Method for determining a high-performance, preheat-free welding process for marine engineering steels.

Abstract

This invention provides a method for establishing a high-performance, preheat-free welding process for marine engineering steels. [Solution] The steps are: to obtain a first cold cracking susceptibility index, the critical constraint distance and critical constraint degree of the base material test specimen; to obtain the minimum diffusible hydrogen content of the welding material and select the actual welding material based on the minimum diffusible hydrogen content; to obtain a new base material by optimizing its carbon equivalent based on the cold cracking susceptibility coefficient of the base material test specimen; to obtain a second cold cracking susceptibility index smaller than the first cold cracking susceptibility index and use the new base material corresponding to this susceptibility index as the actual base material; and to determine the time t required for the post-weld peak temperature of the actual welding material and the actual base material to cool to 100°C with different welding heat inputs. 100 and the critical cooling time t of the welded joint cr Obtain t 100 and t cr The welding heat input when the difference is maximum is defined as the actual welding heat input.

Description

[Technical Field]

[0001] This invention belongs to the field of welding technology, and more specifically, to a method for determining a high-performance, preheat-free welding process for marine engineering steel. [Background technology]

[0002] When constructing offshore facilities in certain sea areas, ambient temperatures can reach -5 to -20°C, making cold cracking a significant problem in welding. Hysteresis from cold cracking is particularly harmful and poses a major hidden risk to the safety of offshore engineering structures. Preheating before welding provides the temperature and time conditions for hydrogen diffusion and escape, as well as appropriately improving the microstructure to reduce hardenability and alleviate residual stress to some extent. Currently, preheating is necessary for welding processes in low-temperature environments to eliminate the effects of cold cracking. However, for thick and complex structures, preheating the entire structure is difficult in actual production, or the facilities at the construction site do not have the necessary preheating conditions. In conventional welding processes without preheating, measures such as designing undermatched weld joints are mainly employed to reduce the tendency for cold cracking, but this causes problems with the load-bearing capacity of the joints.

[0003] Chinese patent CN117778898A discloses high-performance marine engineering steel and a method for manufacturing the same, enabling preheating-free welding at room temperature. However, because it requires the manufacture of special welding wires and steel materials to achieve preheating-free welding, its application is limited and it cannot be applied to various welding scenarios. Many preheating-free welding processes avoid cold cracking of welded joints by selecting undermatched welding materials and welding them. Chinese patent CN117226213A discloses an arc welding process for marine corrosion-resistant steel with a yield strength of 420 MPa. In this patent, welding parameters are continuously tested through orthogonal testing to obtain a process that enables preheating-free welding of steel materials at room temperature, but it has the disadvantages of being costly, requiring long testing times, and being inefficient. Conventional techniques that can achieve preheating-free welding lack versatility and often involve developing welding processes through a finite number of repeated trials, without a complete quantitative analysis theoretical system. Therefore, in order to meet the need for efficient manufacturing of large-scale marine engineering equipment such as deep-water conduit support platforms in extreme environments, and to improve welding efficiency, there is an urgent need to acquire a method for achieving a high-performance welding process for 420 MPa class thick marine engineering steel plates without preheating in low-temperature environments. [Overview of the project]

[0004] In response to the shortcomings of the prior art, the objective of the present invention is to provide a method for determining a high-performance, preheat-free welding process for marine engineering steel, thereby solving the problems of the low efficiency and poor versatility of conventional welding process development methods.

[0005] To achieve the above objective, the present invention provides a method for determining a high-performance, preheat-free welding process for marine engineering steel including the following S1 to S6, S1: Obtain the first low-temperature cracking susceptibility index required for preheating-free welding at a specific temperature. S2: Critical constraint distance L of the base material test specimen at the specified temperature. cr and critical constraint degree R crObtain the minimum diffusible hydrogen content [H] of the welding consumable required for welding without preheating based on the first low-temperature cracking susceptibility index cr Obtain [H] cr Select an actual welding consumable based on [H] 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: 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 becomes lower than the first low-temperature cracking susceptibility index S6: 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 Obtain t 100 Based on t, obtain the critical cooling time t of the welded joint cr Obtain t 100 The difference between 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 theoretical system is used to realize the development of a welding process without preheating for steel materials such as steel for marine engineering like 420 MPa grade thick plates under various low-temperature environments. The development process is simple, has high versatility for the environment, can obtain a welding process without preheating in various temperature environments, and the performance of the welded joint actually obtained by welding with the obtained welding process is excellent

[0007] Furthermore, in step S6, a double ellipsoid heat source model is selected, and the welding heat input 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 applicability to various welding process types.

