JP4327051B2 - Steel for plastic molds with excellent specularity - Google Patents
Steel for plastic molds with excellent specularity Download PDFInfo
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- JP4327051B2 JP4327051B2 JP2004260508A JP2004260508A JP4327051B2 JP 4327051 B2 JP4327051 B2 JP 4327051B2 JP 2004260508 A JP2004260508 A JP 2004260508A JP 2004260508 A JP2004260508 A JP 2004260508A JP 4327051 B2 JP4327051 B2 JP 4327051B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 20
- 239000010959 steel Substances 0.000 title claims description 19
- 229920003023 plastic Polymers 0.000 title claims description 17
- 238000007619 statistical method Methods 0.000 claims description 9
- 229910001214 P-type tool steel Inorganic materials 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 2
- 238000003483 aging Methods 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 150000004767 nitrides Chemical class 0.000 description 6
- 238000011156 evaluation Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 230000002411 adverse Effects 0.000 description 4
- 230000032683 aging Effects 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 229910017767 Cu—Al Inorganic materials 0.000 description 3
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000004881 precipitation hardening Methods 0.000 description 3
- 230000001105 regulatory effect Effects 0.000 description 3
- 238000005336 cracking Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 150000003568 thioethers Chemical class 0.000 description 2
- 229910000760 Hardened steel Inorganic materials 0.000 description 1
- -1 S 3 Chemical class 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 238000009863 impact test Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
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- Moulds For Moulding Plastics Or The Like (AREA)
Description
本発明は、耐割れ性、鏡面性に優れたプラスチック金型用鋼に関するものである。 The present invention relates to a steel for plastic molds excellent in crack resistance and specularity.
従来、プラスチック部品およびプラスチック製品成形用の金型は、自動車部品を始め、事務機器部品、精密機械部品、電気部品、光学機器部品などに到るまで、種々の部品、製品を製造するために、鏡面加工が加えられ、使用されている。特に光学レンズや注射器などの医療機器等の透明なプラスチック製品などは、それらの表面は極めて平滑な表面肌が求められている。従って、その形成に用いる金型用鋼は高度な鏡面仕上げ性が要求されている。 Conventionally, molds for molding plastic parts and plastic products are used to manufacture various parts and products from automobile parts to office equipment parts, precision machine parts, electrical parts, optical equipment parts, etc. Mirror finish is added and used. In particular, transparent plastic products such as optical lenses and syringes are required to have an extremely smooth surface. Therefore, the mold steel used for the formation is required to have a high degree of mirror finish.
また、最近、プラスチック成形用金型用鋼においても多品種少量生産の傾向があると同時に、全体の費用に占める金型製作費の比率上昇に伴い、金型製作の簡便化、切削工具の寿命延長による低コスト化、高精密化等の厳しい条件が求められるようになって来ているのが実情である。このような技術背景のもとに、一方で硬さ４０ＨＲＣ前後で使用されるプラスチック金型用鋼は、鏡面性および被削性などが必要とされる。 Recently, plastic mold metal has a tendency to produce a variety of products in small quantities, and at the same time, the mold production cost has become simpler as the ratio of mold production costs to the total cost has increased. The actual situation is that strict conditions such as cost reduction and high precision by extension have been demanded. On the other hand, the steel for plastic molds used at a hardness of around 40 HRC is required to have specularity, machinability and the like based on such a technical background.
また、近年では、複雑な金型形状に加工されるため、耐割れ性も要求される場合が多くなっている。この耐割れ性の向上に対しては、組織を変化させるか、硬度を下げるなどの対策が採られているが、しかしながら、組織を変化させる場合は特殊な熱処理が必要となる。さらに、硬度を下げた場合には、介在物によるピットが発生し易くなるため、鏡面性が低下するという問題がある。そのため、３５ＨＲＣ前後で使用した場合でも通常の４０ＨＲＣクラスと同等の鏡面性が確保できるプラスチック金型用鋼が望まれてきた。 In recent years, cracking resistance is often required because it is processed into a complicated mold shape. To improve the cracking resistance, measures such as changing the structure or lowering the hardness are taken. However, when the structure is changed, a special heat treatment is required. Further, when the hardness is lowered, pits due to inclusions are likely to occur, and there is a problem that the specularity is lowered. For this reason, there has been a demand for plastic mold steel that can ensure the same specularity as that of the normal 40HRC class even when used at around 35HRC.
上記した背景のもとに、例えば、特開昭６０−６７６４１号公報（特許文献１）に開示されているように、Ｎｉ−Ｃｕ−Ａｌ系析出硬化鋼で、鏡面性に悪影響を及ぼすＡｌ2 Ｓ3 等の硫化物を低減するため、Ｓを０．０１５％以下としている。また、特開２０００−２９７３５３号公報（特許文献２）に開示されているように、Ｎｉ−Ｃｕ−Ａｌ系析出硬化鋼で、耐食性のためＣｒが添加されている。また、鏡面性に悪影響を及ぼす酸化物、窒化物を低減するため、Ｎを０．０２％以下、Ｏを０．００３％以下に規制している。 Based on the above background, for example, as disclosed in Japanese Patent Application Laid-Open No. 60-67641 (Patent Document 1), Ni 2 -Cu—Al precipitation hardening steel is an Al 2 that adversely affects the specularity. In order to reduce sulfides such as S 3 , S is set to 0.015% or less. Further, as disclosed in Japanese Patent Application Laid-Open No. 2000-297353 (Patent Document 2), Ni—Cu—Al based precipitation hardened steel is added with Cr for corrosion resistance. In order to reduce oxides and nitrides that adversely affect the specularity, N is restricted to 0.02% or less and O is restricted to 0.003% or less.
さらに、特開２００４−５９９９３号公報（特許文献３）に開示されているように、Ｎｉ−Ｃｕ−Ａｌ系析出硬化鋼で、被削性のためにＢが添加されている。また、鏡面性に悪影響を及ぼす硫化物、酸化物、窒化物を低減するため、Ｓを０．００２％以下、Ｏを０．００１５％以下、Ｎを０．０１％以下に規制している。 Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 2004-59993 (Patent Document 3), B is added for machinability in Ni—Cu—Al precipitation hardening steel. In order to reduce sulfides, oxides and nitrides that adversely affect the specularity, S is regulated to 0.002% or less, O is regulated to 0.0015% or less, and N is regulated to 0.01% or less.
上述した特許文献１での鋼材では、４０ＨＲＣで使用されるため、硬さを３５ＨＲＣ前後に下げた場合に特に問題となるＡｌＮなどの硬質窒化物については何らの考慮もされていない。また、特許文献２での鋼材では、３８〜４５ＨＲＣで使用されるため、硬さを３５ＨＲＣ前後に下げた場合に特に問題となるＡｌＮの大きさについては何らの考慮もされていない。さらに、特許文献３での鋼材では、４０ＨＲＣで使用され、本発明で課題としたＡｌＮの大きさについては何らの考慮もされていない。 Since the steel material in Patent Document 1 described above is used at 40 HRC, no consideration is given to hard nitrides such as AlN that are particularly problematic when the hardness is lowered to around 35 HRC. In addition, since the steel material of Patent Document 2 is used at 38 to 45 HRC, no consideration is given to the size of AlN that is a particular problem when the hardness is lowered to around 35 HRC. Furthermore, in the steel material of patent document 3, it is used by 40HRC, and no consideration is given to the size of AlN which is a problem in the present invention.
上述したような問題を解消するために、発明者らは鋭意開発を進めた結果、鏡面仕上げ性と耐割れ性を兼備し、３０〜４２ＨＲＣの範囲で、特に３５ＨＲＣ前後で鏡面加工しても介在物起因によるピットで鏡面性が低下せず、４０ＨＲＣクラスと同等の鏡面性が確保できるプラスチック金型用鋼を提供するものである。その発明の要旨とするところは、
（１）質量％で、Ｃ：０．０５〜０．２０％、Ｓｉ：０．１〜２．０％、Ｍｎ：０．５〜２．５％、Ｎｉ：２．０〜４．０％、Ｃｕ：０．５〜２．０％、Ａｌ：０．５〜２．０％、Ｔｉ／Ｎ：０．１〜１．０、Ｏ：２０ｐｐｍ以下、Ｎ：１５０ｐｐｍ以下、Ｓ：０．００５％以下、残部Ｆｅおよび不可避的不純物からなることを特徴とする鏡面性に優れたプラスチック金型用鋼。
（２）硬さ３０〜４２ＨＲＣで、ＡｌＮ介在物の大きさが極値統計法（√ＡＲＥＡmax ）により推定をしたときに５０μｍ以下であることを特徴とする前記（１）に記載の鏡面性に優れたプラスチック金型用鋼にある。
In order to solve the above-mentioned problems, the inventors have intensively developed, and as a result, have both mirror finish and crack resistance, and even in the case of mirror finishing in the range of 30 to 42 HRC, especially around 35 HRC. The object of the present invention is to provide a steel for plastic molds in which the mirror surface property does not deteriorate due to a pit caused by an object and the mirror surface property equivalent to that of the 40HRC class can be secured. The gist of the invention is that
(1) By mass%, C: 0.05 to 0.20%, Si: 0.1 to 2.0%, Mn: 0.5 to 2.5%, Ni: 2.0 to 4.0% Cu: 0.5-2.0%, Al: 0.5-2.0%, Ti / N: 0.1-1.0, O: 20 ppm or less, N: 150 ppm or less, S: 0.005 % For plastic molds excellent in specularity, characterized by comprising not more than%, the balance Fe and inevitable impurities.
(2) The specularity according to (1) above, wherein the hardness is 30 to 42 HRC and the size of the AlN inclusion is 50 μm or less when estimated by an extreme value statistical method (√AREA max ). Excellent in plastic mold steel.
以上述べたように、本発明はＴｉを添加し、粗大ＡｌＮの生成を抑制するために、Ｎを１５０ｐｐｍ以下とし、Ｔｉ／Ｎ：０．１〜１．０とすること、さらに加えて、ＡｌＮの大きさを限定することで、耐割れ性、鏡面仕上げ性に優れた優れたプラスチック金型用鋼によりコストダウンを図ることを可能とした鋼にある。 As described above, in the present invention, in order to suppress the formation of coarse AlN by adding Ti, N is made 150 ppm or less, Ti / N: 0.1 to 1.0, and in addition, AlN By limiting the size of the steel, it is a steel that enables cost reduction by excellent plastic mold steel with excellent crack resistance and mirror finish.
以下、本発明に係る耐割れ性、鏡面仕上げ性に優れたプラスチック金型用鋼の化学成分の組成範囲限定理由について説明する。
Ｃ：０．０５〜０．２０％
Ｃは、硬さおよび焼入れ性を確保するために必要が元素である。その効果を有効に得るためには０．０５％必要である。しかし、過剰に添加した場合には、被削性を低下させ、加えて時効硬化後の靱性および溶接性を低下させるので、その上限を０．２０％とする。好ましくは０．０８〜０．１５％とする。
Hereinafter, the reason for limiting the composition range of the chemical component of the plastic mold steel excellent in crack resistance and mirror finish according to the present invention will be described.
C: 0.05-0.20%
C is an element necessary to ensure hardness and hardenability. In order to obtain the effect effectively, 0.05% is necessary. However, if added excessively, the machinability is lowered, and additionally the toughness and weldability after age hardening are lowered, so the upper limit is made 0.20%. Preferably it is 0.08 to 0.15%.
Ｓｉ：０．１〜２．０％
Ｓｉは、溶製時の脱酸剤として必要不可欠な元素である。そのためには、０．１％が必要であるが、しかし、多すぎると時効硬化後の靱性を低下させるので、その上限を２．０％とする。好ましくは１．０％以下とする。
Ｍｎ：０．５〜２．５％
Ｍｎは、Ｓｉと同様に、溶製時の脱酸剤としての元素である。そのためには、０．５％が必要であるが、しかし、多すぎると被削性および時効硬化後の靱性を低下させるので、その上限を２．５％とする。好ましくは１．０〜２．０％とする。
Si: 0.1 to 2.0%
Si is an indispensable element as a deoxidizer during melting. For that purpose, 0.1% is necessary. However, if it is too much, the toughness after age hardening is lowered, so the upper limit is made 2.0%. Preferably it is 1.0% or less.
Mn: 0.5 to 2.5%
Mn, like Si, is an element as a deoxidizer during melting. For that purpose, 0.5% is necessary, but if it is too much, the machinability and the toughness after age hardening are lowered, so the upper limit is made 2.5%. Preferably it is 1.0 to 2.0%.
Ｎｉ：２．０〜４．０％
Ｎｉは、焼入れ性を高め、また、時効処理時に高硬度を得、さらに、プラスチック金型に必要な加工性を得るための靱性を確保させるために有効な元素である。そのためには２．０％の添加が必要である。しかし、多すぎると被削性を低下させるために、その上限を４．０％とする。好ましくは２．５〜３．５％とする。
Ni: 2.0-4.0%
Ni is an element effective for enhancing hardenability, obtaining high hardness during aging treatment, and ensuring toughness for obtaining workability necessary for a plastic mold. For that purpose, addition of 2.0% is necessary. However, if the amount is too large, the machinability is lowered, so the upper limit is made 4.0%. Preferably it is 2.5 to 3.5%.
