Austenitic stainless steel material and method for manufacturing the same, and articles

Abstract

The present invention provides an austenite-based stainless steel material containing, by mass, 0.024% or less of C, 1.00% or less of Si, 2.00% or less of Mn, 0.045% or less of P, 0.015% or less of S,10.0-15.0% of Ni, 15.0-22.0% of Cr, 2.0-4.0% of Mo, 0.01-0.15% of N, 0.001-0.010% of B, 0.05-1.00% of Co, 0.01-0.30% of V, and 0.01-0.30% of W, the balance being Fe and impurities.

Description

[Technical Field]

[0001] This invention relates to austenitic stainless steel materials, methods for manufacturing the same, and decorative articles. [Background technology]

[0002] Stainless steel is used in a variety of applications due to its excellent properties, such as corrosion resistance. For example, SUS316, a type of austenitic stainless steel with superior corrosion resistance, is often used in the casings and components of smartphones and watches. Furthermore, when stainless steel is used in consumer-visible items such as casings, superior design is required to enhance consumer purchasing intent. While design quality depends on the era and needs, for example, it is required to enhance the gloss and give a sense of luxury by applying mirror polishing after machining the stainless steel. In addition, since scratches caused by abrasion and other factors can impair the design quality, it is also required that the material be scratch-resistant.

[0003] As an austenitic stainless steel material having a composition based on SUS316, for example, Patent Document 1 describes an austenitic stainless steel material containing, by weight %, C: 0.05% or less, Si: 1.0% or less, Mn: 0.5-2.0%, Cr: 16-24%, Ni: 10-16%, N: 0.2% or less, Mo: 4.0% or less, with the remainder being Fe and unavoidable impurities. Patent Document 2 also describes an austenitic stainless steel material containing, by mass %, C: 0.03-0.18%, N: 0.05-0.30%, Si: 1.5% or less, Mn: 2.0% or less, Ni: 8.0-15.0%, Cr: 15.0-25.0%, Mo: 0.20-3.0%, Cu: 2.0% or less, with the remainder being Fe and unavoidable impurities. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2021-504587 [Patent Document 2] Patent No. 5618057 [Overview of the project] [Problems that the invention aims to solve]

[0005] Generally, while SUS316 has excellent corrosion resistance, it suffers from the problem of insufficient machinability due to its high cutting resistance. Furthermore, mirror polishing after machining is difficult for materials with high cutting resistance. On the other hand, while scratch resistance can be improved by increasing the strength of the matrix, increasing the strength of the matrix increases cutting resistance and reduces machinability. Furthermore, while the austenitic stainless steel material described in Patent Document 1 has excellent corrosion resistance and non-magnetic properties, it does not particularly address issues with machinability, mirror polishability, and scratch resistance. Furthermore, while the austenitic stainless steel material described in Patent Document 2 exhibits excellent corrosion resistance as well as machinability such as plastic deformation and cutting, and possesses hydrogen brittleness resistance, it does not particularly address issues with mirror polishability and scratch resistance.

[0006] The present invention was made to solve the above-mentioned problems, and aims to provide an austenitic stainless steel material and a method for manufacturing the same that are excellent in machinability, mirror polishability, and scratch resistance. Furthermore, the present invention aims to provide an aesthetically pleasing article that can be manufactured by cutting and mirror polishing an austenitic stainless steel material, possessing high gloss and a luxurious feel, as well as excellent scratch resistance. [Means for solving the problem]

[0007] The machinability of austenitic stainless steel is influenced by the strength and ductility of the matrix phase. In other words, the machinability of austenitic stainless steel can be improved by reducing the ductility of the matrix phase without increasing its strength. Therefore, we attempted to reduce the ductility of the matrix phase while suppressing an increase in the matrix phase's strength by dissolving small amounts of V and W into the matrix phase. Furthermore, the mirror polishability of austenitic stainless steel is affected by the presence of inclusions, coarse carbides, and δ-ferrite. In addition, if galling occurs during mirror polishing, or if dents generated during hot rolling (hereinafter referred to as "hot dents") remain, these may reduce the gloss, so it is necessary to suppress these as well. Therefore, we attempted to minimize the amount of Al and Ca that form inclusions, suppress the formation of coarse carbides by adjusting the content of S, B, V, and W, improve heat resistance and suppress galling by adding Co and W, and suppress the occurrence of hot dents by adding B. Furthermore, the scratch resistance of austenitic stainless steel can be improved by precipitating fine hard carbides in the matrix. Therefore, we attempted to improve scratch resistance by adding V and W, which readily generate fine hard carbides.

[0008] Based on the above considerations, the inventors fabricated and analyzed austenitic stainless steel materials of various compositions based on the composition of SUS316, which has excellent corrosion resistance. As a result, they found that by using a specific composition, it is possible to improve all of the following: machinability, mirror polishability, and scratch resistance, thus completing the present invention.

[0009] In other words, the present invention relates to an austenitic stainless steel material comprising, by 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: 10.0~15.0%, Cr: 15.0~22.0%, Mo: 2.0~4.0%, N: 0.01~0.15%, B: 0.001~0.010%, Co: 0.05~1.00%, V: 0.01~0.30%, W: 0.01~0.30%, with the remainder being Fe and impurities.

[0010] Furthermore, the present invention includes the austenitic stainless steel material. things It is a product.

[0011] Furthermore, the present invention relates to a method for producing austenitic stainless steel, which involves heating a slab to 1230 to 1300°C and hot-rolling it, wherein the slab contains, by 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%, with the remainder being Fe and impurities, and the δ-ferrite phase at a thickness depth of 5 mm from the surface is 0 to 3.0 volume%, and then hot-rolling it. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an austenitic stainless steel material with excellent machinability, mirror polishability, and scratch resistance, as well as a method for manufacturing the same. Furthermore, according to the present invention, it is possible to manufacture an austenitic stainless steel material by cutting and mirror polishing, providing an aesthetically pleasing article with high gloss and a luxurious feel, as well as excellent scratch resistance. [Modes for carrying out the invention]

[0013] The embodiments of the present invention will be described in detail below. The present invention is not limited to the embodiments described below, and it should be understood that modifications, improvements, etc., made to the embodiments described below, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention, also fall within the scope of the present invention. In this specification, unless otherwise specified, any "%" indication for ingredients refers to "mass%".

[0014] The austenitic stainless steel material according to an embodiment of the present invention 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 balance consists of Fe and impurities. Here, in this specification, "austenitic" means that the metal structure is mainly an austenite phase at normal temperature. Therefore, "austenitic" includes those that slightly contain phases other than the austenite phase (for example, ferrite phase, martensite phase, etc.). Also, in this specification, "stainless steel material" means a material formed from stainless steel, and its material form is not particularly limited. Examples of the material form include plate-like (including strip-like), rod-like, tubular, etc. Further, the material may be various shaped steels such as T-shaped or I-shaped in cross-sectional shape. 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 the austenitic stainless steel material, and are allowed within a range that does not adversely affect the present invention. For example, elements such as O are included in the impurities. O included as an impurity is generally 0.030% or less. Furthermore, regarding the content of each element in this specification, including "xx% or less" means that it is xx% or less, but includes an amount exceeding 0% (especially exceeding the impurity level).

[0015] In addition, the austenitic stainless steel material according to an embodiment of the present invention may further contain one or more selected from Al: 0.03% or less and Ca: 0.006% or less. Therefore, the austenitic stainless steel material according to an embodiment of the present invention containing these elements can be expressed 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 - 15.0%, Cr: 15.0 - 22.0%, Mo: 2.0 - 4.0%, N: 0.01 - 0.15%, B: 0.001 - 0.010%, Co: 0.05 - 1.00%, V: 0.01 - 0.30%, W: 0.01 - 0.30%, further containing one or more selected from Al: 0 - 0.03% and Ca: 0 - 0.006%, and the balance being composed of Fe and impurities. Here, regarding the content of each element in this specification, the inclusion of "0 to xx%" means that it is xx% or less, but also includes the concept of not including 0% (when not included). Hereinafter, each component will be described in detail.

