JPH07126802A - Steel for plastic molding prehardened die - Google Patents

Abstract

PURPOSE:To produce a steel combining excellent machinability and toughness which have not been shown in the conventional steel for a plastic molding prehardened die. CONSTITUTION:This is a steel for a plastic molding prehardened die having a compsn. contg., by weight, 0.08 to 0.17% C, <=0.60% Si, 1.25 to 1.70% Mn, 2.60 to 3.50% Ni, 0.95 to 1.50% Al and 1.80 to 2.50% Cu, and the balance Fe with inevitable impurities. Furthermore, this steel for a plastic molding prehardened die preferably contains Mo and W independently or combindedly by <=0.70% 1/2W+Mo or <=0.50% Cr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a new pre-harden type plastic molding die steel having extremely excellent machinability and sufficient hardness and toughness.

[0002]

2. Description of the Related Art Plastic molded pre-hardened die steels require not only machinability but also strength and wear resistance and appropriate toughness from the viewpoint of shortening the manufacturing period and improving the service life. . However, these required properties are contradictory properties, and a steel that satisfies all the properties has not been obtained. As a plastic molding pre-hardened die steel satisfying the above-mentioned properties to some extent, an intermetallic compound of Al and Ni is precipitated, Cu is contained in about 2%, and a Fe-Cu solid solution is finely precipitated to obtain hardness and A low C-Mn-Ni-Mo (W) -high Cu-Al alloy having a good machinability is proposed in JP-A-63-114942 and JP-A-63-183153.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The alloy described in No. 114942 is an alloy in which Al is limited to 0.9% or less in order to prevent deterioration of mirror surface property and toughness of a mold. With this alloy, although machinability can be secured to some extent by the addition of Cu, it is not possible to obtain machinability until the recent demand for further shortening the die manufacturing period is satisfied.

The alloy described in JP-A-63-183153 has a higher Mn content than that of the above-mentioned alloys, and has a Mn ratio of 1.
It is intended to improve the machinability by lowering it to 20% or less. However, although this alloy improves machinability, it has been found that the toughness deteriorates and cracks occur due to thermal stress when precision die machining is performed. An object of the present invention is to provide a steel having both excellent machinability and toughness, which are not present in conventional plastic molding pre-hardened mold steels.

[0005]

The present inventors have found that low C-Mn-
A detailed study of the relationship between the machinability and toughness of the Ni-Mo (W) -high Cu-Al alloy revealed that the Mn content was increased in comparison with the steel with excellent machinability in which the Al content was increased. Then, the inventors have found that there is an alloy composition range in which the toughness is excellent without impairing the excellent machinability due to the increase in Al, and the present invention has been reached.
That is, in the present invention, C 0.08 to 0.17% by weight% and Si 0.60
% Or less, Mn 1.25 to 1.70%, Ni 2.60 to 3.50%, Al 0.95
-1.50%, Cu 1.80-2.50%, balance Fe and unavoidable impurities. Further, the plastic molding pre-hardened mold steel of the present invention contains Mo and W alone or in combination.
/ 2W + Mo 0.70% or less, or Cr 0.50% or less is preferable.

[0006]

The most characteristic feature of the present invention is low C-Mn-
In the Ni-Mo (W) -high Cu-Al system plastic pre-hardened mold steel, the excellent machinability due to the increase in the amount of Al was not impaired even if Mn, which increases the toughness, was moderately increased. It has been found that it is possible to have both machinability and toughness. The plastic molding pre-hardened die steel of the present invention is supplied in a pre-hardened state (hardened) having a hardness of HRC 40 or higher (generally tempered at 400 ° C. or higher after quenching). The plastic-molded pre-hardened mold steel of the present invention is used as it is by subjecting it to a die-cutting process, a polishing process, and a high degree of mirror finishing and a graining process. Hereinafter, the reason for defining the alloy component range defined in the present invention will be described in detail.

[0007] Al increases the bainite transformation temperature to facilitate obtaining a desired massive upper bainite structure, and causes precipitation (aging) hardening by fine precipitation of Ni-Al intermetallic compound in the tempering (aging) treatment, and causes the massive upper bainite matrix. Together with this, it is one of the most important elements for forming the excellent machinability of the present invention. Al is also an additive element for obtaining the required hardness. In addition, Al has the effect of increasing the nitriding hardness during nitriding. If it is too large, the amount of alumina-based inclusions will increase, which will reduce the mirror finish and also reduce the pitting corrosion resistance, and lead to an excessive decrease in ductility, so 1.50% or less. Since it decreases, it is set to 0.95% or more.

[0008] Mn is an element that enables toughness to be enhanced without deteriorating excellent machinability due to an increase in Al content, and is one of the most important elements of the present invention. Mn is an element that enhances the toughness of the matrix, further enhances the bainite hardenability of the steel, suppresses the formation of ferrite, and is added in order to give an appropriate quenching and tempering (aging) hardness. is there. If it is too large, the toughness becomes too high, and the excellent machinability obtained by adding Al cannot be maintained, so the content is made 1.70% or less. On the other hand, if it is too small, the deterioration of toughness due to the addition of Al cannot be compensated by Mn, so the content is made 1.25% or more.

C is a low C-Mn-Ni-Mo (W) -high Cu-Al type plastic molding prehardened die steel for which the quenching structure is maintained as a massive upper bainite structure with good machinability and It is a basic additive element for providing a base for causing precipitation hardening based on the precipitation of Cu-Fe solid solution, Ni-Al intermetallic compound, Mo, and W carbide in the return. If the amount is too large, the matrix is martensite-structured to reduce the machinability, and excessive carbides are formed to reduce the machinability. Therefore, in the present invention, C is specified to be 0.08 to 0.17%. Si
Is added to enhance the corrosion resistance to the atmosphere during use. If it is too large, it causes the formation of ferrite and also reduces the machinability, so the content is made 0.60% or less.

Ni enhances the hardenability of bainite, suppresses the formation of ferrite, and when tempering (aging), N
The i-Al intermetallic compound is deposited to obtain the required hardness, appropriately reduce the ductility, and improve the machinability. If it is too much, it lowers the bainite transformation temperature, excessively refines the bainite structure, and increases the viscosity of the matrix to lower the machinability, so it is 3.50% or less,
If it is too low, the effect of the above addition cannot be obtained, so it is set to 2.60% or more.

Cu causes precipitation (aging) hardening by fine precipitation of Fe-Cu solid solution in the tempering (aging) treatment of the steel of the present invention, and together with the massive upper bainite matrix, the basic machinability of the steel of the present invention is Cu. It is an element for forming the alloy and for obtaining the required hardness. It also provides excellent corrosion resistance. If it is too large, the hot workability is deteriorated, bainite is made finer, and the machinability is rather deteriorated. Therefore, if it is too low, the effect of the above addition cannot be obtained, so it is made 1.80% or more.

[0012] Cr enhances the corrosion resistance of the steel of the present invention, enhances the hardness during nitriding, and suppresses rusting during polishing or during die storage, and may be added depending on the purpose and application. If it is too large, the bainite structure is refined, and the content is made 0.50% or less in order to maintain particularly high machinability. W and Mo precipitate fine carbides and cause precipitation (aging) hardening in the high temperature tempering (aging) treatment of the steel of the present invention exceeding 500 ° C.
Further, it is an element having an action of enhancing the corrosion resistance against the atmosphere during use, and may be added depending on the purpose and application. In the case of this application, it is not necessary to add a large amount, and if it is too large, the machinability is deteriorated. Therefore, it is preferably 0.70% or less at 1/2 W + Mo, and when the effect of the above addition is particularly desired, it is preferable.
1 / 2W + Mo: 0.10% or more.

[0013]

EXAMPLES Inventive steels and comparative steels having the chemical compositions shown in Table 1 were produced. After quenching these steels at 880 ℃, 550 ℃
Table 2 shows the hardness and the Charpy impact value of the sample obtained by heat treatment at. In addition, in order to evaluate the machinability, JIS
Performing a cutting test using an end mill made of SKH59 Co-containing high-speed tool steel, measuring the wear amount of the flank of the end mill,
The cutting distance until wear progresses to 0.3 mm is JIS SC
Evaluation was made using an index with comparative steel O corresponding to M440 as 100.
The results are also shown in Table 2.

[0014]

[Table 1]

[0015]

[Table 2]

As shown in Table 2, the C content is lower than that of the comparative steel O.
-Mn-Ni-Mo (W) -High invention Cu based on the high Cu-Al system A
To L and comparative steels M and N have excellent machinability and high hardness. Comparative steel M is a steel having less Mn than that of the present invention, and has the same machinability as that of the present invention, but the Charpy impact value is significantly smaller than that of the present invention, and the toughness is inferior. . Further, it is understood that the comparative steel N is a steel having less Al than the present invention, and although the machinability is superior to the comparative steel O, the machinability is inferior to the steel of the present invention. In contrast to such comparative steels O, M, and N, the steel of the present invention is not only excellent in machinability, but also has high toughness and high hardness, and is extremely excellent as a plastic molding prehardened die steel. I understand.

[0017]

INDUSTRIAL APPLICABILITY The steel of the present invention has excellent machinability and toughness, which are not present in conventional plastic forming pre-hardened mold steels, and is a steel indispensable for shortening the mold manufacturing time. . Further, since the steel of the present invention has a high toughness, cracks are unlikely to occur due to the thermal stress associated with die processing, which makes it particularly suitable for performing more precise die processing, and has an extremely great industrial value. .

Claims (4)

[Claims] 1. C 0.08 to 0.17% by weight, Si 0.60% or less, Mn 1.25 to 1.70%, Ni 2.60 to 3.50%, Al 0.95 to
A plastic molding pre-hardened mold steel, which comprises 1.50%, Cu 1.80 to 2.50%, the balance Fe and unavoidable impurities. 2. C 0.08 to 0.17% by weight, Si 0.60% or less, Mn 1.25 to 1.70%, Ni 2.60 to 3.50%, Mo or W alone or in combination of 1 / 2W + Mo 0.70% or less, Al 0.95 to 1.50.
%, Cu 1.80 to 2.50%, the balance Fe and unavoidable impurities, a plastic molding pre-hardened mold steel. 3. C 0.08 to 0.17% by weight%, Si 0.60% or less, Mn 1.25 to 1.70%, Ni 2.60 to 3.50%, Cr 0.50%
Hereinafter, a plastic molding pre-hardened mold steel characterized by comprising Al 0.95 to 1.50%, Cu 1.80 to 2.50%, the balance Fe and inevitable impurities. 4. C 0.08 to 0.17% by weight%, Si 0.60% or less, Mn 1.25 to 1.70%, Ni 2.60 to 3.50%, Cr 0.50%
Hereinafter, Mo and W alone or in combination of 1/2 W + Mo 0.70% or less, Al 0.95 to 1.50%, Cu 1.80 to 2.50%, balance Fe and unavoidable impurities, are used for plastic molding prehardened mold steel. .