JP3736751B2 - Mold steel with excellent machinability and specularity - Google Patents

Description

【００１６】
表１に示すように、Ｎｏ．１〜４は、本発明例であり、Ｎｏ．５〜６は、比較例である。比較例Ｎｏ．５は、Ｍｎが高く、また、Ｍｎ／Ｓが高い値であることから、介在物の形態がＭｎＳであり、そのために介在物硬さが低く、ピット数が多く、かつ鏡面性が悪い。また、比較例Ｎｏ．６は、Ｓが低く、Ｍｎ／Ｓが高い値であることから、介在物の形態がＭｎＳであり、そのために介在物硬さが低く、切削長が短く、しかも鏡面性が悪いことが判る。
【００１７】
【発明の効果】
以上述べたように、本発明によるＭｎ／Ｓを規制し、かつＣｒ、Ｓｅ、Ｔｅを添加することによって、ＭｎＳを硬質介在物とし、かつマトリックスと介在物間の硬度差を小さくすることによって、鏡面仕上げ時に介在物のみが先に研磨されてスジ状の凹形状になることを防ぐことにより、被削性と鏡面性を両立させたプラスチック金型用鋼を製造することが可能としたことは工業的に極めて優れた効果を奏するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to steel for plastic molds excellent in machinability and specularity.
[0002]
[Prior art]
Conventionally, carbon steel and low carbon structural steel have been widely used as plastic mold steels, but in recent years, plastic mold steels have machinability, specularity, corrosion resistance, overlay welding, and embossing. Various properties such as strength and toughness have been demanded. Among these characteristics, machinability and specularity are particularly contradictory characteristics, and in view of quality and mold cost, it has been desired to develop a mold steel that satisfies both these characteristics.
[0003]
From the above request, for example, as disclosed in JP-A-63-183158, C: 0.08 to 0.17%, Si: 0.60% or less, Mn: 0.50 to 1.20%, Ni: 2.50 to 3.50%, Al: 0.85 to 1.50%, Cu: 1.80 to 2.50%, S: 0.05 to 0.16%, balance Fe and normal impurities As in plastic molded prehardened mold steel and JP-A-60-67641, C: 0.05 to 0.18%, Si: 0.15 to 1.0%, Mn: 1.0 to 2 0.0%, Ni: 2.5-3.5%, Al: 0.5-1.5%, Cu: 0.7-1.7%, Mo: 0.1-0.4%, S: When the post-weld aging is performed, the weld steel and the weld heat-affected zone are uniform in the same manner as the base metal. Ing process are possible, and Mn-Ni-Al-Cu-Mo-based age hardenable plastic die steel mirror is good has been proposed.
[0004]
[Problems to be solved by the invention]
However, in the case of the above-mentioned JP-A-63-183158, it contains MnS and is excellent in machinability, but is insufficient in terms of specularity. In the case of Japanese Patent Application Laid-Open No. 60-67641, the upper limit value of S is regulated, and it has good specularity and uniform fort etching, but is insufficient in terms of machinability. There is. Thus, MnS that contributes to improvement of machinability becomes a streak-like recess when the mold is finished to a mirror surface, and the mirror surface property is remarkably deteriorated. On the other hand, mold steels that do not contain MnS have the problem that the machinability is poor and the mold cost is high.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the inventors have made extensive developments. As a result, by adding Cr, Se, and Te, the sulfides are hardened to achieve both specularity and machinability. It provides steel for plastic molds. The gist of the invention is that
(1) By mass%, C: 0.01 to 0.3%, Si: ≦ 1.0%, Mn: 0.1 to 0.4%, Ni: 1.0 to 4.0%, Cr: 0.1 to 5.0%, Al: 0.3 to 1.5%, Cu: 0.3 to 1.5%, S: 0.05 to 0.2%, the balance Fe and unavoidable A mold steel excellent in machinability and specularity, characterized in that it is made of mechanical impurities, Mn / S ≦ 2.0, and inclusion hardness is adjusted to 300 to 500 HV.
(2) A mold steel excellent in machinability and specularity, characterized in that the component composition described in (1) above further contains 0.5% or less of one or two of Se and Te. It is.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reasons for limiting the component composition according to the present invention will be described.
C: 0.01 to 0.3%
C is a basic element for increasing the strength necessary for ensuring hardenability. If it is less than 0.01%, sufficient strength cannot be ensured. The toughness and weldability are lowered, so the range was made 0.01 to 0.3%.
Si: ≦ 1.0%
Si has a deoxidizing action during melting and is added for hardenability. However, excessive addition reduces toughness, so the upper limit was made 1.0%.
[0007]
Mn: 0.1 to 0.4%
Mn, like Si, has a deoxidizing action during melting and is added to ensure hardenability. However, if the amount is less than 0.1%, the effect cannot be obtained, and excessive addition reduces machinability and toughness, so the upper limit was made 0.4%.
Ni: 1.0-4.0%
Ni is an element necessary for securing aging hardness and improving embossing workability. However, if less than 1.0%, the effect cannot be obtained, and excessive addition lowers the thermal conductivity and machinability, so the upper limit was made 4.0%. Preferably it is 2.5 to 3.5%.
[0008]
Cr: 0.1 to 5.0%
Cr is an element that helps to improve the strength by improving the corrosion resistance and hardening of inclusions. Therefore, 0.1% or more is necessary to obtain the effect. However, excessive addition reduces machinability, so the upper limit was made 5.0%. Preferably, the content is 1.0 to 3.0%.
Al: 0.3 to 1.5%
Al is an element that secures aging hardness and improves machinability. However, if less than 0.3%, the effect cannot be obtained, and excessive addition reduces toughness, so the upper limit was made 1.5%. Preferably, the content is 0.5 to 1.0%.
[0009]
Cu: 0.3 to 1.5%
Cu is an element that secures aging hardness and improves machinability. However, if less than 0.3%, the effect cannot be obtained, and excessive addition reduces toughness and hot workability, so the upper limit was made 1.5%. Preferably, the content is 0.5 to 1.0%.
S: 0.05-0.2%
S is an element that improves machinability. However, if it is less than 0.05%, the effect cannot be obtained, and excessive addition deteriorates specularity and corrosion resistance, so the upper limit was made 0.2%.
[0010]
Mn / S ≦ 2.0
Mn / S is regulated to prevent formation of MnS alone, and its upper limit is set to 2.0.
Inclusion hardness is 300-500HV
The inclusion hardness of 300 to 500 HV is set to 300 HV or more in order to ensure the mirror finish. However, if it exceeds 500 HV, unevenness cannot be prevented during embossing, so the upper limit was set to 500 HV.
[0011]
0.5% or less of 1 or 2 types of Se and Te By adding Se and Te together with Cr, MnS is hardly intermingled with either CrS, Cr (S, Se) or Cr (S, Te) It is a thing. That is, it is an element that dissolves in the CrS inclusion and ensures the hardness of the inclusion. Thereby, 400HV can be secured. However, if it exceeds 0.5%, the toughness decreases, so the upper limit was made 0.5%. Desirably, it is 0.3% or less.
As described above, the present invention regulates Mn / S and adds Cr, Se, and Te so that MnS becomes CrS, Cr (S, Se), Cr (S, Te), Cr (S , Se, Te). On the other hand, by reducing the difference in hardness between the matrix and the inclusions, only the inclusions are first polished during the mirror finish to prevent a streak-like concave shape.
[0012]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
Steel having the chemical composition shown in Table 1 is melted in a 200 kg vacuum induction heating melting furnace, cast into an ingot, heated to 1100 ° C., and forged into corners of width 100 mm × length 100 mm × height 100 mm. The solution was subjected to solution treatment and aging treatment and used as a test material. The specimen was used as a machinability test piece and a test piece for specularity evaluation. The results are shown in Table 1. The machinability test and the specularity evaluation test are as follows.
[0013]
As a machinability test according to the present invention,
(Cutting conditions)
End mill: φ5, 2-blade rotation speed: 1900 rpm
Cutting speed: 0.3 m / s
Cutting depth: 1mm
Machining form: Groove machining Cooling method: Air blow (Evaluation method) Cutting length until end mill breakage [0014]
In the specularity evaluation test according to the present invention, # 180 → # 320 → # 800 → # 1200 was performed with wet paper using an automatic polishing apparatus, followed by mirror finishing in the order of diamond paste 3 μm → diamond paste 1 μm. Went. As a result, the number of pits in a test area of 1 mm ² was measured using a stereomicroscope and evaluated visually. The result is the number of pits and specularity in Table 1. Regarding the specularity, ○ indicates good and × indicates poor specularity. In addition, about the form of the inclusion shown in Table 1, the conventional MnS is replaced to become CrS, and Se and Te are dissolved to form Cr (S, Se), Cr (S, Te), Cr (S, Se). , Te) are formed, the hardness is improved, and the mirror finish is also improved.
[0015]
[Table 1]

[0016]
As shown in Table 1, no. 1 to 4 are examples of the present invention. 5 to 6 are comparative examples. Comparative Example No. No. 5 has a high Mn and a high value of Mn / S, and therefore the form of inclusions is MnS. Therefore, the inclusion hardness is low, the number of pits is large, and the specularity is poor. Comparative Example No. No. 6 has a low S and a high value of Mn / S, and therefore the inclusion form is MnS. Therefore, the inclusion hardness is low, the cutting length is short, and the specularity is poor.
[0017]
【The invention's effect】
As described above, by regulating Mn / S according to the present invention and adding Cr, Se, Te, by making MnS hard inclusions and reducing the hardness difference between the matrix and inclusions, By preventing only inclusions from being polished first to form a streak-like concave shape during mirror finishing, it became possible to manufacture steel for plastic molds that achieved both machinability and mirror finish. This is an industrially excellent effect.

Claims (2)

% By mass
C: 0.01 to 0.3%,
Si: ≦ 1.0%,
Mn: 0.1 to 0.4%,
Ni: 1.0-4.0%,
Cr: 0.1 to 5.0%,
Al: 0.3 to 1.5%,
Cu: 0.3 to 1.5%,
S: 0.05-0.2%
Excellent in machinability and specularity, characterized in that it is composed of the balance Fe and inevitable impurities, Mn / S ≦ 2.0, and the inclusion hardness is adjusted to 300 to 500 HV Mold steel. A steel for molds having excellent machinability and specularity, wherein the component composition according to claim 1 further contains 0.5% or less of one or two of Se and Te.