JPS61130468A - 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, 0.25-0.45% C, 0.10-1.50% Si, 0.10-1.50% Mn, 4.0-6.0% Cr, 0.10-1.50% Mo, 1.0-3.0% V, 3.0-5.0% W, 2.0-6.0% C0, 0.002-0.40% S, 0.001-0.40% Te (Te/S=0.04-0.5) and the balance Fe, 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 subject to more severe loads than conventional machines, molds with even better durability are required from the perspective of work efficiency, and mold steel that can meet these requirements is being developed. Development is progressing actively. 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 hypothesized that it would be possible to produce mold steel that has the same characteristics, and as a result of extensive research, we found that by adding S and Te in a specific ratio to the conventional mold steel composition, we could reduce the inclusions themselves that are generated in the steel. It was found that sphericity was promoted, and in particular, most of the large inclusions 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 form not only has good die-carving workability, but also
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. It was confirmed that sulfide-based inclusions can be realized by selecting a To/S weight ratio of 0.04 to 0.5. Furthermore, it can be manufactured by adding Te to molten steel in which components other than Te have been adjusted and dispersing it uniformly, 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. I also learned that it is preferable to
0.25-0.45%, Si: 0.10-1.50%.

Mn: 0. L O~1.50%, Cr:4.0~
6. G%, Mo0°10-1.50%, V:1. Q ~
3.0%, w:3. o ””5.0%, Co2.0~
6.0%, and Te/S in the range of 0.04 to 0.5,
30.002~0.40% or less, Te0.001~
0.40%, 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 have a major axis ratio of 1O or less It is a mold steel with excellent machinability.

Role and range of each component element in the present invention (wt%)
The reason for this limitation is shown below.

C: 0.25-0.45% 0.2 to ensure hardness and wear resistance as mold steel
It is necessary to add 0% or more. However, if added in a large amount, the toughness decreases, making it unsuitable for practical use, so it was limited to 0.45% or less.

Si: 0.10 to 1.50% Si is an effective element for strengthening the matrix in addition to its deoxidizing effect during melting, and must be added in an amount of 0.10% or more. However, if added in a large amount, the amount of carbon increases and the machinability decreases, so it was limited to 1,50% or less.

Mn: 0.10 to 1.50% Mn is an effective element to have a deoxidizing effect during melting and to strengthen the base, and must be added in an amount of 0.10% or more. However, if added in large amounts, toughness and machinability will decrease, so 1. It was limited to so% or less.

Cr: 4.0 to 6.0% This is an effective element for toughening the matrix and ensuring hardenability, wear resistance, and oxidation resistance, and is added in an amount of 4.0% or more.

However, if added in a large amount, the toughness decreases and becomes unsuitable for practical use, so the content was limited to 6.0%.

Co: 2.0 to 6.0% Co is an effective element for strengthening the base and ensuring wear resistance, and is added in an amount of 2.0% or more. However, if added in a large amount, the toughness decreases and becomes unsuitable for practical use, so the content was limited to 6.0% or less.

Mo: 0.10-1.50%, W: 3. Q ~s, o%
, ■: 1.0-3.0% All of the above elements are strong carbide-forming elements, and are effective elements for ensuring heat treatment hardness and wear resistance, and MO is 0.10%.
Above, W is added in an amount of 3.0% or more, and Vl is added in an amount of 0% or more. However, if added in large amounts, manufacturing becomes difficult and the toughness decreases, making it impractical for practical use. Therefore, Mo was limited to 1.50% or less, W to 5.0% or less, and ■ to 3.0% or less.

S: 0.002 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.

Te20,001~0.40%Mn
It is an important element in terms of adjusting the morphology of S-based inclusions and providing free machinability by itself, and is added in an amount of 0.001% or more. If the amount is too large, the hot workability will be poor, so it is limited to 0.40% or less. Furthermore, in order to improve the morphology of fE compound 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-mentioned effects will be reduced and the hot workability will also be reduced, so the weight ratio of Te/S is set in the range of 0.04 to 0.5.

The present inventors have confirmed that the form of sulfide inclusions and the anisotropy of the die-sinking workability and mechanical properties of steel for distribution molding greatly depend on the form and distribution of sulfide inclusions in the steel. We then investigated the properties of steel with various sulfide morphologies. As a result, it was found that relatively large sulfide inclusions with a major axis of 2μ or more affect the strength anisotropy,
If the length ratio is within 10 and the shape is not extremely filamentous, there will be no adverse effect, 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 O is reduced to 0.015% or less by vacuum degassing or the like to suppress the formation of oxide inclusions. Next, this molten steel in the furnace, ladle or tundish has a Te/S of 0.04 to 0.
It is sufficient to add Te so as to satisfy the condition 5 and to disperse it uniformly.Addition of sTe can also be carried out in an injection tube.

When adding Te, it is desirable to remove as much as possible large non-metallic inclusions, which are mainly oxide-based inclusions. It is effective to forcefully stir the mixture by introducing a gas of 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.

As can be seen in the same table, the impact properties of all the steels conventionally used are significantly lower in the direction perpendicular to the forging direction, and show an impact value of A or less compared to that in the forging direction. It can be seen that f1 has strong anisotropy in physical properties. On the other hand, it was confirmed that all of the steels of the present invention, in which S and Te amounts were adjusted and added, had little decrease in impact properties in the direction perpendicular to the forging direction, and exhibited an impact value of 4 or more compared to the impact value in the forging direction. Ta. In other words, it was confirmed that the steel of the present invention does not have very strong anisotropy in mechanical properties after forging or rolling, and has stable properties. The basis for this fact lies in the form and amount of sulfide inclusions in the steel.

In other words, in conventional steel, relatively spherical sulfide inclusions with an axis ratio of 10 or less are distributed in only about 20% of the total, and the rest are elongated sulfide inclusions with an axis ratio of 10 or more. In contrast, in the steel of the present invention, relatively spherical sulfide-based inclusions with a major axis ratio of 10 or less occupy the majority.

Therefore, the impact properties of conventional steels are due to the elongation of sulfide-based inclusions, so when melting thick steel, depending on the direction in which the sample is taken, after adjusting a predetermined amount of alloying elements in a basic electric furnace, Te was added to the ladle according to the sl in the molten steel, dispersed uniformly, and formed into an ingot by the bottom pouring method.

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, after quenching and tempering under predetermined conditions, a sample was taken from the same rough shape, and the strength anisotropy was examined by an impact test (JISa No. Charpy test piece). At the same time, the morphology and distribution of sulfide inclusions were investigated on the specimens after the impact test. The results are summarized in Table 2.

However, most of the sulfide inclusions in the steel of the present invention are close to spherical, so they are less affected by the direction in which the sample is taken, so the mechanical properties of the steel of the present invention are less anisotropic. This is easy to understand.

Next, using a rough mold for a mold manufactured from the sample materials in Table 1,
Die-sinking was performed on a mold for manufacturing lower spindles, and this was put into practical use.

Table 3 shows the die-sinking workability (ratio of time required for die-sinking based on comparative steel) and mold durability (mold life ratio based on comparative steel) of each sample material. Ta.

As seen in the same table, <Compared to conventional steels, the steels of the present invention with adjusted amounts of S and Te require less die-sinking time, and the durability of the manufactured molds is approximately 1.5%. It shows double.

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

Claims (1)

[Claims] (1) C: 0.25-0.45%, Si: 0.
10-1.50%, Mn: 0.10-1.50%, Cr
:4.0~6.0%, Mo:0.10~1.50%, V
:1.0~3.0%, W:3.0~5.0%, C0:2
．． S: 0.002-0.40%, Te: 0.001-0.0% and Te/S: 0.04-0.5.
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.