JPH0512422B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has the property that by aging treatment after overlay welding, the welded steel part and the heat-affected zone can be photo-etched uniformly in the same way as the base metal part, and have good specularity. Mn−Ni
- Al-Cu-Mo age hardenable plastic mold steel, and a machinability-improving alloy component group in the mold steel;
This invention relates to a steel for plastic molds containing either one of the toughness and hardenability-improving alloy component group and the grain refinement-promoting synthetic component group, 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 many characteristics such as machinability, grindability, mirror finish, photoetchability, and weldability. It is required to have good properties such as hardness, electrical discharge machinability, compressive strength, corrosion resistance, wear resistance, and dimensional stability, but it is extremely difficult to fully satisfy these properties in current mold steels. It was hot. Some of these properties are mutually contradictory and some are essentially unavoidable. On the other hand, the roughness of recent plastic molds has tended to increase, but increasing the roughness reduces machinability, and with martensitic transformation steel, it is necessary to eliminate the discontinuous portion of the roughness in the heat affected zone after welding. It is essentially impossible to photo-etch this part uniformly, to suppress the rise in roughness of the electrical discharge machined surface, and to prevent deformation during heat treatment. Although denaturation during heat treatment is avoided by using pre-hardened steel that sacrifices machinability to some extent, the decrease in machinability increases the number of mold manufacturing steps and reduces productivity. In particular, when photo-etching is performed after welding, repeated quenching and tempering is performed to homogenize the structure of the weld and its heat-affected zone with that of the base metal, but this is insufficient and it is difficult to perform uniform photo-etching. It is. 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. For plastic molds, 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, but in order to ensure a uniform photo-etched surface, It is necessary to avoid partially repairing the mold surface by overlay welding, but this is becoming increasingly difficult 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 subsequent photo-etched surface. For this reason, as a result of investigating various mold materials, it was found that photoetching properties are 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, since the cavity is almost completed at the time of overlay welding, re-hardening is not effective as it may cause oxidation and deformation of the cavity. Based on this, the present inventor discovered that Mn-Ni has the characteristic that even if aging is performed after welding, the welded steel and weld heat-affected zone can be uniformly photo-etched in the same way as the base metal. -We proposed an Al-Cu-Mo age-hardening steel for plastic molds (see the back of Japanese Patent Publication No. 53-23764). This mold steel has excellent machinability, and can be easily processed into molds after age hardening to H _R C of approximately 40 or higher, or even after overlay welding. Although uniform photo-etching can be performed without oxidation or change by re-aging and hardening at a similar temperature, plastics with a good photo-etching surface have poor mirror finish properties. It was not fully satisfactory as a mold steel for producing products. According to subsequent studies by the present inventor, the reason for the poor specularity in the steel for molds described in the above publication is S, which is usually contained as an impurity of about 0.05% in the steel components.
Alternatively, S, which is actively included as an alloy component for improving machinability if desired, mainly reacts with Al,
Or, it reacts with Mn to produce sulfides, and these sulfides tend to segregate, and these sulfides are the cause of adverse effects on specularity, and the effects of the formation and segregation of these sulfides on specularity are It has been found that this problem can be avoided by suppressing the S content to about 0.008%. The present invention is based on these findings. The constituent components of the steel of the present invention and their composition ranges are: (1) C: 0.05 to 0.18%, Si: 0.15 to 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: 0.008
(2) Pb: 0.01-0.4%, Se: 0.01-0.5%, Te:
At least one or two or more machinability-improving alloy components selected from 0.01 to 0.3% and Bi: 0.01 to 0.3%. (3) Cr: 0.21-2.50, W: 0.5% or less, Co: 0.5%
At least one or more toughness and hardenability improving alloy components selected from the following: Be: 0.5% or less, B: 0.01% or less. (4) Ti: 0.5% or less, V: 0.5% or less, Nb+Ta:
At least one or two or more grain refinement promoting alloy components selected from 0.3% or less, Zr: 0.5% or less. (5) Pb: 0.01-0.3%, Se: 0.01-0.4%, Te:
At least one or two or more selected from 0.01 to 0.3%, Bi: 0.01 to 0.3%,
At least one or two or more selected from 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: 0.01-0.3%, Se: 0.01-0.4%, Te:
At least one or two or more selected from 0.01 to 0.3%, Bi: 0.01 to 0.3%,
Ti: 0.5% or less, V: 0.5% or less, Nb+Ta: 0.3
% or less, Zr: at least one or two or more selected from 0.5% or less. (7) Cr: 0.21-2.50, W: 0.5% or less, Co: 0.5%
Below, at least one or two or more selected from Be: 0.5% or less, B: 0.01% or less, Ti: 0.5% or less, V: 0.5% or less, Nb+
At least one or two or more selected from Ta: 0.3% or less and Zr: 0.5% or less. (8) Pb: 0.01-0.3%, Se: 0.01-0.4%, Te:
At least one or two or more selected from 0.01 to 0.3%, Bi: 0.01 to 0.3%,
At least one or two or more selected from Cr: 0.21 to 2.50, W: 0.5% or less, Co: 0.5% or less, Be: 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, Zr: at least one or two or more selected from 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 by performing re-aging after welding, the welded steel and the weld heat affected zone can be uniformly photo-etched in the same manner as the base metal, Mn−Ni−Al−Cu−, which has the characteristics of good specularity.
Mo-based age-hardening plastic mold steel, and
(2) Alloy components that improve the machinability of the steel with the basic composition; (3) Alloy components that improve the toughness and hardenability of the base iron in the steel with the basic composition; (5) Both machinability-improving alloy components and toughness/hardenability-improving alloy components in steel with basic component composition; (6) Machinability-improving alloy components and fineness in steel with basic component composition. (7) Both grain-promoting alloy components provide toughness and strength to steels with the basic composition.
Both the hardenability-improving alloy component and the grain refinement-promoting alloy component are added to the steel with the basic composition (8) to further improve its performance.
Mn-Ni-Al-Cu-Mo age-hardening steel for plastic molds. 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. For this reason, C is
It is necessary to limit it to 0.05-0.18%. (2) Silicon Si is added as an element to adjust the solution stiffness of the steel of the present invention, but if the mass of the steel material is large, the solution stiffness cannot be adjusted with manganese alone, so it should be added from 0.15 to 0.15 as long as it does not impair the ductility after aging treatment. Contains 1.0%. (3) Manganese Inclusion of Mn in the steel of the present invention affects the strength of both the solution treatment and aging states.
Together with C, Mn increases the hardenability during cooling from the solution temperature and can increase aging stiffness. In order to adjust the aging stiffness to at least H _R C of about 40 or more, it is necessary to contain Mn in the range of 1.0 to 2.0%. Note that if Mn is less than 1.0%, the effect will be small, and if it is added in an amount of more than 2.0%, it will impair machinability 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 becomes the nucleus of NiAl phase precipitation during subsequent aging treatment. It forms a phase together with Cu. Also, in the statute of limitations
It is an essential component that forms the a' phase together with Al. Further, as will be described later, since it is necessary to ensure photo-etching properties, 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 Al 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 photoetching properties, so it is necessary to add at least 0.5% or more. Furthermore, 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 a′ phase in the aged state of the steel of the present invention.
Effective when Ni and Al contents are low. Further, Cu is an essential alloying component in improving the notch toughness of the steel of the present invention by hot working. Further, since Cu is effective in improving machinability in the solution state, it is necessary to contain it at least 0.7%, but excessive addition of 1.7% or more is disadvantageous in terms of hot embrittlement and economic efficiency. Therefore, the amount of Cu is 0.7 to 1.7%
It is necessary to limit the range of (7) Molybdenum In the steel of the present invention, Mo is an essential alloying component to improve toughness and ensure excellent photo-etching properties. In particular, a suitable small amount of Mo has the property of providing a uniform microstructure and ensuring excellent photoetchability. To that end, at least
It is essential that the content be 0.1% or more, and the maximum is 0.4% or less. However, if Mo is increased to 0.4% or more, for example 0.5% or more, the stiffness increases and machinability deteriorates, making it undesirable as a steel for plastic molds. Further, the photoetching effect is reduced and the cost becomes high. Therefore Mo is 0.1
The limited range is ~0.4%. (8) Sulfur S is normally contained as an impurity, but it forms sulfides with Al or Mn, and the segregation of these sulfides deteriorates specularity. Particularly harmful to specularity
In order to suppress the formation of Al ₂ S ₃ , S should be less than 0.008% within the Al content range of 0.5 to 1.5%. (9) Lead, selenium, tellurium, bismuth In addition to the steel of the present invention, Pb: 0.01~0.4%, Se: 0.01~
If appropriate amounts of at least one or more of Te: 0.01 to 0.3% and Bi: 0.01 to 0.3% are selected and actively added in appropriate amounts, machinability can be significantly improved. However, it is not preferable to add more than the above-mentioned limited amount because it impairs ductility and toughness. Further, if the amount is less than the limited amount, the effect will be small. (10) Chromium, tungsten, cobalt, beryllium, boron When using the steel of the present invention for large molds, Cr: 0.21 to 2.50, W: 0.5% to improve toughness and hardenability.