[0016] <C: 0.024% or less> [[ID=IO]]C is an element that forms an austenite phase (γ phase) and is an element effective for increasing the strength of the parent phase. In particular, C can combine with V or W to precipitate fine hard carbides in the parent phase, so the resistance to galling can be improved. However, if the content of C is too high, the hard carbides tend to coarsen and the mirror polishing property deteriorates. Therefore, the upper limit value of the C content is controlled to 0.024%, preferably 0.023%. On the other hand, the lower limit value of the C content is not particularly limited, but from the viewpoint of obtaining the above effects of C, it is preferably 0.001%, more preferably 0.003%, and still more preferably 0.00s%.

[0017] <Si: 1.00% or less> If the Si content is too high, the workability of austenitic stainless steel will deteriorate. Therefore, the upper limit value of the Si content is controlled to be 1.00%, preferably 0.98%, more preferably 0.96%. On the other hand, the lower limit value of the Si content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0018] <Mn: 2.00% or less> Mn is an element that forms an austenite phase. If the Mn content is too high, the corrosion resistance of austenitic stainless steel will deteriorate. Therefore, the upper limit value of the Mn content is controlled to be 2.00%, preferably 1.95%, more preferably 1.90%. On the other hand, the lower limit value of the Mn content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0019] <P: 0.045% or less> If the P content is too high, the workability of austenitic stainless steel will deteriorate. Therefore, the upper limit value of the P content is controlled to be 0.045%, preferably 0.043%. On the other hand, the lower limit value of the P content is not particularly limited, but is preferably 0.001%, more preferably 0.005%, and even more preferably 0.010%.

[0020] <S: 0.015% or less> If the S content is too high, the manufacturability of austenitic stainless steel will deteriorate, and inclusions are likely to form, impairing the mirror-polishing property. Therefore, the upper limit value of the S content is controlled to be 0.015%, preferably 0.014%. On the other hand, the lower limit value of the S content is not particularly limited, but is preferably 0.0001%, more preferably 0.0003%, and even more preferably 0.0005%.

[0021] <Ni: 10.0 - 15.0%> Ni, like Mn, is an element that forms the austenite phase. Since Ni is expensive, too much Ni content leads to increased manufacturing costs. Therefore, the upper limit of Ni content is controlled to 15.0%, preferably 14.8%, and more preferably 14.6%. On the other hand, if the Ni content is too low, the corrosion resistance and workability of the austenitic stainless steel material will decrease, and it will become difficult to obtain an austenite structure. Therefore, the lower limit of Ni content is controlled to 10.0%, preferably 10.3%, and more preferably 10.5%.

[0022] <Cr:15.0~22.0%> Cr is an effective element for improving the corrosion resistance of austenitic stainless steel. However, if the Cr content is too high, the mirror polishability of the austenitic stainless steel will decrease due to the formation of δ-ferrite. Therefore, the upper limit of the Cr content is controlled to 22.0%, preferably 21.8%, and more preferably 21.6%. On the other hand, if the Cr content is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit of the Cr content is controlled to 15.0%, preferably 15.2%.

[0023] <Mo:2.0~4.0%> Mo is an element added to improve corrosion resistance. However, since Mo is expensive, too much Mo content leads to increased manufacturing costs. Therefore, the upper limit of the Mo content is controlled to 4.0%, preferably 3.9%. On the other hand, the lower limit of the Mo content is 2.0%, preferably 2.1%, more preferably 2.2%, and even more preferably 2.5%, from the viewpoint of ensuring corrosion resistance.

[0024] <N:0.01~0.15%> N is an element that is effective in improving corrosion resistance. To obtain this effect, the lower limit of the N content is controlled to 0.01%, preferably 0.02%. On the other hand, if the N content is too high, the workability of the austenitic stainless steel material will decrease. Therefore, the upper limit of the N content is controlled to 0.15%, preferably 0.14%.

