JP5213168B2 - Steel for plastic molding dies excellent in thermal conductivity and manufacturing method thereof - Google Patents
Steel for plastic molding dies excellent in thermal conductivity and manufacturing method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims description 44
- 239000010959 steel Substances 0.000 title claims description 44
- 238000004519 manufacturing process Methods 0.000 title claims description 9
- 238000010137 moulding (plastic) Methods 0.000 title claims description 6
- 238000005496 tempering Methods 0.000 claims description 18
- 239000000203 mixture Substances 0.000 claims description 11
- 229910001562 pearlite Inorganic materials 0.000 claims description 11
- 239000012535 impurity Substances 0.000 claims description 7
- 229910052757 nitrogen Inorganic materials 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 229910052760 oxygen Inorganic materials 0.000 claims description 5
- 229910052717 sulfur Inorganic materials 0.000 claims description 5
- 229910000859 α-Fe Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 4
- 229910052759 nickel Inorganic materials 0.000 claims description 4
- 230000001105 regulatory effect Effects 0.000 claims description 3
- 229910052720 vanadium Inorganic materials 0.000 claims description 3
- 230000009977 dual effect Effects 0.000 claims description 2
- 238000010438 heat treatment Methods 0.000 description 15
- 238000001816 cooling Methods 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 238000000034 method Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 6
- 238000010606 normalization Methods 0.000 description 6
- 238000012360 testing method Methods 0.000 description 5
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 238000005520 cutting process Methods 0.000 description 3
- 238000005242 forging Methods 0.000 description 3
- 238000005498 polishing Methods 0.000 description 3
- 239000002436 steel type Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- 238000007088 Archimedes method Methods 0.000 description 1
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
- 229910000760 Hardened steel Inorganic materials 0.000 description 1
- 229910001214 P-type tool steel Inorganic materials 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000010962 carbon steel Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000000113 differential scanning calorimetry Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
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- 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
Description
本発明は、熱伝導性に優れたプリハードンタイプのプラスチック成形金型用鋼およびその製造方法に関するものである。 The present invention having excellent thermal conductivity was pre HARDENED type plastic forming shapes die steel and a method for producing the same.
近年、家電をはじめ、自動車部品、ＯＡ機器など、多くの分野で製品のプラスチック化が進んでいる。プラスチック成形用金型材としては、安価な炭素鋼や低合金鋼が使用されており、その多くはプリハードン鋼として提供される。これはあらかじめ調質熱処理により所定の硬度に調整され、機械加工後に金型として使用されるものである。該金型は、溶融したプラスチックを冷却して成形する際には金型温度が上昇するが、熱伝導率が高い金型では成形サイクル時間を短縮でき、生産性の向上が期待できる。
これまでに高熱伝導率を目指す鋼としては、特許文献１および特許文献２に示される鋼がある。
特許文献１に示される鋼はＳｉ量を０．３％未満まで低減することで、熱伝導率を向上させている。また、特許文献２に示される鋼は熱伝導性に優れるフェライト組織を３０％以上とすることで、熱伝導率を向上させている。
In recent years, products are becoming plastic in many fields such as home appliances, automobile parts, and OA equipment. The plastic forming the shape mold material, inexpensive carbon steel or low alloy steel has been used, many of which are provided as a pre-hardened steel. This is adjusted in advance to a predetermined hardness by tempering heat treatment and used as a mold after machining. Mold is when the formed shape to cool the molten plastic mold temperature increases, the high mold thermal conductivity can be shortened formed shape cycle time, improvement of productivity can be expected.
As steels aiming at high thermal conductivity, there are steels shown in
The steel shown in
しかしながら、特許文献１に示される鋼は被削性とのバランスを考慮した成分設計となっており、熱伝導率に関しては十分なものとはいえない。特許文献２に示される鋼は、板厚２００ｍｍを超えるような大型の製品に関しては焼ならし後の冷却速度が遅いことから、プラスチック成形金型用鋼に必要な硬さを確保できないという問題点がある。
However, the steel shown in
本発明は、上記事情を背景としてなされたものであり、被削性を損なうことなく優れた熱伝導率を示し、さらにはプラスチック成形金型用鋼として良好な硬さを有するプラスチック成形金型用鋼およびその製造方法を提供することを目的とする。 The present invention has been made with the above circumstances as the background, it shows excellent thermal conductivity without sacrificing machinability, plastic forming shapes payments further has good hardness as a plastic forming shapes die steel An object of the present invention is to provide mold steel and a method for producing the same.