Below, Co: 0.5% or less, Be: 0.5% or less, B: 0.01
It is effective to select at least one or two or more kinds and actively add and contain them in an appropriate amount of % or less. 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 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. (11) 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. To increase Katasa and solution Katasa more than necessary
Ti: 0.5% or less, V: 0.5% or less, Nb+Ta: 0.3%
Hereinafter, at least one or two or more types of Zr are selected and actively added within the range of 0.5% or less. The steel of the present invention exhibits small dimensional changes (heat treatment distortion) even when subjected to mold cutting in an aging state or overlay welding as required in that case, and even when re-aging is performed after overlay welding, and H _R C In order to obtain a flatness of approximately 40 or more and to ensure excellent photo-etching properties, the above alloy components are adjusted so that the difference in hardness between the welded steel part, weld heat affected zone, and base metal is approximately 2 H _R C or less. and the S contained as an impurity is adjusted to be below a specified amount, and the machinability of the Mn-Ni-Al-Cu-Mo age hardenable basic alloy steel and the steel are as follows. This is an age-hardenable steel for plastic molds containing any one of the alloy component groups for improving toughness, toughness and hardenability, and grain refinement promoting alloy components, singly or in combination.

【table】

[Table] The various components belonging to the machinability-improving alloy component group, the toughness and hardenability-improving alloy component group, and the grain refinement-promoting alloy component group have almost no effect within their respective limited ranges. They can be regarded as equivalents with similar effects. In order to suppress the S content to a low level, that is, less than 0.008%, when producing the steel of the present invention,
After melting in an electric furnace, it is preferable to adopt a method such as reduction and refining by the so-called LF method, and these methods reduce S, reduce sulfides such as Al ₂ S ₃ , and prevent segregation. As a result, a desired mold steel with excellent specularity can be obtained. The following is an example of processing molten steel melted in an electric furnace to reduce S using the LF method. That is, molten steel with an S content of 0.16% melted in a 10-ton electric furnace was transferred to a ladle, and while heating with electrodes, Ar gas was blown from the bottom of the ladle to heat and refine. Then add flux,
Furthermore, heat by blowing Ar gas at 30/min.
Add the required alloying elements, then increase the Ar gas flow rate.
The rate was increased to 45/min, and the reduction refining was completed by stirring without applying electricity. At that time, as shown below, molten steel was obtained in which the S content was extremely low and the O content constituting inclusions was also low. S: 0.007% O: 20 ppm Table 1 shows the chemical composition of the steel of the present invention and comparative material produced as described above.

[Table] After overlay welding of each steel material shown in Table 1, 500℃×4 hours
Aging treatment was performed, and photo-etching was further performed according to the steps shown in FIG. 1, and the surface texture of each was observed, and the quality of the photo-etchability was determined based on the presence or absence of "etching unevenness." Figure 2 is a diagram showing the photo-etching properties in terms of the relationship between the Al content and the Ni content. The shaded area in the figure is the range where "uneven etching" does not occur and good photo-etching properties are exhibited. . The part where "uneven etching" appears and the base material have different degrees of corrosion (roughness) on the etched surface, and during molding of plastic products,
As a result of this being transferred to the surface skin, it causes skin defects. The occurrence of this "uneven etching" is affected by the hardness difference between the base metal and the weld heat affected zone, and in order to obtain uniform photo etching properties by overlay welding and then aging treatment, it is necessary to remove the hardness of the heat affected zone in the area where the hardness decreases. The width d of
H _R
This can be prevented by setting it below C2. Next, the surface of each steel material shown in Table 1 was subjected to mirror finishing treatment, and the surface condition was observed. On the other hand, steel surfaces with poor specularity exhibit a cloudy state due to holes mainly caused by Al ₂ S ₃ falling out.
A steel surface with excellent specularity can be determined by showing a good specular surface. FIG. 3 shows the specularity in terms of the relationship between Al content and S content. From these FIGS. 2 and 3, it can be seen that the material of the present invention has good photo-etching properties and good specularity, but the comparative material does not satisfy either of the properties. Next, as an example of an alloy component that improves machinability, we conducted a cutting test using a slicing machine to perform downward slitting cutting on Copper No. 1, which does not contain Pb, and steel materials containing Pb shown in Table 2. The tool life of the steel containing Pb was significantly better than that of the steel containing no Pb, demonstrating that the addition of alloying components for improving machinability is extremely effective. Furthermore, the addition of a small amount of Pb does not have any adverse effect on age hardening properties, photoetching properties, and specularity. In addition to Pb, Se, Te, and Bi were also extremely effective in improving machinability in the same way as Pb when added in trace amounts within a limited range.

[Table] 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 improve the toughness of the base steel, It is certain that various performances of the basic component steel of the present invention, such as grain refinement, are further improved. Therefore, each of these machinability improving alloy component group, base iron toughness and hardenability improving alloy component group, and grain refinement promoting alloy component group is one type within each group within its limited range. Alternatively, in addition to selectively using two or more types, each group can be added singly or in combination to further improve the performance. It goes without saying that the steel of the present invention can be used not only in plastic molds but also 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 the drawing]

FIG. 1 is a flow sheet showing the photoetching processing conditions for each step. Figure 2 shows the preferred range of photoetchability for Al and
It is a curve diagram shown in relation to Ni content. FIG. 3 is a curve diagram showing the preferable range of specularity in relation to the Al and S contents.

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: 0.008%
It is said that even when aged after welding, the welded steel and weld heat-affected zone can be photo-etched as uniformly as the base metal, and have good specularity. Mn-Ni-Al-Cu-Mo age-hardening steel for plastic molds. 2 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: 0.008%
For the basic alloy composition consisting of less than Pb:
0.01~0.3%, Se: 0.01~0.4%, Te: 0.01~0.3%,
Bi: Contains at least one or more machinability-improving alloy components selected from 0.01 to 0.3%, and consists of residual Fe and impurities. A Mn-Ni-Al-Cu-Mo age hardenable plastic mold steel that allows for uniform photo-etching of the affected area in the same manner as the base material and has good specularity. 3 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: 0.008%
For the basic alloy composition consisting of less than Cr:
0.21-2.5%, W: 0.5% or less, Co: 0.5% or less,
Contains at least one or two or more toughness and hardenability improving alloy components selected from Be: 0.5% or less, B: 0.01% or less, consists of residual Fe and impurities, and is aged after welding. Mn-Ni-Al-Cu has the characteristics that even when the welded steel and the weld heat affected zone are photoetched uniformly in the same way as the base metal, it also has good specularity.
-Mo-based age-hardening steel for plastic molds. 4 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: 0.008%
For the basic alloy composition consisting of:
0.5% or less, V: 0.5% or less, Nb + Ta: 0.3% or less, and Zr: 0.5% or less. Mn-Ni is composed of -Al-Cu-Mo age-hardening 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: 0.008%
For the basic alloy composition consisting of less than Pb:
0.01~0.3%, Se: 0.01~0.4%, Te: 0.01~0.3%,
Bi: at least one or two or more machinability-improving alloy components selected from 0.01 to 0.3%;
Toughness and hardenability of at least one or more selected from Cr: 0.21 to 2.5%, W: 0.5% or less, Co: 0.5% or less, Be: 0.5% or less, B: 0.01% or less Contains improved alloy components, consisting of residual Fe and impurities, and even when aged after welding, the welded steel and weld heat-affected zone can be photo-etched uniformly in the same way as the base metal, and it has a mirror-like finish. Mn−Ni−Al is characterized by good
-Cu-Mo age-hardening steel for plastic molds. 6 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: 0.008%
For the basic alloy composition consisting of less than Pb:
0.01~0.3%, Se: 0.01~0.4%, Te: 0.01~0.3%,
Bi: at least one or two or more machinability-improving alloy components selected from 0.01 to 0.3%;
Ti: 0.5% or less, V: 0.5% or less, Nb+Ta: 0.3%
Below, Zr contains at least one or two or more grain refinement promoting alloy components selected from 0.5% or less, and consists of residual Fe and impurities, and even when aged after welding, welded steel and For Mn-Ni-Al-Cu-Mo age-hardenable plastic molds, the welding heat affected zone can be photo-etched as uniformly as the base metal, and has good specularity. steel. 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: 0.008%
For the basic alloy composition consisting of less than Cr:
0.21-2.5%, W: 0.5% or less, Co: 0.5% or less,
At least one or more toughness and hardenability improving alloy components selected from Be: 0.5% or less, B: 0.01% or less, Ti: 0.5% or less, V: 0.5%
Hereinafter, it contains at least one or two or more grain refinement promoting alloy components selected from Nb + Ta: 0.3% or less and Zr: 0.5% or less, and consists of residual Fe and impurities, and is aged after welding. Mn-Ni-Al-, which has the characteristics of uniform photoetching of the welded steel and weld heat-affected zone in the same way as the base metal, and has good specularity even when the welded steel and weld heat affected zone
Cu-Mo age-hardening 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: 0.008%
For the basic alloy composition consisting of less than Pb:
0.01~0.3%, Se: 0.01~0.4%, Te: 0.01~0.3%,
Bi: at least one or two or more machinability-improving alloy components selected from 0.01 to 0.3%;
Toughness and hardenability of at least one or more selected from Cr: 0.21 to 2.5%, W: 0.5% or less, Co: 0.5% or less, Be: 0.5% or less, B: 0.01% or less Improved alloy ingredients and Ti: 0.5% or less,
V: 0.5% or less, Nb+Ta: 0.3% or less, Zr: 0.5%
At least one or two selected from the following:
The remaining
It consists of Fe and impurities, and even when aging is performed after welding, the welded steel and weld heat affected zone can be photo-etched as uniformly as the base metal.
Mn− has the characteristics of good specularity and
Ni-Al-Cu-Mo age-hardening steel for plastic molds.