JPS62167863A - Free-cutting steel for prehardened metallic mold for molding plastic - Google Patents

Abstract

PURPOSE:To provide a titled steel for a metallic mold having small finish surface roughness and excellent mirror finishing characteristic by decreasing the content of C, specifying the respective contents of Si, Mn, Cr, Mo, Cu, etc., allowing the greater part of ZrO2 and ZrN to co-exist respectively in the form of sulfide and consisting the balance of Fe. CONSTITUTION:The above-mentioned steel for the metallic mold contains, by weight, 0.04-0.30 C, 0.1-1.5 Si, 0.2-2.0 Mn, 0.1-3.5 Cr, 0.1-3.0 Mo, 0.2-3.0 Cu, 0.05-0.20 S, 0.05-0.50 Al, 0.005-0.20 Zr, 0.007-0.012 (O+N), 1.0-4.0 Ni, contg. respectively 70% ZrO2 and ZrN co-existing with sulfide and consists of the balance Fe and unavoidable impurities. The steel of this invention has excellent machinability in addition to the above-mentioned characteristics and therefore, the steel contributes to the improved efficiency in the preparation of the metallic mold. Graining property and mechanical properties are improved by the sulfide finely and uniformly distributed in the inside and outside so that the steel exhibits high toughness and a long life.

Description

DETAILED DESCRIPTION OF THE INVENTION The main feature of the present invention is that it has a small finished surface roughness during cutting and has an excellent mirror finish, and also has excellent texturability and toughness. This relates to steel for forming burihardon molds.

As steel for plastic molds, (1) Good machinability.

(2) Good mirror finish and no pinholes or other fine pits.

(3) Good texturing properties.

(4) Good corrosion resistance and rust resistance.

(5) High strength and wear resistance.

There are 71 such characteristics! - wanted.

High hardness in terms of (2) and (5), (2),
Regarding (4), it is required that the steel has a composition that is essentially easy to clean, and regarding (3), it is required that the hardenability is sufficiently high. In this case, it is particularly 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.

Conventionally, high-hardness pre-hardened steel has problems such as requiring a long time to carve the 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, A, etc. are generally used as free-cutting elements. However, if a sufficient amount of free-cutting elements is added to obtain sufficient machinability, the above-mentioned properties (2), (3), (4), and (5) may deteriorate due to the addition. It was happening.

The steel of the present invention has a weight ratio TeC of 0.04 to 0.30% and a Sin
.

1-1.5%, Mn 0.2-2.0%, Cr 0.1
~3.5%, Mo 0.1~3.0%, CuO02~
3.0%, Ni 1.0-4.0%, S 0.05-0
．． After adding 0.05% to 0.50% of Zr/M and controlling (O+N) to 0.007% to 0.012%, 0.005% to 0.20% of Zr is added. Therefore, fine Zr0 with effective inoculation for sulfides
．． A large number of C/ZrN are generated, which makes the sulfides look fine and uniformly distributed.
Non-uniform machinability, large surface roughness and V8! In addition to improving the anisotropy of mechanical properties, the Cu-Fc metal 11] compound and M
The most distinctive feature is that it has mirror finish properties and texturability due to the finely precipitated carbides of o and Cr* to impart strength and hardness.

In addition, in order to improve properties such as strength, hardness, and hardenability, Ni
Addition of 1.0 to 4.0%, and Se 0.05 to 0.05 as necessary to improve machinability and anisotropy of mechanical properties.
0.15%, Te 0005-0.15%, Ca0゜0
01-0.010%, Mg 0.001-0.010%
It is possible to carry out the addition of

Next, the reason for limiting the component range will be explained.

C is a basic additive element for making 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 C is too large, the base will become martensitic and the machinability and mirror finish will be reduced, and the grinding time will be significantly increased.
The content should be 0.04% or more since it causes the formation of elite and makes it difficult to obtain sufficient tempering hardness.

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 in steelmaking can be obtained, 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 7-elite, and forms M n S-based inclusions in the darkness with S, providing high machinability. It is an essential element for If it is too high, it will reduce machinability, so it should be 2.0% or less, and if it is too low, the above effects cannot be obtained, and it will also impair hot workability.
．． 2% or more.

Cr improves corrosion resistance and hardenability, and also causes fine carbide precipitation during tempering, and moderates the hardness value to 51 during precipitation hardening. If it is too high, ferrite formation will occur, so the content should be 3.5% or less, and if it is too low, the above effects cannot be obtained, so the content should be 0.1% or more.

Mo is an element included to precipitate fine carbides during still temperature tempering treatment at 500° C. or higher, to bring about precipitation hardening, to form strength, and to improve corrosion resistance against the atmosphere during use. If the amount is too high, the machinability and toughness will deteriorate, so the content should be 3.0% or less. If the content is too low, the above effects cannot be obtained, so the content should be 0.1% or more.

Cu is an indispensable element to bring about precipitation hardening and obtain the required hardness in high-temperature tempering treatment at 500° C. or higher, and has the effect of increasing corrosion resistance and suppressing the formation of 7-elite. If it is too large, the 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 content impairs toughness and hot workability, so it should be 0.2% or less. If too low, the above effects cannot be obtained, so 0.05%
% or more.

AI is an element that improves rigidity and mirror finish by increasing the inoculation effect of Zr on sulfides and making the sulfides fine. However, if it is less than 0.05%, the above effect will be small, and if it is too much, the amount of ZrOz produced will be insufficient, and nonmetallic inclusions with hardness that are harmful to machinability due to reoxidation and nitrification during scraping will occur. A lx O
The content is set to 0.5% or less because it facilitates the generation of s and AIN.

Z" is an essential element for improving rigidity and mirror finish. Added Zr becomes Z"0. or ZrN, which has an effective inoculation effect against sulfides.

This inoculation effect results in very good uniformity in the shape, size and distribution of the sulphides. This uniformity significantly improves machinability and mirror finish.

Furthermore, by allowing 70% or more of each of Z r Oz and ZrN to coexist with sulfide, it is possible to suppress a decrease in tool life during cutting. However, if there is too much 2, the above effect will be saturated, and Zr0. and ZrN, which do not coexist with sulfides and exist independently in the base, will increase, which will accelerate mechanical wear of the tool and reduce machinability. The content is set at 0.20% or less because bits generated during polishing deteriorate the mirror finish.If the content is too low, the above effects cannot be obtained, so the content is set at 0.005% or more.

0,N is a constituent element of ZrO2 and ZrN, and is an essential element for the inoculating action against sulfides by the Zr compound Z"02,ZrN, which is a feature of the steel of the present invention. Obtains good machinability. Z r O2 upper l/ZrN
It is necessary that 70% or more of each of Z r 0.
When 005-0.20%, (O+N) is also 0.007
mWj must be 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 sulfides and coarsening of sulfides; Zr carbide forms independently on the base, shortening tool life.

When (O+N) is 0.012%, oxides or nitrides that do not coexist with sulfides and exist independently in the base increase, which may deteriorate machinability and mechanical properties.

Ni is an element to be included to improve hardenability and corrosion resistance, to maintain an appropriate precipitation hardening hardness value during tempering, and to prevent the formation of 7-erite. If it is less than 1.0%, the effect is small (and if it exceeds 4.0%, machinability deteriorates and is not practical.

Sc improves machinability and corrosion resistance. If it exceeds 0.15%, the toughness will decrease significantly, and if it is less than 0.03%, the above effect will be small.

Te, like Se, improves machinability and etchability.

If 0.15% can be used, the toughness will decrease significantly, and 0°05
If it is less than %, the above effect will be small.

The effect of Ca and MB is to help the inoculation effect of Zr compounds on S'de, to make the shape and distribution of S'de uniform, and to suppress the stretchability of sulfide during rolling process by producing Cab and Mgs. , which improves mechanical anisotropy. If it is too large, deoxidation by Ca and Mg will proceed excessively, making it impossible to obtain the inoculation effect, so the content should be 0.010% or less, respectively. If the content is too low, the above effects cannot be obtained, so each content is set at 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 FeBa1').

Further, Table 2 shows the proportion of Zr compounds coexisting with sulfides.

Table 2 As a result of observing microscopic photographs of the cast structures of inventive steel C and conventional steel A, it was found that the distribution of sulfides was almost uniform in both the inventive steel and the conventional steel, and Z'compounds coexisted with sulfides. However, it was found that the size of sulfides in the steel of the present invention is significantly finer than that in the conventional steel.This is due to the sulfide of Z obtained by adding AI. This is due to an increase in the inoculation effect on objects.

In addition, the tJ of the sulfide form in the micrographs of the materials of the present invention aC and the conventional steel A with a forging ratio of 20! According to the L investigation, it is clear that the steel of the present invention contains extremely small sulfides, has a uniform shape distribution, and has a monosulfide form that is favorable for stiffness and mirror finish.

Table 3 shows the HRC3 of the inventive steel and conventional steel after quenching and tempering.
The machinability in 2) is expressed as an index, taking the machinability of conventional steel A as 100. Therefore, the larger the index, the better the machinability1.

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 3 - According to an example in which the finished surface roughness of conventional steel A and present invention steel C%D%E, F was measured by the stylus method, Hwax
Compared to the conventional fI of 45.5 μ-, the steel of the present invention has an fI of 4.5 to 6
．． It can be seen that the finished surface roughness of the steel of the present invention has been significantly improved.

These include the addition of AI and Z' (O+N)%
This is due to the fact that the distribution shape of the sulfides is not only uniform, but also that the sulfides are noticeably finer.

Table 4 compares the mirror finish (pit resistance) of the steel of the present invention with that of conventional steel.

The samples were quenched and tempered to HRC32 with 50III60, and after aging treatment, mirror finishing was performed using a grinder → paper → diamond sand pound method.The number of minute bits generated was counted using a 10x magnifying glass. be.

Table 4 It can be seen that the steel of the present invention has an extremely excellent mirror finish.

This is because the addition of Al lowered the (O+N) concentration and reduced the absolute amount of non-4-group inclusions, and the addition of Al mentioned earlier reduced the inoculant Zr for sulfides.
This is due to the fact that O2 and ZrN have become completely fine and sulfides have also become fine.

As detailed above, the steel of the present invention has an extremely excellent finished surface during cutting, and its greatest feature is that it has excellent mirror finish properties. In addition to improving production efficiency, the uniform distribution of sulfide inside and outside improves grain workability.
It is a free-cutting steel for plastic molding pre-hardened molds that has improved mechanical properties, does not require concerns such as rusting, is tough and has a long life.

Claims (1)

[Claims] 1. C0.04-0.30% by weight, Si 0.1-1
．． 5%, Mn0.2-2.0%, Cr0.1-3.5%
, Mo0.1-3.0%, Cu0.2-3.0%, S0
．． 05-0.20%, Al0.05-0.50%, Zr
0.005-0.20%, (O+N) 0.007-0.
012% and 1.0-4.0% Ni, and further contains 70% each of the Zr compounds ZrO_2 and ZrN.
The above coexists with sulfide, and the remainder is unavoidable impurities and Fe.
Steel for pre-hardened molds for plastic molding with excellent machinability. 2. C0.04-0.30%, Si0.1-1 by weight ratio
．． 5%, Mn0.2-2.0%, Cr0.1-3.5%
, Mo0.1-3.0%, Cu0.2-3.0%, S0
．． 05-0.20%, Al0.05-0.50%, Zr
0.005-0.20%, (O+N) 0.007-0.
012%, Ni1.0~4.0% and Se0.05~
0.15%, Te 0.05-0.15%, one or two
The Zr compounds ZrO_2 and Zr
A steel for pre-hardened molds for plastic molding having excellent machinability, characterized in that 70% or more of each of N coexists with sulfides, and the remainder consists of inevitable impurities and Fe. 3. C0.04-0.30%, Si0.1-1 by weight ratio
．． 5%, Mn0.2-2.0%, Cr0.1-3.5%
, Mo0.1-3.0%, Cu0.2-3.0%, S0
．． 05-0.20%, Al0.05-0.50%, Zr
0.005-0.20%, (O+N) 0.007-0.
012%, Ni1.0-4.0% and Ca0.001
~0.010%, Mg0.001~0.010%, and 70% or more of each of the Zr compounds ZrO_2 and ZrN coexist with sulfide, and the remainder is unavoidable impurities and Fe. Steel for plastic molding pre-hardened molds with excellent machinability. 4. C0.04-0.30%, Si0.1-1 by weight ratio
．． 5%, Mn0.2-2.0%, Cr0.1-3.5%
, Mo0.1-3.0%, Cu0.2-3.0%, S0
．． 05-0.20%, Al0.05-0.50%, Zr
0.005-0.20%, (O+N) 0.007-0.
012%, Ni1.0~4.0% and Se0.05~
0.15%, Te 0.05-0.15% group, C
a0.001~0.010%, Mg0.001~0.0
10% of the Zr compounds ZrO_2 and ZrN each coexist with sulfide, and the remainder consists of inevitable impurities and Fe. Steel for plastic molding pre-hardened molds with excellent machinability.