A 316l series flux-cored wire for efficient welding of cryogenic pipes of LNG ships and a welding method

Abstract

A 316L series flux-cored wire for high-efficiency welding of LNG ship cryogenic pipes and a welding method. The present application belongs to the field of high-efficiency welding of LNG ship cryogenic pipes. The purpose of the present application is to solve the technical problems of low welding efficiency of the existing 316L series welding wire for LNG ship cryogenic pipe welding and low low-temperature impact toughness of the welding joint of the flux-cored wire. The chemical composition of the deposited metal of the 316L series flux-cored wire of the present application under a welding heat input of 12-20 kJ / cm is as follows in terms of percentage by weight: C: 0.017%-0.04%, Si: 0.4%-1%, Mn: 1%-1.5%, Cr: 17%-19%, Ni: 11%-13%, Mo: 2%-2.5%, Cu: <0.1%, and the balance of Fe and inevitable impurities, which is used for welding of 316L series austenitic stainless steel of LNG ship cryogenic pipes.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of LNG ship cryogenic piping high-efficiency welding, and particularly relates to a 316L flux-cored wire for LNG ship cryogenic piping high-efficiency welding and a welding method. BACKGROUND

[0002] LNG, as a new green energy, is stored at -196 DEG C and has a compression rate of up to 600 times, which has the value of adjusting the energy structure. The cryogenic pipe is a core component of the LNG storage and transportation system and is widely used in loading and unloading, vapor gas treatment and ship power devices, etc. The design temperature of the cryogenic pipe is -196 DEG C, the design pressure is 1 MPa, and the commonly used material is austenitic stainless steel. The material performance must be high in low-temperature toughness, weldability and corrosion resistance. When welding important structural components, TIG welding method is often used to ensure the quality. However, due to the characteristics of the welding method, there is a serious problem of low efficiency, which seriously affects the construction progress of the LNG ship. In order to solve this problem, from the aspects of process method and process material, the semi-automatic and automatic welding technology FCAW is researched, which is expected to greatly improve the welding efficiency. The high-performance flux-cored wire matched with the FCAW is researched, which is expected to break through the performance deficiency problem of the conventional FCAW in the welding process of the austenitic stainless steel of the cryogenic pipe.

[0003] The flux-cored wire used in the FCAW welding has the advantages of high deposition efficiency, low spatter, good appearance, wide welding current and voltage adaptability, etc. and has a good application prospect in the LNG industry. It is of great significance to carry out the research on the 316L flux-cored wire for the FCAW of the LNG cryogenic piping high-efficiency welding, break through the high-efficiency welding technology and improve the construction quality and efficiency of the LNG ship. SUMMARY

[0004] The application aims to solve the technical problems of low welding efficiency of the existing 316L welding wire for the LNG ship cryogenic piping welding and low low-temperature impact performance of the welded joint at -196 DEG C, and provides a 316L flux-cored wire for LNG ship cryogenic piping high-efficiency welding and a welding method.

[0005] One of the purposes of the application is to provide a 316L flux-cored wire for LNG ship cryogenic piping high-efficiency welding. The chemical composition of the deposited metal under a welding heat input of 12-20 kJ / cm is as follows in terms of percentage by weight: C: 0.017%-0.04%, Si: 0.4%-1%, Mn: 1%-1.5%, Cr: 17%-19%, Ni: 11%-13%, Mo: 2%-2.5%, Cu: <0.1%, and the balance is Fe and inevitable impurities.

[0006] Further limit, the Cr in the flux-cored wire deposited metal is 17.2%~17.8%, the Ni is 12.5%~13%, and the Cr / Ni ratio is 1.36, the Si in the flux-cored wire deposited metal is 0.5%~0.6%, the Mn is 1.2%~1.45%, and the Mn / Si ratio is 2.67.

[0007] Further limit, the Mo in the flux-cored wire deposited metal is 2.2%~2.4%, the C in the flux-cored wire deposited metal is 0.017%~0.02%.

[0008] Further limit, the chemical composition of the deposited metal is: C: 0.017%~0.02%, Si: 0.5%~0.6%, Mn: 1.2%~1.45%, Cr: 17.2%~17.8%, Ni: 12.5%~13%, Mo: 2.2%~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 inevitable impurities.

[0009] Further limit, the flux-cored wire outer skin is 304L stainless steel.

[0010] Further limit, the inevitable impurities include: P≤0.03%, S≤0.02%, Ti<0.04%, Al<0.02%, Nb<0.03%.

[0011] The second object of the present application is to provide a welding method matched with the above flux-cored wire, and the method is:

[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] Further limit, the welding current is 225.5A, the welding voltage is 29.3V, the welding speed is 3.3mm / s, the welding heat input is 20.0kJ / cm, and the interlayer temperature is controlled at 140℃.

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

[0015] The fourth object of the present application is to provide an application of the above flux-cored wire and matched welding process method in the welding of 316L austenitic stainless steel in the low-temperature pipe system of LNG ship.

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

[0017] Further limited, the ferrite content in the center of the weld is 2-3.5%.

