is necessary to measure multiple times to reduce the test error. The final result is calculated as the average value of multiple measurement values while ensuring the correctness of the test data. Also, since the measurement of the diffusible hydrogen content in the weld metal by gas chromatography is a conventional technique, the description thereof is omitted here.

[0058] In this embodiment, in the numerical simulation calculation in step S5, based on the actual welding process of butt welding of a 40 mm thick plate at an environmental temperature of -10°C, the actual welding process is simulated, the temperature field after welding is calculated, and the time t required for the post-weld peak temperature to cool to 100°C at different welding heat inputs E 100 is analyzed.

[0059] Also, for the critical cooling time t in step S5 cr The meaning of the judgment formula is that after welding under actual welding conditions, the time required for the temperature to cool from the peak temperature to 100°C is t 100 Let it be, and when t 100 >t cr it means that cold cracking of the welded joint can be avoided.

[0060] More specifically, in this embodiment, finally, the optimal welding parameters for shielded arc welding are determined as follows. Welding current 130 ± 10 A, arc voltage 24 ± 1 V, welding speed 15 ± 1 cm / min, welding heat input 10.4 - 15 kJ / cm.

[0061] In this embodiment, after step S6, an inclined Y-shaped specimen root welding crack test is performed using the selected EH420 steel for marine engineering. Double-sided welding is adopted for the restraint welding part, and the assembly gap and the quality of the restraint welding parts on both sides are strictly ensured. By controlling the angular deformation of the actual base material within 5°, cracks are prevented from occurring in the restraint welding part. Specifically, in the inclined Y-shaped root welding crack test, three groups of parallel tests are set up, and the average value of the test results of the three groups is taken as the final result. More specifically, in the inclined Y-shaped root welding crack test, the surface crack rate, cross-section crack rate, and root crack rate of the welded joint are measured by the method described in the above-mentioned CB / T 4364.

[0062] It should be noted that each number described in the embodiments of the present invention is only used for the convenience of explanation and does not limit the scope of the embodiments of the present invention.

[0063] As can be understood by those skilled in the art, the above are only preferred embodiments of the present invention and do not limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should all be included in the protection scope of the present invention.

Claims

1. A method for determining a high-performance preheat-free welding process for steel for ocean engineering, comprising the following S1 to S6, S1: Obtain the first low-temperature cracking susceptibility index required for preheat-free welding at a specific temperature, S2: Critical restraint distance L of the base metal test piece at the specific temperature ｃｒ and critical restraint degree R ｃｒ are obtained, and the minimum diffusible hydrogen content [H] of the welding consumable required for welding without preheating is obtained based on the first low-temperature cracking susceptibility index ｃｒ is obtained, the actual welding consumable is selected based on [H], ｃｒ ​ S3: Optimize the carbon equivalent according to the low-temperature cracking susceptibility coefficient of the base metal test piece to obtain a new base metal, S4: The minimum diffusible hydrogen content [H] ｃｒ , the critical restraint degree R ｃｒ and based on the low-temperature cracking susceptibility coefficient of the new base material, obtain a second low-temperature cracking susceptibility index corresponding to the new base material, S5: Determination of the actual base metal: When the second low-temperature cracking susceptibility index is smaller than the first low-temperature cracking susceptibility index, the new base metal corresponding to the second low-temperature cracking susceptibility index is used as the actual base metal. When the second low-temperature cracking susceptibility index is equal to or greater than the first low-temperature cracking susceptibility index, steps S3 - S5 are repeated until the second low-temperature cracking susceptibility index becomes lower than the first low-temperature cracking susceptibility index, S6: Time t required for the post-weld peak temperature of the actual welding material and the actual base material under different welding input heats to cool to 100°C １００ is obtained, and based on t １００ the critical cooling time t ｃｒ of the welded joint is obtained, and the welding input heat E corresponding to when the difference between t １００ and t ｃｒ is the largest is taken as the actual welding input heat. A method characterized by this.

2. The method according to claim 1, characterized in that in step S6, a double-ellipsoid heat source model is selected, and the heat input during welding is changed by changing the magnitude of the welding current.

3. The method according to claim 2, characterized in that the welding current gradually increases within the range of 140 A to 190 A.

4. The method according to claim 2 or 3, characterized in that the welding current sequentially increases with a gradient value of 5 A.

5. In step S2, the critical restraint distance L is obtained by a rigid restraint welding crack test ｃｒ and the critical restraint degree R ｃｒ are obtained, the test equipment is pre-cooled to a specific temperature before the test, and the environmental humidity during each rigid restraint welding crack test is the same. The method according to claim 1

6. The method according to claim 5, characterized in that in step S2, the welding end of the base metal test piece is processed into a beveled Y-groove, and the angle of the groove is 60° or less.

7. The method according to claim 5 or 6, characterized in that the root gap of the welding end of the base metal test piece is 1 mm to 2 mm.

8. The method according to claim 1, characterized in that in step S2, the minimum diffusible hydrogen content is obtained by gas chromatography, the inner diameter of the column used is 4 mm or more, the carrier gas for obtaining the minimum diffusible hydrogen content by gas chromatography is argon gas with a concentration of 99.9% or more, and the flow rate of the carrier gas of the argon gas is 20 ml / min to 40 ml / min.

9. After step S6, an inclined Y-groove welding crack test is performed using the actual welding material, the actual base metal, and the actual heat input during welding obtained in steps S1 - S6. During the inclined Y-groove welding crack test, double-sided welding is employed for the restrained welded part. The method according to claim 1 is characterized by this.

10. The method according to claim 9, characterized in that in the inclined Y-groove welding crack test, the angular deformation of the actual base metal is controlled within 5°.

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