Stainless steel roll, glass manufacturing apparatus, and glass manufacturing method

Abstract

To provide a technique for suppressing surface roughness of stainless rolls intended for high-temperature applications.SOLUTION: A stainless roll comprises stainless steel. The stainless steel comprises, in mass%, Nb: more than 0.005% to less than 0.40%.SELECTED DRAWING: Figure 3

Description

Technical Field

[0005]

[0001] The present disclosure relates to a stainless steel roll, a glass manufacturing apparatus, and a glass manufacturing method.

Background Art

[0002] A glass manufacturing apparatus includes a plurality of metal rolls that convey a strip-shaped glass ribbon, and nozzles that spray sulfurous acid (SO2) gas onto the lower surface of the glass ribbon (see, for example, Patent Document 1). The sulfurous acid gas reacts with the components of the glass to form a buffer film of sulfate such as sodium sulfate on the lower surface of the glass ribbon.

[0003] Patent Document 2 discloses a heat-resistant cast steel containing, in mass%, C: 0.2% to 0.4%, Si: 2% or less, Mn: 4% or less, Cr: 22% to 26%, Ni: 13% to 25%, Nb: 0.8 to 2%, and N: 0.1 to 0.25% as a material for a coiler drum (a roll for winding a steel sheet). Nb combines with C to precipitate NbC, increasing the creep strength, and also increases the ductility after aging as an effect of reducing the dissolved C. The Nb content is adjusted to 0.8 mass% or more so that the ductility improvement effect can be sufficiently obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Stainless steel rolls made of stainless steel are known. Stainless steel is generally defined as steel with a chromium content of 10.5% by mass or more and a carbon content of 1.2% by mass or less. The surface of stainless steel is covered with a passivation film. This passivation film is a chromium oxide film and prevents internal corrosion of the stainless steel.

[0006] In stainless steel, a phenomenon called sensitization can occur. Sensitization is a phenomenon in which chromium (Cr) and carbon (C) combine at grain boundaries, causing chromium carbides to precipitate, and chromium becomes depleted in the vicinity, resulting in the formation of a chromium-deficient layer. Near the chromium-deficient layer, the chromium oxide film is less likely to form, resulting in reduced corrosion resistance. As a result, red rust forms and the surface roughness increases. Sensitization is more pronounced in cast stainless steel than in rolled stainless steel because cast stainless steel has a higher carbon content than rolled stainless steel. Stainless steel rolls are generally made from cast stainless steel.

[0007] One aspect of this disclosure provides a technology for suppressing surface roughness of stainless steel rolls made of stainless steel. [Means for solving the problem]

[0008] A stainless steel roll according to one aspect of this disclosure is made of stainless steel. The stainless steel contains Nb: greater than 0.005% and less than 0.40% by mass. [Effects of the Invention]

[0009] According to one aspect of this disclosure, when the Nb content exceeds 0.005% by mass, Nb sufficiently bonds with C instead of Cr. This suppresses sensitization, prevents the occurrence of red rust, and suppresses surface roughness of the stainless steel roll. Furthermore, when the Nb content is less than 0.40% by mass, the deposition of Nb oxide particles on the surface of the stainless steel roll is suppressed, thereby suppressing surface roughness of the stainless steel roll. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a cross-sectional view showing a glass manufacturing apparatus according to one embodiment. [Figure 2] Figure 2 is a cross-sectional view showing an example of sensitization of stainless steel. [Figure 3] Figure 3 shows the relationship between the Nb content of stainless steel sheets in Examples 1 to 6 and the arithmetic mean roughness Ra after heat treatment. [Figure 4] Figure 4 shows backscattered electron images of the stainless steel plate according to Example 1 after heat treatment, where (A) is the backscattered electron image of the surface and (B) is the backscattered electron image of the cross-section. [Figure 5] Figure 5 shows backscattered electron images of the stainless steel plate according to Example 4 after heat treatment, where (A) is the backscattered electron image of the surface and (B) is the backscattered electron image of the cross-section. [Figure 6] Figure 6 shows backscattered electron images of a stainless steel plate according to Example 6 after heat treatment, where (A) is a backscattered electron image of the surface, (B) is a backscattered electron image of the cross-section, and (C) is a magnified backscattered electron image of the region enclosed by the white line in (B). [Modes for carrying out the invention]

[0011] Embodiments of this disclosure will be described below with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numeral, and their descriptions may be omitted. In this specification, the numeral "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively.

[0012] Referring to Figure 1, a glass manufacturing apparatus 1 according to one embodiment will be described. In Figure 1, the X-axis, Y-axis, and Z-axis directions are perpendicular to each other, with the X-axis and Y-axis directions being horizontal and the Z-axis direction being vertical. The X-axis direction is the transport direction of the glass ribbon G, and the Y-axis direction is the width direction of the glass ribbon G.

[0013] The glass manufacturing apparatus 1 includes, for example, a molding apparatus 2, a relay apparatus 3, and an annealing apparatus 5, arranged from the upstream side to the downstream side in the conveying direction of the glass ribbon G. The molding apparatus 2 forms the molten glass into a strip-shaped glass ribbon G. The relay apparatus 3 sends the glass ribbon G from the molding apparatus 2 to the annealing apparatus 5. The annealing apparatus 5 anneales the glass ribbon G. The glass manufacturing apparatus 1 manufactures a glass plate by cutting the annealed glass ribbon G.

[0014] Glass ribbon G and glass plate are, for example, alkali-free glass, aluminosilicate glass, borosilicate glass, or soda-lime glass. Alkali-free glass means glass that does not substantially contain alkali metal oxides such as Na2O and K2O. Here, substantially free of alkali metal oxides means that the total amount of alkali metal oxides contained is 0.1% by mass or less.

[0015] Alkali-free glass contains the following oxide-based mass percentages: SiO2: 50%~66%, Al2O3: 10.5%~24%, B2O3: 0%~12%, MgO: 0%~8%, CaO: 0%~14.5%, SrO: 0%~24%, BaO: 0%~13.5%, MgO+CaO+SrO+BaO: 9%~29.5%, and ZrO2: 0%~5%.

[0016] The uses of glass plates are not particularly limited, but for example, they are used as glass substrates for displays (e.g., liquid crystal displays or organic EL displays). When the glass plate is used as a glass substrate for a display, it is alkali-free glass. When the glass plate is used as cover glass, it is chemically strengthened glass. Chemically strengthened glass differs from alkali-free glass in that it contains alkali metal oxides.

[0017] The thickness of the glass plate is selected according to the use of the glass plate. When the use of the glass plate is a cover glass for a display, the thickness of the glass plate is, for example, 0.1 mm to 2.0 mm. When the use of the glass plate is a glass substrate for a display, the thickness of the glass plate is, for example, 0.1 mm to 0.7 mm. When the use of the glass plate is an automobile windshield, the thickness of the glass plate is, for example, 0.2 mm to 3.0 mm.

[0018] Next, referring to FIG. 1 again, the forming device 2, the relay device 3, and the slow cooling device 5 according to an embodiment will be described in this order. The forming device 2 forms a glass ribbon G by, for example, the float process. Note that the forming method may be the fusion process or the like. Hereinafter, the forming device 2 of the float process will be described.

[0019] The forming device 2 includes a bath 21. The bath 21 houses a molten metal M. As the molten metal M, for example, molten tin is used. In addition to molten tin, a molten tin alloy or the like can also be used, and the molten metal M may have a density higher than that of the molten glass. The molten glass is continuously supplied onto the molten metal M and is formed into a strip-shaped glass ribbon G using the smooth liquid surface of the molten metal M.

[0020] The forming device 2 includes a ceiling 22 above the bath 21. The inside of the forming device 2 is filled with a reducing gas to prevent oxidation of the molten metal M and is maintained at a pressure higher than the atmospheric pressure. The reducing gas is, for example, a mixed gas of nitrogen gas and hydrogen gas and contains 85 vol% to 98.5 vol% of nitrogen gas and 1.5 vol% to 15 vol% of hydrogen gas. The reducing gas is supplied from the joints between the bricks of the ceiling 22 and the holes of the ceiling 22.

[0021] The molding apparatus 2 includes a heater 23 for heating the glass ribbon G. The heater 23 is suspended from, for example, the ceiling 22 and heats the glass ribbon G as it passes below. The heater 23 is, for example, an electric heater and is heated by an electric current. Multiple heaters 23 are arranged in a matrix in the transport direction and width direction of the glass ribbon G. By controlling the output of the multiple heaters 23, the temperature distribution of the glass ribbon G can be controlled, and the thickness distribution of the glass ribbon G can be controlled.

[0022] The relay device 3 comprises a dross box 31 and a lift-out roll 32. The dross box 31 collects dross. Dross is an oxide formed when molten metal M, brought into the dross box 31 together with the glass ribbon G, is oxidized. The lift-out roll 32 is installed inside the dross box 31 and lifts the glass ribbon G from the molten metal M. Multiple lift-out rolls 32 are arranged at intervals in the direction of transport of the glass ribbon G (X-axis direction). The number of lift-out rolls 32 is not particularly limited. The lift-out rolls 32 are cylindrical in shape. The lift-out rolls 32 may be solid or hollow. The lift-out rolls 32 are rotationally driven by a drive device (not shown), such as a motor, and the driving force conveys the glass ribbon G diagonally upward. The axial direction of the lift-out rolls 32 is the same as the width direction (Y-axis direction) of the glass ribbon G.

[0023] The relay device 3 may be equipped with a heater 37 on the ceiling to adjust the temperature of the glass ribbon G. The heater 37 may be provided not only above the glass ribbon G but also below it. In the relay device 3, the temperature of the glass ribbon G is preferably (Tg-50)℃ to (Tg+30)℃, with reference to the glass transition point Tg of the glass ribbon G.

[0024] The annealing device 5 comprises an annealing furnace 51 and a layer roll 52. The layer roll 52 conveys the strip-shaped glass ribbon G in the longitudinal direction (X-axis direction) of the glass ribbon G. The annealing furnace 51 is an example of a heat treatment furnace. The layer roll 52 is an example of a conveying roll. Multiple layer rolls 52 are provided at intervals in the conveying direction of the glass ribbon G. The number of layer rolls 52 is not particularly limited. The layer roll 52 is cylindrical in shape. The layer roll 52 may be solid or hollow. The layer roll 52 is rotationally driven by a drive device (not shown), such as a motor, and the driving force conveys the glass ribbon G in the horizontal direction (X-axis direction). The axial direction of the layer roll 52 is the same as the width direction (Y-axis direction) of the glass ribbon G.

[0025] The annealing device 5 slowly cools the glass ribbon G to a temperature below the glass strain point while conveying it with the layer roll 52. The annealing device 5 is equipped with an internal heater (not shown) to adjust the temperature of the glass ribbon G.

[0026] The annealing device 5 includes a supply pipe 53 that sprays a buffer material onto the underside of the glass ribbon G. The buffer material reacts with the underside of the glass ribbon G to form a buffer film on the underside of the glass ribbon G. The buffer film mitigates the collision between the glass ribbon G and the layer roll 52 and suppresses the occurrence of scratches on the underside of the glass ribbon G.

[0027] For example, sulfur oxide gas is used as a buffering agent. The sulfur oxide gas reacts with the underside of the glass ribbon G, forming a buffer film on the underside of the glass ribbon G. The buffer film contains sulfate crystals, etc.

[0028] The supply pipe 53 may also blow a diluent gas along with the sulfur oxide gas. The diluent gas dilutes the sulfur oxide gas and reduces the amount of sulfur oxide gas used while maintaining the airflow velocity. For example, air can be used as the diluent gas.

[0029] A band heater (not shown) may be wrapped around the supply pipe 53. The band heater heats the supply pipe 53, thereby heating the buffer and promoting the reaction between the buffer and the glass ribbon G.

[0030] The supply pipe 53 is positioned, for example, between the first and second layer rolls 52, 52, from the upstream side to the downstream side in the conveying direction of the glass ribbon G. A buffer film can be formed relatively upstream of the annealing device 5, which can suppress the occurrence of scratches on the underside of the glass ribbon G.

[0031] Although not shown in the diagram, the supply pipe 53 may be positioned upstream of the first (upstreamest) layer roll 52. Also, although not shown in the diagram, the supply pipe 53 may be positioned downstream in the conveying direction of the second layer roll 52.

[0032] Incidentally, stainless steel rolls are sometimes used as layer roll 52. Stainless steel rolls are made of stainless steel. Stainless steel is generally a type of steel with a chromium content of 10.5% by mass or more and a carbon content of 1.2% by mass or less. The surface of stainless steel is covered with a passivation film. This passivation film is a chromium oxide film, which prevents internal corrosion of the stainless steel.

[0033] As shown in Figure 2, a phenomenon called sensitization can occur in stainless steel. Sensitization is a phenomenon in which Cr and C combine at the grain boundaries of crystal grains to precipitate Cr carbide 101, and Cr is depleted in its vicinity, forming a Cr-deficient layer 102. Near the Cr-deficient layer 102, it is difficult for Cr oxide film 103 to form, resulting in reduced corrosion resistance. As a result, red rust forms and the surface roughness increases.

[0034] Therefore, in this embodiment, stainless steel containing Nb: more than 0.005% to less than 0.40% by mass is used as the stainless steel constituting the stainless steel roll. If the Nb content exceeds 0.005% by mass, Nb will sufficiently bond with C instead of Cr. This will suppress sensitization, suppress the occurrence of red rust, and suppress surface roughness of the stainless steel roll. Furthermore, if the Nb content is less than 0.40% by mass, the deposition of Nb oxide particles on the surface of the stainless steel roll will be suppressed, thereby suppressing surface roughness of the stainless steel roll.