[0025] <B:0.001~0.010%> B is an effective element for improving hot workability (suppressing the occurrence of hot burrs). To obtain this effect, the lower limit of the B content is controlled to 0.001%, preferably 0.002%. On the other hand, if the B content is too high, the effect of B saturates, and conversely, the mirror polishability decreases due to the formation of boride precipitates. Therefore, the upper limit of the B content is controlled to 0.010%, preferably 0.009%.

[0026] <Co:0.05~1.00%> Co is an element that suppresses burning caused by machining heat in the cutting area when austenitic stainless steel is machined. Co also improves corrosion resistance after mirror polishing. To obtain these effects, the lower limit of the Co content is controlled to 0.05%, preferably 0.06%. On the other hand, if the Co content is too high, the effect of Co saturates, and the cutting resistance increases, reducing machinability. Therefore, the upper limit of the Co content is controlled to 1.00%, preferably 0.98%, more preferably 0.95%.

[0027] <V:0.01~0.30%> V is an element that combines with C to precipitate fine hard carbides in the matrix phase. These fine hard carbides improve scratch resistance without impairing mirror polishability. In addition, some of the V dissolves in the matrix phase, reducing its ductility. This reduces cutting resistance, thus improving machinability. To obtain these effects, the lower limit of the V content is controlled to 0.01%, preferably 0.02%. On the other hand, if the V content is too high, the V carbides and nitrides tend to coarseen, reducing mirror polishability. Therefore, the upper limit of the V content is controlled to 0.30%, preferably 0.29%.

[0028] <W:0.01~0.30%> Similar to V, W is an element that combines with C to precipitate fine hard carbides in the matrix phase. These fine hard carbides can improve the anti-scratch property without impairing the mirror-polishability. Also, a part of W dissolves in the matrix phase to lower the ductility of the matrix phase. As a result, the cutting resistance decreases, so the cutting performance can be improved. To obtain these effects, the lower limit of the content of W is controlled to 0.01%, preferably 0.02%. On the other hand, if the content of W is too high, carbides and nitrides of W tend to coarsen, so the mirror-polishability decreases. Therefore, the upper limit of the content of W is controlled to 0.30%, preferably 0.29%.

[0029] <Al: 0.03% or less> Al is an element that is added as needed for deoxidation in the refining process and improves corrosion resistance and heat resistance. On the other hand, Al is an element that generates inclusions that lower the mirror-polishability. Therefore, the upper limit of the content of Al is controlled to 0.03%, preferably 0.02%. On the other hand, since Al may not be contained, its lower limit is not particularly limited. The lower limit when Al is contained is, for example, 0.01%.

[0030] <Ca: 0.006% or less> Ca is an element that is added as needed to improve hot workability. On the other hand, Ca is an element that generates inclusions that lower the mirror-polishability. Therefore, the upper limit of the content of Ca is controlled to 0.006%, preferably 0.005%. On the other hand, since Ca may not be contained, its lower limit is not particularly limited. The lower limit when Ca is contained is, for example, 0.001%.

[0031] The austenitic stainless steel material according to an embodiment of the present invention preferably satisfies the following formula (1). 5W + 2V + 0.4Co ≥ 0 ···(1) In the formula, each element symbol represents the content (mass%) of each element. The above formula (1) is an index that represents the balance of W, V, and Co content, which affects machinability, mirror polishability, and scratch resistance. By satisfying the above formula (1), the content of W, V, and Co can be controlled to an appropriate balance, making it possible to stably improve machinability, mirror polishability, and scratch resistance.

[0032] In the embodiment of the present invention, the austenitic stainless steel material preferably has a C and N content of less than 0.080%. C and N are elements that affect the hardness of austenitic stainless steel, and by reducing the content of these elements, the austenitic stainless steel can be softened and its workability can be further improved. For this purpose, the total amount of C and N is preferably less than 0.080%, more preferably 0.075% or less, and even more preferably 0.070% or less.

[0033] In the embodiment of the present invention, the austenitic stainless steel material preferably has a microstructure in which the δ-ferrite phase is 0 to 2.0 volume percent. The δ-ferrite phase adversely affects mirror polishability, and its presence in large quantities in austenitic stainless steel reduces the glossiness of the product. Therefore, the amount of δ-ferrite phase is preferably 0 to 2.0 volume%, more preferably 0 to 1.5 volume%, and even more preferably 0 to 1.0 volume%. In this specification, "0% by volume of δ-ferrite phase" means that the δ-ferrite phase is not present.

[0034] The proportion of δ-ferrite phase in the austenitic stainless steel material according to the embodiment of the present invention is determined by magnetic induction. For example, the proportion of δ-ferrite phase can be measured using a ferrite scope (e.g., a FERITSCOPE FMP30 manufactured by Fischer Instruments).

[0035] The austenitic stainless steel material according to the embodiment of the present invention preferably has a cutting resistance of 270 N or less, more preferably 240 N or less, and even more preferably 220 N or less. A cutting resistance within this range can be considered low, thus improving machinability. The lower limit of the cutting resistance is not particularly limited, but for example, it is 100 N. Here, the cutting resistance value can be measured by a cutting test in which austenitic stainless steel material is slotted using an end mill (Korloy; outer diameter φ12 mm). In slotting, the horizontal component force (feed component force) acting in the feed direction is defined as the cutting resistance. The conditions for slotting are as follows. Cutting speed (Vc): 96m / min Rotation speed: 2550 rpm Feed rate per tooth (Fz): 0.025 mm / min Feed rate (Vf): 255 mm / min Axial cutting depth (Ap): 5mm Wet machining (with cutting fluid)

[0036] In the embodiment of the present invention, the austenitic stainless steel material preferably has a glossiness Gs(20°) of 1000% or more after mirror polishing, more preferably 1030% or more, and even more preferably 1050% or more. With glossiness within this range, it can be said that mirror polishability is good and seizing and hot erosion can be suppressed. The upper limit of glossiness Gs(20°) is not particularly limited, but for example it is 1500%. Here, gloss level Gs(20°) refers to a 20-degree specular gloss measured in accordance with JIS Z8741:1997. Gloss level Gs(20°) can be measured in accordance with JIS Z8741:1997 using a gloss meter (Microtrigloss, manufactured by BYK-Gardner). Gloss level Gs(20°) is measured at five arbitrary locations excluding the area within 5 mm from the edge, and the average value is used as the evaluation result. In addition, each measurement position should be spaced at least 5 mm apart.

[0037] The austenitic stainless steel material according to an embodiment of the present invention has a specific wear rate in a pin-on-disk wear test of 60×10 -5 mm 3 / N·m or less, preferably 55×10 -5 mm 3 / N·m or less, more preferably 50×10 -5 mm 3 / N·m or less. If the specific wear rate is within such a range, it can be said that the wear resistance with flaws is good. The lower limit value of the specific wear rate is not particularly limited, but for example, it is 10×10 -5 mm 3 / N·m. Here, the specific wear rate in the pin-on-disk wear test can be measured using a pin-on-disk type wear tester by cutting out a disk-shaped test piece with a diameter of 8 mm from the austenitic stainless steel material. The pin-on-disk wear test is performed by fixing the disk-shaped test piece to a sample holder and pressing the surface of the test piece against a rotating abrasive paper (#800 abrasive paper coated with SiC) with a test load F = 20 N. At this time, the rotation speed is 0.66 m / second, the rotation number is 140 rpm, and the friction distance L is 200 m. Then, the volume of the material lost due to wear is calculated from the difference in the thickness of the test piece before and after the pin-on-disk wear test, and this is taken as the wear loss W (mm 3 ). And the specific wear rate is calculated by the following formula. Specific wear rate (mm 3 / N·m) = Wear loss W / (Test load F × Friction distance L)

[0038] The austenitic stainless steel material according to an embodiment of the present invention is not particularly limited in its type as long as it has the above characteristics. For example, the austenitic stainless steel material according to an embodiment of the present invention may be either a hot-rolled steel material or a cold-rolled steel material.