すなわち、本発明の熱伝導性に優れたプラスチック成形金型用鋼のうち、第１の本発明は、質量割合で、Ｃ：０．４５超〜０．６０％、Ｓｉ：０．０５〜０．２０％、Ｍｎ：０．３〜０．７％、Ｎｉ：０．２〜０．５％、Ｃｒ：０．２〜０．５％、Ｖ：０．０３〜０．１％、Ａｌ：０．０１〜０．０３％、Ｓ：０．０１０％未満、Ｏ：０．００３０％以下、Ｎ：０．０２％以下を含有し、残部がＦｅおよび不可避不純物からなり、かつ不可避不純物中でＰ：０．０１５％以下、Ｃｕ：０．３０％以下、Ｍｏ：０．２０％以下に規制した組成を有し、フェライト・パーライト二相組織からなり、４８Ｗ／ｍ・℃以上の熱伝導率を有することを特徴とする。 That is, among the steels for plastic molds excellent in thermal conductivity of the present invention, the first present invention is C: more than 0.45 to 0.60%, Si: 0.05 to 0 by mass ratio. 20%, Mn: 0.3-0.7%, Ni: 0.2-0.5%, Cr: 0.2-0.5%, V: 0.03-0.1%, Al: 0.01 to 0.03%, S: less than 0.010%, O: 0.0030 % or less, N: 0.02% or less, with the balance being Fe and inevitable impurities, and inevitable impurities P: 0.015% or less, Cu: 0.30% or less, Mo: having the composition was regulated to 0.20% or less, made of ferrite-pearlite dual phase structure, 48W / m · ° C. or higher thermal conductivity It is characterized by having.
第２の本発明の熱伝導性に優れたプラスチック成形金型用鋼は、前記第１の本発明において、焼戻し後の硬さが１８０〜２２０ＨＶであることを特徴とする。 Plastic molding die steel with good heat conductivity of the second present invention, in the first aspect of the present invention, hardness after tempering is characterized in that it is a 180～220HV.
第３の本発明の熱伝導性に優れたプラスチック成形金型用鋼の製造方法は、前記第１の本発明に示された組成を有する鋼を、９００℃〜１０５０℃に加熱してから空冷する焼ならしによってフェライト・パーライト二相組織とし、その後、５００℃〜６５０℃で加熱してから炉冷する焼戻しを行って、焼戻し後の硬さを１８０〜２２０ＨＶとすることを特徴とする。 According to a third aspect of the present invention, there is provided a method for producing a steel for a plastic mold having excellent thermal conductivity. The steel having the composition shown in the first aspect of the present invention is heated to 900 ° C. to 1050 ° C. and then air-cooled. It is characterized in that the ferrite-pearlite two-phase structure is formed by normalizing, and thereafter, tempering is performed by heating at 500 ° C. to 650 ° C. and then furnace cooling, and the hardness after tempering is set to 180 to 220 HV.
以下に、本発明で規定する組成、製造条件の限定理由について説明する。
先ず、本発明における成分限定理由を述べる。なお、各含有量はいずれも質量割合で示されている。
The reasons for limiting the composition and production conditions defined in the present invention will be described below.
First, the reasons for limiting the components in the present invention will be described. Each content is shown as a mass ratio.
Ｃ：０．４５超〜０．６０％
Ｃは焼入性を向上させる元素であり、目的の硬度を得るためにも０．４５％超の添加とする。また、多すぎると溶接が困難になるとともに、硬さが高くなり過ぎて被削性を低下させ、パーライト量の増加により熱伝導率も低下するので、０．６０％以下とする。なお、同様の理由で、上限を０．５５％とするのが望ましい。
C: Over 0.45 to 0.60%
C is an element that improves hardenability, and is added in an amount exceeding 0.45% in order to obtain the desired hardness. If the amount is too large, welding becomes difficult, the hardness becomes too high and the machinability is lowered, and the thermal conductivity is lowered due to the increase in the amount of pearlite, so the content is made 0.60% or less. For the same reason, it is desirable to set the upper limit to 0.55%.
Ｓｉ：０．０５〜０．２０％
Ｓｉは製鋼工程における脱酸剤として使われ、被削性を向上させる効果があることから、最低でも０．０５％の含有量が必要である。しかし、Ｓｉの添加は熱伝導率を低下させるため０．２０％以下とする。なお、同様の理由で、上限を０．１０％とするのが望ましい。
Si: 0.05-0.20%
Since Si is used as a deoxidizing agent in the steel making process and has an effect of improving machinability, a content of at least 0.05% is necessary. However, the addition of Si is 0.20% or less in order to reduce the thermal conductivity. For the same reason, it is desirable to set the upper limit to 0.10%.
Ｍｎ：０．３〜０．７％
Ｍｎは、焼入れ性を向上させ強度を高める効果があり、最低でも０．３％の含有量が必要である。一方、Ｓｉと同様に熱伝導率を低下させるため０．７％以下とする。
Mn: 0.3 to 0.7%
Mn has the effect of improving the hardenability and increasing the strength, and a content of 0.3% is required at the minimum. On the other hand, in order to reduce thermal conductivity like Si, it is made 0.7% or less.
Ｎｉ：０．２〜０．５％、Ｃｒ：０．２〜０．５％
Ｎｉ、Ｃｒはそれぞれ金型の焼入れ性を高め、硬さ、靱性を向上させるのに有効である。本鋼種では熱伝導率を向上させるためＳｉ、Ｍｎを低く抑えており、不足する強度を補うためにもＮｉは０．２％以上、Ｃｒは０．２％以上の添加が必要である。しかし、それぞれ上限値を越えて含有させても、鏡面性や被削性を低下させる要因となることから、各元素の上限値を、Ｎｉは０．５％、Ｃｒは０．５％とする。
Ni: 0.2-0.5%, Cr: 0.2-0.5%
Ni and Cr are effective in increasing the hardenability of the mold and improving the hardness and toughness, respectively. In this steel type, Si and Mn are kept low in order to improve the thermal conductivity. In order to compensate for the insufficient strength, it is necessary to add 0.2% or more of Ni and 0.2% or more of Cr. However, even if each content exceeds the upper limit value, it causes a reduction in specularity and machinability. Therefore, the upper limit value of each element is 0.5% for Ni and 0.5% for Cr. .
Ｓ：０．０１０％未満
Ｓは被削性を向上させる元素であるが、粗大な硫化物系介在物を形成した場合には研磨時のピンホール発生の原因となり鏡面性を低下させるので、０．０１０％未満とする。なお、同様の理由で、上限を０．００７％とするのが望ましい。しかし、少なすぎると被削性が悪化することから、下限を０．００１％にすることが望ましい。
S: Less than 0.010% S is an element that improves machinability. However, when coarse sulfide inclusions are formed, pinholes are generated during polishing and the specularity is reduced. Less than 010%. For the same reason, it is desirable to set the upper limit to 0.007%. However, if the amount is too small, the machinability deteriorates, so the lower limit is preferably made 0.001%.
Ｏ：０．００３０％以下、Ｎ：０．０２％以下
Ｏ、ＮはそれぞれＡｌ等と結合し非金属介在物を形成し、鏡面性に加えて被削性をも低下させるため、Ｏは０．００３０％以下、Ｎは０．０２％以下とする。なお、同様の理由で、Ｏの上限を０．００２０％、Ｎの上限を０．０１％とするのが望ましい。
O: 0.0030 % or less, N: 0.02% or less O and N are each bonded to Al or the like to form non-metallic inclusions and reduce the machinability in addition to the specularity. .0030% or less, and N is 0.02% or less. For the same reason, it is desirable that the upper limit of O is 0.0020% and the upper limit of N is 0.01%.
Ａｌ：０．０１〜０．０３％
Ａｌは脱酸剤として添加され、本鋼種では熱伝導率を向上させるためＳｉを低く抑えていることから、最低でも０．０１％の含有量が必要である。しかし、多すぎるとＡｌ２Ｏ３系介在物が鋼中に残留し被削性や鏡面性を悪化させる原因となるため、０．０３％以下とする。なお、同様の理由で、上限を０．０２％とするのが望ましい。
Al: 0.01-0.03%
Since Al is added as a deoxidizer and Si is kept low to improve the thermal conductivity in this steel type, a content of at least 0.01% is necessary. However, if it is too much, Al 2 O 3 inclusions remain in the steel and cause deterioration of machinability and specularity, so the content is made 0.03% or less. For the same reason, it is desirable to set the upper limit to 0.02%.
Ｖ：０．０３〜０．１％以下
Ｖは結晶粒の微細化に効果があり、焼戻し軟化抵抗を高める効果があることから、最低でも０．０３％の含有量が必要である。一方、多すぎると被削性及び靭性の低下を招くため０．１％以下とする。
V: 0.03 to 0.1% or less V has an effect of refining crystal grains and has an effect of increasing the temper softening resistance. Therefore, a content of 0.03% is required at a minimum. On the other hand, if the amount is too large, the machinability and toughness are reduced.
Ｐ：０．０１５％以下、Ｃｕ：０．３０％以下、Ｍｏ：０．２０％以下
Ｐは鋼の靱性を低下させるために極力低減する方がよく、０．０１５％以下とする。Ｃｕは硬さ確保に有効な元素であるが、多すぎると被削性を低下させるため不純物として扱い、０．３０％以下とする。Ｍｏは炭化物となり、熱伝導率および被削性を低下させる元素であることから０．２０％以下とする。なお、同様の理由で、Ｐの上限を０．００５％、Ｃｕの上限を０．２０％、Ｍｏの上限を０．１０％とするのが望ましい。
P: 0.015% or less, Cu: 0.30% or less, Mo: 0.20% or less P should be reduced as much as possible to reduce the toughness of the steel, and is 0.015% or less. Cu is an element effective for ensuring hardness, but if it is too much, it is treated as an impurity because it lowers machinability, and is 0.30% or less. Mo becomes a carbide and is an element that lowers thermal conductivity and machinability. For the same reason, it is desirable that the upper limit of P is 0.005%, the upper limit of Cu is 0.20%, and the upper limit of Mo is 0.10%.
焼ならし：９００〜１０５０℃加熱、空冷
上記組成の鋼に、９００〜１０５０℃で加熱後、空冷する焼ならしを行うことで、フェライト・パーライトの二相組織が得られる。ここで、加熱温度が９００℃未満であると、十分な硬さが得られない。一方、１０５０℃を超えると結晶粒が粗大化し靭性などが悪化する要因となる。
加熱後の冷却では、空冷（概ね冷却速度５０〜２００℃／時間）で行うことで、上記二相組織が得られる。冷却速度が過大になると、フェライト・パーライト二相組織が得られず、一方、冷却速度が過小になると、目的とする硬さを確保できない。
Normalization: Heating at 900 to 1050 ° C., air cooling The steel having the above composition is heated at 900 to 1050 ° C. and then air cooled to obtain a two-phase structure of ferrite and pearlite. Here, if the heating temperature is less than 900 ° C., sufficient hardness cannot be obtained. On the other hand, if it exceeds 1050 ° C., the crystal grains become coarse and the toughness and the like deteriorate.
In the cooling after the heating, the above two-phase structure can be obtained by air cooling (generally at a cooling rate of 50 to 200 ° C./hour). If the cooling rate is too high, a ferrite-pearlite two-phase structure cannot be obtained. On the other hand, if the cooling rate is too low, the desired hardness cannot be ensured.
焼戻し：５００〜６５０℃加熱、炉冷
上記焼ならし後、５００〜６５０℃での加熱、炉冷による焼戻しを行うことで、上記二相組織を有し、かつビッカース硬さで１８０〜２２０ＨＶの適度な硬さを有するプラスチック成形金型用鋼が得られる。
Tempering: 500 to 650 ° C. heating, furnace cooling After the above normalization, heating at 500 to 650 ° C. and tempering by furnace cooling have the above two-phase structure and a Vickers hardness of 180 to 220 HV. A steel for plastic molds having an appropriate hardness can be obtained.
以上説明したように、本発明の熱伝導性に優れたプラスチック成形金型用鋼によれば、質量割合で、Ｃ：０．４５超〜０．６０％、Ｓｉ：０．０５〜０．２０％、Ｍｎ：０．３〜０．７％、Ｎｉ：０．２〜０．５％、Ｃｒ：０．２〜０．５％、Ｖ：０．０３〜０．１％、Ａｌ：０．０１〜０．０３％、Ｓ：０．０１０％未満、Ｏ：０．００３０％以下、Ｎ：０．０２％以下を含有し、残部がＦｅおよび不可避不純物からなり、かつ不可避不純物中でＰ：０．０１５％以下、Ｃｕ：０．３０％以下、Ｍｏ：０．２０％以下に規制した組成を有し、フェライト・パーライト二相組織からなるので、被削性を損なうことなく優れた熱伝導率を有し、さらにはプラスチック成形金型用鋼として良好な硬さが得られる効果がある。すなわち高品質化とコスト削減に貢献する効果がある。 As described above, according to the steel for plastic molding die excellent in thermal conductivity of the present invention, by mass ratio, C: more than 0.45 to 0.60%, Si: 0.05 to 0.20. %, Mn: 0.3-0.7%, Ni: 0.2-0.5%, Cr: 0.2-0.5%, V: 0.03-0.1%, Al: 0. 01 to 0.03%, S: less than 0.010%, O: 0.0030 % or less, N: 0.02% or less, with the balance being Fe and inevitable impurities, and P: It has a composition regulated to 0.015% or less, Cu: 0.30% or less, and Mo: 0.20% or less, and is composed of a ferrite-pearlite two-phase structure, so it has excellent heat conduction without impairing machinability. Furthermore, there is an effect that good hardness can be obtained as steel for plastic molding dies. In other words, it has the effect of contributing to higher quality and cost reduction.
