JP7391534B2 - Ni-based alloys and filler metals for welding - Google Patents

Description

Embodiments of the present invention relate to a Ni-based alloy for welding and a filler metal.

BACKGROUND ART In recent years, steam temperatures in steam turbines have been increasing, and as a result, materials constituting steam turbines are required to have improved heat resistance strength. In particular, in the A-USC (Advanced Ultra Super Critical) steam turbine currently under development, steam temperatures exceeding or close to 700° C. are assumed. Therefore, since the temperature exceeds the usable temperature of conventional heat-resistant low-alloy steels such as CrMoV steel, the application of Ni-based alloys is being considered.

Application of a 600 series alloy, for example, as the Ni-based alloy is being considered. Examples of turbine rotor materials for steam turbines include 617 alloy and TOS1X (manufactured by Toshiba Corporation). Further, as a typical filler metal used when welding the components constituting the turbine rotor, for example, a filler metal made of 617 alloy is used.

Patent No. 5703177 Patent No. 5254693 Patent No. 6323188 JP 2017-221965 Publication

Welding Society Transactions Vol. 27 No. 2 p144-148 (2009) Effect of Ce addition to filler metal on microcracking susceptibility of alloy 690 multipass wel metal K.Nishimoto,I.Woo and M.Shirai:Underlying Mechanism in the improvement of HAZ cracking Susceptibility by Rare Earth Metal Addition, -Study on Weldability of Cast alloy 718(Report8)-Quarterly,J.JWS,20-1,( 2002), p87-95 Welding Journal/August 2018,vol 98 page243-252 Savage W. F., and Lundin C.D.; “The Varestraint Test”, The Welding Journal, October, 1965, pp. 433- 442. Journal of Welding Society 2009 Volume 78 Issue 4 p.298-300

It has been reported that solidification cracking and liquefaction cracking occur due to welding with conventional 617 alloy filler metals, which are applied to Ni-based alloys such as TOS1X, which have improved strength properties at high temperatures. Several examples of problems with joint quality have been reported. Furthermore, there is a problem in that the strength is insufficient for use with materials such as TOS1X, which have high mechanical properties at high temperatures. Therefore, there is a need for a Ni-based alloy filler material that has strength characteristics at high temperatures and has reduced hot cracking susceptibility.

Up to now, the following efforts have been made regarding Ni-based alloy weld metals and welding materials. Many prior art documents on improving the mechanical properties of Ni-based alloy welding materials are known (for example, Patent Documents 1, 3, and 4). However, there is no specific description regarding hot cracking susceptibility.

On the other hand, as an effort to reduce the susceptibility to hot cracking, it has recently been discovered that adding a rare earth element called REM to the existing component system of Ni-based alloy welding materials can improve susceptibility to liquefaction cracking, which is one type of hot cracking. However, it is known that the effect of reducing solidification cracking susceptibility is poor (for example, Non-Patent Documents 1 and 2).

Furthermore, a technique for suppressing weld hot cracking has also been proposed (for example, Patent Document 2). Although this technique attempts to reduce the solidification cracking susceptibility of Ni-based alloys by adding REM, it is unclear about the effects of REM addition on liquefaction cracking susceptibility and mechanical properties.

Taking this into account, the effects obtained by adding REM are thought to vary depending on the original component system to which it is added; for example, it may be added with the intention of improving not only weld hot cracking but also hot workability ( For example, Patent Document 3). In this way, the performance improvement of Ni-based alloys due to the addition of REM is not limited to a primary effect.

On the other hand, it has been reported that when excessive REM is added to a Ni-based alloy, an intermetallic compound with Ni is formed, resulting in a negative effect of deterioration of performance (for example, Non-Patent Document 1). Therefore, in order to selectively enjoy desired effects by adding REM to Ni-based alloys, it is necessary to adjust the amount of REM added, determine whether the composition of the base material is appropriate for REM addition, and adjust the composition of the base material. ,It's not easy.

