Stainless steel flux-cored wire for welding 5Ni steel

Abstract

The invention relates to a stainless steel flux-cored wire for welding 5% Ni steel, the stainless steel flux-cored wire is prepared by coating powder with a stainless steel strip, the mass of the powder accounts for 22%-28% of the total mass of the flux-cored wire, and a flux core comprises the following components in percentage by weight: 15.0%-30.0% of chromium metal powder, 9.0%-20.0% of nickel metal powder, 3.0%-10.0% of molybdenum metal powder, 2.0%-8.0% of electrolytic manganese metal, 30.0%-35.0% of rutile, 0.5%-3.0% of quartz, 2.0%-8.0% of albite, 0.5%-3.0% of potassium feldspar, 0.5%-5.0% of cryolite and 0.2%-0.5% of self-made raw materials. And the balance of reduced iron powder and inevitable impurities. The external steel strip is an austenitic stainless steel strip 304L, and the carbon content of the external steel strip is smaller than or equal to 0.025%. The flux-cored wire is mainly matched with a steel plate with the Ni content being about 5% for welding, the low-temperature impact of a welded joint of the flux-cored wire at the temperature of-140 DEG C can reach 40 J, the tensile strength is larger than 600 MPa, and the flux-cored wire is good in crack resistance and excellent in comprehensive performance.

Description

Technical Field

[0001] The present invention belongs to the field of welding materials, and particularly relates to a flux-cored wire for welding 5% Ni steel. Background Art

[0002] 5% Ni steel is a steel used for ultra-low temperature pressure vessels. Due to its excellent low-temperature properties, it is widely used in the construction of low-temperature storage tank devices such as liquefied petroleum gas (LPG), liquefied ethylene (LEG), and liquefied ethane (LEC). 5% Ni steel means that the Ni content in the steel reaches about 5%, and it has the advantages of high strength, good low-temperature toughness, and high elongation.

[0003] Due to the high requirements for welding 5% Ni steel, nickel-based alloy materials have been mostly used for welding in the past. For example, in the patent CN113613829A "The Composition of Nickel-Based Alloy Flux-Cored Wire", a flux-cored wire for welding 5-9% Ni steel is disclosed, and its composition is Ni: 45-75%, Cr: ≤20%, Mo: 10-20%, Fe: ≤10%, TiO 2 : 3-11%, Ca: 0.01-2.0%, F: ≤1.0%, Nb ≤0.5%; in the patent CN108526661B "A Gas Shielded Welding Method for a Nickel-Based Solid Wire", the wire uses an INCONEL Filler Metal 625 solid wire. When producing this wire, specific composition steelmaking is required, with high requirements and high costs. However, the development of 5% Ni steel is itself to reduce costs to replace 9% Ni steel, and the welding products disclosed in the above patents all have high costs.

[0004] Ordinary austenitic stainless steel welding materials cannot meet the strength and impact performance requirements of 5% Ni steel, and pure austenitic stainless steel has great limitations in terms of crack resistance.

[0005] In the patent CN112192001B "A Submerged Arc Welding Method for Marine 5Ni Steel", the wire uses a disk-shaped stainless steel wire in accordance with the EN ISO14343-A standard. This wire is a solid submerged arc stainless steel wire. Although the cost is reduced, it is not suitable for all-position welding, and the welding application scenarios are limited. Summary of the Invention

[0006] To solve the problems of the prior art, the present invention discloses a stainless steel flux-cored wire for welding 5% Ni steel, which has high strength of the deposited metal, good low-temperature impact toughness, the mechanical properties of the deposited metal can reach 40J in the -140°C low-temperature impact, good crack resistance, the tensile strength is greater than 600 MPa, and it has excellent welding operability, can be welded in all positions, and is suitable for a variety of welding application scenarios.

