JPH0121865B2 - - Google Patents

Description

[Detailed description of the invention]

purpose of invention

[Industrial application field]

The present invention relates to a steel for plastic molds that has excellent die-carving workability and low mechanical anisotropy.

[Conventional technology]

In recent years, large, high-performance machines have appeared in plastic molding machines, which are helping to improve work efficiency, but the demands on molds have become increasingly strict. That is, while the molding die is subjected to a more severe load than conventional molds, it is also required to have higher durability in terms of work efficiency. On the other hand, in order to cope with the increasing complexity and precision of mold shapes, improving the die-sinking workability of mold steel itself has become a major issue. In order to improve the machinability of steel for plastic molds, machinability-improving elements such as S and Pb have been added for some time, and these have been somewhat effective. Deterioration of mechanical properties due to the addition of sexual elements is unavoidable,
In particular, steel drawn by rolling or forging has strong anisotropy in mechanical properties, which is a major cause of reduced mold durability and weld cracking. This is because MnS sulfide inclusions, which effectively improve machinability, exist in the steel in an expanded form.
It is thought that this is because stress concentration occurs there and a notch phenomenon occurs starting from the inclusion. Inclusions generated from machinability elements also have a negative effect on the carving properties, which are important for steel for plastic molds, especially the mirror finish and texturing properties. It is easily understood that if large inclusions are exposed in the cross section, it will be a problem for mirror finishing. It seems that the exposure of inclusions does not pose much of a problem with graining processability, but
Those skilled in the art are well aware that subtle effects on unevenness significantly impair the aesthetic appearance of the grain. It has been found that the form of inclusions has a large effect on the effects of inclusions on mirror finish and graining properties. If inclusions are stretched out and have a length exceeding a certain limit, they will fall off from the surface during polishing to a mirror finish and the marks will become scratches.
Furthermore, foreign molecules are added to the pattern components of the grain, which impairs its aesthetic appearance. By controlling the morphology of sulfide-based inclusions in mold steel, which is used as a material for plastic molds, the present inventors have achieved good mold carving workability and are expected to improve the life of the mold. I thought I could do it,
As a result of research, it was found that S
It has been found that by adding Te and Te in a specific amount and at a specific ratio, most of the inclusions in steel, especially large inclusions, take on a nearly spherical shape. Furthermore, such mold steel not only has high machinability, but also has high properties required for plastic mold steel, such as mirror finish and grain workability, and also has low anisotropy in mechanical properties. It was confirmed that the durability after molding was also excellent.

[Problems to be solved by the invention]

The purpose of the present invention is to utilize the above-mentioned knowledge obtained by the inventors to improve die engraving workability, that is, the comprehensive characteristics of machinability, mirror finishability, and graining workability, as well as An object of the present invention is to provide steel for plastic molds that has high durability after molding. Composition of the invention

[Means to solve the problem]

The steel for plastic molding molds of the present invention has C:
0.40~0.65%, Si: 0.10~1.50%, Mn: 0.10~
1.50%, Ni: 1.0~3.0%, Cr: 0.50~2.0%,
In addition to Mo: 0.1~1.0% and V: 0.01~0.50%, %Te/%S: 0.04~0.5 S: 0.002~
0.40% and 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 ratio of major axis to minor axis. It is a die steel with excellent die carving workability, characterized by a hardness of 10 or less. The first point in producing the steel for plastic molds of the present invention lies in the proper adjustment of the components. First, molten steel is prepared in a furnace in which the content of alloy components other than S and other elements imparting free machinability is adjusted to a predetermined value. It is preferable to reduce the zero amount to 0.015% or less by vacuum degassing or the like to suppress the generation of oxide inclusions. Next, the %Te/
Te may be added and uniformly dispersed so that %S satisfies the condition of 0.04 to 0.5. Addition of Te can also be carried out in the injection tube. When adding Te,
It is desirable to remove large nonmetallic inclusions, which are mainly oxide inclusions, as much as possible, and for this purpose, it is effective to introduce a non-oxidizing gas such as argon into the molten steel and force stirring. It is.
This operation can be performed prior to the addition of Te, or can be performed while adding Te.

[Effect]

The role of each component element and the reason for limiting the composition range in the steel for plastic forming molds of the present invention are shown below. C: 0.40-0.65% In order to ensure hardness and wear resistance as steel for plastic molding, it is necessary to add 0.40% or more. If added in large amounts, the toughness would decrease and become unsuitable for practical use, so it was limited to 0.65% or less. Si: 0.10-1.50% In addition to deoxidizing during melting, it is an effective element for strengthening the base, and should be added at 0.10% or less. If the amount is too large, there will be many scratches on the ground, which is contrary to the purpose of the present invention.
Since machinability decreases, it should be kept within 1.50%. Mn: 0.10-1.50 This is an effective element for deoxidizing during melting and strengthening the base, and it is necessary to add 0.10% or more. If it becomes too large, toughness and machinability will decrease, so the upper limit is set at 1.50%. Ni: 1.0 to 3.0% Ni is an effective element for strengthening the matrix and ensuring hardenability, and should be added at 1.0% or more. Adding a large amount will reduce machinability and make it unsuitable for practical use, so it was limited to 3.0% or less. Cr: 0.50-2.0% This is an effective element for toughening the base and ensuring hardenability, wear resistance, and oxidation resistance, and is added in an amount of 0.50% or more. On the other hand, if it is too large, the toughness decreases and practicality is lost, so it should be kept at 2.0% or less. Mo: 0.10-1.0% V: 0.01-0.50% These are all strong carbide-forming elements and ensure heat treatment hardness and wear resistance. Mo is
It is necessary to add 0.10% or more of V and 0.01% or more of V. Adding a large amount makes manufacturing difficult and reduces toughness, so Mo should be 1.0% or less and V should be 0.5%.
Limited to the following. S: 0.002-0.40% S is essential for the formation of MnS-based inclusions, which are effective inclusions for improving machinability, and requires addition of 0.002% or more. The machinability improves as the amount increases, but it impairs the purity of the steel and impairs its toughness.
Keep it below 0.40%. Te: 0.001~0.40% This is an important element in adjusting the morphology of MnS-based inclusions and providing free machinability by itself.
Add 0.001% or more. If added in too large a quantity, hot workability will deteriorate, so it should not exceed 0.40%. %Te/%S: 0.04-0.5 In order to improve the morphology of sulfide inclusions, %Te/%S: 0.04-0.5
The ratio of Te/%S is required to be 0.04 or more, but if it exceeds 0.5, the effect will be saturated and the hot workability will also decrease, so the ratio of %Te/%S is set in the range of 0.04 to 0.5. Morphology and distribution of sulfide inclusions As mentioned above, the machinability, mirror finish and graining properties, and anisotropy of mechanical properties of steel for plastic molds are influenced by sulfide inclusions in the steel. Much depends on the form and distribution of objects. The inventors have confirmed that the major axis of the sulfide inclusions is
Relatively large inclusions of 2μ or more affect these properties, and if the large inclusions have a length ratio of 10 or less and are not extremely stretched into a rope-like shape, they will not exhibit any adverse effects; It is sufficient if the condition that the inclusions account for 80% or more of the total sulfide inclusions is satisfied.

【Example】

Steel having the composition shown in Table 1 was melted. For melting, after adjusting the alloying elements to a predetermined amount in a basic electric furnace, Te is added to the ladle according to the amount of S in the molten steel and dispersed uniformly. Agglomerated. The above sample material was hot forged at a forging ratio of about 10 to produce a rough mold. Continuing
Quenched at 850℃ x 2 hours, 570℃ x 12 hours,
After tempering, a sample was taken from the rough shape, and the strength anisotropy was examined by an impact test (JIS No. 3 Shapey test piece). The morphology and distribution of sulfide inclusions were investigated on the test pieces after the impact test.
The results are summarized in Table 2.

【table】

[Table] As shown in Table 2, the conventional steel prepared for comparison has low impact properties in the direction perpendicular to the forging direction.
The impact value is less than 1/2 compared to that in the forging direction, and the mechanical properties are highly anisotropic. On the other hand, all of the steels of the present invention show little decrease in impact properties in the direction perpendicular to the forging direction, and are 1/1/2 of the impact value in the forging direction.
Indicates a value of 2 or more. This is supported by the form and amount of sulfide inclusions in the steel. In the comparison steel, relatively spherical sulfide inclusions with a length ratio of 10 or less accounted for 20% of the total.
The other sulfide inclusions are elongated ones with a major axis ratio of 10 or more, whereas in the steel of the present invention, sulfide inclusions are relatively spherical with a major axis ratio of 10 or less. occupies the majority. Next, a mold for plastic injection molding was shaped using a rough mold for a mold manufactured from the sample materials shown in Table 1, and a part of the cavity surface was textured. Table 3 shows the time required for die engraving of each sample material as a ratio of the time to that of comparative steel.

[Table] When the textured surface was observed, the comparison steel had more than 20 scratches caused by expanded sulfide inclusions, but no scratches were found on the steel according to the present invention. From the above results, compared to conventional steel, S and
It can be seen that all of the steels of the present invention in which the amount of Te was adjusted were added, the time required for die engraving was short, and the texturability was also high. Effects of the Invention The steel for plastic forming molds of the present invention is produced by adding S and Te in appropriate amounts and in a specific quantitative ratio range to steel with a specific alloy composition to adjust the morphology of sulfide-based inclusions. It has good machinability, mirror finishing properties, and graining properties, so it can meet the high requirements for molds. This steel also has low anisotropy in mechanical properties, giving the mold excellent durability.

Claims (1)

[Claims] 1 C: 0.40-0.65%, Si: 0.10-1.50%, Mn:
0.10~1.50%, Ni: 1.0~3.0%, Cr: 0.50~2.0%,
In addition to Mo: 0.10~1.0% and V: 0.01~0.50%, Te/S: 0.04~0.5, S: 0.002~
0.40% and 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 10 or less, a steel for plastic molds with excellent die-carving workability.