Ｃｕ：０．５〜２．０％
Ｃｕは、微細析出による析出硬化をもたらす時効硬さを確保する有効な元素である。そのためには、０．５％の添加が必要である。しかし、多すぎる添加は熱間加工性を低下させるために、その上限を２．０％とする。好ましくは０．８〜１．２％とする。
Ａｌ：０．５〜２．０％
Ａｌは、時効硬さを確保する上で必須の元素である。そのためには、０．５％の添加が必要である。しかし、多すぎる添加は硬質介在物ＡｌＮを生成させ鏡面性を低下させるだけでなく、靱性を低下させるために、その上限を２．０％とする。好ましくは０．８〜１．５％とする。
Cu: 0.5 to 2.0%
Cu is an effective element that ensures aging hardness that causes precipitation hardening due to fine precipitation. For that purpose, addition of 0.5% is necessary. However, too much addition decreases the hot workability, so the upper limit is made 2.0%. Preferably it is 0.8 to 1.2%.
Al: 0.5 to 2.0%
Al is an essential element for securing aging hardness. For that purpose, addition of 0.5% is necessary. However, too much addition generates not only hard inclusions AlN and lowers the specularity but also lowers the toughness, so the upper limit is made 2.0%. Preferably it is 0.8 to 1.5%.
Ｔｉ／Ｎ：０．１〜１．０
Ｎは、硬質介在物ＡｌＮを生成し、鏡面仕上げ性を低下させるため、できるだけ低くすることが望ましいとされてきた。しかしながら、時効硬さを確保するため、Ａｌを多量に添加していることから、Ｎを低くするだけでは、粗大ＡｌＮの生成を確実に抑制することは困難である。また、Ｎを低くするには、製造上多大な労力を必要とし、製造コストの上昇を招くという問題点があった。そこで、本発明では、Ｎが一定量以下であれば、Ｔｉを利用することで、粗大ＡｌＮの生成を抑制できることを見出した。
Ｔｉ／Ｎは、本発明の最大の特徴とするＡｌＮを生成する前にＴｉ添加によって微細ＴｉＮを生成し、粗大ＡｌＮ生成の抑制を図るものである。そのためには、Ｔｉ／Ｎを０．１以上とする必要がある。一方、Ｔｉ／Ｎが１．０を超えると粗大ＴｉＮが生成し、鏡面性に悪影響を及ぼすことから、その範囲を０．１〜１．０とする。好ましくは０．３〜０．８とする。なお、Ｔｉの添加は１０〜５０ｐｐｍとすることが好ましい。
Ti / N: 0.1 to 1.0
N has been considered desirable to be as low as possible in order to produce hard inclusions AlN and reduce the mirror finish. However, since a large amount of Al is added to ensure aging hardness, it is difficult to reliably suppress the formation of coarse AlN only by reducing N. Further, in order to reduce N, there is a problem in that a great deal of labor is required in production, leading to an increase in production cost. Therefore, in the present invention, it has been found that when N is a certain amount or less, the use of Ti can suppress the formation of coarse AlN.
Ti / N is intended to suppress the formation of coarse AlN by producing fine TiN by adding Ti before producing AlN, which is the greatest feature of the present invention. For that purpose, Ti / N needs to be 0.1 or more. On the other hand, when Ti / N exceeds 1.0, coarse TiN is generated and adversely affects the specularity, so the range is set to 0.1 to 1.0. Preferably it is 0.3-0.8. In addition, it is preferable that addition of Ti shall be 10-50 ppm.
