Stainless steel and manufacturing method for stainless steel

Abstract

To provide a stainless steel and the like excellently bondable to a non-metal material.SOLUTION: A stainless steel (1) has an irradiation part (2) irradiated with pulse laser (PL) at least in part on a surface (10). The irradiation part (2) includes a plurality of recesses and a plurality of protrusions adjacent to the recesses. The recesses and the protrusions are in indeterminate forms respectively. The protrusions have a width of 0.1 μm or more and 200 μm or less in a planar view, a gap between the protrusions located with the recesses in between is not beyond 300 μm, and a surface expansion ratio in the irradiation part is 1.1 or larger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to stainless steel and a method for producing stainless steel. [Background technology]

[0002] Taking advantage of its excellent properties such as corrosion resistance, magnetism, and surface appearance, stainless steel is used in a wide range of fields, including automobiles, building materials, and electronic devices. Conventionally, when stainless steel is used as a component material, stainless steel pieces are joined together by various welding or brazing methods.

[0003] In recent years, the trend toward multi-materials, where unique materials are combined in the right places, has been increasing in various fields. As a result, there is a demand for methods to join dissimilar materials, such as combining metal materials with resins, which are difficult to join using conventional methods such as welding.

[0004] As an example of such a joining, direct joining of stainless steel with non-metallic materials such as adhesives or thermoplastic resins is desired. However, stainless steel has a passive film and an oxide film on its surface, and its affinity with non-metallic materials is low, so that it may have poor adhesion and direct joining properties.

[0005] For example, Patent Document 1 discloses a method for joining fluororesin materials, in which one of the materials to be joined is a fluororesin material, and the method includes a step of applying a mixed solution containing sodium to the surface of the other material to be joined, and then irradiating the surface with a laser. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-123153 Summary of the Invention [Problem to be solved by the invention]

[0007] From the viewpoint of environmental protection, there is a growing need to avoid the use of alkaline cleaning or chemicals containing organic solvents. The technology described in Patent Document 1 requires the use of a mixed solution containing sodium. Furthermore, Patent Document 1 does not disclose any specific conditions for laser irradiation.

[0008] An object of one aspect of the present invention is to provide a stainless steel or the like that can be bonded well to a non-metallic material without requiring chemical treatment of the surface. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, a stainless steel according to one embodiment of the present invention has an irradiated area on at least a part of its surface that has been irradiated with a pulsed laser, the irradiated area including a plurality of depressions and a plurality of raised areas adjacent to the depressions, the depressions and the raised areas each having an irregular shape, the raised areas having a width of 0.1 μm or more and 200 μm or less in a planar view, the spacing between the raised areas located on either side of the depressions does not exceed 300 μm, and the surface magnification ratio in the irradiated area is 1.1 or more.

[0010] In order to solve the above problems, a method for producing stainless steel according to one aspect of the present invention includes a step of irradiating at least a part of the surface of the stainless steel with a pulsed laser, the irradiation having a fluence of 1.2 to 6.5 J / cm 2 The overlapping number of pulsed laser marks, as shown in the following formula (1), is set to 0.5 to 200: Number of overlaps = S × fs / (W × VL) (1) In the above formula (1), S is the beam area (mm 2 ), fs is the pulse irradiation speed (Hz), W is the irradiation width (mm), and VL is the feed speed of the irradiated object (mm / s). [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to realize stainless steel or the like that can be bonded well to non-metallic materials without requiring chemical treatment of the surface. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 10 is a schematic diagram illustrating a stainless steel according to a second embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing an electron microscope image taken at a high magnification of the surface of the stainless steel according to the second embodiment of the present invention. [Figure 3] FIG. 10 is a diagram showing an electron microscope image taken at a high magnification of a cross section of stainless steel according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram for explaining an irradiation portion of stainless steel in embodiment 3 of the present invention. [Figure 5] FIG. 10 is a diagram showing an electron microscope image taken at a high magnification of the surface of stainless steel according to the third embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing an electron microscope image taken at a high magnification of a cross section of stainless steel according to a third embodiment of the present invention. [Figure 7] FIG. 10 is a diagram showing an electron microscope image taken at a high magnification of the surface of stainless steel in another configuration example of the third embodiment of the present invention. [Figure 8] FIG. 10 is a view showing an electron microscope image of the surface of the stainless steel according to Example 3 of the present invention. [Figure 9] FIG. 10 is a view showing an electron microscope image of the surface of the stainless steel according to Example 16 of the present invention. [Figure 10] FIG. 10 is a view showing an electron microscope image of the surface of the stainless steel according to Comparative Example 2. [Figure 11] FIG. 10 is a view showing an electron microscope image of the surface of the stainless steel according to Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment 1] An embodiment of the present invention will be described below. Note that the present invention is not limited to the following embodiments or examples, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. Furthermore, in this specification, "A to B" indicates A or more and B or less.

[0014] An object of one embodiment of the present invention is to provide a stainless steel and a method for manufacturing the same that enable the production of composite structural members by combining stainless steel with resin, or stainless steel with dissimilar metals, etc. Such composite structural members can be used in related industrial fields such as transportation equipment, food processing equipment, and chemical equipment. Specific examples include, for example, in the automotive field, vehicle body structures, electronic devices, braking equipment, heat exchange equipment, and battery equipment. One example is a metal-resin bonded body in which a dustproof and waterproof cover for an electronic device component or an EV battery case is bonded to a housing using an adhesive technique.

[0015] [1. Stainless steel] <Surface form> A stainless steel according to one embodiment of the present invention (hereinafter sometimes referred to as "the present stainless steel") has an irradiated portion on at least a part of its surface that has been irradiated with a pulsed laser. The irradiated portion has a fluence of 1.2 to 6.5 J / cm. 2 The overlapping number of pulsed laser marks is 0.5 to 200, and is the portion irradiated with the pulsed laser so that the overlapping number of pulsed laser marks represented by the following formula (1) is 0.5 to 200.

[0016] Number of overlaps = S × fs / (W × VL) (1) In the above formula (1), S is the beam area (mm 2 ), fs is the irradiation speed (Hz), W is the irradiation width (mm), and VL is the feed speed of the irradiated object (mm / s).

[0017] The irradiated area is a portion of the surface of the stainless steel that has a higher affinity with non-metallic materials than other portions. Non-metallic materials are materials that are different from metallic materials such as stainless steel, and examples include adhesives and thermoplastic resins. High affinity with non-metallic materials means, for example, that it is easier to increase the bonding strength between the stainless steel and non-metallic materials.

[0018] This stainless steel is suitable for direct bonding to non-metallic materials, and can also be easily bonded to other stainless steels or other materials via adhesives, which are examples of non-metallic materials.

[0019] The irradiated area is a part of the surface of the stainless steel that is irradiated with a pulsed laser. The pulsed laser has a fluence of 1.2 to 6.5 J / cm. 2 It is preferable that:

[0020] The fluence of a pulsed laser is the value obtained by dividing the pulse energy by the beam diameter, and is the irradiation energy density for each pulse. The fluence of a pulsed laser is determined from the energy of the pulsed laser, the beam diameter of the pulsed laser, and, if necessary, the energy density distribution of the pulsed laser. The fluence of a pulsed laser may be calculated appropriately according to the characteristics of the pulsed laser, and is, for example, calculated as follows: Peak fluence = (E / (π(D / 2) 2 ))×10 8 It can be calculated using the formula below, where E represents pulse energy (J) and D represents beam diameter (μm). Peak fluence represents the fluence value when the pulse laser output is constant and the irradiation distance (focus) of the pulse laser is set to the value at which the fluence is at its maximum. Furthermore, the fluence of the pulse laser can be adjusted by the output of the pulse laser or by the irradiation distance (focus) of the pulse laser.

[0021] The overlapping number of pulsed laser marks is calculated using the above formula (1). The overlapping number indicates the number of overlapping pulse irradiations at any one point in the irradiation area. Even if the fluence of the pulsed laser is the same, the greater the overlapping number, the greater the impact of heat and other factors caused by the pulsed laser irradiation.

