Cr-Ni alloy, method for producing Cr-Ni alloy, and rapidly solidified compact

Abstract

To provide a Cr-Ni based alloy which is a metal material suitable for use in harsh environments such as oil wells, has both high erosion resistance and wear resistance that are equal to or more excellent than a conventional one and is low in cost, and to provide a rapidly solidified molded body made of the Cr-Ni based alloy, an alloy powder, a powder metallurgy molded body, a cast molded body, a production method for the Cr-Ni based alloy, and a mechanical facility and piping members using the Cr-Ni based alloy.SOLUTION: A Cr-Ni based alloy according to the present invention comprises, by mass%: more than 40.0% and 65.0% or less of Cr; 0% or more and 35.0% or less of Fe; 0% or more and less than 2.0% of Mn; and any of (1) to (3) described below, with the remainder being Ni and unavoidable impurities, where the Ni is 15% or more. (1) more than 1.1% and 4.0% or less of C, (2) 0.7% or more and 3.0% or less of B, and (3) 0.5% or more and 2.5% or less of C and more than 0% and 20% or less of Nb.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to the technology of alloys with high corrosion resistance and high strength, and particularly relates to Cr-Ni based alloys, rapidly solidified formed bodies made of Cr-Ni based alloys, alloy powders, powder metallurgy formed bodies, cast formed bodies, a manufacturing method of Cr-Ni based alloys, and mechanical equipment and piping members using Cr-Ni based alloys.

Background Art

[0002] In equipment used for the extraction of crude oil, natural gas, etc. and fluid transportation, a surface modification layer is provided by overlay welding a material excellent in corrosion resistance, wear resistance, etc. on the surface of members accompanied by contact and sliding with other materials, and means may be taken to suppress the wear of equipment members. As such surface modification materials, for example, cobalt (Co)-based alloys such as Stellite (STELLITE is a registered trademark) and Tribaloy (TRIBALOY is a registered trademark), and nickel (Ni)-based alloys such as Colmonoy (COLMONOY is a registered trademark) are commercially available and widely used. However, Co and Ni, which are the main raw materials of these, are expensive, and there is a problem that the material cost increases.

[0003] In contrast, various Cr-based alloys mainly composed of relatively inexpensive chromium (Cr) have been proposed. For example, Japanese Patent Laid-Open No. 10-110206 discloses a manufacturing method of a Cr-Ni based alloy having a chemical composition containing Cr: 82 to 90% by mass, C: 2 to 6% by mass, and the balance being Ni and sub-components of 7.9% by mass or more, and it is said that it can be used for forming a coating having corrosion resistance and wear resistance. Further, Japanese Patent Laid-Open No. 11-285890 discloses a welding rod in which an alloy powder containing high concentrations of Cr and C is coated with a sheath material made of a Cr-Ni containing alloy, and it is said that a welding rod having a desired composition can be efficiently manufactured. Furthermore, Japanese Patent Laid-Open No. 11-293377 discloses a Cr-based alloy for a hearth member of a heating furnace containing Cr: 50 to 80% by mass, at least one of Ti, Mn, Mo, Zr: 2 to 10% by mass, and the balance being Ni and sub-components, and it is said that an alloy excellent in creep resistance and oxidation resistance can be provided with good productivity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0005] The alloy produced by the method described in Japanese Unexamined Patent Application Publication No. 10-110206 has an extremely high Cr content, and it is considered that the melting point of the alloy becomes a high temperature exceeding 1500°C. This leads to an increase in the energy required for the production of the alloy, resulting in high production costs. In addition, the welding rod described in Japanese Unexamined Patent Application Publication No. 11-285890 requires the inclusion of alloy powder in a sheath material, and thus requires higher production costs compared to the case where the alloy itself is made into a wire or powder alone. Further, in the Cr-based alloy described in Japanese Unexamined Patent Application Publication No. 11-293377, it is stated that it is desirable to add 2 mass% or more of Ti, Mn, etc. in order to improve the compressive strength and creep resistance. However, in the Cr-based alloy described in the pamphlet of International Publication No. 2017 / 037851 studied by the inventors, for example, when the content of Mn exceeds 2 mass%, coarse particles of sulfide (e.g., MnS) are formed, which is considered to be a factor in the deterioration of corrosion resistance and mechanical properties. In addition, for example, in the field of oil well drilling, in recent years, as the depth has increased, the environment to which equipment is exposed has become harsher, and there is a strong demand for a metal material that has high corrosion resistance and mechanical properties and is low in cost.

[0006] One aspect of the present disclosure is to provide a Cr-Ni alloy-based metal material that can be suitably used even in a harsh environment such as an oil well, has high corrosion resistance and wear resistance equal to or higher than those of the prior art, and is low in cost. Another aspect of the present disclosure is to provide a rapidly solidified compact, alloy powder, powder metallurgy compact, cast compact made of the Cr-Ni alloy-based metal material, a method for producing the Cr-Ni alloy-based metal material, and mechanical equipment and piping members using the Cr-Ni alloy-based metal material.

Means for Solving the Problems

[0007] Specific means for solving the above problems include the following aspects. <1> By mass, Cr exceeding 40.0% and not exceeding 65.0%, Fe of 0% or more and not exceeding 35.0%, Mn of 0% or more and less than 2.0%, including any one of the following (1) to (3), (1) C exceeding 1.1% and not exceeding 4.0% (2) B of 0.7% or more and not exceeding 3.0% (3) C of 0.5% or more and not exceeding 2.5%, and Nb of more than 0% and not exceeding 20% The balance consists of Ni and unavoidable impurities, and the Ni is 15% or more, a Cr-Ni alloy-based metal material.

[0008] <2> By mass, Cr exceeding 46.0% and not exceeding 65.0%, Fe of 0.1% or more and not exceeding 30.0%, Mn of more than 0% and less than 2.0%, including C exceeding 1.1% and not exceeding 4.0%, The balance consists of Ni and unavoidable impurities, the Cr-Ni alloy-based metal material according to <1>. <3> By mass, More than 45.0% and less than 65.0% of Cr, and 0.1% or more and 35.0% or less of Fe, and More than 0% and less than 2.0% of Mn, and 0.7% or more and 3.0% or less of B, and The balance consisting of Ni and unavoidable impurities, the Cr-Ni alloy according to <1>. <4> More than 40.0% and less than 65.0% of Cr, and 0% or more and 30.0% or less of Fe, and 0.5% or more and 2.5% or less of C and More than 0% and less than 20% of Nb, and The balance consisting of Ni and unavoidable impurities, the Cr-Ni alloy according to <1>. <5> By mass, 0.1% or more and 1.0% or less of Si, 0.005% or more and 0.05% or less of Al, 0.02% or more and 0.3% or less of Sn, 0.1% or more and 5.0% or less of Cu, The Cr-Ni alloy according to any one of <1> to <4>, containing at least one or more of the above. <6> The Cr-Ni alloy is characterized in that a ferrite phase and / or an austenite phase is formed, the Cr-Ni alloy according to any one of <1> to <5>.

[0009] <7> A rapidly solidified compact made of the Cr-Ni alloy according to any one of <1> to <6>. <8> An alloy powder made of the Cr-Ni alloy according to any one of <1> to <6>. <9> A powder metallurgy compact made of the Cr-Ni alloy according to any one of <1> to <6>. <10> A cast compact made of the Cr-Ni alloy according to any one of <1> to <6>.

[0010] <11> A method for producing the Cr-Ni alloy according to any one of <1> to <6>, A melting step of melting the raw materials of the Cr-Ni alloy to form a molten metal, A method for manufacturing a Cr-Ni alloy, comprising an atomizing step of producing alloy powder from the molten metal. <12> A method for manufacturing a Cr-Ni alloy according to any one of <1> to <6>, a melting step of melting the raw material of the Cr-Ni alloy to form a molten metal, a casting step of casting the molten metal to form a cast molded body, a powdering step of mechanically pulverizing the cast molded body to produce alloy powder, and a method for manufacturing a Cr-Ni alloy.

[0011] <13> A method for manufacturing a Cr-Ni alloy according to any one of <1> to <6>, a powder molding step of performing press molding or injection molding using powder of the Cr-Ni alloy as a raw material to form a powder molded body, and a sintering step of subjecting the powder molded body to sintering heat treatment at a temperature below the solidus temperature of the alloy to form a powder metallurgy molded body, and a method for manufacturing a Cr-Ni alloy. <14> A method for manufacturing a Cr-Ni alloy according to any one of <1> to <6>, a melting step of melting the raw material of the Cr-Ni alloy to form a molten metal, a casting step of casting the molten metal to form a cast molded body, and a method for manufacturing a Cr-Ni alloy.

[0012] <15> Mechanical equipment for transporting or processing an object to be transported containing solid matter and / or corrosive components, wherein at least a part of the member itself constituting the mechanical equipment or the surface of the member that contacts the object to be transported is made of the Cr-Ni alloy according to any one of <1> to <6>. <16> A piping member used in a transport path of an object to be transported containing solid matter and / or corrosive components, wherein at least a part of the piping member itself or the surface of the piping member that contacts the object to be transported is made of the Cr-Ni alloy according to any one of <1> to <6>.

Advantages of the Invention

[0013] According to one aspect of the present disclosure, there is provided a Cr-Ni-based alloy which is a metallic material having both corrosion resistance and wear resistance capable of withstanding a severe corrosion environment such as direct contact with fuels of various qualities and deteriorated lubricating oils, and which can be produced at a lower cost than Ni-based alloys and Co-based alloys. According to another aspect of the present disclosure, a rapidly solidified compact, alloy powder, powder metallurgy compact, cast compact made of the Cr-Ni-based alloy of one aspect of the present disclosure, and mechanical equipment and piping members using the Cr-Ni-based alloy can have corrosion resistance and wear resistance higher than or equivalent to those of conventional materials.

Brief Description of the Drawings

[0014]

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MODE FOR CARRYING OUT THE INVENTION

[0015] In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as a lower limit value and an upper limit value. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range of other stepwise descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In this specification, the term "step" includes not only an independent step but also this term if the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps.

[0016] The present inventors investigated and studied the relationship between the chemical composition, the metal structure form, the corrosion resistance, and the earth and sand abrasion resistance in the Cr-Ni alloy, and completed the present invention. Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. However, for the same state and process, the same reference numerals are used and duplicate explanations are omitted. In addition, the present invention is not limited to the embodiments described herein, and it is possible to appropriately combine with known technologies or improve based on known technologies without departing from the technical idea of the invention.

[0017] 〔Chemical composition〕 The Cr-Ni alloy of the present disclosure is, by mass%, more than 40.0% and 65.0% or less of Cr, 0% or more and 35.0% or less of Fe, 0% or more and less than 2.0% of Mn, including any one of the following (1) to (3), (1) C more than 1.1% and 4.0% or less (2) B 0.7% or more and 3.0% or less (3) C 0.5% or more and 2.5% or less, and Nb more than 0% and 20% or less The balance consists of Ni and unavoidable impurities, and the Ni is 15% or more, which is a Cr-Ni alloy. The Cr-Ni alloy of the present disclosure suppresses the Cr content and forms at least one kind of compound of Cr-based carbide, Cr-based boride, and Nb-based carbide in the matrix phase, so that it has high corrosion resistance and wear resistance that can be preferably used even in a harsh environment such as an oil well, and is a low-cost Cr-Ni alloy.

[0018] Hereinafter, the composition (each component) of the Cr-Ni alloy according to the present disclosure will be described. The content of each element is in mass% unless otherwise specified. In addition, for the Cr-Ni alloy according to the present disclosure, it is preferable that the total content of the disclosed components exceeds 99% by mass. For example, the content of components other than the disclosed components, such as impurities mixed in the alloy manufacturing process, is preferably less than 1% by mass in total.

[0019] Cr: More than 40.0% and 65.0% or less Cr is one of the main components of the Cr-Ni based alloys of the present disclosure and is an important component for obtaining good corrosion resistance. The Cr content is more than 40.0%, and from the viewpoints of corrosion resistance and material cost, it is preferable that the Cr component has the maximum content rate. This is because the alloy of the present disclosure has the advantage that the material cost can be reduced compared to, for example, Ni-based alloys having expensive Ni as the maximum component by using inexpensive Cr as the maximum component. Further, by using Cr as the maximum component, an oxide film is easily formed and a passive state is formed, so that the corrosion resistance is improved. When the Cr content rate becomes 40.0% or less, the amount of carbides appearing in the alloy structure decreases, and the wear resistance may become insufficient. Alternatively, the amount of Cr in the alloy structure may decrease and the corrosion resistance may deteriorate. On the other hand, when the Cr content rate exceeds 65.0%, the melting point of the alloy becomes high, the energy required for ingot production by melting or pulverization by atomization increases, the productivity deteriorates, and the production cost increases. Therefore, the Cr content is set to 65.0% or less.

[0020] Further, Cr also becomes a component that contributes to the formation of carbides related to the improvement of wear resistance together with C described later. That is, when including the above-mentioned "(1) C of more than 1.1% and 4.0% or less", Cr constitutes Cr-based carbides together with C. In this form, in order to more surely exhibit the action and effect of Cr, the Cr content rate is preferably more than 46.0%, more preferably 50.0% or more, and still more preferably 55.0% or more.

[0021] Further, Cr also becomes a component that contributes to the formation of borides related to the improvement of wear resistance together with B described later. That is, when including the above-mentioned "(2) B of 0.7% or more and 3.0% or less", Cr constitutes Cr borides together with B. In this form, in order to more surely exhibit the action and effect of Cr, it is preferable that Cr is 45.0% or more, more preferably 50.0% or more, and still more preferably 55.0% or more.

[0022] In addition, Cr, together with C, contributes to the formation of carbides related to the improvement of wear resistance. However, when containing the above-mentioned "(3) 0.5% or more and 2.5% or less of C and more than 0% and 20% or less of Nb", Cr constitutes Cr-based carbides together with C. To more surely exert the action and effect of Cr, the content of Cr is preferably more than 40.0%, and further preferably 43.0% or more. More preferably, it is 50.0% or more, and even more preferably 55.0% or more.

[0023] Fe: 0% or more and 35.0% or less Fe contributes to the formation of carbides together with Cr and the like. When Fe is dissolved in the carbides, the amount of Cr dissolved in the carbides decreases, and the decrease in the Cr concentration in the matrix phase around the carbides is suppressed. In addition, since the decrease in the Cr concentration in the matrix phase leads to a decrease in corrosion resistance, the corrosion resistance is improved by adding Fe. On the other hand, if there is too much Fe, ferrite crystallizes in the primary crystal, and the corrosion potential difference in the matrix phase becomes large, making local corrosion likely to occur. Therefore, the content of Fe contained in the alloy of the present disclosure is 35.0% or less.

[0024] In addition, when containing the above-mentioned "(1) more than 1.1% and 4.0% or less of C", Fe is preferably 0.1% or more and 30.0% or less. Here, as described above, Fe contributes to the formation of carbides together with Cr and the like. When Fe is dissolved in the carbides, the amount of Cr dissolved in the carbides decreases, and the decrease in the Cr concentration in the matrix phase around the carbides is suppressed. In addition, since the decrease in the Cr concentration in the matrix phase leads to a decrease in corrosion resistance, the corrosion resistance is improved by adding Fe. On the other hand, if there is too much Fe, ferrite crystallizes in the primary crystal, and the corrosion potential difference in the matrix phase becomes large, making local corrosion likely to occur. Therefore, in the case of the above-mentioned form, the content of Fe is preferably 30.0% or less. It is more preferable to keep the content low within the range of 0.1% or more as long as the performance of the material is not impaired. Considering wear resistance, the upper limit of the Fe content is preferably 15% or less, and more preferably 8% or less.

[0025] In addition, when Fe contains the above-mentioned "(2) 0.7% or more and 3.0% or less of B", it becomes an essential component to ensure good mechanical properties, and it is preferably 0.1% or more and 35.0% or less. When the Fe content becomes excessive, the σ phase of the brittle intermetallic compound is likely to be generated in the temperature range near 800 °C, and the ductility and toughness of the Cr-Ni alloy are significantly reduced (so-called σ phase embrittlement). Therefore, the content of Fe is set to 35.0% or less, and it is more preferable to keep the content low within the range of 0.1% or more as long as the performance of the material is not impaired. Considering corrosion resistance, the Fe content is preferably 20% or less, more preferably 15% or less.

[0026] In addition, when Fe contains the above-mentioned "(3) 0.5% or more and 2.5% or less of C and more than 0% and 20% or less of Nb", Fe is an element that improves corrosion resistance. By adding Fe, a ferrite phase precipitates, forming a two-phase structure with the austenite phase, and a hard and tough high-strength matrix phase can be formed. On the other hand, increasing the addition amount of Fe may generate the sigma phase, which is a brittle phase, and may impair the mechanical properties. Therefore, in this case, the content of Fe is preferably 30.0% or less. Also, although increasing the addition of Fe tends to increase the strength, on the other hand, the amount of Cr decreases, which becomes a factor deteriorating the corrosion resistance or wear resistance. In order to obtain certain properties of wear resistance and corrosion resistance, it is preferably in the range of 20% or less. More preferably, it is 16% or less. When this alloy is used as a cladding material for inexpensive steel materials, since Fe may be mixed from the base steel material, Fe may be 0%.

[0027] Mn: 0% or more and less than 2.0% Mn is a component that plays a role in desulfurization and deoxidation particularly in the process of mixing and melting raw materials, contributing to the improvement of mechanical properties and the improvement of corrosion resistance to carbon dioxide gas. However, when a deoxidizing element substituting for Mn is added, Mn may be not added (0%). When Mn is contained, the content of Mn is less than 2.0%. When the Mn content becomes 2.0% or more, coarse particles of sulfide (for example, MnS) are formed, which becomes a factor for the deterioration of corrosion resistance and mechanical properties. In order to more surely exhibit the action effect of Mn, it is preferable to set the lower limit of Mn to 0.05%. Also, in the case of the form containing "C exceeding 1.1% and not exceeding 4.0%" and the form containing "B of 0.7% or more and 3.0% or less" described above, Mn is preferably more than 0%.

[0028] In the form containing "C exceeding 1.1% and not exceeding 4.0%" described above, C is more than 1.1% and not exceeding 4.0%. C has the effect of hardening the alloy by crystallizing or precipitating as carbides or dissolving in the matrix other than carbides. In this case, in order to obtain the effect of improving wear resistance, the content of C is preferably more than 1.1% to form massive Cr-based carbides mainly composed of Cr in the matrix. Although the wear resistance tends to improve as the C content increases because the amount of hard carbide particles also increases, the Cr in the matrix is consumed, which is a factor deteriorating the corrosion resistance. Considering the balance between wear resistance and corrosion resistance, C is not more than 4.0%. In order to more surely exhibit the above-described effect of C, the lower limit of C is preferably 1.5% and the upper limit is preferably 3.5%. The massive Cr-based carbides refer to those having a size such that a circle with a diameter of 5 μm or more can be drawn in the carbide, such as the carbides shown in FIG. 8. In FIG. 8, the portions shown in dark gray or black are carbides. The composition of the carbide can be confirmed by, for example, quantitative analysis using an energy dispersive X-ray analyzer. The Cr-based carbide refers to the one containing the most Cr in the above-described quantitative analysis result.

[0029] In the form containing "B of 0.7% or more and 3.0% or less" described above, B is 0.7% or more and 3.0% or less. B (boron) has the effect of crystallizing or precipitating hard borides effective for wear resistance in the matrix phase. In order to obtain the effect of improving wear resistance, the B content should be 0.7% or more, and it is preferable to form massive Cr-based borides mainly composed of Cr in the matrix phase. As the B content increases, the proportion of hard borides in the structure increases and the wear resistance tends to improve. In order to more surely exhibit the effect of B, it is preferable that B is 1.0% or more, more preferably 1.5% or more. On the other hand, when the B content becomes excessively large, Cr in the matrix phase is consumed with the formation of borides, which becomes a factor deteriorating the corrosion resistance. In addition, the crystallization of coarse borides becomes the starting point of cracks during build-up welding. Furthermore, corrosion caused by borides occurs, so the corrosion resistance also decreases. Therefore, considering the balance between wear resistance and corrosion resistance, it is preferable that B is 3.0% or less, more preferably 2.5% or less, and even more preferably 2.0% or less. The massive Cr-based borides refer to, for example, those having a black and elongated shape as seen in Fig. 13 and having an elongated cross-sectional shape with a width of 3 μm or more and a length of 30 μm or more in the width direction. The composition of the boride can be confirmed, for example, by quantitative analysis with an energy dispersive X-ray analyzer (EDX). The Cr-based boride refers to those in which B is detected in the quantitative analysis result by the EDX and Cr is contained most in the metal elements excluding B.

[0030] In the form including the above-mentioned "(3) 0.5% or more and 2.5% or less of C and more than 0% and 20% or less of Nb", C is 0.5% or more and 2.5% or less, and Nb is more than 0% and 20% or less. Here, C has an effect of hardening the alloy by crystallizing or precipitating as a carbide or dissolving in the matrix other than the carbide in the Cr-Ni alloy of the present disclosure. In order to obtain the effect of improving wear resistance, it is preferable to set the C content to 0.5% or more to form massive Nb-based carbides mainly composed of Nb. Also, when the C content increases, the amount of hard Nb-based carbide particles increases and the wear resistance tends to improve. However, when the C amount increases beyond the above ratio, Cr in the matrix (base) is consumed, the hardness increases, but it becomes a factor in deteriorating the corrosion resistance. Considering the balance between wear resistance and corrosion resistance, C was set to 2.5% or less. In order to more surely exhibit the above-described effect of C, it is preferable to set the lower limit of C to 0.8% and the upper limit to 1.5%. In addition, in the Cr-Ni alloy of the present disclosure, Nb has the effect of forming an austenite phase by crystallizing or precipitating as Nb-based carbides or dissolving in the matrix phase other than carbides. In order to obtain the effect of improving wear resistance, the content of Nb is preferably more than 0% to form massive Nb-based carbides mainly composed of Nb. Also, when the Nb content increases, the hard Nb-based carbide particles increase and the wear resistance tends to improve. However, when the amount of Nb increases, it combines with Ni that forms the austenite phase, improving toughness. However, Nb is more expensive than Ni and may deteriorate the cost performance. In addition, by increasing Nb, Cr, Ni, and Fe that form the matrix phase are reduced. Therefore, although the hardness and wear resistance increase, it becomes a factor that deteriorates the mechanical properties and corrosion resistance. Considering the balance between wear resistance and corrosion resistance, and mechanical properties, Nb is set to 20% or less, and the preferable upper limit of Nb is 16%. Also, in order to exhibit wear resistance characteristics, the lower limit is preferably 4%. Further, in order to more surely exhibit the action effect of the above-described Nb-based carbide, the lower limit of Nb is more preferably 6.4%, and the upper limit is preferably 12%. Also, it is desirable to add Nb and C so that the ratio of Nb:C is approximately 8:1 by mass%. Note that the Nb-based carbide refers to, for example, polygonal massive carbides as seen in FIGS. 19 and 20 and those that appear to be amorphous, feathery, dendritic, or linear. The composition of the carbide can be confirmed, for example, by quantitative analysis using an energy dispersive X-ray analyzer. The Nb-based carbide refers to those in which C is detected in the quantitative analysis result and Nb is most contained among the metal elements excluding C.

