JP2007009321A - Steel for plastic molding die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel for a plastic molding die which possesses enough hardness, wear resistance and corrosion resistance, and is excellent in high-precision processability and mirror polishing properties. <P>SOLUTION: The steel for a plastic molding die contains not more than 0.80 wt% C, not less than 0.01 wt% and less than 1.40 wt% Si, not less than 0.05 wt% and not more than 2.0 wt% Mn, not less than 0.005 wt% and not more than 1.00 wt% Ni, not less than 13.0 wt% and not more than 20.0 wt% Cr, not less than 0.20 wt% and not more than 4.0 wt% Mo+1/2W, not less than 0.01 wt% and not more than 1.00 wt% V, not less than 0.36 wt% and not more than 0.80 wt% N, not more than 0.02 wt% O, not more than 0.80 wt% Al, and the remainder substantially including Fe and unavoidable impurities. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to steel for plastic molding dies.

  In recent years, various plastic molded products are used in various fields. In general, a plastic molded product is molded into a desired shape using, for example, a plastic molding die such as an injection molding die.

  By the way, in addition to the main component resin, a filler such as glass fiber may be added to the plastic molding material from the viewpoint of improving the strength of the molded product. Since this type of additive wears the mold, the dimensional accuracy of the obtained plastic molded product is lowered, and the mold life is shortened.

  In addition, the plastic molding material may generate corrosive gas due to the decomposition of the resin during the kneading process. When this type of corrosive gas is compressed in the mold and becomes high temperature and high pressure, the mold is corroded, and the resulting plastic molded product is roughened and burrs are generated.

  Therefore, it is necessary to use a metal material having high hardness, wear resistance, and corrosion resistance as the material for the plastic mold.

  Conventionally, as this type of metal material, for example, martensitic stainless steel such as SUS440C and its improved material is known.

  Further, for example, in Patent Document 1, C: 0.25 to 1.0, Si: maximum 1.0, Mn: maximum 1.6, N: 0.10 to 0.35, Al: Max 1.0, Co: Max 2.8, Cr: 14.0-25.0, Mo: 0.5-3.0, Ni: Max 3.9, V: 0.04-0.4, W : Maximum 3.0, Nb: Maximum 0.18, Ti: Maximum 0.20, the sum of the concentrations of C and N is at least 0.5 and maximum 1.2, the balance being Fe and inevitable impurities An alloy for plastic molding dies is disclosed.

Patent No. 3438121

  However, the alloy described in Patent Document 1 tends to produce coarse crystallized carbonitrides in the production stage, and is caused by the difference in hardness between the generated coarse crystallized carbonitrides and the parent phase. There was a problem that finishing accuracy was poor, such as uneven processing during processing.

  Moreover, in the plastic molding die, the mold inner surface is often mirror-finished from the viewpoint of improving the surface shape of the molded product, but the alloy described in Patent Document 1 is based on coarse crystallized carbonitride. There was a problem that the mirror workability deteriorated.

  However, in the alloy described in Patent Document 1, it may be possible to make coarse crystallized carbonitrides less likely by simply reducing the amount of C. However, if this is done, there is a problem that wear resistance deteriorates. Arise.

  Therefore, the problem to be solved by the present invention is to provide a steel for plastic molds having sufficient hardness, wear resistance, and corrosion resistance, and excellent in precision workability and mirror surface workability. .

  In order to solve the above problems, the plastic mold steel according to the present invention has C: 0.80 wt% or less, Si: 0.01 wt% or more and less than 1.40 wt%, Mn: 0.05 wt% or more and 2.0 wt% %: Ni: 0.005 wt% or more and 1.00 wt% or less, Cr: 13.0 wt% or more and 20.0 wt% or less, Mo + 1 / 2W: 0.20 wt% or more and 4.0 wt% or less, V: 0.01 wt% 1.00 wt% or less, N: 0.36 wt% or more and 0.80 wt% or less, O: 0.02 wt% or less, and Al: 0.80 wt% or less, with the balance being substantially Fe and inevitable The gist is that it consists of impurities.

  Since the steel for plastic molds according to the present invention has the above-described component composition, particularly the C content is decreased and the N content is increased, the necessary hardness is ensured. Therefore, it has sufficient hardness and wear resistance.

  Further, by increasing the content of N, nitrogen is dissolved in the matrix phase and the formed carbonitride is fine, so that the corrosion resistance is excellent.

  Furthermore, by reducing the content of C, coarse crystallized carbonitride is unlikely to occur in the production stage. In addition, undissolved carbonitride at the time of quenching is reduced, and fine carbonitride by quenching and tempering is uniformly dispersed. Therefore, it is particularly excellent in precision workability and mirror surface workability.

  Hereinafter, an embodiment of the present invention will be described in detail. The steel for plastic molds according to the present invention contains the following elements, with the balance being substantially composed of Fe and inevitable impurities. The reasons for specifying the types of elements contained and their contents are as follows.

(1) C: 0.80 wt% or less.
C is an element necessary for ensuring strength and wear resistance, and is an element that combines with carbide-forming elements such as Cr, Mo, W, V, and Nb to generate carbide. C is also an element necessary for ensuring hardness by solid solution in the matrix during quenching and martensite organization.

  However, when the content of C is excessively large, it is easy to combine with the carbide-forming element, and a large amount of carbides crystallize and coarse carbides remain. From the viewpoint of preventing this, the C content is specifically 0.80 wt% or less, preferably 0.65 wt% or less, and more preferably less than 0.25 wt%.

  However, in the present application, the hardness can be increased by increasing the N content. Therefore, by reducing the C content as much as possible, the amount of coarse crystallized carbides and unhardened during quenching can be increased. It is desirable to reduce the amount of molten carbide and uniformly disperse fine carbides by quenching and tempering.

(2) Si: 0.01 wt% or more and less than 1.40 wt%.
Si functions as a deoxidizing element like Al described later. However, Al reacts with N to produce AlN, reducing the solid solution amount of N in the matrix, and at the same time, reducing the precision workability and mirror finish workability by the produced coarse AlN. Therefore, it is preferable to use Si as the deoxidizing element in order to suppress the Al content in the steel. Specifically, the Si content is 0.01 wt% or more, preferably 0.05 wt% or more, and more preferably 0.10 wt% or more.

  However, when the Si content is excessively increased, hot workability and toughness are deteriorated. From the viewpoint of preventing this, the Si content is specifically less than 1.40 wt%, preferably 0.75 wt% or less, and more preferably 0.25 wt% or less.

(3) Mn: 0.05 wt% or more and 2.0 wt% or less.
Mn is added as an element that improves hardenability. Moreover, when S is inevitably contained, Mn is effective in suppressing a decrease in toughness. Specifically, the Mn content is 0.05 wt% or more.

  However, when the Mn content is excessively increased, the hot workability is deteriorated. Therefore, the Mn content is 2.0 wt% or less.

(4) Ni: 0.005 wt% or more and 1.00 wt% or less.
Ni increases the amount of N dissolved. Specifically, the Ni content is 0.005 wt% or more.

  However, when the Ni content is excessively large, retained austenite increases and causes aging of the dimensions. Therefore, the Ni content is specifically 1.00 wt% or less.

(5) Cr: 13.0 wt% or more and 20.0 wt% or less.
Cr increases the amount of N dissolved and improves the corrosion resistance. Moreover, carbonitride is formed. Specifically, the Cr content is 13.0 wt% or more.

  However, if the Cr content is excessively large, the residual γ phase increases and the hardness decreases even if the sub-zero treatment is performed. In addition, the cost increases. Therefore, the Cr content is specifically 20.0 wt% or less.

(6) Mo + 1 / 2W: 0.20 wt% or more and 4.0 wt% or less.
Mo and W increase the amount of N dissolved. Moreover, hardenability is improved. In order to obtain this effect, the contents of Mo and W are specifically 0.20 wt% or more in Mo + 1 / 2W.

  However, when the contents of Mo and W are excessively increased, the formation of crystallized carbonitride is promoted and the impact value is lowered. Therefore, specifically, the contents of Mo and W are 4.0 wt% or less in terms of Mo + 1 / 2W.

(7) V: 0.01 wt% or more and 1.00 wt% or less.
V increases the amount of N dissolved. Moreover, carbonitride is formed, and the crystal grain is refined by the pinning effect, thereby improving the strength. Specifically, the content of V is 0.01 wt% or more.

