JPS5937738B2 - Age-hardening free-cutting steel for plastic molds - Google Patents

Description

[Detailed Description of the Invention] The present invention is characterized in that by aging treatment after overlay welding, the welded steel part and the heat affected zone have a property that allows for uniform photo-etching like the base metal part. Mn-
Ni-AI-Cu-MO-based free-cutting age-hardening plastic mold steel, and a machinability-improving alloy component group in the mold steel,
The present invention relates to a steel for plastic molds containing either one of the alloy component groups for improving toughness and hardenability and the alloy component group for promoting grain refinement, either singly or in combination.

Conventionally, carbon steel and low-alloy structural steel are often used as steel for plastic molds, but steel for plastic molds has characteristics such as machinability, grindability, mirror finish, photo-etchability, Good properties such as weldability, electrical discharge machinability, compressive strength, corrosion resistance, abrasion resistance, and dimensional stability are required, but it is extremely difficult to achieve these properties in current mold steels. Met. Some of these properties are mutually contradictory and some are essentially unavoidable.

On the other hand, there is a tendency for the roughness of recent plastic molds to increase, but increasing the roughness reduces machinability, and with martensitic transformation type steel, the discontinuous part of the roughness in the heat affected zone after welding is eliminated. In fact, it is essentially impossible to uniformly photo-etch this portion, to suppress the rise in roughness of the electrical discharge machined surface, and to prevent deformation during heat treatment. Although deformation during heat treatment is avoided by using pre-hardened steel, which sacrifices machinability to some extent, the decrease in rigidity increases the number of mold manufacturing steps and reduces productivity.

Especially when performing photo-etching after welding,
Although repeated quenching and tempering is performed to homogenize the structure of the weld zone and its heat-affected zone with that of the base metal, it is insufficient and it is difficult to perform uniform photo-etching.

In addition, it is quite difficult to manufacture good quality molds due to scale and distortion caused by heat treatment for homogenization.

Therefore, from the viewpoint of improving the productivity of plastic molds, there is a strong demand for mold materials that can be uniformly etched after overlay welding. Photo-etching or chemical milling methods are used to form a corrosion-resistant film with a desired pattern on the inner surface of the mold using a photographic method for plastic molding molds, but in order to ensure a uniform photo-etched surface, it is necessary to It is necessary to avoid repairing the mold surface by overlay welding, but it is becoming increasingly difficult to do so as patterns and designs on the mold surface become more complex.

In this case, a difference in hardness occurs between the welded steel part and the base metal part during overlay welding, and it becomes extremely difficult to ensure the uniformity of the photo-etched surface afterwards. For this reason, as a result of investigating various mold materials, it was found that photo-etchability is excellent when the metal structure is uniform and there is little variation in roughness.
Conventionally, the metal structure of martensitic steel after welding is composed of martensite → bainite → troostite → sorbite → base metal structure in the welded steel part, heat affected zone, and base metal part.

The only way to equalize both the metal structure and roughness is to requench and retemper. However, at the time of overlay welding, the cavity has already been completed, so oxidation and deformation of the cavity occur and re-quenching is not effective. The steel of the present invention has excellent machinability, so H
By processing the mold in a state that has been age hardened to RC approximately 40 or more, or by processing the mold easily even after overlay welding, and by performing re-age hardening treatment at a temperature of approximately 500℃, Uniform photo-etching can be performed without oxidation or deformation.

The constituent components of the steel of the present invention and their composition ranges are (1) C
:0.05~0.18%, Si:0.15~1.0%,
Mn: 1. C) -2.0%, Ni: 2.5-3.5%
, A12 0.5-1.5%, Cu: 0.7-1.7%,
MO: 0.1-0.4%, S: 0.05-0.3%
Steel consisting of residual Fe and impurities, and steel with the basic composition structure of (1) above, (2) Pb: 0.03 to 0.4%, Se: 0.03
~0.5%, Te: 0.01~0.3%, Bi: 0.0
At least one or two or more machinability improving alloy components selected from 3 to 0.3%.

