JP2005220439A - Die with superior formability into mirror plane, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a die for improving the formability of a component into a mirror plane, and to provide a manufacturing method therefor. <P>SOLUTION: The die for forming a plastic or glass component is made of a stainless steel including, by mass%, 0.15% or less C, 6.0-12.0% Cr, 0.003% or less S and 1.5-5.0% Si. The stainless steel preferably further includes, by mass%, one or more elements among 0.05-3.0% Mn, 4.0-10.0% Ni, 0.2-8.0% Mo, 6.0% or less Cu, 5.0% or less Nb, 8.0% or less Ta, 2.0% or less Al, 3.0% or less Ti and 20.0% or less Co. The method for manufacturing the die comprises producing the stainless steel by a consumable-electrode-type remelting method, tempering it into a hardness of 56 HRC or higher, and machining the forming surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention improves the mirror surface properties of stainless steel having excellent corrosion resistance, and is particularly suitable for mirror molding of plastic and glass parts that require extremely high surface accuracy, such as optical disks and optical lenses, It relates to the manufacturing method.

  Conventionally, in the field of optical disk resin molding such as CD and DVD media, the field of resin or glass molding for optical lenses, and the field of resin molding for optical components such as liquid crystal light guide plates, SUS420J2 of JIS steel grade or similar stainless steel is used. Cutting and grinding molds were used. In cases where extremely high accuracy is required, such as plastic optical parts, amorphous steel such as Ni-P is applied to the SUS420J2 equivalent steel, and then the surface is finished by cutting with a diamond tool. In some cases, copper alloys with few impurities were similarly cut and finished.

On the other hand, as a material for achieving both corrosion resistance and hardness, for example, C is 0.08% by mass (hereinafter referred to as%) or less, and Si is included in 2.0 to 5.0% and Cr is included in 6.0 to 10.0%. Precipitation hardening stainless steel has been proposed. An improved steel aiming at achieving high hardness by adding an appropriate amount of Mn, Ni, Mo, Cu, Nb, Ta, Ti, Co to this stainless steel has been proposed (Patent Document 1). . This improved steel is an excellent material in terms of both high hardness and high corrosion resistance.
JP 2001-107194 A

  Of the molds for molding optical disks and optical parts described above, those made of SUS420J2 are advantageous in that a certain level can be obtained in terms of corrosion resistance and high hardness, but the achieved hardness is limited to 55 HRC at most. There is a problem that the mirror surface is not sufficiently maintained when the molding shots are overlapped. A material to which Ni-P plating or a copper alloy is applied has a lower hardness, which is disadvantageous for long-term stable forming.

  Further, the corrosion resistance of the SUS420J2 level is not sufficient for long-term mass production in the case of a mold for optical disc molding that requires water cooling. Furthermore, since SUS420J2 is accompanied by micron-order chromium carbide precipitation in the structure, there is also a problem that it is difficult to obtain a strict smooth mirror surface on the molding surface. This problem becomes a big problem when putting the next generation high density optical disk aiming at the average surface roughness of the sub-nano order into practical use.

  The object of the present invention is to solve the above-mentioned problems of the super-mirror finish of SUS420J2 in a special mold field for molding plastic or glass parts that require extremely high surface accuracy, and further, SUS420J2 An object of the present invention is to provide a mold having the above-mentioned corrosion resistance and high hardness, and having excellent mirror formability, and a method for producing the same.

  As a result of examining the above problems, the present inventor has found such a special mold material that requires corrosion resistance, high hardness, and a molding surface having a very smooth mirror surface that is unmatched in other mold applications. It was found that stainless steel to which an optimum amount of Si was added was optimum. And while finding the component composition that can achieve a hardness of 56 HRC or higher, tempering the hardness, and performing machining such as cutting or grinding / polishing or lapping to form a molding surface, the molding It has been found that the super-mirror finish of the surface and the mirror surface maintenance during molding can be greatly improved. And, it was found that this stainless steel is optimal for the mold of the present invention to be obtained by a consumable electrode type remelting method, and the present invention has been reached.

  That is, the present invention is a mold for molding a plastic or glass part, and in mass%, C: 0.15% or less, Cr: 6.0 to 12.0%, S: 0.003% or less. Yes, it is made of stainless steel containing Si: 1.5 to 5.0%, and is a mold excellent in mirror formability. Preferably, the stainless steel is Mn: 0.05 to 3.0%, Ni: 4.0 to 10.0%, Mo: 0.2 to 8.0%, Cu: 6.0 by mass%. % Or less, Nb: 5.0% or less, Ta: 8.0% or less, Al: 2.0% or less, Ti: 3.0% or less, Co: 20.0% or less It is the metal mold | die excellent in the mirror surface moldability characterized by including the above. More preferably, the mold is excellent in mirror formability, characterized in that the molding surface has a hardness of 56 HRC or more.

  And the manufacturing method of the metal mold | die of this invention is a manufacturing method of the metal mold | die for shape | molding a plastic or glass component, Comprising: By mass% obtained by performing a consumable electrode type remelting method, C: 0.00 Stainless steel containing 15% or less, Cr: 6.0 to 12.0%, S: 0.003% or less, and containing Si: 1.5 to 5.0% to a hardness of 56 HRC or more In addition, the present invention is a method for producing a mold excellent in mirror formability, characterized in that it is machined to form a molding surface.

  According to the present invention, it is possible to drastically improve the super mirror finish and mirror surface maintainability of a mold having excellent corrosion resistance, and long-term stability of plastic or glass parts that require extremely high surface accuracy such as optical disks and optical lenses. This technology is indispensable for the practical application of molding.

  As described above, an important feature of the present invention is a stainless steel to which an optimum amount of Si is added in addition to excellent corrosion resistance, and a mold that has also reviewed the types and optimum amounts of other constituent elements. By doing so, the high hardness of the molding surface, the super mirror finish, and the mirror surface maintenance during molding can be greatly improved, and furthermore, an optimum manufacturing method for this stainless steel has been found.

  First, the component composition of the present invention will be described. By defining C to be 0.15% or less, the precipitation size of hard carbides in the mold structure can be suppressed to the submicron order, and super-mirror finish can be realized. Preferably it is 0.08% or less. Cr is an indispensable component for ensuring the corrosion resistance of stainless steel, and in the case of the mold application of the present invention, the corrosion resistance is insufficient at less than 6.0%. However, if it exceeds 12.0%, it becomes difficult to obtain a predetermined hardness, desirably a hardness of 56 HRC or higher. Therefore, Cr is set to 6.0 to 12.0%.

  Si is a main element that gives strength to the mold of the present invention. And it is a basic element for realizing the mirror finish that is important for the mold application of the present invention. In other words, an excellent mirror finish is obtained by increasing the temper softening resistance of the matrix and achieving a high hardness during high-temperature tempering without relying on a precipitation strengthening mechanism by conventional fine carbides. If it is less than 1.5%, the effect is insufficient, but if it exceeds 5.0%, the toughness is adversely affected. Therefore, in the present invention, it is defined as 1.5 to 5.0%. Preferably it is 2.0% or more.

  Since S forms a soft compound with Mn and adversely affects the super mirror finish, it is still an important main element for the present invention. In the present invention, the mirror finish is achieved by limiting the content to 0.003% or less.

  Next, a specific component composition suitable for this application is shown as a desirable component composition for the above-mentioned stainless steel. Mn acts as a deoxidizer for steel and is preferably contained in an amount of 0.05% or more. However, if it is too much, the amount of austenite in the mold structure increases excessively and it becomes difficult to obtain a predetermined hardness. Therefore, Mn is preferably 0.05 to 3.0%. Ni imparts corrosion resistance to the steel and makes the phase transformation of the steel desirable due to the balance with Cr, that is, the desired property for transformation from the austenite single phase to the low carbon martensite single phase during solution heat treatment cooling. 4.0% or more is preferable. However, if it exceeds 10.0%, the amount of austenite increases too much and it becomes difficult to obtain a predetermined hardness. Therefore, Ni is preferably 4.0 to 10.0%.

  Mo is one of the main elements contributing to age hardening during solidification and tempering (quenching and tempering) by solid solution and aging treatment as well as improving corrosion resistance. When the above effect is obtained, the effect is insufficient if it is less than 0.2%, but even if added over 8.0%, the effect on the characteristics is low, so Mo is 0.2% to It is preferable to set it to 8.0%. More desirably, it is 2.0% or less. Cu is a main element that contributes to precipitation hardening during aging, and also improves corrosion resistance. However, if it exceeds 6.0%, hot workability is impaired, so Cu is desirably 6.0% or less. In addition, in order to provide 56 HRC or more, which is particularly desirable tempering hardness for the present invention, addition of Cu is preferable, and addition of 3.0% or more is effective.

  Nb has the effect of increasing the aging hardness of stainless steel, but if it exceeds 5.0%, the hot workability is adversely affected. Therefore, even if added or contained, Nb is preferably 5.0% or less. More desirably, it is 0.5% or less. Ta, like Nb, has the effect of increasing the aging hardness of stainless steel, but if it exceeds 8.0%, the hot workability is adversely affected. Therefore, even if added or contained, it is preferably 8.0% or less. . Al and Ti are also elements that contribute to precipitation hardening, but if Al exceeds 2.0%, and if Ti exceeds 3.0%, the toughness decreases, so Al is 2.0%. Hereinafter, Ti is desirably adjusted to 3.0% or less. More preferably, Ti is 2.0% or less.

  Co is an important element that contributes to an increase in hardness when the mold is used by strengthening the solid solution of the matrix in addition to improving the corrosion resistance. However, if it exceeds 20.0%, the machinability (cutting, grinding, lapping workability) is impaired, so even if it is added, it is desirable to make it 20.0% or less.

  The metal mold | die of this invention consists of stainless steel which satisfy | fills such a component composition, Comprising: The remainder can be made into steel substantially made of Fe. For example, other than the above-mentioned element types, Fe and other elements are stainless steel with a total of 10% or less and 5% or less, and the balance is stainless steel composed of Fe and inevitable impurities. Excellent corrosion resistance and high hardness , And can achieve mirror formability and maintainability.

  Further, as described above, the mold of the present invention has an important feature in that a molding surface having a hardness of 56 HRC or more is adopted and achieved. Hardness of 56HRC or higher on the molding surface makes it difficult to scratch during rough polishing of mirror polishing, facilitates mirror finishing, and at the same time improves mirror surface maintenance during molding. In order to achieve such high hardness, the composition of the stainless steel is an important factor.

  And in addition to the component composition of the stainless steel which comprises the metal mold | die of this invention, it is desirable that it is what was obtained by the consumable electrode type remelting method, for example. That is, stainless steel obtained by performing a consumable electrode type remelting method such as a vacuum arc remelting method (VAR) or an electroslag remelting method (ESR) is used for mirror finishing. Non-metallic inclusions such as alumina that cause pinholes are reduced, and more stable super mirror finish can be realized. The consumable electrode type remelting method may be performed once or a plurality of times, and the steel ingot obtained thereby may be hot-worked by forging or rolling.

  First, a steel ingot obtained by the vacuum arc remelting method was hot-worked to prepare a sample composed of the remaining Fe and unavoidable impurities of the chemical components shown in Table 1. And these samples were heat-treated and tempered to a predetermined hardness. The heat treatment conditions and hardness are shown in Table 2.

  Then, the tempered samples were subjected to mirror surface processing under the mirror polishing conditions applied to the molding surface processing of the optical disk mold, and the processed surfaces were evaluated. Table 3 shows the measurement results of nonmetallic inclusions in each sample before processing.

  FIG. 1 and Table 4 show the results of mirror finishing of the present invention and conventional steel, which are obtained from the profile of the machined surface. From the mirror height profile, it can be seen that the conventional steel SUS420J2-based sample has many fine irregularities, but the present invention has few. This convex portion indicates the presence of hard carbides and other hard compounds. Therefore, according to the present invention, it is easy to obtain an ultra-smooth mirror surface on the mold molding surface, so that the surface of the molded product can suppress irregular reflection. Thus, a mold suitable for molding a high-density optical disk, an optical lens, or an optical component can be obtained.

  The mold of the present invention having a high degree of corrosion resistance and high hardness is a so-called super engineering plastic molding die such as PPS resin containing a reinforcing agent such as glass fiber that requires similar characteristics in addition to an optical disk and an optical lens. It can also be applied as a mold.

It is a surface profile of stainless steel after mirror finishing, and is a diagram showing an example of the effect of the present invention.

Claims (4)

A mold for molding a plastic or glass part, wherein C: 0.15% or less, Cr: 6.0 to 12.0%, S: 0.003% or less in terms of mass%, Si: 1 A mold excellent in mirror formability, characterized by comprising stainless steel containing 5 to 5.0%. Stainless steel has a mass% of Mn: 0.05 to 3.0%, Ni: 4.0 to 10.0%, Mo: 0.2 to 8.0%, Cu: 6.0% or less, Nb: Including one or more of 5.0% or less, Ta: 8.0% or less, Al: 2.0% or less, Ti: 3.0% or less, Co: 20.0% or less 2. The mold having excellent mirror formability according to claim 1. The mold having excellent mirror surface moldability according to claim 1 or 2, wherein the molding surface has a hardness of 56 HRC or more. A method for producing a mold for molding a plastic or glass part, obtained by performing a consumable electrode type remelting method, C: 0.15% or less, Cr: 6.0-12. Stainless steel containing 0%, S: 0.003% or less and containing Si: 1.5-5.0% is tempered to a hardness of 56HRC or more, and machined to form a molded surface. A method for producing a mold excellent in mirror formability, characterized by: