WO2023012906A1 - 冷間圧延用鍛鋼ロール - Google Patents
冷間圧延用鍛鋼ロール Download PDFInfo
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- WO2023012906A1 WO2023012906A1 PCT/JP2021/028833 JP2021028833W WO2023012906A1 WO 2023012906 A1 WO2023012906 A1 WO 2023012906A1 JP 2021028833 W JP2021028833 W JP 2021028833W WO 2023012906 A1 WO2023012906 A1 WO 2023012906A1
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- cold rolling
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 98
- 239000010959 steel Substances 0.000 title claims abstract description 98
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Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
- B21B27/02—Shape or construction of rolls
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/38—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for roll bodies
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
Definitions
- the present invention relates to forged steel rolls for cold rolling.
- Iron-based materials such as forged steel are generally used as rolls for cold rolling.
- cold rolling using such a forged steel roll for cold rolling for example, the roughness of the roll surface gradually decreases due to long-term use, and slip occurs between the roll and the material to be rolled during rolling, resulting in rolling failure. Otherwise, the oil film of the lubricating oil supplied between the roll and the steel sheet may break due to changes in rolling conditions, etc., causing direct contact between the roll and the steel sheet and causing seizure.
- thermal shock is applied to the roll surface due to a plate threading accident such as slip or seizure, and cracks may occur on the roll surface due to such thermal shock. If this crack is left as it is, the crack will gradually propagate through the roll. As the crack progresses, the outer surface of the roll may peel off, and such a roll breakage phenomenon is generally called spalling.
- Patent Document 1 C: 0.7 to 1.0%, Si: 0.15 to 1.5%, Mn: 0.15 to 1.5%, Cr: 3.0 to 6.0%, Mo : 3.0 to 5.0%, V: 1.2% or less. Only the surface layer of a cast steel material is heated to a temperature above the transformation point, and after fountain quenching, it is cooled to -30 ° C or less. A process for producing work rolls for metal rolling mills is described which is characterized by subzero treatment at temperature and further tempering at a temperature of 180° C. or higher. According to Patent Document 1, according to the above manufacturing method, if the surface hardness is the same as that of a conventional roll, the tempering temperature can be increased by 40° C. or more, so the effect of significantly increasing the resistance to cracks due to thermal shock at the time of a rolling accident can be obtained. It is stated that there is
- Patent Document 2 in weight percent, C: 0.45 to 0.95%, Mn: 1.0% or less, Cr: 4.5 to 6.0%, Mo: 0.3 to 0.7%, Ni : 0.6 to 2.0%, the balance being Fe and unavoidable impurities, and the Si content as an unavoidable impurity is suppressed to less than 0.1%. It is In Patent Document 2, in a conventional Cr-Mo steel-based roll material, by suppressing the Si content to 0.1% or less as an inevitable impurity and containing 0.6 to 2.0% Ni, It is described that it is possible to obtain a roll material for rolling having high toughness while ensuring the same hardness level as the roll, that is, without impairing wear resistance, spalling resistance and thermal shock crack resistance.
- Patent Document 3 C: 0.90 to 1.10 wt%, Si: 0.5 to 1.0 wt%, Mn: 0.1 to 1.0 wt%, Cr: 4.0 to 6.0 wt%, Mo : 3.0 to 6.0 wt%, V: 0.5 to 2.0 wt%, and Co: 1.0 to 3.0 wt%, the balance being Fe and inevitable impurities.
- a work roll stock for cold rolling of manufacturing is described.
- Patent Document 3 describes that with the above configuration, it is possible to obtain a work roll material for cold rolling that has both wear resistance and thermal shock resistance, which have been considered difficult to achieve in the past.
- Patent Document 4 C: 0.7 to 1.4%, Si: 0.8 to 2.5%, Mn: 0.8 to 2.5%, Ni: 0.5 to 2.5% by weight. %, Cr: 2.5 to 6.5%, Mo: 2.5 to 8.5%, W: 0.3 to 3.0%, V: 0.5 to 4.5%, balance Fe and unavoidable describes a quenched roll for rolling characterized by containing 15% to 40% of retained austenite due to tempering after subzero treatment. Patent Document 4 describes that by allowing the amount of retained austenite to remain in the range of 15 to 40%, the toughness is improved and the propagation of cracks after cracking is prevented.
- Patent Document 5 in mass %, C: 0.6 to 1.2%, Si: 0.4 to 0.8%, Mn: 0.4 to 1.0%, Ni: 0.4 to 1.0%. 0%, Cr: 3.0 to 6.0%, Mo: 0.2 to 0.5%, a forged steel cold rolling roll containing Fe and inevitable impurities, 50 mm from the roll surface
- a forged steel cold rolling roll characterized in that the average particle size of carbides dispersed in the metal structure of the roll surface layer within the roll surface is 1 ⁇ m or less, and the area fraction of the dispersed carbides is 5 to 30%.
- excellent toughness can be secured without using expensive elements such as microalloys or adopting a special manufacturing method. It is described that cracks do not occur during rolling even in a high load environment.
- the crack generation mechanism of cold rolling rolls due to thermal shock has not been clarified.
- the present inventors considered that cracks on the roll surface are generated as follows. First, the thermal shock instantaneously raises the temperature of the roll surface, and when the temperature exceeds a certain value, tempering of the microstructure occurs. This microstructure tempering is accompanied by material shrinkage at the roll surface. Shrinkage of the material then occurs, resulting in tensile stresses in the roll surface, and cracks in the roll surface due to such tensile stresses.
- the present invention has been made in view of the above, and its object is to provide a forged steel roll for cold rolling with improved crack resistance that can reduce the occurrence of cracks due to thermal shock. That's what it is.
- the present invention for achieving the above object is as follows.
- the present invention by using a roll manufactured from forged steel having a Vickers hardness Hv of 400 or more at 400 ° C. as a roll for cold rolling, the occurrence of cracks on the roll surface is significantly suppressed or reduced. be able to. That is, it is possible to remarkably improve the crack resistance of the roll for cold rolling.
- a forged steel roll for cold rolling even if a thermal shock is applied to the roll due to a strip threading accident such as slip or seizure during cold rolling, the crack generated due to the thermal shock Clefts can be made shallower. Therefore, the amount of roll grinding for removing the cracks can be reduced, and therefore the roll unit consumption can be significantly improved.
- the forged steel roll for cold rolling according to the embodiment of the present invention has a Vickers hardness Hv of 400 or more at 400°C.
- thermal shock is applied to the roll surface due to slipping, seizure, and other accidents that occur between the roll and the material to be rolled during rolling, causing cracks on the roll surface. Cracks may occur. When this crack progresses, peeling called spalling may occur on the outer surface of the roll.
- the present inventors focused on the hardness of the roll material at high temperatures as an index of durability against cracking on the roll surface due to thermal shock, and found a correlation between the hardness of the roll material and the occurrence of cracks. investigated the relationship. As a result, the present inventors have found that a roll manufactured from forged steel having a Vickers hardness Hv at 400°C (hereinafter also simply referred to as "high-temperature hardness") of 400 or more is used as a roll for cold rolling. It has been found that the occurrence of cracks on the roll surface can be remarkably suppressed or reduced, that is, the crack resistance of cold rolling rolls can be remarkably improved.
- the forged steel roll for cold rolling according to the embodiment of the present invention has a Vickers hardness Hv of 400 or more at 400°C.
- the higher the temperature the lower the hardness of the roll material.
- the inventors have found that the hardness of conventional forged steel rolls for cold rolling rapidly decreases at high temperatures around 400°C.
- the inventors of the present invention maintain the Vickers hardness Hv of the forged steel roll for cold rolling at a high level of 400 or more even at such high temperatures by devising the manufacturing method while making the chemical composition appropriate. I found that it can be done. According to the embodiment of the present invention, by controlling the Vickers hardness Hv at 400° C.
- the tensile stress generated on the roll surface at high temperature during thermal shock is reduced.
- the Vickers hardness Hv at 400°C is preferably 410 or higher, more preferably 420 or higher, even more preferably 430 or higher, and most preferably 435 or higher or 440 or higher.
- the upper limit of the Vickers hardness Hv at 400 ° C. is not particularly limited, but even if the high-temperature hardness is excessively increased, the effect of suppressing or reducing the occurrence of cracks is saturated, while the toughness may be reduced. . Therefore, the Vickers hardness Hv at 400° C. is preferably 700 or less, and may be 600 or less, 550 or less, or 500 or less.
- “400°C” refers to the temperature of the roll surface.
- “Vickers hardness Hv” refers to the Vickers hardness of a region from the surface of the body of the roll to a depth of 10 mm.
- the “Vickers hardness Hv at 400°C” is obtained by heating a test material sampled from the surface of a forged steel roll for cold rolling from room temperature to 400°C using a high-temperature Vickers hardness meter for 5 minutes. Determined by measuring the hardness when held. The measurement is performed by a method conforming to JIS Z 2252:1991.
- the test material and the indenter are heated, the Vickers hardness is measured at 5 points by adding a load of 300 gf to the 5 mm ⁇ 10 mm measurement surface of the test material with dimensions of 5 mm ⁇ 5 mm ⁇ 10 mm, and their The average value is determined as the Vickers hardness Hv at 400°C. More preferably, the Vickers hardness Hv at 400° C. is 400 or more in the effective diameter region of the roll.
- the effective diameter area refers to the area from the surface to the minimum diameter that can be used for rolling (discard diameter).
- shrinkage start temperature As mentioned above, in order to suppress or reduce the occurrence of cracks on the roll surface due to thermal shock, it is effective to increase the durability of the roll surface against the tensile stress caused by material shrinkage at high temperatures. can be considered as a viable solution.
- the present inventors focused on suppressing or reducing the material shrinkage itself on the roll surface at high temperatures, and thus the generation of tensile stress itself accompanying such material shrinkage, and further studied. . More specifically, the present inventors investigated the correlation between the temperature at which such shrinkage starts in the roll material (hereinafter simply referred to as "shrinkage start temperature”) and the occurrence of cracks.
- the present inventors found that a roll for cold rolling manufactured from forged steel having a Vickers hardness Hv at 400° C. of 400 or higher and a shrinkage start temperature of 300° C. or higher in the heating process is used for cold rolling. It has been found that the use as a roll can significantly suppress or reduce the occurrence of cracks on the roll surface, that is, the crack resistance of the roll for cold rolling can be significantly improved.
- the "shrinkage start temperature” is the temperature on the low temperature side of the thermal expansion curve obtained by measuring the amount of expansion of the roll material in the temperature rising process using a Formaster tester. It refers to the temperature at the point of inflection (when contraction starts).
- FIG. 1 is a graph showing the thermal expansion curve of the roll material in the heating process using a Formaster tester for explaining the shrinkage start temperature according to this embodiment.
- a solid line in FIG. 1 indicates a thermal expansion curve of a test material sampled from a roll material according to Example 3, which will be described later.
- a dashed line in FIG. 1 indicates a thermal expansion curve of a test material sampled from a roll material according to Comparative Example 1, which will be described later. Referring to FIG. 1, in the test material of Comparative Example 1, the slope of the change in the amount of expansion once decreased at 250° C. when the temperature was raised from room temperature.
- the forged steel roll for cold rolling according to the preferred embodiment of the present invention has a shrinkage start temperature of 300°C or higher.
- the shrinkage start temperature is 450° C., which is very high. Therefore, even if a thermal shock is applied to the roll surface due to a threading accident such as slip or seizure, and the temperature rises instantaneously, the material will not shrink on the roll surface, or the amount of shrinkage will be greatly reduced. It becomes possible to According to the forged steel roll for cold rolling according to the preferred embodiment of the present invention, it is possible to suppress or reduce the occurrence of tensile stress accompanying the shrinkage of the material on the roll surface compared to conventional materials. It becomes possible to remarkably suppress or reduce the occurrence of cracks on the roll surface due to such tensile stress.
- the shrinkage initiation temperature is 350°C or higher, 400°C or higher, 450°C or higher, 500°C or higher, 600°C or higher, 650°C or higher, 670°C or higher, 700°C or higher, 750°C or higher, 800°C or higher, or 850°C or higher.
- the shrinkage start temperature is preferably 950° C. or lower.
- the forged steel roll for cold rolling of this embodiment has a Vickers hardness Hv of 400 or more at 400°C, and preferably has a shrinkage initiation temperature of 300°C or more. Therefore, the chemical composition of the forged steel roll for cold rolling may be any chemical composition that can achieve a Vickers hardness Hv of 400 or more at 400°C, preferably a shrinkage start temperature of 300°C or more, It is not particularly limited. More specifically, the object of the present embodiment is to provide a forged steel roll for cold rolling with improved crack resistance that can reduce the occurrence of cracks due to thermal shock as described above. The object is achieved by setting the Vickers hardness Hv of the forged steel roll for cold rolling at 400 ° C.
- the chemical composition of the forged steel roll for cold rolling is not an essential technical feature for achieving the purpose of this embodiment.
- the preferred chemical compositions of the forged cold rolls to achieve the hot hardness and shrinkage onset temperature characteristics are detailed; and is not intended to limit the present embodiments to cold rolling forged steel rolls having such specific chemical compositions.
- "%" which is the unit of content of each element contained in the forged steel roll for cold rolling, means “% by mass” unless otherwise specified.
- the term “to” indicating a numerical range is used to include the numerical values before and after it as a lower limit and an upper limit, unless otherwise specified.
- Carbon (C) is an element necessary for increasing the hardness of the roll surface layer.
- the C content is preferably 0.70% or more.
- the C content may be 0.75% or more, 0.80% or more, 0.85% or more, or 0.90% or more.
- the C content is preferably 1.50% or less.
- C content may be 1.40% or less, 1.30% or less, 1.20% or less, 1.15% or less, 1.10% or less, 1.05% or less, or 1.00% or less .
- Si is an element that generally deoxidizes steel and further enhances hardenability.
- the present inventors further investigated the relationship between the Si content, the high-temperature hardness of the roll, and the shrinkage start temperature. As a result, it was found that there is a strong correlation between these, and that the addition of Si can increase both the high-temperature hardness and the shrinkage start temperature. From the viewpoint of sufficiently improving the high-temperature hardness of the roll, the Si content is preferably 0.40% or more. On the other hand, from the viewpoint of sufficiently improving the shrinkage start temperature, the Si content is preferably 0.45% or more.
- Si content may be 0.50% or more, 0.60% or more, 0.70% or more, 0.75% or more, 0.80% or more, 0.85% or more, or 0.90% or more . Also from the viewpoint of increasing the amount of solid-solution Si, which will be described in detail later, the higher the Si content, the better. On the other hand, if Si is contained excessively, carbides tend to segregate, and sufficient toughness may not be obtained. Therefore, although the upper limit of the Si content is not necessarily limited from the viewpoint of improving the high-temperature hardness and/or the shrinkage start temperature of the roll, the Si content is 1.50% or less from the viewpoint of ensuring sufficient toughness. It is preferable to The Si content may be 1.40% or less, 1.30% or less, 1.20% or less, 1.10% or less, 1.05% or less, 1.00% or less, or 0.95% or less .
- the production method is appropriately controlled to form a solid solution in the matrix. It becomes very important to increase the amount of Si present in the state.
- Mn Manganese (Mn) is an element that effectively increases hardenability.
- the Mn content is preferably 0.20% or more.
- the Mn content may be 0.25% or more, 0.30% or more, 0.35% or more, or 0.40% or more.
- the Mn content is preferably 1.50% or less.
- the Mn content may be 1.40% or less, 1.20% or less, 1.00% or less, 0.80% or less, or 0.60% or less.
- Phosphorus (P) is an unavoidable impurity. That is, the P content is over 0%. P may segregate at grain boundaries and reduce the toughness of the steel material. Therefore, the P content is preferably 0.030% or less. The P content may be 0.025% or less, or 0.020% or less. The lower the P content is, the better. However, excessive reduction of the P content greatly increases refining costs in the steelmaking process. Therefore, considering industrial production, the P content is preferably 0.001% or more. The P content may be 0.002% or more.
- S 0.0200% or less
- Sulfur (S) is an unavoidable impurity. That is, the S content is over 0%. S segregates at grain boundaries and may reduce the toughness and hot workability of steel materials. Therefore, the S content is preferably 0.0200% or less. The S content may be 0.0050% or less, 0.0040% or less, or 0.0030% or less. It is preferable that the S content is as low as possible. However, an excessive reduction in the S content greatly increases the refining cost in the steelmaking process. Therefore, considering industrial production, the S content is preferably 0.0001% or more. The S content may be 0.0002% or more, or 0.0003% or more.
- Aluminum (Al) is an unavoidable impurity. That is, the Al content is over 0%. Al deoxidizes the steel during the molten steel stage. On the other hand, if the Al content is too high, Al nitrides may coarsen and the toughness of the steel material may deteriorate. Therefore, the Al content is preferably 0.050% or less.
- the Al content may be 0.040% or less, or 0.030% or less.
- the Al content may be 0.001% or more, or 0.002% or more. As used herein, Al content means the total Al content in the steel.
- N 0.0200% or less
- Nitrogen (N) is an unavoidable impurity. That is, the N content is over 0%. N increases the strength of steel through solid solution strengthening. On the other hand, if the N content is too high, coarse nitride-based inclusions may be formed and the toughness of the steel material may be lowered. Therefore, the N content is preferably 0.0200% or less. The N content may be 0.0150% or less. The N content may be 0.0001% or more, or 0.0002% or more.
- Oxygen (O) is an unavoidable impurity. That is, the O content is over 0%. O forms coarse oxide-based inclusions and may reduce the toughness of the steel material. Therefore, the O content is preferably 0.0050% or less. The O content may be 0.0040% or less, 0.0035% or less, or 0.0030% or less. It is preferable that the O content is as low as possible. However, the drastic reduction of the O content greatly increases the manufacturing cost. Therefore, considering industrial production, the O content is preferably 0.0001% or more, or 0.0005% or more. The O content may be 0.0007% or more.
- Chromium (Cr) is an element that forms carbides to improve wear resistance.
- Cr is an element that increases tempering resistance and improves high-temperature hardness.
- the Cr content is preferably 2.80% or more.
- the Cr content may be 3.00% or more, 3.20% or more, 3.50% or more, or 4.00% or more.
- the Cr content is preferably 8.00% or less.
- the Cr content may be 7.50% or less, 7.00% or less, 6.50% or less, 6.00% or less, or 5.50% or less.
- Molybdenum is an element that forms carbides to improve wear resistance. Mo is an element that improves high-temperature hardness by secondary hardening. In order to sufficiently obtain these effects, the Mo content is preferably 0.30% or more. Mo content may be 0.35% or more, 0.40% or more, or 0.45% or more. On the other hand, if Mo is contained excessively, carbides may become coarse, and the grindability and toughness of the forged steel roll for cold rolling may deteriorate. Therefore, the Mo content is preferably 3.00% or less. Mo content is 2.80% or less, 2.50% or less, 2.00% or less, 1.80% or less, 1.50% or less, 1.00% or less, 0.80% or less, 0.60% or less or 0.55% or less.
- Copper (Cu) is an unavoidable impurity. That is, the Cu content is over 0%. Cu may reduce the hot workability of steel. Therefore, the Cu content is preferably 0.100% or less. The Cu content may be 0.095% or less, 0.090% or less, 0.085% or less, 0.080% or less, 0.075% or less, or 0.070% or less. The Cu content is preferably as low as possible. However, excessive reduction of Cu content raises manufacturing costs. Therefore, the Cu content is preferably 0.001% or more. The Cu content may be 0.002% or more.
- B boron
- B is an unavoidable impurity. That is, the B content is over 0%. B may reduce the toughness of steel. Therefore, the B content is preferably 0.0100% or less. The B content may be 0.0080% or less, or 0.0060% or less. B content is preferably as low as possible. However, excessive reduction of the B content raises manufacturing costs. Therefore, the B content is preferably 0.0001% or more. The B content may be 0.0002% or more.
- the basic chemical composition of the forged steel roll for cold rolling according to the embodiment of the present invention is as described above. Furthermore, the forged steel roll for cold rolling may contain one or more of the following elements, if necessary.
- Nickel (Ni) is an element that enhances hardenability.
- the Ni content may be 0%, the Ni content is preferably 0.01% or more in order to sufficiently obtain such effects.
- the Ni content may be 0.05% or more, 0.10% or more, 0.15% or more, or 0.20% or more.
- the Ni content is preferably 1.20% or less.
- Ni content is 1.10% or less, 1.00% or less, 0.80% or less, 0.60% or less, 0.45% or less, 0.30% or less, 0.28% or less, 0.26% Below, it may be 0.25% or less or 0.24% or less.
- V Vanadium (V), like Cr and Mo, is an element that forms carbides to improve wear resistance. Further, V is an element that improves high-temperature hardness by secondary hardening.
- the V content may be 0%, the V content is preferably 0.01% or more in order to sufficiently obtain these effects.
- the V content may be 0.05% or more, 0.10% or more, 0.15% or more, 0.20% or more, or 0.25% or more.
- the V content is preferably 2.00% or less.
- the V content may be 1.80% or less, 1.50% or less, 1.00% or less, 0.80% or less, 0.60% or less, or 0.40% or less.
- Niobium is an element that combines with C to form a hard carbide.
- Nb is an element that improves high-temperature hardness by secondary hardening.
- the Nb content may be 0%, the Nb content is preferably 0.01% or more in order to sufficiently obtain these effects.
- the Nb content may be 0.05% or more, 0.10% or more, 0.15% or more, 0.20% or more, or 0.25% or more.
- the Nb content is preferably 1.00% or less.
- the Nb content may be 0.80% or less, 0.60% or less, or 0.40% or less.
- the balance other than the above elements consists of Fe and impurities.
- Impurities are components that are mixed due to various factors in the manufacturing process, including raw materials such as ores and scraps, when the forged steel roll for cold rolling is manufactured industrially.
- the present inventors also controlled the total content of Cr, Mo, V and Nb within a predetermined range, It was found that a Vickers hardness Hv of 400 or more and a shrinkage initiation temperature of 300° C. or more can be achieved more reliably.
- Cr, Mo, V and Nb are elements that form carbides to improve wear resistance and the like.
- the ratio of carbides contained in the roll is small, the ratio of the base metal is large, so the carbides formed by these elements have an extremely small effect on the high-temperature hardness and/or the shrinkage start temperature of the roll. it is conceivable that.
- carbides do not particularly change with temperature or the like, it is considered that as the proportion of carbides in the roll increases, the carbides contribute to raising the high-temperature hardness and/or the shrinkage start temperature.