(3) Cr: 0.21-2.50%, W: 0.5% or less, CO: 0.5% or less, Be: 0.5% or less, B: 0.
At least one or two or more toughness and hardenability improving alloy components selected from 0.01% or less.

(4) Ti: 0.5% or less, V: 0.5% or less, Nb+
At least one or more grain refinement promoting alloy components selected from Ta: 0.3% or less, Zr: 0.5% or less. (5) Pb: 0.03-0.3%, Se: 0.
03-0.4%, Te: 0.01-0.3%, Bi:
At least one or two or more selected from 0.03 to 0.3%, Cr: 0.21 to 2.50%, W: 0
．． 5% or less, CO: 0.5% or less, Be: 0.5% or less, and B: 0.01% or less.

(6) Pb: 0.03-0.3%, Se: 0.03
~0.4%, Te: 0.01~0.3%, Bi: 0.0
At least one or two selected from 3-0.3%
species or more, Ti: 0.5% or less, V: 0.5% or less, N
b+At least one or two or more selected from Ta: 0.3% or less, Zr: 0.5% or less.

(7) Cr: 0.21-2.50%, W: 0.5% or less, CO: 0.5% or less, Be: 0.5% or less, B: 0.
At least one or two or more selected from 0.01% or less, Ti: 0.5% or less, V: 0.5% or less, and Nb.
At least one or two or more selected from the following: Ta: 0.3% or less, Zr: 0.5% or less.

(8) Pb: 0.03-0.3%, Se: 0.0:
3-0.4%, Te: 0.01-0.3%, Bi: 0.
Cr: 0.21-2.50%, W: 0.
5% or less, CO: 0.5% or less, Be: 0.5% or less,
B: At least one or two or more selected from 0.01% or less, Ti: 0.5% or less, V: 0.5%υ
Bottom, at least one or two or more selected from Nb, Ta: 0.3% or less, and Zr: 0.5% or less. It is a steel that contains added. That is, the steel of the present invention has the basic composition as described in (1) above, and is characterized in that by re-aging after welding, the welded steel and the weld heat affected zone can be uniformly photo-etched in the same way as the base metal. Mn with
(1) Ni-AI-Cu-MO age-hardening free-cutting plastic mold steel; (2) machinability-improving alloy components listed above in the steel with the basic component composition; and (3) base iron in the steel with the basic component composition. (4) An alloy component that promotes grain refinement in the steel with the basic component composition; (5) An alloy component that improves machinability and an alloy that improves toughness and hardenability in the steel with the basic component composition. both of the ingredients,
(6) Both the machinability improving alloy component and the grain refinement promoting alloy component are added to the steel with the basic component composition;
Mn-NiAl-Cu-MO based age-hardening free-cutting plastic gold that further improves the performance by adding both of the hardenability improving components and (8) these three alloying components to the steel with the basic component composition. It is mold steel.

Next, the constituent components of the steel of the present invention and the reason for limiting the composition range thereof will be sequentially explained.

(1) Carbon C has the effect of facilitating the formation of martensitic or bainitic structures when the steel of the present invention is cooled relatively quickly from the solution temperature.

On the other hand, excessive addition impairs hot workability and machinability in the solution-treated state and reduces toughness after aging. Therefore, C is 0.0
It is necessary to limit it to 5-0.18%. (2) Silicon Si is added as an element to adjust the solution stiffness of the steel of the present invention. However, if the mass of the steel material is large, the solution stiffness cannot be adjusted with manganese alone. Contain 15 to 1.0%.

(3) Manganese The inclusion of Mn in the steel of the present invention affects the roughness in both the solution treatment and aging states.

Together with C, Mn increases the hardenability during cooling from the solution temperature and can increase aging roughness. In order to adjust the aging strength to at least HRC about 40 or more,
: It is necessary to contain it in the range of 1.0 to 2.0%. It should be noted that if Mn is less than 1.0%, the effect will be small, and if it is added in an amount of more than 20%, it will impair stiffness and toughness, which is not preferable. 4) Nickel In the steel of the present invention, a part of Ni forms a complete solid solution with Cu to prevent red brittleness during hot working, and in the solution state forms an ε phase that becomes the nucleus of NiAl phase precipitation during subsequent aging treatment. is formed with Cu.

Further, in the aged state, it is an essential component that forms the α' phase together with A1. Further, as will be described later, since it is necessary to ensure photo-etchability, it is necessary to limit the amount to a range of 2.5 to 3.5%, and outside this range, the effect is small.

5) Aluminum AI is an essential component for precipitating the NiAl phase in the aged state together with Ni, and as described below, it is necessary to ensure photoetchability, so it is necessary to add at least 0.5% or more.

Further, since addition of a large amount impairs manufacturability, mirror finish properties, and ductility, the upper limit is limited to 1.5%. 6) Copper Cu plays an important role as a nucleus for precipitating the α' phase in the aged state of the steel of the present invention, and is particularly effective when the Nl and AI contents are low.

Further, Cu is an essential alloy component in improving the notch toughness of the steel of the present invention by hot working. In addition, since Cu is effective in improving the stiffness in the solution state, at least 0.7
% or more, but excessive addition of 1.7% or more is disadvantageous in terms of hot brittleness and economic efficiency. Therefore C
The amount of u needs to be limited to a range of 0.7 to 1.7. 7
) Molybdenum In the steel of the present invention, MO is an essential alloying component for improving toughness and ensuring excellent photo-etchability.

In particular, a small amount of MO in a suitable amount has the property of presenting a uniform microstructure and ensuring excellent photo-etching properties. For this purpose, the content must be at least 0.1%, and the maximum content must be 0.4% or less. However, if the MO content is increased to 0.4% or more, for example 0.5% or more, the stiffness increases, making it undesirable as a steel for plastic molds. Moreover, the photo-etching effect is reduced and the cost becomes high. Therefore M.O.
The limited range is 0.1 to 0.4%. (8) S
: 0.05 to 0.3% Since the steel of the present invention is processed into molds in a state that has been age hardened to HRC4O or higher, it is necessary to contain at least 0.05% of S to increase the rigidity.

However, if it is contained in an amount of 0.3% or more, it tends to impair toughness and hot workability. Therefore, the amount of S is 0.05 to 0.
It is necessary to limit the range to 3%. (9) a, selenium, tellurium, bismuth Inventive steel and further Pb: 0.03 to 0
．． 4%, Se: 0.03~0.5%, Te: 0.01~
If at least one or two or more of Bi: 0.3% and Bi: 0.02 to 0.3% are selected and actively added, the stiffness can be significantly improved.

However, adding more than the above-mentioned limited amount is not preferable because it impairs ductility and toughness. Furthermore, if the amount is less than the limited amount, the effect will be small.
(When using the mirror of the present invention in a large mold made of IQI chromium, tungsten, cobalt, beryllium, and boron, Cr: 0.21 to 2.50% W:
It is effective to actively add and contain at least one or more of the following: 0.5% or less, CO: 0.5% or less, Be: 0.5% or less, B: 0.01% or less. It is.

In the case of Cr, it is necessary to limit the content to a range of 0.21% or more and 2.50% or less. Addition of these components is also useful for adjusting solution cracking and aging crackling, but addition of more than the above-mentioned limited amount increases material cost and has little effect, so it is necessary to keep the amount below the limited amount.

II) Titanium, vanadium, niobium + tantalum, zirconium When these alloy components are added to the steel of the present invention, the grain size can be refined and toughened, and it is also effective in improving notch toughness, but adding large amounts can cause aging damage. , Ti: 0.5% or less, V: 0 to increase the solution stiffness more than necessary.
．． 5% or less, Nb + Ta: 0.3% or less, Zr: 0.5
% or less, and actively add and contain at least one or two or more kinds.

The steel of the present invention may be manufactured in exactly the same manner as normally manufactured steel; for example, a steel ingot melted in an arc furnace is rolled or forged into a desired shape, and the product is subjected to age hardening treatment before use.

Dimensional change (heat treatment strain) is small, and HFLC of about 40 or more does not change even if the die is machined in the aging state or overlay welding is performed as necessary, especially after overlay welding and re-aging treatment. The above alloy components are adjusted so that the difference in hardness between the welded steel part, the weld heat affected zone and the base metal is approximately HRC 2 or less in order to ensure excellent photo-etchability. As <Mn-Ni-AI-Cu
- MO-based age-hardenable basic alloy composition steel, and any one of the alloy composition groups selected from among the machinability-improving alloy composition group, the toughness and hardenability improvement alloy composition group, and the grain refinement-promoting alloy composition group. This is age-hardening steel for plastic molds containing additives alone or in combination. Therefore, the various components belonging to the groups of alloy components to improve stiffness, alloy components to improve toughness and hardenability, and alloy components to promote grain refinement have almost similar effects within their respective limited ranges. It can be regarded as the equivalent of

Table 1 shows the chemical composition of an example of the steel of the present invention and a comparative material. Next, after overlay welding the currently used plus kick mold steel (Table 1 steel G), it was tempered at 650° C. for 3 hours, and then subjected to photo-etching according to the process shown in FIG. 4. The surface texture of the steel is shown in FIG.

As you can clearly see in this photo, the photo-etched surface
The unevenness extends from the welded steel part to the heat-affected zone of the base metal.'1 The part where the etching unevenness 11 appears and the base metal differ in the degree of corrosion (roughness) of the etched surface. During molding of plastic products, this is transferred to the surface texture, resulting in poor skin.Etching unevenness also appeared with other comparative steel glazes.

Next, the age hardenable mold steel of the present invention (Steel 31 in Table 1) was overlay welded, subjected to aging treatment at 500° C. for 5 hours, and then subjected to photo-etching, and the surface texture is shown in FIG.

As shown in this photo, it was confirmed that the etching unevenness I1 can be almost completely eliminated. In order to metallurgically elucidate the cause of the +1 etching unevenness 11, the hardness of the base metal and the weld heat affected zone was measured and the results are as shown in FIG.

Overlay welding → In order to obtain uniform fort etching properties through aging treatment, the width d of the roughness reduction area of the heat affected zone is set to 1.0.
mm or less, and the difference in wobble between the two parts (△H) is determined by HRC.
It can be seen that a value of 2 or less is sufficient. In the case of the steel of the present invention, it was confirmed that the difference in roughness between the welded steel part, the heat-affected zone, and the base metal part affected the photo-etchability.

No uneven etching was observed in other steel glazes made of the materials of the present invention.

In addition, as shown in Fig. 7, conventional age hardenable mold steel (No. 1
In surface steel A), 11 etching unevenness 1' occurs,
The inventive steel (Steel 31 in Table 1) could almost eliminate the problem.
In other words, when comparing the chemical components in Table 1, it is recognized that the presence or absence of MO has an effect on the excellent photo-etchability.

In the steel of the present invention, MO has the effect of lowering the bainitic transformation start temperature, promoting age hardenability, and shifting the overaging temperature to a higher temperature side, and as shown in Figure 2, MO has the effect of ensuring uniform photoetchability. In order to make the difference in roughness between the welded steel part, the weld heat affected zone, and the base metal part, which is an index, to HRC2 or less, and to make the width of the roughness reduction area of the affected zone to be about Inm or less, MO should be at least 0. It was also confirmed that it is sufficient to add .1% or more. Next, from a similar point of view, C
When the influence of C was investigated, it was found that the range in which the difference in roughness between the welded steel part and the base metal part in the aging treatment state (before photo-etching) is the smallest is C: 0.05 to 0.15%. Ta.

Furthermore, in order to ensure excellent photo-etchability in the steel of the present invention, we focused on the hardness difference between the weld heat-affected zone and the base metal and added MO. It was also confirmed that this was due to the inclusion of , AI, and Cu.

In addition, in the steel of the present invention containing 0.2% MO, when the limit at which the hardness difference after re-aging becomes HRC2 or less was organized using the amount of Cu as a parameter, Nl, Alj$6
The lower limits of Cu and Cu are 2.5%, 0.5%, and 0.7, respectively.
It has been confirmed that % is suitable. Further, FIG. 4 illustrates the plate-making process and the etching process in the process of creating a photo-etching pattern under the photo-etching processing conditions. Next, as examples of machinability-improving alloy components, the present invention steel containing S (Steel 31 in Table 1) and the conventional steel (Steel 31 in Table 1) are shown.
Table 1 Steel G) and age-hardening mold steel (Table 1 Steel C) that does not contain these components were subjected to a cutting test by downward slit cutting using a milling machine. The results are shown in Table 2. The tool life of the steel E of the present invention containing S shows much better results, that is, the addition of the machinability-improving alloy component is extremely effective. Further, as in Steel E, addition of a small amount of S does not have any adverse effect on age hardenability and photoetchability. *850 G0, Q550'CA
, C Next, FIG. 3 shows the relationship between the tool life and the S content when the samples, each of which had been adjusted to a hardness of about 40 HRC, were cut according to the cutting test conditions shown in Table 2.

As seen in the figure, it can be seen that as the S content increases, the tool life increases. That is, Mn-N
The steel according to the present invention, in which S is added to the i-AI-Cu-VI yarn age-hardening steel, has significantly better rigidity than the conventional plastic mold steels E and F, which contain approximately the same amount of S. Furthermore, it can be seen that when S, Pb, and Te coexist, the tool life increases dramatically. Furthermore, within the above-mentioned limited range of the basic component steel of the present invention, addition of various alloy components belonging to the toughness and hardenability improving alloy component group or the grain refinement promoting alloy component group can strengthen the base iron and refine the grain. It is certain that the various performances of the basic component steel of the present invention are further improved.

Therefore, each of these alloy component groups to be improved in stiffness, alloy component groups to improve toughness and hardenability of base iron, and alloy component groups to promote grain refinement may contain one or more types of alloy components within each group within their limited ranges. In addition to selectively using two or more types, each group can be added singly or in combination to further improve the performance.

In addition to being used in plastic molds, the steel of the present invention can of course be used in a wide range of similar applications.

As described above, the present invention has extremely high performance compared to conventional ones, and is novel and of great industrial value.

[Brief explanation of drawings]

Figure 1 is a relationship curve between the hardness difference between the heat-affected zone and the base metal of overlay welding after tempering or aging treatment and the width of the hardness reduction area of the heat-affected zone, and Figure 2 is a graph showing the hardness decrease. Figure 3 is a diagram showing the relationship between the width of the area and the amount of MO; Figure 3 is a diagram showing the relationship between tool life and S content; Figure 4 is a diagram showing the photo-etching processing conditions for each process; Figures 5 and 6. , 7 are photographs showing the condition of the photo-etched surface of various mold steels.

Claims (1)

[Claims] 1 C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1-0.4%, S: 0.05-0.3%, remaining Fe and impurities, and even when aging is performed after welding, the welded steel and weld heat affected zone are the same as the base metal. M has the characteristic of being able to perform uniform fort etching processing on
n-Ni-Al-Cu-Mo age-hardening free-cutting steel for plastic molds. 2C: 0.05-0.18%, Si: 0.15-1.
0% Mn: 1.0-2.0%, Ni: 2.5-3.5%
, Al: 0.5-1.5%, Cu: 0.7-1.7%,
In addition to the basic alloy components consisting of Mo: 0.1-0.4% and S: 0.05-0.3%, Pb: 0.03-0.
3%, Se: 0.03-0.4%, Te: 0.01-0
．． 3%, Bi: 0.03 to 0.3%, containing at least one or two or more machinability improving alloy components selected from the group consisting of residual Fe and impurities, and aged after welding. For Mn-Ni-Al-Cu-Mo age-hardening free-cutting plastic molds, the welded steel and weld heat-affected zone can be uniformly etched in the same way as the base metal. steel. 3C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1-0.4%, S: 0.05-0.3%, and further Cr: 0.21-2
．． 50%, W: 0.5% or less, Co: 0.5% or less, B
Contains at least one or two or more toughness and hardenability improving alloy components selected from e: 0.5% or less, B: 0.01% or less, and consists of residual Fe and impurities, and welding Mn-Ni-Al-Cu-M has the characteristic that even when post-aging is performed, the deposited steel and weld affected zone can be uniformly fort-etched in the same way as the base metal.
O-based age-hardening free-cutting steel for plastic molds. 4C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1 to 0.4%, S: 0.05 to 0.3%, and further Ti: 0.5% or less, V: 0.5% or less, Nb + Ta: 0 .3% or less, Zr
: Contain at least one or two or more grain refinement promoting alloy components selected from 0.5% or less, and the remaining Fe
Mn- and impurities have the characteristic that even when aging is performed after welding, the deposited steel and weld heat-affected zone can be photo-etched uniformly in the same manner as the base metal.
Ni-Al-Cu-Mo age-hardening free-cutting steel for plastic molds. 5 C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1-0.4%, S: 0.05-0.3%, and Pb: 0.03-0.03%
0.3%, Se: 0.03-0.4%, Te: 0.01
-0.3%, Bi: 0.03-0.3%, at least one or two or more stiffness-improving alloy components, Cr: 0.21-2.50%, W: 0.5% or less, Co: 0.5% or less, Be: 0.5% or less, B: 0.
At least one or two selected from 0.01% or less
Even when aging is performed after welding, the welded steel and weld heat-affected zone have a uniform fortification similar to the base metal. Mn-Ni-Al-Cu-Mo age-hardening free-cutting steel for plastic molds, which is characterized by its ability to be etched. 6C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1-0.4%, S: 0.05-0.3%, and Pb: 0.03-0.03%
0.3%, Se: 0.03-0.4%, Te: 0.01
-0.3%, Bi: 0.03-0.3%, at least one or more machinability improving alloy components selected from the group consisting of Ti: 0.5% or less, V: 0. 5% or less, Nb+
It contains at least one or two or more grain refinement promoting alloy components selected from Ta: 0.3% or less, Zr: 0.5% or less, and is composed of residual Fe and impurities, and is aged after welding. Mn-Ni-Al-Cu-Mo has the characteristic that even when the welded steel and the weld heat affected zone are subjected to uniform fort etching processing in the same manner as the base metal,
Age-hardening free-cutting steel for plastic molds. 7 C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1-0.4%, S: 0.05-0.3%, and further Cr: 0.21-2
．． 50%, W: 0.5% or less, Co: 0.5% or less, B
At least one or two or more toughness and hardenability improving alloy components selected from e: 0.5% or less, B: 0.01% or less, Ti: 0.5% or less, V: 0.5% or less, Nb+Ta: 0.3% or less, and Zr: 0.5% or less. Mn-Ni-Al-C has the characteristic that even when aging is performed after welding, the welded steel and weld heat affected zone can be uniformly fort-etched in the same way as the base metal.
u-Mo age-hardening free-cutting steel for plastic molds. 8 C: 0.05-0.18%, Si: 0.15-1.
0%, Mn: 1.0-2.0%, Ni: 2.5-3.5
%, Al: 0.5-1.5%, Cu: 0.7-1.7%
, Mo: 0.1-0.4%, S: 0.05-0.3%, Pb: 0.03-0.3%
, Se: 0.03-0.4%, Te: 0.01-0.3
%, Bi: at least one or two or more alloy components to be stiffened selected from 0.03 to 0.3%, and C
r: 0.21-2.50%, W: 0.5% or less, Co:
At least one or two or more toughness and hardenability improving alloy components selected from 0.5% or less, Be: 0.5% or less, B: 0.01% or less, and Ti: 0.5 % or less, V
: 0.5% or less, Nb+Ta: 0.3% or less, Zr: 0
．． At least one or two selected from 5% or less
Even when aging is performed after welding, the welded steel and weld heat-affected zone are uniformly fort-etched in the same way as the base metal. Mn-
Ni-Al-Cu-Mo age-hardening free-cutting steel for plastic molds.