Ferritic stainless steel material and its manufacturing method, ferritic stainless steel material for vibration damping heat treatment, and vibration damping member

Abstract

To provide a ferritic stainless steel that is superior in vibration-damping properties and surface appearance.SOLUTION: A ferritic stainless steel has an oxide film on the surface of the base material. The base material comprises, in mass, C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00-35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50-4.00%, N: 0.100% or less, Nb: 0.20-1.00%, with 1.8Cr+2.8Mo: 40.00% or more, and with the balance being Fe and impurities. The oxide film has a brightness index L* of 70.0 or more in the L*a*b*color system, a chromatic index a* of within ±1.0, a chromatic index b* of within ±5.0, and a 85-degree specular gloss Gs (85°) of 50.0% or more. The ferritic stainless steel has a loss factor η of 4.0×10-4 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a ferritic stainless steel material, a method for manufacturing the same, a ferritic stainless steel material for vibration damping heat treatment, and a vibration damping member.

Background Art

[0002] With the electrification of automobiles, the noise and vibration caused by the engine are decreasing, and the quietness inside the vehicle cabin is improving. As a result, noises that were previously masked by engine noise and high-frequency noises peculiar to electrification are more likely to be perceived as abnormal noises by passengers' ears, and the level of vibration damping of materials used in automobiles is increasing. Also, for parts such as slide door rails, vibration damping is required from the perspective of suppressing vibration caused by opening and closing the door.

[0003] Furthermore, in recent years, with the increase in the capacity of electronic devices such as hard disks (hereinafter abbreviated as "HDD"), the amount of heat generated per unit volume has been increasing. In particular, in places where a large number of HDDs are densely installed, such as data centers, the amount of heat generated is large, so cooling using a high-output fan is being carried out. However, a high-output fan is likely to cause resonance of the hard disk due to vibration caused by wind pressure. In electronic devices such as HDDs, vibration can cause malfunctions and failures, so high vibration damping is also required for parts (for example, case materials) used in electronic devices.

[0004] Typical examples of materials having vibration damping properties include rubber and resin. However, rubber and resin generally have low thermal conductivity, so they are difficult to use in applications that require cooling, such as electronic devices. Therefore, a metal material having vibration damping properties and high thermal conductivity is required. Also, rubber and resin often do not have sufficient properties such as strength and corrosion resistance when used in applications where a load is applied, such as a slide door rail, and at least a part is exposed to the outdoor environment. Furthermore, since these parts are easily noticeable to people, a surface appearance such as the silver-white color peculiar to stainless steel is also preferred.

[0005] Metal materials with vibration damping properties can be broadly classified into composite type, ferromagnetic type, dislocation type, and twin type based on the vibration energy attenuation mechanism. Each of these types has its own advantages and disadvantages, but the ferromagnetic type, which has high strength and good vibration damping properties, is preferred. In the ferromagnetic type, when an external force such as vibration is applied, the magnetic domains rearrange in one direction, and when the load is removed, the magnetic domains rearrange randomly. The residual strain at this time can absorb vibration energy and attenuate vibration.

[0006] As a ferromagnetic metal material, for example, in mass%, it has a chemical composition of C: 0.001 - 0.03%, Si: 0.1 - 1.0%, Mn: 0.1 - 2.0%, Ni: 0.01 - 0.6%, Cr: 10.5 - 24.0%, N: 0.001 - (此处原文有误,推测应为0.03%)0.03%, Nb: 0 - 0.8%, Ti: 0 - 0.5%, Cu: (此处原文有误,推测应为0 - 2.0%)0 - 2.0%, Mo: 0 - 2.5%, V: 0 - 1.0%, Al: 0 - 0.3%, Zr: 0 - 0.3%, Co: 0 - 0.6%, REM (rare earth elements): 0 - 0.1%, Ca: 0 - 0.1%, and the balance being Fe and unavoidable impurities. It has a metal structure with a matrix of ferrite single phase, an average crystal grain size of ferrite crystal grains of 0.3 - 3.0 mm, and a ferrite stainless steel material with a residual magnetic flux density of 45 mT or less is known (Patent Document 1).

[0007] Also, in mass%, it has a chemical composition of C: 0.001 - 0.04%, Si: 0.1 - 2.0%, Mn: 0.1 - 1.0%, Ni: 0.01 - 0.6%, Cr: 10.5 - 20.0%, Al: 0.5 - 5.0%, N: 0.001 - 0.03%, Nb: 0 - 0.8%, Ti: 0 - 0.5%, Cu: 0 - 0.3%, Mo: 0 - 0.3%, V: 0 - 0.3%, Zr: 0 - 0.3%, Co: 0 - 0.6%, REM (rare earth elements): 0 - 0.1%, Ca: 0 - 0.1%, and the balance being Fe and unavoidable impurities. It has a metal structure with a matrix of ferrite single phase, an average crystal grain size of ferrite crystal grains of 0.3 - 3.0 mm, and a ferrite stainless steel material with a residual magnetic flux density of 45 mT or less is also known (Patent Document 2).

Prior Art Documents

Patent Documents

[0008] [Patent Document 1] Japanese Patent Publication No. 2017-39955 [Patent Document 2] Japanese Patent Publication No. 2017-39956 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The ferritic stainless steel material described in Patent Document 1 has not had its composition thoroughly examined, making it difficult to obtain the desired vibration damping properties when the Cr and Mo content is low. Furthermore, since the vibration damping heat treatment is performed at high temperatures for a long time, the ferritic stainless steel material described in Patent Document 1 may develop a thick oxide film and become discolored (interference colors occur) during the vibration damping heat treatment, resulting in an unsatisfactory surface appearance. Furthermore, while the vibration damping properties of the ferritic stainless steel material described in Patent Document 2 can be improved by increasing the Al content, Al is an element that oxidizes very easily, so the oxide film tends to become thick during vibration damping heat treatment.

