Stainless steel

Abstract

To provide a ferrite-based stainless steel having excellent damping property when used in use required to have damping property.SOLUTION: Stainless steel comprising, C: 0.001 to 0.030%, Si:0.01 to 5.00%, Mn:0.01 to 1.00%, P:≤0.050%, S:≤0.0100%, Cr:9.0 to 30.0%, Ni:0.01 to 3.00%, Al:0.30 to 5.00%, N:0.001 to 0.050%, B:0.0001 to 0.0050%, further contains either one or both of Ti or Nb in the range of 0.01 to 1.00%, the balance being iron and impurities, having average grain size of 60 μm or more and less than 200 μm, the magnetostriction amplitude of 15 μm / m or more at a magnetic field strength of ±10 kOe, the internal friction of 0.0030 or more, and the loss factor of 0.0010 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to stainless steel that requires vibration damping properties.

Background Art

[0002] Applications that require vibration damping properties include, for example, building materials, general furniture, home appliance applications, cover applications such as hard disks, fuel cells, automotive exhaust system components, and other automotive parts. Examples of automotive exhaust system components include, for example, mufflers, exhaust manifolds, center pipes, catalytic converters, EGR coolers, flexible pipes, flanges, and the like. Other automotive parts include, for example, moldings, fuel supply pipes, battery parts (cases, cells, packs, modules, etc.), fastening parts (clamps, V-bands, etc.), and the like.

[0003] In recent years, vibration damping properties have been required for automotive exhaust system components. The need to reduce noise caused by vibrations of automotive engines and exhaust gases has been increasing in recent years, and noise reduction by simply devising the structure of automotive exhaust system components is not sufficient to completely reduce noise. Therefore, it is extremely effective if the stainless steel itself used for automotive exhaust system components has the ability to absorb vibrations.

[0004] Patent Document 1 discloses a vibration-damping ferritic stainless steel material having a chemical composition of, in mass%, C: 0.001 to 0.03%, Si: 0.1 to 1.0%, Mn: 0.1 to 2.0%, Ni: 0.01 to 0.6%, Cr: 10.5 to 24.0%, N: 0.001 to 0.03%, Nb: 0 to 0.8%, Ti: 0 to 0.5%, Cu: 0 to 2.0%, Mo: 0 to 2.5%, V: 0 to 1.0%, Al: 0 to 0.3%, Zr: 0 to 0.3%, Co: 0 to 0.6%, REM (rare earth element): 0 to 0.1%, Ca: 0 to 0.1%, with the balance being Fe and unavoidable impurities, having a matrix of a single ferritic phase, having a metallographic structure in which the average crystal grain diameter of ferritic crystal grains is 0.3 to 3.0 mm, and having a residual magnetic flux density of 45 mT or less.

[0005] Patent Document 2 discloses a vibration-damping ferritic stainless steel sheet having a chemical composition of, by mass%, C: 0.001 to 0.04%, Si: 0.1 to 2.0%, Mn: 0.1 to 1.0%, Ni: 0.01 to 0.6%, Cr: 10.5 to 20.0%, Al: 0.5 to 5.0%, N: 0.001 to 0.03%, Nb: 0 to 0.8%, Ti: 0 to 0.5%, Cu: 0 to 0.3%, Mo: 0 to 0.3%, V: 0 to 0.3%, Zr: 0 to 0.3%, Co: 0 to 0.6%, REM (rare earth element): 0 to 0.1%, Ca: 0 to 0.1%, the balance being Fe and unavoidable impurities, having a matrix of a single ferrite phase, a metal structure with an average crystal grain size of the ferrite crystal grains being 0.3 to 3.0 mm, and a residual magnetic flux density of 45 mT or less.

[0006] Patent Document 3 discloses a stainless steel containing C: 0.001 to 0.100%, Si: 0.01 to 5.00%, Mn: 0.01 to 2.00%, P: ≤0.050%, S: ≤0.0100%, Cr: 9.0 to 30.0%, Ni: 0.01 to 0.50%, Al: 0.010 to 5.000%, N: 0.001 to 0.050%, B: 0.0001 to 0.0050%, further containing either one or both of Ti and Nb in the range of 0.01 to 1.00% respectively, the balance being iron and impurities, having a crystal grain size number of 6.0 or more and 9.0 or less, and an internal friction of 0.0003 or more.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in the technology described in Patent Document 1, vibration damping performance is achieved by heating at a high temperature so that the average crystal grain size becomes very large, 0.3 mm or more, at the final annealing. However, since the crystal grain size is coarse, there is a problem that the toughness is inferior. In addition, the Al content for exhibiting vibration damping performance is low. Also, in the technology described in Patent Document 2, vibration damping performance is achieved by heating at a high temperature so that the average crystal grain size becomes very large, 0.3 mm or more. However, since the crystal grain size is coarse, there is a problem that the toughness is inferior. Also, in the technology described in Patent Document 3, corrosion resistance and vibration damping performance are improved by containing Al and Si. However, the value of internal friction, which is a characteristic value of the vibration damping performance, is low and the vibration damping performance is insufficient. Thus, in the conventional technology, it has not been possible to improve the vibration damping performance without excessively coarsening the crystal grain size.

[0009] The present invention has been made to solve such problems, and an object thereof is to provide a stainless steel having excellent vibration damping performance when used in applications where vibration damping performance is required.

Means for Solving the Problems

[0010] In order to solve the above-described problems, the present inventors produced steels containing various elements and steels having various crystal grain sizes. Then, it was examined whether the vibration damping performance of stainless steel could be dramatically improved. As a result, it was found that by containing particularly 0.3% or more of Al and optimizing the manufacturing process so that the crystal grain size is 60 or more and less than 200 μm, the magnetostrictive amplitude at a magnetic field strength of ±10 kОe of the stainless steel becomes 15 μm / m or more, and the vibration damping performance is dramatically improved.

[0011] That is, the present invention has been completed based on the above findings, and the gist of the present invention aimed at solving the above problems is as follows.

[0012] [1] By mass% C: 0.001 to 0.030%, Si: 0.01 - 5.00%, Mn: 0.01 - 1.00%, P: ≤ 0.050%, S: ≤ 0.0100%, Cr: 9.0 - 30.0%, Ni: 0.01 - 3.00%, Al: 0.30 - 5.00%, N: 0.001 - 0.050%, contains B: 0.0001 - 0.0050%, further contains either or both of Ti and Nb in the range of 0.01 - 1.00% respectively, the balance being iron and impurities, the average crystal grain size is 60 μm or more and less than 200 μm, the magnetostriction amplitude at a magnetic field strength of ±10 kОe is 15 μm / m, the internal friction is 0.0030 or more, a stainless steel characterized in that the loss coefficient is 0.0010 or more. [2] By mass C: 0.001 - 0.030%, Si: 0.01 - 2.00%, Mn: 0.01 - 1.00%, P: ≤ 0.050%, S: ≤ 0.0100%, Cr: 10.5 - 20.0%, Ni: 0.01 - 3.00%, Al: 0.30 - 3.50%, N: 0.001 - 0.050%, contains B: 0.0001 - 0.0050%, further contains either or both of Ti and Nb in the range of 0.01 - 1.00% respectively, the balance being iron and impurities, the average crystal grain size is 60 μm or more and less than 200 μm, the magnetostriction amplitude at a magnetic field strength of ±10 kОe is 15 μm / m or more, the internal friction is 0.0030 or more, a stainless steel characterized in that the loss coefficient is 0.0010 or more. [3] Further, in mass percentage, Mo: 0.01 to 3.00%, Sn: 0.01 to 3.00%, Cu: 0.01 to 0.50%, W: 0.001 to 1.000%, V: 0.001 to 1.000%, Sb: 0.001 to 0.100%, Co: 0.001 to 0.500%, Ca: 0.0001 to 0.0050%, Mg: 0.0001 to 0.0050%, Zr: 0.0001 to 0.0300%, Ga: 0.0001 to 0.0100%, Ta: 0.001 to 0.050%, REM: 0.001 to 0.100% The stainless steel according to [1] or [2], characterized by containing one or more of the above.

Advantages of the Invention

[0013] According to the present invention, when used in applications where vibration damping properties are required, it is possible to provide a stainless steel having excellent vibration damping properties.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail.

[0015] The inventors prepared steels containing Al at various concentrations in order to improve corrosion resistance and vibration damping properties. Then, the effects of the Al concentration and crystal grain size on the vibration damping properties of the steel were investigated. As a result, it was found that when the Al content of the steel is 0.30% or more and the average crystal grain size is 60 μm or more and less than 200 μm, the magnetostrictive amplitude of the steel becomes as large as 15 μm / m or more, and the internal friction, which is an index of vibration damping properties, becomes extremely large at 0.0030 or more and the loss coefficient becomes 0.0010 or more.

[0016] In addition, it has been found that in addition to the effect of increasing magnetostriction in Al, the threshold value of the Al content for significantly exhibiting vibration damping properties is 0.30% or more.

[0017] Also, although it is known that the larger the average crystal grain size, the more effective it is in exhibiting vibration damping properties, if the average crystal grain size is made too large, the manufacturability and workability will decrease. Therefore, when the inventors of the present invention studied a method capable of exhibiting vibration damping properties without reducing the manufacturability and workability, it was found that by containing 0.30% or more of Al to increase the magnetostriction of the steel component system itself, it is not necessary to make the average crystal grain size excessively coarse. Specifically, if Al is contained in an amount of 0.30% or more, excellent vibration damping properties can be obtained without excessively coarsening the crystal grains (that is, without reducing the manufacturability and workability). More specifically, when the Al content of the steel is 0.30% or more and the average crystal grain size is in the range of 60 μm or more and less than 200 μm, very excellent vibration damping properties are exhibited.

