JPH04263043A - Steel for molding die having high hardness and its manufacture - Google Patents

Abstract

PURPOSE:To obtain hardness about 40 points in HRC value by subjecting a low Ni precipitation hardening steel to an aging treatment. CONSTITUTION:This is a steel for a molding die having high hardness which is constituted of, by weight, 0.05 to 0.20% C, 0.10 to 1.0% Si, 0.8 to 2.0% Mn, 1.8 to <2.5% Ni, 0.5 to 1.5% Al, 0.7 to 1.7% Cu, 0.1 to 0.5% Mo 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 >=700identical, 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 then executing an aging treatment at 400 to 550 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 after solution heat treatment, as shown in Figure 1(a), which is a conceptual diagram of the treatment process, and have excellent properties such as fort etching workability. It is something.

[0003]Recently, particularly thick-walled mold materials have been developed, such as the one shown in Figure 1(b), which is obtained by aging treatment after hot rolling where a specific amount of reduction is applied at a specific temperature. Mn--Ni--Al--Cu--Mo precipitation hardening steel has been proposed in JP-A-63-162811.

[0004] Such conventional precipitation hardening steel is
In all cases, the aging temperature was set at approximately 450 to 550°C, and the aging treatment resulted in a hardness of around 40 in terms of HRC hardness value.

[0005]

[Problem to be solved by the invention] Under these circumstances,
The present inventors have proposed, separately from this application, a steel that can obtain higher hardness than the conventional precipitation hardening steel mentioned above and a steel that can obtain high hardness even after aging treatment in a high temperature range, as steel materials for forming dies. There is. As shown in Figure 1(c), the desired hardness can be obtained by controlling hot working conditions such as rolling or forging and subsequent cooling conditions, and by aging treatment in a predetermined temperature range. Mn-Ni-Al
-Cu-Mo based steel.

However, although these proposed steels have the characteristics of manufacturing conditions as described above, their compositions are not much different from conventional steels, and therefore it is difficult to maintain the desired hardness. One challenge is to reduce costs by reducing elements. On the other hand, the aforementioned Unexamined Patent Publication No. 6
No. 3-162811 discloses a precipitation hardening type steel with low Ni and high hardness.

[0007] Therefore, the present inventors studied the manufacturing conditions of the proposed steel by referring to the composition of this conventional steel and paying particular attention to Ni.
O-series steel with hardness equivalent to conventional steel was obtained.

[0008] The present invention was devised based on the above-mentioned circumstances, and aims to provide a low Ni precipitation hardening steel that can obtain a hardness of around 40 points in terms of HRC value, and a method for producing the same. .

[0009]

[Means for Solving the Problems] As mentioned above, the inventors of the present invention referred to conventional precipitation hardening steels, and as a result of conducting various experiments and research in order to improve the steel that has been proposed separately, we found that rolling Alternatively, by controlling hot working conditions such as forging and subsequent cooling conditions, Mn-Ni-Al-Cu-
By controlling the structure and precipitation of Mo steel and subjecting it to aging treatment at a temperature of 400°C or higher and 550°C or lower, we succeeded in obtaining high hardness at least equivalent to conventional steel.

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: less than 1.8 to 2.5%, Al: 0.5 to 1.5%,
Cu: 0.7-1.7%, Mo: 0.1-0.5%,
The balance consisting of Fe and unavoidable impurities is shown in Fig.
), specifically, when hot working after heating, the processing is completed at 700°C or higher, and then immediately cooled to 400°C or lower at a cooling rate of not less than air cooling and not more than 50°C/sec, and then further cooled to 400°C or less. 1 at temperatures above ℃ and below 550℃
By aging for ~100 hours, the HRC value is 40
They succeeded in obtaining steel with a similar hardness.

The present invention will be explained in detail below.

First, the reason for limiting the composition of the steel of the present invention is 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 to 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% in order 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 to ensure high hardness, so it is 1.8 to 2.5%.
Add less than If it is less than 1.8%, hardness cannot be ensured, so this was set as the lower limit. Further, since addition of 2.5% or more would have a negative effect on ductility and machinability, 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.

Since the steel of the present invention has a hardness of around HRC40 and is processed into a mold, it is necessary to ensure machinability. For this purpose, S may be added up to 0.3%.

[0021] 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. Further, V may be added in an amount of 0.12% or less in order to ensure hardness after aging. Furthermore, in order to refine the grain size and improve toughness, Ti: 0.5% or less, Nb + Ta: 0.3% or less,
Zr: 0.5% or less of at least one kind or two or more kinds may be selected and added. In addition, in order to improve machinability, Pb: 0.03-0.4%, Se: 0.03-0.
5%, Te: 0.01-0.3%, Bi: 0.02-0
．． At least one or two or more kinds may be selected and added in an amount of 3%.

Next, manufacturing conditions will be explained.

[0023] 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.

[0024] 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. Since a cooling rate exceeding 50° C./sec causes production problems such as quench cracking, this was set as the upper limit.

[0027] The aging temperature was limited to 400 to 550°C from the viewpoint of high temperature aging of the present invention. Since sufficient hardness cannot be obtained below 400°C, this was set as the lower limit. Also, 55
If the temperature exceeds 0°C, overaging occurs and the hardness decreases, so this was set as the upper limit.

Regarding the time, one hour or more is sufficient, but if it exceeds 100 hours, it becomes over-aged, so it was set in the range of 1 to 100 hours.

[0029]

[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.

[0031]

[Table 1]

[0032]

[Table 2]

Steels A to D in Table 1 all meet the composition range of the present invention, and numbers 1 to 12 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 40.
It is before and after.

[0034] Numbers 13 to 19 in Table 2 are comparative examples in which any of the manufacturing conditions were outside the scope of the present invention. this house,
Numbers 13 and after are comparative steel materials, and number 13 is a comparative steel material whose aging temperature was set higher than the range of the present invention, but it was overaged and had low hardness. No. 14 is a comparison steel material for which the aging time was set for a long time, and the hardness was low due to overaging. No. 15 is a comparison steel material that is not subjected to aging treatment, but its hardness is insufficient. Numbers 16 to 18 are steel materials obtained by conventional manufacturing methods, that is, comparative steel materials subjected to solution heat treatment and then aged, but with hardness of HRC.
The value is 38-39. Number 19 is a comparative steel material that is maintained at an isothermal temperature after hot rolling. It can be seen that only low hardness can be obtained in this case.

The above invention materials 1 to 12 and comparative steel material 1
FIG. 2 shows the correlation between aging temperature and hardness (HRC value) for Nos. 3 to 19. From the figure, it can be seen that within the aging temperature range of the present invention, the hardness is equivalent to that of the solution heat treated materials 16, 17, and 18.

[0036]

As explained above, according to the present invention, by aging precipitation hardening steel with low Ni, it is possible to obtain a steel material with a hardness of around 40 points in terms of HRC value. Great effects can be expected in terms of cost while ensuring accuracy and longevity during use.

[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: less than 1.8-2.5%, Al: 0.5-1.5%
, Cu: 0.7-1.7%, Mo: 0.1-0.5%
, the remainder consists of Fe and unavoidable impurities, and when hot working after heating, the processing is completed at 700°C or higher, and then immediately cooled to 400°C at a cooling rate of at least 50°C/sec with air cooling.
A high-hardness steel for forming dies, characterized in that it is obtained by cooling to below 0.degree. C. and further aging treatment at a temperature of 400.degree. [Claim 2] C: 0.05 to 0.20% by weight;
Si: 0.10-1.0%, Mn: 0.8-2.0%,
Ni: less than 1.8-2.5%, Al: 0.5-1.5%
, Cu: 0.7-1.7%, Mo: 0.1-0.5%
, when hot working steel consisting of the remainder Fe and unavoidable impurities after heating, the working is completed at 700°C or higher, and then immediately air cooled at a cooling rate of 50°C/sec or less for 4
1. A method for manufacturing a high-hardness steel for forming molds, which comprises cooling to 00°C or lower, and further aging treatment at a temperature of 400°C or higher and 550°C or lower for 1 to 100 hours.