[0010] As described above, vibration-damping heat treatment is performed at high temperatures for extended periods, causing the oxide film to grow to a thickness of several tens of nanometers or more. This leads to interference with visible light, resulting in coloration such as yellow or purple (interference colors). Because these interference colors are highly sensitive to the thickness of the oxide film, the overall color tone of the surface is unlikely to be uniform, impairing its aesthetic appeal. On the other hand, it is conceivable to remove the oxide film, which is a factor in degrading the surface appearance, by polishing or pickling. However, polishing puts strain on the ferritic stainless steel material, which reduces its vibration damping properties. Furthermore, it is extremely difficult to remove the oxide film (especially Al2O3) by pickling, and even if it is removed, the gloss is reduced and surface roughness is likely to occur. Therefore, it was difficult to impart high vibration damping properties while maintaining the silvery-white appearance characteristic of ferritic stainless steel materials.

[0011] This invention was made to solve the above-mentioned problems, and aims to provide a ferritic stainless steel material with excellent vibration damping properties and surface appearance, a method for manufacturing the same, and a vibration damping member. Furthermore, the present invention aims to provide a ferritic stainless steel material for vibration-damping heat treatment that can be manufactured using a ferritic stainless steel material with excellent vibration damping properties and surface appearance. [Means for solving the problem]

[0012] The inventors have diligently conducted research to solve the above-mentioned problems and have found that in a ferritic stainless steel material having an oxide film on the surface of the substrate, the composition of the substrate and the brightness index L of the oxide film are important. * , Chromanetics Index a * and b * We have found that vibration damping properties and surface appearance can be improved by controlling the 85-degree specular gloss Gs(85°) and the loss coefficient η. Furthermore, we have found that a ferritic stainless steel material having such characteristics can be obtained by using a material having a predetermined composition (ferritic stainless steel material for vibration damping heat treatment) and performing vibration damping heat treatment under predetermined conditions. This invention was completed based on these findings.

[0013] In other words, the present invention relates to a ferritic stainless steel material having an oxide film on the surface of the base material, The aforementioned substrate has a composition, by mass, consisting of C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00~35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50~4.00%, N: 0.100% or less, Nb: 0.20~1.00%, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities. The aforementioned oxide film is L * a * b * Lightness index L in a color system * If the index is 70.0 or higher, the Chromanetics index a * within ±1.0, Chromanetics index b* is within ±5.0, and the 85-degree specular gloss Gs(85°) is 50.0% or more, the loss coefficient η of the ferritic stainless steel material is 4.0×10 -4 or more, and it is a ferritic stainless steel material.

[0014] Further, the present invention is a ferritic stainless steel material having an oxide film on the surface of the base material, <​​​​​​​​​​​​​​​​​​​​​​​​​​Furthermore, the present invention relates to a ferritic stainless steel material for vibration-damping heat treatment having a composition, by mass, containing C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00~35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50~4.00%, N: 0.100% or less, and Nb: 0.20~1.00%, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities.

[0016] Furthermore, the present invention relates to a ferritic stainless steel material for vibration-damping heat treatment having a composition, by mass, comprising C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00~35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50~4.00%, N: 0.100% or less, and Nb: 0.20~1.00%, and further comprising one or more elements selected from the following groups A and B, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities. [Group A] One or more selected from Al: 0.10% or less and Ti: 0.10% or less. [Group B] One or more selected from Zr: ≤1.00%, Co: ≤1.00%, V: ≤1.00%, W: ≤1.00%, REM: ≤0.100%, Ca: ≤0.100%, Sn: ≤0.100%, and B: ≤0.0100%.

[0017] Furthermore, the present invention is On the surface of the base material, L * a * b * Lightness index L in a color system * If the index is 70.0 or higher, the Chromanetics index a * within ±1.0, Chromanetics index b * The oxide film has a tolerance of ±5.0 and an 85-degree specular gloss Gs(85°) of 50.0% or more, and a loss factor η of 4.0 × 10 -4 The above is a method for manufacturing ferritic stainless steel, The aforementioned ferritic stainless steel material for vibration damping heat treatment is 1.0 × 10 -2This is a method for manufacturing ferritic stainless steel, which involves heat treatment at 1000-1200°C under an oxygen partial pressure atmosphere of Pa or less, followed by cooling to 800°C at a rate of 30°C / min or more.

[0018] Furthermore, the present invention relates to a vibration damping member that includes the ferritic stainless steel material. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a ferritic stainless steel material with excellent vibration damping properties and surface appearance, a method for manufacturing the same, and a vibration damping member. Furthermore, according to the present invention, it is possible to provide a ferritic stainless steel material for vibration-damping heat treatment that can be manufactured with excellent vibration damping properties and surface appearance. [Modes for carrying out the invention]

[0020] The vibration damping properties of ferromagnetic ferritic stainless steel materials are determined by the magnitude of the deformation (magnetostriction) when magnetic domains move. While Al can increase magnetostriction, it is an element that oxidizes easily, causing the oxide film to discolor (interference colors to occur) during vibration damping heat treatment, which degrades the surface appearance. Similarly, Ti is also an element that oxidizes easily, so the oxide film discolors during vibration damping heat treatment, which also degrades the surface appearance. Therefore, to improve the surface appearance, a composition system was adopted that either does not contain Al and Ti, or has reduced levels of Al and Ti. On the other hand, in order to increase magnetostriction, Cr was added in combination with Mo, and their content was optimized.

[0021] Furthermore, for vibration damping properties in ferritic stainless steel materials to be achieved, it is necessary for magnetic domains to be able to move freely. However, strain (dislocations), precipitates, and grain boundaries in ferritic stainless steel materials hinder the movement of magnetic domains. Heat treatment is necessary to reduce strain (dislocations), precipitates, and grain boundaries in ferritic stainless steel materials, but precipitates formed during melting (especially Nb carbonitrides) are difficult to eliminate by heat treatment. Therefore, in order to reduce precipitates, a composition system was adopted that does not contain Nb or has reduced Nb content.

[0022] Furthermore, if the amount of C and N in ferritic stainless steel is high, they combine with Cr to precipitate Cr carbides and Cr nitrides. These precipitates sensitize the material by removing surrounding Cr, reducing its corrosion resistance. Therefore, to reduce the amount of C and N in the solid solution and suppress sensitization, Nb was added to fix C and N as precipitates. Since Nb carbonitrides (precipitates) precipitate between 800°C and 1000°C and solidify above 1000°C, vibration-damping heat treatment was performed at 1000-1200°C to solidify Ti carbonitrides, and then the cooling rate to 800°C was accelerated to refine the precipitates. Furthermore, the atmosphere during vibration-damping heat treatment was controlled to suppress the oxidation of elements such as Cr, Fe, and Mn, and to form an oxide film that is less prone to discoloration (interference coloration).

[0023] Embodiments of the present invention completed based on the above perspective will be described in detail below. The present invention is not limited to the following embodiments, and it should be understood that modifications, improvements, etc., to the following embodiments, made as appropriate based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention, also fall within the scope of the present invention. In this specification, unless otherwise specified, any "%" indication for ingredients refers to "mass%".

[0024] (1) Ferritic stainless steel The ferritic stainless steel material according to the embodiment of the present invention has an oxide film on the surface of the substrate. In this specification, "stainless steel material" means a material formed from stainless steel, and its shape is not particularly limited. Examples of shapes include plates (including strips), rods, and tubes. Furthermore, it may be various types of shaped steel, such as T-shaped and I-shaped cross-sections. Furthermore, in this specification, "ferritic" refers to materials whose microstructure at room temperature is primarily the ferrite phase. Therefore, "ferritic" also includes materials that contain small amounts of other phases (for example, the austenite phase or martensite phase).

[0025] The base material has a composition consisting of C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, and Nb: 0.20 to 1.00%, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder being Fe and impurities.

[0026] Herein, in this specification, "impurities" means components that are mixed in during the industrial production of ferritic stainless steel materials due to various factors in the raw materials such as ore and scrap, and in the manufacturing process, and which are acceptable as long as they do not adversely affect the present invention. For example, impurities include unavoidable impurities. Examples of impurities include oxygen (O). Regarding the content of each element, "containing xx% or less" means that it contains xx% or less, but also more than 0% (especially above the impurity level).

[0027] Furthermore, the base material may further include one or more materials selected from groups A and B below. [Group A] One or more selected from Al: 0.10% or less and Ti: 0.10% or less. [Group B] One or more selected from Zr: ≤1.00%, Co: ≤1.00%, V: ≤1.00%, W: ≤1.00%, REM: ≤0.100%, Ca: ≤0.100%, Sn: ≤0.100%, and B: ≤0.0100%. The following provides a detailed explanation of each component.

[0028] (C: 0.100% or less) Carbon (C) is an element that affects properties such as intergranular corrosion resistance (sensitization suppression) and workability of ferritic stainless steel. If the C content is too high, the workability and intergranular corrosion resistance of ferritic stainless steel will decrease. Therefore, the upper limit of the C content is 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, there is no particular lower limit for the C content, but reducing the C content leads to an increase in refining costs. Therefore, the lower limit of the C content is preferably 0.001%, and more preferably 0.002%.

[0029] (Si:1.00% or less) Si is an effective element for improving the oxidation resistance of ferritic stainless steel materials. If the Si content is too high, the workability and toughness of the ferritic stainless steel material will decrease. Therefore, the upper limit of the Si content is 1.00%, preferably 0.90%, and more preferably 0.80%. On the other hand, the lower limit of the Si content is not particularly limited, but from the viewpoint of ensuring the effect of Si, it is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0030] (Mn:1.00% or less) Mn is a useful element as a deoxidizing element. If the Mn content is too high, it becomes easier to generate MnS, which acts as a corrosion initiation site, and also destabilizes the ferrite phase. Therefore, the upper limit of the Mn content is 1.00%, preferably 0.90%, and more preferably 0.80%. On the other hand, the lower limit of the Mn content is not particularly limited, but from the viewpoint of ensuring the effect of Mn, it is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0031] (P:0.100% or less) P is an element that affects properties such as weldability and workability of ferritic stainless steel materials. If the P content is too high, the above properties may deteriorate. Therefore, the upper limit of the P content is 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, there is no particular lower limit for the P content, but reducing the P content leads to an increase in refining costs. Therefore, the lower limit of the P content is preferably 0.010%, and more preferably 0.012%.

[0032] (S:0.100% or less) S is an element that generates MnS, which acts as a corrosion initiation site, and affects properties such as toughness of ferritic stainless steel. If the S content is too high, the above properties may deteriorate. Therefore, the upper limit of the S content is 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, there is no particular lower limit for the S content, but reducing the S content leads to an increase in refining costs. Therefore, the lower limit of the S content is preferably 0.0001%, and more preferably 0.0005%.

