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 toughness, corrosion resistance, and vibration-damping properties.SOLUTION: A ferritic stainless steel 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, and Ti: 1.00% or less, with 1.8Cr+2.8Mo: 40.00% or more, and with the balance being Fe and impurities. The ferritic stainless steel has an average grain size of 100-1000 μm, and the number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 100 / mm2 or fewer.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] With the electrification of automobiles, engine noise and vibration have decreased, improving the quietness of the cabin. As a result, noises that were previously masked by engine noise, as well as high-frequency sounds unique to electrification, are more easily perceived as unwanted noises by passengers. Therefore, the level of vibration damping required for materials used in automobiles (especially exhaust gas components such as mufflers) has increased. Furthermore, vibration damping is also required for components such as sliding door rails, from the perspective of suppressing vibrations caused by opening and closing the doors.

[0003] Furthermore, in recent years, as electronic devices such as hard disk drives (hereinafter abbreviated as "HDDs") have increased in capacity, the amount of heat generated per unit volume has also increased. In particular, in places where many HDDs are installed in close proximity, such as data centers, the amount of heat generated becomes large, so cooling is carried out using high-powered fans. However, high-powered fans are prone to causing resonance in hard disks due to vibrations caused by air pressure. In electronic devices such as HDDs, vibrations can cause malfunctions and failures, so high vibration damping properties are required for the components used in electronic devices (for example, case materials).

[0004] While rubber and resin are typical examples of materials with vibration-damping properties, they generally have low thermal conductivity, making them unsuitable for applications requiring cooling, such as electronic equipment. Therefore, metal materials with high thermal conductivity and vibration-damping properties are needed. Furthermore, when rubber and resin are used in applications where at least a portion is exposed to the outdoor environment, their strength, corrosion resistance, and other properties are often insufficient.

[0005] Vibration-damping metal materials are broadly classified into composite, ferromagnetic, dislocation, and twinning types based on their vibration energy damping mechanisms. Each type has its own advantages and disadvantages, but the ferromagnetic type, which offers high strength and good vibration damping, 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 absorbs vibration energy, thereby damping the vibration.

[0006] Examples of ferromagnetic metallic materials include, by mass%, 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: 0.001~0.03%, Nb: 0~0.8%, Ti: 0~0.5%, Cu: 0~2.0%, Mo: 0~2.5%, V: 0~1.0%, Al: 0~0.3%, Zr: 0~ A ferritic stainless steel material is known that has a chemical composition of 0.3%, Co: 0-0.6%, REM (rare earth elements): 0-0.1%, Ca: 0-0.1%, with the remainder being Fe and unavoidable impurities, a metallic structure in which the matrix is ​​a single phase of ferrite and the average grain size of the ferrite crystal grains is 0.3-3.0 mm, and a remanent magnetic flux density of 45 mT or less (Patent Document 1).

[0007] Also, in mass %, 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%, C A ferritic stainless steel material is also known that has a chemical composition of o: 0-0.6%, REM (rare earth elements): 0-0.1%, Ca: 0-0.1%, with the remainder being Fe and unavoidable impurities, a metallic structure in which the matrix is ​​a single phase of ferrite and the average grain size of the ferrite crystal grains is 0.3-3.0 mm, and a remanent magnetic flux density of 45 mT or less (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 project] [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. The ferritic stainless steel material described in Patent Document 2 shows improved vibration damping properties when the Al content is increased, but its toughness decreases. Furthermore, since the composition of the ferritic stainless steel material described in Patent Document 2 has not been thoroughly examined, its corrosion resistance is not sufficient when the Cr content is low.

[0010] This invention was made to solve the above-mentioned problems, and aims to provide a ferritic stainless steel material with excellent toughness, corrosion resistance, and vibration damping properties, 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 ferritic stainless steel materials with excellent toughness, corrosion resistance, and vibration damping properties. [Means for solving the problem]

[0011] The inventors of this invention conducted intensive research to solve the above-mentioned problems and found that toughness, corrosion resistance, and vibration damping properties can be improved by controlling the composition, average grain size, and number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm of ferritic stainless steel material. Furthermore, the inventors also found that a ferritic stainless steel material with these characteristics can be obtained by using a material with 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.

[0012] That is, the present invention contains, on a mass basis, C: 0.100% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.100% or less, S: 0.10% 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, Ti: 1.00% or less, and has a composition in which 1.8Cr + 2.8Mo is 40.00% or more, and the balance consists of Fe and impurities. The average crystal grain diameter is 100 to 1000 μm, The number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 100 pieces / mm 2 or less. the law of nature, (a) to (c) below: (a) Charpy impact value at 0°C is 20 J / cm 2 That's all. (b) Loss factor η is 8.0 × 10 -4 That's all. (c) Pitting potential is 400mV vs. SSE or higher All of the following conditions must be met: It is a ferritic stainless steel material.

[0013] Further, the present invention contains, on a mass basis, 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: 23.56 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, Ti: 1.00% or less, further contains one or more selected from the following Group A and Group B, and 1.8Cr + 2.8Mo: 45.17 % or more, and has a composition in which the balance consists of Fe and impurities. The average crystal grain diameter is 100 to 1000 μm, The number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 100 pieces / mm 2 or less. the law of nature, (a) to (c) below: (a) Charpy impact value at 0°C is 20 J / cm 2 That's all. (b) Loss factor η is 8.0 × 10 -4 That's all. (c) Pitting potential is 400mV vs. SSE or higher All of the following conditions must be met: It is a ferritic stainless steel material. [Group A] One or more selected from Al: 1.00% or less and Nb: 0.20% 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%.

[0014] 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 Ti: 1.00% or less, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities.

[0015] Furthermore, the present invention provides for 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: 23.56 ~35.00%, including Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50~4.00%, N: 0.100% or less, Ti: 1.00% or less, and further including one or more selected from the following groups A and B, 1.8Cr + 2.8Mo: 45.17 This is a ferritic stainless steel material for vibration-damping heat treatment, having a composition in which % or more of the material is present, with the remainder consisting of Fe and impurities. [Group A] One or more selected from Al: 1.00% or less and Nb: 0.20% 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%.

[0016] Furthermore, the present invention relates to a method for manufacturing a ferritic stainless steel material, which involves heat-treating the vibration-damping heat-treated ferritic stainless steel material at 1000 to 1200°C, and then cooling it down to 700°C at a cooling rate of 30°C / min or more.

[0017] Furthermore, the present invention relates to a vibration damping member that includes the ferritic stainless steel material. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a ferritic stainless steel material with excellent toughness, corrosion resistance, and vibration damping properties, 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 using a ferritic stainless steel material with excellent toughness, corrosion resistance, and vibration damping properties. [Modes for carrying out the invention]

[0019] The vibration damping properties of ferromagnetic ferritic stainless steel materials are determined by the magnitude of the deformation (magnetostriction) when magnetic domains move. While aluminum (Al) can increase magnetostriction, it also reduces toughness. Therefore, to ensure toughness, a composition system was adopted that either does not contain Al or has reduced Al content. On the other hand, in order to increase magnetostriction and improve corrosion resistance, Cr was added in combination with Mo, and their content was optimized. Furthermore, for vibration damping to occur in ferritic stainless steel materials, 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. Therefore, the size of precipitates that hinder the movement of magnetic domains was identified, and their quantity (number density) was controlled. In addition, to reduce the grain boundaries that hinder the movement of magnetic domains, the crystal grains were grown, and their average crystal grain size was controlled.

[0020] Heat treatment is necessary to reduce strain (dislocations), precipitates, and grain boundaries in ferritic stainless steel materials. However, precipitates formed during melting (especially Nb carbonitrides) are difficult to remove through heat treatment. Therefore, to reduce precipitates, a composition system was adopted that does not contain Nb or has reduced Nb content. 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 not only cause sensitization, which reduces corrosion resistance by removing surrounding Cr, but Cr carbides in particular precipitate preferentially at grain boundaries, causing a significant decrease in toughness. Therefore, in order to reduce the amount of C and N in solid solution and suppress sensitization and toughness reduction, Ti was added to fix C and N as precipitates. Since Ti carbonitrides (precipitates) precipitate between 700°C and 1000°C and solidify above 1000°C, vibration-damping heat treatment was performed at 1000-1200°C to solidify the Ti carbonitrides, and then the cooling rate to 700°C was accelerated to make the precipitates finer.

[0021] 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%".

[0022] (1) Ferritic stainless steel The ferritic stainless steel material 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, and Ti: 1.00% or less, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder being Fe and impurities.

[0023] 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, austenite or martensite phases). Furthermore, in this specification, "impurities" refers to 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 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). Furthermore, regarding the content of each element, "containing less than or equal to xx%" means that it contains less than or equal to xx%, but also more than 0% (especially above the impurity level).

[0024] Furthermore, the ferritic stainless steel material according to the embodiment of the present invention may further include one or more selected from the following groups A and B. [Group A] One or more selected from Al: 1.00% or less and Nb: 0.20% 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.

[0025] (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%.

[0026] (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%.

[0027] (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%.

[0028] (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%.

[0029] (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%.

[0030] (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%.

[0031] (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%.

[0032] (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%.

[0033] (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%.

[0034] (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%.

[0035] (Ti: 1.00% 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 and surface quality of the ferritic stainless steel material will deteriorate. Therefore, the upper limit of the Ti content is 1.00%, preferably 0.80%, and more preferably 0.50%. 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 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0036] (1.8Cr + 2.8Mo: 40.00% or more) As described above, Cr and Mo are effective elements for improving the corrosion resistance and vibration damping (increase in magnetostriction) 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%.

[0037] (Al: 1.00% or less) Al is an effective element for improving the vibration damping properties (increase in magnetostriction) of ferritic stainless steel materials. However, if the Al content is too high, the toughness of the ferritic stainless steel material will decrease. Therefore, the upper limit of the Al content is 1.00%, preferably 0.50%, more preferably 0.30%, and even more preferably 0.10%. 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%.

[0038] (Nb:0.20% or less) Nb is an element that affects properties such as intergranular corrosion resistance (sensitization suppression) of ferritic stainless steel materials. However, if the Nb content is too high, the amount of precipitates in the ferritic stainless steel material increases, and the vibration damping performance decreases. Therefore, the upper limit of the Nb content is 0.20%, preferably 0.15%, and more preferably 0.10%. On the other hand, the lower limit of the Nb content is not particularly limited, but from the viewpoint of ensuring the effect of Nb, it is preferably 0.001%, more preferably 0.005%, and even more preferably 0.01%.

[0039] (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%.

[0040] (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 a mixture.

[0041] (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%.

[0042] (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%.

[0043] The ferrite stainless steel material according to an embodiment of the present invention has an average crystal grain size of 100 to 1000 μm. By controlling the average crystal grain size to be 100 μm or more, the number of grain boundaries that hinder the movement of magnetic domains, which is effective for the manifestation of vibration damping properties, decreases, so that the vibration damping properties can be improved. From the viewpoint of stably obtaining this effect, the average crystal grain size is preferably 120 μm or more, more preferably 150 μm or more, still more preferably 180 μm or more, and particularly preferably 200 μm or more. Further, by controlling the average crystal grain size to be 1000 μm or less, it is possible to stably suppress the decrease in toughness due to the extreme coarsening of crystal grains. From the viewpoint of stably obtaining this effect, the average crystal grain size is preferably 800 μm or less, more preferably 600 μm or less, and still more preferably 500 μm or less. Here, in this specification, the average crystal grain size means the one measured using an optical microscope described later.

[0044] The ferrite stainless steel material according to an embodiment of the present invention has a number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm of 100 pieces / mm 2 or less. Precipitates with a diameter of 0.5 μm or more and less than 5.0 μm hinder the movement of magnetic domains, so by controlling the number density of these precipitates to 100 pieces / mm 2 or less, the vibration damping properties can be improved. From the viewpoint of stably obtaining this effect, the number density of these precipitates is preferably 95 pieces / mm 2 or less, more preferably 90 pieces / mm 2 or less, and still more preferably 85 pieces / mm 2 or less. In addition, since the lower the number of these precipitates, the better from the viewpoint of vibration damping properties, the lower limit value thereof is not particularly limited, but is generally 10 pieces / mm 2 or more. Here, in this specification, the diameter and number density of precipitates mean the ones measured using a SEM (scanning electron microscope) described later. Further, the diameter of the precipitate is a value calculated by (length of the long side × length of the short side) 1 / 2 Here, in this specification, the diameter and number density of precipitates mean the ones measured using a SEM (scanning electron microscope) described later. Further, the diameter of the precipitate is a value calculated by (length of the long side × length of the short side)

[0045] The ferritic stainless steel material according to the embodiment of the present invention preferably has an absorbed energy (hereinafter referred to as "Charpy impact value") of 20 J / cm² in a Charpy impact test at 0°C. 2 More preferably 25 J / cm 2 More preferably 30 J / cm² 2 That concludes the explanation. By setting the Charpy impact value within this range, the desired toughness can be ensured. While there is no particular upper limit to the Charpy impact value, it is generally 300 J / cm². 2 Preferably 250 J / cm² 2 That is the case. Herein, in this specification, the Charpy impact value means the value measured by the method described later.

