Ferritic stainless steel processed product, method for producing the same, and vibration damping member

Abstract

To provide a processed ferritic stainless steel having excellent dimensional accuracy and damping properties.SOLUTION: A processed ferritic stainless steel contains, in mass percentage, C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 10.50-24.00%, N: 0.030% or less, Cu: 1.00% or less, Mo: 2.50% or less, Si: 3.00% or less, Al: 5.00% or less, Nb: 0.50% or less, Ti: 0.50% or less, with a total content of Nb and Ti being 6(C+N) or more (C and N representing the content of C and N respectively), and the balance being Fe and impurities. The processed ferritic stainless steel has an average crystal grain size of 100 μm or more. The crystal grains with a crystal grain size of 20 μm or less constitute at most 10% of all the crystal grains. A processed part includes at least 30% of crystal grains with an intragranular misorientation of 0.05-2°.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a ferrite stainless steel processed product, a method for manufacturing the same, and a vibration damping member.

Background Art

[0002] Hard disk drives (HDDs) are widely used as recording media. In recent years, the number of personal computers (PCs) equipped with solid state drives (SSDs) has been increasing in terms of light weight and read speed. However, with the cloudification of data storage, the demand in data centers has been increasing. In data centers, HDDs with large capacities are generally adopted. In data centers, since many HDDs are installed densely, there are concerns about vibrations caused by the operation of HDDs and resonances caused by powerful cooling fans. In particular, since there is a strong demand for suppressing these vibrations, which are the causes of malfunctions and failures such as HDD read errors, there is also a demand for improving the vibration damping performance of members such as the casings used for HDDs.

[0003] Typical examples of materials having vibration damping properties include rubber and resin. However, rubber and resin have low rigidity and heat dissipation, and it is difficult to apply them to members such as HDD casings. Therefore, a metallic material having vibration damping properties is required.

[0004] Metallic materials having vibration damping properties are roughly classified into composite type, ferromagnetic type, dislocation type, and twin type according to the vibration energy attenuation mechanism. Among these, the ferromagnetic type rearranges magnetic domains in one direction when an external force such as vibration is applied, and the magnetic domains are randomly rearranged when the load is removed. The residual strain at this time can absorb vibration energy and attenuate vibrations.

[0005] As a ferromagnetic metal material, for example, in terms of mass%, it contains 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%, Ti: 0.5% or less, Cu: 0.3% or less, Mo: 0.3% or less, and the balance is Fe and inevitable impurities. It has a metal structure with a matrix of a single ferrite phase, an average crystal grain size of ferrite crystal grains of 0.3 to 3.0 mm, and a residual magnetic flux density of 45 mT or less. A vibration-damping ferrite stainless steel material has been proposed (Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The ferrite stainless steel material of Patent Document 1 exhibits vibration-damping properties by coarsening ferrite crystal grains and controlling its average crystal grain size to 0.3 to 3.0 mm. In particular, when processing into a predetermined member, after processing the ferrite stainless steel material into the member, final annealing is performed by heating and holding at 900 to 1250°C for 10 minutes or more to coarsen the ferrite crystal grains. However, when performing final annealing under the above conditions, the shape of the processed product is likely to collapse, so it has been difficult to manufacture processed products (for example, HDDs, etc.) that require high dimensional accuracy.

[0008] The present invention has been made to solve the above problems, and an object thereof is to provide a ferrite stainless steel processed product excellent in dimensional accuracy and vibration-damping properties, a manufacturing method thereof, and a vibration-damping member.

Means for Solving the Problems

[0009] As a result of intensive research on the processing and properties of ferritic stainless steel, the inventors have found that by controlling the composition, average crystal grain size, the proportion of crystal grains with a crystal grain size of 20 μm or less, and the proportion of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed part, dimensional accuracy and vibration damping properties can be improved. Further, the inventors have also found that by adjusting the heat treatment conditions and processing conditions, the average crystal grain size, the proportion of crystal grains with a crystal grain size of 20 μm or less, and the proportion of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed part can be controlled. The present invention has been completed based on these findings.

[0010] That is, the present invention contains, on a mass basis, C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 10.50 to 24.00%, N: 0.030% or less, Cu: 1.00% or less, Mo: 2.50% or less, Si: 3.00% or less, Al: 5.00% or less, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6(C + N) or more (C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities, the average crystal grain size is 100 μm or more, the proportion of crystal grains with a crystal grain size of 20 μm or less is 10% or less, and is a ferritic stainless steel processed product in which the proportion of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed part is 30% or more.

[0011] Further, the present invention relates to the above-mentioned ferritic stainless steel processed product to manufacturing do method, comprising Based on mass, it contains C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 10.50 - 24.00%, N: 0.030% or less, Cu: 1.00% or less, Mo: 2.50% or less, Si: 3.00% or less, Al: 5.00% or less, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6(C + N) or more (where C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities. A first heat treatment step of heating a ferritic stainless steel material having such a composition at 900 °C or higher for 10 minutes or more, A processing step of machining and / or welding the ferritic stainless steel material obtained in the first heat treatment step with a strain rate of 20% or less to obtain a processed product, A second heat treatment step of heating the processed product obtained in the processing step at 900 - 1100 °C for t1 - t2 [minutes], including the side of is the method. t1 is -0.16×(T - 800) + 42 (where if it is less than 1, it is 1), t2 is -0.45×(T - 800) + 155, and T represents the heat treatment temperature of the second heat treatment step.

[0012] Furthermore, the present invention is a vibration damping member including the processed ferritic stainless steel product.

Effect of the Invention

[0013] According to the present invention, it is possible to provide a processed ferritic stainless steel product excellent in dimensional accuracy and vibration damping property, a manufacturing method thereof, and a vibration damping member.

Embodiment for Carrying out the Invention

[0014] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that those obtained by appropriately making changes, improvements, etc. to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention also fall within the scope of the present invention. In addition, in this specification, the “%” indication regarding components means “mass %” unless otherwise specified.

[0015] (1) Ferritic stainless steel processed product The ferritic stainless steel (hereinafter abbreviated as “stainless steel”) processed product according to an embodiment of the present invention contains C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 10.50 to 24.00%, N: 0.030% or less, Cu: 1.00% or less, Mo: 2.50% or less, Si: 3.00% or less, Al: 5.00% or less, Nb: 0.50% or less, Ti: 0.50% or less, and the total content of Nb and Ti is 6(C + N) or more (C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities.

[0016] Here, in this specification, “stainless steel processed product” means a product obtained by processing a stainless steel material into a desired shape. Therefore, the composition of the stainless steel processed product is basically the same as the composition of the stainless steel material before being processed into the desired shape. The processing method of the stainless steel material is not particularly limited, and examples include machining such as press working, bending working, and deep drawing working, and welding working. Note that “stainless steel material” is a concept including various shapes such as stainless steel strips and stainless steel plates. Also, in this specification, “impurities” means components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when industrially manufacturing a stainless steel processed product or its stainless steel material before processing, and are allowed within a range that does not adversely affect the present invention. For example, impurities include inevitable impurities.

[0017] Further, the stainless steel processed product according to an embodiment of the present invention may further contain at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, and W: 1.00% or less. In addition, the stainless steel processed product according to the embodiment of the present invention may further contain at least one selected from REM: 0.100% or less and Ca: 0.100% or less. Furthermore, the stainless steel processed product according to the embodiment of the present invention may further contain at least one selected from Sn: 0.10% or less and B: 0.010% or less.

[0018] (C: 0.100% or less) C is an element that affects properties such as the intergranular corrosion resistance (sensitization suppression effect) of the stainless steel processed product and the stainless steel material, and the workability of the stainless steel material. If the content of C is too high, the workability of the stainless steel material and the intergranular corrosion resistance of the stainless steel processed product and the stainless steel material will decrease. Therefore, the upper limit value of the content of C is 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit value of the content of C is not particularly limited, but reducing the content of C will lead to an increase in refining cost. Therefore, the lower limit value of the content of C is preferably 0.0005%, preferably 0.001%.

[0019] (Mn: 1.00% or less) Mn is an element useful as a deoxidizing element. If the content of Mn is too high, it is easy to generate MnS which becomes a corrosion initiation point, and the ferrite phase is destabilized. Therefore, the upper limit value of the content of Mn is 1.00%, preferably 0.90%, more preferably 0.80%. On the other hand, the lower limit value of the content of Mn is not particularly limited, but preferably 0.01%, more preferably 0.05%.

[0020] (Ni: 1.00% or less) Ni is an element effective in improving the corrosion resistance and toughness of the stainless steel processed product and the stainless steel material. If the content of Ni is too high, the ferrite phase is destabilized and the manufacturing cost also increases. Therefore, the upper limit value of the content of Ni is 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit value of the content of Ni is not particularly limited, but from the viewpoint of obtaining the above effects, preferably 0.01%, more preferably 0.05%.

[0021] (P: below 0.100%) P is an element that affects properties such as the weldability and workability of stainless steel materials. If the content of P is too high, there is a risk that the above properties will deteriorate. Therefore, the upper limit value of the content of P is 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit value of the content of P is not particularly limited, but reducing the content of P will lead to an increase in refining cost. Therefore, the lower limit value of the content of P is preferably 0.001%, more preferably 0.010%.

[0022] (S: below 0.050%) S is an element that generates MnS which serves as a corrosion initiation point and affects properties such as the toughness of stainless steel processed products and stainless steel materials. If the content of S is too high, there is a risk that the above properties will deteriorate. Therefore, the upper limit value of the content of S is 0.050%, preferably 0.040%, more preferably 0.030%. On the other hand, the lower limit value of the content of S is not particularly limited, but reducing the content of S will lead to an increase in refining cost. Therefore, the lower limit value of the content of S is preferably 0.0001%, more preferably 0.0005%.

[0023] (Cr: 10.50 - 24.00%) Cr is an element effective in improving the corrosion resistance and oxidation resistance of stainless steel processed products and stainless steel materials. If the content of Cr is too high, the toughness of stainless steel processed products and stainless steel materials will decrease, and it will lead to an increase in manufacturing cost. Therefore, the upper limit value of the content of Cr is 24.00%, preferably 23.50%, more preferably 23.00%. On the other hand, if the content of Cr is too low, the above effects may not be fully obtained. Therefore, the lower limit value of the content of Cr is 10.50%, preferably 10.80%, more preferably 11.00%.

[0024] (N: below 0.030%) N is an element that affects properties such as the intergranular corrosion resistance (sensitization suppression effect) of stainless steel processed products and stainless steel materials, and the workability of stainless steel materials. If the N content is too high, the workability of stainless steel materials, and the intergranular corrosion resistance of stainless steel processed products and stainless steel materials will decrease. Therefore, the upper limit value of the N content is 0.030%, preferably 0.028%, more preferably 0.025%. On the other hand, the lower limit value of the N content is not particularly limited, but reducing the N content will lead to an increase in refining costs. Therefore, the lower limit value of the N content is preferably 0.0005%, preferably 0.001%.

[0025] (Cu: 1.00% or less) Cu is an element effective in improving the corrosion resistance of stainless steel processed products and stainless steel materials. If the Cu content is too high, the ferrite phase will become unstable and the manufacturing cost will also increase. Therefore, the upper limit value of the Cu content is 1.00%, preferably 0.70%, more preferably 0.30%. On the other hand, the lower limit value of the Cu content is not particularly limited, but preferably 0.001%, preferably 0.01%.

[0026] (Mo: 2.50% or less) Mo is an element effective in improving the corrosion resistance and oxidation resistance of stainless steel processed products and stainless steel materials. If the Mo content is too high, the workability of stainless steel materials will decrease and the manufacturing cost will increase. Therefore, the upper limit value of the Mo content is 2.50%, preferably 2.00%, more preferably 1.50%. On the other hand, the lower limit value of the Mo content is not particularly limited, but preferably 0.001%, preferably 0.005%.

[0027] (Si: 3.00% or less) Si is an element effective in improving the vibration damping property and corrosion resistance of stainless steel processed products and stainless steel materials. If the Si content is too high, the workability of the stainless steel material and the toughness of the stainless steel processed product and the stainless steel material will decrease. Therefore, the upper limit value of the Si content is 3.00%, preferably 2.50%, more preferably 2.00%. On the other hand, the lower limit value of Si is not particularly limited, but from the viewpoint of stably improving the vibration damping property of the stainless steel processed product and the stainless steel material, it is preferably 0.01%, more preferably 0.05%, and still more preferably 0.10%.

[0028] (Al: 5.00% or less) Al, like Si, is an element effective in improving the vibration damping property and corrosion resistance of stainless steel processed products and stainless steel materials. If the Al content is too high, the toughness of the stainless steel processed product and the stainless steel material will decrease. Therefore, the Al content is 5.00%, preferably 4.50%, more preferably 4.00%. On the other hand, the lower limit value of the Al content is not particularly limited, but from the viewpoint of obtaining the above effects, it is 0.01%, preferably 0.05%, more preferably 0.10%. In addition, since Al forms an oxide film even in an environment with an extremely low oxygen partial pressure, the oxide film grows in the manufacturing process of the stainless steel processed product, and interference colors are likely to occur. Therefore, heat treatment in a high-vacuum atmosphere or pickling after heat treatment that can suppress the growth of the oxide film cannot be performed. When a stainless steel processed product with high design properties such as color tone is required, it is preferably free of Al. Also, from the viewpoint of stably improving the vibration damping property of the stainless steel processed product and the stainless steel material, the total content of Al and Si is preferably 1.00% or more, more preferably 1.20% or more, and still more preferably 1.50% or more.

