JP6566841B2 - High toughness plastic mold steel with excellent machinability and mirror finish - Google Patents
High toughness plastic mold steel with excellent machinability and mirror finish Download PDFInfo
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本発明はプラスチックの射出成形、圧縮成形、トランスファ成形など、各種の成形の金型として用いられるプラスチック成形金型用鋼に関する。 The present invention relates to a steel for plastic molds used as molds for various moldings such as plastic injection molding, compression molding and transfer molding.
自動車の内装やバンパー等に用いられるプラスチック部材の成型に用いられる金型には２５〜３５ＨＲＣの硬さが必要とされることから、ＪＩＳ ＳＣＭ４４０あるいはＡＩＳＩのＴｙｐｅのＰ２０などの中炭素鋼のプリハードン鋼が用いられている。これらの金型には、一般的な硬さや靭性などの機械的特性に加え、プラスチック製品の意匠性や機能性を持たせるためのシボ加工性が求められる。しかし、中炭素鋼は硬さや靭性はあるものの、ＣやＭｏが多く含まれているために偏析がきつく、被削性を悪化させると共に、鏡面加工性を低下させ、また、シボ加工を行ったときにシボムラを発生させる原因となる。さらに、被削性を向上させるために、Ｓを多量に添加する方法があるが、靭性や鏡面加工性が低下する場合がある。 Pre-hardened steel of medium carbon steel such as JIS SCM440 or AISI Type P20, because the mold used for molding plastic parts used in automobile interiors, bumpers, etc. requires hardness of 25-35 HRC. Is used. In addition to mechanical properties such as general hardness and toughness, these molds are required to have a texture processing property to impart design and functionality of plastic products. However, although medium carbon steel has hardness and toughness, segregation is severe because it contains a large amount of C and Mo, machinability is deteriorated, mirror surface workability is deteriorated, and texture processing is performed. It sometimes causes graininess. Furthermore, in order to improve machinability, there is a method of adding a large amount of S, but the toughness and mirror surface workability may be lowered.
従来の技術として、被削性に優れたプラスチック成型金型用の開発鋼が提案されている（例えば、特許文献１参照。）。この開発鋼はＣａＯの含有量が８〜６２質量％の酸化物系介在物が芯となり、その周囲を１．０質量％以上のＣａを含有する硫化物系介在物が取り囲んだ二重構造介在物であり、硫化物系介在物の占有面積が視野面積３．５ｍｍ2当たり２．０×１０-4ｍｍ2以上である介在物を含有する鋼である。この提案の鋼は、Ｖ量が多いために成分偏析が生じやすく、偏析部と非偏析部の硬さの違いから、鏡面加工時にうねりが生じることがあった。さらに、硫化物のアスペクト比が大きい個所では、被削性が低下してしまい、常に優れた被削性であるとは言えなかった。 As a conventional technique, developed steel for plastic molding dies having excellent machinability has been proposed (for example, see Patent Document 1). This developed steel has a double structure inclusion in which the oxide inclusions with CaO content of 8 to 62% by mass are the core, and the sulfide inclusions containing 1.0% by mass or more of Ca are surrounded. are those, a steel containing sulfide inclusions inclusions occupation area is field area 3.5 mm 2 per 2.0 × 10 -4 mm 2 or more. In this proposed steel, component segregation is likely to occur because of the large amount of V, and undulation may occur during mirror processing due to the difference in hardness between the segregated part and the non-segregated part. Furthermore, at places where the aspect ratio of the sulfide is large, the machinability deteriorates, and it cannot be said that the machinability is always excellent.
また、極めて優れた被切削性を有し、かつ優れた研磨仕上性および耐摩耗性を兼備し、主としてプラスチック成形に使用される金型用鋼が提案されている（例えば、特許文献２参照。）。しかし、この提案の鋼も特許文献１の鋼と同様に、Ｍｏ量が多いために成分偏析が生じやすく、鏡面加工時にうねりが生じることがあった。さらに、硫化物の分布がばらついていたり、またアスペクト比が大きい硫化物があったりすることで、常に優れた被削性であるとは言えなかった。 Further, a steel for molds that has extremely excellent machinability and has excellent polishing finish and wear resistance and is mainly used for plastic molding has been proposed (see, for example, Patent Document 2). ). However, this proposed steel, like the steel of Patent Document 1, has a large amount of Mo, so component segregation is likely to occur, and undulation may occur during mirror finishing. Furthermore, it cannot be said that the machinability is always excellent due to the distribution of sulfides and the presence of sulfides with a large aspect ratio.
本発明が解決しようとする課題は、被削性に優れ、また鏡面加工性にも優れた高靭性プラスチック成形金型用鋼の提供することである。 The problem to be solved by the present invention is to provide a steel for a high toughness plastic molding die which is excellent in machinability and excellent in mirror surface workability.
