WO2023085137A1 - Die steel having excellent mirror finish properties - Google Patents

Die steel having excellent mirror finish properties Download PDF

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WO2023085137A1
WO2023085137A1 PCT/JP2022/040568 JP2022040568W WO2023085137A1 WO 2023085137 A1 WO2023085137 A1 WO 2023085137A1 JP 2022040568 W JP2022040568 W JP 2022040568W WO 2023085137 A1 WO2023085137 A1 WO 2023085137A1
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mass
inclusions
less
steel
mold
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PCT/JP2022/040568
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French (fr)
Japanese (ja)
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貴弘 尾上
泰樹 梶原
直樹 上田
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日本高周波鋼業株式会社
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Priority to CN202280074370.2A priority Critical patent/CN118251511A/en
Publication of WO2023085137A1 publication Critical patent/WO2023085137A1/en

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    • 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
    • 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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the present invention relates to mold steel for mirror-finishing that is suitable for ultra-mirror-finishing for molding ultra-mirror-surface plastic products.
  • Patent Literature 1 discloses steel for plastic molds in which the composition of inclusions is controlled by adding Zr.
  • the oxides in the molten steel are floated, and the proportion of ZrO 2 in the total oxides when the floated surface of the oxides is observed is controlled to 95 area % or more.
  • Patent Literature 2 discloses a highly corrosion-resistant plastic mold steel in which specularity is enhanced by controlling the number density and size of carbonitrides.
  • Patent Document 3 the size of carbides and the distance between carbides are controlled, and the maximum length and area ratio of this material are controlled when the area of the dense zone of carbides is 1000 ⁇ m 2 or more.
  • Patent Document 4 discloses a mold material for plastic injection molding in which the upper limit of nonmetallic inclusions is 0.015% in terms of area percentage.
  • Patent Document 5 discloses precipitating fine carbides containing Mo and W. US Pat.
  • super-mirror-surface plastic molding dies are generally finished with diamond abrasive grains or alumina abrasive grains, and the smaller the diameter of the abrasive grains, the more mirror-like the mold surface can be obtained. Since the polishing work is performed step by step in the order of #3000 ⁇ #8000 ⁇ #14000, the mold surface is finally subjected to long-term polishing with small-diameter abrasive grains.
  • Such long-term polishing causes coarse carbonitrides and non-metallic inclusions contained in the mold material to be dug up by the polishing powder, and coarse carbides and non-metallic inclusions fall off during polishing. , the remaining hole becomes a pinhole, and the super specularity is lost.
  • Such mold steel with poor mirror finish has the problem of incurring extra costs such as repolishing and reworking.
  • pinholes may occur starting from the penetration of abrasives or rust
  • high hardness is required for mold steel from the viewpoint of difficulty of penetration of abrasives
  • corrosion resistance is required for resistance to rusting. is required.
  • plastics are used to reduce coarse carbides and non-metallic inclusions and to increase hardness and corrosion resistance. Improvements have been made in the manufacturing method and composition of mold steel.
  • the conventional mold has a problem in exhibiting the performance required from the recent ultra-mirror plastic molding mold.
  • the composition of inclusions is controlled by adding Zr to the composition.
  • the specularity pinholes do not occur in the high specular surface of #8000, but the hardness of the steel material is as low as about 40 HRC in the ultra-mirror polishing of #14000.
  • the Cr content is low, the corrosion resistance is low, and rust is generated by long-term polishing, and the problem is that pinholes are generated from the rust.
  • Patent Documents 2 and 3 secures hardness and corrosion resistance by using SUS420J2 steel grade, and furthermore, by regulating the number and size of carbides, the specularity is enhanced.
  • these patent documents 2 and 3 do not mention nonmetallic inclusions at all, and do not control nonmetallic inclusions in the mold steel. There is a problem that the occurrence of pinholes due to objects cannot be avoided.
  • the mold steel described in Patent Documents 4 and 5 uses SUS420J2 steel grade to ensure hardness and corrosion resistance, and controls the area ratio of non-metallic inclusions and the amount of oxygen.
  • SUS420J2 steel grade to ensure hardness and corrosion resistance
  • controls the area ratio of non-metallic inclusions and the amount of oxygen to solve the problem of pinhole formation during ultra-mirror polishing.
  • the present invention has been made in view of these problems, and is a die steel that has excellent mirror surface properties suitable for molding ultra-mirror plastic products, as well as excellent wear resistance and mirror finish properties. intended to provide
  • the mold steel excellent in mirror finish according to the present invention is C: 0.20 to 0.50% by mass, Si: 0.10 to 1.50% by mass, Mn: 0.10 to 0.70% by mass, Cr: 10.5 to 20.0% by mass, Ni: 1.00% by mass or less, Mo: 0.05 to 1.00% by mass, V: 0.01 to 1.00% by mass contains Balance: having a composition consisting of Fe and unavoidable impurities, Among the unavoidable impurities, the following components are Al: 0.007 to 0.035% by mass, S: 0.0020% by mass or less, O: 0.0015% by mass or less, Ca: 0.0020% by mass or less, Mg: regulated to 0.0020% by mass or less, In the cross section of the steel material, the area ratio of non-metallic inclusions having an equivalent circle diameter of 8.0 ⁇ m or more is 0.00016% or less, Non-metallic inclusions having an equivalent circle diameter of 5.0 ⁇ m or more and containing 2% by mass or more of any component
  • this mold steel with excellent mirror finish For example, it is characterized by further containing W in the range of Mo+1/2W: 0.05 to 1.00% by mass.
  • FIG. 2 illustrates a method of analyzing detected particles
  • C 0.20 to 0.50% by mass
  • C is an important element that forms carbides and dissolves in the matrix of steel materials to improve hardness. In order to obtain a super mirror surface, it is necessary that the quenching and tempering hardness of the mold is 45 HRC or more. On the other hand, when C exceeds 0.50% by mass, coarse carbides are formed, impairing ultra-mirror finish and corrosion resistance. Therefore, C is 0.20 to 0.50% by mass, preferably 0.24 to 0.45% by mass.
  • Si 0.10 to 1.50% by mass
  • Si is basically added as a deoxidizing agent for molten steel, and is an element that improves the machinability of steel materials. Therefore, by adding Si, it is possible to suppress the mold manufacturing cost. If the Si content is less than 0.10% by mass, machinability is not sufficient. On the other hand, when Si exceeds 1.50% by mass, the segregation of components is increased, the polished surface is undulated, and the thermal conductivity is lowered. Therefore, Si should be 0.10 to 1.50% by mass, preferably 0.18 to 1.20% by mass.
  • Mn 0.10 to 0.70% by mass
  • Mn is an element that improves the hardenability of steel materials. If the Mn content is less than 0.10% by mass, sufficient hardenability cannot be obtained. On the other hand, when Mn exceeds 0.70% by mass, the segregation of components is increased, causing undulations on the polished surface. Therefore, Mn is 0.10 to 0.70% by mass, preferably 0.30 to 0.60% by mass.
  • Cr 10.5 to 20.0% by mass
  • Cr is an element necessary for improving the hardenability and corrosion resistance of steel. If Cr is less than 10.5% by mass, sufficient hardenability and corrosion resistance cannot be obtained. On the other hand, when Cr exceeds 20.0% by mass, coarse carbides are formed and super specularity cannot be obtained. Therefore, 10.5 to 20.0% by mass of Cr is added. Preferably, Cr is 12.0-16.0 mass %.
  • Ni 1.00% by mass or less
  • Ni is an element that improves the hardenability and corrosion resistance of steel. If the Ni content is less than 0.05% by mass, the effect of improving hardenability and corrosion resistance cannot be obtained. Therefore, Ni is preferably 0.05% by mass or more. On the other hand, when Ni exceeds 1.00% by mass, the amount of retained austenite after quenching and tempering increases, making it difficult to obtain super specularity. Therefore, 1.00% by mass or less of Ni is added. Preferably, Ni is added in an amount of 0.05% by mass or more, more preferably 0.10 to 0.50% by mass.
  • Mo 0.05 to 1.00% by mass
  • Mo is an element that improves corrosion resistance and quenching and tempering hardness. If the Mo content is less than 0.05% by mass, the effect of improving corrosion resistance and quenching and tempering hardness cannot be obtained. If the Mo content exceeds 1.00% by mass, coarse carbides are formed, making it impossible to obtain super specularity and increasing production costs. Therefore, 0.05 to 1.00 mass %, preferably 0.10 to 0.60 mass % of Mo is added.
  • V 0.01 to 1.00% by mass V is effective in preventing coarsening of crystal grains during steel material quenching. If V is less than 0.01% by mass, the effect of preventing grain coarsening cannot be obtained. On the other hand, when V exceeds 1.00% by mass, coarse carbides are formed, super specularity cannot be obtained, and the cost increases. Therefore, 0.01 to 1.00 mass %, preferably 0.04 to 0.30 mass % of V is added.
  • Al 0.035% by mass or less
  • Al is basically an element added as a deoxidizing agent for molten steel, but when Al combines with O to form non-metallic inclusions made of Al 2 O 3 and remains in the molten steel and solidifies, cause pinholes. If Al exceeds 0.035% by mass, clusters of Al 2 O 3 remain and cause pinholes, making it impossible to obtain a super mirror surface. Therefore, the allowable amount of Al is set to 0.035% by mass.
  • S 0.0020% by mass or less
  • S is an impurity contained in molten steel, and combines with Mn and Ca to form sulfide-based nonmetallic inclusions such as MnS and CaS. These sulfides have the characteristic of being easily polished compared to the matrix and other non-metallic inclusions, and thus have the problem of causing pinholes and orange peel.
  • S exceeds 0.0020% by mass, nonmetallic inclusions containing CaS shown in FIG. 2 increase. As a result, pinholes and orange peel are generated, making it impossible to obtain a super-specular surface. Therefore, the content of S is set to 0.0020% by mass or less.