[0031] The balance is Ni and unavoidable impurities: Elements other than those described above are Ni and inevitable impurities. Among these, Ni is one of the main elements of the coating layer, and most of it is dissolved in the matrix phase other than carbides and hardly dissolved in carbides. The solid solution of Ni in the matrix phase stabilizes the austenite phase constituting the matrix phase, suppresses the formation of ferrite in the primary crystal, and has the effect of improving corrosion resistance. To fully exert this effect, the Ni content is preferably in a range exceeding the above-mentioned Fe content. Also, the Ni content is preferably 15% or more, more preferably 25% or more, and even more preferably 30% or more. On the other hand, if Ni becomes excessively high, the above-mentioned effects of Cr may be impaired, so the upper limit of the Ni content is preferably less than the Cr content. In addition, the balance contains, in addition to the aforementioned Ni, impurities inevitably contained during manufacturing. Among these impurities, the impurities that should be particularly restricted are as follows. The impurities P and S tend to segregate at grain boundaries and cause corrosion resistance, so P is limited to 0.02% or less and S is limited to less than 0.005%. For S, 0.003% or less is preferable, and 0.002% or less is even more preferable. In addition, O, N, etc. also combine with Cr to form oxide-based and nitride-based inclusions, reducing cleanliness and degrading corrosion resistance and fatigue strength, so it is preferably suppressed as low as possible. For this reason, preferable O is 0.002% or less and N is 0.04% or less. Also, a small amount of Ta may be mixed into Nb as an impurity, but if Ta is within the range of 0.2% or less, the influence is small and there is no need to specifically limit it low, and it can be mixed without problem.

[0032] Si: 0.1% or more and 1.0% or less Si is one of the optional components of the Cr-Ni alloy of the present disclosure and is a component that plays a role in deoxidation and contributes to the improvement of mechanical properties. When Si is contained, the Si content is preferably 0.1% or more and 1.0% or less. If the Si content is less than 0.1%, the effects based on Si tend to be insufficient. Also, when Si exceeds 1%, coarse particles of oxide (for example, SiO2) are formed, which becomes a factor in the deterioration of mechanical properties. Al: 0.005% or more and 0.05% or less Al is also one of the optional components of the Cr-Ni alloy of the present disclosure, and it is a component that contributes to the improvement of the deoxidation effect when combined with Mn and Si. When Al is contained, the content of Al is preferably 0.005% or more and 0.05% or less. If the Al content is less than 0.005%, the action effect of Al may not be sufficiently obtained. Also, if the Al content exceeds 0.05%, coarse particles of oxides and nitrides (e.g., Al2O3 and AlN) are formed, which becomes a factor in the deterioration of mechanical properties.

[0033] Sn: 0.02% or more and 0.3% or less Sn is an optional component that plays a role in passivation film strengthening in the Cr-Ni alloy of the present disclosure and contributes to the improvement of corrosion resistance and wear resistance. Specifically, an improvement in resistance to chloride ions and acidic corrosion environments can be expected. When Sn is contained, the content of Sn is preferably 0.02% or more and 0.3% or less. If the Sn content is less than 0.02%, the action effect based on Sn cannot be sufficiently obtained. Also, if the Sn content exceeds 0.3%, grain boundary segregation of the Sn component occurs, which becomes a factor in the deterioration of the ductility and toughness of the alloy. Cu: 0.1% or more and 5.0% or less Cu is an optional component that contributes to the improvement of corrosion resistance in the Cr-Ni alloy of the present disclosure. When Cu is contained, its content is preferably 0.1% or more and 5.0% or less. If the Cu content is less than 0.1%, the action effect based on Cu cannot be sufficiently obtained. Also, if the Cu content exceeds 5.0%, Cu precipitates are likely to be generated, which becomes a factor in the deterioration of the ductility and toughness of the alloy.

[0034] As described above, the alloy of the present disclosure is preferably formed into alloy powder and used for forming a surface modification layer by overlay welding. It may be pulverized into powder by gas atomization in which the molten alloy of the present disclosure is introduced into a high-speed air flow of an inert gas and pulverized, and may be applied by a PTA (Plasma transfer arc) overlay welding apparatus. In a PTA overlay welding apparatus, powder needs to move smoothly because the powder is conveyed by flowing through a pipeline up to the application part at the tip of the welding torch. On the other hand, the powder obtained by gas atomization is spherical and has good fluidity, which is preferable. Further, an alloy powder obtained by pulverizing the alloy of the present disclosure by a powder metallurgy method and sintered into a rod-shaped powder metallurgy compact can also be used as a welding rod.

[0035] <Method for manufacturing Cr-Ni alloy> Next, a method for manufacturing the Cr-Ni alloy of the present disclosure will be described. FIG. 1 is an example of a method for manufacturing a Cr-Ni alloy product according to the present disclosure, and is a process diagram showing a method for manufacturing an alloy powder (here, powder and overlay welding material) which is a rapidly solidified cast formed body. As shown in FIG. 1, first, a melting step (step 1: S1) is performed in which a raw material of a Cr-Ni alloy is melted to form a molten metal 10 so as to have a desired composition. There is no particular limitation on the method of melting the raw material, and a conventional method in the production of high corrosion resistance and high strength alloys can be used. The molten metal 10 may be refined by a predetermined method to form a highly purified molten metal 12 with a reduced content of impurity components (FIG. 3).

[0036] Next, an atomization step (step 2: S2) is performed using the molten metal 10 or the purified molten metal 12 as starting materials, whereby alloy powder 20 of a Cr-Ni-based alloy can be obtained. As an example of the type of atomization method, there is a method of obtaining powder by pulverizing molten metal by spraying a high-pressure medium against the flow of the molten metal, which is classified into gas atomization or water atomization depending on the type of medium used. Although there is no particular limitation on the atomization method in the present disclosure, for the purpose of build-up powder, it is preferable to use the gas atomization method by which cleaner and more homogeneous composition and spherical particles can be obtained. The obtained alloy powder 20 can be suitably used, for example, as a welding material, a material for powder metallurgy, or a material for additive manufacturing. Further, the target composition is preferably an alloy containing carbides and being a two-phase alloy in which the matrix phase is composed of a ferrite phase and an austenite phase or a single-phase alloy of an austenite phase. In the case of a two-phase alloy, it is desirable that the austenite phase preferably exhibits a volume fraction of 20% or more. Next, a classification step (step 3: S3) may be performed on the alloy powder 20 obtained by performing the atomization step S2 in order to make the particle sizes uniform to a desired size. The classification step S3 is not an essential step, but when the alloy powder 20 is used as a build-up material, it is preferable to perform classification from the viewpoints of stable powder supply to a welding apparatus and stabilization of the build-up construction process. Although there is no particular limitation on the particle size to be classified, for example, for PTA build-up welding, a particle size range of 63 μm or more and 250 μm or less may be extracted and used. Further, when used for a powder metallurgy compact described later, classification and selection may be performed in a particle size range of, for example, 1 μm to 50 μm from the viewpoints of dimensional accuracy of the compact and prevention of residual voids.