[0018] In addition, in order to manufacture steel (the steel of the present invention) having the above characteristics (especially the average crystal grain size), the conditions of the finishing annealing process (cold-rolled sheet annealing process) are very important. Specifically, regarding the annealing conditions, the average crystal grain size can be kept within the above range by setting the annealing temperature to 900°C or higher and lower than 1000°C, preferably 950 - 980°C, and the annealing time to 150 seconds or less, preferably 120 seconds or less.

[0019] Hereinafter, the chemical composition of the stainless steel according to the present embodiment will be described in more detail. Unless otherwise noted, the % of the element content in this specification means mass %. Also, the stainless steel of the present embodiment is a ferritic stainless steel.

[0020] C: 0.001 - 0.030% Since C reduces intergranular corrosion resistance and workability, its content needs to be kept low. Therefore, the upper limit of the C content is set to 0.030% or less. However, excessively reducing the C content increases refining costs, so the lower limit of the C content is set to 0.001% or more. The preferred range of the C content is 0.002 - 0.030%, and the more desirable range is 0.003 - 0.010%.

[0021] Si: 0.01 - 5.00% Si is a very beneficial element that not only concentrates on the steel surface to suppress corrosion occurrence but also reduces the corrosion rate of the base metal. In addition, Si improves the damping property of the steel. Therefore, the lower limit of the Si content is set to 0.01% or more. However, excessive Si content causes a decrease in the elongation of the steel, reduces workability, and also reduces corrosion resistance. Excessive Si content also causes an increase in hardness, leading to surface defects and rusting from the surface defects. Therefore, the upper limit of the Si content is set to 5.00% or less. The preferred range of the Si content is 0.10 - 2.00%, the more preferred range is 0.20 - 1.80%, and the even more preferred range is 0.30 - 1.50%.

[0022] Mn: 0.01 - 1.00% Mn is useful as a deoxidizing element, but containing an excessive amount of Mn deteriorates corrosion resistance. Therefore, the Mn content is set to 0.01 - 1.00%. The preferred range of the Mn content is 0.05 - 0.80%, and the more preferred range is 0.10 - 0.50%.

[0023] P: 0.050% or less P is an element that deteriorates workability and weldability and also reduces corrosion resistance. Therefore, it is necessary to limit its content. Therefore, the P content is set to 0.050% or less. The more preferred range of the P content is 0.030% or less. However, excessively reducing the P content increases refining costs, so the lower limit of the P content may be set to 0.001% or more.

[0024] S: 0.0100% or less Since S is an element that deteriorates corrosion resistance, it is necessary to limit its content. Therefore, the S content is set to 0.0100% or less. A more preferable range of the S content is 0.0070% or less. However, excessively lowering the S content increases the refining cost, so the lower limit of the S content may be set to 0.0001% or more.

[0025] Cr: 9.0 - 30.0% In order to ensure corrosion resistance in a chloride environment, Cr needs to be contained in an amount of 9.0% or more. The higher the Cr content, the better the corrosion resistance, but the workability and manufacturability decrease. Therefore, the upper limit of the Cr amount is set to 30.0% or less. The preferable range of the Cr amount is 10.5 - 25.0%, a more preferable range is 10.5 - 20.0%, an even more preferable range is 11.0 - 20.0%, and an even more preferable range is 11.5 - 18.0%.

[0026] Ni: 0.01 - 3.00% Ni can be contained in an amount of 0.01% or more in order to improve corrosion resistance and toughness. However, containing a large amount of Ni leads to an increase in alloy cost, so the upper limit of the Ni amount is set to 3.00% or less. The preferable range of the Ni amount is 0.02 - 2.50%, a more preferable range is 0.05 - 2.00%, and a more desirable range is 0.10 - 1.50%.

[0027] Either one or both of Ti and Nb are each 0.01 - 1.00% Ti and Nb need to be contained in an amount of 0.01% or more, either one or both, in order to prevent sensitization of the stainless steel. When the Ti content is less than 0.01%, the corrosion resistance deteriorates due to sensitization. However, containing a large amount of Ti leads to an increase in alloy cost, a decrease in toughness, a decrease in corrosion resistance due to an increase in inclusions in the steel, and a decrease in manufacturability, so the upper limit of the Ti amount is set to 1.00% or less. The preferable range of the Ti amount is 0.03 - 0.50%, and a more preferable range is 0.10 - 0.25%.

[0028] Nb is also an element useful for preventing the sensitization of stainless steel. Furthermore, it is useful for improving high-temperature strength and the intergranular corrosion resistance of welded parts. However, excessive inclusion of Nb reduces workability and manufacturability. Therefore, the Nb content is set to 0.01 - 1.00%. The preferred range of the Nb content is 0.05 - 0.50%.

[0029] Al: 0.30 - 5.00% Al is an important element in this embodiment. Al has the effect of increasing magnetostriction and significantly enhancing the manifestation of vibration damping properties. Therefore, the lower limit of the Al content is set to 0.30% or more. However, excessive inclusion of Al causes a decrease in the elongation of the material, reducing workability. Also, excessive inclusion of Al causes an increase in hardness, leading to surface defects and rusting from the surface defects. Therefore, the upper limit of the Al content is set to 5.00% or less. Preferably, the upper limit of the Al content is 3.50% or less. The preferred range of the Al content is 0.50 - 3.80%, a more preferred range is 0.80 - 3.50%, and an even more preferred range is 1.00 - 3.20%.

[0030] N: 0.001 - 0.050% N is an element useful for pitting corrosion resistance, but it reduces intergranular corrosion resistance and workability. Therefore, it is necessary to keep the N content low. Therefore, the upper limit of the N content is set to 0.050% or less. However, excessively lowering the N content increases the refining cost, so the lower limit of the N content is set to 0.001% or more. The preferred range of the N content is 0.002 - 0.020%.

[0031] B: 0.0001 - 0.0050% B is an element useful for improving secondary workability and can be contained at 0.0050% or less. The lower limit of the B content is set to 0.0001% or more to obtain a stable effect. The preferred range of the B content is 0.0005 - 0.0040%.

[0032] The above is the basic chemical composition of the stainless steel of the present embodiment, and the balance is iron and impurities. However, in the present embodiment, the following elements can be further contained as required.

[0033] Mo, Sn, Cu, W, V, Sb, Co, Ca, Mg, Zr, Ga, Ta, REM may contain one or more of these according to the purpose. The lower limit of these elements is 0% or more, preferably more than 0%.

[0034] Mo: 0.01 - 3.00% Mo can be contained at 0.01% or more in order to improve corrosion resistance. However, excessive content deteriorates workability and is expensive, leading to cost increase. Therefore, the upper limit of the Mo amount is set to 3.00% or less. The preferable range of the Mo amount is 0.05 - 1.00%.

[0035] Sn: 0.01 - 3.00% Sn can be contained at 0.01% or more in order to improve corrosion resistance. However, excessive content leads to cost increase. Therefore, the upper limit of the Sn amount is set to 3.00% or less. The preferable range of the Sn amount is 0.05 - 1.00%.

[0036] Cu: 0.01 - 0.50% Cu can be contained at 0.01% or more in order to improve corrosion resistance. However, excessive content leads to cost increase. Therefore, the upper limit of the Cu amount is set to 0.50% or less. The preferable range of the Cu amount is 0.02 - 0.40%, and the more desirable range is 0.05 - 0.30%.

[0037] W: 0.001 - 1.000% W can be contained at 0.001% or more in order to improve corrosion resistance. However, excessive addition deteriorates workability and manufacturability, so the upper limit is set to 1.000% or less. The preferable range of the W amount is 0.005 - 0.800%.

[0038] V: 0.001 - 1.000% V can be contained in an amount of 0.001% or more in order to improve corrosion resistance. However, excessive addition may reduce workability and manufacturability, so the upper limit is set to 1.000% or less. The preferable range of the V content is 0.005 - 0.500%.

[0039] Sb: 0.001 - 0.100% Sb can be contained in an amount of 0.001% or more in order to improve general corrosion resistance. However, excessive addition may reduce workability and manufacturability, so the upper limit is set to 0.100% or less. The preferable range of the Sb content is 0.010 - 0.080%.

[0040] Co: 0.001 - 0.500% Co can be contained in an amount of 0.001% or more in order to improve secondary workability and toughness. However, excessive addition may reduce workability, so the upper limit is set to 0.500% or less. The preferable range of the Co content is 0.010 - 0.300%.

[0041] Ca: 0.0001 - 0.0050% Ca is contained for desulfurization, but if contained in excess, water-soluble inclusion CaS is generated, reducing corrosion resistance. Therefore, Ca can be contained in the range of 0.0001 - 0.0050%. The preferable range of the Ca content is 0.0005 - 0.0030%.

[0042] Mg: 0.0001 - 0.0050% Mg is useful for refining the structure and improving workability and toughness. Therefore, it can be contained in an amount of 0.0001% or more. However, excessive addition may reduce corrosion resistance, so the upper limit is set to 0.0050% or less. The preferable range of the Mg content is 0.0005 - 0.0030%.

[0043] Zr: 0.0001 - 0.0300% Zr can be contained in an amount of 0.0001% or more in order to improve corrosion resistance. However, excessive addition may reduce workability and manufacturability, so the upper limit is set to 0.0300% or less. The preferable range of the Zr content is 0.0010 - 0.0100%.