また、本発明の熱伝導性に優れたプラスチック成形金型用鋼の製造方法は、前記本発明に示された組成を有する鋼を、９００℃〜１０５０℃に加熱してから空冷する焼ならしによってフェライト・パーライト二相組織とし、その後、５００℃〜６５０℃で加熱してから炉冷する焼戻しを行って、焼戻し後の硬さを１８０〜２２０ＨＶとするので、被削性、熱伝導率、硬さが良好なプラスチック成形金型用鋼を確実に得られる効果がある。 Further, the method for producing a steel for a plastic mold having excellent thermal conductivity according to the present invention is a normalization in which the steel having the composition shown in the present invention is heated to 900 ° C. to 1050 ° C. and then air-cooled. Thus, a ferrite-pearlite two-phase structure is formed, and then tempering is performed by heating at 500 ° C. to 650 ° C. and then furnace cooling, and the hardness after tempering is 180 to 220 HV. Therefore, machinability, thermal conductivity, hardness is reliably obtain the effect of good plastic forming shapes die steel.
本発明のプラスチック成形金型用鋼は、常法により溶製することができる。Ｓ、Ｏ、Ｎなどを規制する製法としては、真空溶解法、電気炉溶解法、取鍋精錬法、エレクトロスラグ再溶解法などがあるが、本発明では、これらの製法を適宜採用することで、所定の組成に調整する。
溶製により得られる鋼塊は、必要に応じて鍛造等の加工を行い、さらに熱処理を行う。鍛造等の加工は常法により行うことができる。ただし、熱処理においては、焼ならし、焼戻しにより行うものとし、それぞれの条件を適正に定めるのが望ましい。
焼ならしに際しては、９００℃〜１０５０℃に加熱してから空冷するのが最適である。これにより、フェライトとパーライトとが混在する二相組織が確実に得られる。
The steel for plastic molds of the present invention can be melted by a conventional method. Production methods that regulate S, O, N, etc. include vacuum melting method, electric furnace melting method, ladle refining method, electroslag remelting method, etc., but in the present invention, these manufacturing methods can be appropriately adopted. , Adjusted to a predetermined composition.
The steel ingot obtained by melting is subjected to processing such as forging as necessary and further subjected to heat treatment. Processing such as forging can be performed by a conventional method. However, the heat treatment is performed by normalization and tempering, and it is desirable to appropriately determine the respective conditions.
When normalizing, it is optimal to heat to 900 ° C. to 1050 ° C. and then air cool. This ensures a two-phase structure in which ferrite and pearlite are mixed.
上記焼ならし後に、適正な焼戻しを行うことで、所望の硬さが得られる。該焼戻しの条件としては、５００℃〜６５０℃で加熱してから炉冷するのが最適である。該焼戻しによって１８０〜２２０ＨＶという、プリハードンタイプのプラスチック成形金型鋼として適度な硬さを得ることができる。
このプリハードン金型用鋼は、必要に応じて切削加工、鏡面研磨が行われる。切削加工においては、良好な被削性を示し、切削加工を円滑かつ高品質に行うことができる。また、鏡面研磨によっては、優れた鏡面性を示す。
A desired hardness can be obtained by performing appropriate tempering after the above normalization. As the tempering condition, it is optimal to heat at 500 ° C. to 650 ° C. and then cool in the furnace. By the tempering, an appropriate hardness of 180 to 220 HV as a pre-hardened type plastic mold steel can be obtained.
This pre-hardened mold steel is subjected to cutting and mirror polishing as necessary. In cutting, good machinability is exhibited, and cutting can be performed smoothly and with high quality. In addition, excellent mirror surface properties are exhibited by mirror polishing.
以下に、本発明の実施例を従来材と比較して説明する。表１に各供試材の化学成分（残部：Ｆｅおよびその他の不純物）を示す。供試材としては、本発明の成分範囲になる発明鋼と、本発明の成分範囲を外れた比較鋼とを用意した。 Examples of the present invention will be described below in comparison with conventional materials. Table 1 shows chemical components (remainder: Fe and other impurities) of each test material. As test materials, an inventive steel that falls within the component range of the present invention and a comparative steel that deviates from the component range of the present invention were prepared.
上記各供試材の成分となるように調整し、真空誘導溶解法（ＶＩＭ法）により溶製した２０ｋｇおよび５０ｋｇ鋼塊を、１１００℃〜１３００まで加熱して熱間鍛造を行い、幅１３０ｍｍ、厚さ３０ｍｍの鍛造板を製作した。供試材のミクロ組織はすべてフェライト・パーライト組織とし、比較鋼１〜５については所定の硬さ（１８０〜２２０ＨＶ）を得るために８８０℃の焼鈍を施し、焼鈍では硬さの確保が難しい本発明鋼および比較鋼６、比較鋼７については、８８０℃〜１０２０℃加熱、空冷の焼ならし、及び５８０℃加熱、炉冷の焼戻しを施した。
20 kg and 50 kg steel ingots prepared by vacuum induction melting method (VIM method) were adjusted to be components of each of the above test materials, heated to 1100 ° C. to 1300 to perform hot forging, width 130 mm, A forged plate having a thickness of 30 mm was produced. The microstructures of the test materials are all ferrite and pearlite structures, and
本鋼種においては、焼ならし一焼戻し熱処理における硬さはほぼ焼ならし条件により決定され、焼戻しは大型部材における残留応力除去などを目的とするものである。このように製作した各供試材より熱伝導率試験片を採取し、熱伝導率測定を行った。熱伝導率は以下の式で表され、密度はアルキメデス法により求め、比熱はセイコーインスツルメンツ製ＤＳＣ２２０Ｃを用いて示差走査熱量（ＤＳＣ）法により求め、熱拡散率はアルバック理工製ＴＣ７０００を用いてレーザーフラッシュ法により求めた。 In this steel type, the hardness in the normalizing and tempering heat treatment is almost determined by the normalizing conditions, and the tempering is intended for the purpose of removing the residual stress in the large member. A thermal conductivity test piece was collected from each sample material thus manufactured, and the thermal conductivity was measured. The thermal conductivity is represented by the following formula, the density is determined by the Archimedes method, the specific heat is determined by a differential scanning calorimetry (DSC) method using a DSC220C manufactured by Seiko Instruments, and the thermal diffusivity is measured by a laser flash using a TC7000 manufactured by ULVAC-RIKO. Obtained by law.
熱伝導率（Ｗ／ｍ・Ｋ）＝密度（ｋｇ／ｍ３）×比熱（Ｊ／ｋｇ・Ｋ）×熱拡散率（ｍ２／ｓ） Thermal conductivity (W / m · K) = density (kg / m 3 ) × specific heat (J / kg · K) × thermal diffusivity (m 2 / s)
表２に本発明鋼と比較鋼の熱処理条件と硬さおよび熱伝導率を示す。また、図１にＳｉ量と熱伝導率の関係を、図２にＭｎ量と熱伝導率の関係を示す。これら成分と熱伝導率との間には、ほぼ比例関係が認められる。本発明鋼はＳｉおよびＭｎを低減することで熱伝導率を向上させており、化学組成が本発明で規定する範囲を外れている比較鋼１〜６に比べて、熱伝導率が４８Ｗ／ｍ・℃以上と優れている。また、熱処理条件を焼ならし−焼戻しとすることでプラスチック成形金型用鋼に必要な硬さを確保しており、化学組成が本発明で規定する範囲を外れている比較鋼７では硬さが本発明の目標値（１８０〜２２０ＨＶ）を満足できないという結果が得られた。
Table 2 shows the heat treatment conditions, hardness and thermal conductivity of the inventive steel and the comparative steel. FIG. 1 shows the relationship between the amount of Si and the thermal conductivity, and FIG. 2 shows the relationship between the amount of Mn and the thermal conductivity. There is a nearly proportional relationship between these components and thermal conductivity. The steel of the present invention is improved in thermal conductivity by reducing Si and Mn, and the thermal conductivity is 48 W / m as compared with
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