JPS6039740B2 - Steel for plastic molds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for plastic molds with good performance, and more specifically, to a steel for large molds that has focused improvements in machinability, grain workability, and cross-sectional uniformity of heat treatment hardness. The present invention relates to steel for plastic molds suitable for.

Various types of copper have been used as steel for plastic molds depending on the purpose, such as carbon steel, medium-carbon low-alloy steel, or medium-alloy steel.

Classifying these in terms of performance, we find that low-cost, low-life molds are made of HRC2-type carbon steel, long-life molds are made of HRC27-grade medium-carbon low-alloy steel, and long-life molds are made of HRC4 female-type medium carbon steel. Steel is mainly used. On the other hand, if we look at the recent needs for plastic molds, we can see that they are large molds with HRC2
A highly durable mold of HRC33 class, which is an intermediate class between class 7 and HRC4 broadside, is required, and conventional medium-carbon low-alloy steel or medium-alloy steel cannot fully meet the required characteristics, so this will be replaced. There is a strong demand for the development of new alloys. In response to the above requirements, the inventors of the present application focused on investigating the cross-sectional uniformity of machinability, texturability, and heat treatment hardness, and found that the alloy system shown below is extremely suitable for use in large molds. I saw it and put it out.

That is, in the present invention, C: 0.2 to 0.1 by weight.
5%, Si: 2.0% or less, Mn: 2.0% or less, Cr
:0.5~4.0%, Mo:0.03~2.0%, V:
0.01-2.0%, S: 0.036-0.15% A steel for plastic molds with excellent texturability, the balance being substantially Fe.

{2-Nj in weight for the basic component of m above
: Steel for plastic molds with excellent texturability, containing 1.20% or less and the remainder being substantially Fe.

Glue In addition to the basic components of {1} above, Ca
:0.0005-0.010%, Pb:0.03-0.
20%, Te: 0.01-0.15%, Bi: 0.01
-0.20% of at least one kind, the remainder being substantially Fe, and having excellent texturability for plastic molding.

{4} Add Nj by weight to the basic component of m above.
: 1.20% or less and Ca: 0.0005-0.010%
, Pb: 0.03-0.20%, Te: 0.01-0.
16% Bi: 0.01 to 0.20% Bi: A steel for plastic molds having excellent texturability, the remainder being substantially Fe.

As mentioned above, the steel of the present invention has been alloy designed to cope with the increase in size of plastic molding molds, and the feature of the steel of the present invention is 600q, which sufficiently eliminates competing strain.
A height of HRC 33 or higher can be obtained by the Akatsuki restoration treatment of 0 or more, and even in a large mold, there is little difference in hardness between the surface layer and the center, and a uniform cross-sectional hardness is obtained, so the mold life is good.

In addition, the microstructure after tempering becomes a tempered martensite and phosphorus tempered bainite structure that is advantageous for machinability and graining under a wide range of cutting conditions, resulting in overall excellent machinability and mild graining unevenness. It has many conditions suitable for large plastic molds. Next, the reason for limiting the composition range of the steel of the present invention will be described below.

C: 0.2-0.5% The hardness required for plastic molds is usually HRC33
Therefore, in order to secure this hardness level by tempering treatment at 600℃ or higher (tempering at 600℃ or higher is necessary to completely remove heat treatment distortion due to quenching), it is necessary to achieve at least 0.2% or higher hardness. Must be included.

However, if it is contained in a large amount, residual austenite will be formed and toughness, weldability, etc. will deteriorate, so it is limited to 0.5% or less. Si: 2.0% or less In addition to having a deoxidizing effect during melting, it is an effective element for strengthening the base, and it is desirable to actively include it.

However, if it is contained in a large amount, it will cause a lot of roughness and at the same time reduce machinability, so it was limited to 2.0% or less. Mn: 2.0
It is an effective element for deoxidizing and desulfurizing effects during melting, as well as for ensuring competitiveness as the size increases, and it is desirable to actively include it.

However, if it contains a large amount, machinability will decrease, so 2.0%
Limited to the following. Cr: 0.5-4.0% As the size of the mold increases, it also ensures good hardenability.
It is an element necessary to improve texturing property, and must be contained in an amount of at least 0.5%.

However, if it is contained in a large amount, the bainite nose will shift to the long-term side, and a martensitic structure with rich ballability will be generated.
Since machinability deteriorates, it is limited to 4.0% or less. Mo:
0.03-2.0% This is an element necessary to ensure hardenability and bran softening resistance as molds become larger.
In order to ensure hardness of HRC 33 or higher with tempering treatment of 60,000 or more, it is necessary to contain at least 0.03% or more.

However, if it is contained in a large amount, machinability and toughness deteriorate, so it was limited to 2.0% or less. V: 0.01-2.0% It is an extremely effective element for ensuring resistance to moth softening, and HRC33 is achieved by tempering at 600°C or higher.
In order to ensure the above hardness, it is necessary to contain at least 0.01% or more.

However, if it is contained in a large amount, machinability and quality deteriorate, so the content was limited to 2.0% or less. S:0.036~0.15
% An element necessary to ensure good machinability, and must be contained in an amount of at least 0.036%.

However, if it is contained in an amount more than necessary, there will be an increase in roughness and black splints caused by the segregation of sulfides, resulting in poor mirror finish and graining properties, so the content was limited to 0.15% or less. A steel suitable for use in large plastic molds can be manufactured with the above-mentioned composition, but the performance can be significantly improved by further containing appropriate amounts of the following elements.

Ni: 1.20% or less Ni is an effective element for improving hardenability, but if contained in a large amount, machinability deteriorates, so Ni is limited to 1.20% or less.

Ca: 0.0005~0.010%, Pb: 0.03~
0.20%, Te: 0.01-0.15%, Bi: 0.
01 to 0.20% All of the above elements are effective elements for improving machinability, Ca: 0.0005% or more, Pb: 0.03% or more, Te: 0.01% or more, Bi:
It is necessary to contain at least one of 0.01% or more of Ca: 0.01% or more, but if it is contained more than necessary, it tends to cause ground curls, black spots, etc.
005-0.010%, Pb: 0.03-0.20%,
Te: 0.01-0.15%, Bi: 0.01-0.2
It was limited to a range of 0%.

Next, the characteristics of the steel of the present invention will be explained in detail using examples.

<Example> Steel according to the present invention having the chemical composition shown in Table 1 and a medium carbon low alloy steel conventionally used for large plastic molds were melted and various characteristic values were investigated.

Note that No. 1 to 18 are the steels of the present invention, and No. 9 to 21 are steels of the present invention.
are the S55C series, SCM5 series, and SC produced for comparison.
It is copper corresponding to M3 series. Tempering methodPlastic molds require a high degree of dimensional accuracy.

Table 1 Accordingly, if the tempering temperature is too low, the heat treatment strain due to hardening will not disappear sufficiently and warpage or bending will occur after die carving. It is desirable to process at a temperature higher than that.

For these reasons, the lower limit of the tempering temperature is restricted, but on the other hand, the plastic mold that is the object of the present invention needs to have a hardness of at least HRC33 or higher in the used state, so it is necessary to perform a mound tempering process of 60,000 or higher. In, H
There was a demand for an alloy that would provide a hardness of RC33 or higher, and therefore, the test materials shown in Table 1 were used to measure the hardness of the steel. The results are shown in Table 2 together with the heat treatment conditions.

As shown in Table 2, the HRC of conventionally used medium carbon low alloy steel is reduced by tempering at 600q○ or more.
Although it is extremely difficult to ensure a hardness of 33 or higher, this goal can be easily achieved with the steel of the present invention.

Therefore, even if the height is adjusted, there is no fear of warpage or bending of the mold due to residual heat treatment distortion during quenching, indicating that a high degree of dimensional accuracy can be stably maintained for a long period of time.
Uniformity of hardness in the second surface cross section Generally speaking, the larger the material, the lower the hardness in the center compared to the hardness in the surface layer.

However, in plastic molds, such hardness differences are a major cause of shortening the life of the mold, and uniformity of cross-sectional hardness is particularly important for large molds.
Then, the test materials shown in Table 1 were forged into various sizes with a diameter of 100 to 600, and then quenched and tempered to investigate the uniformity of cross-sectional hardness. The results are shown in the figure. In the figure, the steel No. of the present invention is distributed between the upper limit line 1 and the lower limit line 2. As can be seen in the figure, there is a remarkable tendency for the difference in hardness between the surface layer and the center to increase as the diameter increases with conventionally used medium carbon low alloy steels, but this is not the case with the steel of the present invention. Even in a large material with a diameter of 60 ribs, the difference in hardness between the surface layer and the center is less than HRC3. Therefore, the uniformity of the cross-sectional hardness of plastic molds manufactured using the steel of the present invention is extremely good even in large-sized molds, indicating that good results can be achieved in terms of mold life. Machinability Steel for plastic molds needs to have good machinability under a wide range of cutting conditions because it is necessary to carve it into a complex shape.

Therefore, it is not necessarily appropriate to judge the machinability of mold steel based on the results of a simple cutting test. Therefore, after adjusting the test materials in Table 1 to a practical level of hardness through a competitive hardening process, we carved an actual mold and compared the time required for the die-sinking process. The sex was determined. The results are shown in Table 3. Table 3 * Time ratio required for mold coloring processing using comparative steel 20 as standard K
As shown in the table, the die-sinking processing time of the steel of the present invention is 50 to 70% shorter than that of the conventional practical steel.
The machinability is shown to be excellent overall.

This is related to the graining properties described below, but the microstructure of the steel of the present invention is composed of tempered martensite and tempered bainite structures in the quenched and tempered state, and the uniformity of the structure is maintained. , it appears to exhibit excellent machinability under a wide range of cutting conditions. Practical lifespan Automobile front grills were mass-produced using various plastic molds having the hardness shown in Table 3.

The mold life at that time is also listed in Table 3. In addition, the mold life is that of comparative steel No. It is expressed as a relative life based on the mold manufactured from No. 20. As shown in Table 3, the molds manufactured using the steel of the present invention have a longer mold life and exhibit better durability than molds manufactured using conventional steel.

Among them, No. 1 containing Ni in particular. 3, 4 and no
．． Nos. 12 to 18 show better durability. Texturing property Among the properties that steel for plastic molding molds should have, texturing property is one of the important properties.

In other words, corrosion treatment is sometimes applied to the surface of a mold to make plastic products matte, but at this time unevenness in texture tends to occur, which affects the aesthetic appearance of plastic products, so it is important to keep the degree of unevenness in texture as light as possible. I need to hold it down. The major cause of uneven graining is the microstructure of the mold, that is, the coexistence of structures with greatly different degrees of corrosion along the segregation zones. It is necessary to measure the uniformity of the tissue. Therefore, in conventional practical steels, a uniform heat treatment is sometimes performed before the quenching-tempering treatment, but in the case of the invention steel, the microstructure during the quenching-tempering treatment changes due to the balance of alloying elements. Since it is composed of Cyto, Akatsukimoto, and Shibainite, there is no difference in the degree of corrosion, and therefore, even if uniform heat treatment is not performed before the nuka-iring and tempering treatment, noticeable unevenness in graining does not occur. . As seen in the above examples, the steel for plastic molds of the present invention has excellent cross-sectional uniformity of heat treatment hardness, machinability, and graining workability, and has an HRC of 30% even when tempered at a high temperature of 60,000 or higher without residual heat treatment distortion. Because it has a certain level of hardness, it is an extremely suitable steel for plastic molds for large molds.

[Brief explanation of the drawing]

The figure shows the difference in hardness between the surface layer and the center of a large material. 1: Upper limit line, 2: Lower limit line.

Claims (1)

[Claims] 1 By weight: C: 0.2 to 0.5%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.5 to 4.0%, Mo
:0.03~2.0%, V:0.01~2.0%, S:
Steel for plastic molds with excellent texturability, consisting of 0.036 to 0.15% and the remainder substantially Fe. 2 By weight C: 0.2-0.5%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.5-4.0%, Mo
:0.03~2.0%, V:0.01~2.0%, S:
A steel for plastic molds with excellent texturability, consisting of 0.036 to 0.15%, Ni: 1.20% or less, and the remainder substantially Fe. 3 By weight C: 0.2-0.5%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.5-4.0%, Mo
:0.03~2.0%, V:0.01~2.0%, S:
0.036-0.15% and further Ca: 0.0005
~0.010%, Pb:0.03~0.20%, Te:
Steel for plastic molding molds containing at least one of Bi: 0.01-0.15% and Bi: 0.01-0.20%, the remainder being substantially Fe, and having excellent texturability. 4 By weight: C: 0.2-0.5%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.5-4.0%, Mo
:0.03~2.0%, V:0.01~2.0%, S:
0.036 to 0.15%, further Ni: 1.20% or less, Ca: 0.0005 to 0.0100%, Pb: 0
．． 03-0.20%, Te: 0.01-0.15%, B
A steel for plastic molding molds having excellent texturability and containing at least one i:0.01 to 0.20%, the remainder being substantially Fe.