[0029] (Including Nb: 0.50% or less, Ti: 0.50% or less, and the total content of Nb and Ti: 6(C + N) or more) Nb and Ti are elements that affect the properties such as the intergranular corrosion resistance (sensitization suppression effect) of stainless steel processed products and stainless steel materials. If the Nb content is too high, the workability of the stainless steel material, and the toughness of the stainless steel processed product and the stainless steel material will decrease. Therefore, the upper limit value of the Nb content is 0.50%, preferably 0.48%, more preferably 0.45%. Also, if the Ti content is too high, the workability of the stainless steel material, and the surface quality of the stainless steel processed product and the stainless steel material will decrease. Therefore, the upper limit value of the Ti content is 0.50%, preferably 0.48%, more preferably 0.45%. On the other hand, the lower limit value of the total content of Nb and Ti is controlled in relation to the contents of C and N that reduce intergranular corrosion resistance. Specifically, the lower limit value of the total content of Nb and Ti is 6(C + N), preferably 7(C + N). Here, C and N represent the contents of C and N, respectively.

[0030] (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 elements effective for improving the oxidation resistance of the stainless steel processed product and the stainless steel material. If the contents of Zr, Co, V, and W are too high, the workability of the stainless steel material, and the toughness of the stainless steel processed product and the stainless steel material will decrease, and it will lead to an increase in manufacturing cost. Therefore, the upper limit value of the contents of Zr, Co, V, and W is all 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit value of the contents of Zr, Co, V, and W is not particularly limited, but preferably 0.001%, more preferably 0.01%.

[0031] (REM: 0.100% or less, Ca: 0.100% or less) REM (rare earth elements) and Ca are elements effective in improving the oxidation resistance of stainless steel processed products and stainless steel materials. If the contents of REM and Ca are too high, it will lead to an increase in the manufacturing costs of stainless steel processed products and stainless steel materials. Therefore, the upper limit values of the contents of REM and Ca are both 0.100%, preferably 0.080%, and more preferably 0.050%. On the other hand, the lower limit values of REM and Ca are not particularly limited, but are preferably 0.0001% and more preferably 0.003%. Note that REM refers to the general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu). These may be used alone or as a mixture.

[0032] (Sn: 0.10% or less) Sn is an element effective in improving the corrosion resistance of stainless steel processed products and stainless steel materials. If the content of Sn is too high, Sn will segregate and the manufacturability will decrease. Therefore, the upper limit value of the content of Sn is 0.10%, preferably 0.08%, and more preferably 0.05%. On the other hand, the lower limit value of the content of Sn is not particularly limited, but is preferably 0.001% and more preferably 0.005%.

[0033] (B: 0.010% or less) B is an element effective in improving the secondary workability of stainless steel materials. If the content of B is too high, the fatigue strength of stainless steel processed products and stainless steel materials will decrease. Therefore, the upper limit value of the content of B is 0.010%, preferably 0.008%, and more preferably 0.005%. On the other hand, the lower limit value of the content of B is not particularly limited, but is preferably 0.0001% and more preferably 0.0005%.

[0034] The stainless steel processed product according to an embodiment of the present invention has an average crystal grain size of 100 μm or more, preferably 120 μm or more, more preferably 150 μm or more. By setting the average crystal grain size to 100 μm or more, the number of crystal grain boundaries that hinder the movement of magnetic domains effective for the manifestation of vibration damping properties decreases, so that the vibration damping properties can be improved. The upper limit value of the average crystal grain size is not particularly limited, but is preferably 500 μm, more preferably 450 μm, and still more preferably 400 μm. With such an upper limit value, it is possible to stably suppress the decrease in toughness due to the extreme coarsening of crystal grains. Here, in this specification, the average crystal grain size means the one measured by the method described in the examples described later.

[0035] The stainless steel processed product according to an embodiment of the present invention has a ratio of crystal grains with a crystal grain size of 20 μm or less of 10% or less, preferably 8% or less, more preferably 6% or less. By setting the ratio of crystal grains with a crystal grain size of 20 μm or less to 10% or less, the number of crystal grain boundaries that hinder the movement of magnetic domains effective for the manifestation of vibration damping properties decreases, so that the vibration damping properties can be improved. Note that the ratio of crystal grains with a crystal grain size of 20 μm or less is preferably as small as possible and may be 0%. Here, in this specification, the ratio of crystal grains with a crystal grain size of 20 μm or less means the one measured by the method described in the examples described later.

[0036] The stainless steel processed product according to an embodiment of the present invention has a ratio of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed portion of 30% or more, preferably 32% or more, more preferably 35% or more, still more preferably 38% or more. By setting the ratio of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed portion to 30% or more, the dimensional accuracy can be improved by reducing the strain (residual strain) introduced into the processed portion. The upper limit value of the ratio of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed portion is not particularly limited, but is preferably 70%, more preferably 68%, and still more preferably 65%. Here, in this specification, the "processed part" means the part where the stainless steel material has been processed. Also, the ratio of the crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed part means the one measured by the method described in the examples below.

[0037] The stainless steel processed product according to an embodiment of the present invention has a loss factor η that is preferably 2.0×10 -4 or more, more preferably 5.0×10 -4 or more. By setting the loss factor η within such a range, the desired vibration damping property can be ensured. Note that the upper limit value of the loss factor η is not particularly limited, but generally it is 10.0×10 -3 , preferably 5.0×10 -3 . Here, in this specification, the loss factor η means the one measured by the method described in the examples below.

[0038] The thickness of the stainless steel material constituting the stainless steel processed product according to an 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. Also, the thickness of this stainless steel material is preferably 0.2 mm or more, more preferably 0.3 mm or more.

[0039] (2) Manufacturing method of the stainless steel processed product The manufacturing method of the stainless steel processed product according to an embodiment of the present invention can be carried out according to a method known in the art using a stainless steel material having the above composition. A typical manufacturing method of the stainless steel processed product according to an embodiment of the present invention will be described below.

[0040] The manufacturing method of the stainless steel processed product according to an embodiment of the present invention includes a first heat treatment step of heating the stainless steel material at 900°C or higher for a predetermined time, a processing step of obtaining a processed product by machining and / or welding the stainless steel material obtained in the first heat treatment step with a strain rate of 20% or less, and a second heat treatment step of heating the processed product obtained in the processing step at 900 to 1100°C for a predetermined time.

[0041] The stainless steel material having the above composition can be manufactured by a conventional method. Specifically, first, the stainless steel having the above composition is melted and then forged or cast, and then hot-rolled to obtain a hot-rolled material. Next, annealing, pickling, and cold rolling are sequentially performed on the hot-rolled material to obtain a cold-rolled material. Next, annealing and pickling are sequentially performed on the cold-rolled material to obtain a cold-rolled annealed material. Note that the conditions in each process may be appropriately adjusted according to the composition of the stainless steel and the like, and are not particularly limited. The hot-rolled material, cold-rolled material, or cold-rolled annealed material produced by such a method can be used as the stainless steel material. Among them, the stainless steel material is preferably a cold-rolled annealed material.

[0042] In the first heat treatment step, the heat treatment (recrystallization treatment) of the stainless steel material is performed by heating at 900 °C or higher, preferably 1000 °C or higher, for 10 minutes or more. By heating at 900 °C or higher for 10 minutes or more, the crystal grains can be grown so that the average crystal grain size becomes 100 μm or more. The upper limit value of the heating temperature is not particularly limited, but since excessive growth of the crystal grains may reduce the toughness, it is preferably 1200 °C, more preferably 1180 °C. Also, the upper limit value of the heating time may be appropriately adjusted according to the heating temperature, but is generally 120 minutes. The heat treatment can be performed, for example, using a heating furnace. The form of the heating furnace may be a batch type or a continuous type. In addition, since this stainless steel material has oxidation resistance, the atmosphere of the heat treatment may be an air atmosphere or a non-oxidizing atmosphere (for example, a vacuum, hydrogen gas atmosphere). From the viewpoint of suppressing excessive growth of the oxide film, it is preferably performed in a non-oxidizing atmosphere.

[0043] In the processing step, as the processing method, machining and / or welding with a strain rate of 20% or less is used. The machining process is not particularly limited, and processes such as pressing, bending, and deep drawing can be used. Also, the welding process is not particularly limited, and known methods in the technical field such as arc welding (such as TIG welding), electron beam welding, laser welding, plasma arc welding, and spot welding can be used. Welding is preferably performed without using a filler metal.