[0007] To achieve the above technical objectives, the technical solution of the present invention is: a stainless steel flux-cored wire for welding 5% Ni steel, which is made by covering a flux powder forming a core with a 304L stainless steel strip. The composition of the core is as follows: metal chromium powder 15.0 - 30.0%, metal nickel powder 9.0 - 20.0%, metal molybdenum powder 3.0 - 10.0%, electrolytic metal manganese 2.0 - 8.0%, rutile 30.0 - 35.0%, quartz 0.5 - 3.0%, albite 2.0 - 8.0%, orthoclase 0.5 - 3.0%, cryolite 0.5 - 5.0%, self-made raw material 0.2 - 0.5%, and the balance is reduced iron powder and inevitable impurities;

[0008] Among them, the self-made raw material is prepared by the following method: a mixture of potassium titanate, bismuth oxide and magnesium carbonate with a weight percentage of 32 - 35% is wet-mixed with a mixture of magnesium oxide and manganese oxide with a weight percentage of 65 - 68%.

[0009] Preferably, the preparation method of the self-made raw material is: a mixture of potassium titanate, bismuth oxide and lithium carbonate with a weight percentage of 35% in a ratio of 4:3:3 is wet-mixed with a mixture of iron oxide and manganese oxide with a weight percentage of 65% in a ratio of 2:1, and after high-temperature baking, it is dried and processed into pellets and passed through an 80-mesh sieve; the parameters of the high-temperature baking are: temperature 750°C, time 60 min.

[0010] Among them, in the flux-cored wire, the weight of the core accounts for 22.0% - 28.0% of the total weight of the entire wire. Preferably, in the flux-cored wire, the weight of the core accounts for 24.0% - 26.0% of the total weight of the entire wire.

[0011] Among them, the chemical composition of the deposited metal obtained after welding with the core includes: C ≤ 0.030%, Si ≤ 1.0%, Mn: 1.0 - 2.5%, Cr: 18.0 - 22.0%, Ni: 11.0 - 15.0%, Mo: 1.0 - 2.0%, and the balance is Fe and inevitable impurities.

[0012] Among them, the content of each component of the deposited metal obtained after welding with the core satisfies the following relational formula:

[0013] 1.1 ≤ X / Y ≤ 1.7;

[0014] X = %Cr + %Mo + 1.5%Si;

[0015] Y = %Ni + 30%C + 0.5%Mn.

[0016] Among them, the shielding gas used for the flux-cored wire is 100% CO 2 for welding.

[0017] The steel strip of the welding wire is made of austenitic stainless steel 304L, with a carbon content of ≤0.025%.

[0018] The welding wire of the present invention is applicable to all-position welding.

[0019] The design concept of the welding material of the present invention is to balance the tissue relationship between austenite and ferrite. At low temperatures, the ferrite phase will embrittle, and the low-temperature impact toughness will drop sharply. While a pure austenite structure is prone to cracking. Therefore, through a reasonable ratio of austenite and ferrite forming elements, it can obtain good tensile strength, low-temperature impact toughness, crack resistance, and excellent welding workability.

[0020] Carbon: It is an austenite forming element, but too high a carbon content will cause the combination of other elements to form carbides, especially when forming Cr-rich M 23 C 6 type carbides, which will reduce corrosion resistance; the increase in carbon content will also lead to poor weldability. However, considering cost and the raw materials available on the market, the total content in the present invention should account for less than 0.04% of the total weight of the welding wire.

[0021] Silicon: In the present invention, its function is to increase the wettability of the molten iron and is also a deoxidizer, which is composed of what is provided by the steel strip itself and the addition of quartz powder in the flux-cored wire. When the amount is insufficient, the weld bead is relatively convex and prone to porosity; too high a content will affect weldability and also promote the formation of ferrite. The total content of silicon should account for less than 1.0% of the total weight of the welding wire.

[0022] Manganese: In the present invention, its function is to increase the surface tension of the molten iron. When the amount is excessive, it makes the molten iron difficult to spread to both sides, affecting the weld bead formation; it is also a deoxidizer. When the content is too low, pores are easily generated in the weld seam. In addition, manganese is an austenite forming element and can be added to the flux-cored wire in the form of the steel strip itself or electrolytic manganese metal. The total content of manganese accounts for 1.0 - 2.5% of the total weight of the welding wire.

[0023] Chromium: In the present invention, its function is to provide corrosion resistance. Because the affinity of chromium for oxygen is much higher than that of iron, the presence of chromium increases the stability of this oxide, can improve the hardenability and wear resistance of the steel, can also improve strength, and is also the main ferrite forming element. It can be added to the flux-cored wire in the form of the steel strip itself and chromium powder. The total content of chromium accounts for 18.0 - 22.0% of the total weight of the welding wire.

[0024] Nickel: In the present invention, its function is to improve the low-temperature impact toughness and hardenability of the welding material, can also improve the corrosion resistance and has the effect of refining the grains. Nickel is the main austenite forming element. It can be added to the flux-cored wire in the form of nickel powder. The total content of nickel accounts for 11.0 - 15.0% of the total weight of the welding wire.

[0025] Molybdenum: In the present invention, its function is to significantly improve the hardenability and hot strength of steel, prevent temper brittleness, refine the grains of steel, and appropriately increase the room temperature yield strength and tensile strength. Molybdenum is a ferrite-forming element, which can promote the formation and retention of ferrite in the steel structure. It can be added to the flux-cored wire in the form of metallic molybdenum powder, and the total content of molybdenum accounts for 1.0 - 2.0% by weight of the entire welding wire.

[0026] Self-made raw materials: Potassium titanate, bismuth oxide and lithium carbonate with a weight percentage of 32 - 35% are mixed with iron oxide and manganese oxide with a weight percentage of 65 - 68%. After wet mixing, they are baked at high temperature for standby, and after drying, they are processed into granules and passed through an 80-mesh sieve. The parameters of the high-temperature baking are: temperature 750°C, time 60 min. It is better to mix potassium titanate, bismuth oxide and lithium carbonate in a ratio of 4:3:3, and it is better to mix iron oxide and manganese oxide in a ratio of 2:1. Among them, potassium and lithium act as arc stabilizers to stabilize the arc. If the content is insufficient, a stable arc and droplet transfer cannot be formed. However, due to their strong hygroscopicity, when there is too much, it cannot be removed by drying, and wormhole defects will be generated during welding; bismuth acts as a slag removal agent to improve the slag removal property, but too high a content will lead to too good slag removal, and the molten slag cannot hold the molten iron during vertical welding and overhead welding, resulting in weld beads. During welding, the oxygen ions provided by iron oxide and manganese oxide can reduce the surface tension and make the weld bead have a beautiful shape. However, when there is too much, it will reduce the melting point of the molten slag, and the weld bead will become convex during all-position welding, affecting the shape and also prone to porosity. Therefore, the total content of the self-made raw materials added to the flux-cored wire accounts for 0.2 - 0.5% by weight of the entire welding wire.

[0027] The nickel content in the welding wire of the present invention is only 11 - 15%, which is much lower than the nickel content in nickel-based welding wires on the market, and has a great advantage in cost. At the same time, the mechanical properties of the deposited metal of the present invention can reach 40 J in the -140°C low-temperature impact test, the tensile strength is greater than 600 MPa, the crack resistance is good, and the comprehensive performance is excellent, and the comprehensive performance is not reduced due to the cost reduction. The stainless steel flux-cored wire of the present invention has excellent low-temperature impact performance and tensile strength, and at the same time has excellent crack resistance, is suitable for welding 5% Ni steel plates, and can be widely used in the construction of low-temperature storage tank devices such as liquefied petroleum gas (LPG), liquefied ethylene (LEG), and liquefied ethane (LEC). Brief Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the parent material group plate method for the 5% Ni steel welding crack test. Detailed Embodiments

[0029] To better understand the present invention, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

[0030] The present invention is composed of a stainless steel strip (304L) and a welding flux (flux-cored). The welding flux is wrapped inside the strip. A 304L stainless steel strip with a thickness of 0.4 mm, a width of 10 mm, and a weight of 3000 g is selected and rolled into a U shape. The composition of the strip (weight percentage %) is shown in Table 1.

[0031] Table 1 Composition of the strip outer skin (wt%)

[0032] C Si Mn P S Cr Ni Mo 0.014 0.328 1.34 0.015 0.005 18.35 8.25 0.055

[0033] The powders with a total weight of 1000 g are mixed evenly according to the weight ratio in Table 2 below, and then added to the strip at a filling rate of 25%. After that, it is drawn multiple times to the corresponding diameter, and then precision wound into coils and divided into finished flux-cored wires with a wire diameter of 1.2 mm.

