90kg-grade ultralow-temperature high-strength steel welding rod and preparation method thereof

Abstract

The invention provides a 90kg-grade ultralow-temperature high-strength steel welding rod and a preparation method thereof, and the welding rod comprises a core wire and a coating covering the surface of the core wire, the coating is prepared from, by weight, 35%-45% of marble, 15%-20% of fluorite, 3%-5% of silica powder, 2%-4% of rutile, 1%-2% of manganese metal, 1%-2% of ferrosilicon, 15%-20% of nickel metal, 5%-10% of ferrotitanium, 2%-5% of ferromolybdenum, 0.4%-0.8% of sodium alginate, 0.3%-0.9% of sodium carbonate, 0.2%-0.5% of lanthanum oxide and the balance iron powder. According to the welding rod, under the high channel temperature welding condition, the mechanical property of deposited metal can obtain high tensile strength in the welding state and the heat treatment state, and good low-temperature toughness is achieved.

Description

Technical Field

[0001] This invention belongs to the field of welding electrode production, and in particular relates to a 90 kg-class ultra-low temperature high-strength steel welding electrode and its preparation method. Background Technology

[0002] With the rapid development of my country's nuclear power, hydropower, and pressure vessel industries, the strength levels of steel used in these industries have significantly improved in recent years. For example, high-strength steel with a strength level of over 655 MPa has been developed for nuclear power plant containment vessels, while the hydropower industry has achieved a full range of high-strength steels for hydropower applications at 600 MPa, 800 MPa, and 1000 MPa levels. However, these steels are also difficult to weld, with complex welding processes. They generally suffer from problems such as high sensitivity to welding cracks, difficulty in controlling welding deformation and stress, and extremely high requirements for controlling preheating temperature, interpass temperature, post-heat treatment, and heat treatment. Therefore, it is necessary to invent a 90 kg-class ultra-low temperature high-strength steel welding electrode with a tensile strength of over 900 MPa in low-temperature environments. Summary of the Invention

[0003] In view of this, the present invention aims to provide a 90 kg-class ultra-low temperature high-strength steel welding electrode and its preparation method.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A 90 kg-grade ultra-low temperature high-strength steel welding electrode, the electrode comprising a core and a coating covering the surface of the core, wherein the coating comprises the following raw materials by weight percentage: marble 35-45%, fluorite 15-20%, silica powder 3-5%, rutile 2-4%, metallic manganese 1-2%, ferrosilicon 1-2%, metallic nickel 15-20%, ferrotitanium 5-10%, ferromolybdenum 2-5%, sodium alginate 0.4-0.8%, soda ash 0.3-0.9%, lanthanum oxide 0.2-0.5%, and the balance iron powder.

[0006] The influence of the ratio of marble to fluorite on the droplet transition morphology and physical properties of the slag is as follows: coarse droplet transition is the basic transition morphology of this type of electrode. As the ratio of marble to fluorite increases, the droplets become significantly finer and the droplet transition frequency increases. At the same time, it has a certain effect on reducing spatter and improving all-position weldability. However, if the marble content is too high, it will increase the arc blowing force, intensify the intensity of the molten pool "tumbling", reduce the calmness of the molten pool, and cause adverse effects.

[0007] Marble and fluorite have different melting temperatures. After marble decomposes at a high temperature (approximately 850℃), its decomposition product CaO has a melting point of 2572℃, much higher than that of CaF2. The marble / fluorite ratio in the flux coating affects its softening temperature. As the marble / fluorite ratio increases, the softening temperature of the flux coating increases, and the electrode sleeve needs to be lengthened accordingly. An appropriate sleeve length will reduce spatter and improve process performance, but an excessively long sleeve will worsen the process performance. A marble / fluorite ratio of 1.5-3 is preferable.

[0008] Carbon (C): Carbon expands austenite and strengthens weld metal. As the C content increases, the weld metal strength increases, but its toughness decreases. At high temperatures, its strengthening effect is significantly reduced due to carbide polymerization. Therefore, the C content in the weld metal should be controlled as low as possible, ideally below 0.070%, to promote the formation of low-carbon bainite and reduce carbide formation.

