Austenitic stainless steel material, method for manufacturing the same, and appearance design article

Abstract

An austenitic stainless steel material containing, in mass, C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, W: 0.01 to 0.30%, and the remainder consisting of Fe and impurities.

Description

TECHNICAL FIELD

[0001] The present application relates to an austenitic stainless steel material and a manufacturing method thereof, and a design object. BACKGROUND

[0002] A stainless steel material is used for various purposes because of its excellent properties such as corrosion resistance. For example, in a frame of a smart phone, a watch, or the like, a constituent member, SUS316, which is one of austenitic stainless steel materials excellent in corrosion resistance, is often used.

[0003] In addition, in the case where a stainless steel material is used in an object that a consumer can visually recognize such as a frame, the stainless steel material is required to be excellent in design from the viewpoint of increasing the consumer's purchase enthusiasm. The design depends on the times and needs, but for example, it is required to impart a high grade by increasing the glossiness by mirror polishing after cutting processing of the stainless steel material. In addition, if a flaw is generated due to friction or the like, the design is impaired, and thus it is also required that the flaw is not easily generated.

[0004] As an austenitic stainless steel material having a composition based on SUS316, for example, in Patent Literature 1, an austenitic stainless steel material containing, in terms of mass %, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5 to 2.0%, Cr: 16 to 24%, Ni: 10 to 16%, N: 0.2% or less, Mo: 4.0% or less, and the remainder consisting of Fe and inevitable impurities is described. In addition, in Patent Literature 2, an austenitic stainless steel material containing, in terms of mass %, C: 0.03 to 0.18%, N: 0.05 to 0.30%, Si: 1.5% or less, Mn: 2.0% or less, Ni: 8.0 to 15.0%, Cr: 15.0 to 25.0%, Mo: 0.20 to 3.0%, Cu: 2.0% or less, and the remainder consisting of Fe and inevitable impurities is described.

[0005] PRIOR ART DOCUMENTS

[0006] PATENT LITERATURE

[0007] Patent Literature 1: Japanese Patent Application Laid-Open No. 2021-504587

[0008] Patent Literature 2: Japanese Patent No. 5618057 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] Generally, SUS316, although excellent in corrosion resistance, has a problem in that the machinability is insufficient because of high cutting resistance. In addition, with respect to mirror polishing after cutting processing, there is a tendency that mirror polishing is difficult to perform for the case where the cutting resistance is high. On the other hand, although the flaw resistance can be improved by increasing the strength of the matrix phase, if the strength of the matrix phase is increased, the cutting resistance becomes high and the machinability is reduced.

[0011] In addition, although the austenitic stainless steel material of Patent Document 1 is excellent in corrosion resistance and non-magnetic properties, the machinability, mirror polishing properties, and flaw resistance are not particularly problematic.

[0012] In addition, although the austenitic stainless steel material of Patent Document 2 is excellent in workability such as plastic working and cutting processing, and corrosion resistance, and has a hydrogen embrittlement resistance function, the mirror polishing properties and flaw resistance are not particularly problematic.

[0013] The present application has been made in order to solve the above-described problems, and has an object to provide an austenitic stainless steel material excellent in machinability, mirror polishing properties, and flaw resistance, and a manufacturing method thereof.

[0014] In addition, the present application has an object to provide a design object which can be manufactured by cutting processing and mirror polishing of an austenitic stainless steel material, and which is high in gloss and has a high-class appearance, and is excellent in flaw resistance.

[0015] Means for solving the problems

[0016] The machinability of the austenitic stainless steel material is affected by the strength and ductility degree of the matrix phase. That is, the machinability of the austenitic stainless steel material can be improved by reducing the ductility of the matrix phase without increasing the strength of the matrix phase. Therefore, it is attempted to reduce the ductility of the matrix phase and suppress the increase in the strength of the matrix phase by solid-solutionizing a small amount of V and W in the matrix phase.

[0017] In addition, the mirror polishing properties of the austenitic stainless steel material are affected by the presence of inclusions, coarse carbides, and δ-ferrite. In addition, if burn is generated due to mirror polishing, or scale-like folding flaws (hereinafter referred to as "hot-rolled scale-like folding") generated at the time of hot rolling remain, it is possible that the gloss is reduced, and therefore it is also necessary to suppress these problems. Therefore, it is attempted to reduce Al and Ca, which form inclusions, as much as possible, to adjust the contents of S, B, V, and W, to suppress the generation of coarse carbides, to suppress burn by increasing the heat resistance by the addition of Co and W, and to suppress the generation of hot-rolled scale-like folding by the addition of B.

