JPS63183153A - Steel for prehardening metal mold for plastic molding - Google Patents

Abstract

PURPOSE:To manufacture a steel for prehardening metal mold for plastic molding having superior machinability and grinding finish characteristic, by incorporating specific percentage of C, Si, Mn, Ni, Al, and Cu to Fe. CONSTITUTION:A steel which has a composition consisting of, by weight 0.08-0.17% C, <=0.60% Si, 0.50-1.20% Mn, 2.50-3.50% Ni, 0.85-1.50% Al, 1.80-2.50% Cu, and the balance Fe with usual impurities and containing, if necessary, <=0.50$ Cr and/or either or both of Mo and W independently or in combination so that 1/2W+Mo=0.10-0.70% is satisfied is prepared. This steel is provided in a prehardened state with a hardness of HRC37 or above and is subjected, in this state, to die sinking and grinding work, and further to high-degree mirror finish and crimping working treatment and used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a new pre-hardened type steel for plastic molds having extremely excellent wave cutting properties and polishing finish properties.

[Conventional technology]

As a steel for high-grade plastic molds, it (1) has a good mirror finish and does not produce pinholes or other machine bits, (2) has good texturing properties, and (3) has good corrosion and rust resistance. (4) Good strength, wear resistance, and appropriate toughness; (5) Good machinability.

However, in recent years, shortened mold production times and good plastic molding skin have been raised as particularly important customer demands, and the combination of excellent machinability (tool life, cutting skin) with high hardness and mirror finish properties. The challenge was to develop steel for molds.

[Problem that the invention seeks to solve]

Increasing the cutting surface and mirror finish properties of conventional steels conversely leads to a reduction in the life of cutting tools, and it has not been easy to achieve both characteristics.

The object of the present invention is to provide an alloy that simultaneously satisfies the above-mentioned required properties.

[Means for solving problems]

That is, the steel of the present invention has low C-medium to low Mn-N1-M.

It is an alloy whose basic components are (W)-high Cu-high Al system, which produces a uniform upper bainite structure through quenching, and is further tempered at a high temperature of 500°C or higher to form Fe-Cu into a low C bainite base. , Ni-Al intermetallic compound.

M o (W) Precipitates carbides, imparts high strength through aging (precipitation) hardening, causes moderate embrittlement, imparts extremely good cutting texture and tool life, and, in combination with high hardness, It shows particularly excellent mirror finish. In addition, the inclusion of Cr, Mo, W, Cu, and Ni provides excellent corrosion resistance and rust resistance, and there is little hardening due to electric discharge machining, which also makes finishing easy.

The steel of the present invention is supplied in a pre-hardened state (generally tempered at 400°C or higher after quenching) with a hardness of HRC37 or higher, and can be directly processed through die engraving and polishing, as well as a high degree of mirror finish and graining. It is used by applying

Therefore, there is no need for heat treatment on the part of the user, and the combination of extremely good machinability, high hardness and uniform matrix, and the inherently excellent cleanliness of the steel provides extremely excellent polishing workability, mirror finish, and This is a new steel for plastic molds and engraving molds that provides texture workability and provides a long service life without worrying about settling or wear.

〔Example〕

The present invention will be explained below based on examples.

Table 1 shows the chemical composition of examples of the developed steel and comparative steel.
Comparative steel H has the highest quality mirror-finished skin and grained surface,
It is a type steel with particularly excellent toughness. Comparative steel I is slightly A
Although the steel has a lower l content and has good toughness, its machinability is lower than that of the steel of the present invention. Comparison steel J is 80M44
It is 0.

Table 1 Table 2 shows 80M440 (HRC35) in the case of cutting with an end mill of the invention steel HRC43 heat treated.
The machinability index and the maximum roughness ratio of the cut surface are shown based on .

Table 2 The steel of the present invention has a high hardness level of around HRC43, has much better machinability than S0M440 (HRC35,1), and has a much finer roughness on the cut surface.
This shows that it is highly effective in reducing the number of steps required for subsequent polishing.

Table 3 shows the cross-sectional dimensions of the steel of the present invention: 50 m1t x 150
For IImt forged and drawn material, after quenching and tempering to around HRC43, test pieces were prepared parallel (L) and perpendicular (T) to the forging direction.
) direction and tensile test and Charpy impact test (
2mo+μ notch) is shown.

Table 3 Inventive steel has lower elongation, reduction of area, and Charpy impact value in a tensile test than Comparative Steel I, which makes it extremely easy to remove chips by shearing during cutting, thereby making it easier to remove cutting tools. The life and roughness of the cut surface are particularly good, and the cut surface is greatly improved compared to the comparative steel weight and J (50M440).

On the other hand, elongation, reduction of area and Charpy impact value are low;
When used as a mold with a complex shape or thin wall part,
In some cases, it may be necessary to lower the hardness slightly in consideration of toughness.

In the case of comparative steel I, which has a lower Al content than the invention steel, the toughness,
Although the ductility is good, it does not reach the level of machinability of the steel of the present invention, which aims at extremely excellent machinability.

Table 4 shows the results of the rusting resistance test of the steel of the present invention in a salt water atmosphere.

The samples in Table 4 are 25IX x 25 mm, and after paper->puff mirror finishing, the number of rusted pieces is shown as an index when immersed in a salt water atmosphere for 2 hours, with the comparison steel weight with a lower Al content as 100. .

Although the steel of the present invention is not as good as comparative steel H, which does not contain Al, due to examination from the melting and ingot technology aspects, it has Al The generation of non-metallic inclusions can be suppressed to a small amount, and as a result, the number of rust-resistant inclusions comparable to Comparative Steel I is maintained.

Table 5 shows the time required for polishing after cutting of the steel of the present invention in comparison with comparative steel.

The samples in Table 5 were 50+nn+X50nm, and after heat treatment, they were cut with an end mill, and then polished to a mirror finish using a grindstone → paper → diamond compound polishing method.
The time required to complete finishing is expressed as an index with the comparative steel weight as 100.

The steel of the present invention has high hardness, does not cause deep abrasiveness, allows smooth removal of chips during polishing, and exhibits excellent polishability.

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

C maintains the quenched structure of the steel of the present invention into a blocky upper bainite structure with good machinability, and suppresses Cu-Fe during tempering.
, Ni-Al intermetallic compound and Mo, is the basic additive element to provide a matrix for precipitation hardening based on the precipitation of W carbides. If it is too large, the matrix becomes martensitic, reducing machinability, and excessive carbides are formed, reducing machinability.

In addition, it deteriorates electrical discharge machinability, reduces mirror finish properties, increases electrical discharge hardenability, and increases the number of polishing steps after electrical discharge machining, so it should be kept at 0.1.7% or less. If it is too low, it may lead to ferrite precipitation. , and sufficient tempering and aging) hardness cannot be obtained, so it is 0 in relation to the alloy composition of Al and other alloys.
．． 08% or more.

Mn is added to improve the bainite hardenability of the steel of the present invention, to suppress the formation of ferrite, and to provide appropriate quenching, tempering, and aging hardness. If it is too large, it will lower the bainite transformation temperature, make the bainite structure excessively fine, and increase the viscosity of the base, reducing machinability.
．． The content should be 20% or less, and if it is too low, the effect of the above addition cannot be obtained, so the content should be 0.50% or more.

Si is added depending on the purpose and use in order to improve corrosion resistance against the atmosphere during use. 0.60% as too much will lead to the formation of ferrite and reduce machinability.
The following shall apply.

Ni increases the bainitic hardenability of the steel of the present invention, suppresses the formation of ferrite, and improves the hardenability of the steel during tempering and aging.

By precipitating a Ni-Al intermetallic compound, we obtain the high hardness that is a feature of the steel of the present invention, and moderately reduce the ductility.
Added to improve machinability. If it is too high, it will lower the bainite transformation temperature, make the bainite structure excessively fine, and increase the viscosity of the base, reducing machinability, so it should be 3.50% or less, and if it is too low, the effect of the above addition will not be achieved. Therefore, it should be set at 2.50% or more.

Cr is added depending on the purpose and use in order to increase the corrosion resistance of the steel of the present invention and its hardness during nitriding, and to suppress rusting during polishing or storage of molds.

If it is too large, the bainite structure becomes fine and it becomes difficult to maintain the characteristics of the steel of the present invention, which aims at particularly high machinability, so the content is set to 0.50% or less.

W and Mo precipitate fine carbides during the high-temperature annealing and aging treatment of the steel of the present invention at temperatures exceeding 500°C.
1. In order to harden the steel of the present invention and to increase its corrosion resistance against the atmosphere during use.
Added depending on usage. When added, generally M
O is added alone, but depending on the purpose and use, combined addition of MO1W or W alone may be added. Regarding the maximum hardness of precipitation hardening, MO is advantageous, but regarding softening resistance, W is advantageous in the case of a single use, where it is not necessary to add a large amount, and too much will lead to a decrease in machinability. 1/2W+Mo should be 0.70% or less, and if it is too low, the effect of the above addition cannot be obtained, so 1/2W+Mo should be 0.1%.
0% or more.

In the annealing and aging treatment of the steel of the present invention, Cu is
-Precipitation (age) hardening due to the fine precipitation of Cu intermetallic compounds, combined with the massive upper bainite base, provides the steel of the present invention with extremely excellent machinability, and is the most effective method for obtaining the required hardness. It is one of the important additive elements and provides excellent corrosion resistance. If it is too high, it will reduce hot workability, and it will also make bainite finer, which will actually reduce machinability, so it should be 2.50% or less, and if it is too low, the above effects of addition cannot be obtained, so 1.
80% or more.

Al increases the bainite transformation temperature and makes it easier to obtain the desired massive upper bainite. During the tempering and aging treatment, Al brings about precipitation (age) hardening due to the fine precipitation of Ni-Al intermetallic compounds, which, together with the massive upper bainite base, It is an important additive element for providing the steel of the present invention with extremely high hardness and excellent machinability.

It also has the effect of increasing nitriding hardness during nitriding.

If it is too large, the tendency to form alumina-based inclusions will increase,
It lowers manufacturability, mirror finish and corrosion resistance, and leads to an excessive decrease in ductility, so it should be 1.50% or less, and if it is too low, the above-mentioned effect of addition cannot be obtained, so 0.
85% or more.

〔Effect of the invention〕

As detailed above, the steel of the present invention has an H
Even with the hardness of RC43 class, it maintains particularly good machinability, reduces polishing man-hours, and has excellent mirror finish, pitting corrosion resistance, electric discharge machinability, and texturability. HRC3
8-44) Steel for molds is provided.

Claims (1)

[Claims] 1 C 0.08 to 0.17%, Si 0.60% or less, M
n0.50-1.20%, Ni2.50-3.50%,
Al0.85-1.50%, Cu1.80-2.50%
, the balance being Fe and ordinary impurities. 2 C0.08-0.17%, Si0.60% or less, M
n0.50-1.20%, Ni2.50-3.50%,
Mo, W alone or in combination 1/2W+Mo0.10~0
．． 70%, Al0.85~1.50%, Cu1.80~
A steel for pre-hardened molds for plastic molding, characterized in that it consists of 2.50%, the balance being Fe and ordinary impurities. 3 C0.08-0.17%, Si0.60% or less, M
n0.50-1.20%, Ni2.50-3.50%,
Cr0.50% or less, Al0.85-1.50%, Cu
A steel for pre-hardened molds for plastic molding, comprising 1.80 to 2.50%, the balance being Fe and ordinary impurities. 4 C0.08-0.17%, Si0.60% or less, M
n0.50-1.20%, Ni2.50-3.50%,
Cr0.50% or less, Mo, W alone or in combination 1/2
W+Mo0.10-0.70%, Al0.85-1.5
0% Cu, 1.80-2.50% Cu, the balance Fe and normal impurities.