[0009] Manganese (Mn): Mn is a major alloying element in welds, playing a role in strengthening the matrix, improving hardenability, and enhancing low-temperature toughness. It also contributes to deoxidation, desulfurization, and heat release during welding. However, studies have shown that excessive Mn can increase temper brittleness. Therefore, the amount of Mn added must be controlled.

[0010] Ni element: Ni element plays a solid solution strengthening role, and at the same time can improve the toughness of ferrite, especially the low temperature toughness. As the Ni content in the weld metal increases, the low temperature impact toughness of the weld metal tends to stabilize. Ni can also improve the hardenability of the weld metal.

[0011] Mo (Mo): Mo can improve hardenability and heat resistance, reduce temper brittleness, and inhibit the segregation of impurity elements such as P, S, and As. In Mn-containing welds, the hardness, yield strength, and tensile strength of the weld all increase with increasing Mo content, but increasing Mo content is detrimental to weld toughness.

[0012] Si (Si): In the welding process, appropriate amounts of Si can deoxidize, release heat, increase chemical activity, improve slag fluidity, reduce weld porosity sensitivity, and produce finer weld beads. However, excessive Si increases slag acidity and viscosity, easily producing non-metallic inclusions, which is detrimental to weld and mechanical properties. At high Ni content, Si acts as an embrittlement element, segregating with Ni at the original austenite grain boundaries, leading to reduced grain boundary cohesion and increased temper brittleness. Therefore, while meeting welding operation requirements, the Si content should be appropriately controlled.

[0013] Lanthanum oxide: Lanthanum reacts with oxygen and sulfur to form spherical or dot-like rare earth oxide sulfides, replacing easily formed, chain-like or film-like low-melting-point inclusions such as MnO and FeS distributed at grain boundaries. These chain-like inclusions severely disrupt the matrix, acting as crack initiation points and stress concentration points, leading to decreased toughness. Changing the inclusion morphology transforms elongated MnS inclusions into fine, spherical, diffusely distributed lanthanum sulfide oxides or sulfides, eliminating stress concentration sources. Refining grain size with lanthanum can inhibit austenite grain growth and promote the formation of acicular ferrite. Acicular ferrite has fine grains and large-angle interlaced grain boundaries, effectively hindering crack propagation and representing an ideal high-toughness microstructure. However, excessive lanthanum forms large-particle compounds, becoming stress concentration and crack initiation sources, and lanthanum oxide is costly. Therefore, the addition of lanthanum oxide is controlled at 0.2-0.5%; too little has little effect.

[0014] The Influence of Iron Powder on Electrode Processing Performance: Adding a certain amount of iron powder to marble-fluorite type electrodes generally does not reduce the droplet particle size or change the droplet transition morphology. However, iron powder does have a certain impact on the conductivity of the electrode coating, welding process performance, and deposition efficiency. Using iron powder with small particle size and irregular shape can improve the conductivity of the arc, increase arc stability, suppress spatter, and produce a softer arc. However, excessive conductivity can lead to a decrease in arc voltage, reduced penetration depth, and thinner molten metal. Shallow penetration can easily result in defects such as undercut when welding fillet welds. Here, we choose to use FHT100.25 iron powder, which has small particle size, irregular shape, and large specific surface area. However, due to the manufacturing process of iron powder and its easy oxidation characteristics, its oxygen content is difficult to control. As the specific gravity of the iron powder increases, the oxygen content increases, which can cause the welding slag to become thinner, spatter to increase, and alloy element loss. Therefore, the amount of iron powder added should be controlled. In this application example, the development of low-hydrogen high-strength steel welding electrodes involves adding appropriate amounts of iron powder, which helps improve the electrode's deposition efficiency and also enhances its process performance. Preferably, the amount of iron powder is controlled at around 2-5%.

[0015] Adding appropriate acidic minerals (silicon micron powder, rutile) to alkaline welding electrodes can, firstly, adjust the acidity and alkalinity of the welding slag, thereby affecting the transition of manganese-silicon alloys, and secondly, reduce the viscosity of the slag and improve the stability of the welding arc.