[0044] When machining is used as the processing method, since the stainless steel material obtained in the first heat treatment process has large crystal grains, if a large strain is introduced, there is a risk of cracking in the processed part. Also, unevenness along the shape of the large crystal grains is likely to occur, resulting in a decrease in appearance and dimensional accuracy. Furthermore, when a large strain is introduced, in the second heat treatment process, fine recrystallized grains are generated as the driving force for recrystallization, and there is also a risk that these fine recrystallized grains will hinder the movement of magnetic domains and reduce the vibration damping performance. Therefore, when machining is used, it is carried out under conditions such that the strain rate is 20% or less, preferably 18% or less, more preferably 15% or less. By controlling the strain rate to 20% or less, it is possible to suppress cracking in the processed part, a decrease in appearance and dimensional accuracy, and also suppress a decrease in vibration damping performance because the movement of grain boundaries becomes dominant over recrystallization in the second heat treatment process. Here, in this specification, the "strain rate" means the reduction rate (cross-sectional shrinkage rate) of the cross-sectional area before and after processing. In the case of welding, since the strain rate does not exceed 20%, the strain rate in the case of welding is not particularly limited.

[0045] In the second heat treatment process, the processed product obtained in the processing process is heated at 900 to 1100 °C for t1 to t2 [minutes]. By performing the second heat treatment process, the strain introduced in the processing process can be removed, and the vibration damping performance and dimensional accuracy of the stainless steel processed product can be improved. Here, t1 is -0.16×(T - 800) + 42 (where if it is less than 1, it is 1), t2 is -0.45×(T - 800) + 155, and T represents the heat treatment temperature of the second heat treatment process. If the heating temperature is less than 900 °C or the heating time is less than t1, the strain introduced in the processing step is not sufficiently removed, and the vibration damping property deteriorates. Further, if the heating temperature exceeds 1100 °C or the heating time exceeds t2, the dimensional accuracy of the stainless steel processed product cannot be ensured, and the manufacturing cost also increases.

[0046] In the second heat treatment step, the heating rate is not particularly limited, but it is preferably 50 °C / min or more. If the heating rate is less than 50 °C / min, Cr carbides and the like are likely to be generated using the strain introduced in the processing step as a driving force, so the corrosion resistance may decrease. Note that the upper limit value of the heating rate is not particularly limited, but it is preferably 900 °C / min.

[0047] The cooling rate after the second heat treatment step is not particularly limited, but it is preferably 50 °C / min or less. If the cooling rate exceeds 50 °C / min, the dimensional accuracy may decrease due to thermal stress. Note that the lower limit value of the cooling rate is not particularly limited, but considering the manufacturing efficiency, it is preferably 2 °C / min.

[0048] (3) Vibration damping member The vibration damping member according to the embodiment of the present invention includes the above-described stainless steel processed product. Since the above-described stainless steel processed product is excellent in dimensional accuracy and vibration damping property, this vibration damping member is also excellent in dimensional accuracy and vibration damping property. Examples of the vibration damping member are not particularly limited, but it is preferable that they are various members that require dimensional accuracy and vibration damping property. Examples of such members include the housing of an HDD.

Examples

[0049] Hereinafter, the content of the present invention will be described in detail with reference to examples, but the present invention is not construed as being limited thereto.

[0050] (Examples 1 to 6 and Comparative Examples 1 to 8) Ferritic stainless steel processed products were produced according to the following procedure. A stainless steel having the composition shown in Table 1 was melted, hot-rolled to obtain a hot-rolled sheet with a thickness of 3.0 mm, and then the hot-rolled sheet was 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, and then the cold-rolled sheet was finish-annealed at 1000 °C and pickled to obtain a cold-rolled annealed sheet. Next, a test piece with a width of 50 mm in the width direction and 300 mm in the rolling direction was cut out from the cold-rolled annealed sheet by cutting.

[0051]

Table 1

[0052] Next, the above test piece was placed in an elema electric furnace, and a first heat treatment step of heating at 1100 °C for 30 minutes in an air atmosphere was performed. Next, mechanical processing or welding was performed on the test piece obtained in the first heat treatment step. For mechanical processing, after attaching the test piece to a tensile testing machine so that the rolling direction of the test piece becomes the tensile direction, it was pulled at a constant speed of 10 mm / min, and tensile processing was performed so as to obtain the strain rate shown in Table 2. For welding, pseudo-welding processing was performed in which the surface of the central part of the test piece was melted in the same manner as TIG dressing welding (however, welding was not performed). The welding conditions were a welding current of 90 A, a welding speed of 60 cm / min, and a welding electrode diameter of 1.6 mm.

[0053] Next, the processed test piece subjected to mechanical processing or welding was placed in an elema electric furnace, and a second heat treatment step of heating under the conditions shown in Table 2 in an air atmosphere was performed. At this time, the heating rate until reaching the predetermined temperature was 50 °C / min. Also, the cooling rate after the second heat treatment step was 30 °C / min. The following evaluations were performed on the processed test piece thus obtained.

[0054] (Average crystal grain size) After cutting out a 30 mm × 10 mm test piece for measurement from the above-mentioned processed test piece by cutting, resin embedding was performed so that the surface parallel to the rolling direction of the plate thickness and perpendicular to the width direction became the observation surface. Next, after mirror finishing the test piece for measurement with resin embedding by wet polishing, the metallic structure revealed by etching with hydrofluoric nitric acid was observed with an optical microscope. The observation with the optical microscope was carried out in accordance with JIS G0551:2013. A straight line was drawn at an arbitrary position on the optical microscope image (50 times magnification), the number of intersections between the straight line and the crystal grain boundaries was measured, and the average section length was taken as the crystal grain size. The measurement of the crystal grain size was performed by drawing 20 or more straight lines in any 5 fields of view and measuring them, and their average value was taken as the average crystal grain size. Regarding the test piece subjected to welding, the crystal grain size was measured for each of the base material part without welding and the welded part with welding, and their average value was taken as the average crystal grain size.

[0055] (Ratio of crystal grains with a crystal grain size of 20 μm or less) In the optical microscope image used for the measurement of the average crystal grain size, the crystal grains with a crystal grain size of 20 μm or less were filled with black using image analysis software, and the area ratio of the portion filled with black in the image was calculated by performing binarization processing of the image analysis. The calculation of the area ratio was performed in any 5 fields of view in the same manner as the measurement of the average crystal grain size, and their average value was taken as the ratio of crystal grains with a crystal grain size of 20 μm or less.

[0056] (Ratio of crystal grains with an in-grain orientation difference of 0.05 to 2° in the processed part) Regarding the above-mentioned processed test piece subjected to tensile processing, after cutting out a 10 mm × 10 mm test piece for measurement by cutting, resin embedding was performed so that the surface parallel to the rolling direction of the plate thickness and perpendicular to the width direction became the observation surface. On the other hand, regarding the above-mentioned processed test piece subjected to welding, after cutting out a test piece for measurement including the welded part by cutting, resin embedding was performed so that the welded part became the observation surface. Next, after mirror finishing the test piece with resin embedding by wet polishing using SiC abrasive paper and diamond paste, polishing with colloidal silica abrasive was performed. For the test piece processed in this way, crystal orientation measurement was performed by the EBSD method. For the crystal orientation measurement, a FE-SEM equipped with an OIM (orientation Imaging Microscopy) system was used. Also, the evaluation area was set to 100 μm square, and at least one grain boundary was included in the field of view. The measurement results were used to measure the area ratio of the average crystal orientation difference in the field of view using a KAM map (Kernel Average Misorientation Map), and the ratio of the grains with an intra-grain orientation difference of 0.05 to 2° with respect to all the grains with crystal orientation differences was calculated. Note that the points with an intra-grain orientation difference of 5° or more were excluded because they were grain boundaries.

[0057] (Vibration damping property: loss coefficient η) A test specimen for measurement with a width of 10 mm and a rolling direction length of 250 mm was cut out from the above processing test specimen by cutting. Using this test specimen for measurement, the loss coefficient η was measured according to the "central excitation method" specified in JIS K7391:2008. Specifically, the test specimen with the 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 coefficient η was derived based on the anti-resonance frequency at which the mechanical impedance peaks and the frequency at which the amplitude drops by 3 dB from the peak. In this evaluation, when the loss coefficient η was 2×10 -4 or more, it was judged that the vibration damping property was good.

[0058] (Dimensional accuracy: thermal deformation) The above processing test specimen was placed on a flat table, and a range of 30 mm from one end (one end in the rolling direction) of the processing test specimen was brought into contact with the table and fixed with a clamp, and the height (warp height) at which the other end (the other end in the rolling direction) floated from the table was measured. The warp height was measured at both ends of the test specimen in the rolling direction, and their average value was taken as the warp height. In this evaluation, when the warp height was 3 mm or less, it was marked as 〇 (less thermal deformation), and when the warp height exceeded 3 mm, it was marked as × (more thermal deformation). The above evaluation results are shown in Table 2.

