JP2843375B2 - Free-cutting stainless steel for molds with excellent rust resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is characterized by having extremely excellent machinability, and also having excellent rust resistance, and is mainly used for a plastic molding die holder or The present invention relates to a free-cutting stainless steel for molds used for dies such as plastic molding.

[Conventional technology]

A large nesting hole is formed in the steel for the holder, which forms the outer frame of the plastic molding die, to tighten the body of the nested plastic mold. Excellent machinability is required. In addition, the holder is provided with a water cooling hole for shortening the molding cycle of plastic, and when rust is generated in this hole, the cooling effect is reduced, so that it is required to have excellent rust resistance and the like. .

Conventionally, SCM440 has been used for steel for plastic mold holders.
C-Mn-Cr-Mo-Fe-based steels have been used among low alloys, but in recent years, as mold processing companies have strongly demanded shortening of production delivery time and reduction of processing costs, etc. It has become. In order to reduce the number of processing steps in response to this demand, for example, as proposed in Japanese Patent Publication No. 52-1372, low alloys containing S as an element imparting free cutting properties have a low C-
Mn-Cr-Mo-S-Fe type steel and the like are generally used.

[Problems to be solved by the invention]

However, the low-alloy low-C-Mn-Cr-S-Fe-based plastic molding die holder steel described above is a low-Cr system and has a large amount of sulfide precipitation, so that rust easily occurs in water-cooled holes, There is a problem that the cooling effect is reduced.

In addition, as a tool steel with excellent machinability, Japanese Patent Publication No. 63-6638
No. 4, JP-B-63-66385 and JP-B-63-66386 are disclosed, however, they are not sufficient in terms of rust resistance and are not sufficient as plastic molding die holders and steel for die. there were.
The reason is that the steel disclosed in these known examples is relatively Cr
If the steel content is low, or if the Cr content is high, C
This is because the amount of the steel is large, and in this case, the carbide becomes excessively large or large, which is disadvantageous to rust resistance.

The present invention provides low-medium C-Mn-Ni-high Cr-Fe-based martensitic stainless steels by adding a small amount of S and dispersing MnS in the matrix to impart excellent machinability. It has excellent cutting ability and rust resistance, which are the required characteristics of steel for plastic mold holders, and is excellent in rust resistance, which has strength enough to be satisfied as a mold holder material. It is an object of the present invention to provide a hot-cutting stainless steel for molds.

[Means for solving the problem]

The steel of the present invention contains 14.00 to 17.00% of Cr, which is considerably higher than conventional steels for plastic molding, as a means to combine rust resistance and excellent machinability with respect to the C content. The Cr content ratio Cr / C should be 35 or more, and S should be
0.02 to 0.15% is added. It is also commonly added
Mo is not added to prevent deterioration of machinability. When S is added as a free-cutting element, rust resistance is degraded by sulfides. In the present invention, this disadvantage is compensated for by increasing the Cr content and the balance of Cr and C, and is improved. .

That is, in the first invention of the present invention, C 0.
20 ~ 0.50%, Si 2.00% or less, Mn 3.00% or less, S 0.02 ~
0.15% or less, Ni 3.00% or less, Cr 14.00 to 17.00%, and the ratio of Cr to C is Cr / C ≧ 35, with the balance being Fe and unavoidable impurities. Excellent rust resistance. The second invention is a free-cutting stainless steel for molds, wherein the weight percent is C 0.20 to 0.50%, Si 2.00% or less, Mn 3.00% or less, S 0.20 to 0.15% or less, Ni 3.00% or less, Cr 14.00-1
7.00%, and the ratio of the Cr amount to the C amount is Cr / C ≧ 35, Ca 0.01% or less, Ce 0.10% or less, Se 0.10% or less, Z
r Including one or more of 0.10% or less (2
It is a free-cutting stainless steel for molds with excellent rust resistance, characterized by being composed of 0.10% or less in the case of more than one kind), the balance being Fe and unavoidable impurities. In the third invention, C is 0.20 to 0.50%, Si is 2.00% or less, and Mn is 3.00% by weight.
%, S 0.02-0.15%, Ni 3.00% or less, Cr 14.00-1
7.00%, and the ratio of the Cr amount to the C amount is Cr / C ≧ 35, contains one or two of Cu 3.00% or less and Co 3.00% or less, and is composed of Fe and unavoidable impurities. The fourth invention is a free-cutting stainless steel for molds having excellent rust resistance. The fourth invention is, in terms of% by weight, C 0.20 to 0.50%, Si 2.00
% Or less, Mn 3.00 or less, S 0.02 to 0.15%, Ni 3.00% or less, Cr 14.00 to 17.00%, and the ratio of Cr to C is Cr / C ≧ 35, Cu 3.00% or less, Co 3.00% or less Of 1
Species or two and one or more of Ca 0.01% or less, Ce 0.10% or less, Se 0.10% or less, Zr 0.10% or less (in the case of two or more, 0.10% or less in total ), A free-cutting stainless steel for molds with excellent rust resistance, characterized by the balance of Fe and unavoidable impurities.

 Hereinafter, the present invention will be described in more detail.

The steel of the present invention is a steel having a low-medium C-Mn-S-Ni-high Cr-Fe alloy system as a basic component, and has a uniform martensitic structure by air cooling after quenching heating or hot working. And can maintain hardness around HRC30 by high-temperature tempering at 600 ° C or higher.Also, due to solid solution in a large amount of Cr base, an oxide film is formed and excellent rust resistance is obtained. Have Furthermore, when Co and Cu are contained singly or in combination, the effect of rust resistance is further improved.
Also, by dispersing a small amount of MnS in the base, the ductility of the base is appropriately reduced, and excellent machinability is obtained.
Further, when at least one of Ca, Ce, Se, and Zr is contained, MnS is further refined and uniformly dispersed, so that the machinability is further improved.

The steel of the present invention is supplied in a pre-hardened state having a hardness of about HRC30, and is used after being subjected to die-sinking and then polished.

Therefore, it does not require heat treatment after engraving, provides good machinability, shows excellent rust resistance, and prevents a decrease in cooling effect during plastic molding. Excellent free-cutting stainless steel for molds.

[Action]

 Next, the reasons for limiting the components of the steel of the present invention will be described.

C is a basic additive element necessary for maintaining a hardness of about 30 HRC by tempering at 600 ° C. or higher. If it is too large, it will form huge residual carbides and reduce machinability, so 0.
If it is too low, the effect of the above addition cannot be obtained, so it is made 0.20% or more.

Si is an element added as a deoxidizing agent at the time of producing a steel ingot, and if it is too much, the mechanical properties are reduced.

Mn is an important element added to enhance the hardenability of the steel of the present invention, to suppress the formation of ferrite, and to provide appropriate quenching and tempering hardness. If the content is too large, the viscosity of the base is increased and the machinability is reduced.

Ni is added to enhance the hardenability of the steel of the present invention and to suppress the formation of ferrite. If the content is too large, the viscosity of the base is increased and the machinability is reduced.

Cr is a very important element that enhances the rust resistance of the steel of the present invention. In the tempering treatment, Cr-based carbides are formed and added to form the strength of the steel of the present invention. If it is too large, the machinability will deteriorate.
If the amount is too low, the effect of the above addition cannot be obtained, so the content is made 14.00% or more.

In the present invention, the balance between C and Cr is required,
The ratio of the Cr amount to the amount Cr / C is 35 or more. The reason for this is
Cr in the matrix forms an oxide film, suppresses the progress of rust, and imparts good rust resistance. However, Cr is a carbide forming element, and when the amount of C increases, Cr and C A carbide is formed in between, and the amount of Cr in the matrix becomes poor. Therefore, in the balance between Cr and C, if Cr / C is less than 35, good rust resistance cannot be obtained, so Cr / C is made 35 or more.

When Cr / C is less than 35, for example, even when Cr is in the range of 14.00 to 17.00%, C exceeds 0.50%. For example, when C is about 0.60 to 0.80%, the amount of Cr in the matrix becomes poor, and the particle size becomes 20%.
A coarse residual carbide of about 30 [mu] m is formed, the oxide film on the periphery is destroyed, and rust develops. Therefore, C is 0.60
Rust of about 0.80% or more easily occurs as compared with the steel of the present invention.

Cu is added to impart excellent rust resistance to the steel of the present invention. If the content is too large, the hot workability is reduced and the machinability is also reduced.

Co, like Cu, is added to impart excellent rust resistance to the steel of the present invention. If too much, the specific machinability will decrease.
3.00% or less.

S is added to form MnS together with Mn and disperse in the matrix to impart excellent machinability to the steel of the present invention. If it is too large, huge MnS will be formed, leading to deterioration of machinability and rusting resistance.
If the amount is too small, the effect of the above addition cannot be obtained, so the content is made 0.02% or more.

Ca, Ce, Se, and Zr are all added to uniformly and finely disperse MnS and to impart excellent machinability. If it is too large, the hot workability is reduced, and the machinability is also reduced. Therefore, Ca 0.01% or less, Ce 0.10% or less, Se
0.10% or less, Zr 0.10% or less, and in the case of any two or more, the total is 0.10% or less.

〔Example〕

 Hereinafter, the steel of the present invention will be described based on examples.

Table 1 shows the chemical compositions of the steel of the present invention, the conventional steel, and the comparative steel used in the examples. Conventional steel M is the same as
Steel equivalent to 1372. Conventional steel N is SCM440.
The comparative steels O and P have the same Cr content as the steel of the present invention, but C
Since the amount is large, the value of Cr / C is low.

Table 2 shows the steels of the present invention, conventional steels and comparative steels, HRC30
After quenching and tempering with the target of, the result of the machinability test with an end mill is indicated by the machinability index based on the conventional steel N, and the mirror-finished 15 mm × 20 mm Perform a rust resistance test by spraying a 5% NaCl aqueous solution for 3 hours.
The measurement results of the rusting area are similarly shown by the rusting index based on the conventional steel N.

FIG. 1 shows a sketch of the steels A, H, I of the present invention and the conventional steel N observed and sketched.

According to Table 2, the machinability of the steel of the present invention is slightly inferior to that of the conventional steel N, but is superior to that of the conventional steel M, and the rust resistance is much better than that of the conventional steels M and N. I understand. The rusting resistance of the comparative steels O and P is slightly better than that of the conventional steel, but much lower than that of the steel of the present invention.

[Effects of the Invention] The present invention provides a base material having a high Cr martensite structure.
By dispersing MnS uniformly and adjusting it to about 30 HRC by heat treatment, it has both excellent machinability and rust resistance,
In addition, it has the necessary strength as a steel for a holder or a steel for a mold for a plastic mold. Therefore, the number of processing steps is greatly reduced during the production of the mold, and when the mold is water-cooled at the time of plastic molding, the cooling effect is prevented from being reduced, and the molding cycle can be greatly accelerated, so that the industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a sketch diagram showing the rusting state of the present invention A, H, I and conventional steel N during a rusting resistance test.

Claims (4)

(57) [Claims] (1) In weight%, C 0.20 to 0.50%, Si 2.00% or less, Mn 3.00% or less, S 0.02 to 0.15%, Ni 3.00% or less,
Cr 14.00-17.00%, and the ratio of Cr amount to C amount is Cr /
A free-cutting stainless steel for molds with excellent rust resistance, characterized by C ≧ 35 and the balance of Fe and unavoidable impurities. 2. In% by weight, C 0.20 to 0.50%, Si 2.00% or less, Mn 3.00% or less, S 0.02 to 0.15%, Ni 3.00% or less,
Cr 14.00-17.00%, and the ratio of Cr amount to C amount is Cr /
C ≧ 35, Ca 0.01% or less, Ce 0.10% or less, Se 0.10
% Or less, Zr 0.10% or less, including one or more of them (in the case of two or more, the total is 0.10% or less), the balance
Free-cutting stainless steel for molds with excellent rust resistance characterized by Fe and unavoidable impurities. (3) In weight%, C 0.20 to 0.50%, Si 2.00% or less, Mn 3.00% or less, S 0.02 to 0.15%, Ni 3.00% or less,
Cr 14.00-17.00%, and the ratio of Cr amount to C amount is Cr /
A free-cutting stainless steel metal excellent in rust resistance, characterized by C ≧ 35, containing one or two kinds of Cu 3.00% or less and Co 3.00% or less, with the balance being Fe and unavoidable impurities. Mold steel. (4) In weight%, C 0.20 to 0.50%, Si 2.00% or less, Mn 3.00% or less, S 0.02 to 0.15%, Ni 3.00% or less,
Cr 14.00-17.00%, and the ratio of the amount of Cr to the amount of C is C
r / C ≧ 35, one or two of Cu 3.00% or less, Co 3.00% or less, and Ca 0.01% or less, Ce 0.10% or less,
Any one or more of Se 0.1% or less and Zr 0.10% or less
A free-cutting stainless steel for molds with excellent rust resistance, containing at least one kind (in the case of two or more kinds, 0.10% or less in total) and the balance of Fe and inevitable impurities.