[0016] In summary, reducing carbon elements decreases carbide formation, thus making it possible to achieve ultra-low temperature toughness. Lower manganese and silicon content, with manganese content below 1% and silicon content below 0.3% in the weld metal, ensures efficient deoxidation, sulfurization, and phosphorus treatment while reducing the proportion of retained austenite. Adding high nickel enhances solid solution strengthening, improves hardenability, refines ferrite grains, and improves low-temperature toughness; however, excessive nickel can stabilize the austenite phase, increasing the proportion of retained austenite, while insufficient nickel fails to meet high strength requirements. Adding a small amount of molybdenum inhibits the transformation from austenite to pearlite, thereby improving hardenability and enhancing bainite formation. Furthermore, when the molybdenum content is 0.6-0.7%, it can reduce or suppress temper brittleness caused by other manganese and silicon elements. At higher tempering temperatures, dispersed special carbides form, exhibiting a secondary hardening effect, improving the steel's hot strength and creep limit.

[0017] Furthermore, the mass ratio of marble to fluorite is 1.5-3.

[0018] Furthermore, the iron powder is FHT100.25 iron powder, and the weight percentage of the iron powder is 2-5%.

[0019] Furthermore, the welding core is an H08E wire rod.

[0020] The present invention also provides a method for preparing a 90 kg-class ultra-low temperature high-strength steel welding electrode as described above, the method comprising the following steps:

[0021] 1) Take the raw materials of the medicinal peel according to the proportion and mix them evenly to obtain the mixed medicinal powder;

[0022] 2) Add binder to the mixed powder, stir evenly, and then use a hydraulic welding electrode production equipment to evenly press and coat it onto the welding core;

[0023] 3) After grinding the core coated in step 2) to form the clamping end and the arc-starting end, dry it using a welding electrode drying oven to prepare a 90 kg-class ultra-low temperature high-strength steel welding electrode.

[0024] Furthermore, the binder is a potassium-sodium mixed water glass with a modulus of 3.05-3.15, a potassium-sodium ratio of 2-3:1, and a concentration of 42-44° Baume degrees.

[0025] Furthermore, the amount of binder added is 18-27% of the weight of the mixed powder.

[0026] Furthermore, the drying method in step 3) is as follows: successively drying at a low temperature of 50-90℃ for 1.5-2.0 hours, at a medium temperature of 90-150℃ for 1.0-1.5 hours, and at a high temperature of 350-400℃ for 1.5-2 hours.

[0027] Compared with existing technologies, the 90 kg-class ultra-low temperature high-strength steel welding electrode of the present invention has the following advantages:

[0028] 1. The welding electrode described in this invention can be used for welding at higher pass temperatures, thereby shortening construction time, reducing welding construction costs, and shortening the construction cycle.

[0029] 2. The welding electrode described in this invention has excellent welding processability, stable arc, minimal spatter, easy slag removal, and aesthetically pleasing weld formation.

[0030] 3. Under high pass temperature welding conditions, the mechanical properties of the weld metal of the electrode described in this invention can obtain high tensile strength in both the welded state and the heat-treated state, and can be stable above 820MPa; the KV2 (Charpy V-notch impact absorption energy) of the weld metal can be guaranteed to be above 60J at -80℃, and it has good low temperature toughness. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 The weld metallographic structure of the electrode deposited metal obtained in Example 1;

[0033] Figure 2 The metallographic structure of the electrode deposited metal in the heat-treated state obtained in Example 1;

[0034] Figure 3 A schematic diagram of preparation and sampling for the deposited metal test. Detailed Implementation

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a 90 kg-grade ultra-low temperature high-strength steel welding electrode, comprising a core and a coating covering the surface of the core. The coating comprises the following raw materials by weight percentage: marble 35-45%, fluorite 15-20%, silica powder 3-5%, rutile 2-4%, manganese 1-2%, ferrosilicon 1-2%, nickel 15-20%, ferrotitanium 5-10%, ferromolybdenum 2-5%, sodium alginate 0.4-0.8%, soda ash 0.3-0.9%, lanthanum oxide 0.2-0.5%, and the balance iron powder.

[0038] The mass ratio of marble to fluorite is 1.5-3, the iron powder is FHT100.25 iron powder, and the welding core is H08E wire rod.

[0039] Specifically, the drug coatings in Examples 1-4 were made from the raw materials listed in Table 1.

[0040] Table 1. Composition (%) of the drug coating in Examples 1-4

[0041] project Example 1 Example 2 Example 3 Example 4 marble 36 40 40 45 fluorite 20 18 16 15 Silica powder 5 3 3.5 3.5 Rutile 4 3 2 2 metallic manganese 1.0 2.0 1.8 1.7 Ferrosilicon 2.0 1 1.5 1.5 Nickel 15 17 20 18 Titanium Iron 6 10 8 6 Ferromolybdenum 5 2 3 4 Sodium alginate 0.4 0.6 0.8 0.6 baking soda 0.9 0.8 0.5 0.3 Lanthanum oxide 0.5 0.3 0.2 0.2 Iron powder 4.2 2.3 2.7 2.2 total 100 100 100 100

[0042] The aforementioned 90 kg-class ultra-low temperature high-strength steel welding electrode was prepared by the following method:

[0043] 1) Take all the materials according to the above proportions and mix them evenly to obtain a mixed powder;

[0044] 2) Use potassium-sodium mixed water glass with a modulus of 3.15, a potassium-sodium ratio of 3:1, and a concentration of 44° Baume as a binder. The amount added is 24% of the weight of the mixed powder. After the binder is added to the mixed powder and stirred evenly, it is evenly pressed onto the 4 mm diameter welding core using a hydraulic welding rod production equipment. The welding core is H08E wire rod.

[0045] 3) After grinding out the clamping end and the arc-starting end, the electrode is dried in a welding electrode drying oven by holding it at a low temperature of 60℃ for 1.5 hours, a medium temperature of 150℃ for 1.5 hours, and a high temperature of 400℃ for 1.5 hours.

[0046] Figure 1-2 The images show the metallographic structures of Example 1 in the weld and heat-treated states at 500x magnification. It can be seen that the microstructure is a mixture of proeutectoid ferrite, granular bainite, a small amount of pearlite, and retained austenite. Carbides are distributed in fine particles within the matrix. After heat treatment, the microstructure is significantly refined, and the amount of carbide precipitation increases.

[0047] The following comparison will highlight the areas for improvement.

[0048] Comparative Example 1

[0049] The difference from Example 1 is that lanthanum oxide is not added.

[0050] Comparative Example 2

[0051] The difference from Example 1 is that the content of marble is 43%, the content of fluorite is 13%, and the mass ratio of marble to fluorite is 3.3.

[0052] Comparative Example 3

[0053] The difference from Example 1 is that the content of marble is 32%, the content of fluorite is 24%, and the mass ratio of marble to fluorite is 1.3.

[0054] Comparative Example 4

[0055] The difference from Example 1 is that the content of metallic nickel is adjusted to 10%.

[0056] Comparative Example 5

[0057] The difference from Example 1 is that the iron powder used is FHT100B iron powder.

[0058] Table 2. Composition (%) of the drug coating in Example 1 and Comparative Examples 1-5

[0059]

[0060] Electrode test:

[0061] The welding rods used in the experiment were Φ4.0mm, and the equipment was a Panasonic YD-400AT3HV DC welding machine with DC reverse polarity. The welding rods were preheated to 400℃ and held for 2 hours before welding; the welding position was flat welding. Two sets of test plates were prepared. One set was used to determine the mechanical properties of the deposited metal under as-welded conditions, and the other set was used to determine the mechanical properties of the deposited metal under heat-treated conditions. (Heat treatment conditions: temperature 550±10℃, holding time 6 hours, heating and cooling rate ≤50℃ / h above 400℃, air cooling after removal from the furnace below 300℃.)

[0062] The base material used in the experiment was a sheet material with a yield strength greater than 800 MPa. The chemical composition and mechanical properties of the sheet material are as follows:

[0063] Table 3 Chemical composition of the board (mass fraction %)

[0064] C Si Mn S P Cr Ni Mo V 0.10 0.26 0.52 0.006 0.008 0.51 4.98 0.52 0.05

[0065] Table 4 Mechanical properties of sheet metal

[0066] The welding process parameters and requirements for preparing the deposited metal test plate are as follows:

[0067] Table 5 Welding process parameters for test plates

[0068]

[0069] By using a higher runner temperature and higher hardenability, the formation of low-carbon bainite is ensured. The preparation of the weld metal test plate is as follows: Figure 3 As shown, the requirements are as follows:

[0070] Table 6 Requirements for preparing test plates for welded metal (Unit: mm)

[0071] Test plate length l Test plate width b1 Test plate thickness h1 pad width b2 Pad thickness h2 Root gap b3 ≥400 ≥150 20±4 ≥30 ≥8 16±2

[0072] Table 7. Composition of deposited metal (%)

[0073]

[0074]

[0075] Table 8 Properties of deposited metal in the welded state

[0076]

[0077] Table 9 Heat-treated state of deposited metal

[0078]

[0079] The welding electrode prepared by this invention exhibits excellent welding process performance, stable arc, minimal spatter, easy slag removal, and aesthetically pleasing weld formation in welding tests. Generally, according to national standards, the interpass temperature of high-strength steel welding electrodes should be controlled between 90-110℃, while the interpass temperature of the welding electrode described in this invention can be controlled between 180-230℃. Welding at higher pass temperatures can shorten construction time, reduce welding costs, and shorten the construction cycle.

[0080] By comparing the various embodiments and comparative examples, it is shown that adding lanthanum oxide can improve the KV2 of the deposited metal at -20℃ and -80℃. The ratio of marble to fluorite can only produce high-performance welding wire under certain conditions. The nickel content and the specifications of the iron powder used also affect the performance of the material. The loose density of HT100B iron powder and FHT100.25 iron powder are different, which affects the melting efficiency. In addition, FHT100B iron powder contains boron, while FHT100.25 iron powder does not contain boron. The impact performance of the boron-free iron powder is much better than that of the boron-containing iron powder.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A 90 kg-class ultra-low temperature high-strength steel welding electrode, characterized in that: The welding electrode comprises a core and a coating covering the surface of the core. The coating comprises the following raw materials by weight percentage: marble 35-45%, fluorite 15-20%, silica fume 3-5%, rutile 2-4%, manganese 1-2%, ferrosilicon 1-2%, nickel 15-20%, ferrotitanium 5-10%, ferromolybdenum 2-5%, sodium alginate 0.4-0.8%, soda ash 0.3-0.9%, lanthanum oxide 0.2-0.5%, and the balance iron powder.

2. The 90 kg-class ultra-low temperature high-strength steel welding electrode according to claim 1, characterized in that: The mass ratio of marble to fluorite is 1.5-3.

3. The 90 kg-class ultra-low temperature high-strength steel welding electrode according to claim 1, characterized in that: The iron powder is FHT100.25 iron powder.

4. The 90 kg-class ultra-low temperature high-strength steel welding electrode according to claim 1, characterized in that: The welding core is an H08E wire rod.

5. A method for preparing a 90 kg-class ultra-low temperature high-strength steel welding electrode as described in any one of claims 1-4, characterized in that: The method includes the following steps: 1) Take the raw materials of the medicinal peel according to the proportion and mix them evenly to obtain the mixed medicinal powder; 2) Add binder to the mixed powder, stir evenly, and then use a hydraulic welding electrode production equipment to evenly press and coat it onto the welding core; 3) After grinding the core coated in step 2) to form the clamping end and the arc-starting end, dry it using a welding electrode drying oven to prepare a 90 kg-class ultra-low temperature high-strength steel welding electrode.

6. The method for preparing the 90 kg-class ultra-low temperature high-strength steel welding electrode according to claim 5, characterized in that: The binder is a potassium-sodium mixed water glass with a modulus of 3.05-3.15, a potassium-sodium ratio of 2-3:1, and a concentration of 42-44° Baume.

7. The method for preparing 90 kg-class ultra-low temperature high-strength steel welding electrodes according to claim 5, characterized in that: The amount of binder added is 18-27% of the weight of the mixed powder.

8. The method for preparing 90 kg-class ultra-low temperature high-strength steel welding electrodes according to claim 5, characterized in that: The drying method in step 3) is as follows: successively heat at a low temperature of 50-90℃ for 1.5-2.0 hours, heat at a medium temperature of 90-150℃ for 1.0-1.5 hours, and heat at a high temperature of 350-400℃ for 1.5-2 hours.

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