JPH04263040A - Steel for molding die having high hardness and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a steel having high hardness of >=45 points in HRC value and useful as a steel for a die for plastic molding. CONSTITUTION:This is a steel for a die for molding having high hardness which is constituted of, by weight, 0.05 to 0.20% C, 0.10 to l.0% Si, 0.8 to 2.0% Mn, 2.5 to 3.5% Ni, 0.5 to 1.5% Al, 0.7 to 1.7% Cu, 0.1 to 0.5% Mo, >0.5 to 1.2% V and the balance Fe with inevitable impurities and obtained at the time of heating it and thereafter executing a hot working, by finishing the working at >=700 deg.C, thereafter immediately cooling it to <=400 deg.C at the cooling rate of that of air cooling or above to <=50 deg.C/sec, and furthermore, executing aging treatment at 450 to 570 deg.C for 1 to 100hr.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precipitation-hardening structural steel whose main use is a mold, particularly a plastic mold, and a method for manufacturing the same.

0002

BACKGROUND OF THE INVENTION Conventionally, age-hardening steel for plastic molds has been described, for example, in Denki Steel Vol. 41,No.
．． 1, pp. 27-33 (published by Daido Steel Research Group), Special Steel Vol. 20, No. 4, pp. 58-61 (published by Special Steel Club),
Mn-Ni
An age-hardening steel for plastic molds based on -Al-Cu-Mo is disclosed. These steels are obtained by aging treatment at around 500°C after solution heat treatment, as shown in Figure 1(a), which is a conceptual diagram of the treatment process, and they have excellent properties such as fort etching processability. It has excellent properties.

[0003] Recently, as shown in Fig. 1(b), especially thick-walled mold materials have been developed, 450 to 550
JP-A-63-162811 proposes a Mn-Ni-Al-Cu-Mo precipitation hardened steel obtained by holding the steel in a temperature range of 1 to 100 hours.

[0004] Such conventional precipitation hardening steel is
The former is subjected to solution treatment and the latter is subjected to aging treatment at approximately 450 to 550°C after hot rolling.
(see Figures 1(a) and (b)), both have a hardness of H
The RC hardness value is around 40.

[0005]

[Problems to be Solved by the Invention] However, with the recent diversification of types of plastic resins and plastic products, steel materials for molding molds are also required to have higher hardness. In particular, recently there are cases where molds for molding plastics containing glass fibers are required to have a hardness of over 45 in HRC value, and therefore conventional precipitation hardened steels are not able to adequately support molds for molding plastics. It is in.

The present invention has been devised in view of the above-mentioned problems, and has a high hardness of 45 points or more in terms of HRC value, and is particularly suitable for use as molds for molding plastics in recent years. The purpose is to provide a manufacturing method.

[0007]

[Means for Solving the Problems] The present inventors have conducted various experiments and research with reference to conventional precipitation hardening steel and the manufacturing method shown in FIGS. 1(a) and (b), and have found that rolling or Controlling the structure and precipitation of Mn-Ni-Al-Cu-Mo-V steel by controlling hot working conditions such as forging and subsequent cooling conditions, and aging treatment at a temperature of 450°C or higher and 570°C or lower. As a result, we succeeded in obtaining a steel with higher hardness than conventional materials.

That is, the present inventors have determined that the constituent components and their composition ranges are C: 0.05 to 0.20%, S: 0.05% to 0.20%, S:
i: 0.10-1.0%, Mn: 0.8-2.0%, N
i: 2.5-3.5%, Al: 0.5-1.5%, Cu
:0.7~1.7%, Mo:0.1~0.5%, V:
More than 0.5% to 1.2%, the balance consisting of Fe and unavoidable impurities is processed through the process shown in Figure 1(a), specifically at 700°C or higher during hot processing after heating. The hardness exceeds 45 in HRC value by immediately cooling to 400°C or less at a cooling rate of not less than air cooling and not more than 50°C/sec, and then aging for 1 to 100 hours at a temperature of not less than 450°C and not more than 570°C. We succeeded in obtaining steel.

The present invention will be explained in detail below.

First, the reasons for limiting the composition of the steel of the present invention are as follows.

C: C has the effect of facilitating the formation of martensite and bainite structures when the steel of the present invention is air-cooled or controlled cooled after hot working, so it is 0.05-0.05% by weight (the same applies hereinafter). Add 20%. If it is less than 0.05%, no effect on structure control will be observed, so this was set as the lower limit. Furthermore, addition of more than 0.20% impairs the machinability of the steel and reduces the toughness after aging, so this was set as the upper limit.

Si: Si is 0.1 to ensure hardness.
Add in a range of 0 to 1.0%. If it is less than 0.10%, hardness cannot be ensured, so this was set as the lower limit. Also, 1.
If it exceeds 0%, the ductility and machinability deteriorate, so this was set as the upper limit.

Mn: Like C and Si, Mn is added in a range of 0.8 to 2.0% to ensure hardness. 0.8
%, hardness cannot be ensured, so this was set as the lower limit. Further, if it exceeds 2.0%, the ductility and machinability deteriorate, so this was set as the upper limit.

Ni: In the steel of the present invention, a part of Ni is completely dissolved in solid solution with Cu to prevent red brittleness during hot working,
Hardenability is increased and hardness is ensured in the cooled state after hot rolling. In addition, in the aged state, it forms a NiAl phase with Al and is an essential component that ensures high hardness, so 2.5 to 3.5%
Added. If it is less than 2.5%, hardness cannot be ensured, so this was set as the lower limit. Further, if it exceeds 3.5%, it will have a negative effect on ductility and machinability, so this was set as the upper limit.

Al: Al and Ni in the aged state
It is an essential component for precipitating the Al phase, and has a content of 0.5 to 1
．． Add 5%. If it is less than 0.5%, the effect on hardness will be reduced, so this was set as the lower limit. Moreover, if it exceeds 1.5%, the manufacturability, mirror finish, and ductility are impaired, so this was set as the upper limit.

Cu: Cu plays an important role as a nucleus for precipitating the ε-Cu phase in the aged state, and is also effective in improving machinability, so it is added in an amount of 0.7 to 1.7%. If the content is less than 0.7%, these effects will be reduced, so this was set as the lower limit. Moreover, if it exceeds 1.7%, it becomes disadvantageous in terms of surface flaws during manufacturing and economical efficiency, so this is set as the upper limit.

Mo: Mo is added in an amount of 0.1 to 0.5% for the purpose of making the structure uniform and improving strength and toughness. 0.
If it is less than 1%, these effects will not be observed, so this was set as the lower limit. Moreover, if it exceeds 0.5%, the hardness becomes too high, which has an adverse effect on machinability and ductility, so this is set as the upper limit.

V: V is added in a range of more than 0.5% and less than 1.2% to ensure hardness in an aged state. 0.
If it is less than 5%, it becomes difficult to ensure hardness, so this was set as the lower limit. Further, if it exceeds 1.2%, the ductility and machinability deteriorate, so this was set as the upper limit.

Since the steel of the present invention has a hardness exceeding HRC45 and is processed into a mold, it is necessary to ensure machinability. For this purpose, S may be added up to 0.3%.

[0020] When applying the steel of the present invention to a large mold, in order to ensure hardenability, Cr: 0.21 to 2.5
0%, W: 0.5% or less, Co: 0.5% or less, Be:
At least one or two or more types of B: 0.5% or less and B: 0.01% or less may be selected and added. In addition, in order to refine the grain size and improve toughness, at least one or two or more of Ti: 0.5% or less, Nb+Ta: 0.3% or less, and Zr: 0.5% or less are added. Also good. Furthermore, in order to improve machinability, Pb: 0.03
~0.4%, Se: 0.03~0.5%, Te: 0.0
At least one or two or more of Bi: 1 to 0.3% and Bi: 0.02 to 0.3% may be selected and added.

Next, manufacturing conditions will be explained.

[0022] When heating the steel having the above-mentioned composition, the heating temperature is preferably in the range of 1300 to 950°C. If the temperature is lower than 950°C, solid solution of various components may not be sufficient and the hardness after aging may decrease. Furthermore, if the temperature exceeds 1300°C, there is a risk of deterioration in hot workability due to scale formation or grain boundary melting.

[0023] The reason for finishing hot rolling at 700°C or higher is that if the finishing temperature falls below this temperature,
This was set as the lower limit because the effect of cooling near the transformation point decreases and the effect of microstructure control is no longer recognized, and the anisotropy of the material increases.

Regarding the working rate, a working rate of at least 5% is required to ensure the effect of dispersing the precipitation sites during aging.

Immediately after hot working, air cooling at 50°C/se or higher
The reason for cooling at a cooling rate of less than c is to change the structure of the steel to martensite or bainite, and to prevent some precipitation hardening elements such as Ni, Al, and Cu from precipitating during cooling after processing. The purpose is to suppress this and contribute more effectively to precipitation hardening during subsequent aging. Since the above effect was not observed at a cooling rate lower than that of air cooling, this was set as the lower limit. A cooling rate exceeding 50° C./sec causes manufacturing problems such as quench cracking, so this was set as the upper limit.

[0026] The aging temperature was limited to 450 to 570°C from the viewpoint of high temperature aging of the present invention. As is clear from Figure 2, which shows the correlation between aging temperature and hardness, if the temperature falls below 450°C, sufficient hardness cannot be obtained, so this is the lower limit, while if it exceeds 570°C, overaging occurs and the hardness decreases. This was set as the upper limit because it would be low.

Regarding the time, 1 hour is sufficient, but if it exceeds 100 hours, it will be overdue, so 1 hour is sufficient.
It was set as the range of ~100 hours.

[0028]

[Examples] Examples of the present invention will be described in detail below.

The table below shows the composition, manufacturing conditions, and hardness of the steel materials used in the test. Among them, Table 1 shows the composition of steel materials,
Table 2 shows the manufacturing conditions and hardness of the present invention material and comparative material, respectively.

[0030]

[Table 1]

[0031]

[Table 2]

Steels A to F in Table 1 all meet the composition range of the present invention, and numbers 1 to 14 in Table 2 are examples that satisfy all of the manufacturing conditions of the present invention. As is clear from the same table, all the materials of the present invention have an HRC value of 45.
That's all.

[0033] Numbers 15 to 23 in Table 2 are comparative examples in which any of the manufacturing conditions were outside the scope of the present invention. this house,
Number 15 has an aging temperature lower than the range of the present invention, and number 16
is a comparative steel material with a high aging temperature. From the same table, the HRC value of both steel materials remains around 40. Further, FIG. 2 is a diagram showing the correlation between aging temperature and hardness as described above, and it can be seen from this diagram that the HRC value is less than 45 when the aging temperature range of the present invention is exceeded. Next, No. 17 is a comparison steel material for which the aging time is set for a long time, but the hardness is still low due to overaging. No. 18 is a comparison steel material that is not subjected to aging treatment, but this also has insufficient hardness. Next, numbers 19-2
2 is a steel material obtained by the conventional manufacturing method as shown in FIG. 1(a), that is, a comparative steel material subjected to solution heat treatment and then aged, and has a hardness of 39 to 42 in HRC value. Number 23 is a comparative steel material that is maintained at an isothermal temperature after hot rolling as shown in FIG. 1(b). In this case as well, it can be seen that only low hardness can be obtained at an aging temperature of 520°C.

[0034]

[Effects of the Invention] As explained above, according to the present invention, it is possible to obtain a steel material with high hardness of 45 points or more in HRC value by omitting the solution treatment temperature and aging precipitation effect type steel. It can be expected to have great effects in terms of specularity, precision, and lifespan when using molds.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing the manufacturing conditions of steel; (a) and (b) are diagrams showing the manufacturing conditions of conventional precipitation hardening steel, and (c) is a diagram showing the manufacturing conditions of the steel of the present invention.

FIG. 2 is a diagram showing the correlation between aging temperature and HRC value.

Claims (2)

[Claims] Claim 1: C: 0.05 to 0.20% by weight;
Si: 0.10-1.0%, Mn: 0.8-2.0%,
Ni: 2.5-3.5%, Al: 0.5-1.5%, C
u: 0.7-1.7%, Mo: 0.1-0.5%, V
: More than 0.5% to 1.2%, the balance consists of Fe and unavoidable impurities, and when hot working after heating, the processing is completed at 700°C or higher, and then immediately air cooled at 50°C/sec or higher.
Cool to 400℃ or less at the following cooling rate, and further cool to 45℃.
A high hardness steel for forming dies, characterized in that it is obtained by aging treatment at a temperature of 0°C or higher and 570°C or lower for 1 to 100 hours. [Claim 2] C: 0.05 to 0.20% by weight;
Si: 0.10-1.0%, Mn: 0.8-2.0%,
Ni: 2.5-3.5%, Al: 0.5-1.5%, C
u: 0.7-1.7%, Mo: 0.1-0.5%, V
: More than 0.5% to 1.2%, balance Fe and unavoidable impurities when hot working steel at 700°C after heating.
Finish the processing with the above steps, and then immediately cool it in air at 50℃/s or more.
1. A method for producing a high-hardness steel for forming molds, which comprises cooling to 400° C. or less at a cooling rate of EC or less, and further aging treatment at a temperature of 450° C. or higher and 570° C. or lower for 1 to 100 hours.