- the total content of Cr, Mo, V and Nb is 4.50% while controlling the content of each alloying element contained in the roll within the range described above.
- the above is controlled to Cr+Mo+V+Nb ⁇ 4.50.
- a sufficient amount of carbide can be formed in the roll to achieve a Vickers hardness Hv of 400 or higher at 400°C and a shrinkage initiation temperature of 300°C or higher.
- the total content of Cr, Mo, V and Nb is 4.80% or more, 5.00% or more, 5.20% or more, 5.50% or more, 5.60% or more, 5.70% or more, It may be 5.80% or more, 6.00% or more, or 6.30% or more.
- the total content of Cr, Mo, V and Nb is preferably 14.00% or less.
- the total content of Cr, Mo, V and Nb is 12.00% or less, 10.00% or less, 9.00% or less, 8.50% or less, 8.00% or less, or 7.50% % or less.
- a preferred method for manufacturing a forged steel roll for cold rolling includes: a casting process for casting an ingot from molten steel having the chemical composition previously described in relation to the cold rolling forged steel roll; Forging in which the cast ingot is held at a heating temperature of 1200 to 1300° C. for 10 hours or more, and then formed into a roll shape at a forging temperature of 1100 to 1200° C. that is 50 to 150° C. lower than the heating temperature. process, An annealing step of annealing the formed roll, Rough processing step of rough processing the obtained roll into a desired roll shape, A quenching step in which the rough-processed roll is held at a quenching temperature of 900 to 1100 ° C.
- a quenching step in which the cooling is performed for 300 seconds; It includes a tempering process for adjusting the hardness of the roll, and a finishing process for processing into the final roll shape by grinding. Each step will be described in more detail below.
- ingots are cast by any suitable casting method known to those skilled in the art from molten steel having the chemical composition described above in connection with cold roll forged steel rolls.
- the casting method may be, for example, a bottom pouring ingot casting method.
- an electroslag remelting (ESR) method or the like may be performed using a cast ingot as an electrode to reduce segregation and inclusions.
- ESR electroslag remelting
- the casting method may be, for example, a casting method or a centrifugal casting method.
- a cast ingot is first heated and held in a heating furnace, and then forged into a roll shape.
- a heating temperature of 1200 to 1300° C., preferably 1250 to 1300° C. is maintained for 10 hours or more, preferably 15 hours or more.
- the forging temperature is 1100 to 1200° C.
- the forging temperature is 50 to 150° C., preferably 60 to 100° C. lower than the heating temperature.
- the finally obtained forged steel roll for cold rolling reliably achieves desired high-temperature hardness and/or shrinkage initiation temperature. becomes possible.
- Forging is carried out after the above heating and holding. If the forging temperature at that time is lower than 1100° C., the ductility of the ingot is lowered and forging cracks are likely to occur. On the other hand, if the forging temperature is higher than 1200° C., forging cracks are likely to occur due to the formation of voids in the rolls. Therefore, in order to prevent such forging cracks, the forging temperature must be 1100 to 1200°C. For example, when the temperature of the ingot drops to 900° C. during forging, the ingot is introduced into the heating furnace, heated again to a predetermined forging temperature, and then the ingot is removed from the heating furnace and forged. .
- Such a decrease in temperature can be confirmed, for example, by measurement using a surface thermometer or by visual observation, such as a change in the color of the steel surface.
- Such heating and forging may be repeated multiple times.
- the temperature difference from the heating temperature of 1200 to 1300 ° C before forging is within the range of 50 to 150 ° C. must be properly selected. This is because if the temperature difference between the heating temperature and the forging temperature is too small or too large, precipitates such as Si-based carbides precipitated in the forging process remain without solid solution in the subsequent annealing process. This is because it is easy to From the viewpoint of more reliably reducing Si-based precipitates, the ratio of heating temperature to forging temperature is preferably 60 to 100.degree.
- the annealing and roughing steps can be performed under any suitable conditions known to those skilled in the art.
- the annealing step can be performed in an atmosphere furnace, such as an electric furnace or a gas furnace, under suitable conditions to facilitate roughing in the subsequent roughing step.
- the Si-based precipitates precipitated in the previous forging process are dissolved again in this annealing process.
- the roll after the annealing step may be roughed into a desired roll shape by grinding, for example, using a grinder.
- a quenching process is performed on the body surface layer of the roll after the roughing process.
- the quenching process includes holding at a quenching temperature of 900-1100° C. for 30-180 seconds and then cooling.
- the cooling is performed at a cooling rate such that it takes 30 to 300 seconds for the surface temperature of the roll to reach 800° C. from the quenching temperature.
- the desired high-temperature hardness and/or shrinkage start temperature can be obtained in the finally obtained forged steel roll for cold rolling.
- Heating and holding in the quenching process can be performed using any appropriate means such as induction heating, and cooling can be performed by water cooling or the like.
- the well-known sub-zero treatment on the body surface layer of the roll after the quenching process may be performed to transform the retained austenite into martensite.
- Tempeering process A tempering process is performed on the roll after the quenching process. In this tempering process, the martensite and bainite formed at a predetermined depth from the surface of the roll body are tempered, thereby adjusting the hardness of the roll.
- the tempering temperature is preferably 100 to 600°C.
- the tempering process can be carried out in a heated furnace, atmosphere furnace, such as an electric furnace or a gas furnace.
- a finishing process is performed on the roll after the tempering process.
- the roll is processed into a desired final roll shape by grinding using a grinder.
- a forged steel roll for cold rolling according to the embodiment of the present invention having desired hot hardness and/or shrinkage start temperature can be manufactured.
- the forged steel roll for cold rolling according to the embodiment of the present invention can be applied in various cold rolling. It can be applied as work rolls in inter-reverse rolling mill. Moreover, the forged steel roll for cold rolling according to the embodiment of the present invention can also be applied to skin-pass rolling (temper rolling). From the viewpoint of suppressing or reducing the occurrence of cracks due to thermal shock, it is preferably applied as a forged steel roll for cold rolling other than skin-pass rolling.
- forged steel rolls for cold rolling according to embodiments of the present invention were manufactured under various conditions.
- the Vickers hardness Hv at 400° C. and the shrinkage start temperature in the temperature rising process were measured for the obtained test material, and the relationship between the Vickers hardness Hv and shrinkage start temperature and crack generation due to thermal shock was investigated.
- the ingot is introduced into the heating furnace, heated again to the predetermined forging temperature, then removed from the heating furnace and forged. Repeated heating and forging like leverage.
- the roll formed by forging was introduced into a gas furnace, held at 900° C. for 10 hours, and then annealed by holding at 600° C. for 15 hours. Then, the annealed roll was ground using a grinder to rough-process it into a roll shape with a diameter of ⁇ 650 mm, a length of 2000 mm, and a total length of 4000 mm.
- the quenching process was performed on the rough-processed roll.
- heating is performed by induction heating at the quenching temperature and holding time shown in Table 1 below, and then cooling is performed so that the time required for the surface temperature of the roll to reach 800 ° C from the quenching temperature is the time shown in Table 1 below.
- Water cooling was carried out at high speed.
- the roll was immersed in a coolant and cooled to -60 to -140°C to carry out sub-zero treatment.
- the roll after the quenching process was introduced into a heating furnace and tempered at 150°C.
- the tempered roll was ground using a grinder and finished into a final roll shape with a roll body diameter of ⁇ 645 mm, a body length of 1950 mm, and a total length of 3950 mm to obtain a forged steel roll for cold rolling.
- Vickers hardness Hv at 400° C., shrinkage initiation temperature, and cracking due to thermal shock were measured by the following methods.