[0022] When calculating the number of overlaps, the beam area S [mm 2 ]is π(D / 2) 2 The pulsed laser beam diameter D is the so-called full width at half maximum, measured as the distance (full width) between two points where the beam intensity is half the maximum intensity (beam center position) in the beam intensity distribution on a plane perpendicular to the beam propagation direction. The pulsed laser irradiation speed fs can also be referred to as the irradiation frequency or pulse frequency. The pulsed laser irradiation width is the width of the irradiated area formed on the stainless steel, and indicates the length of the range of movement in the direction of movement of the pulsed laser position irradiated on the irradiated object during pulsed laser irradiation. The irradiated object is the stainless steel on which the irradiated area is formed, and can also be considered the base material of the stainless steel. In pulsed laser irradiation, the irradiated object is irradiated while moving in any direction, and the speed of this movement is the feed speed VL of the irradiated object.

[0023] The overlap number of the pulsed laser marks is 0.5 to 200. From the viewpoint of improving the affinity with the non-metallic material in the irradiated portion, the overlap number is preferably 1.5 or more. Furthermore, when the overlap number exceeds 50, the irradiation effect becomes almost saturated. From the viewpoint of manufacturability, it is not preferable to have an excessive overlap number, so it is preferable to set it to 50 or less.

[0024] By irradiating the surface of the stainless steel with a pulsed laser so that the fluence and overlapping number are within the above-mentioned ranges, an irradiated portion with good affinity for non-metallic materials is formed.

[0025] The energy imparted to the irradiated area by a pulsed laser can be calculated by multiplying the fluence by the number of overlaps. However, even if the surface of stainless steel is irradiated with the same amount of energy using a continuous wave laser instead of a pulsed laser, it will not be possible to obtain an irradiated area with good affinity for non-metallic materials like this stainless steel. This stainless steel has an irradiated area irradiated by pulsed irradiation from a pulsed laser, thereby achieving improved affinity for non-metallic materials.

[0026] The irradiated portion preferably has a minimum autocorrelation length Sal of 45 μm or less. The minimum autocorrelation length Sal is a numerical value that represents the density of the uneven shape of the surface shape of stainless steel or the like, expressed in units of length, and is an index of surface roughness. The smaller the value of the minimum autocorrelation length Sal, the finer the surface. If the irradiated portion has the above-mentioned minimum autocorrelation length Sal, it can be said that it has good affinity with non-metallic materials. From the viewpoint of obtaining an anchor effect, it is more preferable that the irradiated portion has a minimum autocorrelation length Sal of 1 μm or more.

[0027] The minimum autocorrelation length Sal can be measured using a stylus surface roughness measuring instrument (for example, SURFCOM2900DX manufactured by Tokyo Seimitsu Co., Ltd.).

[0028] However, the minimum autocorrelation length Sal is merely one of the indicators of the surface morphology of the irradiated portion irradiated with a pulsed laser under the above-mentioned conditions. It is obvious to those skilled in the art that the surface morphology of the irradiated portion irradiated with a pulsed laser varies in detail depending on the irradiation conditions, and that it is impossible or impractical to define it uniquely. The present inventors have newly discovered that, even though the surface morphology varies depending on the pulsed laser irradiation conditions, an irradiated portion irradiated with a pulsed laser under the above-mentioned conditions has excellent affinity with non-metallic materials.

[0029] This irradiated stainless steel eliminates the need for surface treatment with alkaline cleaners or chemicals containing organic solvents to improve its compatibility with non-metallic materials. This reduces environmental impact while promoting the use of multi-materials in stainless steel products, enabling a wide variety of products to be created. This effect also contributes to the achievement of Goal 12.4 of the United Nations' Sustainable Development Goals (SDGs), including "Environmentally sound management of chemicals and minimize their adverse impacts on human health and the environment."

[0030] <Component composition> The stainless steel may contain, by mass%, C: 0.005 to 0.300%, Si: 0.01 to 3.00%, Mn: 0.01 to 15.00%, P: 0.045% or less, S: 0.0300% or less, Ni: 0.01 to 20.00%, Cr: 10.0 to 35.0%, Cu: 0.01 to 3.50%, N: 0.400% or less, Al: 0.001 to 3.500%, with the remainder consisting of Fe and unavoidable impurities.

[0031] (C) Carbon (C) has a strong solid-solution strengthening effect on stainless steel and is also effective in increasing the strength of stainless steel. However, excessive addition of C reduces the workability and corrosion resistance of stainless steel. Therefore, the present stainless steel may contain 0.005% by mass to 0.300% by mass of C, and preferably 0.010% by mass to 0.150% by mass of C.

[0032] (Si) Silicon (Si) is an effective deoxidizer for stainless steel and also has a solid-solution strengthening effect. However, excessive Si addition can cause deterioration in workability and toughness. Therefore, the present stainless steel may contain 0.01% to 3.00% by mass of Si, and preferably 0.20% to 2.00% by mass of Si.

[0033] (Mn) Manganese (Mn) is an element that is effective in increasing the strength of stainless steel. However, excessive addition of Mn leads to a decrease in the hot workability of stainless steel. Therefore, the present stainless steel may contain 0.01% by mass to 15.00% by mass of Mn, and preferably 0.20% by mass to 10.00% by mass of Mn.

[0034] (P) P (phosphorus) is an element that is mixed into stainless steel during its manufacturing process, and the lower the P content, the better. From the viewpoint of manufacturability, the present stainless steel may contain 0.045 mass% or less of P. If the P content is 0.045 mass% or less, adverse effects on material properties such as ductility can be reduced in the present stainless steel. Furthermore, the present stainless steel preferably contains 0.005 mass% to 0.040 mass% of P.

[0035] (S) S (sulfur) is an element that is mixed into stainless steel during its manufacturing process, and the lower the S content, the better. From the viewpoint of manufacturability, the present stainless steel may contain 0.0300% by mass or less of S. If the S content is 0.0300% by mass or less, adverse effects on material properties such as ductility can be reduced in the present stainless steel. Furthermore, the present stainless steel preferably contains 0.0001% by mass or more and 0.0030% by mass or less of S.

[0036] (Ni) Ni (nickel) is an element that is effective in improving the corrosion resistance and toughness of stainless steel. However, Ni is an expensive element, and adding too much increases manufacturing costs. Therefore, the present stainless steel may contain 0.01% to 20.00% by mass of Ni, and preferably 0.10% to 12.00% by mass of Ni.

[0037] (Cr) Cr (chromium) is an element effective in ensuring the corrosion resistance of stainless steel. However, excessive Cr addition reduces the workability and toughness of stainless steel. Therefore, the present stainless steel may contain 10.0 to 35.0 mass% Cr, and preferably 12.0 to 30.0 mass% Cr.

[0038] (Cu) Copper (Cu) is an element effective in increasing the strength of stainless steel. However, if excessive Cu is added, a CuMn phase forms in the center of the slab during solidification, reducing the hot workability of the slab. Therefore, the present stainless steel may contain 0.01% by mass or more and 3.50% by mass or less of Cu, and preferably 0.10% by mass or more and 2.20% by mass or less of Cu.

[0039] (N) Nitrogen (N) is an element that strengthens the solid solution and improves the corrosion resistance of stainless steel. However, excessive addition of N reduces the workability of stainless steel. Therefore, the present stainless steel may contain up to 0.400% by mass of N, and preferably contains 0.001% to 0.350% by mass of N.

[0040] (Al) Aluminum (Al) is an element that deoxidizes stainless steel. However, excessive addition of Al can degrade surface quality. Therefore, the stainless steel may contain 0.001% to 3.500% by mass of Al, and preferably 0.001% to 1.800% by mass of Al.

[0041] <Other elements> In addition to the above elements, the present stainless steel may further contain, by mass%, at least one selected from the group consisting of Mo: 0.01 to 3.20%, Nb: 0.60% or less, Ti: 0.60% or less, V: 0.60% or less, B: 0.010% or less, Ca: 0.0002 to 0.0150%, Hf: 0.001 to 0.600%, Zr: 0.01 to 0.60%, Sb: 0.005 to 0.600%, Co: 0.60% or less, W: 0.60% or less, Ta: 0.001 to 1.000%, Sn: 0.002 to 1.000%, Ga: 0.0002 to 0.5000%, Mg: 0.0003 to 0.0050%, and REM: 0.001 to 0.200%.