[0018] Further, the flaw resistance of the austenitic stainless steel material can be improved by precipitating fine hard carbides in the matrix phase. Therefore, attempts have been made to improve the flaw resistance by adding V and W, which easily generate fine hard carbides.

[0019] Based on the above, the inventors of the present application produced austenitic stainless steel materials of various compositions based on the composition of SUS316, which is excellent in corrosion resistance, and analyzed them, and as a result, found that by setting the composition to a specific composition, it is possible to improve the machinability, mirror polishing property, and flaw resistance all together, thereby completing the present application.

[0020] That is, the present application relates to an austenitic stainless steel material containing, on a mass basis, C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, and W: 0.01 to 0.30%, with the remainder consisting of Fe and impurities.

[0021] Further, the present application relates to a design article including the above-described austenitic stainless steel material.

[0022] Further, the present application relates to a method of producing an austenitic stainless steel material, in which a slab containing, on a mass basis, C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, and W: 0.01 to 0.30%, with the remainder consisting of Fe and impurities, and in which the δ ferrite phase at a depth of 5 mm from the surface is 0 to 3.0% by volume, is heated to 1230 to 1300°C and hot-rolled.

[0023] Effects of the Invention

[0024] According to the present application, it is possible to provide an austenitic stainless steel material excellent in machinability, mirror polishing property, and flaw resistance, and a method of producing the same.

[0025] Further, according to the present application, it is possible to provide a design article that can be produced by subjecting an austenitic stainless steel material to machining and mirror polishing, and that is high in gloss and has a high-class appearance and excellent flaw resistance. DETAILED DESCRIPTION

[0026] Hereinafter, the embodiments of the present application will be specifically described. The present application is not limited to the following embodiments, and it should be understood that the modes obtained by appropriately applying changes, modifications, and the like to the following embodiments based on general knowledge of those skilled in the art within the scope of the gist of the present application are also within the scope of the present application.

[0027] Further, in the present specification, the "%" expression related to components means "mass %" unless otherwise specified.

[0028] The austenitic stainless steel material of the embodiment of the present application contains C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, W: 0.01 to 0.30%, and the remainder consists of Fe and impurities.

[0029] Here, in the present specification, the "austenitic system" means that the metal structure is mainly austenite phase at normal temperature. Therefore, the "austenitic system" also includes a small amount of phases other than the austenite phase (for example, ferrite phase, martensite phase, and the like).

[0030] Further, in the present specification, the "stainless steel material" means a material formed of stainless steel, and the material shape is not particularly limited. As examples of the material shape, a plate shape (including a strip shape), a bar shape, a pipe shape, and the like can be given. Further, the material can be various shaped steels having a T-shaped cross-sectional shape, an I-shaped cross-sectional shape, and the like.

[0031] Further, in the present specification, the "impurities" mean components mixed due to various reasons of raw materials such as ores, waste materials, manufacturing processes, and the like when the austenitic stainless steel material is industrially manufactured, and substances allowed within a range that does not adversely affect the present application. For example, O and the like are included in the impurities. O included as the impurities is generally 0.030% or less.

[0032] Further, regarding the content of each element in the present specification, the inclusion of "xx% or less" means xx% or less but including an amount exceeding 0% (particularly, exceeding the impurity level).

[0033] In addition, the austenitic stainless steel material of the embodiment of the present application can further contain one or more selected from the group consisting of Al: 0.03% or less, Ca: 0.006% or less. Therefore, the austenitic stainless steel material of the embodiment of the present application containing these elements can be represented as containing C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, W: 0.01 to 0.30%, further containing one or more selected from the group consisting of Al: 0 to 0.03%, Ca: 0 to 0.006%, and the remainder consisting of Fe and impurities.

[0034] Here, regarding the content of each element in the present specification, the inclusion of "0 to xx%" means the concept of xx% or less but also including 0% (not included).

[0035] Hereinafter, each component will be described in detail.

[0036] <C: 0.024% or less>

[0037] C is an element for generating an austenite phase (γ phase) and is effective for improving the strength of the matrix phase. In particular, C can bond with V and W to cause fine hard carbides to precipitate in the matrix phase, and thus the flaw resistance can be improved. However, when the content of C is too much, the hard carbides tend to become coarse, and the mirror polishing property is reduced. Therefore, the upper limit value of the content of C is controlled to 0.024%, and preferably to 0.023%. On the other hand, the lower limit value of the content of C is not particularly limited, but from the viewpoint of obtaining the above-mentioned effects by C, it is preferably 0.001%, more preferably 0.003%, and further preferably 0.005%.

[0038] <Si: 1.00% or less>

[0039] When the content of Si is too much, the workability of the austenitic stainless steel material is reduced. Therefore, the upper limit value of the content of Si is controlled to 1.00%, and preferably to 0.98%, and more preferably to 0.96%. On the other hand, the lower limit value of the content of Si is not particularly limited, but it is preferably 0.01%, more preferably 0.05%, and further preferably 0.10%.

[0040] <Mn: 2.00% or less>

[0041] Mn is an element for generating the austenite phase. When the content of Mn is too much, the corrosion resistance of the austenitic stainless steel material decreases. Therefore, the upper limit value of the content of Mn is controlled to 2.00%, preferably to 1.95%, more preferably to 1.90%. On the other hand, the lower limit value of the content of Mn is not particularly limited, but is preferably 0.01%, more preferably 0.05%, further preferably 0.10%.

[0042] < P : 0.045% or less >

[0043] When the content of P is too much, the workability of the austenitic stainless steel material decreases. Therefore, the upper limit value of the content of P is controlled to 0.045%, preferably to 0.043%. On the other hand, the lower limit value of the content of P is not particularly limited, but is preferably 0.001%, more preferably 0.005%, further preferably 0.010%.

[0044] < S : 0.015% or less >

[0045] When the content of S is too much, the manufacturability of the austenitic stainless steel material decreases, and it becomes easy to generate inclusions, thereby deteriorating the mirror polishing property. Therefore, the upper limit value of the content of S is controlled to 0.015%, preferably to 0.014%. On the other hand, the lower limit value of the content of S is not particularly limited, but is preferably 0.0001%, more preferably 0.0003%, further preferably 0.0005%.

[0046] < Ni : 10.0 to 15.0% >

[0047] Ni is also an element for generating the austenite phase like Mn. Since Ni is expensive, when the content is too much, it leads to an increase in the manufacturing cost. Therefore, the upper limit value of the content of Ni is controlled to 15.0%, preferably to 14.8%, more preferably to 14.6%. On the other hand, when the content of Ni is too little, the corrosion resistance and the workability of the austenitic stainless steel material decrease, and it becomes difficult to obtain the austenite structure. Therefore, the lower limit value of the content of Ni is controlled to 10.0%, preferably to 10.3%, more preferably to 10.5%.

[0048] < Cr : 15.0 to 22.0% >

[0049] Cr is an element effective for improving the corrosion resistance of the austenitic stainless steel material. However, when the content of Cr is too much, the mirror polishing property of the austenitic stainless steel material decreases due to the generation of δ-ferrite. Therefore, the upper limit value of the content of Cr is controlled to 22.0%, preferably to 21.8%, more preferably to 21.6%. On the other hand, when the content of Cr is too little, the corrosion resistance cannot be sufficiently obtained. Therefore, the lower limit value of the content of Cr is controlled to 15.0%, preferably to 15.2%.

[0050] < Mo : 2.0 to 4.0 % >

[0051] Mo is an element added to improve corrosion resistance. However, Mo is expensive, and therefore, when the content of Mo is excessive, the manufacturing cost increases. Therefore, the upper limit value of the content of Mo is controlled to 4.0%, and preferably to 3.9%. On the other hand, from the viewpoint of ensuring corrosion resistance, the lower limit value of the content of Mo is 2.0%, preferably 2.1%, more preferably 2.2%, and further preferably 2.5%.

[0052] < N : 0.01 to 0.15 % >

[0053] N is an element effective for improvement of corrosion resistance. In order to obtain this effect, the lower limit value of the content of N is controlled to 0.01%, and preferably to 0.02%. On the other hand, when the content of N is excessive, the workability of the austenitic stainless steel material decreases. Therefore, the upper limit value of the content of N is controlled to 0.15%, and preferably to 0.14%.

[0054] < B : 0.001 to 0.010 % >

[0055] B is an element effective for improvement of hot rolling workability (inhibition of generation of hot rolled scale folds). In order to obtain this effect, the lower limit value of the content of B is controlled to 0.001%, and preferably to 0.002%. On the other hand, when the content of B is excessive, the effect brought by B is saturated, and on the contrary, mirror polishing properties decrease due to generation of boride precipitates. Therefore, the upper limit value of the content of B is controlled to 0.010%, and preferably to 0.009%.

[0056] < Co : 0.05 to 1.00 % >

[0057] Co is an element that suppresses burning caused by processing heat of a cut portion when the austenitic stainless steel material is subjected to cutting processing. In addition, Co is also an element that improves corrosion resistance after mirror polishing. In order to obtain these effects, the lower limit value of the content of Co is controlled to 0.05%, and preferably to 0.06%. On the other hand, when the content of Co is excessive, the effect brought by Co is saturated, and cutting resistance increases so that the cutting properties decrease. Therefore, the upper limit value of the content of Co is controlled to 1.00%, and preferably to 0.98%, and more preferably to 0.95%.

[0058] < V : 0.01 to 0.30 % >

[0059] V is an element which bonds with C to cause fine hard carbide to precipitate in the matrix phase. With this fine hard carbide, it is possible to improve the flaw resistance without impairing the mirror polishing properties. In addition, a part of V is solid-solved in the matrix phase to lower the ductility of the matrix phase. Thus, the cutting resistance is lowered, and therefore it is possible to improve the machinability. In order to obtain these effects, the lower limit value of the content of V is controlled to 0.01%, and preferably to 0.02%. On the other hand, when the content of V is too much, the carbide and nitride of V become easy to coarsen, and therefore the mirror polishing properties are lowered. Thus, the upper limit value of the content of V is controlled to 0.30%, and preferably to 0.29%.

[0060] < W : 0.01 to 0.30 % >

[0061] W is also an element which bonds with C to cause fine hard carbide to precipitate in the matrix phase, like V. With this fine hard carbide, it is possible to improve the flaw resistance without impairing the mirror polishing properties. In addition, a part of W is solid-solved in the matrix phase to lower the ductility of the matrix phase. Thus, the cutting resistance is lowered, and therefore it is possible to improve the machinability. In order to obtain these effects, the lower limit value of the content of W is controlled to 0.01%, and preferably to 0.02%. On the other hand, when the content of W is too much, the carbide and nitride of W become easy to coarsen, and therefore the mirror polishing properties are lowered. Thus, the upper limit value of the content of W is controlled to 0.30%, and preferably to 0.29%.

[0062] < Al : 0.03 % or less >

[0063] Al is an element which is added as necessary in order to perform deoxidation in the refining step, and which improves the corrosion resistance and the heat resistance. On the other hand, Al is an element which generates inclusions which lower the mirror polishing properties. Thus, the upper limit value of the content of Al is controlled to 0.03%, and preferably to 0.02%. On the other hand, it is also possible to not contain Al, and therefore the lower limit value thereof is not particularly limited. The lower limit value in the case of containing Al is, for example, 0.01%.

[0064] < Ca : 0.006 % or less >

[0065] Ca is an element which is added as necessary in order to improve the hot rolling workability. On the other hand, Ca is an element which generates inclusions which lower the mirror polishing properties. Thus, the upper limit value of the content of Ca is controlled to 0.006%, and preferably to 0.005%. On the other hand, it is also possible to not contain Ca, and therefore the lower limit value thereof is not particularly limited. The lower limit value in the case of containing Ca is, for example, 0.001%.

[0066] The austenitic stainless steel material of the embodiment of the present application preferably satisfies the following formula (1).

[0067] 5W + 2V + 0.45 - Co ≥ 0 (1)

[0068] In the formula, each symbol of the element represents the content (mass %) of each element.

[0069] The above formula (1) is an index indicating the balance of the contents of W, V, and Co, which affect the machinability, mirror polishing property, and flaw resistance. By satisfying the above formula (1), the contents of W, V, and Co can be controlled to an appropriate balance, and thus the machinability, mirror polishing property, and flaw resistance can be stably improved.

[0070] It is preferable that the contents of C and N of the austenitic stainless steel material of the embodiment of the present application be less than 0.080%.

[0071] C and N are also elements that affect the hardness of the austenitic stainless steel material, and by reducing the contents of these elements, the austenitic stainless steel material can be softened to be more workable. For this purpose, the total amount of C and N is preferably less than 0.080%, more preferably 0.075% or less, and further preferably 0.070% or less.

[0072] The austenitic stainless steel material of the embodiment of the present application preferably has a metal structure in which the δ-ferrite phase is 0 to 2.0% by volume.