[0037] Next, when a build-up welding process (step 4: S4) is performed on a desired base material 41 using the alloy powder 20, a build-up welding material 40 is obtained in which an alloy coating layer 42 is formed, which is a rapidly solidified compact having a rapidly solidified structure in which the molten alloy powder 20 is rapidly cooled and solidified due to the temperature difference between the base material 41 and the outside air. In the case of the form including “(2) 0.7% or more and 3.0% or less of B” of the present disclosure, the rapidly solidified structure preferably has a metal structure having massive Cr borides of a size capable of drawing a circle with a diameter of 3 μm or more inside thereof. In the present disclosure, the build-up welding process S4 is assumed to include thermal spraying using metal powder. The obtained build-up welding material 40 may be used as it is as a member constituting various devices, but a shaping process (step 5: S5) for shaping the dimensions and shape of the build-up welding material 40 may be further performed in consideration of connection to other members. Examples of the means for shaping include cutting using a milling machine or polishing using a grindstone.

[0038] In addition, as a rapidly solidified compact having a rapidly solidified structure, for example, a molten Cr—Ni-based alloy may be sprayed onto a roll rotating at high speed to be rapidly cooled into a thin strip-shaped cast compact, or the above alloy powder may be laminated while being sprayed to form a laminated compact (rapidly solidified compact) having a rapidly solidified structure. Further, as a method for obtaining an alloy powder different from the above, a powdering process of mechanically pulverizing the cast compact obtained by the casting process into an alloy powder may be applied to produce the alloy powder. In this case, for example, a ball mill or the like can be applied as the powdering process.

[0039] FIG. 2 is an example of a method for manufacturing a Cr—Ni-based alloy according to the present disclosure, and is a process diagram showing a method for manufacturing a powder metallurgy compact. As shown in FIG. 2, the manufacturing process of the powder metallurgy compact is the same as the manufacturing method of the rapidly solidified compact in FIG. 1 up to the atomization process S2 or the classification process S3, and is different in that a powder forming process (step 6: S6) and a sintering process (step 7: S7) are performed instead of the build-up welding process S4. Therefore, the powder forming process S6 and the sintering process S7 will be described. By using the alloy powder 20 obtained by performing the atomization step S2 or further obtained through the classification step S3, the desired powder compact 60 can be obtained by performing the powder molding step S6. There is no particular limitation on the powder molding method. For example, in the case of the metal powder injection molding method, plastic or wax is kneaded with the alloy powder 20 as a binder to impart fluidity and moldability, and the resulting mixture is filled into a mold by an injection molding machine for molding in the powder molding sub-step (step 6a: S6a), and a debinding step (step 6b: S6b) for removing the binder remaining in the obtained powder compact 60 can be performed. In the debinding step, for example, the powder compact is immersed in a solvent or heated in a predetermined atmosphere.

[0040] Next, a sintering step S7 is performed to form a powder metallurgy compact 70 by subjecting the powder compact 60 to a sintering heat treatment below the solidus temperature of the alloy. There is no particular limitation on the sintering heat treatment method, and conventional methods can be used. When the aforementioned debinding step S6b is performed by heating, the debinding step and the sintering step can be performed together by adjusting the temperature and atmosphere at a point before reaching the sintering temperature in this sintering step S7. From the viewpoint of densification of the powder metallurgy compact 70, it is more preferable to include a hot isostatic pressing (HIP) treatment below the solidus temperature of the alloy and at 500 atmospheres or more and 3000 atmospheres or less. The obtained powder metallurgy compact 70 has a sintered structure and can be directly used as a member constituting various devices. If the powder metallurgy compact 70 is rod-shaped, it can be applied, for example, as an electrode rod of an arc welding machine and used for build-up welding on a desired base material. Also, similar to the case of the aforementioned build-up welding material, a shaping step S5 for shaping the dimensions and shape of the powder metallurgy compact 70 may be further performed in consideration of connection to other members, etc., to obtain a shaped body 50. Examples of the shaping means include cutting by a milling machine and polishing by a grindstone.

[0041] Figure 3 is an example of a method for manufacturing a Cr-Ni alloy according to the present disclosure, and is a process diagram showing a method for manufacturing a cast formed body. As shown in Figure 3, the manufacturing process of the cast formed body is different in that the melting process S1 is the same as the method for manufacturing the rapidly solidified formed body of Figure 1, and then a casting process (step 8: S8) is performed. The molten metal 10 obtained by performing the melting process S1, or the purified molten metal 12 obtained through the electrode manufacturing process S1a and the remelting process S1b, can be filled into a desired casting mold in the casting process S8, and then cooled and hardened to obtain a cast formed body 80. Note that there is no particular limitation on the casting method. In addition, in order to further reduce the content rates of impurity components (O, P, and S) in the alloy (to increase the cleanliness of the alloy), after the melting process S1 mixes and melts the raw materials of the Cr-Ni alloy to form the molten metal 10, it may be once solidified by casting to manufacture a consumable electrode 11 in an electrode manufacturing process (step 1a: S1a), and a remelting process (step 1b: S1b) for remelting the consumable electrode to prepare a purified molten metal 12 may be applied. As long as the cleanliness of the alloy can be increased, there is no particular limitation on the remelting method. For example, vacuum arc remelting (VAR) or electroslag remelting (ESR) can be preferably used. When the remelting process is applied, the ingot obtained by remelting becomes the cast formed body. The obtained cast formed body 80 has a casting structure. For example, by using a mold having a cooling mechanism such as a water cooling pipe inside the wall surface, it can be made into a rapidly solidified formed body exhibiting a rapidly solidified structure in which the cast molten metal is rapidly cooled and solidified. The cast formed body 80 may be directly used as a member constituting various devices, but a shaping process S5 for shaping the dimensions and shape of the cast formed body 80 may be further performed in consideration of connections to other members to obtain a shaped body 50. Examples of the shaping means include cutting by a milling machine, grinding by a grindstone, polishing, and the like.

[0042] <Alloy product> The Cr-Ni alloy manufactured as described above can achieve both corrosion resistance and wear resistance (resistance to earth and sand wear). As a result, the Cr-Ni alloy products of the present disclosure can be suitably used as various members used in severe corrosion and wear environments. Examples of such applicable members include automotive members (e.g., fuel injection device members, roller chain members, turbocharger members, engine exhaust system members, bearing members), railway-related members (e.g., bearing members, pantograph members), rolling bearings and sliding bearing members (e.g., linear bearing members, windmill bearing members, waterwheel bearing members, ventilation fan bearing members, mixing drum bearing members, compressor bearing members, elevator bearing members, escalator bearing members, planetary exploration machine bearing members), construction equipment members (e.g., endless track members, mixing drum members), ship and submarine members (e.g., screw members), environmental equipment members (e.g., garbage incinerator members, crushing machines), bicycle, motorcycle and water bike members (e.g., roller chain members, sprocket members), machining device members (e.g., molds, rolling rolls, cutting tool members), oil well equipment members (e.g., members (shafts, bearings) of rotating machines (compressors, pumps)), seawater environment equipment members (e.g., seawater desalination plant equipment members, umbilical cables), chemical plant equipment members (e.g., liquefied natural gas vaporizer members), power generation equipment-related members (e.g., coal gasification device members, heat-resistant piping members, fuel cell separators members, fuel reforming equipment members), and the like. Among the aforementioned members, application to oil well equipment members, machining devices, and environmental equipment members is particularly preferred.

[0043] FIG. 4(a) is an example of a Cr-Ni alloy product according to the present disclosure and an industrial product using the same, and is a schematic cross-sectional view of a screw pump used for transporting a fluid such as crude oil containing a corrosive component such as an organic acid containing earth and sand (solid matter). In a screw pump, for example, in addition to the screw surface and the casing surface that come into contact with the conveyed object, the Cr-Ni alloy product of the present disclosure can be suitably used as an alloy coating layer such as the inner surface of a piping member connected to the suction port and the discharge port (not shown). The alloy coating layer can be manufactured in the form of a build-up welding material. Figure 4(b) is another example of the Cr-Ni alloy product of the present disclosure and industrial products using the same, and is a schematic cross-sectional view of an injection mold. In the injection mold, for example, the Cr-Ni alloy product of the present disclosure can be suitably used as an alloy coating layer on the surface of the mold base material that comes into contact with molten plastic, a mixture of metal powder and binder, etc. filled in the space provided between the upper mold and the lower mold. The alloy coating layer can be manufactured in the form of a build-up welding material. Figure 4(c) is another example of the Cr-Ni alloy product of the present disclosure and industrial products using the same, and is a schematic cross-sectional view of a crushing machine called a jaw crusher that crushes conveyed objects such as rocks and concrete waste materials between oscillating toothed plates. In the crushing machine, for example, the Cr-Ni alloy product of the present disclosure can be suitably used as an alloy coating layer on the surface of the fixed toothed plate and the movable toothed plate that come into contact with the object to be crushed such as rocks. The alloy coating layer can be manufactured in the form of a build-up welding material. In addition, in the above application examples to industrial products, an example of providing an alloy coating layer on the surface of the target member has been described, but the entire target member may be composed of the Cr-Ni alloy product of the present disclosure.

Examples

[0044] Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples. Note that the present disclosure is not limited to these examples. (Method for Evaluating Characteristics of Test Pieces) (1) Evaluation of Abrasion Resistance (Abrasion Resistance to Earth and Sand) Equipment for crude oil extraction is subject to abrasion by gravel etc. in the crude oil that comes into contact with it. Therefore, an earth and sand abrasion test was carried out as an evaluation of abrasion resistance. The test method conformed to ASTM standard G65. After measuring the weight of the test piece obtained by cutting and polishing the molded body of each composition before the test, while pressing a rotating rubber disk against the test piece with a predetermined load, test silica sand was continuously supplied between the contact surfaces of the two for 10 minutes. Then, the weight of the test piece was measured to obtain the mass change before and after the test, and the abrasion volume AVL (unit: mm 3 ) was calculated taking into account the change in diameter due to the wear of the rubber disk accompanying the test. The measurement results of the wear volume were evaluated as grade A for "AVL < 180", grade B for "180 ≤ AVL < 360", and grade C for "360 ≤ AVL", respectively. The results of the evaluation of the earth and sand abrasion resistance are shown together in Tables 1 to 4.

[0045] (2) Corrosion resistance evaluation The equipment for crude oil extraction assumed as the application field of the present disclosure is exposed to a strong acid corrosion environment due to the influence of hydrogen sulfide contained in the crude oil and hydrochloric acid generated by the decomposition of inorganic chlorides. Therefore, a boiling sulfuric acid immersion test was carried out as the corrosion resistance evaluation. The test method complied with JIS standard G0591: Method for sulfuric acid corrosion test of stainless steel, and the test solution used was sulfuric acid with pH 1 diluted with pure water to a concentration of 5 mass%. The test pieces obtained by cutting and polishing the molded bodies of each composition were weighed before the test, and then immersed in the boiling test solution for 6 hours. After that, the mass of the test pieces was measured to obtain the mass change before and after the test, and the value obtained by dividing this by the surface area of the test piece before the test and the test time was calculated as the corrosion rate m (unit: g / (m 2 ·h)). The measurement results of the corrosion rate were evaluated as grade A for "m < 3×10 0 ", grade B for "3×10 0 ≤ m < 10 2 ", and grade C for "10 2 ≤ m", respectively. The results of the corrosion resistance evaluation are shown together in Tables 1 to 4. (3) Microstructure observation To investigate the relationship with corrosion resistance and earth and sand abrasion resistance, the cut surfaces of some test pieces were mirror-polished and observed by a scanning electron microscope (SEM).

[0046] 〔Example 1〕 The raw materials were mixed to have the composition shown in Table 1, melted by a high-frequency melting method (melting temperature: 1500 °C or higher, in a reduced-pressure Ar atmosphere) to form a molten metal, and then the molten metal was cast to produce a cast-shaped body. Since the cooling rate during build-up application of the alloy of the present disclosure is high, a mold with an elongated shape having a diameter of about 20 mm was selected so that the structure of the cast-shaped body would be a quenched structure similar to that of a build-up welding bead. Each cast-shaped body was cut and polished into a predetermined test piece shape according to each of the above-described test methods. Nos. 1 to 4 shown in Table 1 are comparative examples in which C was fixed at 1.0%, and Nos. 5 to 8 have the composition of the inventive examples in which C was increased to 2.0 to 2.9%. Nos. 9 to 14 have the composition of the inventive examples in which Cr is about 55% or about 60%, the composition other than C is generally fixed, and C is changed to 1.5 to 2.5%. Further, No. 15 is a comparative example in which C was increased to 4.5%, and No. 16 has the composition of the inventive examples in which Cr was reduced to 45.0%. Note that those indicated as "<0.1%" contained a very small amount of less than 0.1%.

[0047]

Table 1

[0048] Figure 5 shows the test results of the corrosion rate m and the wear volume AVL for each test piece. The circled numbers written horizontally for each plot correspond to the Nos. of the respective compositions shown in Table 1. Regarding the earth and sand abrasion resistance, all of the Comparative Example No. 1-4 alloys with C of 1.0 mass% were judged as C grade, and the earth and sand abrasion resistance was poor. The scanning electron microscope (SEM) observation images of the Comparative Example No. 1-4 alloys are shown in FIGS. 6 and 7. The No. 1 alloy had a two-phase structure with island-shaped phases in the phase having a fine eutectic structure. Also, all of the No. 2-4 alloys had a structure in which fine crystallized substances or precipitates, regarded as carbides, were dispersed throughout. Here, when comparing the No. 2 alloy and the No. 4 alloy, in the matrix that appears white in the No. 2 alloy, a gray part that extends linearly can be seen, but its length is as short as several μm. On the other hand, the structure of the No. 4 alloy is similar to that of the No. 2 alloy, but the gray part that extends linearly is as long as several tens of μm, and it is considered that the carbide has grown compared to the No. 2 alloy. The reason for such a difference in structure is due to the balance between Ni and Fe, but in any composition, the width of the carbide was as thin as 1 μm or less and it is considered that it did not contribute to the improvement of the earth and sand abrasion resistance.

[0049] On the other hand, in the case of the No. 5-16 alloys containing more than 1.1 mass% of C of the present invention examples, the earth and sand abrasion resistance reached A grade; AVL < 180 in all alloys. Here, FIGS. 8 shows the SEM observation images of the No. 5 and No. 6 alloys, and FIG. 9 shows the SEM observation images of the No. 7 and No. 8 alloys. In any of the images, it can be seen that, different from the case of containing 1.0 mass% of C shown in FIGS. 6 and 7 above, massive carbides, which are dark gray or black and have a size generally exceeding 20 μm, are dispersed. As a result of analyzing this massive carbide with an X-ray analyzer, it was a Cr-based carbide mainly composed of Cr. It is considered that this massive Cr carbide crystallized and grew in the liquid phase of the alloy melted during the build-up process, and remained in a dispersed state in the structure when it was rapidly cooled and solidified. Here, looking at the relationship between the amount of massive carbide occupying the observation region and the earth and sand abrasion resistance, for the No. 1-4 alloys where no massive carbide appears, AVL > 400, while for the No. 5-8 alloys with a large amount of carbide, AVL < 180, and it is considered that the earth and sand abrasion resistance was improved by the increase in the amount of massive carbide in the structure. Note that the difference in the color tone of the carbides indicates that the carbide forms of the two are different. The region that appears black is M7C3-type Cr carbide, and the region that appears dark gray is considered to be M 23 C6-type Cr carbide. The Vickers hardness of each form of Cr carbide is considered to exceed 1000, and both contribute to the improvement of earth and sand abrasion resistance. On the other hand, No. 16 of the present invention example has a lower Cr content than other present invention examples and has a B blade evaluation. However, compared with No. 1 to No. 4 and No. 51 to No. 56 of the comparative examples described below, it is equivalent or better. When C exceeds 1.1% by mass, Cr is preferably more than 46.0%.

[0050] Next, FIG. 10 shows SEM observation images of No. 9 to No. 11 alloys. From the color tone of the images, all are considered to be M7C3-type carbides. However, the size of the carbides in No. 9 alloy containing 1.5% by mass of C is approximately around 15 μm, while the size of the carbides in No. 10 alloy containing 2.0% by mass of C is approximately around 20 μm, and the size of the carbides in No. 11 alloy containing 2.5% by mass of C is approximately around 30 μm, and the proportion of carbides in the observation region is increasing. Looking at FIG. 5 here, the wear volume AVL decreases in the order of No. 9, No. 10, and No. 11 alloys, and it is considered that the wear resistance to earth and sand has been improved by the increase in carbides in the structure. Next, FIG. 11 shows SEM observation images of No. 12 to No. 14 alloys. From the color tone of the images, the carbides of No. 12 and No. 13 alloys are M 23 C6-type, and No. 14 alloy is mainly considered to be M7C3-type. Although there are differences in the carbide form and individual size between the two, it is considered that the higher the C content, the larger the proportion of carbides in the structure, which results in the difference in wear resistance to earth and sand. Note that according to the study using equilibrium phase diagram calculation etc. by the inventors, when C is relatively low in the alloys of the present disclosure, the carbides are M 23In the C6 type, when the amount of C increases, the M7C3 type appears, and the more Cr there is, the more C is required for the appearance of M7C3. Comparing FIGS. 10 and 11, the carbide in FIG. 10 with 55% by mass of Cr is of the M7C3 type, while the carbide in FIG. 11 with 60% by mass of Cr is M 23 The C6 type occupies many parts and is in good agreement with the above tendency.

[0051] 〔Example 2〕 The raw materials were mixed to have the composition shown in Table 2, melted by high-frequency melting method (melting temperature 1500 °C or higher, in a reduced-pressure Ar atmosphere) to form a molten metal, and then the molten metal was cast to produce a cast molded body. Since the cooling rate during build-up construction is fast in the build-up material to which the alloy of the present disclosure is applied, a mold with an elongated shape having a diameter of about 20 mm was selected so that the structure of the cast molded body would be a rapidly cooled structure similar to the build-up weld bead. Each cast molded body was cut and polished into a predetermined test piece shape according to each of the above test methods. Nos. 21 to 26 and 28 shown in Table 2 have the compositions of the present invention examples, and No. 27 is a comparative example in which B exceeds the upper limit. The wear resistance (earth and sand wear resistance) evaluation, corrosion resistance evaluation, and microstructure observation were performed in the same manner as in Example 1 above. Note that those indicated as "<0.1%" contained extremely small amounts less than 0.1%.

[0052]

Table 2

[0053] FIG. 12 shows the test results of the corrosion rate m and the wear volume AVL for each test piece. The numbers in parentheses written horizontally for each plot correspond to the Nos. of the respective compositions shown in Table 2. Regarding the earth and sand abrasion resistance, the alloys of Nos. 21 to 26 of the present invention examples achieved an A grade in earth and sand abrasion resistance; AVL < 180. Here, FIGS. 13 to 15 show the SEM observation images of the alloys of Nos. 21 to 26 of the present invention examples. In any of the images, massive borides having an elongated cross-sectional shape with a size generally exceeding 3 μm in the width direction and 30 μm in the longitudinal direction and being black are dispersed. As a result of analyzing this massive boride with an X-ray analyzer, it was a Cr-based boride mainly composed of Cr. It is considered that this massive Cr boride crystallized and grew in the liquid phase of the alloy melted during the build-up welding operation, and remained dispersed in the structure as it was when it was rapidly cooled and solidified. This massive Cr boride is considered to be a hard material with a Vickers hardness exceeding 1000, and it is considered that the increase in this hard Cr boride contributed to the improvement of the earth and sand abrasion resistance. Next, the comparative example No. 27 alloy with B being 4.0 mass% achieved an A grade in earth and sand abrasion resistance, but the corrosion resistance was a very poor result of grade C. The SEM observation image is shown in FIG. 16. Compared with Nos. 21 to 26, the most Cr borides are dispersed in No. 27. From this, it is considered that in No. 27, more Cr was consumed during the crystallization of the Cr boride, and the Cr in other matrix phases decreased, resulting in deteriorated corrosion resistance. Next, the present invention example No. 28 alloy with Cr being 42.0% had both corrosion resistance and wear resistance of grade B. The SEM observation image is shown in FIG. 17. Compared with Nos. 21 to 26, each Cr boride was thin and short. This is considered to be due to the decrease in the crystallization amount of the Cr boride due to the small amount of Cr and the small amount of Cr originally contained in the matrix phase. Although No. 28 is inferior to other present invention examples, it is equivalent or better compared to Nos. 51 to 56 of the comparative examples described below. In addition, when constituting the Cr boride, the Cr amount is preferably 45% or more.

[0054] 〔Example 3〕 The raw materials were mixed to obtain the composition shown in Table 3, and melted by high-frequency melting (melting temperature 1500°C or higher, in a reduced pressure Ar atmosphere) to form a molten metal, which was then cast to produce a cast compact. Since the cooling rate during the overlay application is fast for the overlay material to which the alloy of the present disclosure is applied, a long and narrow mold with a diameter of about 20 mm was selected to be used so that the structure of the cast compact would be a quenched structure similar to that of the overlay weld bead. Each cast compact was cut and polished to a predetermined test piece shape according to each of the above-mentioned test methods. Nos. 31 to 35 shown in Table 3 are examples of the present invention in which C is fixed at 1.0%, Nos. 36 and 37 are examples of the present invention in which C is more than 1.0%, and Nos. 38 and 39 are examples of the present invention in which C is less than 1.0%. No. 40 is an example of the present invention in which C is added by 2.2% to increase the ratio of C to Nb. No. 41 is an example of the present invention in which the composition is similar to No. 34, and the Nb and C ratio is increased while keeping the ratio at 8:1. The abrasion resistance (resistance to abrasion by soil and sand), corrosion resistance, and structure observation were carried out in the same manner as in Example 1 above.

