JPH025813B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to improvements in steel for plastic forming molds.

[Conventional technology]

Generally, it goes without saying that tool steel for forming should have high toughness and wear resistance, but steel for plastic forming molds also needs to have excellent workability including machinability. be. Conventionally, in order to improve the machinability of steel, S,
Addition of elements such as Se, Te, Bi, and Ca is being carried out. Since these have a negative effect on toughness, their content must be selected appropriately. S is the most typical machinability improving element, and serves this purpose mainly by forming MnS-based inclusions. However, the shape of these sulfide-based inclusions is a problem, and if they exist in a form stretched in a certain direction due to processing, they will increase the anisotropy of the mechanical properties of the material, which is undesirable.

[Problem to be solved by the invention]

In view of the above circumstances, an object of the present invention is to provide a tool steel containing S as an element for improving machinability, which achieves excellent toughness while exhibiting low anisotropy in mechanical properties centered on toughness. The object of the present invention is to provide materials, particularly steel for plastic molds.

[Means to solve the problem]

The steel for plastic molding molds of the present invention, which satisfies these demands, contains S: 0.035-0.40% and Zr: 0.001-0.5%, with the remainder being substantially Fe
Among the sulfide inclusions with a major axis of 2 μ or more existing in the steel, at least 80% have a major axis of 10 or less, and the area ratio occupied by Zr (C, N) is 0.4%. It is characterized by a hardness of HRC18 or higher. The following groups are representative of the alloying elements necessary for tool steel and their addition amounts: (1) C: 0.40-1.5%, Si: 0.10-2.5% and
Mn: 0.1-2.5% Typical steels containing this alloy component are:
It is S55C. (2) C: 0.30-0.60%, Si: 0.10-2.0%, Mn:
0.1~2.0%, Cr: 0.2~2.0% and Mo: 0.05~
1.0% Steel with this composition is SCM440. (3) C: 0.20-0.50%, Si: 0.10-2.0%, Mn:
0.10~2.5%, Cr: 1.5~3.5%, Mo: 0.10~1.5
% and V: 0.01 to 0.50% Some of the so-called "Cr-Mo-V steels" fall under this category. (4) C: 0.30-0.90%, Si: 0.10-1.5%, Mn:
0.10~1.5%, Cr: 6.5~15%, Mo: 0.01~1.50
% and V: 0.01 to 1.0% Other parts of "Cr-Mo-V steel" have this composition. (5) C: 0.95-2.0%, Si: 0.10-2.0%, Mn:
0.10~2.5%, Cr: 9.0~15%, Mo: 0.20~1.5%
and V: 0.01-1.0% This is the composition of SKD11 steel. (6) C: 0.10-0.25%, Si: 0.10-1.0%, Mn:
0.40~2.0%, Ni: 2.0~4.0%, Mo: 0.05~1.0
%, Cu: 0.50-1.5% and Al: 0.50-1.5% The so-called "3Ni-1Cu-Al steel" belongs to this category. (7) C: 0.10% or less, Si: 0.30% or less, Mn: 0.30
% or less, Ni: 10.0 to 25%, Cr: 7.0% or less,
Mo: 3.0~15%, Co: 5.0~25%, Al: 0.01~
1.0%, Ti: 1.0% or less, B: 0.20% or less, and
Ca: 0.10% or less “Marage steel” falls under this category.

[Effect]

In general, machinability and toughness are properties that are difficult to coexist, and it has been difficult until now to create tool steel that is excellent in both. The inventors conducted research on controlling the morphology of sulfide-based inclusions by using a specific amount of Zr in addition to an appropriate amount of the machinability-improving element S, and found that the presence of Zr Knowing that Zr (C, N), which is inevitably generated with the process, greatly impairs machinability, by regulating its amount, we were able to create a tool steel with excellent machinability and toughness. We were able to. The S content of 0.005 to 0.40% is determined mainly by the limit at which the desired machinability improvement effect can be obtained and the cleanliness of the steel, but it is also related to the Zr content. The lower limit of the addition amount of Zr of 0.001 to 0.5% is the minimum limit at which the above-mentioned effect of controlling the shape of sulfide-based inclusions is recognized, and the upper limit is the minimum limit for improving machinability and This value is from the standpoint of avoiding a decrease in hot workability. Both were determined in relation to the amount of S mentioned above. Regarding the morphology of sulfide inclusions, it is known that they greatly affect the anisotropy of the mechanical properties of steel, but their relationship with the practical properties of tool steels, especially mold steels, especially toughness, is unknown. Therefore, the inventors conducted a detailed investigation through numerous experiments. As a result, it was found that among the sulfide inclusions, large ones with a major axis of 2 μ or more affect the strength anisotropy, and even if they are large, if the major axis ratio is within 10 and they are not extremely elongated, If there is no negative effect, and if such large and not very long sulfide inclusions account for 80% or more of the total sulfide inclusions, then practically desirable isotropy can be achieved. I found out what to do. It is already known that sulfide-based inclusions (mainly MnS) in steel are easily stretched and become string-like during processing, but in steel containing Zr, Zr dissolves in MnS and As a result, the inventors found that the sulfide inclusions were relatively well maintained in a spherical shape. The form of the sulfide-based inclusions as described above is achieved by combining the appropriate addition amounts of S: 0.005 to 0.4% and Zr: 0.001 to 0.5%. Appropriate quantitative ratios can be easily determined by experiment. Zr(C,N), that is, carbides and nitrides of Zr, are extremely hard and cause significant wear to the cutting edge of the cutting tool, impairing machinability as described above. The inventors' research has revealed that the practically acceptable limit is 0.40% in terms of the area ratio on the cut surface of the steel material. In order to keep the area ratio of Zr (C, N) low while adding and utilizing Zr, care should be taken to avoid the formation of these carbonitrides when melting steel.
Zr is a highly active metal and easily bonds with N, C, and O, especially N, so when it is added, it eliminates N ₂ in the atmosphere.
Zr using Ar as a carrier gas to avoid reaction with
Addition methods such as powder lance injection are recommended. The respective roles played by other additive elements necessary for tool steel in the steel for plastic forming molds of the present invention are not fundamentally different from those known for conventional tool steels, but the characteristics of the present invention are This will be explained below in connection with. C: In order to ensure the hardness and wear resistance of tool steel, especially mold steel, the content is selected depending on the purpose of use. Excessive presence reduces toughness. Si: In addition to having a deoxidizing effect during melting, Si is useful for strengthening the matrix, so it is contained in a relatively large amount in the steel of the present invention. However, if the amount is too high, the toughness and resistance to softening at high temperatures will be reduced, leading to more scratches on the ground. Also,
It is also unfavorable for machinability. Mn: In addition to deoxidizing and desulfurizing effects during melting, Mn is also effective in improving hardenability, and is also used in a relatively large amount in the present invention. The limitations are a decrease in machinability and a decrease in toughness due to coarsening of crystallinity. Ni: Effective in strengthening the matrix and ensuring hardenability, it is added in the required amount depending on the purpose of the steel. However, there is a limit in terms of machinability. Cr: It strengthens the base and helps ensure hardenability, wear resistance, and oxidation resistance, so it is also added more actively for the purpose of use. The negative effects on both toughness and machinability define practical limits. Co: Still effective in strengthening the base and providing resistance to softening at high temperatures. However, if too much is added, the toughness will decrease and it will also be economically disadvantageous. Mo, W and V: These are all strong carbide forming elements and are useful for providing wear resistance, heat treat hardness and resistance to temper softening at high temperatures. Addition of a large amount also reduces toughness, makes manufacturing difficult, and impractical in terms of machinability. Cu: Promotes precipitation hardening and is effective in ensuring wear resistance. However, the presence of a large amount is unfavorable for toughness. Al: In addition to acting as a deoxidizing agent during melting, it improves toughness through grain refinement, and is effective in ensuring heat treatment hardness and wear resistance through precipitation hardening. However, if too much is added, it will cause more scratches on the ground, so there is naturally a limit. Ti: Refines crystal grains and increases toughness. However, like Al, it not only causes an increase in ground defects, which are excessively present, but also impairs toughness. The steel of the present invention has the advantage that it already has good machinability in each of the above compositions, but if even higher machinability is desired, in addition to a predetermined amount of S,
Pb: 0.30% or less, Se: 0.30% or less, Bi: 0.30% or less, Te: 0.15% or less, and Ca: 0.01% or less.
A species or two or more species can be included.

【Example】

Steel having the alloy composition shown in Table 1 was melted. (The numerical value is weight %, and the remainder is essentially Fe.)
These are composed of the existing tool steel and the steel of the present invention, which has the basic composition of the existing tool steel and has adjusted the amount of S and Zr. Each specimen was subjected to the required heat treatment, its hardness was measured, the shape of sulfide inclusions and the area ratio of Zr (C, N) were examined, and the aspect ratio of the impact value was measured. Next, practical molds were made from each sample material and their workability was evaluated. The above results are summarized in Table 2. The evaluation is the ease of machining and the required machining time (for example, for machinability, cutting time +
The productivity value is the total amount of time required for changing tools and processing chips, and the productivity value is calculated by comparing the time required for the same machining operation and calculating the value of the comparative example (if there are two types, the representative one). In the example, it is expressed as a ratio of how much work can be done within the same amount of time when 1 is taken as 1. As shown in Table 2, the examples of the present invention have lower anisotropy of mechanical properties than the comparative examples, and in terms of machinability, mirror finish,
It has excellent texturability and meets the requirements for plastic mold materials. The reason why workability is good is because most of the sulfide inclusions are relatively spherical, and if the inclusions are stretched, it takes a long time to reach a certain finish. Not only that, but there is a high possibility that they will appear as scratches when mirror finishing or texture processing is performed.

【table】

【table】

【table】

【Effect of the invention】

The steel for plastic molding molds of the present invention reduces the anisotropy of mechanical properties centered on toughness by regulating the morphology of sulfide inclusions, and also reduces the anisotropy of mechanical properties such as toughness. By keeping the area ratio below a certain limit, it was possible to improve machinability and other machinability. Therefore, this steel is an excellent material for plastic molds.

Claims (1)

[Claims] 1 C: 0.40-1.5%, Si: 0.10-2.5% and
Contains Mn: 0.10-2.5%, S: 0.035-0.40% and Zr: 0.001-0.5%, with the remainder being substantially
Has a composition consisting of Fe and exists in steel with a long diameter of 2μ
At least 80% of the above sulfide inclusions have a length ratio of 10 or less, an area ratio occupied by Zr (C, N) of 0.4% or less, and a hardness of HRC 18 or more. Steel for plastic molds. 2 C: 0.30-0.60%, Si: 0.10-2.0%, Mn:
0.1~2.0%, Cr: 0.2~2.0% and Mo: 0.05~1.0
With %, S: 0.035-0.40% and Zr: 0.001
~0.5%, with the remainder essentially consisting of Fe, and at least 80% of the sulfide inclusions with a major axis of 2 μ or more present in the steel have a major axis ratio of 10 or less, and A steel for plastic molds, characterized in that the area ratio occupied by (C, N) is 0.4% or less, and the hardness is HRC 18 or more. 3 C: 0.20-0.50%, Si: 0.10-2.0%, Mn:
0.10~2.5%, Cr: 1.5~3.5%, Mo: 0.10~1.5%
and V: 0.01~0.50%, S: 0.035~
0.40% and Zr: 0.001 to 0.5%, with the remainder substantially consisting of Fe, and at least 80% of the sulfide inclusions with a major axis of 2 μ or more present in the steel have a major axis ratio of 10 Below, Zr(C,N)
The area ratio occupied by is 0.4% or less, and the hardness is
A steel for plastic molds characterized by an HRC of 18 or higher. 4 C: 0.30-0.90%, Si: 0.10-1.5%, Mn:
0.10~1.5%, Cr: 6.5~15%, Mo: 0.01~1.50%
and V: 0.01~1.0%, S: 0.035~
0.40% and Zr: 0.001 to 0.5%, with the remainder substantially consisting of Fe, and at least 80% of the sulfide inclusions with a major axis of 2 μ or more present in the steel have a major axis ratio of 10 Below, Zr(C,N)
The area ratio occupied by is 0.4% or less, and the hardness is
A steel for plastic molds characterized by an HRC of 18 or higher. 5 C: 0.95-2.0%, Si: 0.10-2.0%, Mn:
0.10-2.5%, Cr: 9.0-15%, Mo: 0.20-1.5% and V: 0.01-1.0%, S: 0.035-0.40
% and Zr: 0.001 to 0.5%, with the remainder substantially consisting of Fe, and at least 80% of the sulfide inclusions with a major axis of 2μ or more present in the steel.
%, the length ratio is 10 or less, the area ratio occupied by Zr (C, N) is 0.4% or less, and the steel has a hardness of HRC 18 or more. 6 C: 0.10-0.25%, Si: 0.10-1.0%, Mn:
0.40~2.0%, Ni: 2.0~4.0%, Mo: 0.05~1.0%,
Along with Cu: 0.50~1.5% and Al: 0.50~1.5%,
Contains S: 0.035 to 0.40% and Zr: 0.001 to 0.5%, with the remainder consisting essentially of Fe, and at least 80% of the sulfide inclusions with a major diameter of 2μ or more present in the steel. The length to breadth ratio is 10 or less,
The area ratio occupied by Zr (C, N) is 0.4% or less,
A steel for plastic molds characterized by a hardness of HRC18 or higher. 7 C: 0.10% or less, Si: 0.30% or less, Mn: 0.30
% or less, Ni: 10.0 to 25%, Cr: 7.0% or less, Mo:
3.0~15%, Co: 5.0~25%, Al: 0.01~1.0%,
Ti: 1.0% or less, B: 0.20% or less, and Ca: 0.10
% or less, S: 0.035-0.40% and Zr:
0.001 to 0.5%, with the remainder substantially consisting of Fe, and at least 80% of the sulfide inclusions with a major axis of 2 μ or more present in the steel have a major axis ratio of 10
or less, and the area ratio occupied by Zr (C, N) is 0.4
% or less and a hardness of HRC18 or higher.