[0059]

Table 2

[0060] As shown in Table 2, Examples 1 to 6, in which the composition, average crystal grain size, ratio of crystal grains with a crystal grain size of 20 μm or less, and ratio of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed portion satisfy a predetermined range, have a loss coefficient η of 2×10 -4 or more, and since there was little thermal deformation, it was confirmed that they were excellent in dimensional accuracy and vibration damping performance. On the other hand, in Comparative Examples 1 and 5, since the strain rate imparted by machining was too high, the ratio of crystal grains with a crystal grain size of 20 μm or less exceeded 10%. As a result, the loss coefficient was high and the vibration damping performance was not sufficient. In Comparative Examples 2 and 6, since the temperature of the second heat treatment step was low and the time was too short, the ratio of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed portion was less than 30%. As a result, the loss coefficient was high and the vibration damping performance was not sufficient. In Comparative Examples 3, 4, 7, and 8, since the time of the second heat treatment step was too long, the ratio of crystal grains with an intragranular orientation difference of 0.05 to 2° in the processed portion was less than 30%. As a result, thermal deformation increased and the dimensional accuracy was not sufficient.

[0061] As can be seen from the above results, according to the present invention, it is possible to provide a ferritic stainless steel processed product excellent in dimensional accuracy and vibration damping performance, a method for manufacturing the same, and a vibration damping member.

Claims

1. Based on mass, it contains C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 10.50 - 24.00%, N: 0.030% or less, Cu: 1.00% or less, Mo: 2.50% or less, Si: 3.00% or less, Al: 5.00% or less, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6(C + N) or more (C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities, the average crystal grain size is 100 μm or more, the proportion of crystal grains with a crystal grain size of 20 μm or less is 10% or less, a ferritic stainless steel processed product in which the proportion of crystal grains with an in-grain orientation difference of 0.05 - 2° in the processed part is 30% or more.

2. The ferritic stainless steel processed product according to Claim 1, wherein the total content of Al and Si is 1.00% or more based on mass.

3. The ferritic stainless steel processed product according to Claim 1 or 2, further containing at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less based on mass.

4. The ferritic stainless steel processed product according to any one of Claims 1 to 3, further containing at least one selected from REM: 0.100% or less, Ca: 0.100% or less based on mass.

5. The ferritic stainless steel processed product according to any one of Claims 1 to 4, further containing at least one selected from Sn: 0.10% or less, B: 0.010% or less based on mass.

6. A method for manufacturing the ferritic stainless steel processed product according to Claim 1, a first heat treatment step of heating a ferritic stainless steel material having a composition containing C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 10.50 - 24.00%, N: 0.030% or less, Cu: 1.00% or less, Mo: 2.50% or less, Si: 3.00% or less, Al: 5.00% or less, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti being 6(C + N) or more (C and N represent the contents of C and N respectively), and the balance consisting of Fe and impurities at 900°C or higher for 10 minutes or more, A processing step of subjecting the ferritic stainless steel material obtained in the first heat treatment step to machining and / or welding with a strain rate of 20% or less to obtain a processed product; A second heat treatment step of heating the processed product obtained in the processing step at 900 to 1100 °C for t1 to t2 [minutes]; A method comprising: t1 is -0.16×(T - 800) + 42 (where if it is less than 1, it is 1), t2 is -0.45×(T - 800) + 155, and T represents the heat treatment temperature of the second heat treatment step.

7. A method for manufacturing a ferritic stainless steel processed product according to claim 2, The method according to claim 6, wherein the ferritic stainless steel material has a total content of Al and Si of 1.00% or more based on mass.

8. A method for manufacturing a ferritic stainless steel processed product according to claim 3, The method according to claim 6 or 7, wherein the ferritic stainless steel material further contains at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, and W: 1.00% or less based on mass.

9. A method for manufacturing a ferritic stainless steel processed product according to claim 4, The method according to any one of claims 6 to 8, wherein the ferritic stainless steel material further contains at least one selected from REM: 0.100% or less and Ca: 0.100% or less based on mass.

10. A method for manufacturing a ferritic stainless steel processed product according to claim 5, The method according to any one of claims 6 to 9, wherein the ferritic stainless steel material further contains at least one selected from Sn: 0.10% or less and B: 0.010% or less based on mass.

11. The method according to any one of claims 6 to 10, wherein the cooling rate after the second heat treatment step is 50 °C / min or less.

12. The method according to any one of claims 6 to 11, wherein the heating rate during the second heat treatment step is 50 °C / min or more.

13. A vibration damping member including a ferritic stainless steel processed product according to any one of claims 1 to 5.

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