[0042] (Mo) Molybdenum (Mo) is an element that is effective in improving the corrosion resistance of stainless steel. However, because Mo is an expensive element, excessive addition is undesirable. Therefore, the present stainless steel may contain 0.01% by mass or more and 3.20% by mass or less of Mo, and preferably 0.10% by mass or more and 1.50% by mass or less of Mo.

[0043] (Nb) Niobium (Nb) is an element that is effective in refining and homogenizing the structure of stainless steel. Therefore, the present stainless steel may contain up to 0.60 mass% Nb, and preferably contains 0.01 mass% to 0.50 mass% Nb.

[0044] (Ti) Ti (titanium) is an element that has a deoxidizing effect on stainless steel, so the present stainless steel may contain up to 0.60 mass% Ti, and preferably contains 0.01 mass% to 0.50 mass% Ti.

[0045] (V) Vanadium (V) is an element that is effective in improving the corrosion resistance of stainless steel. However, because V is an expensive element, excessive addition is undesirable. Therefore, the present stainless steel may contain up to 0.60 mass% V, and preferably contains 0.05 mass% to 0.50 mass% V.

[0046] (B) Boron (B) is an element that improves the hot workability of stainless steel and is effective in reducing edge breaks and slicing during hot rolling. Therefore, the present stainless steel may contain up to 0.010% by mass of B, and preferably contains 0.0005% to 0.0050% by mass of B.

[0047] (Ca) Ca (calcium) effectively prevents edge breakage during hot rolling of stainless steel. However, excessive addition of Ca may result in a decrease in corrosion resistance. Therefore, the present stainless steel may contain 0.0002% by mass or more and 0.0150% by mass or less of Ca, and preferably contains 0.0002% by mass or more and 0.0050% by mass or less of Ca.

[0048] (Hf) Hf (hafnium) is an element that improves the corrosion resistance and high-temperature strength of stainless steel. However, excessive addition of Hf can lead to deterioration in workability and manufacturability. Therefore, the present stainless steel may contain 0.001% to 0.600% by mass of Hf, and preferably 0.005% to 0.050% by mass of Hf.

[0049] (Zr) Zirconium (Zr) is an element that improves the hot workability of stainless steel and is also effective in improving oxidation resistance. Therefore, the present stainless steel may contain 0.01 to 0.60 mass% Zr, and preferably 0.05 to 0.50 mass% Zr.

[0050] (Sb) Sb (antimony) is an element that improves the high-temperature strength of stainless steel. However, excessive addition of Sb can reduce weldability and toughness. Therefore, the present stainless steel may contain 0.005% by mass to 0.600% by mass of Sb, and preferably 0.010% by mass to 0.400% by mass of Sb.

[0051] (Co) Co (cobalt) is an element that improves the high-temperature strength of stainless steel. However, excessive addition of Co can reduce toughness and lead to reduced manufacturability. Therefore, the present stainless steel may contain up to 0.60% by mass of Co, and preferably contains 0.05% to 0.50% by mass of Co.

[0052] (W) W (tungsten) is an element that is effective in improving the corrosion resistance of stainless steel. However, because W is an expensive element, adding excessive amounts is undesirable. Therefore, the present stainless steel may contain up to 0.60 mass% W, and preferably contains 0.05 mass% to 0.50 mass% W.

[0053] (Ta) Ta (tantalum) is an element that improves the high-temperature strength of stainless steel. However, excessive addition of Ta can reduce weldability and toughness. Therefore, the present stainless steel may contain 0.001% by mass to 1.000% by mass of Ta, and preferably 0.005% by mass to 0.500% by mass of Ta.

[0054] (Sn) Sn (tin) is an element that improves the corrosion resistance and high-temperature strength of stainless steel. However, excessive addition of Sn can lead to a decrease in toughness and manufacturability. Therefore, the present stainless steel may contain 0.002 to 1.000 mass% Sn, and preferably 0.002 to 0.500 mass% Sn.

[0055] (Ga) Gallium (Ga) is an element that improves the corrosion resistance and hydrogen embrittlement resistance of stainless steel. However, excessive addition of Ga can reduce weldability and toughness. Therefore, the stainless steel may contain 0.0002% to 0.5000% by mass of Ga, and preferably 0.0002% to 0.3000% by mass of Ga.

[0056] (Mg) Magnesium (Mg) is a deoxidizing element in stainless steel, and also refines the structure of slabs, improving formability. However, excessive addition of Mg can lead to deterioration in corrosion resistance, weldability, and surface quality. Therefore, the present stainless steel may contain 0.0003% to 0.0050% by mass of Mg, and preferably 0.0003% to 0.0030% by mass of Mg.

[0057] (REM) REM (rare earth elements) is a collective term for Sc (scandium) and 15 elements (lanthanoids) ranging from La (lanthanum) to Lu (lutetium). REM may be added as a single element or as a mixture of multiple elements. REM improves the cleanliness of stainless steel and effectively prevents edge breakage during hot rolling. However, excessive addition of REM may increase alloy costs and reduce manufacturability. Therefore, the present stainless steel may contain 0.001% by mass or more and 0.200% by mass or less of REM, and preferably 0.005% by mass or more and 0.100% by mass or less of REM.

[0058] (Fe and unavoidable impurities) The remainder of the stainless steel other than the above-mentioned components consists of iron (Fe) and unavoidable impurities. These unavoidable impurities are components other than the above-mentioned components that are mixed in due to the raw materials and manufacturing process, and may be mixed into the stainless steel to the extent that they do not affect the properties of the above-mentioned components.

[0059] 2. Stainless steel manufacturing method A method for producing stainless steel according to one embodiment of the present invention (hereinafter sometimes referred to as "the present production method") may include a general stainless steel production process. The present production method also includes a step of irradiating the surface of the stainless steel with a pulsed laser.

[0060] An example of the present manufacturing method will be described below, but the present invention is not limited to this.

[0061] In this manufacturing method, for example, a slab is produced by continuously casting molten steel with adjusted composition, and a slab surface grinding process is carried out. The obtained slab is then heated to 1100°C or higher and 1300°C or lower, and hot-rolled to produce a hot-rolled steel strip. The obtained hot-rolled steel strip is then subjected to bell annealing, annealing, cold rolling, and pickling processes to obtain a stainless steel substrate.

[0062] Here, the steps of annealing, pickling and cold rolling may be repeatedly carried out to adjust the thickness to the final thickness, and the annealed material, bright annealed material or temper rolled material may be used as the substrate.

[0063] (irradiation process) The resulting stainless steel is then subjected to an irradiation process. The irradiation process involves irradiating at least a portion of the surface of the stainless steel with a pulsed laser. The "at least a portion of the surface of the stainless steel" refers to the irradiated portion on the surface of the stainless steel, which improves its affinity with non-metallic materials.

[0064] In the irradiation process, the pulse laser irradiation is performed with a fluence of 1.2 to 6.5 J / cm 2 The overlapping number of pulse laser marks, as shown in the following formula (1), is set to 0.5 to 200.

[0065] Number of overlaps = S × fs / (W × VL) (1) In the above formula (1), S is the beam area (mm 2 ), fs is the irradiation speed (Hz), W is the irradiation width (mm), and VL is the feed speed of the irradiated object (mm / s).

[0066] The pulse laser irradiation conditions are as described above in the section [1. Stainless steel], so a detailed explanation will be omitted here.

[0067] (Cr concentration ratio) It is preferable that the irradiation in the irradiation step be carried out so that the ratio of the Cr concentration ratio after irradiation to before irradiation, expressed by the following formula (2) (after irradiation / before irradiation), in the surface layer including up to 5 nm from the surface of the stainless steel in the thickness direction, is 0.65 or less.

[0068] Cr concentration ratio = Cr / (Cr + Fe + Si + Mn + Ni) (2) The content (mass %) of each element contained in the stainless steel is substituted for the element symbol in the formula (2), and 0 is substituted for elements that are not added.

[0069] Irradiation with a pulsed laser causes element segregation in the surface layer of stainless steel due to evaporation or melting and solidification of constituent elements. The surface layer of stainless steel refers to the layered portion that includes the portion from the surface of the stainless steel to a depth of 5 nm in the thickness direction. Due to this segregation, the Cr concentration ratio of the component composition in the surface layer of stainless steel changes between before and after irradiation. The Cr concentration ratio in the surface layer of stainless steel is expressed by the above formula (2) and is a value that indicates the concentration ratio of Cr among the major components in the surface layer of this stainless steel.

[0070] In the surface layer of the stainless steel, it is preferable that the Cr concentration ratio after irradiation with a pulsed laser is 0.65 or less of the Cr concentration ratio before irradiation. In other words, it is preferable that the Cr concentration ratio after irradiation is reduced to 65% or less of the Cr concentration ratio before irradiation from the viewpoint of affinity with non-metallic materials in the irradiated portion of the stainless steel.

[0071] The Cr concentration ratio is preferably calculated as the average value of measurement results from multiple locations in the surface layer of the stainless steel before and after irradiation. Alternatively, the Cr concentration ratio may be calculated as the measurement result from a single location in the surface layer of the stainless steel before and after irradiation. The measurement location in the surface layer of the stainless steel may be determined so that it is the same location before and after irradiation, or may be determined randomly.

[0072] The component composition of the surface layer of the present stainless steel can be measured using a glow discharge optical emission spectrometer (for example, GDA750 manufactured by Rigaku Corporation).

[0073] [Embodiment 2] Another embodiment of the present invention will be described below with reference to the drawings. Note that the configuration other than that described in this embodiment is the same as that of the first embodiment.

[0074] In the first embodiment, the surface morphology of stainless steel having an irradiated portion formed on at least a part of the surface was described based on pulse laser irradiation conditions based on the new findings of the inventors. In the second embodiment, a specific example of the surface morphology of stainless steel will be described.

[0075] (stainless steel) Fig. 1 is a schematic diagram for explaining stainless steel in embodiment 2 of the present invention. The diagram indicated by reference numeral 1001 in Fig. 1 is a schematic cross-sectional view of the stainless steel, and the diagram indicated by reference numeral 1002 in Fig. 1 is a schematic perspective view showing the state in which the stainless steel is irradiated with a pulsed laser.

[0076] As shown in FIG. 1 , the stainless steel 1 in this embodiment has an irradiated portion 2 irradiated with a pulsed laser PL on at least a portion of its surface 10. For ease of explanation, the stainless steel immediately prior to being subjected to the pulsed laser irradiation process may be referred to as the "stainless steel intermediate product." Furthermore, the portion of the surface 10 that is not irradiated with the pulsed laser may be referred to as the non-irradiated portion 11. The stainless steel 1 in this embodiment may include the non-irradiated portion 11 on the surface 10. The non-irradiated portion 11 may be the surface of the stainless steel intermediate product.

[0077] In the following description, the direction perpendicular to the surface 10 of the stainless steel 1 (the surface of the non-irradiated portion 11) is referred to as the Z-axis direction, the direction along the feed direction FD of the stainless steel of the intermediate product in the process of irradiating the pulsed laser PL is referred to as the Y-axis direction, and the direction perpendicular to the Z-axis direction and the Y-axis direction is referred to as the X-axis direction. In the example shown in FIG. 1, the Y-axis direction is along the longitudinal direction of the stainless steel 1 (or the stainless steel of the intermediate product), and the X-axis direction is along the width direction of the stainless steel 1 (or the stainless steel of the intermediate product). In the example shown in FIG. 1, the width W1 of the irradiated portion 2 is the same as the width of the stainless steel 1.

[0078] The stainless steel 1 in one embodiment of the present invention may typically be a stainless steel plate. The stainless steel 1 is not limited to a plate shape and may be a stainless steel material having another shape. In this case, the surface 10 may be the plate surface of the stainless steel 1, or may be a portion of the surface of the stainless steel 1 that has a planar shape. When the stainless steel 1 is a stainless steel material, the irradiated portion 2 may be formed by irradiating at least a portion of the planar surface of the stainless steel material of the intermediate product with a pulsed laser PL.

[0079] The chemical composition of the stainless steel 1 is the same as that described in the first embodiment, and therefore will not be described further. Furthermore, the stainless steel 1 of this embodiment can be manufactured by forming the irradiation section 2 using a method similar to that described in the first embodiment. The stainless steel 1 having the irradiation section 2 achieves the same effects as those described in the first embodiment. That is, the stainless steel 1 does not require alkaline cleaning or chemical treatment containing organic solvents or the like on its surface to improve its affinity with non-metallic materials, for example. Therefore, while reducing the environmental impact, it is possible to promote the multi-materialization of products containing the stainless steel 1, thereby realizing a wide variety of products.

[0080] Specific examples of the irradiation portion 2 on the stainless steel 1 will be described below with reference to Figures 2 and 3. Figure 2 is a diagram showing an electron microscope image taken at high magnification of the surface of the stainless steel according to embodiment 2 of the present invention. Figure 3 is a diagram showing an electron microscope image taken at high magnification of the cross section of the stainless steel according to embodiment 2 of the present invention.

[0081] As shown in Figures 2 and 3, in the stainless steel 1 of this embodiment, the irradiated area 2 includes multiple depressions 3 and multiple protrusions 4 adjacent to the depressions 3. The irradiated area 2 can be formed by irradiating the surface of the stainless steel of the intermediate product with a pulsed laser PL under the conditions described in the first embodiment. The depressions 3 and protrusions 4 each have an irregular shape. Any one point in the irradiated area 2 is irradiated with overlapping pulses of the pulsed laser PL. As a result, the irregularly shaped depressions 3 and protrusions 4 shown in Figures 2 and 3 are formed.

[0082] In the stainless steel 1, the raised portions 4 have a width W4 of 0.1 μm or more and 200 μm or less in plan view, the spacing D4 between the raised portions 4 positioned on either side of the depression 3 does not exceed 300 μm, and the surface magnification ratio in the irradiated area 2 may be 1.1 or more. The width W4 and spacing D4 are measured, for example, from the appearance of the irradiated area 2 shown in an electron microscope image taken at a magnification suitable for observation (e.g., 200 to 2000 times) using a scanning electron microscope (SEM). In the stainless steel 1 of this embodiment, the width W4 of each of the multiple raised portions 4 measured in the appearance is in the range of 0.1 μm or more and 200 μm or less, and the spacing D4 between the raised portions 4 does not exceed 300 μm. In stainless steel 1, the upper limit of the surface expansion ratio of the irradiation section 2 is not necessarily limited, but in the examples shown in Figures 2 and 3, for example, the surface expansion ratio may be 1.1 or more and 3.0 or less, 1.1 or more and 2.5 or less, or 1.1 or more and 2.0 or less.

[0083] In the stainless steel 1 of this embodiment, the width W4 of each of the multiple raised portions 4 may be within a range of 0.1 μm to 100 μm, or within a range of 0.1 μm to 70 μm. Furthermore, in the stainless steel 1 of this embodiment, the spacing D4 between the raised portions 4 need not exceed 200 μm, and may not exceed 150 μm. The lower limit of the numerical range for the spacing D4 may be specified as, for example, 0.1 μm. However, in practice, it is not easy or practical to specify a lower limit for the numerical range for the spacing D4. This is because there may be raised portions 4 that appear to be substantially adjacent to each other in the above appearance.

[0084] As described above, a small spacing D4 and a small width W4 mean that the irradiated portion 2 has a dense uneven structure. In the irradiated portion 2, assuming that the spacing D4 is small, if the width W4 of the multiple raised portions 4 becomes smaller overall, the number (density) of the raised portions 4 increases, thereby improving the affinity of the irradiated portion 2 with non-metallic materials. Furthermore, for example, if the spacing D4 of the multiple raised portions 4 becomes smaller overall, the number (density) of the raised portions 4 increases, thereby improving the affinity of the irradiated portion 2 with non-metallic materials.

[0085] The surface expansion ratio is a value calculated as the ratio of the surface area of the irradiated portion 2 to the surface area before irradiation with the pulsed laser PL. If the stainless steel 1 has a non-irradiated portion 11, the surface expansion ratio can be calculated using the surface areas of the non-irradiated portion 11 and the irradiated portion 2 in the same range. Alternatively, if the stainless steel 1 does not have a non-irradiated portion 11, the surface expansion ratio can be calculated using the surface area of a specific range of the irradiated portion 2 when it is assumed to be flat and the actual surface area of the irradiated portion 2. To calculate the surface expansion ratio of the stainless steel 1, for example, a 3D measuring laser microscope LEXT OLS4100 (manufactured by Olympus) can be used. For example, during the production of stainless steel 1, the value of the surface expansion ratio can be determined by calculating the ratio of the surface area after irradiation with the pulsed laser PL (the surface area of the irradiated portion 2) to the surface area before irradiation with the pulsed laser PL (the surface area of the stainless steel of the intermediate product) as 1. Measurement conditions for the 3D measuring laser microscope can be, for example, an objective lens magnification of 20x, a zoom lens magnification of 1x (field of view 640 μm square), laser observation, high definition (pitch 0.200), and brightness 35.0 to 40.0. In the following description, the same measurement conditions can be used when using a 3D measuring laser microscope.

[0086] In this specification, the surface of the stainless steel of the intermediate product before the irradiated portion 2 is formed by irradiation with the pulsed laser PL is referred to as the imaginary surface VF. If the stainless steel 1 has a non-irradiated portion 11, the height position of the imaginary surface VF may be the same as the surface of the non-irradiated portion 11. Alternatively, if the stainless steel 1 does not have a non-irradiated portion 11, the position of the imaginary surface VF can be identified by virtually smoothing the surface of the irradiated portion 2 in a cross-sectional view using a known method. In a cross-sectional view, the depression 3 has a depth H3 from the imaginary surface VF that is greater than 0.1 μm, and the protrusion 4 has a height H4 from the imaginary surface VF that is greater than 0.1 μm.

[0087] The depth H3 of the depressions 3 and the height H4 of the protrusions 4 are measured, for example, in an electron microscope image of the cross section of the irradiated area 2 (a cross section perpendicular to the plate surface of the stainless steel 1) taken using an SEM at a magnification suitable for observation (e.g., 200 to 2000 times). In the stainless steel 1 of this embodiment, the depth H3 of each of the multiple depressions 3 measured in the cross section is greater than 0.1 μm, and the height H4 of each of the multiple protrusions 4 is greater than 0.1 μm. This provides an anchor effect in the irradiated area 2, effectively improving the affinity of the irradiated area 2 with non-metallic materials.

[0088] In the stainless steel 1 of this embodiment, the depth H3 of any of the multiple depressions 3 may be in the range of more than 0.1 μm and not more than 100 μm, or in the range of more than 0.1 μm and not more than 70 μm. Also, in the stainless steel 1 of this embodiment, the height H4 of any of the multiple protrusions 4 may be in the range of more than 0.1 μm and not more than 100 μm, or in the range of more than 0.1 μm and not more than 70 μm.

[0089] 2, each of the plurality of depressions 3 may be surrounded by a protrusion 4 and have a smooth bottom surface 30 with an average diameter of 0.1 μm or more and 200 μm or less. The average diameter of the bottom surface 30 is calculated based on the appearance of the irradiated area 2 shown in an electron microscope image taken at a magnification suitable for observation (e.g., 200 to 2000 times) using an SEM. In the stainless steel 1 of this embodiment, the average value of the major axis and minor axis of the bottom surface 30 observed in the appearance (plan view) can be used as the average diameter of the bottom surface 30.

[0090] In the stainless steel 1 of this embodiment, the bottom surfaces 30 of the plurality of depressions 3 observed in the above appearance all have an average diameter in the range of 0.1 μm or more and 200 μm or less. In the stainless steel 1 of this embodiment, the bottom surfaces 30 of the plurality of depressions 3 observed in the above appearance may all have an average diameter in the range of 0.1 μm or more and 150 μm or less, or may have an average diameter in the range of 0.1 μm or more and 120 μm or less. In the irradiated portion 2, when the average diameter of the bottom surfaces 30 of the plurality of depressions 3 as a whole becomes smaller, the number (density) of the protrusions 4 increases, thereby improving the affinity of the irradiated portion 2 with non-metallic materials.

[0091] 2, the multiple raised portions 4 are connected to each other to form a network structure, and as part of the network structure, multiple protrusions 40 protrude upward. Furthermore, the distance D3 between adjacent depressions 3 with a raised portion 4 interposed therebetween does not exceed 300 μm.

[0092] In the stainless steel 1 of this embodiment, points (hereinafter sometimes referred to as "specific points") on the bottom surfaces 30 of the depressions 3 observed in the above appearance where the lines representing the major and minor axes overlap can be identified, and the distance between the specific points on the bottom surfaces 30 of adjacent depressions 3 with a protrusion 4 interposed therebetween can be determined as the spacing D3 between the depressions 3. In the stainless steel 1 of this embodiment, the spacing D3 between the depressions 3 does not need to exceed 200 μm or 150 μm. The lower limit of the numerical range for the spacing D3 may be specified as, for example, 1.0 μm. However, in practice, it is not easy or practical to specify a lower limit for the numerical range for the spacing D3. This is because, in the above appearance, the bottom surfaces 30 of the multiple depressions 3 each have a distorted and irregular shape, and the spacing D3 in areas where multiple protrusions 4 are densely packed can be numerically very small.

[0093] As described in the first embodiment, the minimum autocorrelation length Sal of the irradiating unit 2 may be 45.0 μm or less. The minimum autocorrelation length Sal of the irradiating unit 2 may be 1.0 μm or more. This makes it easier to further increase the affinity with non-metallic materials. The minimum autocorrelation length Sal of the irradiating unit 2 may be 4.0 μm or more.

[0094] 2, the tops of at least some of the protrusions 40 may be spherical or teardrop-shaped, which allows the stainless steel 1 and the non-metallic material to be joined or bonded together with the non-metallic material embedded in the protrusions 40, thereby providing a favorable anchoring effect.

[0095] (Stainless steel manufacturing method) As explained in the first embodiment, the fluence is 1.2 to 6.5 J / cm 2 The irradiated portion 2 can be formed by irradiating with the pulsed laser PL so that the overlapping number of the pulsed laser marks expressed by the following formula (1) is 0.5 to 200: Number of overlaps = S × fs / (W × VL) (1) In the above formula (1), S is the beam area (mm 2 ), fs is the pulse irradiation speed (Hz), W is the irradiation width (mm), and VL is the feed speed of the irradiated object (mm / s).

[0096] In the above formula (1), the overlap number can be said to be calculated by dividing the laser irradiation area per unit time by the irradiated area per unit time. This laser irradiation area per unit time is obtained by integrating the area irradiated with the pulsed laser PL (i.e., the beam area) without considering overlap. On the other hand, the irradiated area per unit time means the area of the irradiated area formed per unit time. The pulsed laser PL is irradiated evenly and distributed while scanning the irradiation width W at a predetermined scanning speed. The scanning speed of the pulsed laser PL is assumed to have no effect on the calculation of the overlap number in the above formula (1).

[0097] In one embodiment of the method for producing stainless steel 1, the pulse duration of the pulse laser PL is 8 μs to 20 μs (pulse irradiation rate: 50 kHz to 125 kHz), and the feed speed VL of the irradiated object (stainless steel intermediate product) in the feed direction FD may be 400.0 mm / s or less. The pulse duration of the pulse laser PL may be 8 μs or more and 20 μs or less, or 8 μs or more and 12.5 μs or less. The feed speed VL of the irradiated object in the feed direction FD may be 0.1 mm / s or more and 400.0 mm / s or less, or 1.0 mm / s or more and 20.0 mm / s or less.

[0098] When analyzing the chemical composition of the surface layer of this stainless steel by glow discharge optical emission spectrometry, the irradiation width W must be larger than the electrode diameter of the glow discharge optical emission spectrometry (GDS) device. The electrode diameter of the GDS device is generally 4 mm, and by setting the feed rate VL to 400.0 mm / s or less, the beam diameter in the above formula (1) becomes 90 μm, that is, the beam area S becomes 6.36 × 10 -3 mm 2 The irradiation width W is set to 4 mm or more, and the overlap number can be easily set to 0.5 to 200.

[0099] In one embodiment of the method for manufacturing stainless steel 1, irradiation with a pulsed laser PL may be performed in the atmosphere. By irradiating with a pulsed laser PL so as to satisfy the above conditions, the irradiated portion 2 can be formed even in the atmosphere, and stainless steel 1 with improved affinity for non-metallic materials in the irradiated portion 2 can be obtained. Of course, the irradiated portion 2 may also be formed by irradiating with a pulsed laser PL under inert gas (helium, argon) conditions.

[0100] In one embodiment of the method for producing stainless steel 1, the pulsed laser PL may be, for example, a fiber laser. The pulsed laser PL may have, for example, a peak wavelength of 1080 nm to 1090 nm. In the method for producing stainless steel 1, the pulsed laser PL is not particularly limited as long as it satisfies the pulse energy conditions (the above-mentioned fluence conditions), and the specific irradiation conditions may be adjusted as appropriate.

[0101] In the method for producing stainless steel 1 in one embodiment, the same conditions as those in the first embodiment can be used, and a repeated description will be omitted. For example, irradiation with a pulsed laser PL may be performed so that the Cr concentration ratio in the above-mentioned formula (2) is 0.65 or less.

[0102] [Embodiment 3] Another embodiment of the present invention will be described below with reference to the drawings. Note that the configuration other than that described in this embodiment is the same as that of the first and second embodiments.

[0103] In the second embodiment, a stainless steel 1 was described that has an irradiated portion 2 formed by irradiating a pulsed laser PL while moving an irradiated object (in other words, a stage on which the irradiated object is placed). In the third embodiment, a specific example of the surface morphology of stainless steel that has an irradiated portion 2 formed by repeatedly performing a series of processes: stopping the irradiated object and irradiating it with a pulsed laser PL, then temporarily stopping the irradiation of the pulsed laser PL and moving the irradiated object a predetermined distance, and then stopping the irradiated object and irradiating it with the pulsed laser PL, will be described.

[0104] Specific examples of the irradiated portion 2 in the stainless steel 1 of this embodiment will be described below with reference to FIGS. 4 to 6. FIG. 4 is a schematic diagram for explaining the irradiated portion of the stainless steel in embodiment 3 of the present invention. The view indicated by reference numeral 4001 in FIG. 4 is a schematic plan view of the stainless steel, and the view indicated by reference numeral 4002 in FIG. 4 is a schematic cross-sectional view of the stainless steel. FIG. 5 is a diagram showing an electron microscope image taken at a high magnification of the surface of the stainless steel in embodiment 3 of the present invention. FIG. 6 is a diagram showing an electron microscope image taken at a high magnification of the cross-section of the stainless steel in embodiment 3 of the present invention. FIGS. 5 and 6 show examples of irradiated portions formed by stopping the irradiated object and performing a process of irradiating the pulsed laser PL once.

[0105] 4 to 6, in the stainless steel 1 of this embodiment, the irradiation section 2 includes a plurality of depressions 3 and a plurality of protrusions 4 adjacent to the depressions 3. At least some of the plurality of depressions 3 are first grooves 31 having a groove shape extending in a first direction X1 along the surface 10, and the first grooves 31 have an opening width W2 in a direction (second direction X2) perpendicular to the first direction X1 on the surface 10 that is smaller than 300 μm. The plurality of protrusions 4 include first ridges 41 located adjacent to the first grooves 31 and extending in the first direction X1 along the first grooves 31, and second ridges 42 located adjacent to the first grooves 31 on the opposite side to the first ridges 41 and extending in the first direction X1 along the first grooves 31. The surface magnification ratio in the irradiation section 2 may be 2.0 or more. In the examples shown in Figures 4 to 6, the first direction X1 may be along the X-axis direction (see Figure 1) of the stainless steel 1 (or the stainless steel of the intermediate product), and the second direction X2 may be along the Y-axis direction (see Figure 1) of the stainless steel 1 (or the stainless steel of the intermediate product).

[0106] The opening width W2 is measured, for example, from the appearance of the irradiated area 2 shown in an electron microscope image taken using an SEM at a magnification suitable for observation (e.g., 200 to 2000 times). In the stainless steel 1 of this embodiment, the opening width is measured at 25 arbitrary locations of the first groove portion 31 in the appearance, and the average of 25 values obtained is taken as the opening width W2. In the stainless steel 1, the opening width W2 of all of the multiple first groove portions 31 may be smaller than 200 μm or smaller than 160 μm. The opening width W2 may be 1.0 μm or greater. In the example shown in FIGS. 4 to 6, the surface expansion ratio of the stainless steel 1 may be, for example, 2.0 to 4.0, 2.5 to 4.0, 3.0 or greater, or 3.0 to 4.0.

[0107] For the stainless steel 1, for example, the surface area can be measured by irradiating a measurement laser along the second direction X2 using a 3D measuring laser microscope LEXT OLS4100, and the surface expansion ratio can be calculated.

[0108] In the stainless steel 1 of this embodiment, the height H5 of the first rib portion 41 may be greater than the height H6 of the second rib portion 42, and the width W5 of the first rib portion 41 may be greater than the width W6 of the second rib portion 42. The heights H5 and H6 can be determined in a cross section such as that shown in FIG. 6. As shown in FIGS. 5 and 6, it is not easy to calculate specific values for the widths W5 and W6, but it can be seen that the width W6 is clearly greater than the width W5.

[0109] The stainless steel 1 in one embodiment includes a plurality of first groove portions 31, and the spacing D31 between the first groove portions 31 may not exceed 300 μm. In the stainless steel 1 of this embodiment, the midpoints of the 25 opening widths measured for the opening width W2 as described above were identified, and the distance between the 25 midpoints was calculated for two adjacent first groove portions 31, and the average of the 25 values obtained was used as the spacing D31.

[0110] The stainless steel 1 of this embodiment is, for example, in a state where the movement of the irradiated object in the feeding direction is stopped, and the fluence is 1.2 to 6.5 J / cm 2 The first groove portion 31 can be formed by irradiating the pulsed laser PL so that the overlapping number of the pulsed laser marks expressed by the following formula (3) is 0.5 to 200: Number of overlaps = S × fs / (W × D) (3) In the above formula (3), S is the beam area (mm 2 ), fs is the pulse irradiation rate (Hz), W is the irradiation width (mm), and D is the beam diameter (mm).

[0111] For example, the movement of the irradiated object in the feed direction is stopped for one second, and the pulsed laser PL is irradiated. Then, the irradiation of the pulsed laser PL is stopped, and the movement of the irradiated object in the feed direction is resumed. Next, when the irradiated object has moved a distance corresponding to the spacing between the plurality of first groove portions 31 in the irradiated unit 2, the movement of the irradiated object is stopped for one second, and the pulsed laser PL is irradiated. By repeating this operation, an irradiated unit 2 having a plurality of first groove portions 31 can be formed.

[0112] (Another configuration example) Fig. 7 is a diagram showing an electron microscope image taken at a high magnification of the surface of a stainless steel in another configuration example of embodiment 3 of the present invention. As shown in Fig. 7, in stainless steel 1, at least some of the multiple recesses 3 are second groove portions 32 having a groove shape extending in a second direction X2 that intersects with first direction X1 along surface 10, and second groove portions 32 have an opening width W3 on surface 10 in a direction perpendicular to second direction X2 that is smaller than 300 µm, and irradiation unit 2 includes groove intersection portions 33 where first groove portions 31 and second groove portions 32 intersect.

[0113] For example, the direction of the irradiated portion of the pulsed laser PL is rotated 90° from the state in which the first groove portion 31 is formed to form the second groove portion 32, thereby manufacturing a stainless steel 1 having the irradiated portion 2 of the example shown in Fig. 7. Alternatively, after the first groove portion 31 is formed, the direction of the irradiated object is rotated 90° around the direction from the irradiated portion of the pulsed laser PL toward the irradiated object as the rotation axis, and the irradiated object is placed on a table that moves the irradiated object, thereby forming the second groove portion 32.

[0114] The opening width W3 is measured, for example, from the appearance of the irradiated area 2 shown in an electron microscope image taken using an SEM at a magnification suitable for observation (e.g., 200 to 2000 times). In the stainless steel 1 of this embodiment, the opening width is measured at 25 arbitrary locations of the second groove portion 32 in the appearance, and the average of 25 values obtained is taken as the opening width W3. In the stainless steel 1, the opening width W3 of all of the multiple second groove portions 32 may be smaller than 200 μm or smaller than 160 μm. The opening width W3 may be 1.0 μm or greater.

[0115] [3. Summary] The stainless steel according to the first aspect of the present invention has an irradiated portion on at least a part of the surface that has been irradiated with a pulsed laser, and the irradiated portion has a fluence of 1.2 to 6.5 J / cm 2 and the overlap number of pulsed laser marks expressed by the following formula (1) is 0.5 to 200; Number of overlaps = S × fs / (W × VL) (1) In the above formula (1), S is the beam area (mm 2 ), fs is the irradiation speed (Hz), W is the irradiation width (mm), and VL is the feed speed of the irradiated object (mm / s).

[0116] The stainless steel according to a second aspect of the present invention may be the same as that of the first aspect, and may contain, by mass%, C: 0.005-0.300%, Si: 0.01-3.00%, Mn: 0.01-15.00%, P: 0.045% or less, S: 0.0300% or less, Ni: 0.01-20.00%, Cr: 10.0-35.0%, Cu: 0.01-3.50%, N: 0.400% or less, Al: 0.001-3.500%, with the balance being Fe and unavoidable impurities.

[0117] The stainless steel according to a third aspect of the present invention, in accordance with the second aspect, may further include, by mass%, at least one selected from the group consisting of Mo: 0.01 to 3.20%, Nb: 0.60% or less, Ti: 0.60% or less, V: 0.60% or less, B: 0.010% or less, Ca: 0.0002 to 0.0150%, Hf: 0.001 to 0.600%, Zr: 0.01 to 0.60%, Sb: 0.005 to 0.600%, Co: 0.60% or less, W: 0.60% or less, Ta: 0.001 to 1.000%, Sn: 0.002 to 1.000%, Ga: 0.0002 to 0.5000%, Mg: 0.0003 to 0.0050%, and REM: 0.001 to 0.200%.

[0118] The stainless steel according to a fourth aspect of the present invention may be any one of the first to third aspects, wherein the overlap number is 1.5 to 50.

[0119] The stainless steel according to a fifth aspect of the present invention is any one of the first to fourth aspects, wherein the irradiated portion may have a minimum autocorrelation length Sal of 45 μm or less.

[0120] A method for producing stainless steel according to a sixth aspect of the present invention includes a step of irradiating at least a part of the surface of the stainless steel with a pulsed laser, the irradiation having a fluence of 1.2 to 6.5 J / cm. 2 The overlapping number of pulsed laser marks, as shown in the following formula (1), is set to 0.5 to 200: Number of overlaps = S × fs(W × VL) (1) In the above formula (1), S is the beam area (mm 2 ), fs is the irradiation speed (Hz), W is the irradiation width (mm), and VL is the feed speed of the irradiated object (mm / s).

[0121] A seventh aspect of the present invention relates to a method of manufacturing a stainless steel according to the sixth aspect, wherein the irradiation is carried out so that the ratio of the Cr concentration rate after the irradiation to the Cr concentration rate before the irradiation, expressed by the following formula (2) (after the irradiation / before the irradiation), in a surface layer including a depth of up to 5 nm from the surface in a thickness direction, is 0.65 or less: Cr concentration ratio = Cr / (Cr + Fe + Si + Mn + Ni) (2) The content (mass %) of each element contained in the stainless steel is substituted into the element symbol in the formula (2), and 0 is substituted for elements that are not added. [Example]

[0122] Examples 1 to 16 An embodiment of the present invention will now be described.

[0123] [Evaluation conditions] <Component composition> The component compositions (A1 to A13) of stainless steel according to an example of the present invention or a comparative example are shown in the following Table 1. All values in Table 1 indicate the content of each component in mass %.

[0124] [Table 1]

[0125] <Manufacturing method> Slabs were produced by casting molten steel whose compositions were adjusted as shown in A1 to A13 in Table 1, and a slab surface grinding process was carried out. The obtained slabs were heated to 1100°C or higher and 1300°C or lower, and then hot-rolled to produce hot-rolled steel strips. The obtained hot-rolled steel strips were subjected to the processes of bell annealing, annealing, cold rolling, and pickling to obtain base materials.

[0126] The obtained substrate was formed into a rectangular test piece (hereinafter referred to as "test piece") of 25 mm (width direction) x 100 mm (length direction), and an area of 25 mm (width direction) x 12.5±0.5 mm (length direction) was irradiated with a pulsed laser under the conditions shown in Table 2 below. A Laser Clear 50 (manufactured by IHI Inspection and Measurement Co., Ltd.) was used for the pulsed laser irradiation. A fiber laser with a peak wavelength of 1080 nm to 1090 nm was used as the pulsed laser. The fluence was adjusted by changing the irradiation distance (focus) of the pulsed laser.

[0127] <Evaluation method> (Water immersion test and tensile test) The irradiated areas of the two test pieces were joined together using a urethane adhesive, which was then immediately dried and cured, using a method based on the shear adhesion test specified in JIS K 6850. The urethane adhesive was applied to the test pieces to a thickness (distance between the two test pieces) of approximately 3 mm.

[0128] The bonded test pieces were immersed in pure water at 40°C for 10 days. After that, the bonded area of the two test pieces was broken at room temperature (25°C) at 50 mm / min, and the maximum test load was applied to a bonded area of 312.5 mm. 2 The breaking load was calculated by dividing the measured value by (25 mm x 12.5 mm).

[0129] The fractured portion was visually observed and evaluated as either interfacial failure or cohesive failure. Interfacial failure indicates fracture at the interface between the test piece and the adhesive, while cohesive failure indicates fracture in the adhesive portion other than the interface. If cohesive failure occurred before interfacial failure, the test piece was evaluated as "passed," indicating a good bond between the test piece and the adhesive.

[0130] (Minimum autocorrelation length Sal) The surface roughness of the irradiated area of the test piece was evaluated by the minimum autocorrelation length Sal, which was measured using a stylus-type surface roughness measuring instrument (SURFCOM2900DX, manufactured by Tokyo Seimitsu Co., Ltd.).

[0131] (Cr concentration ratio) The average Cr concentration ratio of the surface layer of the test piece before and after irradiation with a pulsed laser was measured using a glow discharge optical emission spectrometer (GDA750 manufactured by Rigaku Corporation). The Cr concentration ratio was calculated according to the above formula (2).

[0132] In Table 2 below, the ratio of the Cr concentration rate after irradiation to the Cr concentration rate before irradiation (after irradiation / before irradiation) is shown as "Cr ratio."

[0133] [Table 2]

[0134] 〔result〕 8 to 11 are electron microscope images of the surface morphology of the irradiated area of the test pieces according to the examples and comparative examples. Fig. 8 corresponds to Example 3, Fig. 9 to Example 16, Fig. 10 to Comparative Example 2, and Fig. 11 to Comparative Example 4, respectively.

[0135] As shown in Figures 8 and 9, the irradiated area of the test piece according to one example of the present invention had a surface formed by molten metal, and an uneven surface morphology with fine groove-like structures or ridges was observed. On the other hand, as shown in Figures 10 and 11, the irradiated area of the test piece according to the comparative example had a relatively flat surface.

[0136] Furthermore, as shown in Table 2, cohesive failure was observed in all test pieces according to the example of the present invention, but no interfacial failure was observed. This result indicates that this stainless steel has good affinity with non-metallic materials in the irradiated area.

[0137] On the other hand, in the test pieces according to the comparative examples, interfacial failure was observed in all of them. In other words, when the test pieces were not irradiated with a pulsed laser or were irradiated with a pulsed laser under conditions outside the range specified in the present invention, good affinity with non-metallic materials was not obtained.

[0138] Examples 21 to 36 Further examples and comparative examples of the present invention will be described below. The component compositions of the stainless steels in the following examples and comparative examples are the same as the component compositions (A1 to A13) shown in Table 1 above. Stainless steels were produced in the same manner as described in the second embodiment, and designated Examples 21 to 36. The produced stainless steels were evaluated using the same evaluation methods as described above.

[0139] In addition, the appearance and cross section of the irradiated area of each test piece were observed using an SEM, and the width W4, etc. of the depressions and protrusions contained in the irradiated area were measured in the same manner as described in the second embodiment.

[0140] For each stainless steel, the average diameter of the bottom surface of the depressions was measured as follows. Specifically, SEM images of five average locations were visually observed, and the long and short diameters of the bottom surface at any five locations in each SEM image were measured using the scale bar on the SEM image. The average diameter of the bottom surface was calculated by averaging the values for a total of 25 bottom surfaces.

[0141] The results are shown in Table 3 below. In Table 3 below, the width W4, spacing D4, height H4, depth H3, and spacing D3 of each stainless steel indicate the minimum and maximum values of multiple values measured (calculated) for the test specimen.

[0142] [Table 3]

[0143] As shown in Table 3, all of the stainless steels (Examples Nos. 21 to 36) manufactured using the manufacturing method of one embodiment of the present invention described above had the specified properties, and the bond between the test specimen and the adhesive was good (the failure mode was "cohesion" and was evaluated as passing).

[0144] In contrast, the stainless steels (Comparative Examples Nos. 11 to 16) manufactured under conditions where at least one of the fluence and overlap number was outside the range of the present invention did not satisfy the standard for at least one of the specified properties, and the bond between the test piece and the adhesive was poor (the failure mode was "interface" and the test piece was evaluated as failing).

[0145] Examples 41 to 56 Further examples and comparative examples of the present invention will be described below. The component compositions of the stainless steels in the following examples and comparative examples are the same as the component compositions (A1 to A13) shown in Table 1 above. Stainless steels were produced in the same manner as described in the third embodiment, and designated Examples 41 to 56. The produced stainless steels were evaluated using the same evaluation methods as described above.

[0146] For each stainless steel, the groove opening width was measured as follows. That is, in visual observation of SEM images taken at five average locations, the opening widths of five arbitrary locations of a certain groove in each SEM image were measured using the scale bar of the SEM image. A total of 25 opening width values obtained in this way were averaged to calculate the opening width W2 of a certain groove. By performing this for multiple grooves, the groove opening width W2 for each of the multiple grooves was determined.

[0147] The midpoints of the openings were identified for the 25 locations where the opening widths were measured, and the distance between the 25 midpoints of two adjacent grooves was calculated. The average of the 25 values obtained was used to determine the spacing D31 between the two adjacent grooves. Similarly, the spacing D31 was determined for each of multiple combinations of adjacent grooves. The first ridge height H5 and the second ridge height H6 were calculated by visually observing SEM images of cross sections taken at five average locations, measuring the ridge height in each SEM image using the scale bar on the SEM image, and averaging the five values obtained. This was performed for multiple grooves to determine the first ridge height H5 and the second ridge height H6 for each of the multiple grooves.

[0148] The results are shown in Table 4 below. In Table 4 below, the opening width W4, spacing D31, height H5, and height H6 for each stainless steel indicate the minimum and maximum values of the multiple values measured (calculated) for the test specimen.

[0149] [Table 4]

[0150] As shown in Table 4, all of the stainless steels (Examples Nos. 41 to 56) manufactured using the manufacturing method of one embodiment of the present invention described above had the specified properties, and the bond between the test specimen and the adhesive was good (the failure mode was "cohesion" and was evaluated as passing).

[0151] In contrast, the stainless steels (Comparative Examples Nos. 21 to 26) manufactured under conditions where at least one of the fluence and overlap number was outside the range of the present invention did not satisfy the standard for at least one of the specified properties, and the bond between the test piece and the adhesive was poor (the failure mode was "interface" and the test piece was evaluated as failing). [Explanation of symbols]

[0152] 1. Stainless steel 2. Irradiation unit 3. Recess 4 Ridges 11 Non-irradiated area PL pulsed laser

Claims

1. At least a part of the surface has an irradiated portion irradiated with a pulsed laser, the irradiating portion includes a plurality of recessed portions and a plurality of raised portions adjacent to the recessed portions; the recessed portion and the raised portion each have an irregular shape; the raised portion has a width of 0.1 μm or more and 200 μm or less in a plan view, and the interval between the raised portions positioned on either side of the recessed portion does not exceed 300 μm; The stainless steel has a surface expansion ratio of 1.1 or more in the irradiated portion.

2. a surface before the irradiated portion is formed by the irradiation of the pulsed laser is defined as a virtual surface; the recessed portion has a depth from the imaginary plane greater than 0.1 μm in a cross-sectional view; The stainless steel according to claim 1 , wherein the protrusion has a height from the imaginary plane greater than 0.1 μm in a cross-sectional view.

3. The stainless steel according to claim 1, containing, by mass%, C: 0.005 to 0.300%, Si: 0.01 to 3.00%, Mn: 0.01 to 15.00%, P: 0.045% or less, S: 0.0300% or less, Ni: 0.01 to 20.00%, Cr: 10.0 to 35.0%, Cu: 0.01 to 3.50%, N: 0.400% or less, Al: 0.001 to 3.500%, and the balance consisting of Fe and unavoidable impurities.

4. The stainless steel according to claim 3, further comprising at least one selected from the group consisting of, in mass%, Mo: 0.01 to 3.20%, Nb: 0.60% or less, Ti: 0.60% or less, V: 0.60% or less, B: 0.010% or less, Ca: 0.0002 to 0.0150%, Hf: 0.001 to 0.600%, Zr: 0.01 to 0.60%, Sb: 0.005 to 0.600%, Co: 0.60% or less, W: 0.60% or less, Ta: 0.001 to 1.000%, Sn: 0.002 to 1.000%, Ga: 0.0002 to 0.5000%, Mg: 0.0003 to 0.0050%, and REM: 0.001 to 0.200%.

5. The stainless steel according to claim 1 , wherein the irradiated portion has a minimum autocorrelation length Sal of 45.0 μm or less.

6. each of the plurality of recesses is surrounded by the protrusion, has an average diameter of 0.1 μm or more and 200 μm or less, and has a smooth bottom surface; the plurality of raised portions are connected to each other to form a net-like structure, and have a plurality of protrusions protruding upward as part of the net-like structure, The stainless steel according to claim 1, wherein the distance between adjacent depressions with the intervening protrusions does not exceed 300 μm.

7. The stainless steel of claim 6, wherein the apex of at least some of the protrusions is spherical or teardrop-shaped.

8. At least some of the recessed portions are first groove portions having a groove shape extending in a first direction along the surface, The first groove portion has an opening width in the surface in a direction perpendicular to the first direction that is smaller than 300 μm, The plurality of ridges are a first ridge portion located adjacent to the first groove portion and extending in the first direction along the first groove portion; a second ridge portion located adjacent to the first groove portion on the opposite side to the first ridge portion and extending in the first direction along the first groove portion, The stainless steel according to claim 1, wherein the surface expansion ratio in the irradiated portion is 2.0 or more.

9. The height of the first ridge portion is greater than the height of the second ridge portion; The stainless steel of claim 8 , wherein the width of the first rib portion is greater than the width of the second rib portion.

10. a plurality of the first grooves; 9. The stainless steel of claim 8, wherein the spacing between the first grooves does not exceed 300 μm.

11. at least some of the recessed portions are second groove portions having a groove shape extending along the surface in a second direction intersecting the first direction, the second groove has an opening width in the surface in a direction perpendicular to the second direction that is smaller than 300 μm; The stainless steel according to claim 8 , wherein the irradiating portion includes a groove intersection where the first groove portion and the second groove portion intersect.

12. irradiating at least a portion of the surface of the stainless steel with a pulsed laser; The irradiation has a fluence of 1.2 to 6.5 J / cm ２ and the number of overlapping pulse laser marks represented by the following formula (1) is 0.5 to 200; Number of overlaps=S×fs / (W×VL) (1) In the above formula (1), S is the beam area (mm ２ ), fs represents the pulse irradiation speed (Hz), W represents the irradiation width (mm), and VL represents the feed speed of the irradiated object (mm / s).

13. 13. The method for producing stainless steel according to claim 12, wherein the irradiation is performed so that a ratio of a Cr concentration rate after the irradiation to a Cr concentration rate before the irradiation, which is expressed by the following formula (2) (after the irradiation / before the irradiation), in a surface layer including a region extending from the surface to 5 nm in a thickness direction, is 0.65 or less: Cr concentration ratio=Cr / (Cr+Fe+Si+Mn+Ni) (2) The element symbols in formula (2) are substituted with the content (mass%) of each element contained in the stainless steel, and 0 is substituted for elements that are not added.

14. 13. The method for producing stainless steel according to claim 12, wherein the pulse time of the pulsed laser during the irradiation is 8 μs to 20 μs, and the feed speed of the irradiated object is 400.0 mm / s or less.

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