[0008] Furthermore, gradually increasing the welding current within the range of 140A to 190A improves the stability of the molten pool, reducing arc drift and instability caused by insufficient current. If the welding current is less than 140A, there is a problem in that the weld area cannot be completely melted, and if the welding current exceeds 190A, defects such as weld undercuts and burn-through may occur.

[0009] Furthermore, the welding current increases progressively with a gradient of 5A.

[0010] Furthermore, in step S2, the critical restraint distance L is determined by a rigid restraint welding crack test. cr and the critical constraint degree R cr The test equipment is pre-cooled to a specific temperature before each test, and the ambient humidity is the same for every rigid-restrained weld crack test.

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

[0012] Furthermore, the distance between the roots of the weld ends of the base material test specimen 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, the carrier gas used to obtain the minimum diffusible hydrogen content by gas chromatography is argon gas with a concentration of 99.9% or higher, and the carrier gas flow rate of the argon gas is 20 ml / min to 40 ml / min. By setting the flow rate within this range, the separation efficiency and analysis speed of the welded test specimen in the column are increased.

[0014] Furthermore, after step S6, an oblique Y-groove weld cracking test is performed using the actual weld material, actual base material, and actual welding heat input obtained in steps S1-S6, and double-sided welding is employed for the constrained weld during the oblique Y-groove weld cracking test.

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

[0016] The technical means of the present invention have the following beneficial effects compared to the prior art. (1) In light of the fact that conventional no-preheating welding processes are only applicable in room temperature environments, the present invention provides a method for developing a no-preheating welding process in low-temperature environments. This method efficiently develops high-performance no-preheating welding processes for various types of marine engineering steel in various low-temperature environments through a complete quantitative analysis theoretical framework. Specifically, it obtains a cold cracking susceptibility index that enables no-preheating welding at a specific temperature, measures the critical degree of constraint by a stiffness-adjustable constrained welding cracking test, quantitatively evaluates the cold cracking susceptibility of marine engineering steel by fully considering the carbon equivalent of the base metal, the diffusible hydrogen content of the weld material, and the actual constraint state of the welded joint, and thereby optimizes the weld material by limiting the diffusible hydrogen content of the weld material, and optimizes the base metal based on a cold cracking susceptibility coefficient related to the base metal's composition, so that the chemical composition of the base metal, the diffusible hydrogen content of the weld material, and the degree of constraint of the welded joint can satisfy the cold cracking susceptibility index required to achieve no-preheating welding. Furthermore, numerical simulation calculations are performed for butt welded joints with different welding heat inputs, and the critical cooling time t of low-alloy high-strength steel is determined. cr The optimal welding heat input is selected based on the following criteria.

[0017] (2) In this invention, the chemical composition of the base material, the diffusible hydrogen content of the welding material, and the influence of welding heat input on low-temperature cracking of welded joints are comprehensively considered, and the above complete quantitative analysis theoretical system enables the development of a welding process without preheating for steel materials such as 420 MPa class thick plates for marine engineering under various low-temperature conditions. The development process of the welding process is relatively simple, there is no need to perform orthogonal testing, the acquisition method is more applicable to various welding environments, and welding can be performed using welding materials with matched strength (equivalent strength) in actual welding, resulting in superior overall performance of the welded joint.

[0018] (3) In this invention, when simulating with different welding heat inputs, a current gradient is provided to change the welding heat input, and by gradually increasing the welding current within the range of 140A to 190A, the stability of the molten pool is improved, and arc drift and instability due to insufficient current are reduced. If the welding current is less than 140A, there is a problem that the weld cannot be completely melted, and if the welding current exceeds 190A, defects such as welding undercuts and burn-through may occur.

