JPS59179761A - Tool steel - Google Patents

Abstract

PURPOSE:To obtain a tool steel having improved hardenability and resistance to tempering at high temp. as well as high hardness, high suitability to mirror finishing and corrosion resistance by providing a specified composition contg. C, Si, Mn, Cr, Mo and Cu and by properly regulating the balance between C and Cr. CONSTITUTION:This tool steel having high hardness and corrosion resistance consists of, by weight, 0.35-0.55% C, 0.5-3% Si, <=2% Mn, 6-14% Cr, 0.2- 4% Mo, 0.1-3% Cu and the balance Fe with inevitable impurities while satisfying an equation Cr%+15.5C%<=20. The steel may further contain 0.001-0.5% REM other than Y and/or 0.001-1.0% Y. The steel is suitable for use as material of a metallic mold capable of giving a highly accurate article having a long life especially when used to mold plastics.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-hardness, corrosion-resistant tool steel, and more particularly, to a tool steel that has high hardness and excellent corrosion resistance and is particularly suitable for molds used for molding plastics. .

Conventionally, JIS 5US molds are used for molding plastic products that require high mirror surfaces such as lenses and dust covers.
420JZ, 5KD61, etc. were used. On the other hand, when molds require corrosion resistance, 17-4PH stainless steel is used, and when molds require long life, 5KDII, which provides high hardness, is used as a general-purpose steel. Ta.

However, in recent plastic molding, as the demand for plastic products increases, the number of products processed increases, and the requirements for the precision and finish of the products are becoming stricter. Furthermore, various flame-retardant resins have been developed and are actively commercialized for various uses. As described above, molds for molding plastic products are being forced to meet increasingly severe conditions, and the requirements for the tool steel used as the material are also becoming more complex. Therefore, the current situation is that conventional tool steels cannot meet the above requirements.

In other words, 5KD61 has poor corrosion resistance and wear resistance, and
US420JZ, 17-4PH series 7.7 > Less steel has good corrosion resistance but poor wear resistance, and 5KDII can achieve high hardness, but on the other hand, it has the problem of poor corrosion resistance and specularity. Was. However, the current situation is that these conventional steels cannot cope with the harsh conditions that require high hardness, high specularity, and corrosion resistance at the same time, especially in molds for plastic ink molding. .

Therefore, in the process of developing a tool steel that can meet these requirements, the present inventors investigated what kind of alloying components should be used in order to make the tool steel have high hardness, high specularity, and corrosion resistance at the same time. As a result of various studies on whether a correlation should be established, we found that the formation of giant carbides can be prevented by appropriately adjusting the composition/herance of carbon (C) and carbide-forming elements, especially chromium (Cr). It has been found that there is a composition range in which an excellent specular surface can be obtained by obtaining both high hardness and high hardness. Furthermore, they discovered that by synergistically containing copper (Cu) as an element effective for corrosion resistance, it is possible to have corrosion resistance in addition to the above-mentioned properties of high hardness and high specularity, and have completed this invention. It has come to this.

Furthermore, the present inventors reconsidered the method of adding Ni, Co, and V to conventional steel for plastic molds, and found that Ni, Co, and V are required to meet the high requirements for tool steel. It was found that it is harmful to specularity. In other words, Ni produces residual austenite when hardening tool steel, resulting in a decrease in hardness and a concomitant deterioration in specularity, while Co reduces the hardenability of tool steel, making it impossible to obtain high hardness. As a result, it is harmful to the specularity, and the carbide formed in the rough V tends to fall off the surface.
It was found that the specularity was reduced.

This invention was made based on the above knowledge, and does not add Ni, Co, or V that are harmful to specularity, and
In addition to maintaining an appropriate compositional balance with the metal, we also contain an appropriate amount of elements that contribute to improving corrosion resistance.The synergistic effect of these elements allows us to create molds that require particularly high specularity, such as molds for plastic molding, as well as various other types of molds. The purpose of the present invention is to provide a high-hardness, corrosion-resistant tool steel suitable for use as tools.

That is, the high hardness corrosion resistant tool steel of this invention has a weight ratio of:
C: 0.35-0.55%, St.0.5-3%, Mn
: 2% or less, Cr: 6-14%, Mo: 0.2-4%,
Cu: Contains O, J-3%, and the relationship between C and Cr satisfies Cr (%) + 15.5 C (%) ≦ 20, and the remainder consists of Fe and inevitable impurities. It is.

In addition, another invention that achieves the same object further includes the constituent elements of the above invention excluding Y < REM (rare earth element): Q,
It is characterized by containing one or more of OO1 to 0.5% and Y: 0.001 to 1.0%, with the balance consisting of Fe and inevitable impurities.

The present invention will be explained in detail below.

The tool steel of this invention does not contain Nj, Co, and V, which are elements harmful to the specularity of tool steel, as described above, and adjusts the composition balance of other elements, especially C and Cr. By preventing the formation of giant carbides and obtaining high hardness, it has excellent specularity, and at the same time,
Cu.

By containing Mo, REM, Y, etc., it has high corrosion resistance. The tool steel that is the object of this invention is generally used as a mold after being quenched and tempered, so W C, Cr is used to improve hardenability and high temperature tempering resistance. , S
i, Mo, Cu, Y.

The composition of REM is set within an appropriate range.

Next, the reason for limiting the component range (weight %) of the tool steel according to the present invention will be explained.

C: 0.35 to 0.55% C is an element that increases the hardness of martensite, forms special carbides during high-temperature tempering, and contributes to secondary hardening. The amount of C is limited by the correlation with the amount of Cr, as will be described later, but if it is less than 0.35%, the hardness after quenching and tempering will be low, and if it exceeds 0.55%, the corrosion resistance will decrease and The amount of C was limited to a range of 0.35 to 0.55% since it forms giant carbides and reduces specularity.

Cr: 6 to 14% Cr is an element that improves corrosion resistance by forming an oxide film and making it passivated, and also improves hardenability by dissolving in the ferrite matrix during hardening. However, if the Cr content is less than 6%, it will have little effect on improving corrosion resistance and hardenability, while if it exceeds 14%, the hardness and toughness will decrease, so the Cr content should be 6 to 14%.
limited to the range of

As mentioned above, the amount of C and the amount of Cr were determined by examining the relationship between C and Cr mainly from the viewpoint of hardness and corrosion resistance, and C: 0.35.
~0.55%, Cr: limited to a range of 6 to 14%, but
Furthermore, the amount of giant carbonization that lowers the specularity is Cr (%)
We found that it is determined by the value of +15.5C (%),
The amount of C and Cr that will not damage the specularity is Cr (%
)+15.5C(%)≦20.

Therefore, the amount of C and the amount of Cr are C: 0.35 to 0.55%,
Cr: 6-14%, Cr (%) + 15.5C (%
)≦20.

Si: 0.5-3% Si is added as a deoxidizing agent, and is an element that increases high-temperature tempering hardness and corrosion resistance. but,
If it is less than 0.5%, deoxidation will be insufficient and nonmetallic inclusions will increase, which is undesirable. If it exceeds 3%, hot workability and toughness will decrease, so the amount of Si should be 0.5 to 3%.
% range.

Mn: 2% or less Mn is an element that acts as a deoxidizing and desulfurizing agent, improves the cleanliness of steel, and contributes to improving hardenability. However, since too much Mn impairs workability, the amount of Mn was limited to 2% or less.

Mo: 0.2-4% MO is an element that improves corrosion resistance, hardening and tempering resistance, and toughness. However, if it is less than 0.2%, the effect is small;
If it exceeds this, the toughness and hot workability will be reduced, so the MO amount was limited to a range of 0.2 to 4%.

Cu: O, 1-3% Cu is an element that is effective in improving corrosion resistance and also effective in increasing high-temperature tempering hardness.

However, if it is less than 0.1%, the effect is small;
Exceeding this will reduce hot workability and toughness.
The amount of Cu was limited to a range of 0.1 to 3%.

This invention is constructed by adding each of the above elements to Fe, but in order to further improve corrosion resistance, hardenability, and toughness, it is preferable to include one or more of REM and Y.

REM is an effective element for improving hardenability, corrosion resistance, toughness, and hot workability. However, if it is less than 0.001%, the effect is small, and 0.5%
If the R
The amount of EM was limited to a range of 0.001 to 0.5%.

Y is an element that improves corrosion resistance. However, 0.0
Y
The amount was limited to a range of 0.001-1.0%.

Next, embodiments of the invention will be described.

The steel according to the present invention was melted in the above-mentioned composition range, and for comparison, conventional 5trs42°JZ, 5KDII
, 17-4PH stainless steel + Z steel, etc. were melted.

Table 1 shows the results of chemical analysis of the components of the inventive steel and the conventional steel, respectively.

In addition, the value of Cr (%) + 15.5C (%) is calculated and shown.

/ / / Next, the inventive steel and the conventional steel obtained by melting were quenched and tempered at the predetermined temperatures shown in Table 2, and then the hardness (HRC) and specific wear amount (+nm2/kg) were determined for each.
), corrosion wear amount (%), mirror polishability (pieces/cm2
) was measured. The measurement results are shown in Table 2.

The hardness (HRC) is a value measured using a Rockwell hardness tester, and the specific wear amount (mm2/kg) is measured using an Okoshi type rapid wear tester using annealed SCM 415 as a mating material at a friction speed of 2. .9m/sec, friction distance 20
Measurement was carried out under the conditions of 0 m and a friction load of 6.5 kg.

In addition, the corrosion wear amount (%) was determined by suspending each specimen in an atmosphere of gas generated from acrylonitrile-butadiene-styrene copolymer resin (abbreviation: ABS resin) heated to 250°C for 24 hours. After holding the specimen, the specimen was slid on #l 000 paper with a constant surface pressure, suspended again under the same conditions in a gas atmosphere, and then slid on the same paper, which was repeated 20 times. Evaluation was made based on weight loss. Furthermore, the mirror polishability was evaluated by the number of bits after polishing with tire mondo abrasive grains of one color with an average grain size.

/ As is clear from Tables 1 and 2, the steel of the present invention has the following properties:
Hardness, corrosion and wear resistance compared to comparative steel.

It was confirmed that it has excellent specularity and a good specific wear amount.

Among these, tempering hardness is one of the important properties of the steel of the present invention, especially when used in plastic molds. When heat treating molded steel, it is often tempered at a relatively high temperature from the viewpoint of temperature rise during use or heat treatment distortion, but the steel of the present invention has an HRC5B or higher when tempered at 500°C. Hardness is obtained. This means that
This also affects the specific wear amount, and the specific wear amount of the steel of the present invention is 1.
1~2.8X10-7"/kg, comparative steel No.
It can be seen that the wear resistance is superior to that of 7°9.11.12. On the other hand, the comparative material N018 has a tempering hardness of HRC5.
9.8 and specific wear amount is 0.9×10'mm2/
kg, but on the other hand, the mirror polishing performance has deteriorated significantly. This is because the C content is very high at 1.40%, and the value of Cr (%) + 15.5C (%) is 33.22, which is much larger than the upper limit of 20. A similar tendency can be seen in comparative steel No. 11.13. On the other hand, it is clear that the steel of the present invention is also extremely excellent in specularity.

In this way, the comparative steel cannot satisfy all of the properties of high hardness, high specularity, and machinability, and there is a relationship in which if one property is good, the other property is bad. In contrast, the tool steel of the present invention has properties that simultaneously satisfy high hardness, high specularity, and corrosion resistance.

Next, an example of use of the tool steel according to the present invention will be explained.

When the inventive steel of sample material No. 1 shown in Table 1 was used for a roll for magnetic tape production, conventional steel (SUS
420 JZ), an average lifespan of 1.5 times was obtained. The cause of the lifespan in both cases was abrasion occurring on the roll surface.

Usage Example■ When the inventive steel of the sample No. 094 shown in Table 1 was used in a mold for molding cassettes and reels, conventional steel (SKD
11), an average life span of 1.8 times was obtained. The cause of the lifespan in this case was corrosive wear on the mating surfaces of the molds.

As is clear from the above description, the tool steel according to the present invention contains C and Cr within a predetermined range, maintains an appropriate component balance between C and Cr, eliminates giant carbides, and has high hardness. It also synergistically contains elements that contribute to improving quenching and tempering resistance and corrosion resistance, so it has high hardness, high specularity, and corrosion resistance at the same time, and is also inexpensive. It has a significant effect.

Patent applicant: Daido Steel Co., Ltd. Representative Patent Attorney Yutaka Shio

Claims (2)

[Claims] (1) C: 0.35 to 0.55% by weight. Si: 0.5-3%, Mn: 2% or less, Cr: 6-14
%, Mo: 0.2-4%, Cu: 0.1-3%, and the relationship between C and Cr is Cr(%)+15.5C(%).
)≦20, and the remainder consists of Fe and unavoidable impurities. (2) C+0.35 to 0.55% by weight. Si: 0.5-3%, Mn: 2% or less, Cr: 6-14
%, Mo: 0.2-4%, Cu: 0.1-3%, and the relationship between C and Cr is Cr(%)+15.5C(%).
)≦20, roughly excluding Y<REM+0.0O1~0.5
%, Y:O, OO, 1 to 1.0%, and the balance is Fe and inevitable impurities.