[0039] The austenitic stainless steel material according to the embodiment of the present invention can be manufactured by methods known in the art, except for melting stainless steel that satisfies the above composition. A typical manufacturing method is described below, but the manufacturing method of the austenitic stainless steel material according to the embodiment of the present invention is not limited to the following.

[0040] An austenitic stainless steel material according to an embodiment of the present invention can be manufactured, for example, by hot-rolling a slab having the above composition. Depending on the application, cold rolling may be performed after hot rolling. Furthermore, annealing and pickling may be performed after hot rolling and cold rolling, respectively, as needed. The conditions for hot rolling and cold rolling are not particularly limited and can be adjusted as appropriate according to the component composition. For example, in hot rolling, the heating temperature before rolling is set to 1200-1300°C, and after hot rolling, annealing can be performed at 1000-1200°C as needed. It is preferable that the heating temperature before rolling be 1230-1300°C. Furthermore, it is preferable to anneal at 1000-1150°C after cold rolling as needed.

[0041] Furthermore, as described above, the austenitic stainless steel material according to the embodiment of the present invention preferably has a δ-ferrite phase of 0 to 2.0 volume%, but in order to manufacture such an austenitic stainless steel material, it is preferable that the δ-ferrite phase at a depth of 5 mm in the thickness direction from the surface of the slab subjected to hot rolling be 0 to 3.0 volume%, and that the heating temperature before hot rolling be 1230 to 1300°C. If the δ-ferrite phase at that position in the slab exceeds 3.0 volume%, the δ-ferrite phase tends to remain in the austenitic stainless steel material, resulting in a decrease in mirror polishability. While a lower limit on the proportion of δ-ferrite phase at the relevant location in the slab is not strictly necessary, it is preferable to set it to 0.1 volume% or more, and more preferably 0.2 volume% or more, from the viewpoint of suppressing S segregation at grain boundaries and suppressing the occurrence of burr defects during hot rolling. Note that if burr defects occur, the amount of material removed during polishing increases, thus increasing the load on the machining process.

[0042] Here, the proportion of the δ-ferrite phase at a depth of 5 mm from the surface of the slab can be determined as follows. First, the oxide scale on the surface of the slab is removed, and then the slab is cut in the thickness direction. Next, at the cross-section of the slab in the thickness direction, the position at a depth of 5 mm from the surface of the slab is identified, and the proportion of the δ-ferrite phase at that position is measured using a ferritescope (for example, a FERITSCOPE FMP30 from Fischer Instruments).

[0043] The austenitic stainless steel material according to the embodiment of the present invention has excellent machinability, mirror polishability, and scratch resistance, and can therefore be used in a variety of applications where these properties are required. For example, the austenitic stainless steel material according to the embodiment of the present invention is suitable for use in decorative articles where various design qualities such as a sense of luxury and substantiality are required. Examples of decorative articles include mobile devices such as cell phones, smartphones, tablet devices, and laptop computers, as well as casings for watches, nameplates, and works of art.

[0044] The decorative article according to an embodiment of the present invention includes the above-mentioned austenitic stainless steel material. The decorative articles according to the embodiments of the present invention can be manufactured by cutting and mirror polishing the above-mentioned austenitic stainless steel material, and have a high gloss and a luxurious feel, as well as excellent scratch resistance. The methods for cutting and mirror polishing are not particularly limited, and methods known in the art can be used. For example, cutting can be performed using cutting tools such as turning tools, drills, end mills, and milling cutters.

[0045] The decorative article according to the embodiment of the present invention may further include other components besides the austenitic stainless steel material described above. These other components can be appropriately selected depending on the type of decorative article and are not particularly limited. [Examples]

[0046] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0047] (Examples 1-12 and Comparative Examples 1-9) Stainless steel having the composition shown in Table 1 (the remainder being Fe and impurities) was melted to obtain slabs. For a portion of the obtained slabs, the oxide scale on the surface was removed, and the slab was cut in the thickness direction. At the cut surface, a position 5 mm deep from the slab surface was identified, and the proportion of the δ-ferrite phase was measured at that position using a ferrite scope (Fischer Instruments FERITSCOPE FMP30). The results are shown in Table 2. Next, the obtained slabs were heated to the temperatures shown in Table 2, hot-rolled to obtain hot-rolled sheets, and then annealed at 1000-1200°C to obtain hot-rolled annealed sheets. Next, the hot-rolled annealed sheets were cold-rolled to obtain 6.0 mm cold-rolled sheets, and then annealed at 1000-1150°C to obtain cold-rolled annealed sheets (austenitic stainless steel sheets).

[0048] [Table 1]

[0049] [Table 2]

[0050] The austenitic stainless steel sheets obtained above were evaluated as follows.

[0051] <Proportion of δ-ferrite phase> Test specimens were cut from austenitic stainless steel sheets, and the proportion of the δ-ferrite phase was measured using a ferritescope (Fischer Instruments FERITSCOPE FMP30). Measurements were taken at three arbitrary locations on the surface of the specimen, and the average value was used as the result.

[0052] <Machinability: Cutting resistance value> The cutting resistance was measured according to the method described above. In this evaluation, if the cutting resistance is 270 N or less, it can be determined that the cutting resistance is low and the cutting performance is excellent.

[0053] <Mirror polishability: Gloss level Gs (20°)> After preparing test specimens by cutting the austenitic stainless steel sheets obtained above to the specified size, the test specimens were placed on a lapping plate and mirror-polished by lapping. For the lapping process, alumina slurry and diamond slurry abrasives were used as lapping agents, with the lapping plate rotating at 90 rpm and a pressing force of 150-300 g / cm². 2 The adjustments were made within the specified range, and then polishing was performed. The gloss level Gs(20°) of the surface of the mirror-polished test specimen was measured according to the method described above. In this evaluation, if the gloss level Gs(20°) is 1000% or higher, it can be judged that the gloss level is high and the mirror polishability is excellent.

[0054] <Scratch resistance: Specific abrasion rate> After cutting the austenitic stainless steel sheet obtained above to the specified size to prepare test specimens, a pin-on-disk abrasion test was performed according to the method described above, and the specific wear amount was calculated. In this evaluation, the specific wear amount was 60 × 10⁻⁶. -5 mm 3 If the value is less than / N·m, it can be judged that the specific wear rate is low and the scratch resistance is excellent.

[0055] <Vickers hardness> After cutting the austenitic stainless steel sheet obtained above to the specified size to prepare test specimens, the Vickers hardness of the rolled surface (surface) of the test specimens was measured in accordance with JIS Z2244:2009. The Vickers hardness measurement was performed under a load of 5 kg. In this evaluation, if the Vickers hardness is less than 220 HV, it can be judged to have excellent machinability.

[0056] The results of each of the above evaluations are shown in Table 3.

[0057] [Table 3]

[0058] As shown in Table 3, the austenitic stainless steel sheets of Examples 1 to 12 had the specified composition and therefore exhibited excellent machinability, mirror polishability, and scratch resistance. In contrast, the austenitic stainless steel sheet of Comparative Example 1 had too much Co and too little Mo, resulting in high cutting resistance and insufficient machinability. The austenitic stainless steel sheet in Comparative Example 2 had a high W content, resulting in a low gloss index Gs(20°) and insufficient mirror polishability. This is thought to be due to the coarsening of the W carbides and nitrides. The austenitic stainless steel sheet in Comparative Example 3 had a high V content, resulting in a low gloss index Gs(20°) and insufficient mirror polishability. This is thought to be due to the coarsening of the V carbides and nitrides. The austenitic stainless steel sheet in Comparative Example 4 did not contain Co, resulting in a low gloss index Gs(20°) and insufficient mirror polishability. This is thought to be because burning occurred during cutting, and the burning could not be removed even by mirror polishing.

[0059] The austenitic stainless steel sheet of Comparative Example 5, lacking V, had a low gloss index Gs(20°), insufficient mirror polishability, a high specific abrasion rate, and insufficient scratch resistance. This is thought to be because fine hard carbides could not be precipitated in the matrix, resulting in coarser carbides and nitrides. The austenitic stainless steel sheet of Comparative Example 6 did not contain W. Furthermore, this austenitic stainless steel sheet had an excessive amount of δ-ferrite phase. As a result, these factors led to a low gloss index Gs(20°) and insufficient mirror polishability. Additionally, the austenitic stainless steel sheet of Comparative Example 6 had a high specific abrasion rate and insufficient scratch resistance. This is thought to be because fine hard carbides could not be precipitated in the matrix, resulting in coarser carbides and nitrides. The austenitic stainless steel sheet in Comparative Example 7 had a low gloss index Gs(20°) and insufficient mirror polishability due to excessive C and S content. This is thought to be because the hard carbides became coarse. The austenitic stainless steel sheet of Comparative Example 8 did not contain B. Furthermore, this austenitic stainless steel sheet had an excessive amount of δ-ferrite phase. Therefore, due to these factors, the gloss index Gs(20°) was low and the mirror polishability was insufficient. This is thought to be because hot burrs occurred, and these burrs could not be removed even by mirror polishing. The austenitic stainless steel sheet in Comparative Example 9 had too much Cr content. Furthermore, this austenitic stainless steel sheet also had too much δ-ferrite phase. As a result, its gloss index Gs(20°) was low, and its mirror polishability was insufficient. This is thought to be due to the large amount of δ-ferrite remaining in the sheet.

[0060] As can be seen from the above results, the present invention provides an austenitic stainless steel material and a method for manufacturing the same that are excellent in machinability, mirror polishability, and scratch resistance. Furthermore, according to the present invention, it is possible to manufacture an austenitic stainless steel material by cutting and mirror polishing, providing an aesthetically pleasing article with high gloss and a luxurious feel, as well as excellent scratch resistance.

Claims

1. Austenitic stainless steel material containing, by 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%, with the remainder being Fe and impurities.

2. An austenitic stainless steel material according to claim 1, satisfying the following formula (1). 5W+2V+0.45-Co≧0...(1) In the formula, each element symbol represents the content (mass %) of each element.

3. The austenitic stainless steel material according to claim 1 or 2, wherein the total amount of C and N is less than 0.080% by mass.

4. The austenitic stainless steel material according to claim 1 or 2, having a metallic structure in which the δ-ferrite phase is 0 to 2.0 volume percent.

5. The austenitic stainless steel material according to claim 1 or 2, further comprising one or more selected from Al: 0.03% or less and Ca: 0.006% or less by mass.

6. An austenitic stainless steel material according to claim 1 or 2, wherein the cutting resistance value is 270 N or less.

7. The austenitic stainless steel material according to claim 1 or 2, wherein the glossiness Gs (20°) after mirror polishing is 1000% or more.

8. The specific wear amount in the pin-on-disk wear test was 60 × 10⁻⁶. -5 mm 3 An austenitic stainless steel material according to claim 1 or 2, wherein the value is less than or equal to / N·m.

9. An article comprising the austenitic stainless steel material according to claim 1 or 2.

10. A method for producing austenitic stainless steel, comprising heating a slab to 1230 to 1300°C and hot rolling it, wherein the slab contains, by 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%, with the remainder being Fe and impurities, and the δ-ferrite phase at a thickness depth of 5 mm from the surface is 0 to 3.0 volume%, and hot rolling it.

11. The method for manufacturing an austenitic stainless steel material according to claim 10, wherein the slab satisfies the following formula (1). 5W+2V+0.45-Co≧0...(1) In the formula, each element symbol represents the content (mass %) of each element.

12. The method for producing an austenitic stainless steel material according to claim 10 or 11, wherein the slab has a total amount of C and N of less than 0.080% by mass.

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