As mentioned above, although there are many examples regarding the mechanical properties of Ni-based alloy weld metals or welding materials, there are few examples of efforts to suppress hot cracking during welding, especially in both solidification cracking and liquefaction cracking. , no welding material provides a weld metal with cracking resistance superior to known materials.

Here, Ni-based alloys have excellent mechanical properties from low to high temperatures, and are often more expensive than other metals, so they can be used in equipment used in harsh environments or in important equipment. used in some parts. In addition, many of the devices in which Ni-based alloys are used have a high public interest, and are often devices that are strongly required to be safe. The welded parts of these important equipment are usually confirmed to have no harmful defects such as cracks or holes inside the welded part through radiographic inspection or ultrasonic testing, and if a defect is discovered, repair welding is carried out to ensure that it is sound. Used as welded joints.

However, some of the cracks associated with hot cracking are minute, on the order of tens of micrometers, and may be difficult to detect with inspections and tests using current technology. If such equipment is operated with hot cracks still present in the welded parts, there is a possibility that the inherent defects will lead to destruction that is not expected in the design. There is a possibility of causing an accident or damage of an unpredictable scale. Against this background, there is a strong demand for suppressing the occurrence of hot cracks in welded parts of Ni-based alloys.

Based on the above-mentioned conventional circumstances, the problem to be solved by the present invention is to create a welding material that has excellent high-temperature mechanical properties, is less prone to hot cracking than conventional filler metals, and has excellent weldability and manufacturability. An object of the present invention is to provide a Ni-based alloy and a filler metal for use in the present invention.

The Ni-based alloy for welding of the embodiment has C: 0.05-0.15, Cr: 20-24, Co: 10-15, Mo: 8-10, Al: 0.8-1. 5, Ti: 0.6 or less, Si: 0.5 or less, Mn: 0.5 or less, Cu: 0.5 or less, Fe: 3.0 or less, REM: 0.002 to 0.03, P: 0 0.02 or less, S: 0.015 or less, and the remainder consists of Ni and inevitable impurities.

FIG. 1 is a diagram showing a schematic configuration of a Balestrain test device. Diagram for explaining the procedure of a transvalle train test. Diagram for explaining the procedure of a transvalle train test. Diagram for explaining the procedure of a transvalle train test. The figure for explaining the method of calculating BTRSC from a test result. Diagram for explaining the procedure of the Longivalle restraint test.

Hereinafter, a Ni-based alloy for welding and a filler metal according to an embodiment will be described.

The Ni-based alloy for welding according to the embodiment has the composition range shown below. In addition, in the following description, % representing a composition component is mass % unless otherwise specified.
In mass%, C: 0.05 to 0.15, Cr: 20 to 24, Co: 10 to 15, Mo: 8 to 10, Al: 0.8 to 1.5, Ti: 0.6 or less, Si : 0.5 or less, Mn: 0.5 or less, Cu: 0.5 or less, Fe: 3.0 or less, REM: 0.002 to 0.03, P: 0.02 or less, S: 0.015 or less The remainder consists of Ni and unavoidable impurities.

The Ni-based alloy for welding having the above-mentioned composition range can be used, for example, as a filler material for welding. For example, it can be used as a filler material when welding turbine rotor components made of Ni-based alloys. Further, it can be used as a filler material when welding a turbine rotor component made of a Ni-based alloy and a turbine rotor component made of low alloy steel (for example, CrMoV steel or 12Cr steel). This filler metal is used for TIG welding and the like.

Examples of turbine rotors welded using the above-described filler metal include turbine rotors that can be used in high-temperature steam environments exceeding or close to 700°C. Note that components to be welded using this filler metal are not limited to turbine rotor components, and can be used, for example, in high-temperature steam environments exceeding or close to 700 degrees Celsius, and in high-temperature carbon dioxide environments. Other components may also be used.

Further, the Ni-based alloy having the above-mentioned composition range has low sensitivity to hot cracking and is excellent in weldability and manufacturability. Filler metals made using this Ni-based alloy also have low hot cracking susceptibility and are excellent in weldability and manufacturability.

Note that the component system of this embodiment conforms to AWS A5.14 ERNiCrCoMo-1 and JIS Z 3334 SNi6617. This means that if a welding business obtains a construction method based on the standard, they can do so smoothly, and if they have a construction method for the same standard material, they do not need to obtain it again. This means that it also has practical convenience.

Next, the reason for limiting the range of each composition in the Ni-based welding alloy in the above-described embodiment will be explained.

(1) C (carbon), Cr (chromium), Co (cobalt), Mo (molybdenum), Fe (iron), Al (aluminum), Ti (titanium), Cu (copper)
In order to satisfy the range specified in AWS A5.14 ERNiCrCoMo-1, C: 0.05 to 0.15, Cr: 20 to 24, Co: 10 to 15, Mo: 8 to 10, Fe: 3.0 or less, Al: 0.8 to 1.5, Ti: 0.6 or less, Cu: 0.5 or less.

(2) Si (silicon)
Si has the effect of improving the flow of hot water. On the other hand, if the Si content exceeds 0.5%, weldability will be reduced. Therefore, the Si content was set to 0.5% or less. Further, it is more preferable that the Si content is 0.01 to 0.25%.

(3) Mn (manganese)
Mn becomes S (sulfur) and MnS, which is caused by brittleness, and has the effect of preventing brittleness and improving melt flow. On the other hand, when the Mn content exceeds 0.5%, weldability is reduced. Therefore, the Mn content was set to 0.5% or less. Further, it is more preferable that the Mn content is 0.15 to 0.4%. Here, in order to obtain the above effects of Mn, it is desirable that Mn be contained in an amount of at least 0.1% or more.

(4) REM (Ce in Table 1)
REM is a general term for Sc, Y, and lanthanoids (atomic numbers 57-71). REM may be added as a mixture of multiple types of REM called misch metal, or may be added as one or more separated elements. Note that the content is preferably 0.002 to 0.03%. REM, including Ce, La, and Nd, suppresses the grain boundary segregation of P and S by forming finely formed phases together with P and S in the grains in the metal structure, thereby improving grain boundary bonding strength. Also, by forming a compound during solidification during welding, it has the effect of raising the solidus temperature. Therefore, REM including Ce, La, and Nd are useful elements for reducing the susceptibility to solidification cracking of the weld, and their content is preferably 0.002% or more. On the other hand, if REM is added in excess, in addition to the above effects being saturated, a REM-Ni intermetallic compound, which is an intermetallic compound with a low melting point, is formed, which reduces the bonding strength of grain boundaries and increases hot cracking susceptibility. increase Therefore, the content was set at 0.03% or less.

(5) P (phosphorus), S (sulfur)
P and S are classified as inevitable impurities in the Ni-based alloy for welding in the embodiment. It is desirable that the residual content of these unavoidable impurities be as close to 0% as possible. Furthermore, among these unavoidable impurities, it is preferable to suppress at least P to 0.02% or less and S to 0.015% or less, so that the residual content of each of them approaches 0% as much as possible. Even more desirable. In addition, when the content of P or S exceeds the above range, dephosphorization treatment or desulfurization treatment is performed to bring the content within the above range.

(6) N (nitrogen), B (boron), Nb (niobium)
N, B, and Nb are classified as inevitable impurities in the Ni-based alloy for welding in the embodiment. Among these, N promotes the formation of a composite compound of (Ti, Nb) (N, C) during the solidification process of molten metal. As a result, it affects phase formation and the order of their formation during solidification. This causes an expansion of the solidification temperature range and increases the susceptibility to solidification cracking. In order to suppress this, the content is preferably 0.02% or less, and more preferably 0.01% or less.

Although B segregates at grain boundaries and has the effect of improving high-temperature strength, an increase in B content causes grain boundary embrittlement and reduces weldability. Therefore, the content of B is preferably 0.005% or less.

Nb solidifies in the γ' (Ni ₃ (Al, Ti)) phase and has the effect of strengthening and stabilizing the γ' phase, but if the Nb content exceeds 0.4%, it will liquefy. Increased cracking susceptibility. Therefore, the Nb content is preferably 0.4% or less.

Here, a Ni-based welding alloy according to an embodiment and a filler metal manufactured using this Ni-based welding alloy will be described. The Ni-based alloy for welding in the embodiment is produced by vacuum induction melting (VIM) of the composition components constituting the Ni-based alloy for welding, and by pouring the molten metal into a predetermined mold to form an ingot. do.

In addition, the filler metal of the embodiment is produced by vacuum induction melting (VIM) of the composition components constituting the Ni-based alloy for welding in the embodiment, and injecting the molten metal into a predetermined mold to form an ingot. It is manufactured by drawing a machined ingot into a wire shape.

Next, it will be explained that the Ni-based alloy in the chemical composition range of the embodiment has low hot cracking susceptibility. Table 1 shows the chemical composition of the samples used for hot cracking susceptibility evaluation. Note that Examples 1 and 2 are Ni-based alloys to which REM is added so as to have the chemical composition of this embodiment. Comparative Examples 1 and 2 are Ni-based alloys that satisfy AWS A5.14 ERNiCrCoMo-1 and whose compositions are outside the chemical composition range of the embodiment.

The hot cracking susceptibility evaluation test was carried out by the Balestrain test described in Non-Patent Document 4 and Non-Patent Document 5. BTRSC obtained by the Transvalle Strain test is widely known as an indicator of solidification cracking susceptibility, and BTRLC obtained by the Longivalle strain test is widely known as an index of liquefaction cracking susceptibility, and the smaller the value of each, the less likely hot cracking will occur.

Here, the transvare strain test used to evaluate the solidification cracking susceptibility of the examples will be explained. Solidification cracks occur during the solidification process of molten metal, which cannot withstand the solidification shrinkage force in the final state of solidification in which the liquid phase and solid phase coexist, and the metal opens and solidifies as it is.

When looking at the above-mentioned liquid phase-solid phase mixed region from a temperature perspective, it includes a temperature region where ductility is extremely low (solidification brittle temperature region) that passes shortly after solidification begins, and therefore the liquid phase-solid phase mixed region is The wider it is, the more likely it is that solidification cracks will occur. For example, if welding is performed with a higher heat input on welding base materials with the same composition, the welded base material will be heated more and it will take longer to cool the molten part, which will lengthen the time required for solidification. As a result, the liquid phase-solid phase coexistence region at the melting site becomes wider, and solidification cracking becomes more likely to occur.

In the Transvare Strain test, a liquid-solid phase mixed region is generated, a crack is forcibly generated in that region, and the liquid-solid phase mixed region is measured through the length of the crack to determine the solidification brittleness temperature range (Brittleness). This is a test method to obtain the temperature range. Strictly speaking, the liquid-solid phase mixed temperature range and the solidification brittle temperature range are different, but for convenience, they are considered to be the same. The index obtained from the results of the transvalle train test is expressed as BTRSC.

Next, the procedure of the transvalle train test will be explained. FIG. 1 shows the configuration of a Balestrain test device 100. The Balestrain test device 100 includes a bending block 101 having a specified curvature (R) on the contact surface with the test piece so that a specified strain is applied by bending the test piece, and a bending block 101 that presses the test piece against the bending block 101 to cause plastic deformation. The test piece is composed of a movable yoke 102 having a pressing force sufficient to cause the welding process to occur, and a welding torch 103 whose purpose is to generate a welding arc and form a molten pool on the test piece.

As shown in FIG. 2, when performing a transvalle train test, a test piece 110 to be evaluated is sandwiched between the yoke 102 and the bending block 101, and then an arc is generated between the welding torch 103 and the test piece 110 to perform the test. Melt one surface. Next, the welding torch 103 is moved at a specified speed to a specified position as shown in FIG. 3 while the arc is being generated. Next, as shown in FIG. 4, after reaching the specified position, the arc is extinguished and at the same time the yoke 102 is pushed down. As a result, the test piece 110 bends to a specified curvature along the direction of the weld line, and a specified strain is generated on the molten surface, so that cracks can be forcibly generated in the vicinity of the molten pool.

When the arc is extinguished, the state near the molten pool is completely liquid just below the welding torch 103 due to the molten pool formed before the arc is extinguished, but when the direction is opposite to the direction of torch movement, the liquid phase changes as solidification begins. - There is a region where the solid phase is mixed, and eventually the solid phase state is completely solidified. The cracks that occurred during the test occurred in the liquid-solid phase mixed region.

Next, a method for deriving BTRSC from the cracks obtained in the test will be explained. FIG. 5(a) shows a conceptual diagram when the arc is extinguished, and FIG. 5(b) shows a graph showing the relationship between the distance of the remelted part from the molten pool boundary and the temperature. Note that, in the upper part of the graph in FIG. 5(b), part A including the molten pool shown in FIG. 5(a) is shown in an enlarged manner. First, a crack with the maximum length (for example, crack 110a shown in FIG. 5(b)) is selected from among the cracks obtained in the test, and its length is measured. After that, from the temperature distribution at each distance from the molten pool at the time of arc extinguishment and the measured crack length, as shown in Figure 5(b), which was obtained in advance under the same test conditions, the starting and ending points of the crack were determined. Each temperature is derived. The difference in temperature between the starting point and the ending point obtained here is expressed as BTRSC. The smaller the value of BTRSC, the lower the cracking susceptibility and the higher the solidification cracking resistance. This index is generally used for relative comparisons between materials of the same type.

Next, the Longivare strain test used to evaluate liquefaction cracking susceptibility will be explained. Liquefaction cracking occurs when a low melting point compound or eutectic is generated at the grain boundary due to heating during welding, or when components are segregated, the material is melted and opened due to shrinkage strain during solidification. Unlike solidification cracking, the location where cracking occurs is in the base material to be welded, and it occurs in the coarse grain region of the weld heat affected zone. Therefore, in the LongiValle restraint test to evaluate liquefaction cracking susceptibility, the test piece 110 is The welding torch 103 is moved in the direction indicated by the arrow in the figure. After generating an arc, the method of obtaining the temperature difference between the starting point and the ending point from the crack length is the same as the transvalle strain test, and the result is expressed as BTRLC. The smaller the value of BTRLC, the lower the cracking susceptibility and the higher the liquefaction cracking resistance. This index is generally used for relative comparisons between materials of the same type.

Here, the samples having the chemical composition shown in Table 1 are prepared by melting each Ni-based alloy in a vacuum induction melting furnace to produce a steel ingot, hot forging this steel ingot, and then forming it into a member of a predetermined size. These samples were subjected to mechanical processing, etc., and a Balestrain test was conducted using these samples. The results are listed as BTRSC and BTRLC in Table 2. It can be seen that Examples 1 and 2 have lower BTRSC and BTRLC than Comparative Example 1, indicating that they are excellent in solidification cracking susceptibility and liquefaction cracking susceptibility. From these results, it can be seen that the Ni-based welding alloy and filler metal of this embodiment have low hot cracking susceptibility. The conditions for conducting the Balestrain test are shown in Table 3.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents.

100... Balestrain test device, 101... Bending block, 102... Yoke, 103... Welding torch, 110... Test piece.

Claims (4)

In mass%, C: 0.05 to 0.15, Cr: 20 to 24, Co: 10 to 15, Mo: 8 to 10, Al: 0.8 to 1.5, Ti: 0.6 or less, Si : 0.5 or less, Mn: 0.5 or less, Cu: 0.5 or less, Fe: 0.5 or less, REM: 0.002 to 0.03, P: 0.02 or less, S: 0.015 or less A Ni-based alloy for welding, characterized in that the remainder consists of Ni and inevitable impurities. The Ni-based alloy for welding according to claim 1,
A Ni-based alloy for welding, characterized in that among the inevitable impurities, Nb is 0.4% by mass or less, B is 0.005% by mass or less, and N is 0.02% by mass or less. The Ni-based alloy for welding according to claim 1 or 2,
The REM is a Ni-based alloy for welding, characterized in that it contains at least Ce. A filler material produced using the Ni-based alloy for welding according to any one of claims 1 to 3 .

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