[0044] Ga: 0.0001 to 0.0100% Ga can be contained in an amount of 0.0001% or more in order to improve corrosion resistance and hydrogen embrittlement resistance. However, excessive addition may reduce workability and manufacturability, so the upper limit is set to 0.0100% or less. The preferred range of the amount of Ga is 0.0005 to 0.0050%.

[0045] Ta: 0.001 to 0.050% Ta can be contained in an amount of 0.001% or more in order to improve corrosion resistance. However, excessive addition may reduce workability and manufacturability, so the upper limit is set to 0.050%. The preferred range of the amount of Ta is 0.005 to 0.030%.

[0046] REM: 0.001 to 0.100% Since REM has an effect such as a deoxidation effect and is a useful element in refining, it can be contained in an amount of 0.001% or more. However, excessive addition may reduce workability and manufacturability, so the upper limit is set to 0.100% or less. The preferred range of the amount of REM is 0.003 to 0.050%.

[0047] Here, REM (rare earth element) refers to the general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu) according to a general definition. REM is one or more selected from these rare earth elements, and the amount of REM is the total amount of rare earth elements.

[0048] The stainless steel of the present embodiment is composed of Fe and impurities (including inevitable impurities) other than the elements described above. However, in addition to each element described above, it can be contained within a range that does not impair the effects of the present invention.

[0049] In the production of stainless steel, scrap raw materials are often used. For this reason, various impurity elements inevitably mix into the stainless steel. It is difficult to uniquely determine the content of the impurity elements. Therefore, the impurities in the present invention mean elements contained in an amount that does not inhibit the effects of the present invention.

[0050] The average crystal grain size of the stainless steel of this embodiment is in the range of 60 μm or more and less than 200 μm as described above. The desirable range of the average crystal grain size is 70 μm or more and less than 180 μm, and the more desirable range is 80 μm or more and less than 160 μm. By setting the average crystal grain size to 60 μm or more, it is possible to prevent a decrease in the mechanical properties of the steel while making the internal friction and loss coefficient large values. Also, by setting the average crystal grain size to less than 200 μm, it is possible to make the internal friction and loss coefficient high values without an excessive decrease in workability and manufacturability, and improve the vibration damping property. The average crystal grain size can be measured as follows. First, a test piece with a length of 30 mm and a width of 20 mm is cut out from the steel (for example, a steel plate), embedded in resin so that a cross-sectional structure parallel to the rolling direction and perpendicular to the steel plate surface can be observed, and mirror polishing and etching are performed. Then, it is measured according to the cutting method of JIS G 0551:2020. The measurement is performed at 5 test numbers (number of fields of view) from the center of the plate thickness, and the average value is adopted as the average crystal grain size.

[0051] In the stainless steel of this embodiment, the magnetostrictive amplitude at a magnetic field strength of ±10 kОe is in the range of 15 μm / m or more. When the magnetostrictive amplitude is 15 μm / m or more, the vibration damping property is improved. The magnetostriction important for the manifestation of vibration damping properties can be measured by a method called the strain gauge method, in which a strain gauge is attached to the surface of a sample to measure the deformation due to magnetostriction. Specifically, using "BHSZ-01" manufactured by Riken Denshi Co., Ltd. as a magnetic measurement device and "KFGS-5-120-C1-11 L50C2R (resistance value 120 Ω, gauge length 5 mm)" manufactured by Kyowa Electronic Instruments Co., Ltd. as a strain gauge, the magnetic field strength is changed up to ±10 kОe between the yokes of an electromagnet to measure the magnetostriction. When the maximum value - minimum value of the elongation due to magnetostriction is defined as the magnetostriction amplitude, if this magnetostriction amplitude is 15 μm / m or more, the vibration damping property is improved. The magnetostriction amplitude is desirably 20 μm / m or more, more desirably 30 μm / m or more.

[0052] Also, the internal friction, which is one of the indices of vibration damping properties, is measured by applying bending vibration to the sample at room temperature using the half-width method (resonance method). This is a method that utilizes the fact that the energy distribution of internal friction appears as a frequency distribution centered on the natural vibration. The internal friction Q -1 is calculated using the following formula (1).

[0053] Q -1 = 1 / √3 × (ω2 - ω1) / ω0…(1)

[0054] In the above formula (1), Q -1 , ω2, ω1, and ω0 are as follows. Q -1 : Internal friction ω0: Natural frequency ω1: When the displacement intensity of the sample at the natural frequency is V0, the frequency at which it becomes V0 / 2 (low frequency side) ω2: When the displacement intensity of the sample at the natural frequency is V0, the frequency at which it becomes V0 / 2 (high frequency side)

[0055] Steel with an internal friction of 0.0030 or more exhibits excellent vibration damping properties. The internal friction is desirably 0.0040 or more, more desirably 0.0050 or more.