[0019] (4) In this invention, the argon gas used in gas chromatography has a high relative molecular weight and a low thermal conductivity, which ensures the purity of the sample and the accuracy of the analytical results during the analysis process, as well as the stability of the baseline and the sensitivity of the measuring instrument. Within the planned flow rate range, welded samples exhibit higher separation efficiency and analysis speed in columns of 4 mm or larger. [Brief explanation of the drawing]

[0020] [Figure 1] This is a flowchart of the method for determining a high-performance, preheat-free welding process for marine engineering steel provided in Example 1. [Figure 2] This is a schematic diagram of the structure of the welded specimen in the rigid-restrained weld cracking test selected in Example 2. [Figure 3] This is a schematic diagram of the structure of the welded specimen after the rigid-restrained weld cracking test in Example 2.

[0021] In all drawings, the same reference numerals are used to indicate the same element or structure. 1 - Movable end, 2 - Test weld, 3 - Fixed end. [Modes for carrying out the invention]

[0022] To further clarify 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 examples. The specific examples described herein are merely interpretive and not limiting of the present invention.

[0023] In this specification, the term "and / or" describes 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, or 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., used in this specification and in the claims are for distinguishing different subjects and not to describe a particular order of subjects. For example, "first response message" and "second response message" are used to distinguish different response messages and are not a particular order for describing response messages.

[0025] In the embodiments of the present invention, terms such as “exemplary” or “for example” are used for illustrative purposes, demonstration, 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 preferable or superior to other embodiments or designs. Specifically, the use of terms such as “exemplary” or “for example” is intended to specifically illustrate the relevant concepts.

[0026] In describing embodiments of the present invention, unless otherwise specified, the term "multiple" refers to two or more items. For example, "multiple processing units" refers to two or more processing units, and "multiple elements" refers to two or more elements.

[0027] Example 1 This embodiment provides a method for establishing a high-performance, preheat-free welding process for marine engineering steel. The method includes the following steps, as shown in Figure 1. S1: Obtain the first low-temperature cracking susceptibility index required for preheating-free welding at a specific temperature. Specifically, based on the ambient temperature T0, the following preheating temperature determination formula allows for the achievement of a low-temperature cracking susceptibility index P that enables welding without preheating in low-temperature environments. w Obtain it.

number

[0028] S2: Critical constraint distance L of the base material test specimen at a specific temperature cr and critical constraint degree R cr Based on the first cold cracking susceptibility index, the minimum diffusible hydrogen content [H] of the weld material required for welding without preheating is obtained. cr Obtain [H] cr The actual welding material is selected based on this.

[0029] Specifically, a dedicated oblique Y-groove test specimen is designed and fabricated, and a rigidity-constrained weld cracking test is performed at a predetermined ambient temperature. The critical constraint distance L corresponds to cases where cracking occurs in the test specimen and cases where it does not. cr and critical constraint degree R cr Obtain it.

[0030] In rigid-constrained weld crack testing, the type of welding method selected corresponds to 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 consumable electrode gas shielded welding can be developed. The type of welding material corresponds to the welding method, for example, welding rods, flux-cored wires, solid wires, etc., corresponding to each welding method. The type of shielding gas can be determined according to the welding material to be obtained. The size of the test weld and the groove shape use an oblique Y groove. To ensure the accuracy of the results, the test equipment must be pre-cooled to a specific temperature before the test.

[0031] Furthermore, the ambient humidity was the same for each rigidity-constrained weld cracking test.

[0032] In this embodiment, the welding parameters for the rigid-restrained weld cracking test are designed as follows. 1. For 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 consumable electrode gas shielded welding, when using a 1.2 mm welding wire and CO2 as the shielding gas, the welding current is 200 A and the welding speed is 190 mm / min. When using a mixed gas of 80% Ar and 20% CO2 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 280A and the welding speed is 350mm / min.

[0033] The selected restraint distance starts at 1.60 mm. In the rigid restraint weld cracking test, if a crack occurs on the surface or cross-section of the test weld, the restraint distance is increased; if there is no crack on the surface or cross-section, the restraint distance is decreased. In this example, the critical restraint distance finally measured was 50 mm.

[0034] Subsequently, based on the following high-strength steel welding cold cracking sensitivity index formula, the minimum diffusible hydrogen content [H] in the weld metal that enables preheating-free welding is determined by the method for measuring diffusible hydrogen in the weld metal described in "Method for measuring diffusible hydrogen in weld metal (GB / T 3965-2012)". cr Obtain it.

number

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

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

[0037] In this embodiment, a low-temperature oblique Y-groove weld crack test is performed based on the actual weld material obtained, the optimized actual base material, and the optimal welding heat input E obtained in S5 to verify whether or not low-temperature cracking occurs in the welded joint when preheating-free welding is achieved with the preferred weld material, optimized base material, and selected welding heat input.

[0038] In other preferred embodiments, the carrier gas flow rate 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 between any two of the above values.

[0039] S: By optimizing the carbon equivalent of the base material specimen multiple times based on its low-temperature cracking susceptibility coefficient, various new base materials with different compositions are obtained.

[0040] The base material specimen used in this example is EH420 marine engineering steel. Its chemical composition is shown in Table 1. The cold cracking susceptibility coefficient P of the steel. cm It is 0.159.

[0041] Table 1: Composition (wt%) of EH420 marine engineering steel [Table 1]

[0042] When adjusting the chemical composition of the base material specimen, first the content of Mn and Si elements is reduced, adjusting the Mn content by 0.01% each time, adjusting the Si content by 0.005% each time, and sequentially reducing the C, Cu, and Cr elements as needed, with a total adjustment gradient of 0.001% each time. When adjusting the chemical composition of the steel, it is necessary to consider the mechanical properties, grain size, and content of ferrite, pearlite, and bainite structures of the steel, and select the steel chemical composition that achieves the standard mechanical properties while providing the best performance. Finally, the selected base material composition should satisfy the cold cracking susceptibility index without preheating under a specified low-temperature environment. The specific optimal method is conventional technology, so its explanation is omitted here.

[0043] S4: Minimum diffusible hydrogen content [H] cr , the critical constraint degree R cr Furthermore, based on the cold cracking susceptibility coefficient of the new base material, a second cold cracking susceptibility index corresponding to the new base material is obtained.

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

[0045] S6: The time required for the actual weld material and base material to cool to a peak temperature of 100°C after welding with different welding heat inputs. 100 Obtain t 100 Based on the critical cooling time t of the welded joint cr Obtain t 100 and t cr The actual welding heat input E is defined as the value corresponding to the maximum difference between the two values.

[0046] Specifically, numerical simulation calculations are performed for butt welded joints with different welding heat inputs E. During the numerical simulation, a double ellipsoid heat source model is used, and the welding heat input is varied by changing the magnitude of the welding current. In particular, the current for shielded metal arc welding increases from 140A, increasing by 5A each time until it reaches 190A, resulting in a total of 10 groups of welding heat inputs. In other preferred embodiments, a larger welding heat input can be obtained by reducing the increasing gradient. For example, gradient values ​​such as 2A and 4A are used.

[0047] Under different welding heat input conditions for each group, the center of the weld joint at a stable intermediate stage of the welding condition was selected as the measurement node, and the temperature was measured. The node temperature was defined as a time variable, and a simulated thermal cycle curve of the node was extracted. The time t required to cool from the peak temperature to 100°C was determined. 100 Calculate the time t required to cool from the post-weld peak temperature down to 100°C. 100 After analyzing the welding heat input E and optimizing the composition, the actual base material P cm The weld metal diffusible hydrogen content [H] and critical constraint degree R of the actually selected welding material. cr The critical cooling time t for low alloy high strength steel cr Substitute this into the judgment formula, t 100 -tcr Let E be the actual welding heat input, corresponding to the maximum value of [the specified value].

number

[0048] In the formula, t cr is the critical cooling time, and P cm [H] is the cold cracking susceptibility coefficient, [H] is the diffusible hydrogen content of the weld metal of the selected weld material, E is the selected welding heat input, and R cr ΔR is the critical constraint, and ΔR is the additional constraint with local preheating, where ΔR=0 because we are using a welding process without preheating.

[0049] In other preferred embodiments, the Y-groove angle of the base material specimen was 60° or less, and the distance between the roots of the weld ends of the base material specimen was 1 mm to 2 mm, ensuring the quality of the weld after welding.

[0050] In this embodiment, the test specimens for rigid-restrained weld crack testing, the test specimens for oblique Y-groove weld crack testing, and the welding materials all require pre-treatment before welding. For example, the grooves are polished using a grinder or wire brush to remove rust and burrs, oil stains on the groove surface of the test specimens are removed with alcohol or acetone, the welding materials are dried at a predetermined temperature according to the instructions for use, and then kept warm while waiting.

[0051] Example 2 In this embodiment, the method procedure for obtaining the welding process is the same as steps S1-S5 of Embodiment 1, and includes the following steps. S1: Obtain the first low-temperature cracking susceptibility index required for preheating-free welding at a specific temperature. S2: Critical constraint distance L of the base material test specimen at a specific temperature cr and critical constraint degree R cr Based on the first cold cracking susceptibility index, the minimum diffusible hydrogen content [H] of the weld material required for welding without preheating is obtained. cr Obtain [H] cr The actual welding material is selected based on this. S3: The carbon equivalent of the base material specimen is optimized based on its low-temperature cracking susceptibility coefficient to obtain a new base material after the compositional change. S4: Minimum diffusible hydrogen content [H] cr , critical constraint R cr Furthermore, a second cold cracking susceptibility index corresponding to the new base material is obtained based on the cold cracking susceptibility coefficient of the new base material. S5: Determination of the actual base material: If the second cold cracking susceptibility index is smaller than the first cold cracking susceptibility index, a new base material corresponding to the second cold cracking susceptibility index is designated as the actual base material. If the second cold cracking susceptibility index is equal to or greater than the first cold cracking susceptibility index, steps S3-S5 are repeated until the second cold cracking susceptibility index becomes smaller than the first cold cracking susceptibility index. S6: The time required to cool the actual weld material and base material from the peak temperature to 100°C after welding, with different welding heat inputs. 100 Obtain t 100 Based on the critical cooling time t of the welded joint cr Obtain t 100 and t cr The actual welding heat input E is defined as the value corresponding to the maximum difference between the two values.

[0052] In this embodiment, the specific ambient temperature is set to -10°C, and when acquiring the welding process, as shown in Figure 2, EH420 marine engineering steel is selected as the welded test specimen for the rigid-restrained weld crack test, with a thickness t of 40 mm, which is the standard specification for marine engineering steel (the structure is shown in Figure 2). An oblique Y groove is made at the weld end, with a groove angle of 60°, and the gap at the root during welding is 1 mm to 2 mm, 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 two gap values ​​mentioned above, which is 1.5 mm in this embodiment. After acquiring the welding process, EH420 marine engineering steel is selected as the test specimen for the oblique Y groove weld crack test, with a thickness of 40 mm, and the size and groove shape are processed according to the test specimen size described in national standard CB / T 4364 (Oblique Y groove weld crack test method).

[0053] When preheating is not performed before welding, the minimum welding cold cracking sensitivity coefficient obtained based on formula (1) in Example 1, which prevents welding cold cracking, is 0.2653.

[0054] The welding machines, auxiliary equipment, and test specimens used in rigid-restrained weld cracking tests and oblique Y-groove weld cracking tests are placed in a -10°C low-temperature environment 4 hours before the start of the test, and a dedicated device (e.g., a humidifier) ​​is used to ensure that the ambient humidity for each welding test is consistent.

[0055] In step S2, a rigidity-constrained weld crack test is performed using a conventional rigidity-adjustable constrained weld joint crack test apparatus. A test specimen specifically for oblique Y grooves is attached to the rigidity-adjustable constrained weld joint crack test apparatus, and as shown in Figure 3, the adjustable restraint distance W between the movable end 1 and the fixed end 3 can be changed by adjusting the movable end 1. During welding, it is strictly guaranteed that the set restraint distance does not change, and a restraint load is applied to the test specimen, and the restraint stress maintains the load for 48 hours. Thereafter, the adjustable restraint distance W (i.e., degree of restraint) of the test specimen shown in Figure 3 is continuously adjusted, and the above test is repeated at least three times to obtain the critical restraint stress corresponding to when a crack occurs and when it does not occur in the test weld 2, and the critical restraint stress σ is obtained using equations (4) and (5). cr The critical constraint R cr Convert to (the critical constraint degree is also obtained using this method in Example 1).

number

[0056] In the formula, m is the constraint stress transformation coefficient, a is the linear expansion coefficient, and h w is the height of the weld, η is the welding thermal efficiency, E is the welding heat input, and C v is the volumetric specific heat, and l w This is the average width of the welded joint.

[0057] In this embodiment, the diffusible hydrogen content of the weld metal of different weld materials is measured by gas chromatography, and multiple measurements are required for each group of tests to reduce test errors. The final result is calculated by averaging multiple measurements while ensuring the accuracy of the test data. Furthermore, since the measurement of diffusible hydrogen content in weld metal by gas chromatography is a conventional technique, a detailed explanation is omitted here.

[0058] In this embodiment, the numerical simulation calculation in step S5 simulates the actual welding process based on the actual welding process of butt welding of 40 mm thick plates at an ambient temperature of -10°C, calculates the temperature field after welding, and determines the time t required for the post-weld peak temperature to cool to 100°C at different welding heat inputs E. 100 Analyze it.

[0059] Furthermore, the critical cooling time t in step S5 cr The meaning of the judgment formula is the time required to cool from the peak temperature to 100°C after welding under the actual welding conditions. 100 to, t 100 >t cr In this case, cold cracking of welded joints can be avoided.

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

[0061] In this embodiment, after step S6, a diagonal Y-groove weld cracking test is performed using selected EH420 marine engineering steel. Double-sided welding is employed for the constrained weld to strictly guarantee the quality of the assembly gap and the constrained welds on both sides, and the angular deformation of the actual base material is controlled to within 5° to prevent cracking in the constrained weld. Specifically, in the diagonal Y-groove weld cracking 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 diagonal Y-groove weld cracking test, the surface cracking rate, section cracking rate, and root cracking rate of the welded joint are measured by the method described in CB / T 4364 above.

[0062] The figures described in the embodiments of the present invention are used solely for explanatory purposes and do not limit the scope of the embodiments of the present invention.

[0063] As those skilled in the art will understand, the foregoing are merely preferred embodiments of the present invention and do not limit it. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should all be within the scope of protection of the present invention.

Claims

1. A method for determining a high-performance, preheat-free welding process for marine engineering steel, 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: Critical constraint distance L of the base material test specimen at the specified temperature. ｃｒ and critical constraint degree R ｃｒ Based on the first cold cracking susceptibility index, the minimum diffusible hydrogen content [H] of the weld material required for welding without preheating is obtained. ｃｒ Obtain [H] ｃｒ Based on this, select the actual welding material. S3: A new base material is obtained by optimizing its carbon equivalent based on the low-temperature cracking susceptibility coefficient of the base material test specimen. S4: Minimum diffusible hydrogen content [H] ｃｒ , the critical constraint degree R ｃｒ Furthermore, based on the cold cracking susceptibility coefficient of the new base material, a second cold cracking susceptibility index corresponding to the new base material is obtained. S5: Determination of the actual base material: If the second cold cracking susceptibility index is smaller than the first cold cracking susceptibility index, a new base material corresponding to the second cold cracking susceptibility index is used as the actual base material, and if the second cold cracking susceptibility index is equal to or greater than the first cold cracking susceptibility index, steps S3-S5 are repeated until the second cold cracking susceptibility index becomes lower than the first cold cracking susceptibility index. S6: The time t required for the post-weld peak temperature of the actual welding material and the actual base material under different welding heat inputs 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 when the difference between t １００ and t ｃｒ is maximum, the welding heat input E corresponding thereto is set as the actual welding heat input. 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 welding heat input 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 is sequentially increased with a gradient value of 5A.

5. In step S2, the critical restraint distance L is determined by a rigid restraint welding crack test. ｃｒ and the critical constraint degree R ｃｒ The method according to claim 1, characterized in that a certain temperature is obtained, the test equipment is pre-cooled to a specific temperature before the test, and the ambient humidity is the same for each rigidity-constrained weld crack test.

6. The method according to claim 5, characterized in that in step S2, the weld end of the base material test piece is processed into an oblique Y groove, and the groove angle is 60° or less.

7. The method according to claim 5 or 6, characterized in that the distance between the roots of the weld ends of the base material test specimen 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 used when obtaining the minimum diffusible hydrogen content by gas chromatography is argon gas with a concentration of 99.9% or more, and the carrier gas flow rate of the argon gas is 20 ml / min to 40 ml / min.

9. The method according to claim 1, characterized in that, after step S6, an oblique Y groove weld crack test is performed using the actual weld material, actual base material, and actual welding heat input obtained in steps S1-S6, and double-sided welding is employed for the constrained weld during the oblique Y groove weld crack test.

10. The method according to claim 9, characterized in that the angular deformation of the actual base material is controlled to within 5° in an oblique Y groove weld crack test.

Images