上述したような先行技術の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、請求項に示す合金成分範囲、硫化物面積率、硫化物中のＣａ量、硫化物中のＣｒ量および硫化物中の（Ｃａ＋Ｃｒ）量、硫化物の単位面積あたりに占める個数、５０μｍ2以上の面積を有する硫化物の個数割合、およびアスペクト比を制限することで、被削性および鏡面加工性に優れた高靭性のプラスチック成形金型用の鋼が得られることを見出した。 In order to solve the problems of the prior art as described above, the inventors have made extensive developments, and as a result, the alloy component range, the sulfide area ratio, the Ca content in the sulfide, and the Cr in the sulfide are shown in the claims. By limiting the amount and the amount of (Ca + Cr) in the sulfide, the number of sulfides per unit area, the number ratio of sulfides with an area of 50 μm 2 or more, and the aspect ratio, machinability and mirror finish It has been found that a steel having a high toughness and excellent for plastic molding dies can be obtained.
そこで、上記の課題を解決するための本発明の手段では、第１の手段は、質量％で、Ｃ：０．１２〜０．３０％、Ｓｉ：０．２６〜０．３７％、Ｍｎ：１．１０〜１．８０％、Ｓ：０．００５〜０．０５０％、Ｃｒ：１．３５〜２．９０％、Ｍｏ：０．１０〜０．２４％、Ｖ：０．０１〜０．０４％、Ｎ：≦０．０１８０％、Ａｌ：≦０．０２５％を含有し、残部Ｆｅおよび不可避不純物からなる鋼である。かつ、これら鋼中に含有される硫化物中に占めるＣａ、Ｃｒの割合は、Ｃａ：≦５．０％、Ｃｒ：≦２５．０％、かつ（Ｃａ＋Ｃｒ）≦２８．０％で、これら鋼中に含有される硫化物の面積率：０．０５〜０．２０％で、１ｍｍ2当たりの硫化物の個数：≧９個で、全硫化物の個数の中で５０μｍ2以上の面積を有する硫化物の個数の割合は：２〜４２％で、さらに硫化物の平均アスペクト比：≦９であり、被削性および鏡面加工性に優れた高靭性のプラスチック成形金型用鋼である。 Therefore, in the means of the present invention for solving the above problems, the first means is mass%, C: 0.12 to 0.30%, Si: 0.26 to 0.37%, Mn: 1.10 to 1.80%, S: 0.005 to 0.050%, Cr: 1.35 to 2.90%, Mo: 0.10 to 0.24%, V: 0.01 to 0.8. This steel contains 04%, N: ≦ 0.0180%, Al: ≦ 0.025%, and is composed of the remaining Fe and inevitable impurities. And the ratio of Ca and Cr in the sulfide contained in these steels is Ca: ≦ 5.0%, Cr: ≦ 25.0%, and (Ca + Cr) ≦ 28.0%. The area ratio of the sulfide contained therein: 0.05 to 0.20%, the number of sulfides per mm 2 : ≧ 9, and the area of 50 μm 2 or more in the total number of sulfides The ratio of the number of sulfides is 2 to 42%, and the average aspect ratio of sulfide is ≦ 9, and it is a high toughness plastic molding die steel excellent in machinability and mirror surface workability.
本願発明の金型鋼は、請求項に記載の化学成分を含有し、かつ、その鋼に含有の、硫化物中のＣａ量、Ｃｒ量および（Ｃａ＋Ｃｒ）量、ならびに硫化物の面積率、１ｍｍ2当たりの硫化物の個数、５０μｍ2以上の面積を有する硫化物の個数の割合、硫化物の平均アスペクト比が請求項に規定する範囲とすることにより、このプラスチック成形金型用鋼は自動車の内装やバンパー等に用いられるプラスチック部材の射出成形や圧縮成形やトランスファ成形などのプラスチック成形において優れた靱性、被削性および鏡面加工性を有して加工することできる鋼となっている。 The mold steel of the present invention contains the chemical components described in the claims, and the Ca content, the Cr content and the (Ca + Cr) content in the sulfide, and the sulfide area ratio, 1 mm 2. By making the number of sulfides per unit, the ratio of the number of sulfides having an area of 50 μm 2 or more, and the average aspect ratio of sulfides within the ranges specified in the claims, this plastic molding steel is used for automobile interiors. Steel that can be machined with excellent toughness, machinability and mirror finish in plastic molding such as injection molding, compression molding and transfer molding of plastic members used for bumpers and the like.
発明を実施するための形態の記載に先立って、本願の請求項に係る鋼の構成要件である各化学成分の含有される限定理由および該鋼中に含有される硫化物の各特性の限定理由について記載する。なお、化学成分における％は質量％である。 Prior to the description of the mode for carrying out the invention, the reason for limitation of each chemical component which is a constituent element of the steel according to the claims of the present application and the reason for limitation of each characteristic of sulfide contained in the steel Is described. In addition,% in a chemical component is the mass%.
Ｃ：０．１２〜０．３０％
Ｃは、鋼中に硬質炭化物を形成し、鋼の硬さおよび耐摩耗性を向上させるとともに焼入性を高める元素である。これらの効果を得るためには、Ｃは０．１２％以上が含有される必要がある。一方、Ｃは０．３０％より多く鋼中に含有されると、粗大な炭化物を形成して、靱性を悪化し、さらに鏡面加工性を悪化し、また、鋼中に偏析帯を形成しやすく、シボムラが発生する要因となる。そこで、Ｃは０．１２〜０．３０％とする。
C: 0.12-0.30%
C is an element that forms hard carbides in the steel, improves the hardness and wear resistance of the steel, and enhances the hardenability. In order to obtain these effects, C needs to be contained by 0.12% or more. On the other hand, when C is contained in the steel in an amount of more than 0.30%, coarse carbides are formed, the toughness is deteriorated, the mirror workability is further deteriorated, and the segregation band is easily formed in the steel. This is a factor that causes graininess. Therefore, C is set to 0.12 to 0.30%.
Ｓｉ：０．２６〜０．３７％
Ｓｉは、精錬時の脱酸剤であり、さらに鋼の硬さを得るために必要な元素である。このためには、Ｓｉは０．２６％以上含有される必要がある。一方、Ｓｉは０．３７％より多いと、鋼の靱性が悪化する。そこで、Ｓｉは０．２６〜０．３７％とする。
Si: 0.26-0.37%
Si is a deoxidizer at the time of refining, and is an element necessary for obtaining the hardness of steel. For this purpose, Si needs to be contained by 0.26% or more. On the other hand, if the Si content exceeds 0.37%, the toughness of the steel deteriorates. Therefore, Si is 0.26 to 0.37%.
Ｍｎ：１．１０〜１．８０％
Ｍｎは、精錬時の脱酸剤であり、さらに鋼の焼入性を得るために必要な元素であり、また、硫化物を形成して鋼の被削性を向上させる元素である。これらの効果を得るためには、Ｍｎは１．１０％以上を含有する必要がある。一方、Ｍｎは１．８０％より多く鋼中に含有されると、マトリックスを脆化し、靱性や被削性が悪化する。そこで、Ｍｎは１．１０〜１．８０％とする。
Mn: 1.10 to 1.80%
Mn is a deoxidizer at the time of refining, is an element necessary for obtaining hardenability of steel, and is an element that forms sulfides and improves the machinability of steel. In order to acquire these effects, Mn needs to contain 1.10% or more. On the other hand, if Mn is contained in the steel in an amount of more than 1.80%, the matrix becomes brittle and the toughness and machinability deteriorate. Therefore, Mn is 1.10 to 1.80%.
Ｓ：０．００５〜０．０５０％
Ｓは、切削中の応力集中源となる硫化物を鋼中に形成し、被削性を向上させる元素である。これらの効果を得るためには、Ｓは０．００５％以上含有される必要がある。一方、Ｓは０．０５０％以上含有されると、鋼中に含有される硫化物が粗大となり、靱性の低下を招き、また鋼の鏡面加工時にピットやうねりを鏡面中に発生させる原因となる。そこでＳは０．００５〜０．０５０％とする。
S: 0.005 to 0.050%
S is an element that improves the machinability by forming sulfide in the steel, which becomes a stress concentration source during cutting. In order to obtain these effects, S needs to be contained by 0.005% or more. On the other hand, when S is contained in an amount of 0.050% or more, sulfides contained in the steel become coarse, leading to a decrease in toughness, and causing pits and undulations in the mirror surface during mirror processing of steel. . Therefore, S is made 0.005 to 0.050%.
Ｃｒ：１．３５〜２．９０％
Ｃｒは、鋼中に硬質炭化物を形成して、鋼の硬さおよび耐摩耗性を向上させるとともに、焼入性を高めるために必要であり、また、鋼中に硫化物を形成して被削性を向上させる元素である。これらの効果を得るために、Ｃｒは１．３５％以上を含有させる必要がある。一方、Ｃｒは２．９０％より多いと、鋼中に粗大な炭化物を形成して鋼の靱性および被削性を悪化する。そこで、Ｃｒは１．３５〜２．９０％とする。
Cr: 1.35 to 2.90%
Cr is necessary to form hard carbides in the steel to improve the hardness and wear resistance of the steel and to improve hardenability. It is an element that improves the properties. In order to obtain these effects, Cr needs to be contained in an amount of 1.35% or more. On the other hand, if the Cr content is more than 2.90%, coarse carbides are formed in the steel to deteriorate the toughness and machinability of the steel. Therefore, Cr is set to 1.35 to 2.90%.
Ｍｏ：０．１０〜０．２４％
Ｍｏは、鋼中に硬質炭化物を形成して、鋼の硬さおよび耐摩耗性を向上させるとともに、焼入性および焼戻し軟化抵抗性を高める元素である。これらの効果を得るために、Ｍｏは０．１０％以上を含有させる必要がある。一方、Ｍｏは０．２４％より多いと、鋼中に粗大な炭化物を形成し、靱性を悪化し、鏡面加工時にピットを形成しやすくし、また、シボムラが発生する要因となる。そこで、Ｍｏは０．１０〜０．２４％とする。
Mo: 0.10 to 0.24%
Mo is an element that forms hard carbides in the steel to improve the hardness and wear resistance of the steel, and enhances the hardenability and temper softening resistance. In order to obtain these effects, Mo needs to contain 0.10% or more. On the other hand, if the Mo content is more than 0.24%, coarse carbides are formed in the steel, the toughness is deteriorated, pits are easily formed during mirror finishing, and grain unevenness occurs. Therefore, Mo is set to 0.10 to 0.24%.
Ｖ：０．０１〜０．０４％
Ｖは、鋼中に硬質炭窒化物を形成して、鋼の焼入れ時の結晶粒の粗大化を抑制する効果があり、靱性の向上に寄与する元素である。これらの効果を得るために、Ｖは０．０１％以上を含有させる必要がある。一方、Ｖは０．０４％より多いと、鋼中に粗大な看過物を生成し、靱性を悪化し、鋼の鏡面加工時にピットを形成し易くする。また、偏析帯を形成しやすく、シボムラが発生する原因となる。そこで、Ｖは０．０１〜０．０４％とする。
V: 0.01-0.04%
V is an element that forms hard carbonitrides in the steel and has an effect of suppressing coarsening of crystal grains during quenching of the steel and contributes to improvement of toughness. In order to acquire these effects, it is necessary to contain V 0.01% or more. On the other hand, if V is more than 0.04%, coarse overlooked matter is generated in the steel, the toughness is deteriorated, and pits are easily formed during mirror finishing of the steel. In addition, segregation bands are easily formed, which causes uneven graining. Therefore, V is set to 0.01 to 0.04%.
Ｎ：≦０．０１８０％
Ｎは、鋼中に窒化物を形成して結晶粒の粗大化を防止し、靱性の低下に寄与する元素である。このためには、Ｎは０．０１８０％以下とする必要がある。一方、Ｎは０．０１８０％より多いと、粗大な窒化物を形成して靱性を悪化し、鋼の鏡面加工時にピットを形成しやすくする。そこで、Ｎは０．０１８０％以下とする。
N: ≦ 0.0180%
N is an element that forms nitrides in the steel to prevent coarsening of crystal grains and contributes to a decrease in toughness. For this purpose, N needs to be 0.0180% or less. On the other hand, when N is more than 0.0180%, coarse nitrides are formed to deteriorate toughness, and pits are easily formed during mirror finishing of steel. Therefore, N is set to 0.0180% or less.
Ａｌ：≦０．０２５％
Ａｌは、鋼の精錬時の脱酸の働きを有するが、０．０２５％より多いと、粗大な酸窒化物を形成して鋼の靱性および鏡面加工性を悪化する。そこで、Ａｌは０．０２５％以下とする。
Al: ≦ 0.025%
Al has a function of deoxidation at the time of refining steel, but if it exceeds 0.025%, coarse oxynitride is formed to deteriorate the toughness and mirror finish of the steel. Therefore, Al is made 0.025% or less.
硫化物に占めるＣａ、Ｃｒの割合は、Ｃａ：≦５．０％、Ｃｒ：≦２５．０％、かつ（Ｃａ＋Ｃｒ）：≦２８．０％
硫化物に占めるＣａ、Ｃｒは、硫化物の形状を球状にし、また粗大にする効果があり、さらに鋼の被削性を向上させる効果を有する。しかし、硫化物中のＣａが５．０％より多く、Ｃｒが２５．０％より多く、かつＣａとＣｒの合計で２８％より多いと、硫化物が粗大になりすぎ、鋼の靱性が低下し、シボ加工ムラや鏡面加工性の悪化を招く。そこで、硫化物中に占めるＣａ、Ｃｒの割合は、Ｃａは５．０％以下、Ｃｒは２５．０％以下、かつ（Ｃａ＋Ｃｒ）は２８．０％以下とする。
The proportions of Ca and Cr in the sulfides are: Ca: ≦ 5.0%, Cr: ≦ 25.0%, and (Ca + Cr): ≦ 28.0%
Ca and Cr occupying sulfides have the effect of making the shape of sulfides spherical and coarse, and also have the effect of improving the machinability of steel. However, if the Ca content in the sulfide is more than 5.0%, Cr is more than 25.0% and the total of Ca and Cr is more than 28%, the sulfide becomes too coarse and the toughness of the steel decreases. In addition, the texture processing unevenness and the mirror surface workability are deteriorated. Therefore, the proportions of Ca and Cr in the sulfide are set to 5.0% or less for Ca, 25.0% or less for Cr, and 28.0% or less for (Ca + Cr).
鋼中に含有される硫化物の面積率：０．０５〜０．２０％
鋼中に含有される硫化物の面積率は、鋼の被削性を示す値である。この硫化物の面積率が０．０５％より小さいと鋼は良好な被削性を得られない。一方、硫化物の面積率が０．２０％より大きいと鋼の靱性が低下し、シボ加工ムラや鏡面加工性の悪化を招く。そこで、鋼中に含有される硫化物の面積率は０．０５〜０．２０％とする。
Area ratio of sulfide contained in steel: 0.05 to 0.20%
The area ratio of sulfide contained in steel is a value indicating the machinability of steel. If the area ratio of the sulfide is less than 0.05%, the steel cannot obtain good machinability. On the other hand, if the area ratio of the sulfide is larger than 0.20%, the toughness of the steel is lowered, resulting in uneven texture processing and deterioration of mirror surface workability. Therefore, the area ratio of sulfide contained in the steel is set to 0.05 to 0.20%.
１ｍｍ2当たりの硫化物の個数：≧９個
１ｍｍ2当たりの硫化物の個数は、９個より少なく、硫化物の分布が一定で存在しないので、良好な被削性が得られない。そこで、１ｍｍ2当たりの硫化物の個数は９個以上とする。
Number of sulfides per 1 mm 2 : ≧ 9 The number of sulfides per 1 mm 2 is less than 9 and the distribution of sulfides does not exist, so that good machinability cannot be obtained. Therefore, the number of sulfides per 1 mm 2 is 9 or more.
５０μｍ2以上の面積の硫化物の個数の割合：２〜４２％
５０μｍ2以上の面積の硫化物の個数の割合は、良好な被削性を得るために必要な値である。良好な被削性を得るためには、５０μｍ2以上の面積の硫化物の個数の割合は２％以上とする。一方、５０μｍ2以上の面積の硫化物の個数の割合が４２％を超えると、鋼の靱性が低下し、シボ加工ムラを生じ、さらに鏡面加工時にピットを形成しやすくなる。そこで、５０μｍ2以上の面積の硫化物の個数の割合は２〜４２％とする。
Ratio of the number of sulfides having an area of 50 μm 2 or more: 2 to 42%
The ratio of the number of sulfides having an area of 50 μm 2 or more is a value necessary for obtaining good machinability. In order to obtain good machinability, the ratio of the number of sulfides having an area of 50 μm 2 or more is set to 2% or more. On the other hand, when the ratio of the number of sulfides having an area of 50 μm 2 or more exceeds 42%, the toughness of the steel is lowered, uneven texture is generated, and pits are easily formed during mirror finishing. Therefore, the ratio of the number of sulfides having an area of 50 μm 2 or more is set to 2 to 42%.
硫化物中の平均アスペクト比：≦９
硫化物中の平均アスペクト（縦横）比は、鋼の被削性の向上を左右する値である。アスペクト比が９より大きいと、硫化物が細長くなりすぎ、切削中の応力集中源になりにくく、したがって被削性を向上させる効果が得られない。そこで、硫化物中の平均アスペクト比は９以下とする。
Average aspect ratio in sulfide: ≤9
The average aspect ratio in the sulfide is a value that affects the improvement of the machinability of the steel. If the aspect ratio is greater than 9, the sulfide becomes too long and is not likely to become a stress concentration source during cutting, and therefore the effect of improving machinability cannot be obtained. Therefore, the average aspect ratio in the sulfide is 9 or less.
ここで、発明を実施するための形態について、表を参照して以下に説明する。 Here, the form for inventing is demonstrated below with reference to a table | surface.
の表１に示す化学成分からなる発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各１００ｋｇを真空誘導溶解炉にて溶製した。得られた各鋼を鍛伸して縦横の各辺が５０ｍｍからなる角材とした。これらの角材を８５０〜９００℃に加熱した後、空冷により焼入れした。次いで、５００〜６００℃に加熱した後、空冷する焼戻し処理を少なくとも２回行なって、これら角材の焼入焼戻し硬さを３０ＨＲＣとなるように調整し、プラスチック製品成形用の金型に要求される硬さとした。なお、表１における化学成分は％で示している。 No. of invention steel which consists of a chemical component shown in Table 1 of No.1. 1-19 and No. of comparative steel. 100 kg of 20 to 34 were melted in a vacuum induction melting furnace. Each steel obtained was forged to obtain a square bar having sides of 50 mm in length and width. These squares were heated to 850 to 900 ° C. and then quenched by air cooling. Next, after heating to 500 to 600 ° C., the tempering treatment of air cooling is performed at least twice to adjust the quenching and tempering hardness of these square members to 30 HRC, which is required for a mold for plastic product molding. It was hard. The chemical components in Table 1 are shown in%.
上記の発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼の焼入焼戻し後の各角材を用いて、各角材の中心部から縦横が１０ｍｍ×３０ｍｍ角で長さが３０ｍｍからなる各試材を割り出した。これらの発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各試料の３０ｍｍ×３０ｍｍの面を鏡面研磨し、これらの鏡面研磨した面の１０箇所を光学顕微鏡により６５０μｍ×９００μｍの視野として写真に撮影した。次いで、これらの１０か所の顕微鏡写真から、硫化物の面積率、１ｍｍ2当たりの硫化物の個数、５０μｍ2以上の面積を有する硫化物の個数の割合、および硫化物の平均アスペクト比をそれぞれ求めた。 No. of the above invention steel. 1-19 and No. of comparative steel. Using each square bar after quenching and tempering of each steel of 20 to 34, each specimen having a length of 10 mm × 30 mm square and a length of 30 mm was determined from the center of each square bar. No. of these invention steels. 1-19 and No. of comparative steel. The 30 mm × 30 mm surface of each of the samples 20 to 34 was mirror-polished, and 10 portions of these mirror-polished surfaces were photographed as a 650 μm × 900 μm field of view with an optical microscope. Then, from these 10 micrographs, the area ratio of sulfide, the number of sulfides per mm 2 , the ratio of the number of sulfides having an area of 50 μm 2 or more, and the average aspect ratio of sulfides, respectively. Asked.
上記の発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼の焼入焼戻し後の各角材を用いて、各角材の中心部から縦横が５ｍｍ×１５ｍｍ角で長さが１５ｍｍからなる各試料を形成した。これらの発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各試料の１５ｍｍ×１５ｍｍ面を鏡面研磨し、ＥＤＳを用いて各発明鋼および比較鋼のそれぞれの研磨面で観測された硫化物の２０個をランダムに選んで、その部分の硫化物中のＣａ量の％、硫化物中のＣｒ量の％、および硫化物中の（Ｃａ＋Ｃｒ）量の％を測定し、それらの平均値を求めた。 No. of the above invention steel. 1-19 and No. of comparative steel. Using each square bar after quenching and tempering each steel of 20 to 34, each sample having a length and width of 5 mm × 15 mm square and a length of 15 mm was formed from the center of each square bar. No. of these invention steels. 1-19 and No. of comparative steel. 15-mm × 15-mm surface of each sample of 20 to 34 is mirror-polished, and 20 sulfides observed on each polished surface of each invention steel and comparative steel are randomly selected using EDS, and sulfidation of that portion is performed. The% of the Ca content in the product, the% of the Cr content in the sulfide, and the% of the (Ca + Cr) content in the sulfide were measured and their average values were determined.
さらに、発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼について、それらの鋼中に占める硫化物の面積率の％、それらの各鋼の１ｍｍ2当たりの硫化物の個数、それらの各鋼の５０μｍ2以上の面積を有する硫化物の個数割合の％、さらにそれらの各鋼に含まれる硫化物の平均アスペクト（縦横）比を求めた。 Furthermore, No. of invention steel. 1-19 and No. of comparative steel. For each steel of 20 to 34,% of the area ratio of sulfides in the steels, the number of sulfides per 1 mm 2 of each steel, sulfides having an area of 50 μm 2 or more of each steel % Of the number of each and the average aspect (length / width) ratio of the sulfide contained in each steel.
また、さらに、発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼の焼入焼戻し後の各角材を用いて、その角材の中心部から１０ｍｍ×１０ｍｍ角で長さが５５ｍｍの試料を割り出した。この試料を２ｍｍＵノッチを有するシャルピー試験片に加工して、衝撃値の測定を行った。ＡＩＳＩのＴｙｐｅのＰ２０では、プラスチック製品成形用の金型で必要とされる３０ＨＲＣで、２０Ｊ／ｃｍ2の衝撃値が得られるとされている。そこで、本願の発明では、２０Ｊ／ｃｍ2を基準として、２５Ｊ／ｃｍ2より高い衝撃値が得られれば、靱性は優れているとして○とし、２０Ｊ／ｃｍ2以下の衝撃値であれば、靱性は悪いとして×として評価した。 Furthermore, No. of invention steel. 1-19 and No. of comparative steel. Using each square bar after quenching and tempering of each steel of 20 to 34, a sample having a length of 10 mm × 10 mm square and a length of 55 mm was determined from the center part of the square bar. This sample was processed into a Charpy test piece having a 2 mmU notch, and the impact value was measured. In AISI Type P20, an impact value of 20 J / cm 2 can be obtained at 30 HRC required for a mold for molding plastic products. Therefore, in the invention of the present application, if an impact value higher than 25 J / cm 2 is obtained on the basis of 20 J / cm 2 , the toughness is considered to be excellent, and if the impact value is 20 J / cm 2 or less, the toughness Was rated as x as bad.
さらに、発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼の焼入焼戻し後の各角材を用いて、これらの角材からなる試料の幅５０ｍｍで長さ１５０ｍｍの面をドリルで穿孔していき、穿孔できた穴数で被削性を評価した。この場合、ドリルはＳＫＨ５１製のφ８ストレートドリルを用いた。切削条件は、回転数を６４０ｒｐｍ、送りを５６ｍｍ／ｍｉｎ、穿孔深さを４０ｍｍとし、潤滑油をかけながら穿孔した。ＡＩＳＩのＴｙｐｅのＰ２０をこの方法で評価した結果、９０穴開けることができたことから、１００穴以上開けられる場合は被削性は優れているとして○と評価し、１００穴未満開けられる場合は被削性は悪いとして×と評価した。 Furthermore, No. of invention steel. 1-19 and No. of comparative steel. Using each square bar after quenching and tempering of each steel of 20 to 34, a 50 mm wide and 150 mm long surface of a sample made of these square bars is drilled, and the machinability is achieved by the number of drilled holes. Evaluated. In this case, a φ8 straight drill made of SKH51 was used as the drill. Cutting conditions were such that the number of rotations was 640 rpm, the feed was 56 mm / min, the drilling depth was 40 mm, and the drilling was performed while lubricating oil was applied. As a result of evaluating AISI Type P20 by this method, it was possible to drill 90 holes. If 100 holes or more can be drilled, the machinability is evaluated as good, and if less than 100 holes are drilled, Since the machinability was bad, it was evaluated as x.
また、さらに、発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼の焼入焼戻し後の各角材を用いて、試料の中心部から縦横１０ｍｍ×３０ｍｍで長さ３０ｍｍの試料を割出し、３０ｍｍ×３０ｍｍ面を＃１８０〜＃８０００までの研磨紙で研磨した。目視により研磨後の表面に研磨面に歪みが発生した状態の磨きムラやピットがないかを観察した。さらに３０ｍｍ×３０ｍｍの面にシボ加工を行って、帯状のムラや意匠以外の凹凸が発生することなく、均質な凹凸ができているかについて観察した。この結果、磨きムラやピットはなく、シボ加工が均質な状態となっている場合は、鏡面加工性は優れているとして○と評価し、磨きムラやピットがあったりして、シボ加工が不均一な状態となっている場合は、鏡面加工性は悪いとして×と評価した。 Furthermore, No. of invention steel. 1-19 and No. of comparative steel. Using each square bar after quenching and tempering 20-34 steel, 10 mm × 30 mm length and 30 mm length sample is indexed from the center of the sample, and 30 mm × 30 mm surface is polished from # 180 to # 8000 Polished with paper. The surface after polishing was visually observed for uneven polishing and pits with distortion on the polished surface. Furthermore, the surface of 30 mm × 30 mm was subjected to texturing, and it was observed whether uniform irregularities were formed without generating irregularities other than strip-shaped unevenness and design. As a result, if there is no polishing unevenness or pits and the wrinkle processing is in a homogeneous state, it is evaluated as ○ because the mirror surface workability is excellent, and there is uneven polishing and pits, so that wrinkle processing is not possible. When it was in a uniform state, the mirror surface workability was poor and was evaluated as x.
以上、発明鋼のＮｏ．１〜１９および比較鋼のＮｏ．２０〜３４の各鋼に関して、上記した硫化物中のＣａ量、硫化物中のＣｒ量、硫化物中の（Ｃａ＋Ｃｒ）量、鋼中の硫化物の面積率、鋼の１ｍ2当たりの硫化物の個数、５０μｍ2以上の面積を有する硫化物の個数の割合、および、これらの鋼の靱性、被削性ならびに鏡面加工性の評価を表２に記載した。 As mentioned above, the No. of invention steel. 1-19 and No. of comparative steel. Regarding each steel of 20 to 34, the amount of Ca in the sulfide, the amount of Cr in the sulfide, the amount of (Ca + Cr) in the sulfide, the area ratio of the sulfide in the steel, the sulfide per 1 m 2 of the steel Table 2 shows the evaluation of the ratio of the number of sulfides, the ratio of the number of sulfides having an area of 50 μm 2 or more, and the toughness, machinability and mirror surface workability of these steels.
本願の発明鋼のＮｏ．１〜１９の各鋼の全ての鋼は、表１に示すように、請求項に規定する範囲の各化学成分を有している。さらに、表２に示すように、本願の発明鋼のＮｏ．１〜１９の各鋼に含有される硫化物中の、Ｃａの量は５．０％以下、Ｃｒの量は２５．０％以下、および（Ｃａ＋Ｃｒ）の量は２８．０％以下である。さらに本願の発明鋼のＮｏ．１〜１９の各鋼に対する硫化物の面積率の割合は０．０５〜０．２０％である。また、さらに本願の発明鋼のＮｏ．１〜１９の各鋼における、１ｍｍ2当たりの硫化物の個数は９個以上、全硫化物の個数中で５０μｍ2以上の面積を有する硫化物の個数の割合は２〜４２％、および硫化物の平均アスペクト比は９以下である。これらの結果、本願の発明鋼のＮｏ．１〜１９の各鋼の靱性、被削性および鏡面加工性はいずれも○と評価されて優れている。 No. of invention steel of this application. As shown in Table 1, all of the steels 1 to 19 have chemical components in the ranges specified in the claims. Furthermore, as shown in Table 2, the invention steel No. In the sulfides contained in each of the steels 1 to 19, the amount of Ca is 5.0% or less, the amount of Cr is 25.0% or less, and the amount of (Ca + Cr) is 28.0% or less. Furthermore, No. of invention steel of this application. The ratio of the area ratio of sulfide to each steel of 1 to 19 is 0.05 to 0.20%. Further, the invention steel No. In each steel of 1 to 19, the number of sulfides per mm 2 is 9 or more, the ratio of the number of sulfides having an area of 50 μm 2 or more in the total number of sulfides is 2 to 42%, and sulfides The average aspect ratio is 9 or less. As a result, No. of the invention steel of the present application. The toughness, machinability and mirror surface workability of each of the steels 1 to 19 are all evaluated as “good” and excellent.
本願の発明鋼のＮｏ．１〜１９に対して、比較鋼のＮｏ．２０〜３４の各鋼では、表１に示すように、比較鋼において、Ｎｏ．２０はＣおよびＭｏが、Ｎｏ．２１はＡｌが、Ｎｏ．２２はＣが、Ｎｏ．２３はＮが、Ｎｏ．２４はＳｉが、Ｎｏ．２５はＳが、Ｎｏ．２７はＭｎが、Ｎｏ．２８はＣｒが、Ｎｏ．２９はＭｎおよびＣｒが、Ｎｏ．３２はＶが、Ｎｏ．３３はＣおよびＳが、比較鋼のＮｏ．２６、Ｎｏ．３０、Ｎｏ．３１およびＮｏ．３４の４件を除いて、本願の請求項に係る化学成分の範囲を外れている。一方、表２に示すように、比較鋼のＮｏ．２５は、硫化物の面積率が０．０１％で発明鋼の硫化物の面積率の０．０５〜０．２０％の範囲より小さく、１ｍｍ2当たりの硫化物の個数が６個で発明鋼の１ｍｍ2当たりの硫化物の９個以上より少なく、かつ５０μｍ2以上の面積を有する硫化物の個数割合が１％で発明鋼の２〜４２％より低いものである。比較鋼のＮｏ．２６は、硫化物中のＣａが６．３％で発明鋼の硫化物中のＣａが５．０％より大きく、硫化物中の（Ｃａ＋Ｃｒ）が２９．２％で発明鋼の（Ｃａ＋Ｃｒ）が２８．０％より大きいものである。比較鋼のＮｏ．３０は、５０μｍ2以上の面積を有する硫化物の個数割合が５３％で発明鋼の２〜４２％より高いものである。比較鋼のＮｏ．３１は、硫化物の平均アスペクト比が１１で発明鋼の硫化物の平均アスペクト比の９以下よりも多いものである。比較鋼のＮｏ．３３は、硫化物の面積率が０．５６％で発明鋼の硫化物の面積率の０．０５〜０．２０％の範囲より大きいものである。比較鋼のＮｏ．３４は、硫化物中のＣｒが２６．０％で発明鋼の硫化物中のＣｒが２５．０％より大きく、硫化物中の（Ｃａ＋Ｃｒ）が３０．２％で発明鋼の（Ｃａ＋Ｃｒ）が２８．０％より大きいものである。 No. of invention steel of this application. No. 1 to 19 of the comparative steel. In each steel of 20 to 34, as shown in Table 1, in the comparative steel, No. No. 20 is C and Mo. No. 21 is Al. 22 is C. 23 is N. No. 24 is Si. 25 is S. 27 is Mn. No. 28 is Cr. No. 29 is Mn and Cr. 32 is V. In No. 33, C and S are No. of comparative steel. 26, no. 30, no. 31 and no. Except for 34 cases of 34, it is out of the scope of chemical components according to the claims of this application. On the other hand, as shown in Table 2, No. of the comparative steel. 25, the area ratio of sulfide is 0.01%, which is smaller than the range of 0.05 to 0.20% of the area ratio of sulfide of the invention steel, and the number of sulfides per mm 2 is 6 and the invention steel. The ratio of the number of sulfides having less than 9 or more of sulfides per 1 mm 2 and having an area of 50 μm 2 or more is 1%, which is lower than 2 to 42% of the inventive steel. No. of comparative steel. 26, the Ca in the sulfide is 6.3%, the Ca in the sulfide of the invention steel is greater than 5.0%, the (Ca + Cr) in the sulfide is 29.2%, and the (Ca + Cr) of the invention steel is It is larger than 28.0%. No. of comparative steel. No. 30 has a ratio of the number of sulfides having an area of 50 μm 2 or more at 53%, which is higher than 2 to 42% of the inventive steel. No. of comparative steel. No. 31 has an average aspect ratio of the sulfide of 11, which is more than 9 or less of the average aspect ratio of the sulfide of the inventive steel. No. of comparative steel. No. 33 has a sulfide area ratio of 0.56%, which is larger than the range of 0.05 to 0.20% of the sulfide area ratio of the invention steel. No. of comparative steel. 34, Cr in the sulfide is 26.0%, Cr in the sulfide of the invention steel is greater than 25.0%, (Ca + Cr) in the sulfide is 30.2%, and (Ca + Cr) of the invention steel is It is larger than 28.0%.
以上のように、比較鋼は表１に示す化学成分と表２に示す硫化物中のＣａ、硫化物中のＣｒ、硫化物中の（Ｃａ＋Ｃｒ）あるいは硫化物の面積率、１ｍｍ2当たりの硫化物の個数、５０μｍ2以上の面積を有する硫化物の個数割合、硫化物の平均アスペクト比の、いずれかが発明鋼のそれらの範囲と相違しており、このために比較鋼は靱性、被削性、鏡面加工性が×となっている。しかし、本願の発明鋼は靱性、被削性、鏡面加工性ともに○であって被削性および鏡面加工性に優れた高靱性のプラスチック成形金型用鋼である。 As described above, the comparative steel has the chemical composition shown in Table 1 and Ca in the sulfide shown in Table 2, Cr in the sulfide, (Ca + Cr) in the sulfide, or the area ratio of sulfide, sulfide per 1 mm 2. The number of products, the ratio of the number of sulfides with an area of 50 μm 2 or more, and the average aspect ratio of sulfides are different from those of the invention steels. And mirror finish are x. However, the invention steel of the present application is a tough plastic molding die steel having excellent toughness, machinability and mirror surface workability and excellent machinability and mirror surface workability.
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