[0034] Table 2 Composition of the flux core (g)

[0035]

[0036]

[0037] The welding operation test arrangements are shown in Table 3:

[0038] Table 3 Welding operation test arrangements

[0039]

[0040]

[0041] The results after the welding operation tests of the examples and comparative examples are shown in Table 4.

[0042] Table 4 Operation test results

[0043]

[0044]

[0045] From Comparative Tests 1, 2, 3, 4, 5, 6, 7, it can be seen that the contents of chromium metal powder, nickel metal powder, and molybdenum metal powder have no obvious effect on the operability; from Comparative Tests 8 and 9, it can be known that adding too much electrolytic manganese will cause a strong arc, and the molten iron will drip down at the overhead welding position and cannot be welded; from Comparative Tests 10, 11, 12, 13, it can be known that insufficient addition of rutile and quartz will cause insufficient slag coverage during high-current welding, and excessive addition will make the arc stronger, which has a greater impact on welding at the vertical welding and overhead welding positions, and may even cause welding to be impossible. This is because both rutile and quartz are slag formers, which play a role in slag formation, but excessive addition will reduce the arc quality; from Comparative Tests 14, 15, 16, 17, it can be known that albite and orthoclase have a greater impact on the arc strength. Albite can increase the arc strength and improve the arc blow force, while orthoclase can stabilize the arc and reduce the arc blow force. Too strong or too weak an arc will both cause impossible all-position welding; from Comparative Tests 18 and 19, it can be known that cryolite can reduce the porosity tendency of the weld, but excessive addition will cause poor fluidity and undercut at the weld bead edge.

[0046] Because effective all-position welding could not be carried out in some of these tests, no subsequent tests were conducted. Only Tests 1, 2, 3, 4, 5, 6, 7, and 9 were used for the detection of deposited test plates, chemical compositions, and crack resistance.

[0047] The mechanical properties of the deposited test plates are shown in Table 5, and the chemical compositions of the deposited metal are shown in Table 6.

[0048] Table 5 Mechanical Properties of Deposited Test Plates

[0049]

[0050] Table 6 Chemical Compositions of Deposited Metal (wt％)

[0051] Test C Mn Si P S Cr Ni Mo X / Y 1 0.027 1.81 0.61 0.013 0.006 20.27 13.24 1.15 1.49 2 0.029 1.76 0.63 0.012 0.007 18.59 13.17 1.19 1.39 3 0.029 1.77 0.6 0.013 0.006 22.97 13.1 1.1 1.68 4 0.031 1.84 0.62 0.013 0.007 20.09 11.8 1.22 1.63 5 0.03 1.85 0.59 0.011 0.007 20.11 16.8 1.12 1.19 6 0.028 1.81 0.59 0.014 0.005 20.34 13.2 0.01 1.42 7 0.029 1.79 0.061 0.013 0.005 20.3 13.19 1.89 1.49 9 0.028 1.45 0.061 0.013 0.006 20.11 13.29 1.11 1.43

[0052] Where: X = %Cr + %Mo + 1.5%Si; Y = %Ni + 30%C + 0.5%Mn

[0053] From the mechanical properties and chemical compositions of Comparative Tests 1, 2, 3, 4, 5, 6, 7, and 9, it can be known that the mechanical properties of the examples can meet the design requirements. Cr, Mo, and Mn can improve the tensile strength of the deposited metal, and Ni can improve the impact performance of the deposited metal; when the chemical compositions are rationally proportioned so that the value of X / Y is between 1.4 and 1.6, the low-temperature impact performance of the deposited metal can be significantly improved.

[0054] In addition, the crack resistance of the welded joints of the present invention is also described. In view of the lack of a unified verification standard for the crack resistance of flux-cored wires, a welding crack test method for 5Ni steel was developed with reference to GB / T4364-2013 "Test Method for Welding Crack of Inclined Y-Groove". The specific method is as follows:

[0055] 1) Perform back - welding with parameters 180A / 30V, observe for cracks, and mark the crack length.

[0056] 2) Plate - assembling method: Use 5% Ni steel base material. The plate - assembling method is shown in Figure 1 , and the specifications of the crack - resistant plate are shown in Table 7. The chemical compositions and mechanical properties of the base materials used in the tests are shown in Table 8.

[0057] Table 7 Specifications of the crack - resistant plate

[0058]

[0059] Table 8 Compositions and properties of the crack - resistant plate

[0060]

[0061] The crack - resistance test results are shown in Table 9.

[0062] Table 9 Test results of the crack - resistance test

[0063]

[0064] From the chemical compositions and crack - resistance properties of Comparative Tests 1, 2, 3, 4, 5, 6, 7, and 9, it can be seen that when the X / Y ratio is between 1.4 and 1.6, the crack - resistance performance of the welding wire is the best. When the ratio deviates from this range, especially when it is less than 1.4, the crack - resistance performance deteriorates severely. This is because this ratio is a simple algorithm for the ratio of ferrite to austenite. The smaller the value, the higher the austenite content in the structure, and the worse the crack - resistance.

[0065] The stainless - steel flux - cored wire of the present invention has excellent low - temperature impact performance and tensile strength, and at the same time has excellent crack - resistance performance. It is suitable for welding 5% Ni steel plates and can be widely used in the construction of low - temperature storage tank devices for storing liquefied petroleum gas (LPG), liquefied ethylene (LEG), liquefied ethane (LEC), etc.

[0066] The above - described embodiments are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A stainless steel flux-cored welding wire for welding 5% Ni steel, characterized in that: The flux-cored welding wire is made of a 304L stainless steel strip coated with powder constituting a flux core, and the composition of the flux core is as follows: 15.0-30.0% of metal chromium powder, 9.0-20.0% of metal nickel powder, 3.0-10.0% of metal molybdenum powder, 2.0-8.0% of electrolytic manganese, 30.0-35.0% of rutile, 0.5-3.0% of quartz, 2.0-8.0% of albite, 0.5-3.0% of potassium feldspar, 0.5-5.0% of cryolite, 0.2-0.5% of homemade raw materials, and the balance is iron powder and inevitable impurities; The self-made raw material is prepared by the following method: a mixture of potassium titanate, bismuth oxide and magnesium carbonate with a weight percentage of 32-35% is wet-mixed with a mixture of magnesium oxide and manganese oxide with a weight percentage of 65-68%.

2. The stainless steel flux-cored welding wire for welding 5% Ni steel according to claim 1, characterized in that: The preparation method of the self-made raw material is to wet-mix a mixture of potassium titanate, bismuth oxide and lithium carbonate with a weight percentage of 32-35%, and a mixture of iron oxide and manganese oxide with a weight percentage of 65-68%, and then bake at high temperature, dry, and then process and granulate through an 80-mesh screen to make it; The ratio of potassium titanate, bismuth oxide and lithium carbonate is 4:3:3; the ratio of iron oxide and manganese oxide is 2:1; The high temperature baking parameters are: temperature 750° C., time 60 min.

3. The stainless steel flux-cored welding wire for welding 5% Ni steel according to claim 1, characterized in that: In the flux-cored welding wire, the weight of the flux core accounts for 22% to 28% of the total weight of the flux-cored welding wire.

4. The stainless steel flux-cored welding wire for welding 5% Ni steel according to claim 1, characterized in that: The chemical composition of the deposited metal obtained after welding the flux core comprises: C≤0.030%, Si≤1.0%, Mn: 1.0-2.5%, Cr: 18.0-22.0%, Ni: 11.0-15.0%, Mo: 1.0-2.0%, and the balance is Fe and unavoidable impurities.

5. The stainless steel flux-cored welding wire for welding 5% Ni steel according to claim 1, characterized in that: The contents of various components of the deposited metal obtained by welding the flux core satisfy the following relationship: 1.1≤X / Y≤1.7; X = %Cr + %Mo + 1.5%Si; Y=%Ni+30%C+0.5%Mn.

6. The stainless steel flux-cored welding wire for welding 5% Ni steel according to claim 1, characterized in that: The flux-cored welding wire is welded using a shielding gas of 100% CO2.

Images