  However, when the V content is excessively large, coarse carbonitrides are likely to be produced, and precision workability and mirror finish workability are deteriorated. Therefore, the V content is specifically 1.00 wt% or less.

(8) N: 0.36 wt% or more and 0.80 wt% or less.
N is an interstitial element and contributes to improving the hardness of the martensite structure. In order to obtain the effect, the N content is specifically 0.36 wt% or more. The N content can be added by dissolving under pressure according to the Sieverts law.

  However, if the content of N is excessively large, the concentration of N during solidification tends to cause blow holes (hereinafter referred to as “N blow”) due to N, and suppression of N blow by pressurization is suppressed. It becomes difficult. Therefore, the N content is specifically 0.80 wt% or less.

(9) O: 0.02 wt% or less.
O is an element inevitably contained in the molten steel. When the amount of O increases, Si and Al and coarse oxides are formed, which become inclusions, and deteriorate toughness, precision workability, and mirror surface workability. Therefore, it is desirable that the O content is as low as possible. Specifically, the content of O is 0.02 wt% or less, preferably 0.01 wt% or less.

(10) Al: 0.80 wt% or less.
Al functions as a deoxidizing element like Si. However, if the Al content is excessively large, coarse AlN is likely to be generated, and the precision workability and mirror surface workability are significantly reduced. Therefore, the Al content is specifically 0.80 wt% or less.

  In addition to the essential elements described above, the steel for plastic molds according to the present invention may optionally contain one or more elements selected from the following elements. The reason why the contents of these elements are specified is as follows.

<1> P: 0.030 wt% or less, S: 0.030 wt% or less.
P and S are inevitably contained in the steel. P segregates to the grain boundaries, and S forms sulfides, both of which reduce toughness. Accordingly, the content of P and S is preferably at most 0.030 wt%.

<2> Cu: 0.001 wt% to 0.50 wt%, Co: 0.001 wt% to 0.50 wt%, B: 0.0005 wt% to 0.010 wt%.
Cu, Co, and B all contribute to the improvement of hardenability. Specifically, the content of Cu is 0.001 wt% or more. Specifically, the Co content is 0.001 wt% or more. Specifically, the content of B is 0.0005 wt% or more.

  However, even if the contents of Cu, Co, and B are excessively increased, the effect of hardenability is saturated. In addition, the cost increases. Therefore, the Cu content is specifically 0.50 wt% or less. Specifically, the Co content is 0.50 wt% or less. Specifically, the content of B is 0.010 wt% or less.

<3> Se: 0.001 wt% to 0.30 wt%, Te: 0.001 wt% to 0.30 wt%, Ca: 0.001 wt% to 0.10 wt%, Pb: 0.001 wt% to 0 20 wt% or less, Bi: 0.001 wt% or more and 0.30 wt% or less.
Se, Te, Ca, Pb, and Bi contribute to improvement of machinability. Specifically, the Se content is 0.001 wt% or more. Specifically, the content of Te is 0.001 wt% or more. Specifically, the content of Ca is 0.001 wt% or more. Specifically, the content of Pb is 0.001 wt% or more. Specifically, the Bi content is 0.001 wt% or more.

  However, if the content of Se, Te, Ca, Pb, Bi is excessively increased, the toughness is lowered. Therefore, the Se content is specifically 0.30 wt% or less. Specifically, the Te content is 0.30 wt% or less. Specifically, the Ca content is 0.10 wt% or less. Specifically, the content of Pb is 0.20 wt% or less. Specifically, the Bi content is 0.30 wt% or less.

<4> Ti: 0.20 wt% or less, Nb: 0.001 wt% or more and 0.30 wt% or less, Ta: 0.001 wt% or more and 0.30 wt% or less, Zr: 0.001 wt% or more and 0.30 wt% or less.
Ti, Nb, Ta, and Zr combine with C and N to form carbonitrides, and contribute to suppressing coarsening of crystal grains. Specifically, the Ti content is 0.01 wt% or more. Specifically, the content of Nb is 0.001 wt% or more. Specifically, the content of Ta is 0.001 wt% or more. Specifically, the content of Zr is 0.001 wt% or more.

  However, when the content of Ti, Nb, Ta, Zr is excessively increased, the toughness is lowered. Therefore, the Ti content is specifically 0.20 wt% or less. Specifically, the content of Nb is 0.30 wt% or less. Specifically, the content of Ta is 0.30 wt% or less. Specifically, the content of Zr is 0.30 wt% or less.

  Moreover, the steel for plastic molding metal mold | die mentioned above is good in the particle size of the carbonitride contained being 4.0 micrometers or less, Preferably it is 3.5 micrometers or less, More preferably, it is 3.0 micrometers or less. This is because it is particularly excellent in precision workability and mirror surface workability.

  The particle size of carbonitride is the total number of carbonitrides observed by corroding the measurement surface of the finish-polished sample with a corrosive liquid and observing this measurement surface with an optical microscope, scanning electron microscope, or the like. The typical value of the particle size in which 90% or more is the value or less is indicated.

Next, an example of a method for producing the plastic molding steel will be described.
Plastic molding die steel having the above-mentioned composition is melted in a melting furnace such as a pressurizable high frequency induction furnace, cast into an ingot, etc., and then these ingots are hot forged or hot rolled to obtain the necessary dimensions. And a method of manufacturing the steel material.

  An example of the heat treatment for the plastic mold steel is as follows. Specifically, the annealing can be performed, for example, by heating at 850 to 900 ° C. for 3 to 5 hours, then furnace-cooling to about 600 ° C. at a rate of 10 to 20 ° C./hour, and then air cooling. Further, the quenching / tempering is specifically carried out, for example, by heating at 1000 to 1200 ° C. for 0.5 to 1.5 hours, followed by oil cooling and quenching, and then at −196 ° C. or −76 ° C. to reach 0.00. Sub-zero treatment can be performed for 5 to 1 hour, and then heated at 200 to 700 ° C. for 0.5 to 1.5 hours, followed by air cooling and tempering.

Hereinafter, the present invention will be described more specifically with reference to examples.
After melting the steel having the chemical composition shown in Table 1 (steel according to Examples 1 to 16, steel according to Comparative Example 1 to Comparative Example 6) in a pressurizable high frequency induction furnace, it was cast to 50 kg, Each 60 mm square bar was manufactured by hot forging.

  Next, about each steel which concerns on an Example and a comparative example, as shown in Table 2, it hardened at 1030 to 1150 degreeC, and also about -76 degreeC about the steel which concerns on Examples 1-16, or -196 degreeC After the sub-zero treatment, tempering was performed at a temperature of 200 ° C. to 475 ° C. Various characteristics of the samples after these heat treatments were evaluated as follows.

<Particle size of carbonitride>
A cube block having a side of 15 mm was cut out from each bar, and after heat treatment, the measurement surface was polished to # 1500. Subsequently, buffing was performed using 1 μm diamond paste, and final polishing was performed. Subsequently, the measurement surface was corroded using Villera corrosive liquid. Next, the measurement surface was photographed with an optical microscope (10 fields at 400 magnifications), and the value of the particle size at which 90% or more of the total number of observed carbonitrides was less than that value was used as a representative value. A carbon nitride having a particle size of 4.0 μm or less was accepted.

<Hardness>
A cube block having a side of 10 mm was cut out from each bar, and after heat treatment, the measurement surface and the ground contact surface were polished to # 400, and then the hardness was measured by Rockwell C scale. A sample having a hardness of HRC 55 or higher was accepted.

<Abrasion resistance>
Wear resistance was evaluated using a pin-on-disk friction and wear tester. That is, two pins φ8 mm × 2 were cut out from each bar and subjected to heat treatment. The disc cut out from S45C was used. The test conditions were a sliding speed of 1.6 m / s, a sliding distance of 5000 m, a pressing load of 10.5 kgf, and no lubricating oil. The weight of the pin was measured before and after the test, and the wear weight was measured from this. In Table 3, the wear weight ratio between the steel according to the example and the steel according to the remaining comparative examples when the wear amount of the steel according to comparative example 1 (SUS440C) is 100 is shown. A wear weight ratio of less than 130 was accepted.

<Corrosion resistance>
A round bar of φ15 mm × 60 mm was processed from each bar, and after heat treatment, the surface was made equivalent to # 400 by finishing. Next, a salt spray test was performed in accordance with JIS Z 2371 to confirm the rusting state. In Table 3, A indicates that no rust has occurred, B indicates that rust has slightly occurred, C indicates that rust has occurred, and D indicates that rust has occurred on the entire surface. The above was regarded as passing.

