Welding rod capable of post-weld stress relief heat treatment, preparation method and deposited metal

Abstract

The present invention provides a welding rod capable of post-weld stress relief heat treatment, a preparation method, and deposited metal. The welding rod has low requirements for the purity control of the welding core and has low cost. All alloying elements in the flux transition can be controlled and adjusted through the flux transition, thereby improving welding efficiency and reducing production costs. The toughness of the heat-treated weld is less sensitive to the sulfur and phosphorus content. The welding rod has the characteristics of simple manufacturing process, low manufacturing cost, high welding efficiency, and high weld toughness, and can fully adapt to the process of post-weld stress relief heat treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of welding materials, and in particular to a welding rod capable of post-weld stress relief heat treatment, a preparation method and deposited metal. Background Art

[0002] Storage pressure vessels are sealed containers for storing liquid or gas resources. They are typical welding engineering structures with complex structures and high stress concentration. Their storage media are mostly flammable and explosive petroleum, liquefied gas and high-pressure hydrogen. Therefore, pressure vessels have high requirements for safety and extremely strict requirements for construction quality. They have high requirements for the strength, hydrogen content, low-temperature toughness, etc. of welding materials. Usually, high-requirement pressure vessels need to undergo post-weld stress relief heat treatment (PWHT), and overall stress relief heat treatment is preferred. The advantages of post-weld stress relief heat treatment of pressure vessels are as follows: ① Eliminate welding stress and improve the stability and safety of the container by effectively relaxing welding stress; ② Improve material properties: Heat treatment can reduce the hardness of the weld joint area, improve the plasticity and toughness of the material, and ensure the safety of the container; ③ Ensure dimensional stability during processing or use, avoid structural distortion under welding stress, and ensure long-term stable use of the container; ④ Improve the joint's resistance to brittle fracture, stress resistance and corrosion resistance. Post-weld stress relief heat treatment (PWHT) usually requires keeping the temperature at 500-650℃ for 3 to 6 hours, followed by slow cooling to eliminate structural welding stress.

[0003] Studies have shown that stress relief heat treatment of low-alloy steel weld metal will cause the weld metallographic structure to grow and coarsen, the precipitates to grow, the sulfur and phosphorus components to segregate at the grain boundaries (temper embrittlement), and the residual austenite structure to decompose, ultimately leading to the deterioration of the mechanical properties of the weld metal (mainly low-temperature toughness). The rule is that the higher the weld metal strength and the higher the degree of alloying, the more obvious the stress relief heat treatment embrittlement effect of the weld metal, resulting in great restrictions on the application of pressure vessels made of high-strength steel that can be stress-relieved after welding.

[0004] Currently, high-quality, high-strength welding consumables that can be stress-relieved after welding are largely dominated by Kobelco's LB series welding consumables, including LB-52L, LB-65L, and LB-80LSR welding rods. Similar strength welding consumables that can be stress-relieved after welding have become available in China, with compositions broadly similar to those of the Japanese LB series. These include consumables with yield strengths of 500-600 MPa, as described in patents CN114310031A and CN113458648A, and consumables with yield strengths greater than 780 MPa, as described in patent CN116748737A. For 60 kg welding materials with lower strength, a 2.5% nickel, low molybdenum, titanium and boron micro-alloyed alloy system can be used to obtain a good strength-toughness match, and its sulfur and phosphorus content needs to be controlled at a low level as much as possible; for 80 kg welding materials with higher strength, a high nickel (close to 4%) chromium and molybdenum reinforced alloy system can be used to obtain a better strength-toughness match. The total sulfur and phosphorus content of the weld metal at this strength level must be controlled at an extremely low level, usually below 100 ppm, and actually controlled at 50-70 ppm. This places higher requirements on the purity control of the welding core material of the welding material. Usually, a special high-purity welding core material with controlled sulfur and phosphorus content is required, and the raw materials of the electrode coating also have higher purity requirements, which greatly increases the production cost of the welding rod. Summary of the Invention

[0005] In view of this, the present invention aims to propose a welding rod that can be subjected to stress relief heat treatment after welding, a preparation method and a deposited metal to solve the problem in the prior art that the total sulfur and phosphorus content of the weld metal after welding must be controlled to be less than or equal to 100 ppm, and the purity requirements of the welding rod core and flux coating are high, which greatly increases the production cost of the welding rod.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A welding rod capable of post-weld stress relief heat treatment, comprising a welding core and a coating wrapped around the surface of the welding core, wherein the coating accounts for 55% to 65% of the welding core by weight, and the coating comprises, by weight percentage: 20% to 33% marble, 15% to 25% fluorite, 1% to 5% rare earth fluoride, 0.3% to 1% lithium fluoride, 3% to 5% quartz, 3% to 9% rutile, 4% to 9% 30# ferrotitanium, 1.5% to 3% metal manganese powder, 1% to 2% 45# ferrosilicon powder, 15% to 2% atomized iron powder. % to 23%, metallic nickel powder 10% to 15%, metallic molybdenum powder 0.3% to 0.7%, nickel-magnesium alloy 1% to 2%, metallic magnesium-aluminum powder 0.5% to 1.1%, sodium water glass powder 2% to 4%, and the binder is potassium-sodium water glass with a modulus of 3.0; the components of the welding core include, by weight percentage, C≤0.08%, Si≤0.10%, 0.40%<Mn<0.65%, P≤0.010%, S≤0.005%, P+S≤0.015%, and the balance is Fe.

[0008] The welding rod capable of post-weld stress relief heat treatment described in the present application has low requirements for the purity control of the welding core, low cost, and low sensitivity of the heat-treated weld toughness to the sulfur and phosphorus content. It has the characteristics of simple manufacturing process, low manufacturing cost, high welding efficiency, and high weld toughness, and can fully adapt to the process of post-weld stress relief heat treatment.

[0009] Furthermore, the outer diameter of the coating of the 4.0 mm welding rod is 6.8 to 7.0 mm.

[0010] This setting can enhance the performance of the weld, improve its strength and toughness, and can also adapt to different welding conditions and positions, providing better welding adaptability.

[0011] The present application also provides a welding rod deposited metal, which is welded using the aforementioned welding rod and comprises the following chemical composition in weight percentage:

[0012] C: 0.04~0.07%, Mn: 0.6~1.2%, Si: 0.20~0.50%, P: ≤0.010%, S: ≤0.005%, P+S≤0.015%, Ni: 5.00~6.50%, Mo: 0.10~0.30%, Ti: 0.020~0.050%, Cr≤0.10%, RE<0.0050%, and the balance is Fe.

[0013] This setting can reduce the requirements for sulfur and phosphorus content, reduce production costs and control difficulty, and the composition design of the deposited metal is simple and reasonable, easy to implement. The weld toughness is less sensitive to stress relief heat treatment embrittlement caused by sulfur and phosphorus, and can meet the stringent performance requirements of high strength and high toughness of the weld metal in the welded state and the stress relief heat treatment state.

[0014] Furthermore, the diffusible hydrogen content Hd of the deposited metal is ≤4 ml / 100 g.

[0015] This setting helps to maintain the toughness of the weld metal, avoid embrittlement, ensure that the weld can still maintain good toughness under low temperature or high stress conditions, make the weld have good crack resistance, and the welding rod has all-position welding adaptability.

[0016] Furthermore, the deposited metal meets the following properties: yield strength ≥800 MPa, tensile strength ≥850 MPa, impact energy at -40°C ≥70 J, and impact energy at -50°C ≥50 J.

[0017] This setting can ensure the reliability of the weld metal under high load and high stress conditions, meet the needs of high-strength structures, and is suitable for heavy-load and high-strength applications. It enables the weld metal to maintain good toughness in low-temperature environments, effectively resist brittle fracture, and ensure reliability under extreme conditions.

[0018] The present application also provides a method for preparing a welding rod capable of post-weld stress relief heat treatment, which is used for the aforementioned welding rod capable of post-weld stress relief heat treatment, comprising the following steps:

[0019] Step 1: Weigh the various components of the coating according to the proportion, add the binder and mix evenly to obtain a mixture;

[0020] Step 2: coating the mixture on the surface of the welding core, and then baking it to obtain the welding rod.

[0021] This preparation method has simple steps, is easy to operate, can improve production efficiency, reduce production costs, and is suitable for large-scale production.

[0022] Furthermore, in step 1, the binder is potassium-sodium water glass with a modulus of 2.9 to 3.1, a concentration of 40 to 42 Be, potassium: sodium = 1:3, and the potassium-sodium water glass accounts for 25% of the weight of the mixture.

[0023] This setting can effectively combine the coating components together to form a stable mixture, improve the overall strength and toughness of the coating, and ensure the stability of the electrode during welding.

[0024] Furthermore, in step 2, the welding rod is first dried in an environment of 80-90° C. for 5-6 hours, and then dried in an environment of 350-400° C. for 1-2 hours to produce a finished welding rod.

[0025] By drying in stages, cracking or peeling of the coating caused by rapid temperature changes can be avoided, ensuring the integrity of the welding rod.

[0026] Compared with the prior art, the welding rod capable of post-weld stress relief heat treatment, preparation method, and deposited metal of the present invention have the following advantages:

[0027] 1) The purity control requirements for the welding core are not high, the cost is low, and the coating transfers all the alloying elements. The alloying level can be controlled and adjusted through the coating transfer, thereby improving welding efficiency and reducing production costs. The toughness of the heat-treated weld is less sensitive to the sulfur and phosphorus content. It has the characteristics of simple manufacturing process, low manufacturing cost, high welding efficiency and high weld toughness, and can fully adapt to the process of post-weld stress relief heat treatment;

[0028] 2) It can reduce the requirements for sulfur and phosphorus content, reduce production costs and control difficulty, the composition design of the deposited metal is simple and reasonable, and easy to implement. The weld toughness is less sensitive to the stress relief heat treatment embrittlement caused by sulfur and phosphorus, and can meet the stringent performance requirements of high strength and high toughness of the weld metal in the welded state and the stress relief heat treatment state. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A metallographic diagram of the weld structure in the welded state according to an embodiment of the present invention;

[0030] Figure 2 This is a metallographic diagram of the weld structure after stress relief heat treatment according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] The present application provides a welding rod capable of post-weld stress relief heat treatment, comprising a welding core and a coating wrapped around the surface of the welding core, wherein the coating accounts for 55% to 65% by weight of the welding core, and the coating comprises, by weight, 20% to 33% of marble, 15% to 25% of fluorite, 1% to 5% of rare earth fluoride, 0.3% to 1% of lithium fluoride, 3% to 5% of quartz, 3% to 9% of rutile, 4% to 9% of 30# ferrotitanium, 1.5% to 3% of metallic manganese powder, 1% to 2% of 45# ferrosilicon powder, and 15% to 23% of atomized iron powder. , 10% to 15% of metallic nickel powder, 0.3% to 0.7% of metallic molybdenum powder, 1% to 2% of nickel-magnesium alloy, 0.5% to 1.1% of metallic magnesium-aluminum powder, 2% to 4% of sodium water glass powder, and a binder of potassium-sodium water glass with a modulus of 3.0; the welding core adopts a carbon steel H08E welding core, and the components of the welding core include, by weight percentage, C≤0.08%, Si≤0.10%, 0.40%<Mn<0.65%, P≤0.010%, S≤0.005%, P+S≤0.015%, and the balance is Fe.

[0034] The welding rod capable of post-weld stress relief heat treatment described in the present application adopts a carbon steel H08E welding core, which has low requirements for the purity control of the welding core and low cost. The flux coating transitions all alloying elements, and the alloying level can be controlled and adjusted through the flux coating transition, thereby improving welding efficiency and reducing production costs. The toughness of the heat-treated weld is less sensitive to the sulfur and phosphorus content. The welding rod has the characteristics of simple manufacturing process, low manufacturing cost, high welding efficiency, and high weld toughness, and can fully adapt to the process of post-weld stress relief heat treatment.