- the five measurement positions were set at intervals of 2.5 mm including both ends in the 10 mm direction (depth direction) of the measurement surface.
- the shrinkage start temperature was measured using a Formaster tester (Formastor-EDP manufactured by Fuji Denpakoki Co., Ltd.). Specifically, first, a test material having a size of ⁇ 3 mm ⁇ 10 mm was sampled from the surface of the central portion of the trunk portion of the forged steel roll. Using a Formaster testing machine (Fuji Denpakoki Formastor-EDP), a test material with a thermocouple attached was heated in a vacuum (1 ⁇ 10 -3 Pa) from room temperature at a heating rate of 180 ° C./min.
- the amount of expansion of the 10 mm side of was measured.
- the temperature of the inflection point on the low temperature side of the thermal expansion curve obtained based on the measurement results (for example, the thermal expansion curve shown in FIG. 1) is obtained, and the obtained value is the shrinkage start temperature of each roll material. decided as
- FIG. 2 is a schematic diagram schematically showing a thermal shock test using a drop weight friction and thermal shock tester for each test material of Examples and Comparative Examples.
- each test material 13 was subjected to a thermal shock test using a drop weight friction thermal shock tester 10 shown in FIG.
- a test material 13 having dimensions of 20 mm ⁇ 20 mm ⁇ 30 mm was sampled from the surface of the central portion of the trunk portion of the forged steel roll.
- a drop-weight friction and thermal shock tester 10 is used to rotate the pinion 11 by dropping a weight onto a rack (not shown), and a surface 13A of 20 mm ⁇ 30 mm of the test material 13 is subjected to JIS G 3505: 2017 standard.
- a biting material 12 made of a soft steel wire rod SWRM6 having a diameter of 5 mm and a length of 10 mm was strongly brought into contact with the surface 13A of the test material 13 in the longitudinal direction to give a thermal shock.
- the thermal shock test the cross-section of the contact surface of the test material 13 was observed for crack generation, and the crack resistance was evaluated based on the maximum crack depth. More specifically, the case where the maximum crack depth was less than 400 ⁇ m was judged as acceptable, while the case where the maximum crack depth was 400 ⁇ m or more was judged as unacceptable.
- Table 1 The results are shown in Table 1 below.
- the roll when the maximum crack depth was less than 400 ⁇ m, the roll was evaluated as a forged steel roll for cold rolling with improved crack resistance.
- the desired high-temperature hardness and shrinkage start temperature were not obtained, and the maximum crack depth was 400 ⁇ m or more, and sufficient crack resistance could be achieved. I didn't.
- the heating temperature in the forging process was inappropriate or the holding time was short, so that the amount of Si present in a solid solution state in the matrix of the roll could not be sufficiently secured. Conceivable.
- the desired high-temperature hardness and shrinkage initiation temperature could not be obtained, the maximum crack depth was 400 ⁇ m or more, and sufficient crack resistance could not be achieved.
- the temperature difference between the heating temperature and the forging temperature in the forging process was not appropriate, so the Si-based precipitates precipitated in the forging process were sufficiently removed in the subsequent annealing process. It is considered that the solid solution could not be re-dissolved.
- the desired high-temperature hardness and shrinkage initiation temperature could not be obtained, the maximum crack depth was 400 ⁇ m or more, and sufficient crack resistance could not be achieved.
- Examples 1 to 22 having a Vickers hardness Hv at 400° C. of 400 or more have a maximum crack depth of 390 ⁇ m or less, and have higher crack resistance than Comparative Examples 1 to 15. was able to achieve In Examples 2 to 22, in which the shrinkage initiation temperature was 300° C. or higher, the maximum crack depth was 320 ⁇ m or less, and compared with Example 1, the crack resistance was further improved.
- Examples 5 to 7 and 15, which have a Vickers hardness Hv at 400°C of 435 or more (and a shrinkage start temperature of 670°C or more), have a maximum crack depth of less than 200 ⁇ m, exhibiting extremely high crack resistance. was able to achieve
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Abstract
Description
(1)400℃におけるビッカース硬さHvが400以上である、冷間圧延用鍛鋼ロール。
(2)化学組成が、質量%で、
C:0.70~1.50%、
Si:0.40~1.50%、
Mn:0.20~1.50%、
P:0.030%以下、
S:0.0200%以下、
Al:0.050%以下、
N:0.0200%以下、
O:0.0050%以下、
Cr:2.80~8.00%、
Mo:0.30~3.00%、
Cu:0.100%以下、
B:0.0100%以下、
Ni:0~1.20%、
V:0~2.00%、
Nb:0~1.00%、並びに
残部:Fe及び不純物からなり、かつ
下記式1を満たす、上記(1)に記載の冷間圧延用鍛鋼ロール。
4.50≦Cr+Mo+V+Nb≦14.00 ・・・式1
ここで、式1中の各元素記号には、各元素の含有量(質量%)が代入され、元素を含まない場合は0が代入される。
(3)前記化学組成が、質量%で、
Ni:0.05~1.20%、
V:0.10~2.00%、及び
Nb:0.10~1.00%
からなる群より選ばれる1種以上を含有する、上記(2)に記載の冷間圧延用鍛鋼ロール。
(4)昇温過程における収縮開始温度が300℃以上である、上記(1)~(3)のいずれか1項に記載の冷間圧延用鍛鋼ロール。
本発明の実施形態に係る冷間圧延用鍛鋼ロールは、400℃におけるビッカース硬さHvが400以上である。
本発明の実施形態に係る冷間圧延用鍛鋼ロールでは、400℃におけるビッカース硬さHvは400以上である。一般的に、温度が高くなるにつれて、ロール材料の硬度は低下する。これに関連して、本発明者らは、従来の冷間圧延用鍛鋼ロールでは、400℃付近の高温下で硬度が急激に低下することを見出した。さらに本発明者らは、化学組成を適切なものとしつつ、製造方法を工夫することにより、このような高温下でも冷間圧延用鍛鋼ロールのビッカース硬さHvを400以上の高いレベルに維持することができることを見出した。本発明の実施形態によれば、冷間圧延用鍛鋼ロールの400℃におけるビッカース硬さHvをこのような範囲に制御することで、熱衝撃の際の高温下においてロール表面に生じる引張応力に対して高い耐久性を得ることができ、結果として当該熱衝撃によるロール表面のき裂の発生を顕著に抑制又は低減することが可能となる。
先に述べたとおり、熱衝撃によるロール表面のき裂の発生を抑制又は低減するためには、高温下での材料収縮に伴って生じるロール表面の引張応力に対する耐久性を高めることが1つの有効な解決策として考えられる。本発明者らは、これに加えて、高温下でのロール表面における材料収縮自体、ひいてはこのような材料収縮に伴う引張応力の発生自体を抑制又は低減することに着目してさらに検討を行った。より具体的には、本発明者らは、ロール材料においてこのような収縮が開始する温度(以下、単に「収縮開始温度」という)とき裂の発生との間の相関関係について調べた。その結果、本発明者らは、400℃におけるビッカース硬さHvが400以上であることに加えて、昇温過程における収縮開始温度が300℃以上である鍛鋼から製造されたロールを冷間圧延用ロールとして使用することで、ロール表面におけるき裂の発生をさらにより顕著に抑制又は低減できること、すなわち冷間圧延用ロールの耐き裂性をさらにより顕著に向上させることができることを見出した。
本実施形態の冷間圧延用鍛鋼ロールは、400℃において400以上のビッカース硬さHv、好ましくはそれに加えて300℃以上の収縮開始温度を有する。それゆえ当該冷間圧延用鍛鋼ロールの化学組成は、400℃において400以上のビッカース硬さHv、好ましくはそれに加えて300℃以上の収縮開始温度を達成し得る任意の化学組成であってよく、特に限定されるものではない。より詳しくは、本実施形態は、上記のとおり熱衝撃によるき裂の発生を低減することが可能な耐き裂性が改善された冷間圧延用鍛鋼ロールを提供することを目的とするものであって、冷間圧延用鍛鋼ロールの400℃におけるビッカース硬さHvを400以上とすること、さらに好ましくは冷間圧延用鍛鋼ロールの収縮開始温度を300℃以上とすることによって当該目的を達成するものである。したがって、冷間圧延用鍛鋼ロールの化学組成は、本実施形態の目的を達成する上で必須の技術的特徴ではない。以下の記載において、高温硬さ及び収縮開始温度の特徴を達成するための冷間圧延用鍛鋼ロールの好ましい化学組成について詳しく説明するが、これらの説明は、冷間圧延用鍛鋼ロールの好ましい化学組成の単なる例示を意図するものであって、本実施形態をこのような特定の化学組成を有する冷間圧延用鍛鋼ロールに限定することを意図するものではない。以下の説明において、冷間圧延用鍛鋼ロールに含まれる各元素の含有量の単位である「%」は、特に断りがない限り「質量%」を意味するものである。また、本明細書において、数値範囲を示す「~」とは、特に断りがない場合、その前後に記載される数値を下限値及び上限値として含む意味で使用される。
炭素(C)は、ロール表層の硬さを高めるのに必要な元素である。このような効果を十分に得るために、C含有量は0.70%以上とすることが好ましい。C含有量は0.75%以上、0.80%以上、0.85%以上又は0.90%以上であってもよい。一方で、Cを過度に含有すると、粗大な炭化物が生成し、上記の効果が十分に得られない場合がある。したがって、C含有量は1.50%以下とすることが好ましい。C含有量は1.40%以下、1.30%以下、1.20%以下、1.15%以下、1.10%以下、1.05%以下又は1.00%以下であってもよい。
シリコン(Si)は、一般的に鋼を脱酸し、さらに焼入れ性を高める元素である。今回、さらに、本発明者らは、Si含有量とロールの高温硬さ及び収縮開始温度との関係について調査した。その結果、これらの間には強い相関関係があり、Siを添加することで高温硬さと収縮開始温度の両方を高くすることができることを見出した。ロールの高温硬さを十分に向上させるという観点からは、Si含有量は0.40%以上とすることが好ましい。一方で、収縮開始温度を十分に向上させるという観点からは、Si含有量は0.45%以上とすることが好ましい。Si含有量は0.50%以上、0.60%以上、0.70%以上、0.75%以上、0.80%以上、0.85%以上又は0.90%以上であってもよい。後で詳しく説明する固溶Si量を増加させる観点からも、Si含有量は高い方が好ましい。一方で、Siを過度に含有すると、炭化物が偏析しやすくなって十分な靱性が得られない場合がある。したがって、ロールの高温硬さ及び/又は収縮開始温度の向上という観点からは必ずしもSi含有量の上限値は限定されないものの、十分な靱性を確保するという観点から、Si含有量は1.50%以下とすることが好ましい。Si含有量は1.40%以下、1.30%以下、1.20%以下、1.10%以下、1.05%以下、1.00%以下又は0.95%以下であってもよい。
マンガン(Mn)は、焼入れ性を有効に高める元素である。このような効果を十分に得るために、Mn含有量は0.20%以上とすることが好ましい。Mn含有量は0.25%以上、0.30%以上、0.35%以上又は0.40%以上であってもよい。一方で、Mnを過度に含有すると、十分な靱性が得られない場合がある。したがって、焼入れ性を有効に高めかつ十分な靱性を確保するために、Mn含有量は1.50%以下とすることが好ましい。Mn含有量は1.40%以下、1.20%以下、1.00%以下、0.80%以下又は0.60%以下であってもよい。
燐(P)は、不可避に含有される不純物である。すなわち、P含有量は0%超である。Pは、粒界に偏析して、鋼材の靱性が低下する場合がある。したがって、P含有量は0.030%以下とすることが好ましい。P含有量は、0.025%以下、又は0.020%以下であってもよい。P含有量はなるべく低い方が好ましい。ただし、P含有量の過剰な低減は、製鋼工程の精錬コストを大幅に高める。したがって、工業生産を考慮すれば、P含有量は0.001%以上とすることが好ましい。P含有量は、0.002%以上であってもよい。