[0055] [Table 3]

[0056] Figure 18 shows the test results for the corrosion rate m and wear volume AVL for each test piece. The numbers in parentheses next to each plot correspond to the No. of each composition shown in Table 3. All of the alloys were judged to be grade A in both the abrasion resistance and the corrosion resistance, and good properties were obtained. Figures 19 to 23 show scanning electron microscope (SEM) images of the alloys of the invention examples. For example, alloy No. 31 in Figure 19 had block-, rod-, and dot-like crystallizations or precipitates of 20 μm or less that were visible in white contrast, and the matrix was a two-phase structure containing a ferrite phase that was visible in dark gray contrast and an island-shaped austenite phase that was visible in light gray contrast. Similarly, for the No.32 alloy, the entire structure was composed of precipitates or crystallization products in the form of lumps, rods, dots, feathers, and dendrites with a size of 20 μm or less, all of which appeared as white contrasts and were dispersed throughout. As a result of analyzing these parts that appeared as white contrasts using EDX and X-rays, they were found to be Nb-based carbides with Nb as the main component. In addition, in a part of the island-shaped austenite phase in the two-phase structure, there was a eutectic-like structure that appeared as a black contrast. As a result of analysis using EDX and X-rays, it was found to be a Cr-based carbide with Cr as the main component. On the other hand, the No.33 alloy also has Nb-based carbides that appear as white contrasts. However, unlike the No.1 and No.2 alloys, lumpy Nb-based carbides of about 10 μm were not observed. Instead, it was a structure in which crystallization products or precipitates in the form of rods, dots, feathers, and dendrites with a size of 20 μm or less were dispersed.

[0057] Similarly, Figures 20 to 23 show SEM observation images of the structures of the No.34 to 41 alloys of the present invention examples. For all of these alloys, the entire structure was composed of precipitates or crystallization products in the form of lumps, rods, dots, feathers, and dendrites that spread out in a similar manner to the aforementioned No.31 to 33 alloys and were dispersed throughout. All of these alloys were determined to be Grade A in both earth and sand abrasion resistance and corrosion resistance, and good characteristics were obtained. By the way, when wear is suppressed by dispersing hard particles (Nb-based carbides) in the structure, if the strength of the hard particles themselves is low, the effect will be small. Therefore, it is considered desirable for the hard particles to be in the form of lumps of a certain size. However, for example, in alloy No.33 of the present invention examples, although most of the eutectic Nb-based carbides are present and no lumpy Nb-based carbides are observed, good characteristics in earth and sand abrasion resistance are obtained compared to other alloys disclosed in the present application. This is because in the alloys disclosed in the present application, Nb-based carbides exist in the hard ferrite phase among the two-phase structures that make up the matrix phase. Therefore, the ferrite phase compensates for the strength of the Nb-based carbides, and it is considered that this eutectic region acts as virtual hard particles. Therefore, it is considered that the wear resistance of the alloys of the present disclosure is affected not only by the number and size of massive Nb-based carbides, but also by the total area, distribution state, and shape of the Nb-based carbide phase. For the SEM photographs of each alloy taken in a plurality of fields including the SEM photographs of FIGS. 19 to 23, the portion of the Nb-based carbide that appears as white contrast and the other portion were binarized by image analysis software, and the area ratio occupied by the Nb-based carbide in the entire field of view was calculated, and it was generally in the range of 6 to 20%.

[0058] In addition, according to the studies using equilibrium diagram calculations and the like by the inventors, in the alloys of the present disclosure, Cr-based carbides appear not only when there is a large amount of Cr, but also when C is added in excess relative to Nb. At this time, the Cr-based carbide is mainly M 23 C6 type. In No. 32, 33, and 36 alloys, eutectic Cr-based carbides appear inside the austenite phase. In addition, in No. 40 where the ratio of C to Nb is increased, elongated massive Cr-based carbides appear. These Cr-based carbides are hard and contribute to wear resistance in the same way as Nb-based carbides. On the other hand, since Cr in the parent phase is consumed for the formation of Cr-based carbides, there is a concern that the corrosion resistance may deteriorate. Therefore, it is necessary to pay attention so that the addition amount of C does not become excessively large.

[0059] 〔Comparative Example〕 For comparison of the levels of corrosion resistance and wear resistance (resistance to earth and sand wear) in the Cr-Ni-based alloys of the present disclosure, four types of powders having compositions corresponding to commercially available surface modification build-up materials shown in Table 4 and two types of Cr-based alloy powders (50Cr, 63Cr) without addition of C, B, and Nb were used. The welded beads formed by applying and forming on the SUS304 base material with a PTA build-up welding apparatus were cut and polished to prepare test pieces, and a boiling sulfuric acid immersion test and an earth and sand wear test were carried out. Each test condition was the same as that shown in the characteristic evaluation method of the test pieces described above. Table 4 shows the compositions, corrosion resistance, and earth and sand wear resistance results of the commercially available build-up materials and the comparative example Cr-based alloys, and FIG. 24 shows the test results of the corrosion rate and earth and sand wear volume of each build-up material. Among the build-up materials compared this time, there was no material that achieved Grade A in both corrosion resistance and earth and sand abrasion resistance. It can be seen that the alloys of the present disclosure achieve both corrosion resistance and earth and sand abrasion resistance equal to or better than those of commercially available Nos. 51 to 54.

[0060]

Table 4

[0061] The above-described embodiments and examples have been described to assist in the understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, a part of the configuration of the embodiment can be replaced with a configuration of a person skilled in the art's common general knowledge, and a configuration of a person skilled in the art's common general knowledge can also be added to the configuration of the embodiment. That is, the present invention can delete, replace with other configurations, or add other configurations to a part of the configurations of the embodiments and examples in this specification without departing from the technical idea of the invention.

Explanation of Reference Numerals

[0062] 10…Molten metal 11…Consumable electrode 12…Purified molten metal 20…Alloy powder 40…Build-up welding material 41…Base material 42…Alloy coating layer 50…Shaped body 60…Powder formed body 70…Powder metallurgy formed body 80…Cast formed body

Claims

**Claim 1** A method for manufacturing an alloy powder for additive manufacturing, which is laminated while being melted to obtain a laminated formed body having a rapidly solidified structure, comprising: a melting step of melting a raw material of a Cr-Ni alloy to form a molten metal; a casting step of casting the molten metal to form a cast formed body; a powdering step of mechanically pulverizing the cast formed body to produce an alloy powder, wherein the alloy powder contains, by mass%, more than 40.0% and at most 65.0% of Cr, 4.0% or more and 30.0% or less of Fe, 0.5% or more and 2.5% or less of C, 6.4% or more and 20% or less of Nb, the balance consisting of Ni and unavoidable impurities, wherein the Ni is 15% or more, and has a structure in which precipitated or deposited Nb-based carbides are dispersed, a method for manufacturing an alloy powder for additive manufacturing. **Claim 2** A method for manufacturing a laminated formed body, comprising laminating while melting the alloy powder for additive manufacturing according to Claim 1 to obtain a laminated formed body having a rapidly solidified structure. **Claim 3** A method for manufacturing an alloy powder for build-up welding, which is build-up welded on a base material to obtain a build-up welding material having an alloy coating layer with a rapidly solidified structure, comprising: a melting step of melting a raw material of a Cr-Ni alloy to form a molten metal; a casting step of casting the molten metal to form a cast formed body; a powdering step of mechanically pulverizing the cast formed body to produce an alloy powder, wherein the alloy powder contains, by mass%, more than 40.0% and at most 65.0% of Cr, 4.0% or more and 30.0% or less of Fe, 0.5% or more and 2.5% or less of C, 6.4% or more and 20% or less of Nb, the balance consisting of Ni and unavoidable impurities, The Ni is 15% or more, having a structure in which precipitated or deposited Nb-based carbides are dispersed, A method for producing a build-up alloy powder.

4. A method for producing a build-up welding material, comprising build-up welding the build-up alloy powder according to Claim 3 onto a substrate to obtain a build-up welding material having an alloy coating layer with a rapidly solidified structure.

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