Ｏ：２０ｐｐｍ以下
Ｏは、本発明に係る鏡面仕上げ性に優れたプラスチック成形金型用鋼を得るために、その溶製時に２０ｐｐｍ以下とすることが必要となる。これを超えると鏡面仕上げ性が低下するためである。好ましくは１２ｐｐｍ以下とする。
Ｎ：１５０ｐｐｍ以下
Ｎは、Ａｌと窒化物を生成し、オーステナイト粒を微細化し、均一な組織が得られるが、硬質介在物ＡｌＮを生成し易く、鏡面仕上げ性を低下させるため、少ない方が望ましい。しかし、単にＮ量を減らすだけでは粗大ＡｌＮの生成抑制に対する効果は小さく、Ｔｉを利用し、Ｔｉ／Ｎで一定範囲内とすることで粗大ＡｌＮの抑制が可能である。しかし、Ｎが多すぎるとＴｉ添加の効果も無く硬質の粗大な窒化物を生成し、鏡面仕上げ性の低下を招くこととなるため、１５０ｐｐｍ以下とする。好ましくは１００ｐｐｍ以下とする。
O: 20 ppm or less O is required to be 20 ppm or less at the time of melting in order to obtain a steel for plastic molds having excellent mirror finish according to the present invention. This is because if it exceeds this, the mirror finish will be deteriorated. Preferably it is 12 ppm or less.
N: 150 ppm or less N produces Al and nitrides, austenite grains are refined and a uniform structure can be obtained, but it is easy to produce hard inclusions AlN and lowers the mirror finish, so less is desirable. . However, simply reducing the amount of N has little effect on suppressing the formation of coarse AlN, and the use of Ti and Ti / N within a certain range can suppress coarse AlN. However, if there is too much N, there is no effect of adding Ti, and a hard coarse nitride is produced, resulting in a decrease in mirror finish. Preferably it is 100 ppm or less.
Ｓ：０．００５％以下
Ｓは、Ｏと同様に、本発明に係る鏡面仕上げ性に優れたプラスチック成形金型用鋼を得るために、その溶製時に０．００５％以下とすることが必要となる。これを超えると鏡面仕上げ性が低下するためである。好ましくは０．００２％以下とする。
硬さ３０〜４２ＨＲＣ
硬さは、鏡面仕上げ性を確保するためであり、そのためには３０ＨＲＣ以上必要である。しかし、４２ＨＲＣを超えると被削性および耐割れ性が低下することから、その硬さを、３０〜４２ＨＲＣとする。
S: 0.005% or less S, like O, needs to be 0.005% or less at the time of melting in order to obtain a steel for plastic molds having excellent mirror finish according to the present invention. It becomes. This is because if it exceeds this, the mirror finish will be deteriorated. Preferably it is 0.002% or less.
Hardness 30-42HRC
The hardness is for ensuring the mirror finish, and for that purpose it needs 30 HRC or more. However, if it exceeds 42 HRC, the machinability and crack resistance deteriorate, so the hardness is set to 30 to 42 HRC.
ＡｌＮ介在物の大きさが極値統計法（√ＡＲＥＡmax ）により推定をしたときに５０μｍ以下
ＡｌＮ介在物の大きさが５０μｍを超えると、鏡面性を確保することが出来ない。従って、鏡面性を確保するためには、ＡｌＮ介在物の大きさが５０μｍ以下にする必要がある。ここで、極値統計法とは、ある母集団から複数個の試験片を採取し、個々の試験片に存在する最大介在物（硬質の介在物で、鏡面性および被削性に影響を及ぼす硫化物系介在物を除く非金属介在物）の大きさを測定し、それを極値確率紙にプロットすることにより、母集団あるいは任意の体積（面積）中に存在する最大の介在物の大きさ（√ＡＲＥＡmax ）を予測するものであり、他の介在物評価方法と同様に量産材の介在物評価に用いられており、特に今回の供試材においては、１視野の面積を１０ｍｍ×１０ｍｍとし、各供試材につき３０視野毎に介在物の測定を行ない予測面積を３００００ｍｍ2 として、極値統計法により最大介在物の大きさを推定したものである。
When the size of AlN inclusions is estimated by the extreme value statistical method (√AREA max ), if the size of AlN inclusions exceeds 50 μm, the specularity cannot be secured. Therefore, in order to ensure the specularity, the size of the AlN inclusions needs to be 50 μm or less. Here, the extreme value statistical method is a method in which a plurality of specimens are collected from a certain population, and the maximum inclusions (hard inclusions, which affect the specularity and machinability of each specimen). By measuring the size of non-metallic inclusions (excluding sulfide inclusions) and plotting it on extreme probability paper, the size of the largest inclusion in a population or any volume (area) (√AREA max ) is predicted, and is used for the evaluation of inclusions in mass-produced materials in the same way as other inclusion evaluation methods. Especially in this test material, the area of one field of view is 10 mm × Inclusions were measured for every 30 fields of view for each specimen, and the predicted area was 30000 mm 2 , and the size of the maximum inclusions was estimated by the extreme value statistical method.
本発明に係る耐割れ性、鏡面仕上げ性に優れたプラスチック金型用鋼において、極値統計法（√ＡＲＥＡmax ）により推定をしたときの最大のＡｌＮ硬質介在物の大きさが５０μｍ以下であることが必要となる。ここでＡｌＮ硬質介在物の大きさを５０μｍ以下としたのは、ＡｌＮ硬質介在物の大きさがこれ以上となると、鏡面仕上げ性が低下するためである。また、本発明に係るプラスチック金型用鋼は、圧延もしくは鍛造を行った後、８００〜１０００℃で溶体化処理および４５０〜６００℃での時効硬化処理を行ない、時効硬化を利用したプラスチック金型用鋼にある。 In the plastic mold steel excellent in crack resistance and mirror finish according to the present invention, the maximum AlN hard inclusion size is 50 μm or less when estimated by the extreme value statistical method (√AREA max ). It will be necessary. Here, the reason why the size of the AlN hard inclusions is set to 50 μm or less is that when the size of the AlN hard inclusions is more than this, the mirror finish is deteriorated. Moreover, the steel for plastic molds according to the present invention is a plastic mold using age hardening by performing solution treatment at 800 to 1000 ° C. and age hardening at 450 to 600 ° C. after rolling or forging. In steel.
以下、本発明について実施例によって具体的に説明する。
表１に示す化学成分組成を有するプラスチック成形金型用鋼を６０ｔ電気炉で溶解し、取鍋にてＮ2 ガス流入量を変化させて取鍋精錬を行ない、引続きＲＨ脱ガスした後インゴットに鋳造した鋳片を１３００℃に加熱し、角１００×１００×１００ｍｍに鍛伸し、８７０℃の温度にて焼鈍した後、９８０℃での溶体化処理を行ない、引続き５００〜６００℃に加熱した後、時効硬化処理し供試材を作成した。この供試材を熱処理後の硬さ、極値統計法（√ＡＲＥＡmax ）により推定されたＡｌＮ硬質介在物の大きさ、鏡面仕上げ性、およびシャルピー衝撃値による靱性特性を評価した。この結果を表２に示す。
Hereinafter, the present invention will be specifically described with reference to examples.
Steel for plastic molds having the chemical composition shown in Table 1 is melted in a 60-ton electric furnace, ladle refining is performed by changing the N 2 gas inflow rate in the ladle, and then RH is degassed before being ingot. The cast slab was heated to 1300 ° C., forged to 100 × 100 × 100 mm, annealed at a temperature of 870 ° C., then subjected to a solution treatment at 980 ° C., and subsequently heated to 500 to 600 ° C. Thereafter, age hardening treatment was performed to prepare a test material. The specimens were evaluated for hardness after heat treatment, size of AlN hard inclusions estimated by the extreme value statistical method (√AREA max ), mirror finish, and toughness characteristics by Charpy impact value. The results are shown in Table 2.
表２に示す硬質窒化物ＡｌＮの極値統計法による評価方法は、上述した方法により√ＡＲＥＡmax で表す。また、鏡面性評価方法は、自動研磨装置で研磨を行った後、鏡面加工面のピットの個数を計測し、ピット個数が特に少ないものから、
◎：優れる、○：良い、×劣る、の３段階で評価した。 さらに、耐割れ性評価としては、２ｍｍＵノッチシャルピー試験片を作製し、シャルピー衝撃試験により評価した。
The evaluation method by the extreme value statistical method of hard nitride AlN shown in Table 2 is represented by √ AREA max by the method described above. The specularity evaluation method measures the number of pits on the mirror-finished surface after polishing with an automatic polishing apparatus, and the number of pits is particularly small.
◎: Excellent, ○: Good, × Inferior in three levels. Furthermore, as evaluation of crack resistance, 2 mm U-notch Charpy test pieces were prepared and evaluated by Charpy impact test.
表２に示すＮｏ．１〜１１は、本発明例であり、Ｎｏ．１２〜１７は、比較例である。Ｎｏ．１２は表１に示すように、Ｔｉ／Ｎ比の値が大きいために、ＴｉＮ介在物によるピットが発生し鏡面仕上げ性が劣る。Ｎｏ．１３はＴｉ／Ｎ比の値が小さいために、√ＡＲＥＡmax の値が大きく、かつ鏡面仕上げ性が劣る。Ｎｏ．１４はＮ量が多いために√ＡＲＥＡmax の値が大きく、かつ鏡面仕上げ性が劣る。すなわち、粗大ＡｌＮの生成が見られた。 No. shown in Table 2 1 to 11 are examples of the present invention. 12 to 17 are comparative examples. No. As shown in Table 1, No. 12 has a large Ti / N ratio value, so that pits are generated due to inclusions of TiN, resulting in poor mirror finish. No. No. 13 has a small Ti / N ratio, so the value of √AREA max is large and the mirror finish is inferior. No. No. 14 has a large amount of N, so the value of √AREA max is large and the mirror finish is inferior. That is, generation of coarse AlN was observed.
Ｎｏ．１５は硬さ（ＨＲＣ）が大きいために、鏡面仕上げ性は優れているものの、シャルピー衝撃値が劣る。すなわち、耐割れ性が劣る。Ｎｏ．１６は硬さ（ＨＲＣ）が小さいために、鏡面仕上げ性が劣る。Ｎｏ．１７はＳ量が多いために、ＭｎＳ介在物によるピットが発生し鏡面仕上げ性が劣り、かつシャルピー衝撃値が劣る。これに対し、本発明例であるＮｏ．１〜１１はいずれの特性においても優れていることが判る。 No. Since No. 15 has high hardness (HRC), the mirror finish is excellent, but the Charpy impact value is inferior. That is, crack resistance is inferior. No. Since No. 16 has low hardness (HRC), the mirror finish is inferior. No. Since No. 17 has a large amount of S, pits due to MnS inclusions are generated, the mirror finish is inferior, and the Charpy impact value is inferior. On the other hand, No. which is an example of the present invention. It can be seen that 1 to 11 are excellent in any characteristics.
以上述べたように、耐割れ性を高めるため、硬さを３５ＨＲＣ程度まで下げると介在物によるピットが発生し易くなる。特に、ＡｌＮなどの硬質介在物はピットになり易くなる。これを極値統計法により、その大きさを制限することにより、鏡面性が確保出来、しかも、ＡｌＮの大きさは、ただＮを下げるだけでなく、ＴｉをＴｉ／Ｎ：０．１〜１．０の範囲で添加することにより、ＡｌＮの大きさを限定することが可能となり、耐割れ性、鏡面仕上げ性に優れたプラスチック金型用鋼を安価に製造することが出来るものである。
特許出願人 山陽特殊製鋼株式会社
代理人 弁理士 椎 名 彊
As described above, if the hardness is lowered to about 35 HRC in order to improve crack resistance, pits due to inclusions are likely to occur. In particular, hard inclusions such as AlN tend to become pits. By limiting the size of this by the extreme value statistical method, the specularity can be secured, and the size of AlN not only lowers N but also Ti is Ti / N: 0.1-1 By adding in the range of 0.0, it is possible to limit the size of AlN, and it is possible to produce a steel for plastic molds excellent in crack resistance and mirror finish at low cost.
Patent Applicant Sanyo Special Steel Co., Ltd.
Attorney Atsushi Shiina
Claims (2)
Ｃ：０．０５〜０．２０％、
Ｓｉ：０．１〜２．０％、
Ｍｎ：０．５〜２．５％、
Ｎｉ：２．０〜４．０％、
Ｃｕ：０．５〜２．０％、
Ａｌ：０．５〜２．０％、
Ｔｉ／Ｎ：０．１〜１．０、
Ｏ：２０ｐｐｍ以下、
Ｎ：１５０ｐｐｍ以下、
Ｓ：０．００５％以下、
残部Ｆｅおよび不可避的不純物からなることを特徴とする鏡面性に優れたプラスチック金型用鋼。 % By mass
C: 0.05-0.20%,
Si: 0.1 to 2.0%,
Mn: 0.5 to 2.5%
Ni: 2.0 to 4.0%,
Cu: 0.5 to 2.0%,
Al: 0.5 to 2.0%,
Ti / N: 0.1 to 1.0,
O: 20 ppm or less,
N: 150 ppm or less,
S: 0.005% or less,
A plastic mold steel excellent in specularity, characterized by comprising the balance Fe and inevitable impurities.
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| WO2008130054A1 (en) * | 2007-04-18 | 2008-10-30 | Nippon Steel Corporation | Hot-worked steel material having excellent machinability and impact value |
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