JP7709249B2 - stainless steel - Google Patents

Description

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

Applications requiring vibration damping properties include, for example, building materials, general furniture, home appliances, covers for hard disks, fuel cells, automobile exhaust system parts, and other automobile parts. Examples of automobile exhaust system parts include mufflers, exhaust manifolds, center pipes, catalytic converters, EGR coolers, flexible pipes, and flanges. Other automobile parts include, for example, moldings, fuel filler pipes, battery parts (cases, cells, packs, modules, etc.), and fastening parts (clamps, V-bands, etc.).

In recent years, automobile exhaust system parts have been required to have vibration-damping properties. There has been an increasing need to reduce noise caused by automobile engine vibrations and exhaust gases, and noise reduction cannot be achieved by simply modifying the structure of automobile exhaust system parts. For this reason, it would be extremely effective if the stainless steel used in automobile exhaust system parts itself had the ability to absorb vibrations.

Patent document 1 lists the following composition 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: 0-0.3 %, Co: 0-0.6%, REM (rare earth elements): 0-0.1%, Ca: 0-0.1%, balance Fe and unavoidable impurities, the matrix is a single ferritic phase, the metal structure has an average crystal grain size of 0.3-3.0 mm, and the residual magnetic flux density is 45 mT or less.

Patent document 2 lists the following composition by 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. The chemical composition of the material is 0.3%, Co: 0-0.6%, REM (rare earth elements): 0-0.1%, Ca: 0-0.1%, the balance being Fe and unavoidable impurities, the matrix is a single ferrite phase, the metal structure has a ferrite crystal grain average grain size of 0.3-3.0 mm, and the residual magnetic flux density is 45 mT or less.

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

JP 2017-39955 A JP 2017-39956 A JP 2021-4384 A

However, in the technology described in Patent Document 1, vibration-damping properties are exhibited by heating at high temperatures during final annealing so that the average crystal grain size becomes very large, at 0.3 mm or more, but there is a problem that the toughness is inferior because the crystal grain size is coarse. Also, the Al content required for exhibiting vibration-damping properties is low.
In addition, in the technology described in Patent Document 2, vibration-damping properties are exhibited by heating at high temperatures so that the average crystal grain size becomes very large, at 0.3 mm or more. However, since the crystal grain size is coarse, there is an issue that toughness is inferior.
In addition, in the technology described in Patent Document 3, the corrosion resistance and vibration damping properties are improved by including Al and Si, but the value of internal friction, which is a characteristic value of the vibration damping properties, is low, and the vibration damping properties are insufficient.
As described above, with conventional techniques, it has not been possible to improve vibration-damping properties without excessively coarsening the crystal grain size.

The present invention was made to solve these problems, and aims to provide a stainless steel that has excellent vibration damping properties when used in applications that require vibration damping properties.

In order to solve the above-mentioned problems, the inventors produced steels containing various elements and having various crystal grain sizes. They then investigated whether it would be possible to dramatically improve the vibration-damping properties of stainless steels. As a result, they discovered that by adding 0.3% or more of Al and optimizing the manufacturing process to make the crystal grain size 60 to less than 200 μm, the magnetostriction amplitude of the stainless steel at a magnetic field strength of ±10 kOe becomes 15 μm/m or more, dramatically improving the vibration-damping properties.

In other words, the present invention was completed based on the above findings, and the gist of the present invention, which aims to solve the above problems, is as follows.

[1] C: 0.001 to 0.030% by mass,
Si: 0.01-5.00%,
Mn: 0.01-1.00%,
P:≦0.050%,
S:≦0.0100%,
Cr: 9.0-30.0%,
Ni: 0.01 to 3.00%,
Al: 0.30-5.00%,
N: 0.001 to 0.050%,
B: 0.0001 to 0.0050%;
Further, either or both of Ti and Nb are contained in the range of 0.01 to 1.00%,
The balance is 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 kOe is 15 μm/m.
The internal friction is 0.0030 or more,
A stainless steel characterized by having a loss factor of 0.0010 or more.
[2] C: 0.001 to 0.030% by mass,
Si: 0.01-2.00%,
Mn: 0.01-1.00%,
P:≦0.050%,
S:≦0.0100%,
Cr: 10.5-20.0%,
Ni: 0.01 to 3.00%,
Al: 0.30-3.50%,
N: 0.001 to 0.050%,
B: 0.0001 to 0.0050%;
Further, either or both of Ti and Nb are contained in the range of 0.01 to 1.00%,
The balance is 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 kOe is 15 μm/m or more,
The internal friction is 0.0030 or more,
A stainless steel characterized by having a loss factor of 0.0010 or more.
[3] Further, in mass%,
Mo: 0.01-3.00%,
Sn: 0.01-3.00%,
Cu: 0.01 to 0.50%,
W: 0.001-1.000%,
V: 0.001-1.000%,
Sb: 0.001 to 0.100%,
Co: 0.001 to 0.500%,
Ca: 0.0001-0.0050%,
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: 0.001~0.100%
The stainless steel according to [1] or [2], characterized in that it contains one or more of the following:

The present invention provides stainless steel with excellent vibration damping properties when used in applications that require vibration damping properties.

The following describes in detail the embodiments of the present invention.

The inventors produced steel containing various concentrations of Al in order to improve corrosion resistance and vibration damping. They then investigated the effects of Al concentration and crystal grain size on the vibration damping properties of the steel. As a result, they found that by setting the Al content of the steel to 0.30% or more and the average crystal grain size to 60 μm or more and less than 200 μm, the magnetostriction amplitude of the steel becomes large at 15 μm/m or more, and the internal friction, which is an index of vibration damping properties, becomes very large at 0.0030 or more and the loss factor becomes very large at 0.0010 or more.

Al also has the effect of increasing magnetostriction, and it was found that the threshold amount of Al that significantly exhibits vibration damping properties is 0.30% or more.

It is known that the larger the average crystal grain size, the more effective it is in expressing vibration-damping properties, but if the average crystal grain size is made too large, manufacturability and workability are reduced. The inventors of the present invention therefore investigated a method for expressing vibration-damping properties without reducing manufacturability and workability, and discovered that by increasing the magnetostriction of the steel composition system itself by adding 0.30% or more of Al, there is no need to make the average crystal grain size excessively coarse. Specifically, if the steel contains 0.30% or more of Al, excellent vibration-damping properties can be obtained without excessively coarsening the crystal grains (i.e., without reducing manufacturability and workability). More specifically, very excellent vibration-damping properties are expressed 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.

In addition, in order to manufacture steel (the steel of the present invention) having the above characteristics (particularly the average grain size), the conditions of the finish annealing process (cold-rolled sheet annealing process) are extremely important. Specifically, with regard to the annealing conditions, the average 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 to 980°C, and the annealing time to 150 seconds or less, preferably 120 seconds or less.

The chemical composition of the stainless steel according to this embodiment is described in more detail below. In this specification, unless otherwise noted, the percentage of element content means mass percent. In addition, the stainless steel according to this embodiment is a ferritic stainless steel.

C: 0.001-0.030%
C reduces intergranular corrosion resistance and workability, so its content must be kept low. Therefore, the upper limit of the C content is set to 0.030% or less. However, excessively lowering 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 to 0.030%, and the more preferred range is 0.003 to 0.010%.

Si: 0.01-5.00%
Silicon is a very useful element that not only inhibits corrosion by concentrating on the steel surface, but also reduces the corrosion rate of the base material. Silicon also improves the vibration damping properties of steel. Therefore, the lower limit of the silicon content is set to 0.01% or more. However, excessive silicon content reduces the elongation of steel, lowers workability, and also reduces corrosion resistance. Excessive silicon content also increases hardness, causing surface defects, which then cause rusting. Therefore, the upper limit of silicon content is set to 5.00% or less. The preferred range of silicon content is 0.10-2.00%, more preferably 0.20-1.80%, and even more preferably 0.30-1.50%.

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

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. A more preferable range of the P content is 0.030% or less. However, since excessively lowering the P content increases refining costs, the lower limit of the P content may be set to 0.001% or more.

S: 0.0100% or less S is an element that deteriorates corrosion resistance, so its content must be limited. 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, since excessively lowering the S content increases refining costs, the lower limit of the S content may be set to 0.0001% or more.

Cr:9.0~30.0%
A Cr content of 9.0% or more is necessary to ensure corrosion resistance in salt damage environments. The higher the Cr content, the better the corrosion resistance, but the worse the workability and manufacturability. Therefore, the upper limit of the Cr content is set to 30.0% or less. The preferred range of the Cr content is 10.5 to 25.0%, more preferably 10.5 to 20.0%, even more preferably 11.0 to 20.0%, and even more preferably 11.5 to 18.0%.

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, since a large amount of Ni content leads to an increase in alloy cost, the upper limit of the Ni content is set to 3.00% or less. The Ni content is preferably in the range of 0.02 to 2.50%, more preferably in the range of 0.05 to 2.00%, and even more preferably in the range of 0.10 to 1.50%.

Either or both of Ti and Nb are 0.01 to 1.00%
In order to prevent sensitization of stainless steel, it is necessary to contain at least 0.01% of either Ti or Nb.
If the Ti content is less than 0.01%, sensitization occurs and the corrosion resistance deteriorates. However, a large amount of Ti content leads to an increase in alloy cost, a decrease in toughness, and an increase in inclusions in the steel, which leads to a decrease in corrosion resistance and a decrease in manufacturability, so the upper limit of the Ti content is set to 1.00%. The preferred range of the Ti content is 0.03 to 0.50%, and the more preferred range is 0.10 to 0.25%.

Nb is also a useful element for preventing sensitization of stainless steel. It is also useful for improving high-temperature strength and intergranular corrosion resistance of welds. However, excessive Nb content reduces workability and manufacturability. Therefore, the Nb content is set to 0.01 to 1.00%. The preferred range of Nb content is 0.05 to 0.50%.

Al: 0.30-5.00%
Al is an important element in this embodiment. Al has the effect of increasing magnetostriction and making the vibration-damping property more pronounced. Therefore, the lower limit of the Al content is set to 0.30% or more. However, excessive Al content reduces the elongation of the material and reduces the workability. In addition, excessive Al content increases the hardness, causing surface defects, which in turn cause rusting. 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 to 3.80%, more preferably 0.80 to 3.50%, and even more preferably 1.00 to 3.20%.

N: 0.001-0.050%
N is a useful element for pitting corrosion resistance, but it also 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 refining costs, 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 to 0.020%.

B: 0.0001-0.0050%
B is an element useful for improving secondary workability, and may be contained in an amount of 0.0050% or less. The lower limit of the B content is set to 0.0001% or more, at which a stable effect can be obtained. The preferred range of the B content is 0.0005 to 0.0040%.

The above is the basic chemical composition of the stainless steel of this embodiment, with the remainder being iron and impurities, but in this embodiment, the following elements can also be added as necessary.

Mo, Sn, Cu, W, V, Sb, Co, Ca, Mg, Zr, Ga, Ta, and REM may be contained alone or in combination depending on the purpose. The lower limit of these elements is 0% or more, and preferably more than 0%.

Mo: 0.01~3.00%
Mo can be contained in an amount of 0.01% or more to improve corrosion resistance. However, excessive content of Mo deteriorates workability and is expensive, leading to increased costs. Therefore, the upper limit of Mo content is set to 3.00% or less. The preferred range of Mo content is 0.05 to 1.00%.

Sn: 0.01-3.00%
Sn can be contained in an amount of 0.01% or more to improve corrosion resistance. However, excessive content leads to increased costs. Therefore, the upper limit of the Sn content is set to 3.00% or less. The preferred range of the Sn content is 0.05 to 1.00%.

Cu: 0.01~0.50%
Cu can be contained in an amount of 0.01% or more to improve corrosion resistance. However, excessive content leads to increased costs. Therefore, the upper limit of the Cu content is set to 0.50% or less. The preferred range of the Cu content is 0.02 to 0.40%, and the more preferred range is 0.05 to 0.30%.

W: 0.001-1.000%
W can be added in an amount of 0.001% or more to improve corrosion resistance. However, excessive addition of W reduces workability and manufacturability, so the upper limit is set to 1.000%. The preferred range of W content is 0.005 to 0.800%.

V:0.001~1.000%
V can be added in an amount of 0.001% or more to improve corrosion resistance. However, excessive addition of V reduces workability and manufacturability, so the upper limit is set to 1.000%. The preferred range of V content is 0.005 to 0.500%.

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 of Sb reduces workability and manufacturability, so the upper limit is set to 0.100%. The preferred range of Sb content is 0.010 to 0.080%.

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, since excessive addition reduces workability, the upper limit is set to 0.500% or less. The preferred range of Co content is 0.010 to 0.300%.

Ca: 0.0001-0.0050%
Ca is contained for desulfurization, but if contained in excess, water-soluble inclusions CaS are formed, which reduces corrosion resistance. Therefore, Ca can be contained in the range of 0.0001 to 0.0050%. The preferred range of Ca content is 0.0005 to 0.0030%.

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, since excessive addition reduces corrosion resistance, the upper limit is set to 0.0050% or less. The preferred range of Mg content is 0.0005 to 0.0030%.

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 of Zr reduces workability and manufacturability, so the upper limit is set to 0.0300% or less. The preferred range of Zr content is 0.0010 to 0.0100%.

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

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

REM: 0.001~0.100%
REM has a deoxidizing effect and is useful in refining, so it can be contained in an amount of 0.001% or more. However, excessive addition reduces workability and manufacturability, so the upper limit is set to 0.100% or less. The preferred range of REM content is 0.003 to 0.050%.

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

The stainless steel of this embodiment is composed of Fe and impurities (including unavoidable impurities) in addition to the elements described above, but other elements can also be included within the range that does not impair the effects of the present invention.

In addition, scrap raw materials are often used in the production of stainless steel. For this reason, various impurity elements are inevitably mixed into stainless steel. It is difficult to determine the content of the impurity elements in a univocal manner. Therefore, in the present invention, impurities refer to elements contained in amounts that do not impair the effects of the present invention.

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 making the average crystal grain size 60 μm or more, it is possible to prevent the deterioration of the mechanical properties of the steel while making the internal friction and loss factor large. In addition, by making the average crystal grain size less than 200 μm, it is possible to make the internal friction and loss factor high without excessively decreasing the workability and manufacturability, and to improve the vibration damping properties.
The average 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 steel (e.g., steel plate), embedded in resin so that the 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, the measurement is performed according to the cutting method of JIS G 0551:2020. The measurement is performed from the center of the plate thickness with a test number n (number of fields of view): 5, and the average value is adopted as the average grain size.

In the stainless steel of this embodiment, the magnetostriction amplitude is in the range of 15 μm/m or more at a magnetic field strength of ±10 kOe. When the magnetostriction amplitude is 15 μm/m or more, vibration damping properties are improved.
Magnetostriction, which is important for vibration-damping, 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 deformation due to magnetostriction. Specifically, a magnetic measuring device "BHSZ-01" manufactured by Riken Denshi Co., Ltd. and a strain gauge "KFGS-5-120-C1-11 L50C2R (resistance value 120Ω, gauge length 5mm)" manufactured by Kyowa Electric Industry Co., Ltd. are used to measure magnetostriction by changing the magnetic field strength between the yokes of the electromagnets up to ±10 kOe. When the magnetostriction amplitude is defined as the maximum value-minimum value of the elongation due to magnetostriction, if this magnetostriction amplitude is 15 μm/m or more, vibration-damping properties are improved. The magnetostriction amplitude is preferably 20 μm/m or more, more preferably 30 μm/m or more.

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

Q ^-1 = 1/√3 × (ω ₂ - ω ₁ )/ω ₀ ... (1)

In the above formula (1), Q ⁻¹ , ω ₂ , ω ₁ , and ω ₀ are as follows.
Q ^-1 : Internal friction _ω0 : Natural frequency _ω1 : Frequency (low frequency side) at which the displacement strength of the sample at the natural frequency is _V0 /2 when _V0 is the displacement strength of the sample at the natural frequency
_ω2 : When the displacement strength of the sample at the natural frequency is _V0 , the frequency (high frequency side) at which it becomes _V0 /2

Steel with an internal friction of 0.0030 or more exhibits excellent vibration damping properties. The internal friction is preferably 0.0040 or more, and more preferably 0.0050 or more.

The loss factor, like internal friction, is one of the evaluation indices for vibration damping. The loss factor is measured using the "central excitation method" of JIS K 7391:2008 "Test method for vibration damping characteristics of unconstrained vibration-damping composite beams." In this method, the center of the test piece is fixed with a contact tip and vibration is applied via an impedance head, and the mechanical impedance (force/velocity) is calculated from the force signal and acceleration signal output from the impedance head (velocity is calculated by integrating acceleration). The loss factor is then calculated for the anti-resonance frequencies at which the mechanical impedance peaks, particularly in the range of 800 to 2000 Hz.

Steels 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.

In the manufacturing method of the stainless steel of this embodiment, a general method for manufacturing a steel sheet made of ferritic stainless steel is basically applied. For example, molten steel having the above-mentioned chemical composition is prepared in a converter or electric furnace, and refined in an AOD furnace, VOD furnace, or the like. After that, it is made into a steel billet by a continuous casting method or an ingot casting method, and then goes through the steps of hot rolling - annealing of the hot rolled sheet - pickling - cold rolling - finish annealing - pickling to manufacture the stainless steel of this embodiment. If necessary, the annealing of the hot rolled sheet may be omitted, or the cold rolling - finish annealing - pickling may be repeated. Surface grinding may be performed between each step.

However, in order to keep the average crystal grain size within the range of this invention, the conditions of the final annealing process must be strictly controlled.

As described above, the final annealing conditions are an annealing temperature of 900°C or more and less than 1000°C. If the annealing temperature is less than 900°C, the average crystal grain size will be small and the desired vibration damping properties will not be obtained. On the other hand, if the annealing temperature is 1000°C or more, the average crystal grain size will be excessively large, which may result in a decrease in manufacturability and workability (especially toughness). For example, if the annealing temperature is excessively high, thick and dense scale will be formed, which may result in insufficient removal of the scale in the subsequent pickling, making adjustment rolling difficult. For these reasons, the annealing temperature is set to 900°C or more and less than 1000°C, preferably 950 to 980°C.

If the annealing time for the final annealing is too long, the average crystal grain size may become excessively large or the scale may become thick and dense, resulting in poor descaling properties. Therefore, the annealing time is set to 150 seconds or less. A time of 120 seconds or less is preferable. However, if the annealing time is too short, the average crystal grain size will become small and the desired vibration damping properties will not be obtained. Therefore, the annealing time is preferably set to 2 seconds or more.

In addition, the average heating rate up to the annealing temperature and 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, the average heating rate is preferably 15° C./sec or more, more preferably 20° C./sec or more. On the other hand, if the average heating rate is too large, there is a risk of the grains becoming too fine. Therefore, it is preferable to set the average heating rate to 1000° C./sec or less.
The average cooling rate after annealing is also preferably 15°C/sec or more, more preferably 20°C/sec or more, from the viewpoint of suppressing excessive growth of the average crystal grain size. On the other hand, if the average cooling rate is too high, the shape of the product may change. Therefore, it is preferable to set the cooling rate to 500°C/sec or less. The cooling stop temperature is not particularly limited, but may be in the range of 25 to 400°C.

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

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

After the finish annealing, the scale is removed by pickling, but there is no particular restriction on the pickling conditions. For example, pickling is performed in a solution containing nitric acid at 50 g/L or more. The solution may further contain sodium nitrate, sulfuric acid, sodium sulfate, hydrochloric acid, hydrofluoric acid, etc. as appropriate. Furthermore, each acid may be present in the same solution, or pickling may be performed sequentially in multiple tanks. When pickling is performed sequentially in multiple tanks, the order in which the acids are used is not particularly limited and may be in any order. The pickling method may be electrolytic pickling or pickling by immersion only. The nitric acid content is preferably 60 g/L or more, more preferably 70 g/L or more. The total pickling time is 1 second or more.

Salt immersion may be performed before pickling. In this case, the salt immersion may be performed by immersing the steel after the finish annealing in a molten salt mixture of _NaNO3 and NaOH for 1 to 60 seconds.

When cold rolling - finish annealing - pickling are repeated, the conditions for the final finish annealing process and the final pickling process should be strictly controlled as described above, and there is no need to restrict the conditions for the other finish annealing processes and pickling processes.

There are no particular restrictions on the manufacturing process other than the steps described above, but for example, after finish annealing, temper rolling, tension leveling, and polishing processes may be added as necessary.

The above describes the stainless steel of this embodiment, but the dimensions and shape are not particularly important, and the steel may be a steel material arranged in 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 stainless steel is in the form of a steel plate, there are no particular limitations on its thickness, but from the viewpoint of manufacturability, it is preferably 0.1 mm to 10 mm.

The following experiment was conducted to confirm the effects of the present invention in detail. Note that this example shows one embodiment of the present invention, and the present invention is not limited to the following configuration.

Steel with the composition shown in Table 1 was melted, hot rolled to a plate thickness of 4 mm, and then pickled. It was then cold rolled to a plate thickness of 0.8 mm, and finish annealed at 850°C to 1090°C. The annealing atmosphere was air, the heating rate was 20°C/sec, the annealing time was 120 seconds, and the cooling rate was 20°C/sec.

Next, salt immersion and electrolytic pickling were performed. Salt immersion was performed using molten NaOH salt (60 mass%:NaOH+40 mass%: _NaNO3 ) which was a mixture of _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 50g/L. The electrolysis conditions were alternating electrolysis with an anode ^of 30A/dm2 and a cathode of 60A/ ^dm2 for a total of 6.0s.
After pickling, the steel plate was subjected to temper rolling to obtain a final steel plate (stainless steel plate).

A test piece measuring 30 mm in length and 20 mm in width was cut out from the prepared steel plate, embedded in resin so that the cross-sectional structure parallel to the rolling direction and perpendicular to the steel plate surface could be observed, and mirror polished and etched. Measurements were then performed according to the cutting method of JIS G 0551:2020. Measurements were performed from the center of the plate thickness for five tests, and the average value was used as the average crystal grain size.

Magnetostriction measurements were also performed on test pieces measuring 8 mm wide and 10 mm long, cut from the prepared steel sheets so that the rolling direction was the longitudinal direction of the test pieces. The magnetostriction measurements were performed using a method known as the strain gauge method, in which a strain gauge is attached to the surface of the sample to measure deformation due to magnetostriction. The magnetic measuring device used was the "BHSZ-01" manufactured by Riken Denshi Co., Ltd., and the strain gauge used was the "KFGS-5-120-C1-11 L50C2R (resistance value 120 Ω, gauge length 5 mm)". Magnetostriction measurements were performed by varying the magnetic field strength between the electromagnet yokes up to ±10 kOe. This measurement was performed five times (test number n: 5 times), and the average of the maximum and minimum values of the elongation due to magnetostriction in each measurement was defined as the "magnetostriction amplitude (μm/m)".

Further, a test piece having a length of 60 mm and a width of 10 mm was cut out from the prepared steel plate so that the rolling direction was the longitudinal direction of the test piece, and the internal friction was measured using a JE2-RT type room temperature Young's modulus measuring device manufactured by Nippon Technoplus Co., Ltd. The internal friction was measured at room temperature by applying bending vibration to the test piece and using the half-value width method (resonance method). This method 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 was calculated using the following formula.

Q ⁻¹ = 1/√3×(ω ₂ −ω ₁ )/ω ₀ …(2)

Q ⁻¹ , ω ₂ , ω ₁ , and ω ₀ in the formula (2) are as follows, respectively.
Q ^-1 : Internal friction _ω0 : Natural frequency _ω1 : Frequency (low frequency side) at which the displacement strength of the sample at the natural frequency is _V0 /2 when _V0 is the displacement strength of the sample at the natural frequency
_ω2 : When the displacement strength of the sample at the natural frequency is _V0 , the frequency (high frequency side) at which it becomes _V0 /2

Test pieces measuring 250 mm in length and 10 mm in width were cut from the prepared steel plate by electrical discharge machining, and the loss factor was measured. The loss factor was measured using the "central excitation method" of JIS K 7391:2008 "Test method for vibration damping characteristics of unconstrained vibration-damping composite beams." In this method, the center of the test piece is fixed with a contact tip and excited via an impedance head, and the mechanical impedance (force/velocity) is calculated from the force signal and acceleration signal output from the impedance head (velocity is calculated by integrating acceleration). The loss factor was then calculated for the anti-resonance frequencies where the mechanical impedance peaks, particularly in the range of 800 to 2000 Hz.

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

On the other hand, in the case of the steel sheets (Nos. B8 to B11) in which the annealing temperature was set to less than 900° C., the average crystal grain size was less than 60 μm, and the vibration-damping properties were inferior.
The average grain size of the steel sheets (Nos. B12 to B15) in which the annealing temperature was 1000° C. or higher was 200 μm or higher. Furthermore, in these steel sheets, the scale formed was very thick, so that sufficient descaling could not be performed, and the subsequent temper rolling could not be performed.

Regarding magnetostriction amplitude, the examples of the present invention were 15 μm/m or more, whereas the steel types with less than 0.3% Al and steel types with an average crystal grain size of less than 60 μm were less than 15 μm.

Regarding internal friction, the examples of the present invention had a value of 0.0030 or more, whereas the steel types with magnetostriction amplitudes of less than 15 μm/m had a value of less than 0.0030.

The loss factor for the example of the present invention was 0.0010 or more, whereas the loss factor for steel types with magnetostriction amplitudes of less than 15 μm/m was less than 0.0010.

The stainless steel of the present invention is suitable as a component for stainless steel used in applications requiring vibration damping. Applications requiring vibration damping include building materials, general furniture, home appliances, covers for hard disks, fuel cells, automobile exhaust system parts, and other automobile parts. Examples of automobile exhaust system parts include mufflers, exhaust manifolds, center pipes, catalytic converters, EGR coolers, flexible pipes, flanges, etc. Other automobile parts include moldings, fuel filler pipes, battery parts (cases, cells, packs, modules, etc.), fastening parts (clamps, V-bands, etc.), etc.

Claims (3)

C in mass%: 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 to 3.00%,
Al: 0.30-5.00%,
N: 0.001 to 0.050%,
B: 0.0001 to 0.0050%;
Further, either or both of Ti and Nb are contained in the range of 0.01 to 1.00%,
The balance is 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 kOe is 15 μm/m or more,
The internal friction is 0.0030 or more,
A stainless steel characterized by having a loss factor of 0.0010 or more. C in mass%: 0.001 to 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 to 3.00%,
Al: 0.30-3.50%,
N: 0.001 to 0.050%,
B: 0.0001 to 0.0050%;
Further, either or both of Ti and Nb are contained in the range of 0.01 to 1.00%,
The balance is 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 kOe is 15 μm/m or more,
The internal friction is 0.0030 or more,
A stainless steel characterized by having a loss factor of 0.0010 or more. Further, in mass%,
Mo: 0.01-3.00%,
Sn: 0.01-3.00%,
Cu: 0.01 to 0.50%,
W: 0.001-1.000%,
V: 0.001-1.000%,
Sb: 0.001 to 0.100%,
Co: 0.001 to 0.500%,
Ca: 0.0001-0.0050%,
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: 0.001~0.100%
3. The stainless steel according to claim 1, further comprising one or more of the following: