JPS61130469A - Steel for die - Google Patents

Abstract

PURPOSE:To obtain a steel for dies having high suitability to die sinking and low anisotropy in the mechanical properties and contg. sulfide inclusions having increased sphericity by adding S and Te to a steel for dies having a specified composition under restricted conditions. CONSTITUTION:This steel for dies such as dies for hot working or a metallic mold for molding plastics consists of, by weight, 0.30-0.70% C, 0.10-2.50% Si, 0.10-2.50% Mn, 0.10-2.0% Cr, 0.05-1.0% Mo, 0.002-0.40% S, 0.001-0.40% Te (Te/S=0.04-0.5) and the balance Fe or further contains <=1.0% Zr or <=0.3% Bi, and >=80% of sulfide inclusions of >=2mum major axis size in the steel have <=10 ratio between the major and minor axis sizes. The steel has superior durability even after forming into a metallic mold.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mold steel that has less anisotropy in mechanical properties and good die-sinking workability. This invention relates to steel for molds such as hot working molds and plastic molds, in which the form of sulfide inclusions in the steel is adjusted.

In recent years, large and high-performance machines have appeared for processing operations such as presses and forging, and efforts are being made to improve work efficiency, but along with this, the demands on molds have become increasingly strict. It's here.

In other words, while molds are subjected to more severe loads than conventional machines, molds with even better durability are required from the perspective of work efficiency, and mold steels that can meet these demands are needed. is being actively developed. On the other hand, in response to the increasingly complex shapes and high precision of molds, improving the die-scattering workability of mold steel itself has become a major issue.

In order to improve the machinability of mold steel, s
There are mold steels to which machinability-improving elements such as PB, PB, etc. have been added, and they have been somewhat effective. Steel shaped steel drawn by rolling has strong anisotropy in mechanical properties, which is a major cause of decreased durability of molds. This is because sulfide-based inclusions such as MnS, which effectively improve machinability, exist in an extended form, and stress concentration occurs there, causing a notch phenomenon originating from the inclusions. It is considered.

Therefore, attempts have been made to solve the above problem by making the shape of the sulfide inclusions as close to spherical as possible to alleviate stress concentration.

The present inventors believe that by introducing the above-mentioned concept to mold steel, which is the raw material for hot working molds or plastic molds, it is possible to expect an increase in the life of the mold and at the same time to improve the quality of mold engraving. We believe that it is possible to produce mold steel that has the same characteristics, and as a result of much research, we have found that inclusions that are generated in the steel by adding S and ↑e in a specific ratio to the conventional mold steel composition. It was found that the sphericity of the particles was promoted, and that most of the large inclusions in particular had a shape close to a spherical shape with a length-to-width ratio of 10 or less. Furthermore, mold steel having the above-mentioned inclusion morphology not only has good die-carving workability (
It has been confirmed that it has a characteristic of having significantly less anisotropy in mechanical properties, and that it can also be obtained with even better durability after molding. In other words, there is less anisotropy in mechanical properties,
In addition, in order to have good engraving workability, at least 80% of the relatively large sulfides with a major axis of 2 μ or more must have a major axis ratio of 10 or less, and It has been confirmed that such sulfide-based inclusions can be realized by selecting a Te/S weight ratio of 0.04 to 0.5. Furthermore, it can be manufactured by adding T@ to molten steel with adjusted components other than ↑e group and uniformly dispersing it, and prior to the addition of Te,
By introducing non-oxidizing gas into molten steel and forcibly stirring it, we float and remove large-sized inclusions, mainly oxide-based inclusions, which are harmful to machinability, mirror finish, graining, etc. Based on the above new knowledge, the mold steel of the present invention has C:
0.30-0.70%, Si: 0.10-2.50%.

Mn: 0.10~2.50%, (:r:0.10~2
．． 0%, M.

: 0.05 to 1.0% and if necessary Zr 1.0% or less or Bio, 30% or less, and Te/S:
In the range of 0.04 to 0.5, 50.002 to 0.4
0%, Tea.

001 to 0.40%, with the remainder substantially consisting of Fs, 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. It is a type steel with excellent machinability.

The role of each component element in the present invention and the reason for limiting the range are generally already known for each steel, but
It is shown below.

C: 0.30-0.70% 0.3 to ensure hardness and wear resistance as mold steel
It is desirable to add 0% or more. However, if added in large amounts, the toughness will decrease and it will become unsuitable for practical use, so 0.70%
Limited to the following.

Si: 0.10 to 2.50% Si is an element effective in strengthening the matrix in addition to its deoxidizing effect during melting, and is added in an amount of 0.10% or more. However, if a large amount is added, the amount of underground will increase and the machinability will decrease at the same time, so 2.50%
Limited to the following.

Mn: 0.10 to 2.50% Mn is an effective element for providing a deoxidizing effect during melting and for strengthening the base, and must be added in an amount of 0.10% or more. However, if added in large amounts, toughness and machinability will deteriorate, so the content was limited to 2.50% or less.

Cr: 0. l O~2.0% Element effective in toughening the matrix and ensuring hardenability, wear resistance, and oxidation resistance, and is added in an amount of 0.10% or more. However, if added in a large amount, the toughness decreases and becomes unsuitable for practical use, so the content was limited to 2.0% or less.

Mo: 0. 0 5 ~ 1. 0% Mo is a strong carbide-forming element and is an effective element for ensuring heat treatment hardness and wear resistance, and is added in an amount of 0.05% or more. However, adding a large amount makes manufacturing difficult and at the same time reduces toughness, making it unsuitable for practical use, so it was limited to 1.0% or less.

S: O, OO2 to 0.40% S is essential for the formation of MnS-based inclusions, which are effective inclusions for improving machinability, and is added in an amount of 0.002% or more. The machinability improves as the amount increases, but it impairs the cleanliness of the steel and reduces toughness, so it was limited to 0.40% or less.

Te: 0.001 to 0.40% Te is an important element in terms of adjusting the morphology of MnS-based inclusions and providing free machinability by itself, and is added in an amount of 0.001% or more. If too large a quantity, hot workability will be poor, so 0.40
% or less. Furthermore, in order to improve the morphology of sulfide-based inclusions, the weight ratio of Te/S must be 0.04 or more.

However, if the weight ratio of Te/S exceeds 0.5, the above effects will decrease and hot workability will also decrease.
The weight ratio of S is in the range of 0.04 to 0.5.

Morphology of sulfide-based inclusions and distribution The present inventors have discovered that the anisotropy of die-cutting workability and mechanical properties of steel for molding greatly depends on the morphology and distribution of sulfide-based inclusions in the steel. They confirmed the characteristics of steels with various sulfide morphologies.As a result, it was found that relatively large sulfide inclusions with a major diameter of 2 μ or more affect the strength anisotropy.
If this has a length ratio of 10 or less and has a form that is not extremely filamentous, it will not show any adverse effects, and based on the number of such inclusions in the total sulfide inclusions, 80 I learned that it is sufficient as long as the condition of accounting for a large portion of % or more is satisfied.

The first point in manufacturing the mold steel of the present invention described above is proper adjustment of the components. First, molten steel is prepared in which the contents of alloy components other than S and other free-cutting properties imparting elements are adjusted to predetermined values in a furnace. Preferably, the amount of Te/S is reduced to 0.015% or less by vacuum degassing or the like to suppress the formation of oxide inclusions. 0.04~0.
Te may be added so as to satisfy the condition 5 and dispersed uniformly. Te can also be added in an injection tube.

When adding Te, it is desirable to remove as much as possible large nonmetallic inclusions, which are mainly oxide inclusions. It is effective to forcefully stir the mixture by introducing This operation can be performed prior to the addition of Te, or can be performed while adding Te.

Hereinafter, the characteristics of the steel of the present invention will be explained in detail with reference to Examples.

<Example> Table 1 shows the composition of the sample steel.

In melting steel, after adjusting a predetermined amount of alloying elements in a basic electric furnace, Te is added to the ladle according to the amount of S in the molten steel, uniformly dispersed, and ingots are formed by the pouring method. did.

Next, using the test materials shown in Table 1, hot forging was carried out at a forging ratio of about 10 to produce a rough mold. Subsequently, the molds were hardened and tempered under predetermined conditions, and the mirror finish and texture required for plastic molds were investigated. At the same time, the distribution form of sulfide inclusions was investigated. The results are summarized in Table 2.

As shown in the same table, the steels of the present invention are both superior in mirror finishing and graining properties as compared to the comparative steels, indicating that they are suitable as steels for plastic molds. In addition, in the case of the steel of the present invention, as shown in Table 2, the major axis ratio is 10.
The comparatively spherical sulfide inclusions shown below account for most of the sulfide inclusions and are more uniformly distributed than the comparison steel, which has a positive effect on the mirror finish and graining properties. Seem.

As described above, the steel of the present invention is a mold steel for hot working in which the shape of sulfide-based inclusions is adjusted by adding appropriate amounts of S and Te, and it has good die-sinking workability and also contains sulfide-based inclusions. There is little anisotropy in mechanical properties based on the form of system inclusions (also, the mold has good mirror finish and graining properties, and excellent durability can be obtained when using various molds). It is an overall excellent mold steel.

Claims (3)

[Claims] (1) C: 0.30-0.70%, Si: 0.
10-2.50%, Mn: 0.10-2.50%, Cr
:0.10~2.0%, Mo:0.05~1.0% and T
e/S: in the range of 0.04 to 0.5, S: 0.002 to 0
．． 40%, Te: 0.001 to 0.40%, and the remainder is substantially Fe, and at least 80
A die steel with excellent machinability, characterized in that the length ratio is 10 or less. (2) C: 0.30-0.70%, Si: 0.
10-2.50%, Mn: 0.10-2.50%, Cr
:0.10~2.0%, Mo:0.05~1.0%, Z
r1.0% or less and Te/S: 0.04-0.5, S: 0.002-0.40%, Te: 0.001-0.
40%, 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. A mold steel with excellent machinability. (3) C: 0.30-0.70%, Si: 0.
10-2.50%, Mn: 0.10-2.50%, Cr
:0.10~2.0%, Mo:0.05~1.0%, B
i: 0.30% or less and Te/S: in the range of 0.04 to 0.5, S: 0.002 to 0.40%, Te: 0.001 to
0.40%, 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. A mold steel with excellent machinability.