[0035] The Nb content of the stainless steel constituting the stainless steel roll may be greater than 0.005% but less than 0.40%, as described above, but preferably greater than 0.005% but less than 0.30%, more preferably greater than 0.005% but less than 0.20%, even more preferably greater than 0.005% but less than 0.10%, and particularly preferably greater than 0.005% but less than 0.05%. The above Nb content is preferably between 0.01% and 0.36%.

[0036] The surface roughness of the stainless steel roll is represented by the arithmetic mean roughness Ra. The arithmetic mean roughness Ra is preferably 0.01 μm to 0.6 μm. The arithmetic mean roughness Ra is measured in accordance with JIS B0601:2013. The arithmetic mean roughness Ra is more preferably 0.01 μm to 0.4 μm, even more preferably 0.01 μm to 0.3 μm, and particularly preferably 0.01 μm to 0.2 μm.

[0037] The stainless steel constituting the stainless steel roll is not particularly limited, but preferably contains, by mass%, Fe: more than 40% to less than 80%, Cr: more than 15% to less than 30%, Ni: more than 5% to less than 25%, C: more than 0.1% to less than 1.0%, Si: more than 0% to less than 5%, Mn: more than 0% to less than 2%, and Nb: more than 0.005% to less than 0.40%. A specific steel grade is HK40 as described in ASTM (American Society for Testing and Materials) A351. Note that the Nb content of HK40 is not specified in the ASTM standard.

[0038] The stainless steel constituting the stainless steel roll more preferably contains, by mass%, Fe: more than 40% to less than 80%, Cr: more than 15% to less than 30%, Ni: more than 5% to less than 25%, C: more than 0.1% to less than 1.0%, Si: more than 0% to less than 1.5%, Mn: more than 0% to less than 1%, and Nb: more than 0.005% to less than 0.40%.

[0039] If the Si content is less than 1.5% by mass, the deposition of Si oxide particles on the surface of the stainless steel roll can be suppressed, further reducing surface roughness of the stainless steel roll. Similarly, if the Mn content is less than 1%, the deposition of Mn oxide particles on the surface of the stainless steel roll can be suppressed, further reducing surface roughness of the stainless steel roll.

[0040] The stainless steel roll is preferably used to transport glass at temperatures between 500°C and 900°C. The glass to be transported is, for example, a glass ribbon G. At temperatures between 500°C and 900°C, the glass is soft and easily scratched. Furthermore, the temperature at which sensitization can occur is substantially between 500°C and 900°C. If the temperature is too low, sensitization is very slow, and if the temperature is too high, the diffusion rate of Cr is fast, making it difficult for a Cr-deficient layer 102 to form. According to this embodiment, as described above, by keeping the Nb content of the stainless steel constituting the stainless steel roll within a desired range, surface roughness of the stainless steel roll can be suppressed. Therefore, it is possible to suppress scratches on the glass caused by the stainless steel roll. The smoother the surface, the less likely it is to be scratched.

[0041] The effect of suppressing surface roughness of stainless steel rolls is particularly pronounced when the glass used is alkali-free glass. Alkali-free glass substantially does not contain alkali metal oxides such as Na2O and K2O. Therefore, compared to soda-lime glass, alkali-free glass is more difficult to form a buffer film of sufficient thickness using sulfur oxide gas, and is more susceptible to the effects of surface roughness on stainless steel rolls.

[0042] In this embodiment, the stainless steel roll is used as a layer roll 52, but it may also be used as a lift-out roll 32. Furthermore, the stainless steel roll may be used not only for conveying strip-shaped glass ribbons G, but also for conveying glass plates or glass bottles. In addition, the stainless steel roll may be used for conveying objects other than glass. The stainless steel roll can also be used as a base material for rolls coated with ceramic by thermal spraying. [Examples]

[0043] The experimental data is described below. Examples 1 and 6 are comparative examples, and Examples 2 to 5 are examples. In Examples 1 to 6, stainless steel sheets with the chemical compositions shown in Table 1 were prepared. The chemical composition of each stainless steel sheet (excluding C and S content) was measured by X-ray fluorescence analysis. The C and S content of each stainless steel sheet was measured by combustion-infrared absorption spectroscopy.

[0044] Each stainless steel sheet was heated at 750°C for 10 hours in an atmospheric environment, and then the arithmetic mean roughness Ra of the surface of each stainless steel sheet was measured. The arithmetic mean roughness Ra was measured using a contact-type surface roughness meter (Tokyo Seimitsu SURFCOM TOUCH 50). Prior to the heat treatment, the surface of each stainless steel sheet was mirror-polished under the same conditions. Therefore, before the heat treatment, the surface of each stainless steel sheet had the same surface roughness Ra (specifically, 0.1 μm to 0.2 μm).

[0045] Table 1 shows the chemical composition of each stainless steel sheet and its arithmetic mean roughness Ra after heat treatment.

[0046] [Table 1] Figure 3 shows the relationship between the Nb content of stainless steel sheets in Examples 1 to 6 and the arithmetic mean roughness Ra after heat treatment. From Figure 3, it can be seen that the arithmetic mean roughness Ra after heat treatment changes critically when the Nb content is greater than 0.005 mass% and less than 0.40 mass%, and that the arithmetic mean roughness Ra after heat treatment is small when the Nb content is between greater than 0.005 mass% and less than 0.40 mass%.

[0047] Figure 4 shows the backscattered electron beam image (backscattered electron composition image) of the stainless steel plate according to Example 1 after heat treatment, Figure 5 shows the backscattered electron beam image of the stainless steel plate according to Example 4 after heat treatment, and Figure 6 shows the backscattered electron beam image of the stainless steel plate according to Example 6 after heat treatment. These backscattered electron beam images were captured using a scanning electron microscope (HITACHI SU1510).

[0048] In Example 1, the Nb content was low, and a large amount of Fe oxide was observed on the surface after heat treatment, as shown in Figure 4(A). On the other hand, in Examples 4 and 6, the Nb content was high, and there was little Fe oxide on the surface after heat treatment, as shown in Figures 5(A) and 6(A).

[0049] Figures 4(A), 5(A), and 6(A) show that when the Nb content exceeds 0.005% by mass, Nb sufficiently bonds with C instead of Cr, suppressing sensitization and inhibiting the formation of red rust (Fe oxide).

[0050] However, if the Nb content exceeds 0.40% by mass, as shown in Figure 6(C), Nb oxide particles precipitate on the surface of the steel plate, resulting in a rough surface.

[0051] The stainless steel roll, glass manufacturing apparatus, and glass manufacturing method described above are not limited to the embodiments described herein. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure. [Explanation of Symbols]

[0052] 1. Glass manufacturing equipment 52 Layer Rolls (Stainless Steel Rolls) G Glass Ribbon

Claims

1. A stainless steel roll made of stainless steel, The stainless steel roll comprises, by mass%, Nb: more than 0.005% to less than 0.40%, Cr: more than 15% to less than 30%, Ni: more than 5% to less than 25%, C: more than 0.1% to less than 1.0%, Si: more than 0% to less than 5%, Mn: more than 0% to less than 2%, with the remainder being Fe and unavoidable impurities.

2. A stainless steel roll made of stainless steel, The stainless steel roll according to claim 1, wherein the stainless steel comprises, by mass%, Nb: more than 0.005% to less than 0.40%, Cr: more than 15% to less than 30%, Ni: more than 5% to less than 25%, C: more than 0.1% to less than 1.0%, Si: more than 0% to less than 1.5%, Mn: more than 0% to less than 1%, with the remainder being Fe and unavoidable impurities.

3. A stainless steel roll according to claim 1 or 2, used for transporting glass.

4. The stainless steel roll according to claim 3, wherein the temperature of the glass is 500°C to 900°C.

5. The stainless steel roll according to claim 4, wherein the glass is alkali-free glass.

6. A glass manufacturing apparatus comprising a molding device for forming molten glass into a strip-shaped glass ribbon, and an annealing device for slowly cooling the glass ribbon, The slow cooling apparatus comprises a heat treatment furnace and a conveying roll for transporting the glass ribbon inside the heat treatment furnace. The glass manufacturing apparatus wherein the conveying roll is a stainless steel roll as described in claim 1 or 2.

7. The glass manufacturing apparatus according to claim 6, wherein the stainless steel roll is used to convey the glass ribbon at 500°C to 900°C.

8. The glass manufacturing apparatus according to claim 6, wherein the glass ribbon is alkali-free glass.

9. A glass manufacturing method comprising forming molten glass into a strip-shaped glass ribbon, and slowly cooling the glass ribbon while conveying it with a conveyor roll, A glass manufacturing method wherein the conveying roll is a stainless steel roll according to claim 1 or 2.

10. The aforementioned stainless steel roll is used to convey the glass ribbon at a temperature of 500°C to 900°C. The glass manufacturing method according to claim 9.

11. The glass manufacturing method according to claim 9, wherein the glass ribbon is alkali-free glass.

Images