JPS6240420B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a mold steel that has little anisotropy in mechanical properties and has good die-sinking workability.
More specifically, the present invention relates to steel for molds such as hot working molds and plastic molds, in which S and Te are added under limited conditions to adjust the form of sulfide inclusions in the steel. In recent years, large and high-performance machines have appeared for processing operations such as pressing and forging, and efforts are being made to improve work efficiency, but along with this, the demands on forming dies have become increasingly strict. I'm getting old. In other words, while forming 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, some mold steels have traditionally been added with machinability-improving elements such as S.Pb, and this has been somewhat effective. A decrease in mechanical properties is inevitable due to the addition of
This 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 a 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 deduced that it would be possible to produce mold steel with a high
It was found that adding Te in a specific proportion promotes the sphericity of the inclusions themselves formed in steel, and that most of the large inclusions in particular have a morphology close to spherical with a length ratio of 10 or less. Furthermore, the mold steel having the above-mentioned inclusion morphology not only has good die-carving workability, but also has significantly less anisotropy in mechanical properties, and has even better durability after mold forming. I confirmed that I could get what I wanted. In other words, in order to have less anisotropy in mechanical properties and good engraving workability, relatively large sulfides with a major axis of 2μ or more should be used.
At least 80% of it must have a length ratio of 10 or less, and such sulfide inclusions must be
It was confirmed that this can be achieved by selecting a Te/S weight ratio of 0.04 to 0.5. Furthermore, Te
It can be manufactured by adding Te to molten steel with other ingredients adjusted and dispersing it uniformly, and by introducing a non-oxidizing gas into the molten steel and forcibly stirring it before adding Te, It has also been found that it is preferable to remove by flotation separation large-sized inclusions mainly consisting of oxide-based inclusions that are harmful to the properties of graining, mirror finishing, and graining. The mold steel of the present invention based on the above new knowledge has C: 0.80 to 1.60%, Si: 0.10 to 1.50%, Mn:
0.10~1.50%, Cr10.0~15.0%, Mo0.10~1.50
%, V0.05 to 0.80%, and Te/S in the range of 0.04 to 0.5, containing S: 0.002 to 0.40%, Te: 0.001 to 0.40%, and the remainder substantially consisting of Fe. However, it is a mold steel with excellent machinability, characterized in that 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. The role of each component element in the present invention and the reason for limiting the range (wt%) are shown below. C: 0.80-1.60% It is necessary to add 0.80% or more to ensure the hardness and wear resistance of mold steel. However, if added in a large amount, the toughness decreases, making it unsuitable for practical use, so it was limited to 1.60% or less. Si: 0.10-1.50% In addition to its deoxidizing effect during melting, it is an effective element for strengthening the base, and must be added at 0.10% or more. However, if added in large amounts, it would cause more scratches and at the same time reduce machinability, 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 it is necessary to add 0.10% or more. However, if added in large amounts, toughness and machinability will decrease, so it was limited to 1.50% or less. Cr: 10.0 to 15.0% It is an effective element for toughening the matrix and ensuring hardenability, wear resistance, and oxidation resistance, and is added in an amount of 10.0% or more. However, if added in a large amount, the toughness decreases and becomes unsuitable for practical use, so the content was limited to 15.0% or less. Mo: 0.10~1.50%, V: 0.05~0.80% All of the above elements are strong carbide forming elements,
It is an effective element for ensuring heat treatment hardness and wear resistance.
Mo is added in an amount of 0.10% or more, and V is added in an amount of 0.05% or more. However, Mo
was limited to 1.50% or less, and V was limited to 0.80% or less. S: 0.002-0.40% Inclusions effective for improving machinability
0.002% essential for the formation of MnS-based inclusions
Add 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: 0.001-0.40% An important element in adjusting the morphology of MnS-based inclusions and providing free machinability by itself.
Add 0.001% or more. If the amount is too large, hot workability will be poor, so limit it to 0.40% or less. Furthermore, in order to improve the morphology of sulfide 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 hot workability will also be reduced, so the weight ratio of Te/S is set in the range of 0.04 to 0.5. Morphology and distribution of sulfide inclusions The present inventors have confirmed that the die-sinking workability and anisotropy of mechanical properties of mold steel greatly depend on the morphology 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 influence the strength anisotropy, and that these inclusions have a long/minor axis ratio of within 10 and are not extremely stretched into a rope shape. It is recognized that if the sulfide-based inclusions contain sulfide-based inclusions, they do not show 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's ivy. 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, Te may be added to this molten steel in a furnace, ladle, or tundish so that Te/S satisfies the condition of 0.04 to 0.5 and uniformly dispersed. Addition of Te can also be carried out in the injection tube. When adding Te, it is desirable to remove as much as possible large non-metallic inclusions, which are mainly oxide inclusions. As shown in the same table, the steel of the present invention, in which the amounts of S and Te were adjusted and added compared to the conventional steel, required less die-scattering time and the durability of the manufactured mold was 1.2. It shows ~2.5 times. Example Table 1 shows the composition of the sample steel produced.

[Table] When melting steel, after adjusting a predetermined amount of alloying elements in a basic electric furnace, Te is added to S in the molten steel.
It was added to the ladle according to the amount, dispersed uniformly, and formed into an agglomerate by the 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, 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.

【table】

[Table] As shown in the same table, the steels of the present invention are both superior in mirror finish and graining compared to the comparative steels, indicating that they are suitable as steels for plastic molds. In addition, as shown in Table 2, in the case of the steel of the present invention, relatively spherical sulfide inclusions with a length ratio of 10 or less account for most of the sulfide inclusions, which are more uniformly distributed than the comparison steel, resulting in a mirror finish. It is thought that this has a positive effect on texture and texture. As described above, the steel of the present invention is a mold steel for hot working in which the morphology of sulfide-based inclusions is adjusted by adding appropriate amounts of S and Te. The mechanical properties based on the form of inclusions in the system have 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: 0.80-1.60%, Si: 0.10-1.50 in weight%
%, Mn: 0.10~1.50%, Cr: 10.0~15.0%,
Mo: 0.10~1.50%, V: 0.05~0.80% and Te/S:
S: 0.002-0.40%, Te: 0.001 in the range of 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
A mold steel with excellent machinability, characterized by the following: