Fe-based alloy cladding layer and method for forming the same.

Abstract

Provided is a build-up layer that can improve corrosion resistance and wear resistance. [Solution] The Fe-based alloy cladding layer contains C, Si, Mn, Cr, Mo, and V, with the balance being Fe and unavoidable impurities. In the cross section of the Fe-based alloy cladding layer, the ratio of the total area of ​​fine carbides with a diameter of 5 μm or less to the area of ​​the observation region is 0.50% or more and 4.00% or less. The amount of Cr in solid solution contained in the primary crystal is 5 mass% or more. The respective contents [mass%] of C, Si, Mn, Cr, Mo, and V are as follows: 1.60≦C≦3.50 0.20≦Si≦1.50 0.20≦Mn≦1.50 14.0≦Cr≦26.0 0.2≦Mo≦2.0 4.0≦V≦8.0

Description

Technical Field

[0001] The present invention relates to a build-up layer formed of an Fe-based alloy having a predetermined composition and a method for forming the build-up layer.

Background Art

[0002] In the invention described in Patent Document 1, an Fe-based alloy capable of obtaining a build-up layer or a laminated object having high wear resistance and high toughness when used in melt solidification forming such as build-up welding or laminated molding is provided.

[0003] To achieve this object, the Fe-based alloy contains 0.5 ≦ C ≦ 0.9 mass%, 0.5 ≦ Si ≦ 3.0 mass%, 0.1 ≦ Mn ≦ 1.0 mass%, 3.0 ≦ Cr ≦ 8.0 mass%, and 0.1 ≦ Mo ≦ 4.0 mass%, and the balance consists of Fe and inevitable impurities. And it satisfies -0.5 > Si - (5C + 2Mn) > -3.0. Here, by setting the content of Cr within the above numerical range, hardenability and corrosion resistance are enhanced.

[0004] In the invention described in Patent Document 2, using an Fe-based alloy powder that can be a build-up material for forming a build-up layer of martensitic stainless steel containing Cr, even if normal quenching is omitted in the post-weld heat treatment, a build-up layer that exhibits the properties of martensitic stainless steel including wear resistance is formed.

[0005] To achieve this object, the Fe-based alloy powder contains C: 1.4 mass% or more and 3.5 mass% or less, V: 2.0 mass% or more and 10.0 mass% or less, Cr: 15.0 mass% or more and 20.0 mass% or less, Mo: less than 8.0 mass%, Si: less than 2.0 mass%, Mn: less than 2.0 mass%, and the balance consists of Fe and inevitable impurities. And {4.2C - V} satisfies 2.1 mass% or more and 6.1 mass% or less. Here, by setting the content of Cr within the above numerical range, corrosion resistance is enhanced.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-144437 [Patent Document 2] Japanese Patent Publication No. 2020-032449 [Overview of the project] [Problems that the invention aims to solve]

[0007] The inventors of this invention focused on the composition of the Fe-based alloy, the area of ​​granulated carbides contained in the overlay layer formed from the Fe-based alloy, and the amount of chromium dissolved in the primary crystals contained in the overlay layer. They found that these factors improved the corrosion resistance and wear resistance of the overlay layer, leading to the completion of the present invention. The object of the present invention is to provide an overlay layer with excellent corrosion resistance and wear resistance. [Means for solving the problem]

[0008] The present invention relates to an Fe-based alloy cladding layer containing C, Si, Mn, Cr, Mo, and V, with the remainder being Fe and unavoidable impurities. Here, each of C, Si, Mn, Cr, Mo, and V has the following mass % content. 1.60 ≤ C ≤ 3.50 0.20 ≤ Si ≤ 1.50 0.20 ≤ Mn ≤ 1.50 14.0 ≤ Cr ≤ 26.0 0.2 ≤ Mo ≤ 2.0 4.0 ≤ V ≤ 8.0

[0009] In the cross-section of the Fe-based alloy cladding layer, the ratio of the total area of ​​fine-grained carbides with a diameter of 5 μm or less to the area of ​​the observed region is between 0.50% and 4.00%. Furthermore, the amount of Cr solid solution contained in the primary crystal is 5% by mass or more.

[0010] The amount of Cr solid solution can be defined as the average value of the amount of Cr detected at multiple points in the primary crystal.

[0011] The second invention of this application is a method for forming an Fe-based alloy overlay layer on a substrate by melting Fe-based alloy powder. Here, the Fe-based alloy powder contains C, Si, Mn, Cr, Mo, and V in the following mass% amounts, with the remainder being Fe and unavoidable impurities. 1.60 ≤ C ≤ 3.50 0.20 ≤ Si ≤ 1.50 0.20 ≤ Mn ≤ 1.50 14.0 ≤ Cr ≤ 26.0 0.2 ≤ Mo ≤ 2.0 4.0 ≤ V ≤ 8.0

[0012] The Fe-based alloy powder melts under predetermined heat treatment conditions. These heat treatment conditions are such that, in the cross-section of the Fe-based alloy buildup layer, the ratio of the total area of ​​fine-grained carbides with a diameter of 5 μm or less to the area of ​​the observation region is between 0.50% and 4.00%, and the amount of Cr solid solution contained in the primary crystal is 5% by mass or more.

[0013] As described above, when melting the Fe-based alloy powder using laser cladding, the laser output can be set to 2800 [W]. Furthermore, the Fe-based alloy powder can be one with a particle size of 150 μm or less. [Effects of the Invention]

[0014] According to the present invention, corrosion resistance and wear resistance in the build-up layer can be improved. [Modes for carrying out the invention]

[0015] (Composition of Fe-based alloy powder) This section describes the Fe-based alloy powder used to form the buildup layer. The Fe-based alloy powder contains C, Si, Mn, Cr, Mo, and V, with the remainder being Fe and unavoidable impurities. Here, the respective content [mass%] of C, Si, Mn, Cr, Mo, and V satisfies the conditions shown in the following formulas (1) to (6). 1.60 ≤ C ≤ 3.50 ···(1) 0.20 ≦ Si ≦ 1.50 ···(2) 0.20 ≦ Mn ≦ 1.50 ···(3) 14.0 ≦ Cr ≦ 26.0 ···(4) 0.2 ≦ Mo ≦ 2.0 ···(5) 4.0 ≦ V ≦ 8.0 ···(6)

[0016] (Content rate of C) C is an element that contributes to improving the wear resistance of the build-up layer by forming carbides with Cr and V. The content rate of C is 1.60 [mass%] or more and 3.50 [mass%] or less.

[0017] By setting the content rate of C to 1.60 [mass%] or more, sufficient hardness can be obtained. Here, the content rate of C is preferably 1.70 [mass%] or more, and more preferably 1.80 [mass%] or more. On the other hand, when the content rate of C is higher than 3.50 [mass%], the carbides coarsen and the toughness of the build-up layer decreases. Therefore, the content rate of C is set to 3.50 [mass%] or less. Here, the content rate of C is preferably 3.00 [mass%] or less, and more preferably 2.40 [mass%] or less.

[0018] (Content rate of Si) Si is an element that improves the hardness, high-temperature resistance, and toughness of the build-up layer by dissolving in the matrix in Fe. The content rate of Si is from 0.20 [mass%] to 1.50 [mass%].

[0019] By setting the content rate of Si to 0.20 [mass%] or more, the hardness and high-temperature resistance of the build-up layer can be improved. Here, the content rate of Si is preferably 0.25 [mass%] or more, and more preferably 0.30 [mass%] or more. By setting the content rate of Si to 1.50 [mass%] or less, the toughness of the build-up layer can be improved. Here, the content rate of Si is preferably 1.30 [mass%] or less.

[0020] (Content rate of Mn) Mn is an element that can improve the strength of the build-up layer. The Mn content is 0.20 [mass%] or more. Here, the Mn content is preferably 0.25 [mass%] or more, and more preferably 0.30 [mass%] or more.

[0021] On the other hand, if the Mn content is too high, it may reduce the toughness of the build-up layer. Furthermore, the combination of Mn and S to form MnS can also reduce the toughness of the build-up layer and may promote cracking of the build-up layer during processing. Taking this into consideration, the Mn content should be 1.50 [mass%] or less. Here, it is preferable that the Mn content be 1.00 [mass%] or less.

[0022] (Cr content) Cr is an element that can improve the corrosion resistance of the build-up layer. The Cr content is 14.0 [mass%] or more. Here, the Cr content is preferably 15.0 [mass%] or more, and more preferably 16.0 [mass%] or more. On the other hand, if Cr is added in excess, a ferrite phase that inhibits the hardening of the build-up layer may be excessively formed within the build-up layer. Therefore, the Cr content is 26.0 [mass%] or less. Here, the Cr content is preferably 25.0 [mass%] or less, and more preferably 24.0 [mass%] or less.

[0023] (Mo content) Mo is an element that contributes to improving the strength of the build-up layer by solid dissolving in the primary crystal of the build-up layer. The Mo content is 0.2 [mass%] or more. Here, the Mo content is preferably 0.3 [mass%] or more, and more preferably 0.5 [mass%] or more.

[0024] On the other hand, if too much Mo is added, excessive carbides (carbides larger than the fine-grained carbides described later) may precipitate, and these excessive carbides can impair the toughness of the build-up layer. To ensure the toughness of the build-up layer, the Mo content should be 2.0 [mass%] or less. Here, the Mo content is preferably 1.8 [mass%] or less.

[0025] (V content) V combines with C to form fine carbides (fine granular carbides, described later), which contribute to improving the wear resistance of the build-up layer. The V content is 4.0 [mass%] or more. Here, the V content is preferably 4.5 [mass%] or more, and more preferably 5.0 [mass%] or more.

[0026] On the other hand, if V is added in excess, excessive carbides (carbides larger than the fine granular carbides described later) may precipitate, and these excessive carbides can impair the toughness of the build-up layer. To ensure the toughness of the build-up layer, the V content should be 8.0 [mass%] or less. Here, the V content is preferably 7.0 [mass%] or less.

[0027] (Inevitable impurities) Inevitable impurities include the following elements having the following content [mass%]: Co≦0.05, Cu≦0.50, Sn≦0.05, Nb≦0.05, Ta≦0.05, Ti≦0.05, Zr≦0.05, B≦0.01, Ca≦0.01, Se≦0.03, Te≦0.01, Bi≦0.01, Pb≦0.05, Mg ≤ 0.02, REM ≤ 0.01

[0028] (Method for producing Fe-based alloy powder) Fe-based alloy powder having the above-described composition is produced by pulverizing a molten Fe-based alloy. For example, Fe-based alloy powder can be produced using an atomization method, such as gas atomization, water atomization, or disc atomization. Using gas atomization or disc atomization can suppress the inclusion of impurities in the Fe-based alloy powder, and it is preferable to use an inert gas atmosphere. Furthermore, using gas atomization can improve the mass production of Fe-based alloy powder.

[0029] While there are no particular limitations on the particle size distribution of Fe-based alloy powder, it is possible to adjust the particle size distribution of Fe-based alloy powder considering factors such as handling. For example, classification can be used to select only Fe-based alloy powder with a particle size below a predetermined size. The predetermined particle size can be, for example, 150 μm.

[0030] (Method for forming a build-up layer) In this embodiment, the cladding layer is formed by melting Fe-based alloy powder onto the surface of the substrate. Here, known methods can be appropriately employed for forming the cladding layer; for example, laser cladding can be used. Furthermore, various materials (metals) can be used as the substrate on which the cladding layer is formed.

[0031] (Composition of the buildup layer) Since the overlay layer is formed by melting Fe-based alloy powder, the composition of the overlay layer, like that of the Fe-based alloy powder, contains C, Si, Mn, Cr, Mo, and V, with the remainder being Fe and unavoidable impurities. Here, the respective content [mass%] of C, Si, Mn, Cr, Mo, and V satisfies the conditions shown in formulas (1) to (6) above.

[0032] (Percentage of charred area in the overlay layer) As described above, a build-up layer is formed by melting Fe-based alloy powder on the substrate, and this build-up layer contains carbides. When the cross-section of the build-up layer is observed, circular carbides can be seen, and in this embodiment, circular carbides with a diameter (i.e., diameter) of 5 μm or less are called "fine-grained carbides".

[0033] After polishing the cross-section of the build-up layer, fine granular carbides can be identified by observing the microstructure revealed on the cross-section. For example, by observing the microstructure using a scanning electron microscope (SEM) and analyzing the image based on color intensity, fine granular carbides can be identified. By identifying the fine granular carbides, the area of ​​the fine granular carbides revealed on the observation surface can be determined.

[0034] Here, we define the carbide area ratio RA, which is expressed by the following formula (7).

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[0035] In equation (7) above, RA is the carbide area ratio [%], Ao is the area of ​​the observation region in the cross-section of the build-up layer, and Ac is the total area of ​​all fine-grained carbides that appeared within the observation surface. As can be seen from equation (7) above, the carbide area ratio RA is the ratio of the total area of ​​fine-grained carbides Ac to the area of ​​the observation region Ao. Here, the area Ao can be determined by defining the observation region.

[0036] Regarding the total area Ac, if only one fine-grained carbide material is present within the observation surface, the area of ​​that single fine-grained carbide material is the total area Ac. If multiple fine-grained carbide materials are present within the observation surface, the sum of the areas of each material is the total area Ac. Here, if the entire fine-grained carbide material is present within the observation surface, the area of ​​this material should be calculated. On the other hand, if only a portion of the fine-grained carbide material is present within the observation surface, the area of ​​this portion should be calculated.

[0037] In the build-up layer of this embodiment, the carbide area ratio RA is 0.50% or more and 4.00% or less. Including fine granular carbides in the build-up layer can improve the hardness and wear resistance of the build-up layer. To improve the hardness and wear resistance of the build-up layer, the carbide area ratio RA should be 0.50% or more. On the other hand, if the carbide area ratio RA is too high, in other words, if there is an excessive amount of fine granular carbides in the build-up layer, it will adversely affect the toughness of the build-up layer. Taking this into consideration, the carbide area ratio RA should be 4.00% or less.

[0038] Depending on the distribution of fine-grained carbides contained in the build-up layer, the area of ​​fine-grained carbides appearing in the cross-section of the build-up layer may vary depending on the cross-sectional position of the build-up layer. However, regardless of the cross-sectional position of the build-up layer, it is sufficient that the carbide area ratio RA is between 0.50% and 4.00%.

[0039] The formation of fine-grained carbides depends on the carbon content and the melting conditions of the Fe-based alloy powder when forming the cladding layer. In order to set the carbide area ratio RA to between 0.50% and 4.00%, in addition to the carbon content mentioned above, the melting conditions of the Fe-based alloy powder when forming the cladding layer can be predetermined based on experiments, etc. For example, when forming a cladding layer using laser cladding, the carbide area ratio RA can be set to between 0.50% and 4.00% by setting the laser output to 2800W.

[0040] Furthermore, the carbide area ratio RA is preferably 0.90% or higher, and more preferably 1.00% or higher.

[0041] (Cr solid solubility in the buildup layer) Cr is dissolved in the primary crystal of the build-up layer. Here, the primary crystal is the structure that is first formed when the Fe-based alloy powder is melted. Since the Cr dissolved in the primary crystal contributes to improving the corrosion resistance of the build-up layer, the amount of Cr dissolved in the primary crystal should be 5 [mass%] or more in order to improve the corrosion resistance of the build-up layer. Here, it is preferable that the amount of Cr dissolved is 7 [mass%] or more.

[0042] To determine the amount of Cr solid solution, first, the cross-section of the build-up layer is observed to identify the primary crystal. Then, by etching the cross-section of the build-up layer with Virela's reagent (an alcohol solution containing 1-5 g of hydrochloric acid and 1-5 g of picric acid), the region corresponding to the primary crystal turns white, allowing for its identification. After identifying the primary crystal, the amount of Cr is detected at multiple detection points within the primary crystal using energy-dispersive X-ray spectroscopy (EDS), and the average value of the detected Cr amounts is taken as the amount of Cr solid solution. These multiple detection points are located at different positions within the primary crystal, and the number of detection points can be, for example, five or more.

[0043] The amount of chromium dissolved in solid material depends on the chromium content in the Fe-based alloy powder and the melting conditions of the Fe-based alloy powder when forming the cladding layer. To achieve a chromium dissolved content of 5% by mass or more, the melting conditions of the Fe-based alloy powder when forming the cladding layer can be predetermined based on experiments or other methods. For example, when forming a cladding layer using laser cladding, setting the laser output to 2800W can achieve a chromium dissolved content of 5% by mass or more.

[0044] According to the build-up layer of this embodiment, corrosion resistance and wear resistance can be improved. [Examples]

[0045] As Examples 1-14 and Comparative Examples 1-16, raw materials having the chemical components shown in Table 1 below were prepared. Here, the remainder other than C, Si, Mn, Cr, Mo, and V is Fe and unavoidable impurities.

[0046] [Table 1]

[0047] Each raw material was placed in a refractory crucible and melted by high-frequency induction in an Ar gas atmosphere. The molten alloy was then dispensed from a nozzle located at the bottom of the crucible, and Fe-based alloy powder was produced by gas atomization in a nitrogen gas atmosphere. Specifically, by injecting high-pressure argon gas into the molten alloy dispensed from the nozzle, the molten alloy was refined and rapidly cooled, thereby obtaining multiple Fe-based alloy powders.

[0048] From the obtained Fe-based alloy powders, those with a particle size of 150 μm or less were selected by classification. Next, a build-up layer was formed on the surface of the substrate by melting the Fe-based alloy powder (particle size of 150 μm or less) using laser cladding. Here, the laser output for laser cladding was set to 2800 [W], and S45C was used as the substrate material.

[0049] (Evaluation of carbide area ratio RA) The build-up layers (test specimens) obtained in each of Examples 1-14 and Comparative Examples 1-16 were cut in half and the cut surfaces were polished. After etching the polished surfaces with Virela solution, the microstructure of the etched surfaces was observed using a scanning electron microscope (SEM). Fine granular carbides were identified based on the intensity of color by performing image analysis on the backscattered electron images taken of the observation area. Then, the carbide area ratio RA was determined based on the above formula (7) by calculating the area of ​​the fine granular carbides. The results of calculating the carbide area ratio RA are shown in Table 2 below.

[0050] (Evaluation of Cr solid solubility) The build-up layers (test specimens) obtained in each of Examples 1-14 and Comparative Examples 1-16 were cut in half and the cut surfaces were polished. After etching the polished surfaces with Virela's solution, the amount of Cr was detected by energy-dispersive X-ray spectroscopy (EDS) at each of five arbitrary detection points within the region that appeared white due to etching (the region corresponding to the primary crystal). The average value of the Cr detected at the five detection points was defined as the Cr solid solution amount. The measurement results of the Cr solid solution amount are shown in Table 2 below.

[0051] (Evaluation of corrosion resistance) The build-up layers obtained in Examples 1-14 and Comparative Examples 1-16 were subjected to corrosion resistance tests (salt spray tests) in accordance with the provisions of JIS Z2371. Here, the surface of the build-up layer was polished, and then the salt spray test was performed on the polished surface. The conditions for the salt spray test were a salt concentration of 0.1 [mass%] and a test duration of 16 hours.

[0052] After conducting a salt spray test, the test surface sprayed with salt water was photographed, and the rust area ratio Rr, expressed by the following formula (8), was calculated by analyzing the captured images.

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[0053] In equation (8) above, Rr is the rust area percentage [%], At is the total area of ​​the test surface, and Ar is the total area of ​​the region where rust occurred. The areas At and Ar can be determined by analyzing the captured images. Here, if rust occurs in multiple regions, the area Ar is the sum of the areas of the multiple regions where rust occurred.

[0054] For corrosion resistance evaluation, "○" was used if no rust occurred on the test surface, "△" was used if the rust area ratio Rr was less than 5%, and "×" was used if the rust area ratio Rr was 5% or more. The results of the corrosion resistance evaluation are shown in Table 2 below.

[0055] (Evaluation of wear resistance) The wear resistance of the build-up layers obtained in each of Examples 1-14 and Comparative Examples 1-16 was evaluated using the Okoshi Rapid Abrasion Tester. The Okoshi Rapid Abrasion Tester is a device that evaluates the width of wear marks by rotating (sliding) a plate-shaped test piece while applying a load with a ring-shaped pressure member. The test conditions for the Okoshi Rapid Abrasion Tester were as follows: the material of the pressure member was SCM420, the sliding distance was 200 [m], the load was 6.3 [kgf], and the rotation speed was 0.1 [m / s].

[0056] For the evaluation of abrasion resistance, the width of the abrasion marks (hereinafter referred to as the reference width) Wref was used as the reference value when abrasion tests were performed on test pieces coated with hard Cr plating on an S45C substrate using the Okoshi rapid abrasion tester. In addition, the width of the abrasion marks We was measured when abrasion tests were performed on the build-up layers obtained in each of Examples 1 to 14 and Comparative Examples 1 to 16 using the Okoshi rapid abrasion tester. The ratio of the reference width Wref to the width We (hereinafter referred to as the abrasion width ratio) Rw was then calculated. The abrasion width ratio Rw is expressed by the following formula (9).

[0057]

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[0058] In equation (9) above, Rw is the wear width ratio [-], Wref is the reference width described above, and We is the width of the wear marks in the evaluated samples (Examples 1-14 and Comparative Examples 1-16). Here, when the width We is equal to the reference width Wref, the wear width ratio Rw is 1.0. The smaller the width We is compared to the reference width Wref, the higher the wear width ratio Rw is than 1.0, indicating improved wear resistance. On the other hand, the larger the width We is compared to the reference width Wref, the lower the wear width ratio Rw is than 1.0, indicating decreased wear resistance. The results of the wear resistance evaluation are shown in Table 2 below.

[0059] [Table 2]

[0060] For Examples 1 to 14, the corrosion resistance evaluation was all positive (○). Furthermore, the wear width ratio Rw was 1.0 or higher in all cases, confirming excellent wear resistance.

[0061] On the other hand, for Comparative Examples 1-3 and 10-12, the corrosion resistance evaluation was △ or ×, meaning that corrosion resistance could not be guaranteed, and the wear width ratio Rw was lower than 1.0, meaning that wear resistance could not be guaranteed either. For Comparative Examples 4, 7, 15, and 16, the wear width ratio Rw was higher than 1.0, indicating excellent wear resistance, but the corrosion resistance evaluation was ×, meaning that corrosion resistance could not be guaranteed. For Comparative Examples 5, 6, 8, 9, 13, and 14, the corrosion resistance evaluation was ○, but the wear width ratio Rw was lower than 1.0, meaning that wear resistance could not be guaranteed.

Claims

1. An Fe-based alloy cladding layer containing C, Si, Mn, Cr, Mo, and V, with the remainder being Fe and unavoidable impurities, Each of C, Si, Mn, Cr, Mo, and V has the following mass % content: 1.60 ≤ C ≤ 3.50 0.20 ≤ Si ≤ 1.50 0.20 ≤ Mn ≤ 1.50 14.0 ≤ Cr ≤ 26.0 0.2 ≤ Mo ≤ 2.0 4.0 ≤ V ≤ 8.0 In the cross-section of the Fe-based alloy cladding layer, the ratio of the total area of ​​fine-grained carbides with a diameter of 5 μm or less to the area of ​​the observation region is 0.50% or more and 4.00% or less. An Fe-based alloy cladding layer characterized in that the Cr solid solution amount, which is the average value of the Cr detected at multiple points in the primary crystal, is 5% by mass or more.

2. A method for forming an Fe-based alloy buildup layer on a substrate by melting Fe-based alloy powder, The Fe-based alloy powder contains C, Si, Mn, Cr, Mo, and V in the following mass percentages, with the remainder being Fe and unavoidable impurities. 1.60 ≤ C ≤ 3.50 0.20 ≤ Si ≤ 1.50 0.20 ≤ Mn ≤ 1.50 14.0 ≤ Cr ≤ 26.0 0.2 ≤ Mo ≤ 2.0 4.0 ≤ V ≤ 8.0 A method for forming an Fe-based alloy cladding layer, characterized in that, in the cross-section of the Fe-based alloy cladding layer, the ratio of the total area of ​​fine granular carbides with a diameter of 5 μm or less to the area of ​​the observation region is 0.50% or more and 4.00% or less, and the Cr solid solution amount, which is the average value of the Cr detected at multiple points in the primary crystal, is 5% by mass or more, and the Fe-based alloy powder is melted under heat treatment conditions.

3. The method for forming an Fe-based alloy cladding layer according to claim 2, characterized in that the Fe-based alloy powder is melted using laser cladding with the laser output set to 2800 [W].

4. The method for forming an Fe-based alloy overlay layer according to claim 2, characterized in that the particle size of the Fe-based alloy powder is 150 μm or less.

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