[0046] The ferritic stainless steel material according to the embodiment of the present invention has a loss factor η preferably of 8.0 × 10 -4 More preferably 8.1 × 10 -4 More preferably 8.2 × 10 -4 That concludes the explanation. By setting the loss coefficient η within this range, the desired vibration damping performance can be ensured. The upper limit of the loss coefficient η is not particularly limited, but is generally 4.0 × 10⁻⁶. -3 Preferably 3.0 × 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.

[0047] The ferritic stainless steel material according to the embodiment of the present invention has a pitting potential of preferably 400 mV vs. SSE or higher, more preferably 450 mV vs. SSE or higher, and even more preferably 500 mV vs. SSE or higher. By setting the pitting potential within this range, the desired corrosion resistance can be ensured. Furthermore, since a higher pitting potential indicates better corrosion resistance, there is no particular upper limit to its value. Herein, in this specification, pitting potential refers to the potential measured by the method described later.

[0048] 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.

[0049] (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 ferritic stainless steel material described above.

[0050] 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, and Ti: 1.00% or less, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder being Fe and impurities.

[0051] Furthermore, the ferritic stainless steel material for vibration-damping heat treatment according to the embodiment of the present invention 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: 20.00~35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50~4.00%, N: 0.100% or less, and Ti: 1.00% or less, 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 being Fe and impurities. [Group A] One or more selected from Al: 1.00% or less and Nb: 0.20% 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 of each component are as described above, we will omit further explanation.

[0052] 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.

[0053] 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.

[0054] (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 of the above-described ferritic stainless steel material for vibration damping heat treatment. The vibration damping heat treatment is performed by heat treating the ferritic stainless steel material for vibration damping heat treatment at 1000 to 1200°C, and then cooling it down to 700°C at a cooling rate of 30°C / min or more. By heat-treating ferritic stainless steel material for vibration damping at 1000 to 1200°C, 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.

[0055] Furthermore, since the temperature range from the heat treatment temperature of 1000-1200°C to 700°C is the temperature range in which Ti and Nb carbonitrides precipitate, the precipitation of Ti and Nb carbonitrides 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 100 particles / mm². 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.

[0056] (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 toughness, corrosion resistance, and vibration damping properties, this vibration damping member also has excellent toughness, corrosion resistance, and vibration damping properties. 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]

[0057] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Note that Example 6, among the examples shown below, is for reference only.

[0058] (Examples 1-8 and Comparative Examples 1-7) 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.

[0059] [Table 1]

[0060] The above test specimens were placed in an electric furnace and heat-treated at the temperatures shown in Table 2 for 60 minutes. Afterward, they were cooled from the heat-treatment temperature to 700°C at the rates shown in Table 2. The cooling rate of the test specimens was controlled by adjusting the flow rate of the cooling gas (argon gas) introduced into the electric furnace.

[0061] [Table 2]

[0062] The following evaluations were performed on the test specimens that underwent the above heat treatment (vibration-damping heat treatment).

[0063] (Average grain size) 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.

[0064] (Number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm) 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.

[0065] (Toughness: Charpy impact value) A 10 mm wide x 55 mm long test specimen was taken from the above test specimen so that its longitudinal direction was perpendicular to the rolling direction, and a V-notch (notch angle 45°, notch depth 2 mm, notch bottom radius 0.25 mm) was cut into the center of the longitudinal direction. Using this test specimen, a Charpy impact test was performed at a test temperature of 0°C in accordance with JIS Z2242:2018.

[0066] (Corrosion resistance: Pitting potential) A 20mm x 15mm test specimen was cut from the above test piece by cutting. Next, a wire was spot-welded to one end of this test specimen, and the portion other than the 10mm x 10mm test surface was coated with silicone resin. This was then subjected to pitting potential (100 μA / cm²) in a 3.5% by mass NaCl aqueous solution at 30°C. 2The noblest potential (the one exceeding 1000mV vs. SSE) was measured. An Ag / AgCl sample with saturated KCl as the internal solution was used as the reference electrode, and the potential sweep rate was set to 20mV / min. The test was terminated when the pitting potential reached 1000mV vs. SSE. This is because, at potentials higher than this, the influence of the electrolysis reaction of water (O2 generation) becomes significant, making it impossible to accurately capture the corrosion reaction, and it can be determined that the material already possesses sufficient corrosion resistance.

[0067] (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.

[0068] The results of each of the above evaluations are shown in Table 3.

[0069] [Table 3]

[0070] As shown in Table 3, Examples 1 to 8 all exhibited good toughness, corrosion resistance, and vibration damping properties because their composition, average grain size, and number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm met the specified ranges. In contrast, Comparative Example 1 had a small average crystal grain size and a high number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm, resulting in insufficient vibration damping. Comparative Examples 2 and 3 had insufficient toughness and vibration damping due to a high number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm. Comparative Example 4 had a high Nb content and a high number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm, resulting in insufficient toughness and vibration damping properties. Comparative Example 5 had low Cr and Mo content, an inappropriate balance of Cr and Mo (1.8Cr + 2.8Mo was too low), and a high Al content, resulting in insufficient toughness and corrosion resistance. Comparative Example 6 had a low Cr content and an inappropriate balance of Cr and Mo (1.8Cr + 2.8Mo was too low), resulting in insufficient corrosion resistance and vibration damping. Comparative Example 7 had a high Mn content and a low Mo content, and the balance between Cr and Mo was inappropriate (1.8Cr + 2.8Mo was too low), resulting in insufficient corrosion resistance and vibration damping.

[0071] As can be seen from the above results, the present invention provides a ferritic stainless steel material with excellent toughness, corrosion resistance, and vibration damping properties, 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 toughness, corrosion resistance, and vibration damping properties.

Claims

1. On a mass basis, it 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, and Ti: 1.00% or less, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities. The average grain size is 100 to 1000 μm. The number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 100 particles / mm². 2 The following: (a) to (c) below: (a) The Charpy impact value at 0°C is 20 J / cm² or higher. (b) The loss factor η is 8.0 × 10⁻⁴ or greater. (c) Pitting potential is 400 mV vs. SSE or higher. A ferritic stainless steel material that satisfies all of the following requirements.

2. On a mass basis, it 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: 23.56 to 35.00%, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 0.50 to 4.00%, N: 0.100% or less, Ti: 1.00% or less, and further contains one or more selected from the following groups A and B, with a composition of 1.8Cr + 2.8Mo: 45.17% or more, and the remainder consisting of Fe and impurities. The average grain size is 100 to 1000 μm. The number density of precipitates with a diameter of 0.5 μm or more and less than 5.0 μm is 100 particles / mm². 2 The following: (a) to (c) below: (a) The Charpy impact value at 0°C is 20 J / cm² or higher. (b) The loss factor η is 8.0 × 10⁻⁴ or greater. (c) Pitting potential is 400 mV vs. SSE or higher. A ferritic stainless steel material that satisfies all of the following requirements. [Group A] One or more selected from Al: 1.00% or less and Nb: 0.20% 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. A ferritic stainless steel material according to claim 2, having a composition including the aforementioned group A.

4. The ferritic stainless steel material according to claim 2, having a composition including the aforementioned group B.

5. 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 Ti: 1.00% or less, with 1.8Cr + 2.8Mo: 40.00% or more, and the remainder consisting of Fe and impurities.

6. A ferritic stainless steel material for vibration-damping heat treatment having a composition based on 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: 23.56 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 Ti: 1.00% or less, further comprising one or more selected from the following groups A and B, with a composition of 1.8Cr + 2.8Mo: 45.17% or more, and the remainder consisting of Fe and impurities. [Group A] One or more selected from Al: 1.00% or less and Nb: 0.20% 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.

7. The ferritic stainless steel material for vibration-damping heat treatment according to claim 6, having a composition including the aforementioned group A.

8. The ferritic stainless steel material for vibration-damping heat treatment according to claim 6, having a composition including the aforementioned group B.

9. A method for manufacturing a ferritic stainless steel material, comprising heat-treating a vibration-damping heat-treated ferritic stainless steel material according to any one of claims 5 to 8 at 1000 to 1200°C, and then cooling it to 700°C at a cooling rate of 30°C / min or more.

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

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