[0073] The δ-ferrite phase adversely affects the mirror polishing property, and if it is present in a large amount in the austenitic stainless steel material, the gloss of the product is reduced. Therefore, the δ-ferrite phase is preferably 0 to 2.0% by volume, more preferably 0 to 1.5% by volume, and further preferably 0 to 1.0% by volume.

[0074] Here, in the present specification, "the δ-ferrite phase is 0% by volume" means that the δ-ferrite phase is not contained.

[0075] The proportion of the δ-ferrite phase in the austenitic stainless steel material of the embodiment of the present application is found by a magnetic induction method. For example, the proportion of the δ-ferrite phase can be measured using a ferrite scope (for example, FERITSCOPE FMP30 manufactured by Fisher instruments, etc.).

[0076] The cutting resistance value of the austenitic stainless steel material of the embodiment of the present application is preferably 270 N or less, more preferably 240 N or less, and further preferably 220 N or less. If the cutting resistance value is in the above range, it can be said that the cutting resistance is low, and thus the machinability can be improved. Furthermore, the lower limit value of the cutting resistance value is not particularly limited, but is, for example, 100 N.

[0077] Here, the cutting resistance value can be determined by using a cutting test of plunge cutting of the austenite stainless steel material using a ball end mill (Korloy Co.; outer diameter φ 12 mm). In the plunge cutting, a horizontal component force acting in the feed direction (feed component force) is taken as the cutting resistance. The conditions of the plunge cutting are described below.

[0078] Cutting speed (Vc): 96 m / min

[0079] Rotational speed: 2550 rpm

[0080] Feed amount per 1 tool (Fz): 0.025 mm / min

[0081] Feed speed (Vf): 255 mm / min

[0082] Axial depth of cut (Ap): 5 mm

[0083] Wet processing (with cutting oil)

[0084] The austenite stainless steel material of the embodiment of the present application preferably has a glossiness Gs(20°) of 1000% or more, more preferably 1030% or more, and further preferably 1050% or more after mirror polishing. If the glossiness is in such a range, it can be said that the mirror polishing property is good, and the burn, hot rolled scale folding can be suppressed. Further, the upper limit value of the glossiness Gs(20°) is not particularly limited, but is, for example, 1500%.

[0085] Here, the glossiness Gs(20°) means a 20-degree mirror surface glossiness determined in accordance with JIS Z8741:1997. The glossiness Gs(20°) can be determined in accordance with JIS Z8741:1997 using a glossiness meter (Micro-trigloss manufactured by BYK-Gardner Co.). As for the glossiness Gs(20°), the determination is performed at any 5 positions except for the range from the end to 5 mm, and the average value thereof is taken as the evaluation result. In addition, the determination positions are separated by 5 mm or more.

[0086] The austenite stainless steel material of the embodiment of the present application preferably has a specific wear amount of 60 x 10 -5 mm 3 / N·m or less, more preferably 55 x 10 -5 mm 3 / N·m or less, and further preferably 50 x 10 -5 mm 3 / N·m or less in the pin-on-disc sliding wear test. If the specific wear amount is in such a range, it can be said that the flaw resistance is good. Further, the lower limit value of the specific wear amount is not particularly limited, but is, for example, 10 x 10 -5 mm 3N / m.

[0087] Here, the specific wear amount in the pin-on-disc sliding wear test can be measured by cutting a test piece in the shape of a round plate having a diameter of 8 mm from the austenitic stainless steel material, and using a pin-on-disc sliding wear tester. The pin-on-disc sliding wear test is performed by fixing the test piece in the shape of a round plate to a test sample holder, and pressing the surface of the test piece to a rotating abrasive paper (#800 abrasive paper coated with SiC) at a test load F = 20 N. At this time, the rotation speed is set to 0.66 m / sec, the rotation rate is set to 140 rpm, and the friction distance L is set to 200 m. Then, the volume of the material that has disappeared due to wear is calculated from the difference in thickness of the test piece before and after the pin-on-disc sliding wear test, and this is taken as the wear loss W (mm 3 ). Then, the specific wear amount is calculated by the following equation.

[0088] Specific wear amount (mm 3 / N·m) = Wear loss W / (Test load F x Friction distance L)

[0089] The austenitic stainless steel material of the embodiment of the present application is not particularly limited in kind as long as it has the characteristics described above. For example, the austenitic stainless steel material of the embodiment of the present application can be either a hot-rolled steel material or a cold-rolled steel material.

[0090] The austenitic stainless steel material of the embodiment of the present application can be manufactured by a method known in the technical field, in addition to melting a stainless steel satisfying the composition described above. Hereinafter, a typical manufacturing method will be described, but the manufacturing method of the austenitic stainless steel material of the embodiment of the present application is not limited to the following.

