New welded duplex stainless steel material suitable for welding duplex stainless steel, welded joint, and welding method thereof

Abstract

The present disclosure relates to a welded duplex stainless steel material comprising the following alloying elements in weight percent: C max 0.030; Si max 0.50; Mn 0.50-2.50; P max 0.030; S max 0.030; Cr 29.0-32.0; Ni 7.0-11.0; Mo 0.50-1.50; W 3.00-4.50; Cu max 0.50; N 0.25-0.45; Fe and unavoidable impurities balance; and having a ferrite:austenite content by volume of 35:65-65:35. The duplex stainless steel material may be in the form of wire or strip. The welding material is used to join duplex stainless steels, and the welding material has and produces a weld joint with high strength. The present disclosure further relates to welding methods using the welding materials of the present invention in single pass or multi-pass welds.

Description

[Technical field]

[0001] The present disclosure relates to a novel weldable duplex stainless steel material that can be in the form of a wire or strip. The welding material is intended to be used to join duplex stainless steels. The present disclosure further relates to a method of welding using the welding material of the present invention. [Background technology]

[0002] To make parts such as tubes or strips of new alloys marketable, it is often necessary to be able to weld these parts. The welding material used must essentially have the properties of the material of the part, to avoid that the weld produced constitutes a weak point in terms of mechanical properties (such as strength and toughness) and / or corrosion resistance.

[0003] In the oil and gas industry, components constructed from high-strength, highly alloyed duplex stainless steels are increasingly in demand due to their attractiveness as materials with their corrosion resistance and excellent mechanical properties. However, it is difficult to find welding consumables that can provide sufficient strength to welded joints and maintain their strength and toughness when used in single and multi-pass welds.

[0004] Additionally, these highly alloyed duplex stainless steels, when used as filler materials, are also known to suffer from nitrogen losses during welding, and therefore there is a need for welding materials that mitigate the adverse effects of these losses on the strength and toughness of the welded joint.

[0005] Thus, the present disclosure solves or at least alleviates the problems discussed above. Summary of the Invention

[0006] The present disclosure relates to a novel welded duplex stainless steel material, which may be in the form of a wire or strip. The welding material is intended for joining duplex stainless steels and has and produces high strength weld joints. The present disclosure further relates to a welding method using the welding material of the present invention in single or multi-pass welding.

[0007] The present disclosure is further illustrated by the following non-limiting figures: [Brief description of the drawings]

[0008] [Figure 1] Figure 1 shows the intermetallic phases of Example Heat 1, measured using LOM (image analysis: 500x magnification). [Diagram 2] Intermetallic phases of Example Heat 2 measured using LOM (image analysis: 500x magnification) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present inventors have discovered that by balancing the ranges of chromium, nickel, and nitrogen, as well as the ranges of Mo and W, a weldable duplex stainless steel material suitable for welding duplex stainless steels will be obtained.

[0010] The welded duplex stainless steel material of the present invention provides weld joints with both high strength and toughness, even multi-pass weld joints. In addition, when used in welding, the welded duplex stainless steel material will result in low or no formation of intermetallic phases, such as sigma phases and unwanted nitrides, in both the joint and heat affected zone, and the welded duplex stainless steel material of the present invention will also reduce the effects of nitrogen loss in the filler material during welding.

[0011] Furthermore, the inventive alloying element range of the welded duplex stainless steel material ensures that the effects of the welding process do not adversely affect the ferrite:austenite balance, thereby ensuring good mechanical properties and corrosion resistance of the welded joint. Furthermore, the inventive alloying range of the welded duplex stainless steel material provides the material with resistance to precipitation of intermetallic phases, meaning that the material remains ductile despite the frequent heating cycles associated with welding.

[0012] Accordingly, the present disclosure provides a welded duplex stainless steel material comprising the following alloying elements: TIFF2025513033000001.tif84170 by weight and having a ferrite:autenite content by volume of 35:65 to 65:35.

[0013] In this disclosure, the terms "weight %" and "wt%" are used interchangeably.

[0014] According to an embodiment, the welded duplex stainless steel material has a PRE ([Cr] + 3.3 x ([Mo] + 0.5 x [W]) + 16 x [N]) of 43 or greater to provide sufficient corrosion resistance. The values ​​of the alloying elements are in weight percent.

[0015] Furthermore, the present disclosure relates to a welded duplex stainless steel material as defined above or below to obtain a welded joint, the welded joint therefore comprising the same range of alloying elements as the welded duplex stainless steel material as defined above or below.

[0016] The present disclosure also relates to a method for producing a welded joint comprising a material as defined above or below, said method being a single pass or a multi-pass welding process.

[0017] According to the present disclosure, the resulting welded joint may have a yield strength of at least 700 MPa (ISO 6892-1) at room temperature.

[0018] According to the present disclosure, the resulting welded joint can have an impact toughness at room temperature of at least 50 J (ISO 148-1).

[0019] The principles and advantages of the welded duplex stainless steel material of the present invention, as well as the selection of the ranges of alloying elements of the duplex stainless steel that provide unexpected advantages, can be explained as follows. However, the present disclosure is not limited to the exemplary embodiments discussed, and may vary within the scope of the appended claims. The upper and lower limits of the individual elements of the composition are freely combinable within the broadest ranges set in the claims, unless expressly disclosed otherwise. In addition, where ranges are disclosed in this disclosure, such ranges include each end of the range, unless expressly disclosed otherwise. Similarly, where an open range is disclosed, the open range also includes a single end of the open range, unless expressly disclosed otherwise.

[0020] Chromium (Cr) Chromium is an essential element and its range is selected to obtain both the strength and corrosion resistance of the duplex stainless steel of the present invention. To obtain good impact properties and corrosion resistance, the chromium content should be at least 29.0 wt.%.

[0021] However, although chromium is a beneficial element, a high Cr content increases the risk of sigma phase formation during welding, so the content should not be more than 32.0 wt.%.

[0022] Moreover, the inventors have discovered that it is important to ensure that the chromium, nickel, and nitrogen content is balanced in order to avoid the formation of sigma phase and obtain maximum strength. Moreover, as can be seen from the examples of the present disclosure, the chromium content of the present invention is shown to be more than sufficient to compensate for the loss of nitrogen that occurs during the welding process, thereby avoiding loss of strength.

[0023] Thus, the chromium content of the welded duplex stainless steel material of the present invention is therefore 29.0-32.0 wt.%. To further ensure that the above properties are obtained, the chromium content is 29.5-32.0 wt.%, such as 30.0-32.0 wt.%, for example 30.5-31.5 wt.%.

[0024] Nickel (Ni) Ni is used as an austenite stabilizing element and is added to the welded duplex stainless steel material of the present invention at appropriate levels to obtain the desired austenite and ferrite content. To obtain a ferrite:austenite volume ratio of 35-65:65-35, the nickel content should be at least 7.0 wt.%. Furthermore, the inventors have discovered that the recommended nickel content in the welded duplex stainless steel material of the present invention results in high impact toughness with little formation of intermetallic phases such as sigma phase and undesirable nitrides, which have a detrimental effect on impact toughness.

[0025] According to the present disclosure, the maximum nickel content is 11.0 wt.%.

[0026] According to the present disclosure, the Ni content may be 7.5 to 11.0 wt %, such as 8.0 to 11.0 wt %, for example 8.5 to 10.5 wt %.

[0027] Molybdenum (Mo) Mo is an active element that improves strength and corrosion resistance in chloride environments and reducing acids.

[0028] However, the combination of excessive Mo content and high Cr content will increase the risk of sigma phase formation. Therefore, it is important to select the molybdenum content to avoid the formation of sigma phase in the welded joint and obtain the maximum strength of the welded joint. Furthermore, if the welded duplex stainless steel material of the present invention does not contain Mo, excessive nitrides will be formed during cooling.

[0029] Therefore, the Mo content must be at least 0.50% by weight, and the Mo content must be 1.50% by weight or less. The Mo content may be 1.20% by weight or more. Furthermore, the Mo content may be at least 0.50 to 1.00% by weight.

[0030] Tungsten(W) W will improve corrosion resistance in chloride environments, and resistance to pitting and crevice corrosion. However, too high W content in combination with high Cr content will increase the risk of sigma phase precipitation in the welded joint. Therefore, it is very important to optimize the total amount of chromium, molybdenum, and tungsten to avoid the formation of sigma phase and undesirable nitrides.

[0031] Therefore, the content of W is 3.00 to 4.50% by weight. According to an embodiment, the content of W may be 3.00 to 4.00% by weight.

[0032] Nitrogen (N) Nitrogen is a very active element and increases corrosion resistance and strength. To obtain a good effect, at least 0.25% by weight of N must be added.

[0033] However, since the added N must be dissolved in the welded duplex stainless steel material and in the welded joints, the N content must be carefully selected (too high a N content increases the risk of chromium nitride precipitation, especially if the chromium content is also high). Too much nitrogen can also impose a risk of porosity formation in the weld. The N content must therefore be limited to less than 0.45 wt.%.

[0034] Nitrogen is also a very important element for the microstructure of the weld and weld material. During welding, the weld material will lose a large amount of nitrogen by evaporation due to the heat of the welding process. With the loss of nitrogen, the weld joint will have a more ferritic microstructure with larger grains and nitride precipitates. These microstructural changes will adversely affect both the mechanical properties and the corrosion resistance of the weld. However, the inventors have discovered a range of nitrogen in the welded duplex stainless steel material of the present invention where the effects of these losses are reduced, so that the welded duplex stainless steel material can lose nitrogen and still provide a weld joint with excellent mechanical properties and corrosion resistance.

[0035] Therefore, the nitrogen content is 0.25 to 0.45% by weight. Furthermore, the N content can be 0.25 to 0.40% by weight, for example, 0.25 to 0.35% by weight.

[0036] Manganese (Mn) Mn is added to increase the solubility of nitrogen. However, Mn may also form manganese sulfides that act as the starting points for pitting corrosion. Therefore, the Mn content is 0.50% by weight or more and 2.50% by weight or less, and the Mn content may be 0.50 to 2.00% by weight, for example, 0.50 to 1.50% by weight.

[0037] Silicon (Si) Si is utilized as a deoxidizer during steel manufacturing and also improves the fluidity of the molten weld metal. It is known that high silicon content stabilizes the sigma phase. Therefore, the silicon content should be limited to a maximum of 0.50 wt.%. Since Si must be present, it may be present at a content of at least 0.05 wt.% to provide the desired effect. Moreover, according to the present disclosure, the silicon content may be 0.10-0.30 wt.%.

[0038] Carbon (C) C strengthens stainless steels, but also promotes the formation of chromium carbides, which are detrimental to corrosion. Carbon has limited solubility in both ferrite and austenite. Therefore, the carbon content must be limited to a maximum of 0.030% by weight, e.g., a maximum of 0.025% by weight.

[0039] Carbon is not an intentionally added element and there is no critical lower limit for the carbon content. However, keeping the carbon content very low would unduly increase processing costs. Thus, in practice, carbon may be present in an amount of at least 0.01%, or even at least 0.02%.

[0040] According to an embodiment, the carbon content is 0.005 to 0.025% by weight.

[0041] Copper (Cu) Cu can be added to improve resistance to certain corrosive environments, such as acidic environments, and also reduces susceptibility to stress corrosion cracking. Additionally, Cu will increase strength and delay the formation of sigma phase in welded joints.

[0042] Thus, although copper is a beneficial alloying element for increasing strength, it can increase the risk of chromium nitride formation due to its adverse effect on nitrogen solubility, so it is very important to carefully regulate the amount of copper added.

[0043] Therefore, the Cu content is limited to 0.50 wt% or less. According to one embodiment, Cu is intentionally added and the Cu content is between 0.15-0.50 wt%, and according to an embodiment, the Cu content may be 0.20-0.40 wt%.

[0044] Sulfur (S) Sulfur is an impurity element and needs to be removed to improve hot workability. In order to avoid the adverse effects of sulfur, the sulfur content should not exceed 0.030% by weight.

[0045] Rin(P) Phosphorus is also an impurity element, and its adverse effect on hot workability is reduced if the total phosphorus content does not exceed 0.030 wt.%.

[0046] The ferrite content, ferrite:austenite volume ratio of the welding material of the present invention is between 35-65:65-35, according to an embodiment, the ferrite content is at least 45 volume percent and should not exceed 60 volume percent, the remainder being essentially austenite. According to an embodiment, the ferrite content is in the range of 48-55 volume percent, the remainder being essentially austenite. Phase balance is important in welding duplex stainless steel materials, as it helps to obtain optimal mechanical properties and corrosion resistance. In addition, if the ferrite content is too low, there will be an increased risk of intermetallic phases such as sigma phases and unwanted nitrides forming, since ferrite is rich in chromium and molybdenum. Furthermore, if the ferrite content is too high, there will be an increased risk of secondary austenite forming within the ferrite grains. The amount of ferrite can be measured metallographically by examining the microstructure of the weld metal, which has been etched to distinguish ferrite from austenite by color, at a magnification of 200-500 times. The volume percent is the area fraction of the two.

[0047] The number of phase(s) in the microstructure is given in volume percentage (vol%) throughout this disclosure. It should be recognized that a particular volume percentage is generally determined within the art by considering the area fraction of the relevant constituent (phase) in the sample, said area fraction being considered to correspond to the volume percentage.

[0048] The balance of the welded duplex stainless steel material of the present invention is iron (Fe) and unavoidable impurities. Unavoidable impurities are elements that are not intentionally added and may be present in the steel of the present invention due to scrap and / or manufacturing processes used to provide the duplex stainless steel. Examples of such elements include, but are not limited to, Co, V, Ti, Al, Nb, Pb, and Sn. The total content of these elements is less than 0.5 wt.%. Cerium (Ce) may also be present as an impurity, but cerium cannot exceed 0.07 wt.%, as this would cause problems during welding due to the welding arc being disturbed due to cathode spot movement due to Ce / O formation.

[0049] Furthermore, the welding material of the present invention may optionally include alloying elements that may be added to improve the manufacturing process. Examples of such alloying elements that improve the manufacturing process include, but are not limited to, magnesium (Mg), calcium (Ca), and boron (B). These elements may be added individually or in combination, and the total content of these elements is less than 0.50 wt.%.

[0050] Other impurity elements not discussed above may be present in amounts less than 0.1% by weight, and the total amount may be less than 0.5%.

[0051] In addition, the welded duplex stainless steel materials of the present invention can comprise or consist of the alloying elements described herein that are in any of the specific elemental ranges described herein and meet the requirements described herein.

[0052] According to an embodiment, the welded duplex stainless steel material of the present invention is in the form of a welding wire, or a welding strip, or a welding powder.

[0053] The welded duplex stainless steel material of the present invention as defined above or below can be produced by a process comprising the following steps: - melting the raw materials; the melting can be carried out in a high-frequency induction furnace or in an electric arc furnace. - Casting; - optionally solution annealing in the temperature range of 1000-1150°C followed by quenching in water; - hot working; the hot working can be carried out by forging and / or rolling and / or extrusion; - optionally solution annealing in the temperature range of 1000-1150°C followed by quenching in water; and - Cold working; cold working can be performed by drawing or rolling.

[0054] If a powder is produced, conventional powder production processes are used after melting.

[0055] The present disclosure also relates to a welded joint. The welded joint is obtained by the following method, comprising the steps of: - providing a welded duplex stainless steel material as defined above or below; the material being provided in a form, for example in the form of a wire or strip; - providing at least one base material to be welded; examples of base materials include, but are not limited to, duplex stainless steel in the form of a tube of material such as those sold under the trademarks SAF™ 2507 and SAF™ 2906 by Alleima. - applying said welded duplex stainless steel material to and / or onto a base material; - applying shielding gas or flux powder to the area of ​​the resulting weld joint; - Welding the base material and the weld duplex stainless steel material using tungsten inert gas or metal inert gas / metal active gas, or submerged arc welding or electroslag welding.

[0056] If the weld joint is a multi-pass joint, multiple applications of the welded duplex stainless steel material will be made. The weld material will be cooled before a new layer of weld material is applied.

[0057] The present disclosure is further illustrated by the following non-limiting examples. EXAMPLES

[0058] Two heats were made having the chemical compositions shown in Table 2.

[0059] The heat was formed by melting the raw and scrap materials using an induction furnace.

[0060] The melt was cast and the cast product was solution annealed at a temperature range of 1000-1100°C for about 0.5-2 hours and then quenched in water. The formed billet was hot rolled and then drawn into wire. The formed wire was then welded to a base material of duplex stainless steel material of similar composition using TIG and a shielding gas consisting essentially of argon and nitrogen.

[0061] Samples were taken from the welded joints by cutting and milling and the resulting samples were tested as follows; - ISO standard 6892-1 was used to measure Rp0.2 at room temperature. - Impact toughness was measured by measuring Charpy V at both room temperature and -46°C. - The ferrite content was measured using LOM- (image analysis: magnification x500). - The area fractions of the different phases were measured by image analysis. - Intermetallic phases were measured using LOM (image analysis: magnification x500), see figures 1 and 2.

[0062] No intermetallic (unwanted nitride) particles were observed in the LOM images during visual analysis.

[0063] The results of the tests are shown in Table 1. As can be seen, the welded duplex stainless steel provides welded joints with high mechanical strength, no intermetallic phases, and good impact toughness. PRE shows high corrosion resistance. Table 1: Test results TIFF2025513033000002.tif91170 Table 2: Chemical composition of examples Heats marked with an "*" are heats of the present invention and the numbers are weight percent. TIFF2025513033000003.tif151170

Claims

1. Welded duplex stainless steel material containing the following alloying elements: In weight percent, having a ferrite:austenite content by volume of 35:65 to 65:35; Welded duplex stainless steel material.

2. PRE is ≧43 and PRE is of the formula: [Cr] + 3.3 × ([Mo] + 0.5 × [W]) + 16 × [N], where the values ​​of the alloying elements are in weight percent.

2. The welded duplex stainless steel material of claim 1, wherein the welded duplex stainless steel material is calculated from:

3. 2. The welded duplex stainless steel material of claim 1, wherein the Cr content is in the range of 29.5 to 32.0 wt.%.

4. 2. The welded duplex stainless steel material of claim 1, wherein the Mn content is in the range of 0.50 to 1.00 wt.%.

5. 2. The welded duplex stainless steel material of claim 1, wherein the Si content is in the range of 0.10 to 0.30 wt.%.

6. 2. The welded duplex stainless steel material of claim 1, wherein the W content is in the range of 3.00 to 4.00 wt.%.

7. 2. The welded duplex stainless steel material of claim 1, wherein the N content is in the range of 0.25 to 0.40 wt.%.

8. 2. The welded duplex stainless steel material of claim 1, wherein the N content is in the range of 0.25 to 0.35 wt.%.

9. 10. The welded duplex stainless steel material of claim 1, wherein the ferrite:austenite content is in the range of 48-55:52-45 by volume.

10. 10. The welded duplex stainless steel material of claim 1, wherein the weld material has an Rp0.2, determined according to ISO 6892-1, of at least 700 MPa at room temperature.

11. 10. Use of the welded duplex stainless steel material according to claim 1 to obtain a welded joint.

12. 10. A method for producing a welded joint comprising the welded duplex stainless steel material of claim 1, wherein the method is a multi-pass welding process or a single-pass welding process.

13. 13. The method of claim 12, wherein the resulting weld joint has an Rp0.2 of at least 700 MPa as determined according to ISO 6892-1 at room temperature.

14. 13. The method of claim 12, wherein the resulting welded joint has an impact toughness of at least 40J or 50J measured according to ISO 148-1 at -46°C.

15. The method comprises: - providing a welded duplex stainless steel material according to claim 1; - providing at least one base material to be welded; - applying said welded duplex stainless steel material to and / or onto a base material; - applying a shielding gas or flux powder to the area of ​​the resulting weld joint; - Welding base materials together with welded duplex stainless steel materials using tungsten inert gas or metal inert gas / metal active gas or submerged arc welding or electroslag welding The method according to claim 12, comprising the steps of:

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