[0033] (Cr: 20.00~35.00%) Cr is an effective element for improving the corrosion resistance and vibration damping (increase in magnetostriction) of ferritic stainless steel materials. If the Cr content is too high, the toughness of the ferritic stainless steel material will decrease, and manufacturing costs will increase. Therefore, the upper limit of the Cr content is 35.00%, preferably 34.50%, and more preferably 34.00%. On the other hand, if the Cr content is too low, the above effects will not be sufficiently obtained. Therefore, the lower limit of the Cr content is 20.00%, preferably 20.50%, and more preferably 21.00%.

[0034] (Ni: 1.00% or less) Ni is an effective element for improving the corrosion resistance and toughness of ferritic stainless steel materials. If the Ni content is too high, the ferrite phase becomes unstable and the manufacturing cost increases. Therefore, the upper limit of the Ni content is 1.00%, preferably 0.80%, and more preferably 0.60%. On the other hand, the lower limit of the Ni content is not particularly limited, but from the viewpoint of ensuring the effect of Ni, it is preferably 0.01%, and more preferably 0.03%.

[0035] (Cu:1.00% or less) Cu is an effective element for improving the corrosion resistance of ferritic stainless steel materials. If the Cu content is too high, the ferrite phase becomes unstable and manufacturing costs increase. Therefore, the upper limit of the Cu content is 1.00%, preferably 0.70%, and more preferably 0.30%. On the other hand, the lower limit of the Cu content is not particularly limited, but from the viewpoint of ensuring the effect of Cu, it is preferably 0.001%, and more preferably 0.01%.

[0036] (Mo: 0.50~4.00%) Mo is an effective element for improving the corrosion resistance and vibration damping (increase in magnetostriction) of ferritic stainless steel materials. If the Mo content is too high, the workability of the ferritic stainless steel material decreases and the manufacturing cost increases. Therefore, the upper limit of the Mo content is 4.00%, preferably 3.80%, and more preferably 3.60%. On the other hand, if the Mo content is too low, the above effects cannot be sufficiently obtained. Therefore, the lower limit of the Mo content is 0.50%, preferably 0.60%, and more preferably 0.80%.

[0037] (N:0.100% or less) Nitric oxide (N) is an element that affects properties such as intergranular corrosion resistance (sensitization suppression) and workability of ferritic stainless steel. If the N content is too high, the workability and intergranular corrosion resistance of ferritic stainless steel will decrease. Therefore, the upper limit of the N content is 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, there is no particular lower limit for the N content, but reducing the N content leads to an increase in refining costs. Therefore, the lower limit of the N content is preferably 0.001%, more preferably 0.003%, and even more preferably 0.005%.

[0038] (Nb: 0.20~1.00%) Nb is a component that suppresses the sensitization of ferritic stainless steel by forming carbonitrides (precipitates) of C and N. If the Nb content is too high, the amount of precipitates in the ferritic stainless steel increases, and the vibration damping performance decreases. Therefore, the upper limit of the Nb content is 1.00%, preferably 0.80%, and more preferably 0.50%. On the other hand, if the Nb content is too low, the sensitization of the ferritic stainless steel cannot be suppressed, and the corrosion resistance decreases. Therefore, the lower limit of the Nb content is 0.20%, preferably 0.23%, and more preferably 0.25%.

[0039] (1.8Cr + 2.8Mo: 40.00% or more) As mentioned above, Cr and Mo are effective elements for improving the vibration damping (increase in magnetostriction) and corrosion resistance of ferritic stainless steel materials. To effectively obtain these effects, the balance between Cr and Mo is crucial, and the ratio of 1.8Cr + 2.8Mo should be controlled to 40.00% or more, preferably 40.50% or more, and more preferably 41.00% or more. On the other hand, the upper limit of 1.8Cr + 2.8Mo is not particularly limited, but is preferably 74.00%, more preferably 73.00%, and even more preferably 72.00%.

[0040] (Al: 0.10% or less) Al is an effective element for improving the vibration damping properties (increased magnetostriction) of ferritic stainless steel materials. However, if the Al content is too high, the oxide film will become discolored (interference colors will occur) during vibration damping heat treatment, degrading the surface appearance. Therefore, the upper limit of the Al content is 0.10%, preferably 0.09%, and more preferably 0.08%. On the other hand, the lower limit of the Al content is not particularly limited, but from the viewpoint of ensuring the effect of Al, it is preferably 0.001%, more preferably 0.005%, and even more preferably 0.01%.

[0041] (Ti: 0.10% or less) Ti is an element that affects properties such as resistance to intergranular corrosion (sensitization suppression) of ferritic stainless steel materials. If the Ti content is too high, the workability of the ferritic stainless steel material decreases. Also, since Ti, like Al, is an element that oxidizes easily, the oxide film becomes discolored (interference colors occur) during vibration-damping heat treatment, degrading the surface appearance. For this reason, the upper limit of the Ti content is 0.10%, preferably 0.09%, and more preferably 0.08%. On the other hand, the lower limit of the Ti content is not particularly limited, but from the viewpoint of ensuring the effect of Ti, it is preferably 0.001%, more preferably 0.005%, and even more preferably 0.01%.

[0042] (Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less) Zr, Co, V, and W are effective elements for improving the oxidation resistance of ferritic stainless steel materials. If the content of Zr, Co, V, and W is too high, the workability and toughness of the ferritic stainless steel material will decrease, and the manufacturing cost will increase. Therefore, the upper limit for the content of Zr, Co, V, and W is 1.00%, preferably 0.80%, and more preferably 0.60%. On the other hand, the lower limit for the content of Zr, Co, V, and W is not particularly limited, but is preferably 0.001%, and more preferably 0.01%.

[0043] (REM: 0.100% or less, Ca: 0.100% or less) Rare earth elements (REM) and calcium (Ca) are effective elements for improving the oxidation resistance of ferritic stainless steel materials. However, excessively high REM and Ca content leads to increased manufacturing costs for ferritic stainless steel materials. Therefore, the upper limit for the REM and Ca content is 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, the lower limit for the REM and Ca content is not particularly limited, but is preferably 0.0001%, and more preferably 0.003%. REM refers to the collective term for the two elements scandium (Sc) and yttrium (Y), and the 15 elements from lanthanum (La) to lutetium (Lu) (lanthanides). These can be used individually or as mixtures.

[0044] (Sn:0.100% or less) Sn is an effective element for improving the corrosion resistance of ferritic stainless steel materials. If the Sn content is too high, Sn segregates, reducing manufacturability. Therefore, the upper limit of the Sn content is 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, the lower limit of the Sn content is not particularly limited, but is preferably 0.001%, and more preferably 0.005%.

[0045] (B:0.0100% or less) B is an effective element for improving the secondary workability of ferritic stainless steel materials. If the B content is too high, the fatigue strength of the ferritic stainless steel material decreases. Therefore, the upper limit of the B content is 0.0100%, preferably 0.0080%, and more preferably 0.0050%. On the other hand, the lower limit of the B content is not particularly limited, but is preferably 0.0001%, and more preferably 0.0005%.

[0046] The substrate preferably has an average grain size of 100 to 1000 μm. By controlling the average grain size to 100 μm or more, the number of grain boundaries that hinder the movement of magnetic domains, which is effective in exhibiting vibration damping properties, is reduced, thereby improving vibration damping properties. From the viewpoint of stably obtaining this effect, the average grain size is more preferably 120 μm or more, even more preferably 150 μm or more, even more preferably 180 μm or more, and particularly preferably 190 μm or more. Furthermore, by controlling the average grain size to 1000 μm or less, it is possible to stably suppress the decrease in toughness due to extreme grain coarsening. From the viewpoint of stably obtaining this effect, the average grain size is more preferably 800 μm or less, even more preferably 600 μm or less, and even more preferably 500 μm or less. Here, in this specification, the average grain size refers to the grain size measured using an optical microscope, as described later.

[0047] The substrate has a number density of 300 precipitates / mm² with a diameter of 0.5 μm or more and less than 5.0 μm. 2 The following is preferable: Since precipitates with a diameter of 0.5 μm or more and less than 5.0 μm hinder the movement of magnetic domains, the number density of these precipitates should be 300 particles / mm³. 2 The vibration damping properties can be improved by controlling the following. From the viewpoint of stably obtaining this effect, the number density of these precipitates is more preferably 290 particles / mm³. 2 More preferably, 280 pieces / mm 2 The following applies. Note that, from the viewpoint of vibration damping, fewer precipitates are preferable, so the lower limit is not particularly limited, but preferably 100 particles / mm². 2 , more comfortably 120 pieces / mm 2 More preferably 130 pieces / mm 2 That is the case. Here, in this specification, the diameter and number density of precipitates refer to those measured using a scanning electron microscope (SEM), as described later. Furthermore, the diameter of a precipitate is calculated as (length of the long side × length of the short side). 1 / 2 The value will be calculated by [the specified method].

[0048] The oxide film is L * a* b * Lightness index L in a color system * If the index is 70.0 or higher, the Chromanetics index a * within ±1.0, Chromanetics index b * The value is within ±5.0. Brightness index L * , Chromanetics Index a * and b * If the value falls within the above range, it can be said that the desired color tone (silvery white) has been achieved, thus improving the surface appearance of the ferritic stainless steel material. Lightness index L * From the viewpoint of stably ensuring the desired color tone, the lightness index L is preferably 72.0 or higher, and more preferably 75.0 or higher. * The upper limit is not particularly limited, but is generally 90.0. Chromanetics Index a * From the viewpoint of stably ensuring the desired color tone, it is preferably within ±0.8, more preferably within ±0.6. Also, the Chromanetics index b * From the viewpoint of stably obtaining the desired color tone, the range is preferably within ±4.8, and more preferably within ±4.6. Here, in this specification, "lightness index L * " and "Chromanetics Index a * and b * This can be measured in accordance with JIS Z8722:2009.

[0049] The oxide film has an 85-degree specular gloss Gs(85°) of 50.0% or more. If Gs(85°) is within the above range, the desired gloss can be said to be obtained, thus improving the surface appearance of the ferritic stainless steel material. From the viewpoint of stably ensuring the desired gloss, Gs(85°) is preferably 60.0% or more, more preferably 70.0% or more. The upper limit of Gs(85°) is not particularly limited, but is generally 90.0%. Herein, in this specification, "85-degree specular gloss Gs(85°)" can be measured in accordance with JIS Z8741:1997.

[0050] The thickness of the oxide film affects the color tone and gloss of the oxide film, i.e., the surface appearance of the ferritic stainless steel material. From the viewpoint of imparting the desired color tone and gloss to the oxide film, the thickness of the oxide film is preferably 50 nm or less, more preferably 48 nm or less, and even more preferably 45 nm or less. The lower limit of the oxide film thickness is not particularly limited, but is preferably 5 nm, more preferably 7 nm. In this specification, the thickness of the oxide film is defined as the depth from the surface to the point where the oxygen (O) concentration is 1 / 4 of its maximum value in the depth-direction component concentration profile obtained using glow discharge emission spectroscopy (GD-OES).

[0051] The ferritic stainless steel material according to the embodiment of the present invention has a loss factor η of 4.0 × 10 -4 That concludes the explanation. By setting the loss coefficient η within this range, the desired vibration damping performance can be ensured. The loss coefficient η is preferably 4.1 × 10⁻⁶ from the viewpoint of stably ensuring the desired vibration damping performance. -4 More preferably 4.2 × 10 -4 That concludes the explanation. Note that there is no particular upper limit to the loss coefficient η, but it is generally 2.0 × 10⁻⁶. -3 Preferably 1.0 × 10 -3 That is the case. In this specification, the loss coefficient η refers to the value measured by the "central excitation method" described later.

[0052] The thickness of the ferritic stainless steel material according to the embodiment of the present invention is not particularly limited, but is preferably 3.0 mm or less, more preferably 2.8 mm or less, and even more preferably 2.5 mm or less. Furthermore, the thickness of this ferritic stainless steel material is preferably 0.2 mm or more, more preferably 0.3 mm or more.

[0053] (2) Ferritic stainless steel material for vibration damping heat treatment The ferritic stainless steel material for vibration damping heat treatment according to the embodiment of the present invention is the material before vibration damping heat treatment is performed. This ferritic stainless steel material for vibration damping heat treatment has the same composition as the base material of the ferritic stainless steel material described above.

[0054] Therefore, the ferritic stainless steel material for vibration-damping heat treatment according to the embodiment of the present invention has a composition comprising C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, Nb: 0.20 to 1.00%, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities.

[0055] Furthermore, the ferritic stainless steel material for vibration-damping heat treatment according to the embodiment of the present invention has a composition comprising C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00~35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50~4.00%, N: 0.100% or less, Nb: 0.20~1.00%, and further comprising one or more selected from the following groups A and B, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder being Fe and impurities. [Group A] One or more selected from Al: 0.10% or less and Ti: 0.10% or less. [Group B] One or more selected from Zr: ≤1.00%, Co: ≤1.00%, V: ≤1.00%, W: ≤1.00%, REM: ≤0.100%, Ca: ≤0.100%, Sn: ≤0.100%, and B: ≤0.0100%. As details about each component are as described above, we will omit further explanation.

[0056] The ferritic stainless steel material for vibration-damping heat treatment according to the embodiment of the present invention may be either hot-rolled or cold-rolled, and can be manufactured by conventional methods. Specifically, hot-rolled material can be obtained by first melting stainless steel having the above composition, forging or casting it, and then hot-rolling it. Cold-rolled material can be obtained by sequentially performing annealing, pickling, and cold-rolling on hot-rolled material. If necessary, annealing and pickling may be performed sequentially on cold-rolled material. The conditions in each process can be appropriately adjusted according to the composition of the stainless steel, etc., and are not particularly limited.

[0057] The ferritic stainless steel material for vibration damping heat treatment according to the embodiment of the present invention may be processed into a predetermined component, or it may remain in the form of a plate or coil. Processing methods include various press working using a mold, bending, welding, etc.

[0058] (3) Method for manufacturing ferritic stainless steel The method for manufacturing a ferritic stainless steel material according to the embodiment of the present invention is not particularly limited as long as it is a method capable of manufacturing a ferritic stainless steel material having the above-described characteristics. For example, the method for manufacturing a ferritic stainless steel material according to the embodiment of the present invention includes vibration damping heat treatment on the above-described ferritic stainless steel material for vibration damping heat treatment. The vibration damping heat treatment involves applying 1.0 × 10 to the ferritic stainless steel material for vibration damping heat treatment. -2 This process is carried out by heat treatment at 1000-1200°C under an oxygen partial pressure atmosphere of Pa or less, followed by cooling to 800°C at a rate of 30°C / min or more.

[0059] 1.0 × 10 ferritic stainless steel material for vibration damping heat treatment -2 By performing heat treatment under an oxygen partial pressure atmosphere of Pa or less, the oxidation of elements such as Cr, Fe, and Mn is suppressed, and the oxide film does not easily become thick. As a result, the desired color tone and luster can be ensured, thereby improving the surface appearance of ferritic stainless steel materials. From the viewpoint of stably obtaining the above effects, the oxygen partial pressure is preferably 0.5 × 10⁻⁶. -2 Pa(5.0×10 -3Pa), more preferably 0.3 × 10 -2 Pa(3.0×10 -3 The value is Pa). Note that the lower limit of the partial pressure of oxygen is not particularly limited, but is generally 1.0 × 10⁻⁶. -6 It is Pa.

[0060] Furthermore, by heat-treating the ferritic stainless steel material for vibration damping at 1000 to 1200°C, the crystal grains can be grown to an average grain size of 100 to 1000 μm. The heat treatment atmosphere may be an air atmosphere or a non-oxidizing atmosphere. The heat treatment time is not particularly limited, but is preferably 10 to 120 minutes.

[0061] Furthermore, since the temperature range from the heat treatment temperature of 1000-1200°C to 800°C is the temperature range in which Nb carbonitride precipitates, the precipitation of Nb carbonitride can be effectively suppressed by setting the cooling rate in this temperature range to 30°C / min or more, preferably 35°C / min or more, and more preferably 40°C / min or more. As a result, the number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 300 particles / mm³. 2 The following controls are applied. The upper limit of the cooling rate in this temperature range is not particularly limited, but is generally 300°C / min or less, preferably 250°C / min or less, and more preferably 200°C / min or less.