<Precision workability>
A test piece of 60 mm × 60 mm × 100 mm is prepared from each bar, and a solid carbide end mill (6 blades) of φ10 mm is used as a tool, the speed is 120 m / min, the feed is 0.06 mm / rev, the cutting width is 0.5 mm, Processing was performed under the condition of a cutting height of 10 mm. Next, the maximum surface roughness R _y of the processed surface was measured based on JIS B0633. At this time, a sample having a maximum surface roughness _Ry of 2.0 μm or less was accepted.

<Mirror finish processability>
A 50 mm × 45 mm × 12 mm plate was processed from each bar, heat-treated, and then polished to # 14000 by mechanical polishing. Next, chemical etching was performed to prepare a test piece. It was then measured surface roughness _{R a} of the test piece in conformity with JIS B0633. At this time, a sample having _a surface roughness _Ra of 0.05 μm or less was accepted.

  The above evaluation results are shown in Table 3.

  According to Table 3, the following can be understood. That is, the steel according to Comparative Example 1 is inferior in precision workability and mirror finish workability because coarse crystallized carbonitride exists. Moreover, corrosion resistance is also inferior.

  Moreover, since the steel which concerns on the comparative examples 2 and 4 has less N content than regulation, sufficient hardness is not acquired and it is inferior to abrasion resistance.

  Moreover, since the steel according to Comparative Example 3 has a larger O content than specified, a coarse oxide is formed, and the steel according to Comparative Example 4 also has a larger Al content than specified. AlN is formed. Therefore, these are inferior to precision workability.

  Moreover, since the steel which concerns on the comparative example 5 has more V content than regulation, coarse VN is formed. Therefore, it is inferior to precision workability and mirror surface workability.

  Moreover, since the steel which concerns on the comparative example 6 has more O content than regulation, a coarse oxide is formed and it is inferior to precision workability and mirror surface workability.

  In contrast to the steels according to Comparative Examples 1 to 6, all the steels according to Examples 1 to 16 have sufficient hardness, wear resistance, and corrosion resistance, and are excellent in precision workability and mirror surface workability. It was confirmed that

  Therefore, it can be said that the steel according to the present invention can be suitably used as a material for plastic molding dies.

Claims (5)

C: 0.80 wt% or less,
Si: 0.01 wt% or more and less than 1.40 wt%,
Mn: 0.05 wt% or more and 2.0 wt% or less,
Ni: 0.005 wt% or more and 1.00 wt% or less,
Cr: 13.0 wt% or more and 20.0 wt% or less,
Mo + 1 / 2W: 0.20 wt% or more and 4.0 wt% or less,
V: 0.01 wt% or more and 1.00 wt% or less,
N: 0.36 wt% or more and 0.80 wt% or less,
O: 0.02 wt% or less, and
Al: 0.80 wt% or less,
And the balance is substantially made of Fe and unavoidable impurities. P: 0.030 wt% or less, and S: 0.030 wt% or less,
The plastic mold steel according to claim 1, further comprising one or more elements selected from the group consisting of: Cu: 0.001 wt% or more and 0.50 wt% or less,
Co: 0.001 wt% or more and 0.50 wt% or less, and
B: 0.0005 wt% or more and 0.010 wt% or less,
The plastic mold steel according to claim 1 or 2, further comprising one or more elements selected from the group consisting of: Se: 0.001 wt% or more and 0.30 wt% or less,
Te: 0.001 wt% or more and 0.30 wt% or less,
Ca: 0.001 wt% or more and 0.10 wt% or less,
Pb: 0.001 wt% or more and 0.20 wt% or less, and
Bi: 0.001 wt% or more and 0.30 wt% or less,
The plastic mold steel according to any one of claims 1 to 3, further comprising one or more elements selected from the group consisting of: Ti: 0.20 wt% or less,
Nb: 0.001 wt% or more and 0.30 wt% or less,
Ta: 0.001 wt% or more and 0.30 wt% or less, and
Zr: 0.001 wt% or more and 0.30 wt% or less,
5. The plastic mold steel according to claim 1, further comprising one or more elements selected from the group consisting of: