316L series flux-cored wire for efficient welding of LNG ship low-temperature pipe and welding method

Abstract

The invention discloses a 316L-series flux-cored wire for efficient welding of a low-temperature pipe of an LNG ship and a welding method. The invention relates to the field of efficient welding construction of LNG ship low-temperature piping systems. The invention aims to solve the technical problems that the existing 316L series welding wire for welding the LNG ship low-temperature pipe is low in welding efficiency, and the low-temperature impact toughness of a flux-cored wire welding joint at 196 DEG C is low. According to the 316L series flux-cored wire, deposited metal under the welding heat input of 12 kJ / cm to 20 kJ / cm comprises the following chemical components in percentage by weight: 0.017%-0.04% of C, 0.4%-1% of Si, 1%-1.5% of Mn, 17%-19% of Cr, 11%-13% of Ni, 2%-2.5% of Mo and Cult; the low-temperature pipe 316L series austenitic stainless steel welding material is used for welding the low-temperature pipe 316L series austenitic stainless steel of the LNG ship.

Description

Technical Field

[0001] The present invention relates to the field of high-efficiency welding construction of low-temperature pipes of LNG ships, and specifically relates to a 316L series flux-cored welding wire and a welding method for high-efficiency welding of low-temperature pipes of LNG ships. Background Art

[0002] As a new type of green energy, LNG can be stored at -196℃ and its compression rate can be as high as 600 times, which has the value of adjusting the energy structure. Cryogenic pipes are core components of LNG storage and transportation systems. They are widely used in loading and unloading, evaporation gas processing, and ship power plants. The design temperature of cryogenic pipes is -196℃, the design pressure is 1MPa, and the commonly used material is austenitic stainless steel. There are extremely high requirements for material performance, and high and low temperature toughness, high weldability, and high corrosion resistance must be guaranteed. When welding important structural components, TIG welding is often used to ensure quality, but due to the characteristics of the welding method, it has a serious problem of low efficiency, which seriously affects the construction progress of LNG hulls. To solve this problem, starting from the two aspects of process methods and process materials, the efficient semi-automatic and automatic welding technology FCAW is studied, which is expected to greatly improve the welding efficiency. The matching high-performance flux-cored wire is studied, which is expected to break through the performance problems of conventional FCAW in the welding process of austenitic stainless steel cryogenic pipes.

[0003] The flux-cored wire welding used in FCAW has the advantages of high deposition efficiency, low spatter, beautiful forming and a wide range of welding current and voltage adaptability. It has a bright application prospect in the LNG industry. It is of great significance to carry out research on 316L welding wire for efficient welding of FCAW LNG low-temperature piping, break through efficient welding technology, and improve the construction quality and efficiency of LNG ships. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problems of low welding efficiency of the existing 316L welding wire used for welding low-temperature pipes of LNG ships and low low-temperature impact performance of the welded joints at -196°C, and to provide a 316L series flux-cored welding wire and a welding method for efficient welding of low-temperature pipes of LNG ships.

[0005] One of the purposes of the present invention is to provide a 316L series flux-cored welding wire for efficient welding of low-temperature pipes of LNG ships, wherein the chemical composition of the deposited metal of the flux-cored welding wire under a welding heat input of 12 to 20 kJ / cm is as follows by weight: C: 0.017% to 0.04%, Si: 0.4% to 1%, Mn: 1% to 1.5%, Cr: 17% to 19%, Ni: 11% to 13%, Mo: 2% to 2.5%, Cu<0.1%, and the balance is Fe and unavoidable impurities.

[0006] It is further defined that the flux-cored welding wire deposited metal contains 17.2% to 17.8% Cr, 12.5% ​​to 13% Ni, and a Cr / Ni ratio of 1.36; the flux-cored welding wire deposited metal contains 0.5% to 0.6% Si, 1.2% to 1.45% Mn, and a Mn / Si ratio of 2.67.

[0007] It is further defined that the flux-cored welding wire deposited metal contains 2.2% to 2.4% Mo and 0.017% to 0.02% C in the flux-cored welding wire deposited metal.

[0008] It is further defined that the chemical composition of the deposited metal is as follows by weight: C: 0.017% to 0.02%, Si: 0.5% to 0.6%, Mn: 1.2% to 1.45%, Cr: 17.2% to 17.8%, Ni: 12.5% ​​to 13%, Mo: 2.2% to 2.4%, Cu<0.1%, and the Cr / Ni ratio is 1.36, the Mn / Si ratio is 2.67, and the balance is Fe and unavoidable impurities.

[0009] It is further defined that the outer skin of the core is 304L stainless steel.

[0010] It is further defined that the unavoidable impurities include: P≤0.03%, S≤0.02%, Ti<0.04%, Al<0.02%, Nb<0.03%.

[0011] A second object of the present invention is to provide a welding method for the above-mentioned flux-cored welding wire, wherein:

[0012] The welding current is 220-230A, the welding voltage is 29-30V, the welding speed is 3-4mm / s, and the welding heat input is 12-20kJ / cm.

[0013] It is further defined that the welding current is 225.5 A, the welding voltage is 29.3 V, the welding speed is 3.3 mm / s, the welding heat input is 20.0 kJ / cm, and the interlayer temperature is controlled at 140°C.

[0014] The third object of the present invention is to provide a deposited metal of the above-mentioned flux-cored welding wire obtained by the above-mentioned welding method, wherein the deposited metal has a yield strength of ≥500MPa at -196°C, a tensile strength of ≥1100MPa, an elongation of ≥25%, and an average impact energy of the Charpy V-groove at -196°C of ≥46J.

[0015] A fourth object of the present invention is to provide an application of the above-mentioned flux-cored welding wire and the matching welding process method in the welding of 316L austenitic stainless steel for low-temperature piping of LNG ships.

[0016] The fifth object of the present invention is to provide a weld obtained by the above application, wherein the average impact energy of the Charpy V-groove at -196°C at the center of the weld, the junction between the weld and the base material, 2mm outside the junction, and 5mm outside the junction is ≥40J, ≥65J, ≥135J, and ≥220J, respectively.

[0017] It is further defined that the ferrite content in the center of the weld is 2 to 3.5%.

[0018] Compared with the prior art, the present invention has the following significant effects:

[0019] The present invention optimizes the performance and structure of the welded joint by comprehensively regulating the various elemental components of the 316L flux-cored welding wire deposited metal and the welding heat input in the supporting welding process, thereby obtaining excellent low-temperature impact toughness and low-temperature strength. The specific advantages are as follows:

[0020] (1) Stainless steel is highly sensitive to hot cracks and is greatly affected by impurity segregation. To limit the impurity content, P≤0.03% and S≤0.02% in the welding wire. The lower S and P content can effectively prevent the formation of low-melting-point eutectic and the generation of hot cracks. At the same time, it can purify the weld, prevent the generation of brittle and hard phases, and ensure the plastic toughness of the material.

[0021] A certain amount of ferrite must be ensured in the weld, and the best effect is achieved when the content is 3%. Ferrite nucleates non-uniformly in non-metallic inclusions, reducing the segregation of S and P at grain boundaries. Its interlocking structure can hinder crack propagation and improve toughness.

[0022] The C content in the deposited metal needs to be controlled. The best recommended range of C in the welding wire is: C: 0.017% ~ 0.02%, mainly because the C content has a great influence on the plasticity and toughness of the organization. Lower C can effectively prevent the excessive combination of C in stainless steel with the Cr element at the grain boundary, forming a Cr-poor effect and reducing the corrosion resistance of stainless steel. The right amount of C can stabilize austenite, ensure plasticity and toughness, and prevent cold cracks.

[0023] The Mn content in the deposited metal is increased appropriately. The optimal range of Mn in the welding wire is Mn: 1.2% to 1.45%. Mn is a stabilizing element of austenite, which effectively ensures the plasticity and toughness of the material. It can also be used as a deoxidizer and desulfurizer in austenitic stainless steel, transforming small particles, promoting nucleation, and purifying the weld. However, more Mn is likely to generate more manganese oxide, which is mixed in the weld.

[0024] The Si content in the deposited metal is reduced appropriately. The optimal range of Si element in the welding wire is Si: 0.5% to 0.6%. Si element and Mn element jointly deoxidize and purify the weld, while improving the processing performance and acid corrosion resistance. However, Si is easy to cause segregation of low melting point materials, which has a great impact on the impact performance of the weld, so it should not be too high. The optimal Mn / Si ratio is 2.67.

[0025] The Ni content in the deposited metal is increased appropriately. The optimal range of Ni element in the welding wire is Ni: 12.5%~13%. Ni is an austenitizing element that can improve plasticity, weldability, and low-temperature toughness. It is a core element for low-temperature resistance and has corrosion resistance.

[0026] The Cr content in the deposited metal should be limited appropriately. The optimal range of the Cr element in the welding wire is Cr: 17.2%~17.8%. Cr can mainly improve the corrosion resistance of stainless steel to oxidizing acids, improve wear resistance, and improve the strength and hardness of weld metal. However, Cr is a ferritizing element, which has a great influence on the phase transformation of the organization and reduces the plasticity and toughness of the material, so it should be limited.

[0027] The Cr / Ni equivalent is properly controlled in the deposited metal. The solidification transformation of the structure in stainless steel is very complex and is mainly affected by the Cr and Ni elements. The optimal Cr / Ni ratio in the welding wire is in the optimal range of 1.36, which is the AF solidification mode. The weld metal in the AF solidification mode not only has excellent low-temperature impact toughness, but also has higher strength and plasticity, which meets the key points of the present invention.

[0028] (2) The 316L flux-cored welding wire and the supporting welding method of the present invention are applicable to FCAW welding technology, with a wide welding process adaptability, high welding quality, excellent deposited metal performance, and significantly improved impact performance. The average impact energy of the -196℃ Charpy V-groove is ≥46.0J. The material cost changes little and has high benefits. It lays a foundation for welding materials and welding processes for the research on efficient automatic welding technology of low-temperature pipelines of LNG ships.

[0029] (3) The 316L flux-cored welding wire and the matching welding process of the present invention meet the requirements of welding 316L austenitic stainless steel, and the welding wire composition is simple, and at the same time meets the GB / T17853 E316LT1-1 standard and the AWSA5.22 E316LT1-1 standard. It can be used to weld 316L austenitic stainless steel for LNG low-temperature piping, LNG storage tanks, LNG transport ships, LNG satellite stations, LNG tank trucks, ultra-low temperature refrigerators, ultra-low temperature freezing equipment, etc. By using the 316L welding wire and process, the weld can obtain an excellent low-temperature impact performance of 43.6J at -196°C, which is much higher than the conventional commercial welding wire or the classification society standard value of 29J, and the welding efficiency is much higher than TIG welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the shape and size of the deposited metal test groove in Application Example 1 of the present invention;

[0031] Figure 2 A schematic diagram of the shape and size of the butt joint test groove in Application Example 2 of the present invention;

[0032] Figure 3The deposited metal test plate in Application Example 1 of the present invention;

[0033] Figure 4 This is a metallographic diagram of the deposited metal structure of Application Example 1 of the present invention;

[0034] Figure 5 This is a SEM image of the deposited metal structure of Application Example 1 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0037] Embodiment 1:

[0038] The 316L flux-cored welding wire for efficient welding of cryogenic pipes of LNG ships in this embodiment has an outer skin made of 304L stainless steel strip coil, and the chemical composition of the deposited metal is expressed by weight percentage: C: 0.017%, Si: 0.54%, Mn: 1.44%, Cr: 17.38%, Mo: 2.36%, Ni: 12.77%. In addition, the remaining part is composed of Fe and inevitable impurities, and the impurities include: P≤0.03%, S≤0.02%, Ti<0.04%, Al<0.02%, Nb<0.03%.

[0039] Application example 1: Cladding metal test

[0040] Step 1: Prepare the base material: Select 316L steel with a thickness of 20mm, cut the base material into plates, the size of the two plates is 300mm×150mm×20mm, process the groove shape and size, use V-shaped groove, the groove angle is 20°, and the groove root gap is 16mm. Polish and clean the base material and groove, and use acetone to clean. Figure 1 .

[0041] Step 2, welding wire preparation: Use the flux-cored welding wire described in Example 1, the diameter of the formed welding wire is 1.2 mm, and the welding wire should be unpacked before use to prevent it from getting wet. Do not use welding wire that has been wet or rusted.

[0042] Step 3. Preparation before welding: CO2 (99.9%) gas protection is used for welding, and the CO2 gas flow rate is adjusted to 15L / min. A steel liner is used at the bottom, with a thickness of 5mm, a width of 40mm, and a length that fits the entire weld seam, for single-sided welding. The test plate is rigidly constrained by a fixture.

[0043] Step 4, welding parameters: In this embodiment, the process parameters are welding current of 225.5A, welding voltage of 29.3V, welding speed of 3.3mm / s, welding heat input range of 20.0kJ / cm, and interlayer temperature of 140℃.

[0044] Step 5: FCAW conducts deposited metal cladding test.

[0045] The deposited metal of the welding wire under Example 1 was tested, and the yield strength, tensile strength, elongation at room temperature and the yield strength, tensile strength, elongation and average impact energy at -196°C were tested. The test results are shown in Table 1.

[0046] Table 1 Mechanical properties of deposited metal

[0047]

[0048] Under the condition of 20kJ / cm heat input, the average impact toughness of the deposited metal of the invented 316L flux-cored wire at -196℃ reached 46.0J

[0049] Application example 2: Docking test

[0050] Step 1: Prepare the base material: Select 316L steel with a thickness of 20mm, cut the base material into plates, the size of the two plates is 700mm×300mm×20mm, process the groove shape and size, use V-shaped groove, the groove angle is 60°, and the groove root gap is 6mm. Polish and clean the base material and groove, and use acetone to clean. Figure 2 .

[0051] Step 2, welding wire preparation: Use the flux-cored welding wire described in Example 1, the diameter of the formed welding wire is 1.2 mm, and the welding wire should be unpacked before use to prevent it from getting wet. Do not use welding wire that has been wet or rusted.

[0052] Step 3. Preparation before welding: CO2 (99.9%) gas protection is used for welding, and the CO2 gas flow rate is adjusted to 15 / min. A steel liner is used at the bottom, with a thickness of 5mm, a width of 40mm, and a length that fits the entire weld seam, for single-sided welding. The test plate is rigidly constrained by a fixture.

[0053] Step 4, welding parameters: In this embodiment, the process parameters are welding current of 225.5A, welding voltage of 29.3V, welding speed range of 3.3mm / s, welding heat input of 20kJ / cm, and interlayer temperature of 140℃.

[0054] Step 5: FCAW conducts deposited metal cladding test.

[0055] The weld obtained under Example 2 was tested for its room temperature tensile strength and average impact energy at -196°C. The test results are shown in Table 2.

[0056] Table 2 Mechanical properties of welded joints

[0057]

[0058] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A 316L flux-cored welding wire for efficient welding of cryogenic pipes of LNG ships, characterized in that: The chemical composition of the deposited metal at a welding heat input of 12 to 20 kJ / cm is as follows by weight: C: 0.017% to 0.04%, Si: 0.4% to 1%, Mn: 1% to 1.5%, Cr: 17% to 19%, Ni: 11% to 13%, Mo: 2% to 2.5%, Cu<0.1%, and the remainder is Fe and unavoidable impurities.

2. The flux-cored welding wire according to claim 1, characterized in that: The deposited metal contains 17.2% to 17.8% Cr, 12.5% ​​to 13% Ni, and a Cr / Ni ratio of 1.36; 0.5% to 0.6% Si; 1.2% to 1.45% Mn, and a Mn / Si ratio of 2.

67.

3. The flux-cored welding wire according to claim 2, characterized in that: The deposited metal contains Mo: 2.2%~2.4%, and C: 0.017%~0.02%.

4. The flux-cored welding wire according to claim 3, characterized in that: The outer shell is 304L stainless steel.

5. A welding method for use with the flux-cored welding wire according to any one of claims 1 to 4, characterized in that: The method: The welding current is 220-230A, the welding voltage is 29-30V, the welding speed is 3-4mm / s, and the welding heat input is 12-20kJ / cm.

6. The method according to claim 5, characterized in that The welding current was 225.5A, the welding voltage was 29.3V, the welding speed was 3.3mm / s, the welding heat input was 20.0kJ / cm, and the interlayer temperature was controlled at 140℃.

7. The deposited metal of the flux-cored welding wire according to claim 4 obtained by the method according to claim 6, characterized in that: The deposited metal has a yield strength of ≥500MPa, a tensile strength of ≥1100MPa, an elongation of ≥25% at -196°C, and an average impact energy of the Charpy V-groove at -196°C of ≥46J.

8. Use of the flux-cored welding wire according to claim 4 and the method according to claim 6 used therewith in welding 316L austenitic stainless steel for low-temperature piping of LNG ships.

9. The weld obtained by the application of claim 8, characterized in that: The average impact energy of the Charpy V-groove at the center of the weld, the junction between the weld and the base material, 2mm outside the junction, and 5mm outside the junction at -196℃ is ≥40J, ≥65J, ≥135J, and ≥220J, respectively.

10. The weld according to claim 9, characterized in that The ferrite content in the center of the weld is 2-3.5%.

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