[0035] The composition of carbon steel H08E welding core is shown in Table 1 below:

[0036] Table 1

[0037] serial number C Si Mn S P Fe 1 0.079 0.028 0.454 0.0045 0.010 margin 2 0.061 0.022 0.478 0.0050 0.009 margin

[0038] The composition of the electrode coating is shown in Table 2 below:

[0039] Table 2

[0040]

[0041] Marble, fluorite, rutile, and quartz are used to form a basic slag system to protect and refine the weld metal. Their total content is less than 60%, increasing the proportion of metal powder in the coating and improving deposition efficiency. A 40% to 50% metal powder and thicker coating ensure a coating mass factor greater than 50%, effectively transitioning a large amount of alloying elements and enhancing weldability. This electrode is suitable for all-position welding, producing high-quality weld metal. Rare earth microalloying purifies the weld metal, while titanium microalloying promotes the formation of the AF microstructure and refines the resulting AF+B+M mixed microstructure. A suitable high-nickel alloying combination promotes the refinement of the AF+B+M mixed microstructure while also refining the AR (retained austenite) structure between ferrite. The high nickel content stabilizes the AR structure and enhances the weld toughness with consistent results, resulting in a high-strength, high-toughness weld metal. Even after post-weld stress relief heat treatment, the weld toughness remains high.

[0042] As a preferred example of the present application, the outer diameter of the coating of a 4.0 mm welding rod is 6.8 to 7.0 mm.

[0043] Thicker coatings can effectively transfer more alloying elements into the weld metal, enhance the performance of the weld, improve its strength and toughness, and adapt to different welding conditions and positions, providing better welding adaptability.

[0044] Preferably, the outer diameter of the 3.2mm coating is 5.6-5.8mm.

[0045] The present application also provides a deposited metal, which is welded using the aforementioned welding rod and comprises the following chemical composition in weight percentage:

[0046] C: 0.04~0.07%, Mn: 0.6~1.2%, Si: 0.20~0.50%, P: ≤0.010%, S: ≤0.005%, P+S≤0.015%, Ni: 5.00~6.50%, Mo: 0.10~0.30%, Ti: 0.020~0.050%, Cr≤0.10%, RE<0.0050%, and the balance is Fe.

[0047] The carbon content is controlled at 0.04-0.07% to ensure the strength level and appropriate hardenability and prevent the occurrence of welding hot cracks; the silicon content is controlled at 0.20-0.50% to ensure the deoxidation effect of the weld metal and improve the toughness of the weld; the manganese content is controlled at 0.6-1.2% to ensure the deoxidation and desulfurization effect of the weld metal, and at the same time, carbon, nickel and molybdenum elements are combined to obtain appropriate structural transformation characteristics, obtain a weld structure mainly composed of fine bainite type, and avoid the excessive generation of undesirable coarse bainite structure which is detrimental to toughness; the nickel content is controlled at 5.00-6.50%, which is a key control factor in the alloy system of this application. Appropriate high nickel combined with lower levels of silicon, manganese and molybdenum elements can increase the hardenability of the weld, reduce the appearance of proeutectoid ferrite and coarse bainite structure, obtain a fine mixed structure with AF+B+M as the main body, and greatly stabilize the retained austenite A between the lath structures. R , A R In addition to improving toughness, it can hinder the diffusion of carbon between organizations, reduce the coarsening tendency of carbides, absorb a certain amount of impurity elements such as S and P, and reduce the embrittlement caused by grain boundary segregation; the chromium content is controlled within 0.10%, firstly, it is necessary to control the organization type in the alloy system, and secondly, it is to avoid the precipitation of carbides during the stress relief heat treatment process, which causes embrittlement; the molybdenum content is controlled between 0.10 and 0.30%, which is conducive to obtaining a medium-temperature transformation bainite type organization; the titanium content is controlled between 0.020 and 0 Controlling the content of sulfur and phosphorus between 0.0050% and 0.050% can promote the formation of AF structure, split the untransformed austenite, and refine the subsequently formed B+M structure; controlling the content of RE within 0.0050% can purify the grain boundaries; controlling the sulfur and phosphorus content to P: ≤ 0.010%, S: ≤ 0.005%, and P+S ≤ 0.015% can reduce the requirements for sulfur and phosphorus content, reducing production costs and control difficulty. On the other hand, in the alloy welding material of the present application, the sulfur and phosphorus content requirements are sufficient to ensure the toughness of the deposited metal. The composition design of the deposited metal of the present application is simple and reasonable, and it is easy to implement. The weld toughness is less sensitive to stress relief heat treatment embrittlement caused by sulfur and phosphorus, and can meet the stringent performance requirements of high strength and high toughness for the weld metal in both the welded state and the stress relief heat treatment state.

[0048] As a preferred example of the present application, the diffusible hydrogen content Hd of the deposited metal is ≤4 ml / 100 g.

[0049] A lower hydrogen content helps maintain the toughness of the weld metal, avoids embrittlement, ensures that the weld can still maintain good toughness under low temperature or high stress conditions, makes the weld have good crack resistance, and the welding rod has all-position welding adaptability.

[0050] Preferably, 2.32 ml / 100 g<Hd<2.62 ml / 100 g.

[0051] As a preferred example of the present application, the deposited metal meets the following properties: yield strength ≥800 MPa, tensile strength ≥850 MPa, impact energy at -40°C ≥70 J, and impact energy at -50°C ≥50 J.

[0052] Yield strength ≥800MPa and tensile strength ≥850MPa ensure the reliability of the weld metal under high load and high stress conditions, meet the needs of high-strength structures, and are suitable for heavy-load and high-strength applications; -40℃ impact energy ≥70J and -50℃ impact energy ≥50J enable the weld metal to maintain good toughness in low-temperature environments, effectively resist brittle fracture, and ensure reliability under extreme conditions.

[0053] The present application also provides a method for preparing a welding rod, which is used to prepare the welding rod capable of post-weld stress relief heat treatment, comprising the following steps:

[0054] Step 1: Weigh the various components of the coating according to the proportion, add the binder and mix evenly to obtain a mixture;

[0055] Step 2: coating the mixture on the surface of the welding core, and then baking it to obtain the welding rod.

[0056] Weighing and mixing the components in proportion can ensure that the components of the coating are evenly distributed, avoiding differences in welding performance caused by uneven components, thereby improving the consistency and reliability of the welding rod; this preparation method has simple steps and is easy to operate, which can improve production efficiency, reduce production costs, and is suitable for large-scale production.

[0057] As a preferred example of the present application, in step 1, the binder is potassium-sodium water glass with a modulus of 2.9 to 3.1, a concentration of 40 to 42 Be, potassium: sodium = 1:3, and the potassium-sodium water glass accounts for 25% of the weight of the mixture.

[0058] Potassium-sodium water glass, as a binder, can effectively combine the coating components to form a stable mixture, improve the overall strength and toughness of the coating, and ensure the stability of the electrode during welding. Water glass with a modulus of 2.9 to 3.1 can provide appropriate fluidity and adhesion, ensuring that the coating components can be evenly distributed during the mixing and coating process to avoid agglomeration, thereby improving the quality of the electrode.

[0059] As a preferred example of the present application, in step 2, the welding rod is first dried in an environment of 80-90°C for 5-6 hours, and then dried in an environment of 350-400°C for 1-2 hours to make a finished welding rod.

[0060] Low-temperature drying can effectively remove moisture from the welding rod, prevent the generation of steam during high-temperature drying, and avoid bubbles or cracks on the surface of the welding rod, thereby improving the overall quality of the welding rod. High-temperature drying helps to further improve the high-temperature resistance of the coating. By drying in stages, it can avoid cracking or peeling of the coating caused by rapid temperature changes, and ensure the integrity of the welding rod.

[0061] The weld metal welding of the finished electrode was carried out in accordance with SAF5.14-2005 "Code for Boilers and Pressure Vessels". Ordinary low alloy steel plates were used. The grooves were welded after 3 layers of welding rods were piled up. The thickness of the steel plate was 20 mm, the length of the test plate was 400 to 500 mm, and the root gap was 14 mm. The weld metal was subjected to round bar tensile test and -40 ° C and -50 ° C impact test. The composition of the weld metal is shown in Table 3, and the mechanical properties are shown in Table 4. The weld microstructures of the welded state and the stress relief heat treatment state are shown in Table 4. Figure 1 and Figure 2 The weld structure is small and dispersed, and the organizational morphology remains basically unchanged after heat treatment.

[0062] Table 3

[0063]

[0064] Table 4

[0065]

[0066] The present application also provides a welding method for the aforementioned welding rod that can be subjected to stress relief heat treatment after welding, using a 4.0mm welding rod, a welding current of 170±5A, a welding speed of 18±3cm / min, an interpass temperature of 130~170℃, and a DC reverse current during welding.

[0067] This setting can ensure that the electrode maintains a good melting rate and molten pool stability during the welding process, avoid overheating or insufficient melting, improve the quality of the weld, effectively reduce the stress generated during welding, reduce the hardness of the welding heat affected zone, improve the toughness of the weld, and prevent the generation of welding cracks. The use of DC reverse current can improve the stability of the arc, enhance the arc penetration during welding, improve the fluidity of the molten pool, and ensure the uniformity and quality of the weld.

[0068] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A welding rod capable of post-weld stress relief heat treatment, characterized in that: The invention is composed of a welding core and a coating wrapped on the surface of the welding core, wherein the coating accounts for 55% to 65% of the weight of the welding core, and the coating components include, by weight percentage: marble 20% to 33%, fluorite 15% to 25%, rare earth fluoride 1% to 5%, lithium fluoride 0.3% to 1%, quartz 3% to 5%, rutile 3% to 9%, 30# titanium iron 4% to 9%, metal manganese powder 1.5% to 3%, 45# ferrosilicon powder 1% to 2%, atomized iron powder 15% to 23%, gold The welding core comprises 10% to 15% nickel powder, 0.3% to 0.7% metal molybdenum powder, 1% to 2% nickel-magnesium alloy, 0.5% to 1.1% metal magnesium-aluminum powder, 2% to 4% sodium water glass powder, and a binder made of potassium-sodium water glass with a modulus of 3.

0. The welding core comprises the following components by weight percentage: C ≤ 0.08%, Si ≤ 0.10%, 0.40% < Mn < 0.65%, P ≤ 0.010%, S ≤ 0.005%, P + S ≤ 0.015%, and the balance is Fe.

2. The welding rod capable of post-weld stress relief heat treatment according to claim 1, characterized in that: The outer diameter of the coating of a 4.0mm welding rod is 6.8 to 7.0mm.

3. A welding rod deposited metal, which is welded using the welding rod capable of post-weld stress relief heat treatment according to claim 1, characterized in that: The chemical composition includes the following weight percentages: C: 0.04~0.07%, Mn: 0.6~1.2%, Si: 0.20~0.50%, P: ≤0.010%, S: ≤0.005%, P+S≤0.015%, Ni: 5.00~6.50%, Mo: 0.10~0.30%, Ti: 0.020~0.050%, Cr≤0.10%, RE<0.0050%, and the balance is Fe.

4. The electrode deposited metal according to claim 3, characterized in that: The diffusible hydrogen content Hd of the deposited metal is ≤4 ml / 100 g.

5. The electrode deposited metal according to claim 3, characterized in that: The deposited metal meets the following properties: yield strength ≥800 MPa, tensile strength ≥850 MPa, impact energy at -40°C ≥70 J, and impact energy at -50°C ≥50 J.

6. A method for preparing a welding rod for use in the welding rod capable of post-weld stress relief heat treatment according to claim 1, characterized in that: The steps include: Step 1: Weigh the various components of the coating according to the proportion, add the binder and mix evenly to obtain a mixture; Step 2: coating the mixture on the surface of the welding core, and then baking it to obtain the welding rod.

7. The method for preparing a welding rod capable of post-weld stress relief heat treatment according to claim 6, characterized in that: In step 1, the binder is potassium-sodium water glass with a modulus of 2.9 to 3.1, a concentration of 40 to 42 Be, potassium: sodium = 1:3, and the potassium-sodium water glass accounts for 25% of the weight of the mixture.

8. The method for preparing a welding rod capable of post-weld stress relief heat treatment according to claim 6, characterized in that: In step 2, the welding rod is first dried at 80-90°C for 5-6 hours, and then dried at 350-400°C for 1-2 hours to produce a finished welding rod.

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