[0018] Compared with the prior art, the present application has the following remarkable effects:

[0019] The present application optimizes the performance and microstructure of the welded joint by comprehensively controlling the various element components of the 316L flux-cored wire and the welding heat input in the matching welding process, and excellent low-temperature impact toughness and low-temperature strength are obtained. The specific advantages are as follows:

[0020] (1) The hot crack sensitivity of stainless steel is high, and is greatly affected by impurity segregation. In order 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 eutectic and the generation of hot cracks. At the same time, the weld is purified to prevent the generation of brittle hard phases and ensure the plasticity and toughness of the material.

[0021] A certain amount of ferrite needs to be ensured in the weld, and the content is best at 3%. The non-metallic inclusions are non-uniformly nucleated in the ferrite, the segregation of S and P at the grain boundary is reduced, the chain structure can hinder crack propagation, and the toughness is improved.

[0022] The C content in the deposited metal needs to be controlled, and the optimal recommended range of C element in the welding wire is C: 0.017%-0.02%. This is mainly because the C content has a great influence on the plasticity and toughness of the structure. Lower C can effectively prevent the excessive combination of C in stainless steel and Cr element at the grain boundary to form a Cr-poor effect and reduce the corrosion resistance of stainless steel. Appropriate C can stabilize the austenite, ensure the plasticity and toughness, and prevent cold cracking.

[0023] The Mn content in the deposited metal is appropriately increased, and the optimal range of Mn element in the welding wire is Mn: 1.2%-1.45%. Mn is an austenite stabilizing element, which effectively ensures the plasticity and toughness of the material, and can also be used as a deoxidizer and desulfurizer in austenitic stainless steel to transform small particles, promote nucleation, and purify the weld. However, too much Mn can easily generate more manganese oxide and be included in the weld.

[0024] The Si content in the deposited metal is appropriately reduced, and the optimal range of Si element in the welding wire is Si: 0.5%-0.6%. Si element and Mn element jointly deoxidize and purify the weld, and can also improve the processing performance and acid corrosion resistance. However, Si can easily cause low-melting-point segregation, which has a great influence on the impact performance of the weld, and the optimal Mn / Si ratio is 2.67.

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

[0026] The content of Cr in the deposited metal is appropriately limited, the optimal range of Cr element in the welding wire is 17.2% to 17.8%, Cr can mainly improve the corrosion resistance of stainless steel to oxidizing acid, improve the wear resistance, and improve the strength and hardness of the weld metal, but Cr is a ferritizing element, has a great influence on the phase change of the structure, and reduces the plasticity and toughness of the material, and should be limited.

[0027] The Cr / Ni equivalent in the deposited metal is appropriately controlled, the structure of the stainless steel is very complex, is mainly affected by Cr and Ni elements, the optimal range of the Cr / Ni ratio in the welding wire is 1.36, under the AF solidification mode, the weld metal not only has excellent low-temperature impact toughness, but also has high strength and plasticity, and meets the gist of the application.

[0028] (2) The 316L flux-cored wire and the matching welding method have the advantages of being suitable for FCAW welding technology, having a wide welding process adaptation range, high welding quality, excellent deposited metal properties, and significant improvement in impact performance, the average impact energy of the Charpy V-shaped groove at-196 DEG C is greater than or equal to 46.0J, the material cost changes little, and high benefits are obtained. The application lays a foundation for welding materials and welding processes for high-efficiency automatic welding technology of low-temperature pipelines of LNG ships.

[0029] (3) The 316L flux-cored wire and the matching welding process method meet the welding of 316L austenitic stainless steel, the composition of the welding wire is simple, and meets the GB / T17853 E316LT1-1 standard and the AWS A5.22 E316LT1-1 standard. The 316L flux-cored wire and the matching welding process method can be used for welding 316L austenitic stainless steel for LNG low-temperature pipelines, LNG storage tanks, LNG transport ships, LNG satellite stations, LNG tank trucks, ultra-low-temperature refrigerators and ultra-low-temperature freezing equipment, and the like. By using the 316L flux-cored wire and the matching welding process method, the weld can obtain excellent low-temperature impact performance of 43.6J at-196 DEG C, which is much higher than the conventional commercial welding wire or the standard value 29J of the ship classification society, and the welding efficiency is much higher than that of TIG welding. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a schematic diagram of the groove shape and size of the deposited metal in the application example 1 of the application;

[0031] Figure 2 It is a schematic diagram of the groove shape and size of the butt joint in the application example 2 of the application;

[0032] Figure 3The deposited metal test plate in application example 1 of the present application;

[0033] Figure 4 The deposited metal microstructure photomicrograph in application example 1 of the present application;

[0034] Figure 5 The deposited metal SEM photomicrograph in application example 1 of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[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 by commercial channels by those skilled in the art.

[0037] Example 1

[0038] The 316L flux-cored wire for high-efficiency welding of LNG ship cryogenic pipes in this example is made of 304L stainless steel strip, and the chemical composition of the deposited metal is as follows in terms of 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, including: P≤0.03%, S≤0.02%, Ti<0.04%, Al<0.02%, Nb<0.03%.

[0039] Application Example 1: Deposited Metal Test

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

[0041] Step two, welding wire preparation: use the flux-cored wire described in example 1, the formed welding wire diameter is 1.2 mm, the welding wire is sealed and unsealed as needed to prevent moisture, and the welding wire that has been damp or rusted should not be used.

[0042] Step three, preparation before welding: CO2 (99.9%) gas protection is used for welding, and the CO2 gas flow is adjusted to 15 L / min. Steel backing is used at the bottom, the backing thickness is 5 mm, the width is 40 mm, and the length is consistent with the whole weld for single-sided welding. The test plate is rigidly constrained by a clamp.

[0043] Step four, welding parameters: in this embodiment, the welding current is 225.5 A, the welding voltage is 29.3 V, the welding speed is 3.3 mm / s, and the welding heat input is in the range of 20.0 kJ / cm. The interlayer temperature is controlled at 140°C.

[0044] Step five, FCAW is used for deposited metal surfacing test.

[0045] The deposited metal using the welding wire in Example 1 is detected, and the room temperature yield strength, tensile strength, elongation, and -196°C yield strength, tensile strength, elongation, and average impact energy are detected. The detection results are shown in Table 1.

[0046] Table 1 Mechanical properties of deposited metal

[0047]

[0048] Under the condition of 20 kJ / cm heat input, the average value of the low temperature impact toughness of the deposited metal of the 316L flux-cored wire of the application at -196°C reaches 46.0 J

[0049] Application Example 2: butt joint test

[0050] Step one, preparation of base material: 316L steel material with a thickness of 20 mm is selected, the base material is cut into a plate, the size of the two plates is 700 mm x 300 mm x 20 mm, the groove shape and size are processed, a V-shaped groove is used, the groove angle is 60°, and the groove root gap is 6 mm. The base material and the groove are polished, polished and cleaned with acetone, see Figure 2 .

[0051] Step two, welding wire preparation: the flux-cored wire described in Example 1 is used, the formed welding wire diameter is 1.2 mm, the welding wire is sealed and opened as needed to prevent moisture, and the welding wire that has been damp or rusted should not be used.

[0052] Step three, preparation before welding: CO2 (99.9%) gas protection is used for welding, and the CO2 gas flow is adjusted to 15 / min. Steel backing is used at the bottom, the backing thickness is 5 mm, the width is 40 mm, and the length is consistent with the whole weld for single-sided welding. The test plate is rigidly constrained by a clamp.

[0053] Step four, welding parameters: in this embodiment, the welding current is 225.5 A, the welding voltage is 29.3 V, the welding speed range is 3.3 mm / s, and the welding heat input is 20 kJ / cm. The interlayer temperature is controlled at 140℃.

[0054] Step five, FCAW is used to carry out deposited metal surfacing test.

[0055] The weld obtained by using Example 2 is detected, and the tensile strength at room temperature and the average impact energy at-196℃ are detected. The detection results are shown in Table 2.

[0056] Table 2 Mechanical properties of welded joints

[0057]

[0058] The above description is only the preferred specific embodiments of the present application, these specific embodiments are all different implementations based on the overall concept of the present application, and the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A 316L-series flux-cored wire for efficient welding of cryogenic pipes of LNG ships, characterized by, The chemical composition of the deposited metal at a welding heat input of 12-20 kJ / cm is as follows in terms of percentage by weight: C: 0.017%-0.04%, Si: 0.5%-0.6%, Mn: 1.2%-1.45%, Cr: 17.2%-17.8%, Ni: 12.5%-13%, Mo: 2%-2.5%, Cu: <0.1%, the balance being Fe and inevitable impurities, and the Cr / Ni ratio is 1.36 and the Mn / Si ratio is 2.67, and the inevitable impurities include: P: ≤0.03%, S: ≤0.02%, Ti: <0.04%, Al: <0.02%, and Nb: <0.03%.

2. The flux cored welding wire of claim 1, wherein The Mo content in the deposited metal is 2.2%-2.4%, and the C content is 0.017%-0.02%.

3. The flux cored wire of claim 2, wherein The outer skin is made of 304L stainless steel.

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

5. The method of claim 4, wherein, 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 DEG C.

6. The deposit of the flux-cored wire of claim 3, obtained under the method of claim 5, characterized by that, The deposited metal has a yield strength of ≥500 MPa at 196 DEG C, a tensile strength of ≥1100 MPa, an elongation of ≥25%, and a Charpy V-notch average impact energy of ≥46 J at -196 DEG C.

7. The application of the flux-cored wire of claim 3 and the method of claim 5 in the welding of 316L austenitic stainless steel for low-temperature pipelines of LNG ships.

8. The weld seam obtained by the use according to claim 7, characterized in that The Charpy V-notch average impact energy at the weld center, the weld and base material joint, 2 mm outside the joint, and 5 mm outside the joint is ≥40 J, ≥65 J, ≥135 J, and ≥220 J, respectively, at -196 DEG C.

9. The weld of claim 8, wherein, The ferrite content at the weld center is 2-3.5%.

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