JPH042658B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a steel for pre-hardened molds for plastic forming, which has the greatest feature of having a small surface roughness during cutting and excellent mirror finish, and also has excellent texturability and toughness. . Steel for plastic molds should: (1) have good machinability; (2) Good mirror finish and no pinholes or other minute pits. (3) Good texturing properties. (4) Good corrosion resistance and rust resistance. (5) High strength and wear resistance. The following characteristics are required. High hardness in terms of (2) and (5). Regarding (2) and (4), the steel must be of a composition that is essentially easy to clean. Regarding (3), it is required that the hardenability is sufficiently high. In this case, it is sometimes advantageous in terms of mold accuracy, delivery time, and cost to meet the above requirements with prehardened steel that does not require heat treatment by the user. In order to meet the above requirements, many applications have been filed, and Japanese Patent Application Laid-Open No. 55-85655 discloses that C: 0.2 to 0.5.
%, Si: 2.0% or less, Mn: 2.0% or less, Cr: 0.5~
4.0%, Mo: 0.03~2.0%, V: 0.01~2.0%, S:
0.036 to 0.15%, the balance essentially consisting of Fe, further Ni: 1.20% or less, Cu: 2.0 or less, Al: 0.50%
Below, Zr: 0.50% or less, Ti: 0.50% or less, Ca:
0.0005~0.010%, Pb: 0.03~0.20%, Se: 0.03~
Steel for plastic molding molds is disclosed, which has four inventions containing at least one of Te: 0.20%, Te: 0.01 to 0.15%, and Bi: 0.01 to 0.20%. Conventionally, high-hardness pre-hardened steel has had problems such as requiring a long time to form a die by cutting, and the life of the cutting tool is short, increasing the number of tool changes. A method has been adopted to improve machinability by adding free-cutting elements. S, Se, Te, Pb, Ag, etc. are generally used as free-cutting elements. However, if the amount of free-cutting elements required to obtain sufficient machinability is added, there is a problem that the above properties (2), (3), (4), and (5) deteriorate to some extent due to this addition. It was happening. Furthermore, the steel for plastic molds disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-85655 has a low Ni content, so it is difficult to obtain hardness and strength, and the hardenability is also insufficient. The disadvantage is that it cannot be used. The steel of the present invention has a weight ratio of C0.04 to 0.30% and Si0.1 to
1.5%, Mn0.2~2.0%, Cr0.1~3.5%, Mo0.1~
3.0%, Cu0.2~3.0%, Ni1.0~4.0%, S0.05~0.2
%, by adding 0.05 to 0.50% of Al, (O+N)
After controlling Zr to a low level of 0.007 to 0.012%, Zr was reduced to 0.005%.
By adding ~0.20%, a large number of fine ZrO ₂ and ZrN, which have an effective inoculation effect on sulfides, are generated, which makes the sulfides extremely fine and evenly distributes them, making it difficult to use in sulfur free-cutting steel. In addition to significantly improving the conventional problems of uneven machinability, large surface roughness, and anisotropy of mechanical properties, suppressing the amount of C and heat treatment creates a uniform bainitic structure base with Cu-Fe intermetallic compounds and
Its greatest feature is that it has a mirror finish and grain workability due to the fine precipitation of carbides such as Mo and Cr, which gives it strength and hardness. In addition, in order to improve properties such as strength, hardness, and hardenability, more than 1.2% and less than 4.0% Ni is added, and as necessary to improve machinability and anisotropy of mechanical properties. , Se0.05~0.15%, Te0.05~0.15%,
It is possible to add 0.001 to 0.010% of Ca and 0.001 to 0.010% of Mg. Next, the reason for limiting the component range will be explained. C is a basic additive element for converting the quenched structure of the steel of the present invention into a bainitic structure with excellent machinability, mirror finish, and graining workability, and further for providing precipitation hardening with Mo, Cr carbide, or V carbide. be. However, if the C content is too large, the matrix will become martensitic and the machinability and mirror finish will be reduced, and the grinding time will be significantly increased. Since there is no benefit, it should be set at 0.040% or more. Si is contained as a deoxidizing agent and is effective in improving oxidation resistance and hardenability. However, if it is less than 0.1%, no deoxidizing effect can be obtained in steel manufacturing, and if it exceeds 1.5%, the effect of improving oxidation resistance will be reduced and machinability will deteriorate, making it impractical. Mn improves hardenability, adjusts bainite hardness according to the required hardness level, prevents the formation of ferrite, and forms MnS-based inclusions with S to provide high machinability. It is an essential element. If it is too high, the machinability will deteriorate, so the content should be 2.0% or less, and if it is too low, the above effects cannot be obtained and hot workability will be impaired, so the content should be 0.2% or more. Cr increases corrosion resistance and hardenability, and during tempering,
Produces fine carbide precipitation and appropriately adjusts the hardness value during precipitation hardening. If it is too high, it will lead to the formation of ferrite, so it should be set at 3.5% or less, and if it is too low, the above effects cannot be obtained, so it should be set at 0.1% or more. Mo is an element that precipitates fine carbides during high-temperature tempering treatment at 500° C. or higher, brings precipitation hardening, builds strength, and improves corrosion resistance against the atmosphere during use. If it is too high, machinability and toughness will deteriorate, so the content should be 3.0% or less, and if it is too low, the above effects cannot be obtained, so the content should be 0.1% or more. Cu is an essential element for precipitation hardening and obtaining the required hardness during high-temperature tempering treatment at temperatures above 500°C, and has the effect of increasing corrosion resistance and suppressing ferrite formation. If it is too high, machinability will deteriorate, so the content should be 3.0% or less, and if it is too low, the above effects cannot be obtained, so the content should be 0.2% or more. S is an essential element for improving machinability.
Too much will impair toughness and hot workability, so 0.2
% or less, and if it is too low, the above effects cannot be obtained, so it should be 0.05% or more. Al increases the inoculating effect of Zr on sulfides,
An element that improves machinability and mirror finish by making sulfides finer. but
If it is less than 0.05%, the above effect will be small, and if it is too much, the amount of ZrO ₂ produced will be insufficient, and hard nonmetallic inclusions Al ₂ O ₃ and It is set at 0.5% or less because AlN is easily generated. Zr is an essential element for improving machinability and mirror finish. The added Zr becomes ZrO ₂ or ZrN, which has an effective inoculation effect against sulfides.
This inoculation effect results in very good uniformity of the shape, size and distribution of the sulfides. This uniformity significantly improves machinability and mirror finish. Furthermore, by allowing 70% or more of each of ZrO ₂ and ZrN to coexist with sulfide, reduction in tool life during cutting can be suppressed. but
If there is too much Zr, the above effects will be saturated, and ZrO ₂ and ZrN, which do not coexist with sulfides and exist independently in the base, will increase, which will accelerate mechanical wear of the tool, reduce machinability, and reduce the It should be kept at 0.20% or less since it deteriorates the mirror finish due to the generation of bits. If it is too low, the above effect will not be obtained.
Must be 0.005% or more. O, N are constituent elements of NrO ₂ and ZrN,
It is an essential element for the inoculating action against sulfides by the Zr compound ZrO ₂ and ZrN, which is a feature of the steel of the present invention. ZrO ₂ and
It is necessary for more than 70% of ZrN to coexist with sulfide, and in order to further refine the sulfide,
When Zr is 0.005~0.20%, (O+N) is also 0.007~
It must be strictly controlled as low as 0.012%.
If (O+N) is less than 0.007%, the inoculation effect is insufficient, resulting in uneven shape distribution of sulfide and coarsening of sulfide, and coarse Zr carbide is formed independently on the base, shortening tool life. . (O+N) is
If it exceeds 0.012%, the amount of oxides or nitrides that do not coexist with sulfides and exist independently in the base increases, which may deteriorate machinability and mechanical properties. Ni is an element added to improve hardenability and corrosion resistance, to maintain an appropriate precipitation hardness value during tempering, and to prevent the formation of ferrite.
If it is less than 1.2%, the effect is small, and if it exceeds 4.0%, machinability deteriorates and is not practical. Se improves machinability and corrosion resistance. 0.15%
If it exceeds 0.03%, the toughness will be significantly reduced, and if it is less than 0.03%, the above effect will be small. Like Se, Te improves machinability and corrosion resistance. If it exceeds 0.15%, the toughness decreases significantly, and 0.05%
If it is less than that, the above effect will be small. The effects of Ca and Mg help the inoculation effect of Zr compounds on S′de, making the shape and distribution of S′de uniform, and suppressing the elongation of sulfide during rolling processing by producing CaS and MgS. This improves mechanical anisotropy. Too much Ca, Mg
Since the inoculation effect cannot be obtained due to excessive deoxidation by
If it is too low, the above effects cannot be obtained, so each
Must be 0.001% or more. Examples of the steel of the present invention are shown below. Table 1 shows the chemical composition of the test materials (all Fe Bal). Furthermore, Table 2 shows the proportion of Zr compounds coexisting with sulfide.

【table】

[Table] As a result of observing micrographs of the cast structures of inventive steel C and conventional steel A, the distribution of sulfides in both inventive steel and conventional steel was almost uniform, and Zr compounds coexisted with sulfides. There is. However, it was found that the size of sulfides in the steel of the present invention was significantly finer than in the conventional steel. This is due to the increase in the inoculating effect of Zr on sulfides obtained by adding Al. Furthermore, observation of the morphology of sulfides using micrographs of materials with a forging ratio of 20 between inventive steel C and conventional steel A shows that the inventive steel has extremely small sulfides, uniform shape distribution, and excellent machinability and mirror finish. It is clear that the sulfide form is preferable for its properties. Table 3 shows the machinability of the present invention steel and conventional steel in quenching and tempering (H _R C32) in terms of machinability, with the machinability of conventional steel A being 100. Therefore, the larger the index, the better the machinability. From this, it can be seen that the steel of the present invention is clearly superior to the conventional steel in terms of machinability.

[Table] According to an example in which the finished surface roughness of conventional steel A and inventive steels C to R (16 samples) was measured using the stylus method, the inventive steel had an Hmax of 5.5 μm for the conventional steel.
2.0 to 3.0 μm, which indicates that the finished surface roughness of the steel of the present invention is significantly improved. These include the addition of Al and Zr and (O+N)%
This is due to the fact that the sulfide distribution shape is not only uniform due to the control, but also that the sulfide becomes extremely fine. Table 4 shows the mirror finish (bit resistance) of the steel of the present invention.
compared with conventional steel. The sample was quenched and tempered to H _R C32 with a size of 50 mm square, and after aging treatment, it was mirror-finished using a grinder → paper → diamond compound method, and the number of minute bits generated was counted using a 10x magnifying glass. .

【table】

[Table] It can be seen that the steel of the present invention has extremely excellent mirror finish properties. This can be achieved by adding Al (O+N)
This is due to the fact that the absolute amount of nonmetallic inclusions was reduced by lowering the concentration, and that the inoculants ZrO ₂ and ZrN against sulfides were made finer by the addition of Al mentioned above, and the sulfides were also made finer. As detailed above, the steel of the present invention has an extremely excellent finished surface in cutting processing, and its greatest feature is excellent mirror finish. In addition to improving production efficiency, the uniform fine distribution of sulfide inside and outside improves grain workability and mechanical properties, eliminating the need for concerns such as rusting and providing toughness and long life. It is a steel for pre-hardened molds for plastic molding that has free cutting properties.

Claims (1)

[Claims] 1. C0.04~0.30%, Si0.1~1.5% by weight,
Mn0.2~2.0%, Cr0.1~3.5%, Mo0.1~3.0%,
Cu0.2~3.0%, S0.05~0.20%, Al0.05~0.50%,
Contains Zr0.005~0.20%, (O + N) 0.007~0.012%, and Ni over 1.2% and up to 4.0%, and more than 70% of Zr compounds ZrO ₂ and ZrN each coexist with sulfide, with the remainder being unavoidable. A free-cutting steel for pre-hardened molds for plastic forming, which is characterized by containing iron impurities and Fe. 2 C0.04~0.30%, Si0.1~1.5% by weight,
Mn0.2~2.0%, Cr0.1~3.5%, Mo0.1~3.0%,
Cu0.2~3.0%, S0.05~0.20%, Al0.05~0.50%,
Zr0.005~0.20%, (O+N)0.007~0.012%,
Ni over 1.2% and 4.0% or less, and Se 0.05-0.15%,
Contains one or two types of Te 0.05-0.15%, and more than 70% of each of the Zr compounds ZrO ₂ and ZrN coexists with sulfide, and the remainder is unavoidable impurities and
A free-cutting plastic pre-hardened mold steel characterized by being made of Fe. 3 C0.04~0.30%, Si0.1~1.5% by weight,
Mn0.2~2.0%, Cr0.1~3.5%, Mo0.1~3.0%,
Cu0.2~3.0%, S0.05~0.20%, Al0.05~0.50%,
Zr0.005~0.20%, (O+N)0.007~0.012%,
Ni over 1.2% and 4.0% or less, and Ca0.001 to 0.010
%, Mg0.001 to 0.010%, and furthermore, 70% or more of each of the Zr compounds ZrO ₂ and ZrN coexists with sulfide, and the remainder consists of inevitable impurities and Fe. Free-cutting steel for plastic forming pre-hardened mold shapes. 4 C0.04~0.30%, Si0.1~1.5% by weight,
Mn0.2~2.0%, Cr0.1~3.5%, Mo0.1~3.0%,
Cu0.2~3.0%, S0.05~0.20%, Al0.05~0.50%,
Zr0.005~0.20%, (O+N)0.007~0.012%,
Ni over 1.2% and 4.0% or less, and Se 0.05-0.15%,
One or two types of Te0.05~0.15% and Ca0.001~
0.010%, Mg0.001~0.010%, one or two types in combination, and further contains Zr compounds ZrO ₂ and
A free-cutting steel for pre-hardened molds for plastic forming, characterized in that 70% or more of ZrN coexists with sulfides, and the remainder consists of unavoidable impurities and Fe.