[0056] The loss factor, like internal friction, is one of the evaluation indices for vibration damping properties. The loss factor is measured by the "central excitation method" in JIS K 7391:2008 "Test Method for Vibration Damping Characteristics of Unrestrained Vibration Damping Composite Beams". This method is a technique in which the central part of the test piece is fixed with a contact chip and excited through an impedance head, and the mechanical impedance (force / velocity) is obtained from the force signal and acceleration signal output from the impedance head (the velocity is calculated by integrating the acceleration). Then, the loss factor within the range of 800 to 2000 Hz, especially among the anti-resonant frequencies where the mechanical impedance peaks, is calculated.

[0057] Steel grades with a loss factor of 0.0010 or more exhibit excellent vibration damping properties. The loss factor is preferably 0.0015 or more, and more preferably 0.0020 or more.

[0058] In the method for manufacturing the stainless steel of the present embodiment, basically, a general method for manufacturing a steel sheet made of ferritic stainless steel is applied. For example, molten steel having the above chemical composition is prepared in a converter or an electric furnace and refined in an AOD furnace, a VOD furnace, or the like. Then, it is formed into a steel slab by a continuous casting method or an ingot-making method, and then, through the steps of hot rolling - annealing of the hot-rolled sheet - pickling - cold rolling - finish annealing - pickling, the stainless steel of the present embodiment is manufactured. If necessary, the annealing of the hot-rolled sheet may be omitted, or cold rolling - finish annealing - pickling may be repeated. Surface grinding may be performed between each step.

[0059] However, in order to keep the average crystal grain size within the scope of the present invention, the finish annealing process conditions must be strictly controlled.

[0060] As the finish annealing conditions, as described above, the annealing temperature is set to be 900°C or higher and lower than 1000°C. When the annealing temperature is lower than 900°C, the average crystal grain size becomes small and the desired vibration damping property cannot be obtained. On the other hand, when the annealing temperature is 1000°C or higher, the average crystal grain size becomes excessively large, and there is a risk that the manufacturability and workability (especially toughness) will decrease. For example, when the annealing temperature is excessively high, scale is formed thickly and densely, and the removal of scale in subsequent pickling becomes insufficient, making it difficult to perform temper rolling in some cases. From the above, the annealing temperature is 900°C or higher and lower than 1000°C, preferably 950 - 980°C.

[0061] When the annealing time of finish annealing is too long, there is a risk that the average crystal grain size becomes excessively large or scale is formed thickly and densely, resulting in a decrease in descaling property. Therefore, the annealing time is set to 150 seconds or less. Preferably, it is 120 seconds or less. However, if the annealing time is too short, the average crystal grain size becomes small and the desired vibration damping property cannot be obtained. Therefore, it is desirable that the annealing time is 2 seconds or more.

[0062] Also, the average heating rate up to the aforementioned annealing temperature, as well as the average cooling rate after annealing, are preferably controlled from the viewpoint of optimizing the average crystal grain size. Specifically, from the viewpoint of suppressing excessive growth of the average crystal grain size, it is desirable that the average heating rate is 15°C / second or more, more preferably 20°C / second or more. On the other hand, if the average heating rate is excessively large, there is a risk of becoming too fine-grained. Therefore, it is desirable that it is 1000°C / second or less. The average cooling rate after annealing is also preferably controlled from the viewpoint of suppressing excessive growth of the average crystal grain size. Specifically, the average cooling rate is preferably 15°C / second or more, more preferably 20°C / second or more. On the other hand, if the average cooling rate is excessively large, there is a risk that the shape of the product will change. Therefore, it is desirable that it is 500°C / second or less. The cooling stop temperature is not particularly limited, but it may be in the range of 25 - 400°C.

[0063] Here, the "average heating rate" in the present embodiment is defined as the value obtained by dividing the temperature rise range of the steel from the start of heating to the aforementioned annealing temperature by the required time from the start of heating to the aforementioned annealing temperature. Also, the "average cooling rate" is defined as the value obtained by dividing the temperature drop range of the steel from the start of cooling (annealing temperature) to the end of cooling by the required time from the start of cooling to the end of cooling.

[0064] By annealing under the conditions described above, the average crystal grain size can be kept within the scope of the present invention.

[0065] After finish annealing, scale is removed by pickling, but the pickling conditions at that time are not particularly limited. For example, pickling is performed in a solution containing 50 g / L or more of nitric acid. The solution may further appropriately contain sodium nitrate, sulfuric acid, sodium sulfate, hydrochloric acid, hydrofluoric acid, etc. Further, each acid may be present in the same solution, or pickling may be sequentially performed in multiple tanks. When pickling is sequentially performed in multiple tanks, the order of using the acids is not particularly limited and may be any order. The pickling method may be electrolytic pickling or pickling by immersion only. The nitric acid content is desirably 60 g / L or more, more desirably 70 g / L or more. The total pickling time is 1 second or more.

[0066] Also, salt immersion may be performed before pickling. In that case, the salt immersion may be carried out by immersing the steel after finish annealing in a molten salt mixture of NaNO3 and NaOH for 1 to 60 seconds.

[0067] In addition, when cold rolling - finish annealing - pickling is repeatedly performed, the conditions of the last finish annealing process and the last pickling process may be strictly controlled as described above, and there is no particular need to limit the conditions of the other finish annealing processes and pickling processes.

[0068] The manufacturing method of the process other than the processes described above is not particularly specified, but for example, after finish annealing, a temper rolling, a tension leveler, or a polishing process may be provided as necessary.

[0069] The above describes the stainless steel of this embodiment. However, its dimensions and form are not particularly limited, and it may be a steel material shaped into a desired shape. For example, the stainless steel of this embodiment may be a steel plate, a steel bar, or a wire rod. When the form is a steel plate, its thickness is not particularly limited, but from the perspective of manufacturability, it is preferably 0.1 mm to 10 mm.

Example

[0070] In order to confirm the effects of the present invention in detail, the following experiments were conducted. Note that this example shows one example of the present invention, and the present invention is not limited to the following configuration.

[0071] Steel with the composition shown in Table 1 was melted, hot-rolled until the plate thickness reached 4 mm, and then pickled. Subsequently, cold rolling was performed until the plate thickness reached 0.8 mm, and finish annealing was carried out at 850 °C to 1090 °C. The annealing atmosphere was air, the heating rate was 20 °C / second, the annealing time was 120 seconds, and the cooling rate was 20 °C / second.

[0072] Next, salt immersion and electrolytic pickling were performed. Salt immersion was carried out using a molten NaOH salt (60 mass%: NaOH + 40 mass%: NaNO3) mixed with NaNO3 and NaOH. The immersion time was 10 seconds, and the bath temperature was 480 °C. Electrolytic pickling was performed in a solution with a temperature of 60 °C and a nitric acid concentration of 50 g / L. The electrolysis conditions were an anode of 30 A / dm 2 , a cathode of 60 A / dm 2 , and an alternating current electrolysis for a total of 6.0 s. After pickling, temper rolling was performed to obtain a final steel plate (stainless steel plate).

[0073] A test piece with a length of 30 mm and a width of 20 mm was cut out from the fabricated steel plate, embedded in resin so that a cross-sectional structure parallel to the rolling direction and perpendicular to the steel plate surface could be observed, and mirror polishing and etching were performed. Subsequently, measurements were carried out in accordance with the cutting method of JIS G 0551:2020. The measurements were taken 5 times from the center of the plate thickness, and the average value was adopted as the average crystal grain size.

[0074] Also, from the produced steel plate, test pieces with a width of 8 mm and a length of 10 mm were cut out so that the rolling direction was the longitudinal direction of the test piece, and magnetostriction measurement was performed. The magnetostriction measurement was carried out by a method called the strain gauge method, in which a strain gauge was attached to the surface of the sample to measure the deformation due to magnetostriction. As the magnetic measurement device, "BHSZ-01" manufactured by Riken Denshi Co., Ltd. was used, and as the strain gauge, "KFGS-5-120-C1-11 L50C2R (resistance value 120 Ω, gauge length 5 mm)" was used. The magnetic field strength was changed from ±10 kОe between the yokes of the electromagnet to measure magnetostriction. The said measurement was carried out 5 times (test n number: 5 times), and the average value of the maximum value - minimum value of the elongation due to magnetostriction in each measurement was defined as the "magnetostriction amplitude (μm / m)".

[0075] Also, from the produced steel plate, test pieces with a length of 60 mm and a width of 10 mm were cut out so that the rolling direction was the longitudinal direction of the test piece, and internal friction was measured using a JE2-RT type room temperature Young's modulus measuring device manufactured by Nippon Technoplas Co., Ltd. The internal friction was measured at room temperature by applying bending vibration to the test piece and using the half-width method (resonance method). This is a method that utilizes the fact that the energy distribution of internal friction appears as a frequency distribution centered on the natural vibration. -1 was calculated using the following formula.

[0076] Q -1 =1 / √3×(ω2 - ω1) / ω0…(2)

[0077] Q -1 , ω2, ω1, ω0 are as follows respectively. Q -1 : Internal friction ω0: Natural frequency ω1: When the displacement intensity of the sample at the natural frequency is V0, the frequency at which it becomes V0 / 2 (low frequency side) ω2: When the displacement intensity of the sample at the natural frequency is V0, the frequency at which it becomes V0 / 2 (high frequency side)

[0078] A test piece with a length of 250 mm and a width of 10 mm was cut out from the fabricated steel plate by electrical discharge machining, and the loss coefficient was measured. The loss coefficient was measured by the "central excitation method" of JIS K 7391:2008 "Test method for vibration damping characteristics of unconstrained vibration damping composite beams". This method is a method of fixing the central part of the test piece with a contact tip and exciting it through an impedance head. The mechanical impedance (force / velocity) was obtained from the force signal and acceleration signal output from the impedance head (the velocity was calculated by integrating the acceleration). Then, the loss coefficient within the range of 800 to 2000 Hz, especially among the anti-resonant frequencies at which the mechanical impedance peaks, was calculated.

[0079] The experimental results are shown in Table 2. Regarding the average crystal grain size, when the annealing temperature was 900 °C or higher and less than 1000 °C, the average crystal grain size of the steel plate was 60 μm or more and less than 200 μm, resulting in excellent vibration damping performance.

[0080] On the other hand, when the annealing temperature was less than 900 °C, the average crystal grain size of the steel plates (No. B8 to B11) was less than 60 μm in all cases, and the vibration damping performance was inferior. The average crystal grain size of the steel plates (No. B12 to B15) with an annealing temperature of 1000 °C or higher was 200 μm or more in all cases. Also, in these steel plates, since a very thick scale was formed, sufficient descaling could not be performed, and subsequent temper rolling could not be carried out.

[0081] Regarding the magnetostrictive amplitude, the magnetostrictive amplitude of the example of the present invention was 15 μm / m or more, while the steel grades with less than 0.3% Al and the steel grades with an average crystal grain size of less than 60 μm were less than 15 μm.

[0082] Regarding the internal friction, the internal friction of the example of the present invention was 0.0030 or more, while the steel grades with a magnetostrictive amplitude of less than 15 μm / m were less than 0.0030.

[0083] Regarding the loss coefficient, the loss coefficient of the example of the present invention was 0.0010 or more, while the steel grades with a magnetostrictive amplitude of less than 15 μm / m were less than 0.0010.

[0084]

Table 1

[0085]

Table 2

Industrial Applicability

[0086] The stainless steel of the present invention is suitable as a member used for stainless steel used in applications that require vibration damping properties. Applications that require vibration damping properties include building materials, general furniture, home appliance applications, cover applications such as hard disks, fuel cells, automotive exhaust system parts, and other automotive parts. Examples of automotive exhaust system parts include mufflers, exhaust manifolds, center pipes, catalytic converters, EGR coolers, flexible pipes, flanges, etc. Other automotive parts include moldings, fuel supply pipes, battery parts (cases, cells, packs, modules, etc.), fastening parts (clamps, V-bands, etc.), etc.

Claims

1. By mass percentage C: 0.001 - 0.030%, Si: 0.01 - 5.00%, Mn: 0.01 - 1.00%, P: ≤0.050%, S: ≤0.0100%, Cr: 9.0 - 30.0%, Ni: 0.01 - 3.00%, Al: 0.30 - 5.00%, N: 0.001 - 0.050%, B: 0.0001 - 0.0050% are contained, Furthermore, either one or both of Ti and Nb are each contained in the range of 0.01 - 1.00%, The balance is iron and impurities, The average crystal grain size is 60 μm or more and less than 200 μm, The magnetostrictive amplitude at a magnetic field strength of ±10 kОe is 15 μm / m or more, The internal friction is 0.0030 or more, A stainless steel characterized in that the loss coefficient is 0.0010 or more.

2. By mass percentage C: 0.001 - 0.030%, Si: 0.01 - 2.00%, Mn: 0.01 - 1.00%, P: ≤0.050%, S: ≤0.0100%, Cr: 10.5 - 20.0%, Ni: 0.01 - 3.00%, Al: 0.30 - 3.50%, N: 0.001 - 0.050%, B: 0.0001 - 0.0050% are contained, Furthermore, either one or both of Ti and Nb are each contained in the range of 0.01 - 1.00%, The balance is iron and impurities, The average crystal grain size is 60 μm or more and less than 200 μm, The magnetostrictive amplitude at a magnetic field strength of ±10 kОe is 15 μm / m or more, The internal friction is 0.0030 or more, A stainless steel characterized in that the loss coefficient is 0.0010 or more.

3. Furthermore, by mass percentage, Mo: 0.01 - 3.00%, Sn: 0.01 - 3.00%, Cu: 0.01 - 0.50%, W: 0.001 - 1.000%, V: 0.001 - 1.000%, Sb: 0.001 - 0.100%, Co: 0.001 - 0.500%, Ca: 0.0001 - 0.0050%, Mg: 0.0001 - 0.0050%, Zr: 0.0001 - 0.0300%, Ga: 0.0001 - 0.0100%, Ta: 0.001 - 0.050%, REM: 0.001 - 0.100% The stainless steel according to claim 1 or 2, characterized by containing one or more of them.

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