JPS61130467A - 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, 0.30-0.50% C< 0.10-1.50% Si, 0.10-1.50% Mn, 4.0-6.0% Cr, 0.50-2.0% Mo, 0.20-1.50% V, 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 actively underway. 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 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. It was confirmed that 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 Te to molten steel with adjusted components other than Te and uniformly dispersing it, and by introducing a non-oxidizing gas into the molten steel and forcibly stirring it prior to the addition of Te. We also learned that it is preferable to float and remove inclusions of a size that mainly consists of oxide-based inclusions, which are critical to machinability, mirror finish, and graining properties. The mold steel of the present invention is based on G O
, 30-0.50%, So, 10-1.50%, Mn0
°10~1.50%, Cr4.0~6.0%, Mo0
．． 50~2゜0%, VO, 20~1.50% and T
So, 002 in the range of e/S 0.04 to 0°5
~ 0.40%, TsO, OO 1 ~ 0.40%, with the remainder essentially consisting of Fe, and at least 8 of the sulfide inclusions with a major axis of 2 μ or more present in the steel.
It is a mold steel with excellent machinability, characterized in that 0% has a length-to-width ratio of 10 or less.

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

C! 0.30-0.50% 0.3 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 0.65% 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 ground will increase and machinability will decrease, so it was limited to 1.50% or less.

Mn: 0.10 to 1.50% This is an effective element for providing a deoxidizing effect during melting and for strengthening the base, and it is necessary to add 0.10% or more. However, if added in a large amount, toughness and machinability will deteriorate, so it is limited to 1.50% or less.

Cr:4. O ~ 6.0% It is an element effective in 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% or less.

Mo: 0.50-2.0% V: 0.20-1.5
0%The above elements are all cooperative carbide-forming elements and are effective elements for ensuring heat treatment hardness and wear resistance, and Mn is 0.50.
% or more, (■) is added in an amount of 0.20% or more.

However, if added in a large amount, manufacturing becomes difficult and the toughness decreases, making it unsuitable for practical use, so MO was limited to 2.0% or less and V to 1.50% 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.

Te: 0.0 O1 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.

The present inventors have found that the form of sulfide inclusions and the anisotropy of the die engraving workability and mechanical properties of steel for distribution molding greatly depend on the form and distribution of sulfide inclusions in the steel. ! and investigated the properties of steels with various sulfide morphologies.

As a result, it was found that relatively large sulfide inclusions with a major axis of 2 μ or more influenced the strength anisotropy, and that these inclusions had a long-to-minor axis ratio of within 10 and were not extremely fibrously elongated. It is understood that if the sulfide-based inclusions contain sulfide-based inclusions, they will not cause any adverse effects, and that the conditions that such sulfide-based inclusions account for 80% or more of the total sulfide-based inclusions based on their number are satisfied. It was.

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 a furnace in which the content of alloying components other than S and other free-cutting properties imparting elements is adjusted to a predetermined value. It is preferable to reduce the amount of Te/S to 0.015% or less by vacuum degassing or the like to suppress the formation of oxide inclusions. is 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.

The characteristics of the steel of the present invention will be explained in detail below using examples.

(Example) Table 1 shows the composition of the melted test steel.

In melting steel, a predetermined amount of alloying elements are adjusted in a basic electric furnace, and then 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, 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.

As can be seen in the table, the impact properties of the conventionally used steels in the direction perpendicular to the forging direction are significantly lower, and the impact values are lower than those in the forging direction, indicating mechanical properties. It can be confirmed that the anisotropy is strong.

On the other hand, all of the steels of the present invention in which S and Te amounts were adjusted and added showed little decrease in the impact properties in the direction perpendicular to the forging direction, and were approved by W1 to show an impact value of 〃 or more compared to the impact value in the forging direction. did it. In other words, the steel of the present invention does not have very strong anisotropy in mechanical properties after forging or rolling.
It was confirmed that it has stable characteristics. The basis for this fact lies in the form and nature of sulfide inclusions in 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 steel are influenced by the direction in which the sample is taken because the sulfide inclusions are elongated. Therefore, it is easy to understand that the mechanical property anisotropy of the steel of the present invention is small because it is not affected by the direction in which the sample is taken.

Next, using a rough mold for a mold manufactured from the sample materials in Table 1,
A mold for manufacturing counter gears was carved and 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, in which the amounts of S and Te are adjusted, require less die-scabbing time and the durability of the manufactured molds is 1.3~1. It shows 1.4 times.

(Example 2) Table 4 shows the composition of the melted test steel.

In melting the steel, a predetermined amount of alloying elements were adjusted in a basic electric furnace, and then Te was added to the ladle according to the amount of S in the molten steel, uniformly dispersed, and agglomerated by the pouring method. Next, using the test materials shown in Table 4, 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 5.

As seen in the same table, compared to the comparative steels, all the steels of the present invention have excellent mirror finishing properties and graining properties, indicating that they are suitable as steels for plastic molds. In the case, as shown in Table 4, the major axis ratio is 10
Most of the following relatively spherical sulfide inclusions are distributed more uniformly than in the comparison steel, which is thought to have a positive effect on mirror finish and graining properties. .

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. The mechanical properties based on the form of inclusions in the system have little anisotropy, and the mold has good mirror finishing and graining properties, and excellent durability can be obtained when using various molds. It is an excellent mold steel.

Claims (1)

[Claims] (1) C: 0.30-0.50%, Si: 0.
10-1.50%, Mn: 0.10-1.50%, Cr
:4.0~6.0%, Mo:0.50~2.0%, V:
S: 0.002-0.40%, Te: 0.001 in the range of 0.20-1.50% and Te/S: 0.04-0.5
~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.