[0091] The austenitic stainless steel material of the embodiment of the present application can be manufactured, for example, by hot-rolling a slab having the composition described above. In addition, cold-rolling can be performed after hot-rolling, depending on the use. Furthermore, annealing, pickling, etc. can be performed as needed, respectively, after hot-rolling and after cold-rolling.

[0092] The conditions of hot-rolling, cold-rolling, etc. are not particularly limited, and can be appropriately adjusted depending on the composition. For example, in hot-rolling, hot-rolling can be performed by setting the heating temperature before rolling to 1200 to 1300°C, and annealing can be performed at 1000 to 1200°C as needed after hot-rolling. The heating temperature before rolling is preferably set to 1230 to 1300°C. In addition, after cold-rolling, annealing is preferably performed at 1000 to 1150°C as needed.

[0093] Further, as described above, the austenitic stainless steel material of the embodiment of the present application preferably has a δ-ferrite phase of 0 to 2.0% by volume, but in order to produce such an austenitic stainless steel material, it is preferable to set the δ-ferrite phase at a position of a depth of 5 mm in the thickness direction from the surface of a slab for hot rolling to be 0 to 3.0% by volume, and to set the heating temperature before hot rolling to be 1230 to 1300°C. When the δ-ferrite phase at this position of the slab exceeds 3.0% by volume, it results in the δ-ferrite phase being easily left in the austenitic stainless steel material, and as a result, the mirror polishing property is reduced.

[0094] The lower limit of the proportion of the δ-ferrite phase at this position of the slab is not necessarily required, but from the viewpoint of suppressing the segregation of S to the grain boundaries, and suppressing the generation of the scale fold defect in hot rolling, it is preferable to set it to be 0.1% by volume or more, and more preferably to set it to be 0.2% by volume or more. Further, in the case where the scale fold defect is generated, the cutting amount at the time of polishing is increased, and thus the load of cutting processing is increased.

[0095] Here, the proportion of the δ-ferrite phase at the position of the depth of 5 mm in the thickness direction from the surface of the slab can be obtained as described below. First, after the scale of the surface of the slab is removed, the slab is cut in the thickness direction. Next, in the cut surface in the thickness direction of the slab, the position of the depth of 5 mm in the thickness direction from the surface of the slab is determined, and the proportion of the δ-ferrite phase at this position is measured using a ferrite scope (for example, FERITSCOPE FMP30 manufactured by Fisher instruments, or the like).

[0096] The austenitic stainless steel material of the embodiment of the present application is excellent in the cutting property, the mirror polishing property, and the defect resistance, and thus can be used in various uses where these properties are required. For example, the austenitic stainless steel material of the embodiment of the present application is suitable for use in appearance design articles where various appearance design properties such as a sense of luxury, a sense of thickness, and the like are required. As examples of the appearance design articles, mobile phones, smart phones, tablet terminals, mobile terminals such as notebook computers, frames of timepieces, signs, works of art, and the like can be listed.

[0097] The appearance design article of the embodiment of the present application includes the above-described austenitic stainless steel material.

[0098] The appearance design article of the embodiment of the present application can be produced by subjecting the above-described austenitic stainless steel material to cutting processing and mirror polishing, and has a high gloss and a sense of luxury, and is excellent in the defect resistance.

[0099] As the method of cutting processing and mirror polishing, there is no particular limitation, and a method publicly known in the technical field can be utilized. For example, the cutting processing can be performed using a cutting tool such as a turning tool, a drill, an end mill, a milling cutter, and the like.

[0100] The design property article of the embodiment of the present application can further include other components other than the above-described austenite stainless steel material. As the other components, appropriate selection according to the kind of the design property article is possible, and there is no particular limitation.

[0101] Example

[0102] Hereinafter, the content of the present application is explained in detail by citing examples, but the present application is not interpreted by these limitations.

[0103] (Examples 1 to 12 and Comparative Examples 1 to 9)

[0104] A slab was obtained by melting a stainless steel having the composition shown in Table 1 (the remainder being Fe and impurities). For a part of the obtained slab, the scale on the surface of the slab was removed, the slab was cut in the thickness direction, and in the cut surface, the position of the thickness direction depth of 5 mm from the surface of the slab was determined, and at this position, the proportion of the δ ferrite phase was measured using a ferrite scope (FERITSCOPE FMP30 manufactured by Fisher instruments). The results thereof are shown in Table 2. Subsequently, the obtained slab was heated to the temperature shown in Table 2, hot-rolled to produce a hot-rolled sheet, and then annealed at 1000 to 1200°C, whereby a hot-rolled annealed sheet was obtained. Subsequently, the hot-rolled annealed sheet was cold-rolled to produce a cold-rolled sheet of 6.0 mm, and then annealed at 1000 to 1150°C, whereby a cold-rolled annealed sheet (austenite stainless steel sheet) was obtained.

[0105] [Table 1]

[0106]

[0107] [Table 2]

[0108]

[0109] The austenite stainless steel sheet obtained above was evaluated as follows.

[0110] <Proportion of δ ferrite phase>

[0111] A test piece was cut out from the austenite stainless steel sheet, and the proportion of the δ ferrite phase was measured using a ferrite scope (FERITSCOPE FMP30 manufactured by Fisher instruments). In addition, the measurement was performed at any 3 parts on the surface of the test piece, and the average value thereof was taken as the result.

[0112] <Cutting property: cutting resistance value>

[0113] The cutting resistance value was measured by the above-described method. In this evaluation, if the cutting resistance value was 270 N or less, it was judged that the cutting resistance was low and the cuttability was excellent.

[0114] <Polishability: Glossiness Gs (20°)>

[0115] The austenitic stainless steel sheet obtained above was cut to a prescribed size to make a test piece, and then the test piece was disposed on a polishing flat to perform polishing processing, whereby mirror polishing was performed. The polishing processing was performed using an alumina slurry and a diamond slurry polishing agent as a polishing agent, the rotation speed of the polishing flat was adjusted to 90 rpm, and the pressing force was adjusted in the range of 150 to 300 g / cm 2 .

[0116] The glossiness Gs (20°) of the surface of the test piece after mirror polishing was measured by the above-described method. In this evaluation, if the glossiness Gs (20°) was 1000% or more, it was judged that the glossiness was high and the mirror polishability was excellent.

[0117] <Flaw Resistance: Specific Wear Loss>

[0118] The austenitic stainless steel sheet obtained above was cut to a prescribed size to make a test piece, and then pin-on-disc sliding wear testing was performed by the above-described method, and the specific wear loss was calculated. In this evaluation, if the specific wear loss was 60 x 10 -5 mm 3 / N·m or less, it was judged that the specific wear loss was small and the flaw resistance was excellent.

[0119] <Vickers Hardness>

[0120] The austenitic stainless steel sheet obtained above was cut to a prescribed size to make a test piece, and then the Vickers hardness of the rolled surface (surface) of the test piece was measured in accordance with JIS Z 2244:2009. In the measurement of the Vickers hardness, a condition of a load of 5 kg was set.

[0121] In this evaluation, if the Vickers hardness was less than 220 HV, it was judged that the workability was excellent.

[0122] The results of each of the above-described evaluations are shown in Table 3.

[0123] [Table 3]

[0124]

[0125] As shown in Table 3, the austenitic stainless steel sheets of Examples 1 to 12 were excellent in all of the cuttability, the mirror polishability, and the flaw resistance because they had the prescribed composition.

[0126] On the other hand, the austenitic stainless steel sheet of Comparative Example 1 has too much Co and too little Mo, and thus has high cutting resistance and insufficient machinability.

[0127] The austenitic stainless steel sheet of Comparative Example 2 has too much W, and thus has low gloss Gs(20°) and insufficient mirror polishing. It is considered that this is because the carbides and nitrides of W are coarsened.

[0128] The austenitic stainless steel sheet of Comparative Example 3 has too much V, and thus has low gloss Gs(20°) and insufficient mirror polishing. It is considered that this is because the carbides and nitrides of V are coarsened.

[0129] The austenitic stainless steel sheet of Comparative Example 4 does not contain Co, and thus has low gloss Gs(20°) and insufficient mirror polishing. It is considered that this is because burning occurs during cutting, and the burning cannot be removed even by mirror polishing.

[0130] The austenitic stainless steel sheet of Comparative Example 5 does not contain V, and thus has low gloss Gs(20°) and insufficient mirror polishing, and has a large specific wear amount and insufficient flaw resistance. It is considered that this is because fine hard carbides cannot be precipitated in the matrix phase, and the carbides and nitrides are coarsened.

[0131] The austenitic stainless steel sheet of Comparative Example 6 does not contain W. In addition, the amount of δ-ferrite phase of the austenitic stainless steel sheet becomes too much. Thus, the gloss Gs(20°) is low and the mirror polishing is insufficient due to these reasons. In addition, the austenitic stainless steel sheet of Comparative Example 6 has a large specific wear amount and insufficient flaw resistance. It is considered that this is because fine hard carbides cannot be precipitated in the matrix phase, and the carbides and nitrides are coarsened.

[0132] The austenitic stainless steel sheet of Comparative Example 7 has too much C and S, and thus has low gloss Gs(20°) and insufficient mirror polishing. It is considered that this is because the hard carbides are coarsened.

[0133] The austenitic stainless steel sheet of Comparative Example 8 does not contain B. In addition, the amount of δ-ferrite phase of the austenitic stainless steel sheet becomes too much. Thus, the gloss Gs(20°) is low and the mirror polishing is insufficient due to these reasons. It is considered that this is because hot-rolled scale-like folds are generated, and the hot-rolled scale-like folds cannot be removed even by mirror polishing.

[0134] The austenitic stainless steel sheet of Comparative Example 9 has too much Cr. In addition, the amount of δ-ferrite phase of the austenitic stainless steel sheet also becomes too much. Thus, the gloss Gs(20°) is low and the mirror polishing is insufficient. It is considered that this is because δ-ferrite is present in a large amount.

[0135] According to the above results, it is possible to provide an austenitic stainless steel material and a manufacturing method thereof, which have excellent machinability, mirror polishing properties, and flaw resistance, according to the present application.

[0136] In addition, according to the present application, it is possible to provide a design object which can be manufactured by machining and mirror polishing an austenitic stainless steel material, has high gloss and a high-class appearance, and has excellent flaw resistance.

Claims

1. An austenitic stainless steel material comprising, in mass, C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, W: 0.01 to 0.30%, and the balance consisting of Fe and impurities.

2. The austenitic stainless steel material according to claim 1, which satisfies the following formula (1), 5W + 2V + 0.45 - Co > 0 (1) wherein each symbol of the elements represents the content of each element in mass %. 5W + 2V + 0.45 - Co > 0 (1) wherein each symbol of the elements represents the content of each element in mass %. The total amount of C and N is less than 0.080 mass %.

3. The austenitic stainless steel material according to claim 1 or 2, wherein 4. The austenitic stainless steel material according to any one of claims 1 to 3, which has a metal structure in which the δ-ferrite phase is 0 to 2.0% by volume.

5. The austenitic stainless steel material according to any one of claims 1 to 4, which further comprises, in mass, one or more selected from the group consisting of Al: 0.03% or less, and Ca: 0.006% or less.

6. The austenitic stainless steel material according to any one of claims 1 to 5, which has a cutting resistance value of 270 N or less.

7. The austenitic stainless steel material according to any one of claims 1 to 6, which has a glossiness Gs (20°) of 1000% or more after mirror polishing.

9. The austenitic stainless steel material according to any one of claims 1 to 8, which is used for an appearance design article.

8. The austenitic stainless steel material according to any one of claims 1 to 7, having a specific wear amount of 60 x 10 -5 mm 3 / N-m or less in a pin-on-disc sliding wear test.

10. An appearance design article comprising the austenitic stainless steel material according to any one of claims 1 to 9. A slab comprising, in mass, C: 0.024% or less, Si: 1.00% or less, Mn: 2.00% or less, P: 0.045% or less, S: 0.015% or less, Ni: 10.0 to 15.0%, Cr: 15.0 to 22.0%, Mo: 2.0 to 4.0%, N: 0.01 to 0.15%, B: 0.001 to 0.010%, Co: 0.05 to 1.00%, V: 0.01 to 0.30%, W: 0.01 to 0.30%, and the balance consisting of Fe and impurities, is heated to 1230 to 1300°C to perform hot rolling, and the δ-ferrite phase at a depth of 5 mm from the surface in the thickness direction is 0 to 3.0% by volume.

11. A method of producing an austenitic stainless steel material, wherein The slab satisfies the following formula (1), 5W + 2V + 0.45 - Co > 0 (1) wherein each symbol of the elements represents the content of each element in mass %.

12. The method of producing an austenitic stainless steel material according to claim 11, wherein 5W + 2V + 0.45 - Co > 0 (1) wherein each symbol of the elements represents the content of each element in mass %. The total amount of C and N of the slab is less than 0.080 mass %. ​ 13. The method of producing an austenitic stainless steel material according to claim 11 or 12, wherein ​

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