[0062] (4) Vibration damping member The vibration damping member according to an embodiment of the present invention includes the above-mentioned ferritic stainless steel material. Since the above-mentioned ferritic stainless steel material has excellent vibration damping properties and surface appearance, this vibration damping member also has excellent vibration damping properties and surface appearance. Examples of vibration damping materials are not limited to exhaust system components such as exhaust pipes and mufflers, automotive parts such as sliding door rails and battery cases, electronic components such as hard disk covers, and acoustic components. [Examples]

[0063] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0064] (Examples 1-8 and Comparative Examples 1-10) A ferritic stainless steel sheet was fabricated according to the following procedure. Stainless steel having the composition shown in Table 1 was melted and hot-rolled to obtain a hot-rolled sheet with a thickness of 4.0 mm. The hot-rolled sheet was then annealed at 1050°C and pickled to obtain a hot-rolled annealed sheet. Next, the hot-rolled annealed sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 1.0 mm. Then, a test piece measuring 100 mm in the width direction and 300 mm in the rolling direction was cut from the cold-rolled sheet by cutting, and the surface was polished using SiC abrasive paper (#400) so that the polishing marks were parallel to the rolling direction.

[0065] [Table 1]

[0066] The above test specimens were placed in an electric furnace and heat-treated for 60 minutes at the temperatures shown in Table 2 under the oxygen partial pressure atmosphere shown in Table 2. Afterward, they were cooled from the heat-treatment temperature to 800°C at the rates shown in Table 2. The oxygen partial pressure was controlled by adjusting the ratio of oxygen gas to argon gas introduced. The cooling rate of the test specimens was controlled by adjusting the flow rate of the cooling gas introduced into the electric furnace.

[0067] [Table 2]

[0068] The following evaluations were performed on the test specimens that underwent the above heat treatment (vibration-damping heat treatment).

[0069] (Average crystal grain size of the substrate) A 10mm x 10mm measuring specimen was cut from the above test specimen by cutting (at a position at least 20mm away from the edge in the width direction of the plate), and then resin-embedded so that the cross-section in the thickness direction parallel to the rolling direction became the observation surface. Next, the resin-embedded measuring specimen was mirror-finished by wet polishing, and then the metallographic structure revealed by etching with hydrofluoric acid was observed with an optical microscope. Observation with an optical microscope was performed in accordance with JIS G0551:2013, by drawing a straight line at an arbitrary position on the optical microscope image, measuring the number of intersections between the line and the grain boundary, and the average intercept length was defined as the grain size. The grain size was measured by drawing 20 or more straight lines in multiple fields of view, and the average value of these measurements was defined as the average grain size.

[0070] (Number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm in the substrate) A 10mm x 10mm measuring specimen was cut from the above test piece by cutting (at a position at least 20mm away from the edge in the width direction of the plate), and then resin-embedded so that the rolled surface would be the observation surface. Next, the resin-embedded measuring specimen was mirror-finished by wet polishing. On the mirror-finished surface, precipitates were detected using the automatic analysis function of an FE-SEM (SU5000, Hitachi High-Tech Corporation) (precipitates of 0.47 μm or larger can be detected), and the composition of the precipitates was identified by EDX point analysis. In this analysis, the measurement area was 5 mm². 2 The sample size was 2.0 mm × 2.5 mm, the observation magnification was 200x (18 fields of view were measured with 5% overlap of each field of view of 0.48 mm × 0.64 mm), and the EDX analysis beam diameter was 0.05 μm. The number of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm, and with Nb or Ti content of 1% or more as determined by EDX point analysis, was then determined. The diameter of the precipitate was calculated as (length of the long side × length of the short side). 1 / 2 The number of precipitates was calculated by dividing the number of precipitates by the observation area.

[0071] (Thickness of oxide film) A 50mm square test piece was cut from the above test specimen, and its surface was degreased with acetone. Next, the oxide film was analyzed using glow discharge emission spectroscopy (GD-OES) in accordance with JIS K0144:2018. In GD-OES, the thickness of the oxide film was defined as the depth from the surface to the point where the oxygen (O) concentration in the obtained depth-direction component concentration profile was 1 / 4 of its maximum value.

[0072] (Color tone of oxide film) For five arbitrary locations on the oxide film, color measurements were performed using a spectrophotometer with a measurement diameter of 3 mmφ in accordance with JIS Z8722:2009, and the average value was used to determine the CIELAB (L) color in accordance with JIS Z8781-4:2013. * a * b * Lightness index L (color system) * , Chromanetics Index a * , b * As shown.

[0073] The measurement conditions for the above color tones were as follows: Equipment: Konica Minolta CM-700d Spectrophotometer Light source: Pulsed xenon lamp Photodetector: Dual 36-element silicon photodiode array Target mask: φ3mm Measurement: 10° field of view Auxiliary illuminant: D65 Daylight, Color temperature 6504K Specular reflection processing mode: SCI

[0074] (Glossiness of the oxide film) For five arbitrary locations on the oxide film, the 85-degree specular gloss Gs(85°) was measured using a PG-1M gloss meter manufactured by Nippon Denshoku Industries, in accordance with JIS Z8741:1997, and the average value was used as the evaluation result. Each measurement location was spaced at least 5 mm apart.

[0075] (Vibration damping: loss coefficient) A measuring specimen measuring 10 mm in width and 250 mm in rolling direction was cut from the above test specimen by machining. Using this measuring specimen, the loss factor η was measured in accordance with the "central excitation method" specified in JIS K7391:2008. Specifically, the test specimen, with its center fixed, was excited by an impedance head, and the mechanical impedance was derived from the output force signal and acceleration vibration. Then, the loss factor η was derived based on the anti-resonance frequency, which is the peak of the mechanical impedance, and the frequency at which the amplitude drops by 3 dB from the peak.

[0076] The results of each of the above evaluations are shown in Table 3.

[0077] [Table 3]

[0078] As shown in Table 3, Examples 1-8 have a lightness index L of the oxide film. * , Chromanetics Index a * and b * The surface exhibited excellent vibration damping and surface appearance, with a mirror-like gloss of 85 degrees (Gs(85°)) and a loss coefficient η that met the specified range. In contrast, Comparative Example 1 had inappropriate heat treatment temperature and cooling rate, resulting in a small average crystal grain size and a high number density of precipitates, which led to insufficient vibration damping. In Comparative Example 2, the cooling rate after heat treatment was not appropriate, resulting in a high number density of precipitates and consequently insufficient vibration damping. Comparative Example 3 had an unsatisfactory surface appearance because the oxygen partial pressure during heat treatment was not appropriate. Comparative Example 4 had a low Nb content and a high Ti content, resulting in an unsatisfactory surface appearance. Comparative Example 5 had a high Al content, resulting in an unsatisfactory surface appearance. Comparative Examples 6-8 had low levels of Cr and Mo, an inappropriate balance of Cr and Mo (1.8Cr + 2.8Mo was too low), and lacked Nb, while having high levels of Ti and Al, resulting in insufficient surface appearance and vibration damping properties. Comparative Example 9 had a high Mn content and a low Cr content, and the balance between Cr and Mo was inappropriate (1.8Cr + 2.8Mo was too low), resulting in insufficient vibration damping. Comparative Example 10 had insufficient vibration damping properties because it contained a low amount of Mo and the balance between Cr and Mo was inappropriate (1.8Cr + 2.8Mo was too low).

[0079] As can be seen from the above results, the present invention provides a ferritic stainless steel material with excellent vibration damping properties and surface appearance, a method for manufacturing the same, and a vibration damping member. Furthermore, the present invention provides a ferritic stainless steel material for vibration damping heat treatment that can be manufactured to produce a ferritic stainless steel material with excellent vibration damping properties and surface appearance.

Claims

1. A ferritic stainless steel material having an oxide film on the surface of the base material, The aforementioned substrate has a composition, by mass, consisting of C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, Nb: 0.20 to 1.00%, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities. The aforementioned oxide film is L * a * b * Lightness index L in a color system * If the index is 70.0 or higher, the Chromanetics index a * within ±1.0, Chromanetics index b * The coefficient of friction is within ±5.0, and the 85-degree specular gloss Gs (85°) is 50.0% or more. The loss coefficient η of the aforementioned ferritic stainless steel material is 4.0 × 10 -4 That concludes the description of ferritic stainless steel materials.

2. A ferritic stainless steel material having an oxide film on the surface of the base material, The aforementioned substrate, by mass, contains C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, Nb: 0.20 to 1.00%, and further contains one or more selected from the following groups A and B, with a composition of 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities. The oxide film has an L * a * b * lightness index L in the color system * of 70.0 or more, a chromaticity index a * within ±1.0, a chromaticity index b * within ±5.0, and a 85-degree specular gloss Gs(85°) of 50.0% or more, The loss coefficient η of the aforementioned ferritic stainless steel material is 4.0 × 10 -4 That concludes the description of ferritic stainless steel materials. [Group A] One or more selected from Al: 0.10% or less and Ti: 0.10% or less. [Group B] One or more selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

3. The aforementioned base material is a ferritic stainless steel material according to claim 2, having a composition including the group A.

4. The ferritic stainless steel material according to claim 2, wherein the base material has a composition including the group B.

5. The ferritic stainless steel material according to any one of claims 1 to 4, wherein the thickness of the oxide film is 50 nm or less.

6. The aforementioned substrate is (a) and (b) below: (a) The average grain size is 100 to 1000 μm. (b) Number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 300 particles / mm 2 The following is A ferritic stainless steel material according to any one of claims 1 to 4, satisfying one or more of the following conditions.

7. The aforementioned substrate is (a) and (b) below: (a) The average grain size is 100 to 1000 μm. (b) Number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 300 particles / mm 2 The following is A ferritic stainless steel material according to claim 5, satisfying one or more of the following conditions.

8. A ferritic stainless steel material for vibration-damping heat treatment having a composition, on a mass basis, containing C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, and Nb: 0.20 to 1.00%, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities.

9. A ferritic stainless steel material for vibration-damping heat treatment having a composition, on a mass basis, containing C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Cr: 20.00 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, and Nb: 0.20 to 1.00%, further containing one or more selected from the following groups A and B, with a composition of 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities. [Group A] One or more selected from Al: 0.10% or less and Ti: 0.10% or less. [Group B] One or more selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

10. The ferritic stainless steel material for vibration-damping heat treatment according to claim 9, having a composition including the aforementioned group A.

11. The ferritic stainless steel material for vibration damping heat treatment according to claim 9, having a composition including the aforementioned group B.

12. A method for manufacturing a ferritic stainless steel material having an oxide film on the surface of the base material in which the lightness index L* in the L*a*b* color system is 70.0 or more, the Chromanetics index a* is within ±1.0, the Chromanetics index b* is within ±5.0, and the 85-degree specular gloss Gs (85°) is 50.0% or more, and the loss coefficient η is 4.0 × 10⁻⁴ or more, A ferritic stainless steel material for vibration damping heat treatment according to any one of claims 8 to 11, 1.0 × 10 -2 A method for manufacturing ferritic stainless steel, comprising heat treatment at 1000 to 1200°C under an oxygen partial pressure atmosphere of Pa or less, followed by cooling to 800°C at a cooling rate of 30°C / min or more.

13. A vibration damping member comprising a ferritic stainless steel material according to any one of claims 1 to 4.

14. A vibration damping member comprising a ferritic stainless steel material as described in claim 5.

15. A vibration damping member comprising a ferritic stainless steel material as described in claim 6.

16. A vibration damping member comprising a ferritic stainless steel material as described in claim 7.

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