  • O is an impurity contained in molten steel, and is an impurity that combines with Al and the like to form oxide-based nonmetallic inclusions such as Al 2 O 3 and cause pinholes. If this O exceeds 0.0015% by mass, clusters of oxide-based nonmetallic inclusions are formed, or the particle size of the nonmetallic inclusions increases, causing pinholes during mirror polishing. cause. Due to the occurrence of these pinholes, a super-mirror surface cannot be obtained. Therefore, the content of O should be 0.0015% by mass or less, preferably 0.0009% by mass or less.
  • Ca 0.0020% by mass or less
  • Ca combines with O or S to form CaO or CaS, which causes pinholes.
  • Ca is present in molten steel as a main component of slag, which is a refining agent. Therefore, it is important to optimize the stirring conditions of molten steel to prevent slag from entering the molten steel.
  • Ca exceeds 0.0020% by mass, MgO—Al 2 O 3 —CaO-based composite inclusions or MgO—Al 2 O 3 —CaS-based composite inclusions are formed, and pinholes are generated during final polishing of the mold. As a result, a super specular surface cannot be obtained. Therefore, Ca should be 0.0020% by mass or less, preferably 0.0010% by mass or less.
  • Mg: 0.0020% by mass or less Mg is an unavoidable impurity and is restricted to 0.0020% by mass or less.
  • Mo+1/2W 0.05 to 1.00% by mass
  • W is an element that improves corrosion resistance and quenching and tempering hardness.
  • W has the same effect as Mo when its amount is 1/2. That is, if the W content is less than 0.05% by mass in terms of Mo+1/2W, the effect of improving corrosion resistance and quenching and tempering hardness cannot be obtained. If the W content exceeds 1.00% by mass in terms of Mo+1/2W, coarse carbides are formed, making it impossible to obtain super specularity and increasing production costs. Therefore, W is added in an amount of 0.05 to 1.00% by mass, preferably 0.10 to 0.60% by mass as Mo+1/2W, if necessary.
  • the area ratio of non-metallic inclusions with an equivalent circle diameter of 8.0 ⁇ m or more is 0.00016% or less.
  • Non-metallic inclusions with an equivalent circle diameter of 8.0 ⁇ m or more are harmful because they generate pinholes during ultra-mirror finishing of the mold regardless of their composition, so the area ratio of non-metallic inclusions is limited. By doing so, the probability of occurrence of pinholes is reduced. Therefore, the area ratio of nonmetallic inclusions having an equivalent circle diameter of 8.0 ⁇ m or more is set to 0.00016% or less.
  • the non-metallic inclusions mainly become oxide-based inclusions.
  • the main components of these oxide-based inclusions are Ca, Mg, and Al, and the origin of these elements is that Ca is slag used in refining, Mg is a refractory, and Al reduces the amount of oxygen in molten steel. It is derived from a deoxidizing material for The inventors of the present application have studied the relationship between the ultra-mirror surface finishing properties of mold materials and the composition of inclusions. , Al is necessary to control.
  • FIGS. 1 and 2 are scanning electron microscope photographs of non-metallic inclusions present on the mold surface polished to a #14000 ultra-mirror surface.
  • FIG. 1 shows inclusions mainly composed of MgO—Al 2 O 3 and has an X value of less than 0.3.
  • FIG. 2 shows MgO—Al 2 O 3 —CaS (CaS)-based inclusions with an X value of 0.3 or more. Since Mg and Al combine with O to form hard inclusions, it is difficult to form pinholes if the size of the non-metallic inclusions is less than a certain size as shown in FIG. Ca, Mg. It was found that when Al binds to form inclusions, the degree of influence on the mirror-finishability varies depending on the composition ratio of Ca.
  • Ca in the molten steel reacts with a small amount of S to partially form CaS at the boundary between the oxide-based nonmetallic inclusions and the matrix as shown in FIG.
  • Composite inclusions in which oxide-based inclusions containing Ca oxide CaO and sulfide CaS are integrated, are less chemically affected and physically affected during polishing than MgO—Al 2 O 3- based inclusions. Sensitive and preferentially polished. As a result, inclusions are likely to fall off. Furthermore, as the polishing progresses, inclusions fall off and pinholes are generated. Therefore, whether or not Ca is included in the composition of inclusions has a very important effect on the generation of pinholes.
  • the number of inclusions where the X value [Ca]/([Mg] + [Al]) obtained from the composition of inclusions with an equivalent circle diameter of 5 ⁇ m or more is less than 0.3
  • a steel material for plastic molds having a density of less than 8.0 pieces/100 mm 2 and a number density of inclusions with an X value of 0.3 or more of less than 3.0 pieces/100 mm 2 has an ultra-mirror finish. It turned out to be good.
  • the number density of inclusions with an X value of less than 0.3 is less than 8.0 pieces/100 mm 2 and the number density of inclusions with an X value of 0.3 or more is 3.0 Less than pieces/100 mm 2 .
  • the reason why the number density of inclusions is defined in this way is basically obtained from the relationship between the experimental results and the ultra-specularity of the steel material.
  • the MgO--Al 2 O 3 --CaO (CaS)-based inclusions have a shape in which the core of MgO--Al 2 O 3 --CaO is surrounded by brittle CaS. In this case, if the central core is in close contact with the matrix, the inclusions are less likely to fall off, but if the central core is wrapped in CaS, the inclusions are more likely to fall off.
  • the composition is large and the X value is 0.3 or more, pinholes are likely to be generated, and if the number density is 3/mm 2 or more, the super specularity is inferior. It has been found that when the inclusions are mainly non-metallic inclusions, super specularity can be obtained up to a number density of less than 8.0 inclusions/mm 2 . Therefore, the number density of inclusions with an X value of less than 0.3 is allowed up to less than 8.0/100 mm 2 , and the number density of inclusions with an X value of 0.3 or more is up to 3.0/100 mm 2 Permissible.
  • the present invention provides a high-cleanliness steel with inclusions reduced as much as possible, depending on the composition of the remaining oxide inclusions, that is, depending on the ratio of Ca , which was completed by finding that the superspecularity is affected.
  • gas stirring in which inert gas is introduced from the bottom of the ladle, and electromagnetic stirring.
  • the ratio of gas stirring power to electromagnetic stirring power is determined as an operating condition based on the shape of the ladle and the amount of molten steel.
  • the gas agitating force changes and increases even with the same amount of gas as the degree of vacuum increases due to degassing, so control is required.
  • the present inventors examined the state of slag entrainment during the primary refining that could not be removed even in the secondary refining, reviewed the conventional operating conditions, and conducted electromagnetic stirring. was found to be the optimum condition range with .
  • the stirring power was controlled within a range that was sufficient to promote the reaction and not excessive, to prevent slag entrainment during primary refining, to reduce the amount of inclusions to achieve high cleanliness, and to control the X value. . Since the slag component and its viscosity affect the composition of inclusions and the ease with which slag is involved, controlling the slag component together ensures the control of the X value. As a result, compared with conventional mold steel, mold steel suitable for mirror finish could be obtained.
  • Specimens for evaluating mirror-finishability and specimens for evaluating inclusions were taken from this steel material.
  • the mirror-finishability evaluation test piece was taken perpendicular to the forging direction, 50 mm long and 50 mm wide as a test surface (thickness 15 mm), and after performing rough processing, each test piece was subjected to a temperature of 1000 to 1100 ° C. It was quenched at a temperature of 500 to 600° C., subjected to high temperature tempering at a temperature of 500 to 600° C., tempered so that the hardness became 48 to 54 HRC, and finished.
  • this 50 x 50 mm test surface After polishing this 50 x 50 mm test surface with a #600 whetstone, it is polished with abrasive paper from #400 to #1500, and then polished to a super mirror surface of #14000 using diamond abrasive grains of 6 to 1 ⁇ m. A mirror observation was carried out at . This specular observation was determined by a finisher who actually manufactures #14000 ultra-specular plastic molds.
  • the inclusion evaluation test piece is a 20 mm long x 20 mm wide (15 mm thick) sample with the same position and direction as the test piece for the mirror finish evaluation test piece. It was quenched at a temperature of 1000-1100°C. After that, the surface to be measured was polished step by step from #80 to #1500 with abrasive paper, and polished to a super mirror surface of #14000 using diamond abrasive grains of 6 ⁇ m to 1 ⁇ m. Investigation of non-metallic inclusions present in the test pieces was carried out by subjecting the test pieces to SEM (scanning electron microscope)-EDX (energy dispersive X-ray analysis) and particle analysis. The analysis area was set to include about 70% of the area of inclusions.
  • non-metallic inclusions were carried out according to the following procedure. First, a secondary electron image was obtained with an observation field of view of 100 times magnification. At this time, the images were taken so that the base was gray and the non-metallic inclusions were black due to the contrast. Next, as shown in FIG. 3, about 70% of the cross-sectional area of the particles whose black portion in the field of view has an equivalent circle diameter of 3 ⁇ m or more was subjected to composition analysis by EDX. The nearly circular black portion in FIG. 3 is the cross section of the non-metallic inclusion, and the points scattered within this black portion indicate the portions analyzed by EDX (energy dispersive X-ray analysis).
  • EDX energy dispersive X-ray analysis
  • Noise such as dust other than non-metallic inclusions and polishing scratches was removed from the obtained particles by a composition filter.
  • the area ratio of all non-metallic inclusions was obtained from the particles obtained by removing noise.
  • the operator who polishes the surface of the mold to be used for product processing makes a judgment by sensory evaluation of the entire surface of the mold work based on experience. Specifically, sensory evaluation of the finished mirror surface is performed on the entire mold work surface, and if there is a single or multiple pinholes that reduce the specularity, the processor finds it and The die is regrinded to create a new surface, and regrinding is performed until a super-mirror surface is obtained over the entire work surface. Also, in the case of a material with poor mirror finish, it may be judged that it cannot be used. Since the size and appearance frequency of the pinholes are widely evaluated over the entire surface of the mold workpiece, data such as partial surface roughness and reflectance are insufficient. Therefore, based on the sensory evaluation by the processor, those that required regrinding due to inclusions were rated as x, and those that obtained an ultra-mirror surface without regrinding were rated as ⁇ (accepted).
  • the area ratio of nonmetallic inclusions having an equivalent circle diameter of 8.0 ⁇ m or more is 0.00016% or less, and the number density of inclusions having an X value of less than 0.3 is 8.0. /100 mm 2 , and the number density of inclusions with an X value of 0.3 or more is less than 3.0/100 mm 2 , mold steel with excellent mirror finish is obtained. rice field.
  • the mirror-finishability was inferior.
  • the present invention it is possible to easily super-mirror-finish the mold surface, so it is useful for obtaining super-mirror-finished surfaces of plastic products that require molding with such a mold.

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Abstract

The present invention has an area ratio of 0.00016% or less of nonmetal inclusions with an equivalent circle diameter of 8.0 μm or more in a steel material cross section and includes 2 mass% or more of a component that is a nonmetal inclusion with an equivalent circle diameter of 5.0 μm or more selected from the group consisting of Al, Mg, and Ca. When [Ca], [Mg], and [Al] represent the respective contents (mass%) of [Ca], [Mg], and [Al] and X = [Ca]/([Mg]+[Al]), the number density of inclusions with an X value of less than 0.3 is 0.60/100 mm2 or more and less than 8.0/100 mm2, and the number density of inclusions with an X value of 0.3 or more is less than 3.0/100 mm2. In this way, it is possible to obtain a die steel having excellent wear resistance, mirror finish properties, and specular properties suitable for forming an ultra-specular plastic product.

Description

鏡面仕上げ性に優れた金型用鋼Mold steel with excellent mirror finish
　本発明は、超鏡面のプラスチック製品を成形するための超鏡面仕上げ加工に適した鏡面仕上げ加工用金型用鋼に関する。 The present invention relates to mold steel for mirror-finishing that is suitable for ultra-mirror-finishing for molding ultra-mirror-surface plastic products.
　近年の電子機器又は生活用品の容器及びレンズ等に使用されるプラスチック製品は、表面が鏡面であることと、強度が高いこと等が要求される。そのため、このような高鏡面プラスチック製品を成形するための金型には、金型自体の表面の鏡面性が高いこと、耐摩耗性が優れていること、及び耐食性が優れていること等が求められる。このような要請に応える金属材料として、従来、ＳＵＳ４２０系鋼等のマルテンサイトステンレス鋼が使用されている。 In recent years, plastic products used for containers and lenses of electronic devices or daily necessities are required to have a mirror surface and high strength. Therefore, molds for molding such highly specular plastic products are required to have high specularity on the surface of the mold itself, excellent wear resistance, and excellent corrosion resistance. be done. Martensitic stainless steel such as SUS420 series steel is conventionally used as a metal material to meet such demands.
　しかしながら、近時、プラスチック製品に求められる鏡面性は、更に高まっており、同時に、金型表面の仕上げ番手は＃8000の高鏡面から、＃14000の超鏡面へと変化しつつある。このため、金型用鋼にも、超鏡面のプラスチック製品の成形用金型として、鏡面仕上げ性を一層高めた金型用鋼の開発が望まれている。 However, in recent years, the specularity required for plastic products has increased further, and at the same time, the finish count of the mold surface is changing from a high specular surface of #8000 to a super specular surface of #14000. For this reason, there is a demand for the development of mold steel with a further improved specular finish as molds for molding super-mirror-surface plastic products.
　特許文献１には、Ｚｒ添加により介在物組成を制御したプラスチック成形金型用鋼が開示されている。この金型用鋼においては、溶解鋼中の酸化物を浮上させ、酸化物の浮上面を観察したときの全酸化物に占めるＺｒＯ２の割合を９５面積％以上に制御している。特許文献２には、炭窒化物の個数密度と大きさを制御することにより、鏡面性を高めた高耐食性プラスチック成形金型用鋼が開示されている。特許文献３には、炭化物の大きさ及び炭化物間距離を制御すると共に、炭化物密集帯の面積が１０００μｍ２以上であるものを材料目としてときに、この材料目の最大長さと面積率を制御することにより、鏡面性を向上させたプラスチック金型用鋼が開示されている。更に、特許文献４には、非金属介在物の上限を面積百分率で０．０１５％としたプラスチック射出成形用金型材が開示されている。特許文献５には、Ｍｏ及びＷを含む微細炭化物を析出させることが開示されている。 Patent Literature 1 discloses steel for plastic molds in which the composition of inclusions is controlled by adding Zr. In this die steel, the oxides in the molten steel are floated, and the proportion of ZrO 2 in the total oxides when the floated surface of the oxides is observed is controlled to 95 area % or more. Patent Literature 2 discloses a highly corrosion-resistant plastic mold steel in which specularity is enhanced by controlling the number density and size of carbonitrides. In Patent Document 3, the size of carbides and the distance between carbides are controlled, and the maximum length and area ratio of this material are controlled when the area of the dense zone of carbides is 1000 μm 2 or more. Thus, a plastic mold steel with improved specularity is disclosed. Furthermore, Patent Document 4 discloses a mold material for plastic injection molding in which the upper limit of nonmetallic inclusions is 0.015% in terms of area percentage. Patent Document 5 discloses precipitating fine carbides containing Mo and W. US Pat.
特開２００６－２８５６４号公報JP 2006-28564 A 特開２０１４－１８９８２２号公報JP 2014-189822 A 特開２０１５－１６８８５０号公報JP 2015-168850 A 特開昭６４(特開平１)－２５９５０号公報Japanese Patent Application Laid-Open No. 64 (Japanese Patent Application Laid-Open No. 1)-25950 特開平２－１７５８４５号公報JP-A-2-175845
　しかしながら、超鏡面のプラスチック成型用金型は、一般的にダイヤモンド砥粒又はアルミナ砥粒などで仕上げ研磨され、砥粒の径が小さいほど鏡面性の高い金型表面が得られる。研磨作業は#3000→＃8000→＃14000のように段階ごとに研磨するため、金型表面は、最終的には、粒径の小さい砥粒による長時間の研磨にさらされることになる。 However, super-mirror-surface plastic molding dies are generally finished with diamond abrasive grains or alumina abrasive grains, and the smaller the diameter of the abrasive grains, the more mirror-like the mold surface can be obtained. Since the polishing work is performed step by step in the order of #3000→#8000→#14000, the mold surface is finally subjected to long-term polishing with small-diameter abrasive grains.
　そのような長時間の研磨は、金型素材中に含まれる粗大な炭窒化物及び非金属介在物が研磨粉によって掘り返されることで、粗大な炭化物及び非金属介在物は、研磨中に脱落し、残った穴がピンホールとなり、超鏡面性が失われる。このような鏡面仕上げ性の劣る金型用鋼は、磨き直し作業及び再加工などの余計なコストが発生するという問題点がある。 Such long-term polishing causes coarse carbonitrides and non-metallic inclusions contained in the mold material to be dug up by the polishing powder, and coarse carbides and non-metallic inclusions fall off during polishing. , the remaining hole becomes a pinhole, and the super specularity is lost. Such mold steel with poor mirror finish has the problem of incurring extra costs such as repolishing and reworking.
　また、ピンホールは研磨剤の食い込み又は錆びを起点として発生する場合もあるため、金型用鋼には研磨剤の食い込み難さの観点から高硬度が要求され、また錆び難さのための耐食性が求められる。 In addition, since pinholes may occur starting from the penetration of abrasives or rust, high hardness is required for mold steel from the viewpoint of difficulty of penetration of abrasives, and corrosion resistance is required for resistance to rusting. is required.
　そこで、従来、ピンホールが発生しにくく、鏡面仕上げ性が高い金型用鋼を得るため、粗大な炭化物及び非金属介在物が少なくなるように、また、硬度及び耐食性が高くなるように、プラスチック成形金型用鋼の製造方法及び組成等に改良が加えられている。しかしながら、従来の金型では、近時の超鏡面のプラスチック成形用金型からの要求性能を発揮するには、問題がある。 Therefore, conventionally, in order to obtain mold steel that is less likely to cause pinholes and has high mirror finish, plastics are used to reduce coarse carbides and non-metallic inclusions and to increase hardness and corrosion resistance. Improvements have been made in the manufacturing method and composition of mold steel. However, the conventional mold has a problem in exhibiting the performance required from the recent ultra-mirror plastic molding mold.
　特許文献１に記載の金型用鋼は、組成にＺｒを添加することによって、介在物組成を制御しているが、Ｚｒの添加に伴うコストが高いことと、Ｚｒの歩留が安定しない等の問題点がある。また、鏡面性について、＃8000の高鏡面ではピンホールが発生しないが、＃14000の超鏡面研磨時には鋼材の硬度が約４０ＨＲＣと低いことから、超鏡面を得にくいという問題点がある。更に、特許文献１は、実際上その実施例にみるように、Ｃｒ含有量が低いので、耐食性が低く、長時間の研磨で錆びが発生し、錆びを起点にピンホールが発生するという問題点もある。 In the mold steel described in Patent Document 1, the composition of inclusions is controlled by adding Zr to the composition. There are problems with As for the specularity, pinholes do not occur in the high specular surface of #8000, but the hardness of the steel material is as low as about 40 HRC in the ultra-mirror polishing of #14000. Furthermore, as shown in the practical examples of Patent Document 1, since the Cr content is low, the corrosion resistance is low, and rust is generated by long-term polishing, and the problem is that pinholes are generated from the rust. There is also
　特許文献２及び３に記載の金型用鋼は、ＳＵＳ４２０Ｊ２系鋼種を使用することで硬度と耐食性を確保し、更に炭化物の個数と大きさについて規制することにより、鏡面性を高めている。しかしながら、これらの特許文献２及び３は、非金属介在物については何ら言及されておらず、その金型用鋼において、非金属介在物を制御していないため、超鏡面磨き時には、非金属介在物によるピンホールの発生を避けられないという問題点がある。 The mold steel described in Patent Documents 2 and 3 secures hardness and corrosion resistance by using SUS420J2 steel grade, and furthermore, by regulating the number and size of carbides, the specularity is enhanced. However, these patent documents 2 and 3 do not mention nonmetallic inclusions at all, and do not control nonmetallic inclusions in the mold steel. There is a problem that the occurrence of pinholes due to objects cannot be avoided.
　特許文献４及び５に記載の金型用鋼は、ＳＵＳ４２０Ｊ２系鋼種を使用することで硬度と耐食性を確保し、非金属介在物の面積率及び酸素量を制御している。しかしながら、非金属介在物の面積率を制御するだけでは、超鏡面磨き時にはピンホールが発生する問題点を解消できない。 The mold steel described in Patent Documents 4 and 5 uses SUS420J2 steel grade to ensure hardness and corrosion resistance, and controls the area ratio of non-metallic inclusions and the amount of oxygen. However, simply controlling the area ratio of non-metallic inclusions cannot solve the problem of pinhole formation during ultra-mirror polishing.
　本発明はかかる問題点に鑑みてなされたものであって、超鏡面のプラスチック製品を成形するのに好適の優れた鏡面性を有し、耐摩耗性及び鏡面仕上げ性が優れた金型用鋼を提供することを目的とする。 The present invention has been made in view of these problems, and is a die steel that has excellent mirror surface properties suitable for molding ultra-mirror plastic products, as well as excellent wear resistance and mirror finish properties. intended to provide
　本発明に係る鏡面仕上げ性に優れた金型用鋼は、
Ｃ：０．２０～０．５０質量％、
Ｓｉ：０．１０～１．５０質量％、
Ｍｎ：０．１０～０．７０質量％、
Ｃｒ：１０．５～２０．０質量％、
Ｎｉ：１．００質量％以下、
Ｍｏ：０．０５～１．００質量％、
Ｖ：０．０１～１．００質量％
を含有し、
残部：Ｆｅ及び不可避的不純物からなる組成を有し、
前記不可避的不純物のうち、下記成分は、
Ａｌ：０．００７～０．０３５質量％、
Ｓ：０．００２０質量％以下、
Ｏ：０．００１５質量％以下、
Ｃａ：０．００２０質量％以下、
Ｍｇ：０．００２０質量％以下
に規制され、
鋼材断面において、円相当径８．０μｍ以上の非金属介在物の面積率は０．０００１６％以下であり、
円相当径が５．０μｍ以上の非金属介在物であって、Ａｌ、Ｍｇ及びＣａからなる群から選択されたいずれかの成分を２質量％以上含有するものが、
［Ｃａ］、［Ｍｇ］、［Ａｌ］を夫々Ｃａ、Ｍｇ、Ａｌの含有量（質量％）とし、Ｘ＝［Ｃａ］／（［Ｍｇ］＋［Ａｌ］）としたとき、
Ｘ値が０．３未満の介在物の個数密度が０．６０個／１００ｍｍ２以上かつ８．０個／１００ｍｍ２未満であると共に、
Ｘ値が０．３以上の介在物の個数密度が３．０個／１００ｍｍ２未満であることを特徴とする。 The mold steel excellent in mirror finish according to the present invention is
C: 0.20 to 0.50% by mass,
Si: 0.10 to 1.50% by mass,
Mn: 0.10 to 0.70% by mass,
Cr: 10.5 to 20.0% by mass,
Ni: 1.00% by mass or less,
Mo: 0.05 to 1.00% by mass,
V: 0.01 to 1.00% by mass
contains
Balance: having a composition consisting of Fe and unavoidable impurities,
Among the unavoidable impurities, the following components are
Al: 0.007 to 0.035% by mass,
S: 0.0020% by mass or less,
O: 0.0015% by mass or less,
Ca: 0.0020% by mass or less,
Mg: regulated to 0.0020% by mass or less,
In the cross section of the steel material, the area ratio of non-metallic inclusions having an equivalent circle diameter of 8.0 μm or more is 0.00016% or less,
Non-metallic inclusions having an equivalent circle diameter of 5.0 μm or more and containing 2% by mass or more of any component selected from the group consisting of Al, Mg and Ca,
When [Ca], [Mg], and [Al] are the contents (% by mass) of Ca, Mg, and Al, respectively, and X = [Ca] / ([Mg] + [Al]),
The number density of inclusions with an X value of less than 0.3 is 0.60/100 mm 2 or more and less than 8.0/100 mm 2 ,
The number density of inclusions having an X value of 0.3 or more is less than 3.0/100 mm 2 .
　この鏡面仕上げ性に優れた金型用鋼において、
例えば、更に、Ｗを
Ｍｏ＋１／２Ｗ：０．０５～１．００質量％の範囲で含有することを特徴とする。 In this mold steel with excellent mirror finish,
For example, it is characterized by further containing W in the range of Mo+1/2W: 0.05 to 1.00% by mass.
　本発明によれば、超鏡面のプラスチック製品の成形用金型として有効な鏡面仕上げ性を一層高めた金型用鋼が得られる。 According to the present invention, it is possible to obtain a mold steel with a further improved specular finish that is effective as a mold for molding plastic products with an ultra-mirror surface.
ＭｇＯ－Ａｌ２Ｏ３系介在物の走査型電子顕微鏡写真である。4 is a scanning electron micrograph of MgO—Al 2 O 3 system inclusions. ＭｇＯ－Ａｌ２Ｏ３－ＣａＳ系介在物の走査型電子顕微鏡写真である。4 is a scanning electron micrograph of MgO—Al 2 O 3 —CaS-based inclusions. 検出された粒子の分析方法を示す図である。FIG. 2 illustrates a method of analyzing detected particles;
　以下、本発明の実施形態について、具体的に説明する。先ず、本発明に係る鏡面仕上げ性に優れた金型用鋼の組成限定理由について説明する。 The embodiments of the present invention will be specifically described below. First, the reasons for limiting the composition of the mold steel excellent in mirror finish according to the present invention will be explained.
　「Ｃ：０．２０～０．５０質量％」
　Ｃは炭化物を形成とともに、鋼材の基地に固溶して硬さを向上させる重要な元素である。超鏡面を得るためには、金型の焼入焼戻し硬さが4５ＨＲＣ以上であることが必要であり、Ｃが０．２０質量％未満では、十分な硬さを得ることができない。また、Ｃが０．５０質量％を超えると、粗大な炭化物が形成され、超鏡面仕上げ性と耐食性を損なう。このため、Ｃは０．２０～０．５０質量％であり、好ましくは、０．２４～０．４５質量％である。 "C: 0.20 to 0.50% by mass"
C is an important element that forms carbides and dissolves in the matrix of steel materials to improve hardness. In order to obtain a super mirror surface, it is necessary that the quenching and tempering hardness of the mold is 45 HRC or more. On the other hand, when C exceeds 0.50% by mass, coarse carbides are formed, impairing ultra-mirror finish and corrosion resistance. Therefore, C is 0.20 to 0.50% by mass, preferably 0.24 to 0.45% by mass.
　「Ｓｉ：０．１０～１．５０質量％」
　Ｓｉは基本的には溶鋼の脱酸材として添加されるが、鋼材の切削性を向上させる元素である。このため、Ｓｉの添加により、金型製作コストを抑制することができる。Ｓｉが０．１０質量％未満では、切削性が十分ではない。また、Ｓｉが１．５０質量％を超えると、成分偏析を増長させ、磨き面にうねりを発生させると共に、熱伝導率が低下する。このため、Ｓｉは０．１０～１．５０質量％、好ましくは、０．１８～１．２０質量％とする。 "Si: 0.10 to 1.50% by mass"
Si is basically added as a deoxidizing agent for molten steel, and is an element that improves the machinability of steel materials. Therefore, by adding Si, it is possible to suppress the mold manufacturing cost. If the Si content is less than 0.10% by mass, machinability is not sufficient. On the other hand, when Si exceeds 1.50% by mass, the segregation of components is increased, the polished surface is undulated, and the thermal conductivity is lowered. Therefore, Si should be 0.10 to 1.50% by mass, preferably 0.18 to 1.20% by mass.
　「Ｍｎ：０．１０～０．７０質量％」
　Ｍｎは鋼材の焼入性を向上させる元素である。Ｍｎが０．１０質量％未満では、十分な焼入性を得られない。また、Ｍｎが０．７０質量％を超えると、成分偏析を増長させ、磨き面にうねりを発生させる。このため、Ｍｎは０．１０～０．７０質量％であり、好ましくは、０．３０～０．６０質量％である。 "Mn: 0.10 to 0.70% by mass"
Mn is an element that improves the hardenability of steel materials. If the Mn content is less than 0.10% by mass, sufficient hardenability cannot be obtained. On the other hand, when Mn exceeds 0.70% by mass, the segregation of components is increased, causing undulations on the polished surface. Therefore, Mn is 0.10 to 0.70% by mass, preferably 0.30 to 0.60% by mass.
　「Ｃｒ：１０．５～２０．０質量％」
　Ｃｒは鋼材の焼入性及び耐食性を向上させるのに必要な元素である。Ｃｒが１０．５質量％未満では、十分な焼入性及び耐食性が得られない。また、Ｃｒが２０．０質量％を超えると、粗大な炭化物が形成され、超鏡面性が得られなくなる。このため、Ｃｒは１０．５～２０．０質量％添加する。好ましくは、Ｃｒは１２．０～１６．０質量％である。 "Cr: 10.5 to 20.0% by mass"
Cr is an element necessary for improving the hardenability and corrosion resistance of steel. If Cr is less than 10.5% by mass, sufficient hardenability and corrosion resistance cannot be obtained. On the other hand, when Cr exceeds 20.0% by mass, coarse carbides are formed and super specularity cannot be obtained. Therefore, 10.5 to 20.0% by mass of Cr is added. Preferably, Cr is 12.0-16.0 mass %.
　「Ｎｉ：１．００質量％以下」
　Ｎｉは、鋼材の焼入性と耐食性を向上させる元素である。このＮｉの含有量が０．０５質量％未満であると、この焼入性及び耐食性の向上効果が得られない。よって、Ｎｉは０．０５質量％以上が好ましい。一方、Ｎｉが１．００質量％を超えると、焼入焼戻し後の残留オーステナイトが増加して超鏡面性を得にくくなる。このため、Ｎｉを１．００質量％以下添加する。好ましくは、Ｎｉを０．０５質量％以上、更に好ましくは０．１０～０．５０質量％添加する。 "Ni: 1.00% by mass or less"
Ni is an element that improves the hardenability and corrosion resistance of steel. If the Ni content is less than 0.05% by mass, the effect of improving hardenability and corrosion resistance cannot be obtained. Therefore, Ni is preferably 0.05% by mass or more. On the other hand, when Ni exceeds 1.00% by mass, the amount of retained austenite after quenching and tempering increases, making it difficult to obtain super specularity. Therefore, 1.00% by mass or less of Ni is added. Preferably, Ni is added in an amount of 0.05% by mass or more, more preferably 0.10 to 0.50% by mass.
　「Ｍｏ：０．０５～１．００質量％」
　Ｍｏは耐食性及び焼入焼戻し硬さを向上させる元素である。Ｍｏ含有量が０．０５質量％未満では、耐食性及び焼入焼戻し硬さの向上効果を得ることができない。Ｍｏ含有量が１．００質量％を超えると、粗大な炭化物が形成され、超鏡面性が得られないと共に、製造コストが高くなる。このため、Ｍｏを０．０５～１．００質量％、好ましくは０．１０～０．６０質量％添加する。 "Mo: 0.05 to 1.00% by mass"
Mo is an element that improves corrosion resistance and quenching and tempering hardness. If the Mo content is less than 0.05% by mass, the effect of improving corrosion resistance and quenching and tempering hardness cannot be obtained. If the Mo content exceeds 1.00% by mass, coarse carbides are formed, making it impossible to obtain super specularity and increasing production costs. Therefore, 0.05 to 1.00 mass %, preferably 0.10 to 0.60 mass % of Mo is added.
　「Ｖ：０．０１～１．００質量％」
　Ｖは鋼材焼入時の結晶粒の粗大化の防止に有効である。Ｖが０．０１質量％未満では結晶粒粗大化防止効果を得ることができない。一方、Ｖが１．００質量％を超えると、粗大な炭化物が形成され、超鏡面性が得られず、コストも高くなる。このため、Ｖを０．０１～１．００質量％、好ましくは、０．０４～０．３０質量％添加する。 "V: 0.01 to 1.00% by mass"
V is effective in preventing coarsening of crystal grains during steel material quenching. If V is less than 0.01% by mass, the effect of preventing grain coarsening cannot be obtained. On the other hand, when V exceeds 1.00% by mass, coarse carbides are formed, super specularity cannot be obtained, and the cost increases. Therefore, 0.01 to 1.00 mass %, preferably 0.04 to 0.30 mass % of V is added.
　「Ａｌ：０．０３５質量％以下」
　Ａｌは基本的には溶鋼の脱酸材として添加される元素であるが、ＡｌはOと結合してＡｌ２Ｏ３からなる非金属介在物を形成し、溶鋼中に残存して凝固した場合にピンホールの原因となる。Ａｌが０．０３５質量％を超えると、Ａｌ２Ｏ３のクラスターが残留し、ピンホールの原因となるため、超鏡面を得ることができなくなる。このため、Ａｌの許容量は、０．０３５質量％とする。 "Al: 0.035% by mass or less"
Al is basically an element added as a deoxidizing agent for molten steel, but when Al combines with O to form non-metallic inclusions made of Al 2 O 3 and remains in the molten steel and solidifies, cause pinholes. If Al exceeds 0.035% by mass, clusters of Al 2 O 3 remain and cause pinholes, making it impossible to obtain a super mirror surface. Therefore, the allowable amount of Al is set to 0.035% by mass.
　「Ｓ：０．００２０質量％以下」
　Ｓは溶鋼中に含まれる不純物であり、Ｍｎ及びＣａと結合し、ＭｎＳ及びＣａＳ等の硫化物系非金属介在物を形成する。これらの硫化物は、マトリックス及び他の非金属介在物と比べて研磨されやすい特徴を持つため、ピンホール及びオレンジピールを引き起こすという問題点がある。Ｓが０．００２０質量％を超えると、図２に示すＣａＳを含む非金属介在物が増加する。このため、ピンホール及びオレンジピールを生じさせ、超鏡面を得ることができなくなる。このため、Ｓは０．００２０質量％以下とする。 "S: 0.0020% by mass or less"
S is an impurity contained in molten steel, and combines with Mn and Ca to form sulfide-based nonmetallic inclusions such as MnS and CaS. These sulfides have the characteristic of being easily polished compared to the matrix and other non-metallic inclusions, and thus have the problem of causing pinholes and orange peel. When S exceeds 0.0020% by mass, nonmetallic inclusions containing CaS shown in FIG. 2 increase. As a result, pinholes and orange peel are generated, making it impossible to obtain a super-specular surface. Therefore, the content of S is set to 0.0020% by mass or less.
　「Ｏ：０．００１５質量％以下」
　Ｏは溶鋼中に含まれる不純物であり、Ａｌなどと結合し、Ａｌ２Ｏ３などの酸化物系非金属介在物を形成してピンホールの原因となる不純物である。このＯが０．００１５質量％を超えると、酸化物系非金属介在物のクラスターが形成されたり、非金属介在物の粒径が増大したりして、鏡面研磨の際にピンホールが発生する原因となる。このピンホールの発生により、超鏡面が得られなくなる。このため、Ｏは０．００１５質量％以下、好ましくは、０．０００９質量％以下とする。 "O: 0.0015% by mass or less"
O is an impurity contained in molten steel, and is an impurity that combines with Al and the like to form oxide-based nonmetallic inclusions such as Al 2 O 3 and cause pinholes. If this O exceeds 0.0015% by mass, clusters of oxide-based nonmetallic inclusions are formed, or the particle size of the nonmetallic inclusions increases, causing pinholes during mirror polishing. cause. Due to the occurrence of these pinholes, a super-mirror surface cannot be obtained. Therefore, the content of O should be 0.0015% by mass or less, preferably 0.0009% by mass or less.
　「Ｃａ：０．００２０質量％以下」
　ＣａはＯ又はＳと結合して、ＣａＯ又はＣａＳを形成し、ピンホールの原因となる。製鋼工程中で、Ｃａは精錬剤であるスラグの主成分として溶鋼上にあるため、溶鋼の撹拌条件を最適化して、スラグの溶鋼中への混入を防ぐことが重要である。Ｃａが０．００２０質量％を超えると、ＭｇＯ－Ａｌ２Ｏ３－ＣａＯ系複合介在物又はＭｇＯ－Ａｌ２Ｏ３－ＣａＳ系複合介在物を形成し、金型の仕上研磨時にピンホールを発生して、超鏡面を得ることができなくなる。このため、Ｃａは０．００２０質量％以下、好ましくは０．００１０質量％以下とする。 "Ca: 0.0020% by mass or less"
Ca combines with O or S to form CaO or CaS, which causes pinholes. During the steelmaking process, Ca is present in molten steel as a main component of slag, which is a refining agent. Therefore, it is important to optimize the stirring conditions of molten steel to prevent slag from entering the molten steel. When Ca exceeds 0.0020% by mass, MgO—Al 2 O 3 —CaO-based composite inclusions or MgO—Al 2 O 3 —CaS-based composite inclusions are formed, and pinholes are generated during final polishing of the mold. As a result, a super specular surface cannot be obtained. Therefore, Ca should be 0.0020% by mass or less, preferably 0.0010% by mass or less.
　「Ｍｇ：０．００２０質量％以下」
　Ｍｇは不可避的不純物であり、０．００２０質量％以下に規制される。 "Mg: 0.0020% by mass or less"
Mg is an unavoidable impurity and is restricted to 0.0020% by mass or less.
　「Ｍｏ＋１／２Ｗ：０．０５～１．００質量％」
　Ｗは、Ｍｏと同様に、耐食性及び焼入焼戻し硬さを向上させる元素である。Ｗはその量の１／２の量がＭｏと同様の効果を奏する。つまり、Ｗ含有量がＭｏ＋１／２Ｗで０．０５質量％未満では、耐食性及び焼入焼戻し硬さの向上効果を得ることができない。Ｗ含有量がＭｏ＋１／２Ｗで１．００質量％を超えると、粗大な炭化物が形成され、超鏡面性が得られないと共に、製造コストが高くなる。このため、Ｗを、必要に応じて、Ｍｏ＋１／２Ｗで０．０５～１．００質量％、好ましくは０．１０～０．６０質量％添加する。 "Mo+1/2W: 0.05 to 1.00% by mass"
W, like Mo, is an element that improves corrosion resistance and quenching and tempering hardness. W has the same effect as Mo when its amount is 1/2. That is, if the W content is less than 0.05% by mass in terms of Mo+1/2W, the effect of improving corrosion resistance and quenching and tempering hardness cannot be obtained. If the W content exceeds 1.00% by mass in terms of Mo+1/2W, coarse carbides are formed, making it impossible to obtain super specularity and increasing production costs. Therefore, W is added in an amount of 0.05 to 1.00% by mass, preferably 0.10 to 0.60% by mass as Mo+1/2W, if necessary.
　次に、非金属介在物の規制理由について説明する。 Next, I will explain the reasons for regulating non-metallic inclusions.
　鋼材断面において、円相当径８．0μｍ以上の非金属介在物の面積率は０．０００１６％以下である。 In the steel cross section, the area ratio of non-metallic inclusions with an equivalent circle diameter of 8.0 μm or more is 0.00016% or less.
　円相当径が８．０μｍ以上の非金属介在物は、その組成によらず、金型の超鏡面仕上げ加工中にピンホールを発生させ有害であるため、非金属介在物の面積率を制限することにより、ピンホールの発生確率を下げる。このため、円相当径が８．０μｍ以上の非金属介在物の面積率は０．０００１６％以下とする。 Non-metallic inclusions with an equivalent circle diameter of 8.0 μm or more are harmful because they generate pinholes during ultra-mirror finishing of the mold regardless of their composition, so the area ratio of non-metallic inclusions is limited. By doing so, the probability of occurrence of pinholes is reduced. Therefore, the area ratio of nonmetallic inclusions having an equivalent circle diameter of 8.0 μm or more is set to 0.00016% or less.
　また円相当径が５．０μｍ以上の非金属介在物であって、Ａｌ、Ｍｇ及びＣａからなる群から選択されたいずれかの成分を２質量％以上含有するものを対象として、
［Ｃａ］、［Ｍｇ］、［Ａｌ］を夫々［Ｃａ］、［Ｍｇ］、［Ａｌ］の含有量（質量％）とし、Ｘ＝［Ｃａ］／（［Ｍｇ］＋［Ａｌ］）としたとき、
Ｘ値が０．３未満の介在物の個数密度が８．０個／１００ｍｍ２未満であると共に、
Ｘ値が０．３以上の介在物の個数密度が３．０個／１００ｍｍ２未満である。 In addition, for nonmetallic inclusions having an equivalent circle diameter of 5.0 μm or more and containing 2% by mass or more of any component selected from the group consisting of Al, Mg and Ca,
[Ca], [Mg], and [Al] are the contents (% by mass) of [Ca], [Mg], and [Al], respectively, and X = [Ca] / ([Mg] + [Al]) when
The number density of inclusions with an X value of less than 0.3 is less than 8.0/100 mm 2 ,
The number density of inclusions having an X value of 0.3 or more is less than 3.0 pieces/100 mm 2 .
　超鏡面を得るには、高清浄度な金型材料が必要である。本発明の組成の鋼材のように、Ｓ含有量が低い金型材料を精錬すると、非金属介在物の主体は、酸化物系介在物になる。この酸化物系介在物の主成分は、Ｃａ，Ｍｇ，Ａｌであり、これらの元素の起源は、Ｃａは精錬に使うスラグであり、Ｍｇは耐火物であり、Ａｌは溶鋼の酸素量を低減するための脱酸材由来である。本願発明者らは金型材料の超鏡面仕上げ性と介在物組成との関係を研究した結果、金型材料の優れた超鏡面仕上げ性を得るためには、酸化物系介在物のＣａ，Ｍｇ，Ａｌの比率を制御することが必要であることを見いだした。 　In order to obtain an ultra-mirror surface, a highly clean mold material is required. When refining a mold material with a low S content, such as the steel having the composition of the present invention, the non-metallic inclusions mainly become oxide-based inclusions. The main components of these oxide-based inclusions are Ca, Mg, and Al, and the origin of these elements is that Ca is slag used in refining, Mg is a refractory, and Al reduces the amount of oxygen in molten steel. It is derived from a deoxidizing material for The inventors of the present application have studied the relationship between the ultra-mirror surface finishing properties of mold materials and the composition of inclusions. , Al is necessary to control.
　図１及び図２は、＃14000の超鏡面まで研磨した金型表面に存在する非金属介在物の走査型電子顕微鏡による写真である。図１はＭｇＯ－Ａｌ２Ｏ３主体の介在物であり、Ｘ値が０．３未満である。また、図２はＭｇＯ－Ａｌ２Ｏ３－ＣａＳ（ＣａＳ）系介在物であり、Ｘ値が０．３以上である。Ｍｇ及びＡｌは、Oと結びついて硬質介在物を形成するため、図１のように非金属介在物の大きさが一定以下であればピンホールを形成しにくい。溶鋼中のＣａ，Ｍｇ．Ａｌが結びついて介在物を形成した場合、Ｃａの組成割合で鏡面仕上げ性への影響度が変わることが判明した。溶鋼中のＣａは微量のＳと反応し、図２のような酸化物系非金属介在物と基地との境界に、ＣａＳを部分的に形成する。Ｃａの酸化物ＣａＯを含む酸化物系介在物と、硫化物ＣａＳとが一体化した複合系介在物は、ＭｇＯ－Ａｌ２Ｏ３系介在物に比べて、研磨時の化学的影響と物理的影響を受けやすく、優先的に研磨される。このため、介在物が脱落しやすい状態となる。更に、研磨が進むと、介在物が脱落し、ピンホールが発生する。このため、介在物組成にＣａを含むか、又は含まないかは、ピンホールの発生に極めて重要な影響を与える。本発明者らによる研究の結果、円相当径が５μｍ以上の介在物組成から求めたＸ値＝［Ｃａ］／（［Ｍｇ］＋［Ａｌ］）が０．３未満となる介在物が、個数密度で８．０個／１００ｍｍ２未満であると共に、Ｘ値が０．３以上となる介在物の個数密度が３．０個／１００ｍｍ２未満であるプラスチック金型用鋼材は超鏡面仕上げ性が良好であることが判明した。そこで、本発明においては、Ｘ値が０．３未満の介在物の個数密度が８．０個／１００ｍｍ２未満であると共に、Ｘ値が０．３以上の介在物の個数密度が３．０個／１００ｍｍ２未満とする。 FIGS. 1 and 2 are scanning electron microscope photographs of non-metallic inclusions present on the mold surface polished to a #14000 ultra-mirror surface. FIG. 1 shows inclusions mainly composed of MgO—Al 2 O 3 and has an X value of less than 0.3. FIG. 2 shows MgO—Al 2 O 3 —CaS (CaS)-based inclusions with an X value of 0.3 or more. Since Mg and Al combine with O to form hard inclusions, it is difficult to form pinholes if the size of the non-metallic inclusions is less than a certain size as shown in FIG. Ca, Mg. It was found that when Al binds to form inclusions, the degree of influence on the mirror-finishability varies depending on the composition ratio of Ca. Ca in the molten steel reacts with a small amount of S to partially form CaS at the boundary between the oxide-based nonmetallic inclusions and the matrix as shown in FIG. Composite inclusions, in which oxide-based inclusions containing Ca oxide CaO and sulfide CaS are integrated, are less chemically affected and physically affected during polishing than MgO—Al 2 O 3- based inclusions. Sensitive and preferentially polished. As a result, inclusions are likely to fall off. Furthermore, as the polishing progresses, inclusions fall off and pinholes are generated. Therefore, whether or not Ca is included in the composition of inclusions has a very important effect on the generation of pinholes. As a result of research by the present inventors, the number of inclusions where the X value = [Ca]/([Mg] + [Al]) obtained from the composition of inclusions with an equivalent circle diameter of 5 µm or more is less than 0.3 A steel material for plastic molds having a density of less than 8.0 pieces/100 mm 2 and a number density of inclusions with an X value of 0.3 or more of less than 3.0 pieces/100 mm 2 has an ultra-mirror finish. It turned out to be good. Therefore, in the present invention, the number density of inclusions with an X value of less than 0.3 is less than 8.0 pieces/100 mm 2 and the number density of inclusions with an X value of 0.3 or more is 3.0 Less than pieces/100 mm 2 .
　このように介在物の個数密度を規定するのは、基本的には、実験結果と鋼材の超鏡面性との関係から求めたものである。鋼材の超鏡面仕上げ面を観察すると、ＭｇＯ－Ａｌ２Ｏ３－ＣａＯ（ＣａＳ）系介在物は、ＭｇＯ－Ａｌ２Ｏ３－ＣａＯの中心核を脆いＣａＳが包む形状を有している。この場合に、中心核が基地と密着していると、介在物の脱落は起きにくいが、中心核をＣａＳが包み込むようになると、介在物の脱落が生じやすくなる。Ｘが０．３未満の場合は、中心核が基地と比較的密着していることにより介在物の脱落を引き起こしにくいが、Ｘが増加して０．３以上となると、中心核のＣａＳによる包み込みが進行し、介在物の脱落を引き起こしやすくなる。このため、実験結果から、Ｘ＝０．３を境にして、規制すべき介在物の個数密度が変わることが判明した。即ち、円相当径が８μｍ以上の非金属介在物の面積率が０．０００１６％以下という条件の下で、鏡面仕上げ時にピンホールとなりやすい円相当径が５μｍ以上の非金属介在物に関して、Ｃａの組成が多くてＸ値が０．３以上であるとピンホールが生成しやすくなり、個数密度が３個／ｍｍ２以上で超鏡面性が劣り、一方、Ｃａの組成比が少なく、Ｍｇ及びＡｌ主体の非金属介在物であると、個数密度が８．０個／ｍｍ２未満まで超鏡面性が得られるということが判明した。よって、Ｘ値が０．３未満の介在物の個数密度は８．０個／１００ｍｍ２未満まで許容され、Ｘ値が０．３以上の介在物の個数密度は３．０個／１００ｍｍ２まで許容される。 The reason why the number density of inclusions is defined in this way is basically obtained from the relationship between the experimental results and the ultra-specularity of the steel material. Observing the ultra-mirror-finished surface of the steel, the MgO--Al 2 O 3 --CaO (CaS)-based inclusions have a shape in which the core of MgO--Al 2 O 3 --CaO is surrounded by brittle CaS. In this case, if the central core is in close contact with the matrix, the inclusions are less likely to fall off, but if the central core is wrapped in CaS, the inclusions are more likely to fall off. When X is less than 0.3, inclusions are less likely to fall off because the core is in relatively close contact with the matrix, but when X increases to 0.3 or more, the core is wrapped by CaS. progresses, easily causing inclusions to come off. For this reason, it was found from the experimental results that the number density of inclusions to be controlled changes at X=0.3. That is, under the condition that the area ratio of the non-metallic inclusions with an equivalent circle diameter of 8 μm or more is 0.00016% or less, the non-metallic inclusions with an equivalent circle diameter of 5 μm or more that are likely to form pinholes when mirror-finished are Ca. If the composition is large and the X value is 0.3 or more, pinholes are likely to be generated, and if the number density is 3/mm 2 or more, the super specularity is inferior. It has been found that when the inclusions are mainly non-metallic inclusions, super specularity can be obtained up to a number density of less than 8.0 inclusions/mm 2 . Therefore, the number density of inclusions with an X value of less than 0.3 is allowed up to less than 8.0/100 mm 2 , and the number density of inclusions with an X value of 0.3 or more is up to 3.0/100 mm 2 Permissible.
　次に、本発明の範囲に入る実施例について本発明の範囲から外れる比較例と共に説明する。 Next, examples within the scope of the present invention will be described together with comparative examples outside the scope of the present invention.
　量産電気炉と炉外精錬装置を使用した一次精錬時に、脱酸処理、脱硫処理、及び脱ガス処理を通常より強化して、高清浄度鋼を溶製し、電極を製造した。この電極を基に、ＶＡＲ（真空アーク再溶解法）又はＥＳＲ（エレクトロスラグ再溶解法）で２次精錬し、得られた鋼塊を、１５０～２５０ｍｍ厚、２００～４００ｍｍ幅の寸法に熱間鍛造し、その後、焼なまし処理を行った。下記表１に、製造した鋼材の組成を、本発明の実施例１～１４及び本発明の範囲から外れる比較例１６～２３について示す。なお、参考例１５は、Ａｌ成分が本発明の範囲から外れるものであるが、表２に示すように、非金属介在物に関する条件は本発明の範囲を満たしている。但し、表１において、数値は質量％である。本発明は、超鏡面を創り出すために、介在物を極力低減した高清浄度鋼であっても、残存した酸化物系介在物の組成によっては、即ち、介在物に含まれるＣａの割合によっては、超鏡面性が影響を受けることを，見いだして完成されたものである。 At the time of primary refining using a mass-produced electric furnace and an external refining equipment, the deoxidation, desulfurization, and degassing processes were strengthened more than usual, and high-cleanliness steel was melted and electrodes were manufactured. Based on this electrode, secondary refining is performed by VAR (vacuum arc remelting method) or ESR (electroslag remelting method). Forged and then annealed. Table 1 below shows the compositions of the manufactured steel materials for Examples 1 to 14 of the present invention and Comparative Examples 16 to 23 outside the scope of the present invention. In Reference Example 15, the Al component is out of the scope of the present invention, but as shown in Table 2, the conditions for non-metallic inclusions satisfy the scope of the present invention. However, in Table 1, the numerical values are % by mass. In order to create an ultra-mirror surface, the present invention provides a high-cleanliness steel with inclusions reduced as much as possible, depending on the composition of the remaining oxide inclusions, that is, depending on the ratio of Ca , which was completed by finding that the superspecularity is affected.
　Ｃａは一次精錬時にスラグ中に存在するＣａが主な起源なので、本発明においては、精錬時の溶鋼にスラグが巻き込まれないように、操業条件を改善した。高清浄度鋼の精錬は、脱ガスに加えて溶鋼とスラグとの間の反応を促進させて不純物を除去する。反応の促進のためには、溶鋼を撹拌することによって溶鋼上のスラグと溶鋼との直接接触を増加させる必要があるが、過剰な溶鋼撹拌はスラグを溶鋼中に巻込み、浮上分離しきれないスラグが溶鋼中に残存して介在物となる。これにより、高清浄度の溶鋼が得られず、スラグ含有成分が溶鋼中に残存して、鋼材中の介在物が増大する。 Since Ca is mainly derived from Ca present in slag during primary refining, in the present invention, the operating conditions were improved so that slag would not get caught in molten steel during refining. Refining of high-cleanliness steel removes impurities by promoting reactions between molten steel and slag in addition to degassing. In order to promote the reaction, it is necessary to increase the direct contact between the slag on the molten steel and the molten steel by stirring the molten steel. Slag remains in the molten steel and becomes inclusions. As a result, molten steel with high cleanliness cannot be obtained, slag-containing components remain in the molten steel, and inclusions in the steel material increase.
　一方、溶鋼撹拌の方法は、不活性ガスを取鍋底から入れるガス撹拌と電磁撹拌による方法があり、取鍋形状と溶鋼量により、ガス撹拌力と電磁撹拌力の比率を操業条件として決定する。ガスによる撹拌力は、脱ガスよって真空度が上がることにより、同じガス量でも変化し増大するためコントロールが必要となる。本発明者らは、製品に残る介在物の量と組成を分析することにより、二次精錬でも除去できていない一次精錬時のスラグ巻込み状況を検討し、従来の操業条件を見直して電磁撹拌を主撹拌力とする最適条件範囲を見出した。撹拌力を反応の促進に十分でかつ過剰とならない範囲にコントロールし、一次精錬時のスラグ巻込みを防止し、介在物量を減少させて高清浄度を達成し、且つＸ値の制御を行った。スラグ成分及びその粘度が、介在物組成及びスラグの巻き込まれ易さに影響するため、スラグ成分のコントロールも合せて行うことにより、Ｘ値の制御は確実なものになる。これにより、従来の金型用鋼と比較して、鏡面仕上げ性に適した金型鋼とすることができた。 On the other hand, there are two methods of stirring molten steel: gas stirring, in which inert gas is introduced from the bottom of the ladle, and electromagnetic stirring. The ratio of gas stirring power to electromagnetic stirring power is determined as an operating condition based on the shape of the ladle and the amount of molten steel. The gas agitating force changes and increases even with the same amount of gas as the degree of vacuum increases due to degassing, so control is required. By analyzing the amount and composition of inclusions remaining in the product, the present inventors examined the state of slag entrainment during the primary refining that could not be removed even in the secondary refining, reviewed the conventional operating conditions, and conducted electromagnetic stirring. was found to be the optimum condition range with . The stirring power was controlled within a range that was sufficient to promote the reaction and not excessive, to prevent slag entrainment during primary refining, to reduce the amount of inclusions to achieve high cleanliness, and to control the X value. . Since the slag component and its viscosity affect the composition of inclusions and the ease with which slag is involved, controlling the slag component together ensures the control of the X value. As a result, compared with conventional mold steel, mold steel suitable for mirror finish could be obtained.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　この鋼材から、鏡面仕上げ性評価試験片と介在物評価試験片を採取した。鏡面仕上げ性評価試験片は鍛伸方向に対して垂直に、縦５０ｍｍ、横５０ｍｍを試験面（厚さ１５ｍｍ）として採取し、粗加工を実施した後、各試験片を１０００～１１００℃の温度で焼入し、５００～６００℃の温度で高温焼戻しを行い、硬さが４８～５４ＨＲＣになるように調質して、仕上加工を実施した。この５０×５０ｍｍの試験面を砥石＃600で研磨した後、＃400～＃1500まで研磨紙で研磨し、６～１μｍのダイヤモンド砥粒を使用して、＃14000の超鏡面まで磨いて、目視にて鏡面観察を行った。この鏡面観察は実際に＃14000の超鏡面プラスチック金型を製造している仕上加工者が判定した。 Specimens for evaluating mirror-finishability and specimens for evaluating inclusions were taken from this steel material. The mirror-finishability evaluation test piece was taken perpendicular to the forging direction, 50 mm long and 50 mm wide as a test surface (thickness 15 mm), and after performing rough processing, each test piece was subjected to a temperature of 1000 to 1100 ° C. It was quenched at a temperature of 500 to 600° C., subjected to high temperature tempering at a temperature of 500 to 600° C., tempered so that the hardness became 48 to 54 HRC, and finished. After polishing this 50 x 50 mm test surface with a #600 whetstone, it is polished with abrasive paper from #400 to #1500, and then polished to a super mirror surface of #14000 using diamond abrasive grains of 6 to 1 μm. A mirror observation was carried out at . This specular observation was determined by a finisher who actually manufactures #14000 ultra-specular plastic molds.
　介在物評価試験片は、鏡面仕上げ性評価試験片と同じ位置で同じ方向を試験面として、縦２０ｍｍ×横２０ｍｍ（厚さ１５ｍｍ）の大きさのものを採取し、粗加工を実施した後、１０００～１１００℃の温度で焼入処理した。その後、測定面を研磨紙で#80から＃1500まで段階的に磨き、６μｍ～１μｍのダイヤモンド砥粒を使用して、＃14000の超鏡面まで磨いた。試験片に存在する非金属介在物の調査は、試験片をＳＥＭ（走査型電子顕微鏡）－ＥＤＸ（エネルギー分散型Ｘ線分析）と粒子解析をすることによって行った。分析領域は介在物の面積で７０％程度が入る領域とした。 The inclusion evaluation test piece is a 20 mm long x 20 mm wide (15 mm thick) sample with the same position and direction as the test piece for the mirror finish evaluation test piece. It was quenched at a temperature of 1000-1100°C. After that, the surface to be measured was polished step by step from #80 to #1500 with abrasive paper, and polished to a super mirror surface of #14000 using diamond abrasive grains of 6 μm to 1 μm. Investigation of non-metallic inclusions present in the test pieces was carried out by subjecting the test pieces to SEM (scanning electron microscope)-EDX (energy dispersive X-ray analysis) and particle analysis. The analysis area was set to include about 70% of the area of inclusions.
　非金属介在物の評価は以下の手順で実施した。先ず、１００倍の観察視野で、２次電子像を求めた。このとき、コントラストによって基地が灰色、非金属介在物が黒色になるように撮影した。次いで、視野内の黒色の部分が円相当径で３μｍ以上の粒子に対して、図３に示すように、断面積の約７０％の領域をＥＤＸにて組成分析した。図３の円形に近い黒色部分が非金属介在物の断面であり、この黒色部分内に点在する点は、ＥＤＸ（エネルギー分散型Ｘ線分析）で分析した部分を示している。得られた粒子から、非金属介在物以外のホコリ及び研磨傷等のノイズを組成フィルターによって除去した。ノイズを除去して得られた粒子から全非金属介在物の面積率を得た。また、Ａｌ，Ｍｇ，Ｃａのいずれかが２％以上の非金属介在物に対して、Ｘ値を算出し、Ｘ値＜０．３の個数密度（＝検出個数/解析面積）とＸ値≧０．３の個数密度を求めた。 　The evaluation of non-metallic inclusions was carried out according to the following procedure. First, a secondary electron image was obtained with an observation field of view of 100 times magnification. At this time, the images were taken so that the base was gray and the non-metallic inclusions were black due to the contrast. Next, as shown in FIG. 3, about 70% of the cross-sectional area of the particles whose black portion in the field of view has an equivalent circle diameter of 3 μm or more was subjected to composition analysis by EDX. The nearly circular black portion in FIG. 3 is the cross section of the non-metallic inclusion, and the points scattered within this black portion indicate the portions analyzed by EDX (energy dispersive X-ray analysis). Noise such as dust other than non-metallic inclusions and polishing scratches was removed from the obtained particles by a composition filter. The area ratio of all non-metallic inclusions was obtained from the particles obtained by removing noise. In addition, the X value is calculated for nonmetallic inclusions in which any of Al, Mg, and Ca is 2% or more, and the number density of X value < 0.3 (= detected number / analysis area) and X value ≥ A number density of 0.3 was obtained.
　その結果、非金属介在物の測定結果は、下記表２に示すようになった。表２に示す鏡面仕上げ性は、仕上げた金型表面を、十分に明るい照明の下で種々の角度に傾けて、面の反射具合を目視で確認し、有害なピンホールによる鏡面性の低下がある場合は、「×」、鏡面性の低下がない場合は、「○」とした。金型のワーク面の鏡面性評価は、金型を使用して加工された製品の表面の見栄えで最終的に判定される。実際の製品表面での評価は、製品の合否である。しかし、製品不良を発生させる評価は実生産の効率とコストに悪影響を及ぼすため、金型を使用してみての評価は現実的ではない。そこで、製品加工に使用する金型表面を研磨加工する加工者が、経験上から金型ワーク面全体を官能評価して判断することになる。具体的には、金型ワーク面全体を対象として、仕上鏡面を官能評価し、鏡面性を低下させるピンホールが単数又は複数存在する箇所がある場合は、加工者がそれを見つけ出して、その金型を再研磨して新生面を出し、ワーク面全体で超鏡面が得られるまで、再研磨加工することとなる。また、鏡面仕上げ性が劣る材料の場合は、使用不可と判断される場合もある。このピンホールの大きさ及び出現頻度は、金型ワーク面全体で広く評価されるため、部分的な表面粗さ及び反射率等のデータでは不十分である。そこで、加工者の官能評価による判断で、介在物起因で再研磨加工が必要となるものを×、再研磨せずに超鏡面が得られたものを〇（合格）とした。 As a result, the measurement results of non-metallic inclusions are shown in Table 2 below. The mirror-finishability shown in Table 2 was evaluated by tilting the finished mold surface at various angles under sufficiently bright lighting and visually confirming the degree of reflection on the surface. When there was no decrease in specularity, it was rated as "B". The specularity evaluation of the workpiece surface of the mold is finally determined by the appearance of the surface of the product processed using the mold. Evaluation on the actual product surface is acceptance/failure of the product. However, since evaluation that causes product defects adversely affects the efficiency and cost of actual production, evaluation by using a mold is not realistic. Therefore, the operator who polishes the surface of the mold to be used for product processing makes a judgment by sensory evaluation of the entire surface of the mold work based on experience. Specifically, sensory evaluation of the finished mirror surface is performed on the entire mold work surface, and if there is a single or multiple pinholes that reduce the specularity, the processor finds it and The die is regrinded to create a new surface, and regrinding is performed until a super-mirror surface is obtained over the entire work surface. Also, in the case of a material with poor mirror finish, it may be judged that it cannot be used. Since the size and appearance frequency of the pinholes are widely evaluated over the entire surface of the mold workpiece, data such as partial surface roughness and reflectance are insufficient. Therefore, based on the sensory evaluation by the processor, those that required regrinding due to inclusions were rated as x, and those that obtained an ultra-mirror surface without regrinding were rated as ◯ (accepted).
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　この表２に示すように、円相当径８．０μｍ以上の非金属介在物の面積率が０．０００１６％以下であり、Ｘ値が０．３未満の介在物の個数密度が８．０個／１００ｍｍ２未満であり、Ｘ値が０．３以上の介在物の個数密度が３．０個／１００ｍｍ２未満である実施例の場合は、鏡面仕上げ性が優れた金型用鋼が得られた。一方、上記要素のいずれか１個でも本発明の範囲から外れる比較例の場合は、鏡面仕上げ性が劣るものであった。 As shown in Table 2, the area ratio of nonmetallic inclusions having an equivalent circle diameter of 8.0 μm or more is 0.00016% or less, and the number density of inclusions having an X value of less than 0.3 is 8.0. /100 mm 2 , and the number density of inclusions with an X value of 0.3 or more is less than 3.0/100 mm 2 , mold steel with excellent mirror finish is obtained. rice field. On the other hand, in the case of the comparative examples in which even one of the above elements is outside the scope of the present invention, the mirror-finishability was inferior.
　本発明によれば、金型表面の超鏡面仕上げが容易となるので、そのような金型による成形加工が必要なプラスチック製品の表面の超鏡面を得るのに有益である。 According to the present invention, it is possible to easily super-mirror-finish the mold surface, so it is useful for obtaining super-mirror-finished surfaces of plastic products that require molding with such a mold.

Claims (2)

  1. Ｃ：０．２０～０．５０質量％、
    Ｓｉ：０．１０～１．５０質量％、
    Ｍｎ：０．１０～０．７０質量％、
    Ｃｒ：１０．５～２０．０質量％、
    Ｎｉ：１．００質量％以下、
    Ｍｏ：０．０５～１．００質量％、
    Ｖ：０．０１～１．００質量％
    を含有し、
    残部Ｆｅ及び不可避的不純物からなる組成を有し、
    前記不可避的不純物のうち、下記成分は、
    Ａｌ：０．００７～０．０３５質量％、
    Ｓ：０．００２０質量％以下、
    Ｏ：０．００１５質量％以下、
    Ｃａ：０．００２０質量％以下、
    Ｍｇ：０．００２０質量％以下
    に規制され、
    鋼材断面において、円相当径８．０μｍ以上の非金属介在物の面積率は０．０００１６％以下であり、
    円相当径が５．０μｍ以上の非金属介在物であって、Ａｌ、Ｍｇ及びＣａからなる群から選択されたいずれかの成分を２質量％以上含有するものが、
    ［Ｃａ］、［Ｍｇ］、［Ａｌ］を夫々Ｃａ、Ｍｇ、Ａｌの含有量（質量％）とし、Ｘ＝［Ｃａ］／（［Ｍｇ］＋［Ａｌ］）としたとき、
    Ｘ値が０．３未満の介在物の個数密度が０．６０個／１００ｍｍ２以上かつ８．０個／１００ｍｍ２未満であると共に、
    Ｘ値が０．３以上の介在物の個数密度が３．０個／１００ｍｍ２未満であることを特徴とする鏡面仕上げ性に優れた金型用鋼。     C: 0.20 to 0.50% by mass,
    Si: 0.10 to 1.50% by mass,
    Mn: 0.10 to 0.70% by mass,
    Cr: 10.5 to 20.0% by mass,
    Ni: 1.00% by mass or less,
    Mo: 0.05 to 1.00% by mass,
    V: 0.01 to 1.00% by mass
    contains
    Having a composition consisting of the balance Fe and unavoidable impurities,
    Among the unavoidable impurities, the following components are
    Al: 0.007 to 0.035% by mass,
    S: 0.0020% by mass or less,
    O: 0.0015% by mass or less,
    Ca: 0.0020% by mass or less,
    Mg: regulated to 0.0020% by mass or less,
    In the cross section of the steel material, the area ratio of non-metallic inclusions having an equivalent circle diameter of 8.0 μm or more is 0.00016% or less,
    Nonmetallic inclusions having an equivalent circle diameter of 5.0 μm or more and containing 2% by mass or more of any component selected from the group consisting of Al, Mg and Ca,
    When [Ca], [Mg], and [Al] are the contents (% by mass) of Ca, Mg, and Al, respectively, and X = [Ca] / ([Mg] + [Al]),
    The number density of inclusions with an X value of less than 0.3 is 0.60/100 mm 2 or more and less than 8.0/100 mm 2 ,
    A die steel excellent in mirror finish, characterized in that the number density of inclusions having an X value of 0.3 or more is less than 3.0 pieces/100 mm 2 .
  2. 更に、Ｗを、Ｍｏ＋１／２Ｗ：０．０５～１．００質量％の範囲で含有することを特徴とする請求項１に記載の鏡面仕上げ性に優れた金型用鋼。 2. The die steel excellent in mirror finish according to claim 1, further comprising W in the range of Mo+1/2W: 0.05 to 1.00% by mass.
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JPH08100223A (en) * 1994-10-03 1996-04-16 Hitachi Metals Ltd Production of high cleanliness steel
JP2007009321A (en) * 2005-06-02 2007-01-18 Daido Steel Co Ltd Steel for plastic molding die
JP2015045071A (en) * 2013-08-29 2015-03-12 山陽特殊製鋼株式会社 Steel for anticorrosive plastic molding die excellent in specularity
JP2015168850A (en) * 2014-03-06 2015-09-28 日本高周波鋼業株式会社 Steel for high mirror surface plastic mold
JP2017171983A (en) * 2016-03-23 2017-09-28 株式会社神戸製鋼所 Method for reducing coarse inclusion by lf treatment

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CN113355598A (en) * 2021-05-24 2021-09-07 如皋市宏茂重型锻压有限公司 High-grade mirror surface gum die steel and manufacturing process thereof

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Publication number Priority date Publication date Assignee Title
JPH08100223A (en) * 1994-10-03 1996-04-16 Hitachi Metals Ltd Production of high cleanliness steel
JP2007009321A (en) * 2005-06-02 2007-01-18 Daido Steel Co Ltd Steel for plastic molding die
JP2015045071A (en) * 2013-08-29 2015-03-12 山陽特殊製鋼株式会社 Steel for anticorrosive plastic molding die excellent in specularity
JP2015168850A (en) * 2014-03-06 2015-09-28 日本高周波鋼業株式会社 Steel for high mirror surface plastic mold
JP2017171983A (en) * 2016-03-23 2017-09-28 株式会社神戸製鋼所 Method for reducing coarse inclusion by lf treatment

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