硫黄(S)は、不可避に含有される不純物である。すなわち、S含有量は0%超である。Sは、粒界に偏析して、鋼材の靱性及び熱間加工性が低下する場合がある。したがって、S含有量は0.0200%以下とすることが好ましい。S含有量は、0.0050%以下、0.0040%以下、又は0.0030%以下であってもよい。S含有量はなるべく低い方が好ましい。ただし、S含有量の過剰な低減は、製鋼工程の精錬コストを大幅に高める。したがって、工業生産を考慮すれば、S含有量は0.0001%以上とすることが好ましい。S含有量は、0.0002%以上、又は0.0003%以上であってもよい。
アルミニウム(Al)は、不可避に含有される不純物である。すなわち、Al含有量は0%超である。Alは、溶鋼段階で鋼を脱酸する。一方、Al含有量が高過ぎると、Al窒化物が粗大化し、鋼材の靭性が低下する場合がある。したがって、Al含有量は、0.050%以下とすることが好ましい。Al含有量は、0.040%以下、又は0.030%以下であってもよい。Al含有量は、0.001%以上、又は0.002%以上であってもよい。本明細書において、Al含有量は鋼中の全Al含有量を意味する。
窒素(N)は、不可避に含有される不純物である。すなわち、N含有量は0%超である。Nは、固溶強化により鋼の強度を高める。一方、N含有量が高すぎれば、粗大な窒化物系介在物を形成し、鋼材の靭性が低下する場合がある。したがって、N含有量は0.0200%以下とすることが好ましい。N含有量は、0.0150%以下であってもよい。N含有量は、0.0001%以上、又は0.0002%以上であってもよい。
酸素(O)は、不可避に含有される不純物である。すなわち、O含有量は0%超である。Oは粗大な酸化物系介在物を形成し、鋼材の靭性を低下させる場合がある。したがって、O含有量は0.0050%以下とすることが好ましい。O含有量は0.0040%以下、0.0035%以下、又は0.0030%以下であってもよい。O含有量はなるべく低い方が好ましい。ただし、O含有量の極端な低減は、製造コストを大幅に高める。したがって、工業生産を考慮すれば、O含有量は0.0001%以上、又は0.0005%以上とすることが好ましい。O含有量は、0.0007%以上であってもよい。
クロム(Cr)は、炭化物を形成して耐摩耗性を高める元素である。また、Crは、焼戻し抵抗を高めて高温硬さを向上させる元素である。これらの効果を十分に得るために、Cr含有量は2.80%以上とすることが好ましい。Cr含有量は3.00%以上、3.20%以上、3.50%以上又は4.00%以上であってもよい。一方で、Crを過度に含有すると、炭化物が粗大化して、冷間圧延用鍛鋼ロールの研削性や靭性が低下する場合がある。したがって、Cr含有量は8.00%以下とすることが好ましい。Cr含有量は7.50%以下、7.00%以下、6.50%以下、6.00%以下又は5.50%以下であってもよい。
モリブデン(Mo)は、Crと同様に炭化物を形成して耐摩耗性を高める元素である。また、Moは、二次硬化により高温硬さを向上させる元素である。これらの効果を十分に得るために、Mo含有量は0.30%以上とすることが好ましい。Mo含有量は0.35%以上、0.40%以上又は0.45%以上であってもよい。一方で、Moを過度に含有すると、炭化物が粗大化して、冷間圧延用鍛鋼ロールの研削性や靭性が低下する場合がある。したがって、Mo含有量は3.00%以下とすることが好ましい。Mo含有量は2.80%以下、2.50%以下、2.00%以下、1.80%以下、1.50%以下、1.00%以下、0.80%以下、0.60%以下又は0.55%以下であってもよい。
銅(Cu)は、不可避に含有される不純物である。すなわち、Cu含有量は0%超である。Cuは鋼の熱間加工性を低下させる場合がある。したがって、Cu含有量は0.100%以下とすることが好ましい。Cu含有量は、0.095%以下、0.090%以下、0.085%以下、0.080%以下、0.075%以下、又は0.070%以下であってもよい。Cu含有量はなるべく低い方が好ましい。しかしながら、Cu含有量の過剰な低減は製造コストを引き上げる。したがって、Cu含有量は0.001%以上とすることが好ましい。Cu含有量は、0.002%以上であってもよい。
B(ホウ素)は、不可避に含有される不純物である。すなわち、B含有量は0%超である。Bは鋼の靭性を低下させる場合がある。したがって、B含有量は0.0100%以下とすることが好ましい。B含有量は、0.0080%以下、又は0.0060%以下であってもよい。B含有量はなるべく低い方が好ましい。しかしながら、B含有量の過剰な低減は製造コストを引き上げる。したがって、B含有量は0.0001%以上とすることが好ましい。B含有量は、0.0002%以上であってもよい。
ニッケル(Ni)は、焼入れ性を高める元素である。Ni含有量は0%であってもよいが、このような効果を十分に得るためには、Ni含有量は0.01%以上とすることが好ましい。Ni含有量は0.05%以上、0.10%以上、0.15%以上又は0.20%以上であってもよい。一方で、Niを過度に含有すると、残留オーステナイトが過剰に形成され、十分な硬さを維持できなくなる場合がある。したがって、Ni含有量は1.20%以下とすることが好ましい。Ni含有量は1.10%以下、1.00%以下、0.80%以下、0.60%以下、0.45%以下、0.30%以下、0.28%以下、0.26%以下、0.25%以下又は0.24%以下であってもよい。
バナジウム(V)は、CrやMoと同様に炭化物を形成して耐摩耗性を高める元素である。また、Vは、二次硬化により高温硬さを向上させる元素である。V含有量は0%であってもよいが、これらの効果を十分に得るためには、V含有量は0.01%以上とすることが好ましい。V含有量は0.05%以上、0.10%以上、0.15%以上、0.20%以上又は0.25%以上であってもよい。一方で、Vを過度に含有すると、炭化物が粗大化して、冷間圧延用鍛鋼ロールの研削性や靭性が低下する場合がある。したがって、V含有量は2.00%以下とすることが好ましい。V含有量は1.80%以下、1.50%以下、1.00%以下、0.80%以下、0.60%以下又は0.40%以下であってもよい。
ニオブ(Nb)は、Vなどの元素と同様にCと結合して高硬度の炭化物を形成する元素である。また、Nbは、二次硬化により高温硬さを向上させる元素である。Nb含有量は0%であってもよいが、これらの効果を十分に得るためには、Nb含有量は0.01%以上とすることが好ましい。Nb含有量は0.05%以上、0.10%以上、0.15%以上、0.20%以上又は0.25%以上であってもよい。一方で、Nbを過度に含有すると、炭化物が粗大化して、冷間圧延用鍛鋼ロールの研削性や靭性が低下する場合がある。したがって、Nb含有量は1.00%以下とすることが好ましい。Nb含有量は0.80%以下、0.60%以下又は0.40%以下であってもよい。
本発明の実施形態に係る冷間圧延用鍛鋼ロールの化学組成は、下記式1:
4.50≦Cr+Mo+V+Nb≦14.00 ・・・式1
を満たすことが好ましい。ここで、式1中の各元素記号には、各元素の含有量(質量%)が代入され、元素を含まない場合は0が代入される。
次に、本発明の実施形態に係る冷間圧延用鍛鋼ロールの好ましい製造方法について説明する。以下の説明は、本発明の実施形態に係る冷間圧延用鍛鋼ロールを製造するための特徴的な方法の例示を意図するものであって、当該冷間圧延用鍛鋼ロールを以下に説明するような製造方法によって製造されるものに限定することを意図するものではない。
冷間圧延用鍛鋼ロールに関連して先に説明した化学組成を有する溶鋼からインゴットを鋳造する鋳造工程、
鋳造されたインゴットを1200~1300℃の加熱温度で10時間以上保持し、次いで1100~1200℃の鍛造温度であって、前記加熱温度よりも50~150℃低い鍛造温度でロール形状に成形する鍛造工程、
成形されたロールを焼鈍する焼鈍工程、
得られたロールを所望のロール形状に粗加工する粗加工工程、
粗加工されたロールを900~1100℃の焼入れ温度で30~180秒間保持し、次いで冷却する焼入れ工程であって、前記ロールの表面温度が前記焼入れ温度から800℃に達するまでの時間が30~300秒となるように前記冷却が実施される焼入れ工程、
ロールの硬度を調整するための焼戻し工程、及び
研削により最終ロール形状に加工する仕上げ加工工程を含む。以下、各工程についてより詳細に説明する。
鋳造工程では、冷間圧延用鍛鋼ロールに関連して先に説明した化学組成を有する溶鋼から、当業者に公知の任意の適切な鋳造法によりインゴットが鋳造される。例えば、鍛鋼ロールが単体ロールである場合には、鋳造法は、例えば下注ぎ造塊法等であってもよい。また、鋳造したインゴットを電極として、エレクトロスラグ再溶解(ESR)法等を実施して、偏析や介在物を軽減するようにしてもよい。一方、鍛鋼ロールが芯材と外層からなる複合ロールである場合には、鋳造法は、例えば鋳掛け法や遠心鋳造法などであってもよい。
鍛造工程では、まず鋳造されたインゴットが加熱炉内にて加熱保持され、次いで鍛造によりロール形状に成形される。加熱保持においては、1200~1300℃、好ましくは1250~1300℃の加熱温度で、10時間以上、好ましくは15時間以上保持される。鍛造においては、1100~1200℃の鍛造温度であって、前記加熱温度よりも50~150℃、好ましくは60~100℃低い鍛造温度でロール形状に成形される。加熱保持を前記条件で行うことにより、鍛造工程において析出するSi系の炭化物等の析出物が、その後の焼鈍工程で再固溶しやすくなる。これにより、ロールのマトリックス中に固溶状態で存在するSiの量を十分に確保することができる。ロールのマトリックス中に固溶状態で存在するSiの量を十分に確保することで、最終的に得られる冷間圧延用鍛鋼ロールにおいて所望の高温硬さ及び/又は収縮開始温度を確実に達成することが可能となる。
焼鈍工程及び粗加工工程は、当業者に公知の任意の適切な条件下で実施することができる。特に限定されないが、焼鈍工程は、雰囲気炉、例えば電気炉又はガス炉において、次の粗加工工程における粗加工を容易にするのに適切な条件下で実施することができる。先の鍛造工程において析出したSi系析出物は、この焼鈍工程において再固溶される。また、粗加工工程では、焼鈍工程後のロールを、例えば研削盤を用いて研削することにより所望のロール形状に粗加工すればよい。
粗加工工程後のロールの胴部表層に対して焼入れ工程が実施される。焼入れ工程は、900~1100℃の焼入れ温度で30~180秒間保持し、次いで冷却することを含む。当該冷却は、ロールの表面温度が焼入れ温度から800℃に達するまでの時間が30~300秒となるような冷却速度で実施される。このような条件で焼入れ工程を実施することにより、焼鈍工程で再固溶したSiが再びSi系析出物として析出することを抑制することができる。その結果、ロールのマトリックス中に固溶状態で存在するSiの量を十分に確保することができ、最終的に得られる冷間圧延用鍛鋼ロールにおいて所望の高温硬さ及び/又は収縮開始温度を確実に達成することが可能となる。焼入れ工程における加熱保持は、誘導加熱などの任意の適切な手段を用いて行うことができ、冷却は水冷などにより行うことができる。また、必要に応じて又はとりわけ残留オーステナイトが多い場合には、焼入れ工程後のロールの胴部表層に対して周知のサブゼロ処理(例えばロールを冷媒に浸漬して-60~-140℃に冷却)を実施して、当該残留オーステナイトをマルテンサイトに変態させるようにしてもよい。
焼入れ工程後のロールに対して焼戻し工程が実施される。この焼戻し工程において、ロール胴部の表面から所定の深さに生成したマルテンサイト及びベイナイトを焼戻し、それによってロールの硬さを調整することができる。焼戻し温度は、100~600℃とすることが好ましい。焼戻し工程は、加熱炉、雰囲気炉、例えば電気炉又はガス炉において実施することができる。
最後に、焼戻し工程後のロールに対して仕上げ加工工程が実施される。仕上げ加工工程では、例えば研削盤を用いて研削することにより所望の最終ロール形状に加工する。こうして、所望の高温硬さ及び/又は収縮開始温度を有する本発明の実施形態に係る冷間圧延用鍛鋼ロールを製造することができる。
まず、下表1に示す化学組成を有する溶鋼から下注ぎ造塊法によりインゴットを鋳造し、次いで、エレクトロスラグ再溶解(ESR)法を実施した。次に、得られたインゴットに鍛造工程を実施した。鍛造工程では、加熱炉内にて下表1に示す加熱温度及び保持時間で加熱保持し、次いで下表1に示す鍛造温度まで温度を低下させた後、鍛造によりロール胴部の直径φ700mm、胴長2100mm、及び全長4100mmのロール形状に成形した。鍛造中にインゴットの温度が900℃まで低下した場合には、インゴットを加熱炉に導入し、所定の鍛造温度まで再度加熱し、その後、インゴットを加熱炉から取り出して鍛造を実施し、必要に応じてこのような加熱と鍛造を繰り返した。次に、鍛造により成形されたロールをガス炉に導入して、900℃で10時間保持した後、600℃で15時間保持することにより焼鈍を実施した。次いで、焼鈍後のロールを研削盤を用いて研削することにより、ロール胴部の直径φ650mm、胴長2000mm、及び全長4000mmのロール形状に粗加工した。
実施例及び比較例の各鍛鋼ロールの胴部中央部の表面から採取した試験材について、ニコン製QM2型高温ビッカース硬さ計を用い、室温から400℃に昇温し5分間保持した際の硬さを測定することにより、400℃におけるビッカース硬さHvを決定した。測定は、JIS Z 2252:1991に準拠した方法で実施した。より具体的には、まず鍛鋼ロールの胴部中央部の表面から5mm×5mm×10mmの試験材を切り出した。熱電対を取り付けた試験材及び圧子を真空中(3×10-5Torr)で室温から400℃に加熱し、5分間保持した。その後、試験材において5mm×10mmの測定面に荷重300gfを付加し、ビッカース硬さを5点測定し、それらの平均値を400℃におけるビッカース硬さHvとした。5点の測定位置は、測定面の10mm方向(深さ方向)において、両端を含め2.5mmおきの5点とした。
実施例及び比較例の各鍛鋼ロールの胴部中央部の表面から採取した試験材について、フォーマスター試験機(富士電波工機製Formastor‐EDP)を用いて、収縮開始温度を測定した。具体的には、まず鍛鋼ロールの胴部中央部の表面から寸法φ3mm×10mmの試験材を採取した。フォーマスター試験機(富士電波工機製Formastor‐EDP)を用いて、熱電対を取り付けた試験材を真空中(1×10-3Pa)で室温から昇温速度180℃/分で昇温した際の10mmの辺の膨張量を測定した。その測定結果に基づいて得られた熱膨張曲線(例えば、図1に示すような熱膨張曲線)における低温側での変曲点の温度を求め、得られた値を各ロール材料の収縮開始温度として決定した。
図2は、実施例及び比較例の各試験材に対する、落重式摩擦熱衝撃試験機を用いた熱衝撃試験を模式的に示す略図である。耐き裂性を評価するために、図2に示す落重式摩擦熱衝撃試験機10を用いて、各試験材13に対して熱衝撃試験を実施した。まず鍛鋼ロールの胴部中央部の表面から寸法20mm×20mm×30mmの試験材13を採取した。落重式摩擦熱衝撃試験機10により、ラック(図示せず)に重りを落下させることによりピニオン11を回動させ、試験材13の20mm×30mmの表面13Aに、JIS G 3505:2017で規格されている軟鋼線材SWRM6からなる直径5mm×長さ10mmの噛み込み材12を長さ方向に強く接触させて、試験材13の表面13Aに熱衝撃を与えた。熱衝撃試験後の試験材13の接触面断面のき裂発生状況を観察し、き裂の最大深さにより耐き裂性を評価した。より具体的には、き裂の最大深さが400μm未満の場合を合格とし、一方で、き裂の最大深さが400μm以上の場合を不合格とした。その結果を下表1に示す。
11 ピニオン
12 噛み込み材
13 試験材
13A 試験材の表面
Claims (4)
- 400℃におけるビッカース硬さHvが400以上である、冷間圧延用鍛鋼ロール。
- 化学組成が、質量%で、
C:0.70~1.50%、
Si:0.40~1.50%、
Mn:0.20~1.50%、
P:0.030%以下、
S:0.0200%以下、
Al:0.050%以下、
N:0.0200%以下、
O:0.0050%以下、
Cr:2.80~8.00%、
Mo:0.30~3.00%、
Cu:0.100%以下、
B:0.0100%以下、
Ni:0~1.20%、
V:0~2.00%、
Nb:0~1.00%、並びに
残部:Fe及び不純物からなり、かつ
下記式1を満たす、請求項1に記載の冷間圧延用鍛鋼ロール。
4.50≦Cr+Mo+V+Nb≦14.00 ・・・式1
ここで、式1中の各元素記号には、各元素の含有量(質量%)が代入され、元素を含まない場合は0が代入される。 - 前記化学組成が、質量%で、
Ni:0.05~1.20%、
V:0.10~2.00%、及び
Nb:0.10~1.00%
からなる群より選ばれる1種以上を含有する、請求項2に記載の冷間圧延用鍛鋼ロール。 - 昇温過程における収縮開始温度が300℃以上である、請求項1~3のいずれか1項に記載の冷間圧延用鍛鋼ロール。
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JP2023516613A JP7328606B2 (ja) | 2021-08-03 | 2021-08-03 | 冷間圧延用鍛鋼ロール |
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- 2021-08-03 CN CN202180101211.2A patent/CN117794656A/zh active Pending
- 2021-08-03 WO PCT/JP2021/028833 patent/WO2023012906A1/ja active Application Filing
- 2021-08-03 JP JP2023516613A patent/JP7328606B2/ja active Active
- 2021-08-03 KR KR1020247003010A patent/KR20240027054A/ko unknown
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JP2019055419A (ja) * | 2017-09-22 | 2019-04-11 | 新日鐵住金株式会社 | 冷間圧延用ロール |
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