WO2005061747A1

WO2005061747A1 - Hot work tool steel and mold member excellent in resistance to melting

Info

Publication number: WO2005061747A1
Application number: PCT/JP2003/016304
Authority: WO
Inventors: Seiji Kurata; Toshimitsu Fujii
Original assignee: Daido Steel Co.,Ltd
Priority date: 2003-12-19
Filing date: 2003-12-19
Publication date: 2005-07-07
Also published as: CN1878881A; US20070110610A1; AU2003292572A1; EP1696045A1

Abstract

A hot work tool steel having a chemical composition in wt %: C: 0.10 to 0.35 %, Si: less than 0.80 %, Mn: 3.0 % or less, Cr: 2.0 % or more and less than 7.0 %, N: more than 0.05 % and 0.50 % or less, O: 0.0100 % or less, P: 0.050 % or less, Al: 0.050 % or less, with the proviso that 1/2W + Mo: 0.3 to 5.0 %, C + N: 0.20 to 0.60 % and C/N: 6 or less, and the balance: substantially Fe, and optionally V: 0.01 to 0.5 %. The hot work tool steel exhibits excellent resistance to melting, while retaining good toughness and good resistance to heat checking.

Description

Hot work tool steel and mold parts with excellent erosion resistance

The present invention relates to a hot work tool steel and a mold member excellent in erosion resistance and suitable for a mold member for A1 die casting.

Background art

Conventionally, as a material for the die body, core, insert pin, and hot water supply pipe for A1 die casting (hereinafter collectively referred to as mold members), hot materials such as JIS SKD61, SD6, and SKD62 have been used. Tool steel has been used.

Here, Fe and A1 have a strong affinity, and the mold member reacts relatively easily with the A1 molten metal, forming a Fe-A1 intermetallic compound and dropping off the surface layer. No loss occurs. This erosion includes seizures due to galling and seizure.

Erosion is particularly likely to occur at the mold step near the gate, which is in contact with the high-temperature A1 molten metal at high speed, and at the nested pins.

As such erosion increased, the product had convex defects.

However, problems such as difficulty in releasing the product are caused.

Therefore, there has been a demand for a material for a mold member having excellent A1 erosion resistance.

Conventionally, surface treatments such as nitrocarburizing have been performed to improve the A1 erosion resistance, and the surface layer has been modified to have a higher A1 erosion resistance layer than the base metal.

However, even when such a surface treatment is performed, erosion can be prevented during the initial period in which the surface modified layer remains, but the surface modified layer gradually disappears. Thereafter, the base material is melted and causes the same problem as described above.

Therefore, even when the surface layer is modified by surface treatment, Al corrosion resistance is strongly required.

Disclosure of the invention

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a hot work tool steel and a mold member having excellent A1 erosion resistance while maintaining excellent toughness and heat check resistance. Aim.

Claim 1 relates to a hot work tool steel. In weight%, C: 0.10 0.35% Si: 0.80%, Μη: ≤3.0% Cr: 2. (! ~ 7.0%, l / 2W + Mo: 0.3 5.0%, N: more than 0.05 to 0.50%, C + N: 0.20 0.60% (C / N: ≤ 6), 0: ≤ 0.0100%, P: ≤ 0.050%, A1: ≤ 0.050% Is satisfied, and the balance is substantially composed of Fe.

Claim 2 is characterized in that, in claim 1, V: less than 0.5% by weight is further contained.

Claim 3 is characterized in that in any one of claims 1 and 2, one or two of Ni: ≤ 2.0% and Co: ≤ 5.0% are further contained.

Claim 4 claims:! In any one of ~ 3, one or more of Ti: ≤ 1.0%, Ta: ≤ 1.0%, B: ≤ 0.010%, Cu: ≤ 1.0% .

Claim 5 is the invention according to claim 14, wherein S: ≤ 0.050%

Ca: <0.0100%, Se: ≤ 0.0100%, Te: ≤ 0.0 lOi

Mg: <0.0100%, Y: ≤ 0.10% 100% or more.

Claim 6 relates to a mold member, and is characterized in that it is made of hot-rolled steel according to any one of claims 15 to 15.

5 Claim 7 also relates to the die member, and is made of the hot work tool steel according to any one of claims 15 and the surface layer is modified by a surface treatment into a layer with higher A1 erosion resistance than the base metal. It is characterized by quality treatment.

The present inventor has conducted various studies on the A1 erosion resistance of hot work tool steel, and has found that increasing the amount of N improves the A1 erosion resistance. However, when the N content is simply increased, if the V content is large, coarse primary carbonitrides are formed, and the toughness and heat check resistance required for mold members are reduced. In order to prevent the deterioration of characteristics such as lockability, it is effective to reduce the amount of V and to control the C + N amount and the (C / N) ratio within a certain range. I also found out.

The present invention has been made based on such knowledge, and it is intended to increase the amount of N, reduce the amount of V, and control the C + N amount and the (C / N) ratio within a predetermined range. Based on this, the present invention has made it possible to increase the A1 erosion resistance without deteriorating the toughness and heat check resistance of the hot work tool steel.

Conventionally, V has been included as an essential component in hot work tool steels.

For example, in the case of JIS SKD61, 0.8-1.20% of V is contained, in the case of JIS SKD62, 0.20-0.60% of V is contained, and in the case of JIS SKD8, 1.70 2.20% of V is contained. I have.

The function of V in these hot work tool steels is to increase the hardness and wear resistance by carbides of V, and the fine secondary carbides of V are formed by the pinning effect of crystal grains. It refines crystal grains and contributes to ensuring toughness.

On the other hand, the coarse primary carbides of V generated during solidification also have the adverse effect of impairing the toughness and heat check resistance of hot steel. In the hot-rolled steel of the invention, it is possible to eliminate the content of V, which has been indispensable in the past, and in this case, sufficient toughness and heat check resistance can be ensured.

Although the detailed reason is not necessarily clear, in the hot work tool steel of the present invention, N contained in a high content forms fine nitrides with, for example, Cr and the fine nitrides form V nitrides. It replaces fine secondary carbides and refines the crystal grains, ensuring toughness and It is presumed that the lockability is improved.

Rather, in the present invention, by eliminating the V content, it is possible to eliminate the sub-effect of the coarse primary carbides of V and further increase the toughness and the heat-etch resistance.

伹 V has the function of increasing hardness ゃ abrasion resistance.Therefore, in the present invention, if hardness 硬 wear resistance rather than hardness ゃ abrasion resistance is required more, If you want to increase the hardness and abrasion resistance while eliminating V, you can also include V in a small amount below a certain level, and it is possible to select one of them according to fc.

However, even if V is contained, it is necessary to make the content less than 0.5%.

When the hot work tool steel of the present invention as described above is applied to a die member for die force h, the repair cycle of the die member can be extended irrespective of the presence or absence of surface layer modification by surface treatment. In addition, the dimension in degree of the product can be maintained with high accuracy for a long time.

Further, it is possible to omit the surface treatment for modifying the surface layer, thereby reducing the cost required for the mold member.

Furthermore, since the surface treatment can be omitted, it is possible to eliminate the need for reworking the surface treatment every time the mold is repaired, and it is possible to reduce the frequency of the repair, and to reduce the frequency of the repair. Reduced repair costs can also be achieved

However, in the present invention, according to claim 7, the surface layer of the gold member can be modified into a layer having higher A1 erosion resistance than the base material by surface treatment.

By performing such a modification, it is possible to further increase the erosion resistance of the mold member.

The following can be exemplified as surface treatments for surface layer reforming (A) Nitriding treatment

Salt bath nitriding Sulfur nitriding

Gas nitriding Soft nitriding

Plasma nitriding Hard nitriding

2. Coating method

(A) C V D method

Thermal C V D (TiN, TiC compound single layer or multilayer formation, etc.)

Plasma C V D (TiN, TiAIN, TiC, TiCN, DLC compound single layer or multilayer formation, etc.)

(B) PVD method

Ion plating (single or multiple layers of TiN, TiAIN, CrN, TiC, TiCN, DLC compounds, etc.)

Sputter-ring (TiN, TiAIN, CrN, Al 2 0 3 formed of multi-layered monolayers also rather are compounds, etc.)

(C) oxidation _{_{_{(Fe 2 0 3, Fe 3}}} 0 4 monolayers be properly multilayer formation of compounds)

Next, the reasons for limiting each chemical component in the present invention will be described in detail below. C: 0.10-0.35%

C is an element necessary to secure hardness and wear resistance. To ensure sufficient hardness and wear resistance as a hot-work steel, it is necessary to add 0.10% or more.

However, if added excessively, coarse eutectic carbides are formed during smelting, and carbides that do not form a solid solution during quenching increase, leading to a decrease in toughness and heat check resistance. 0.35%.

Si: <0.80%

Si is an element required as a deoxidizing element. It is also an effective element for improving machinability and temper softening resistance.

However, when the amount of addition is large, the toughness ヒー heat check resistance decreases. Therefore, it must be less than 0.80%. Desirably, it is more than 0.10 to 0.50%.

Mn: ≤ 3.0%

Mn is a component necessary as a deoxidizing element and for ensuring hardenability and hardness, and is desirably added in an amount of 0.02% or more. More preferably, it is 0.1% or more, and still more preferably 0.3% or more.

On the other hand, if the addition amount is large, the workability is reduced, so the content should be 3.0% or less. Preferably it is 2.0% or less, more preferably 1.0% or less.

Cr: 2.0 to less than 7.0%

Cr is an element necessary for strengthening the matrix by forming carbides, improving wear resistance, and ensuring hardenability, and is added in an amount of 2.0% or more. It is preferably at least 3.0%, more preferably at least 4.0%.

However, excessive addition causes a decrease in hardenability and hot strength, so it is set to less than 7.0%. Preferably, it should be 6.5% or less.

1 / 2W + MO: 0.3-5.0%

It is necessary to form carbides to strengthen the matrix and improve wear resistance and to ensure hardenability. To obtain such an effect, it is necessary to add 0.3% or more.

However, an excessive addition causes a decrease in toughness, so the upper limit is made 5.0%. In addition, Mo and W have the same effect, and W has about twice the atomic weight of Mo. Therefore, in the present invention, it is defined by the Mo equivalent. The addition method may be used alone or in combination.

N: Over 0.05 to 0.50%

A1 is an element necessary to increase the erosion resistance and hardness. The formation of fine nitrides and carbonitrides may have an effect on the improvement of A1 erosion resistance.

To obtain the effect, it is necessary to add more than 0.05%.

However, if added excessively, the amount of coarse eutectic carbonitride increases and the toughness and heat check properties decrease, and it can be added depending on the alloy composition. Since there is a limit, the upper limit is set to 0.50%.

CIN: 0.20-0.60%

In order to suppress the formation of eutectic carbonitride and improve toughness, it is necessary to keep the C + N content below 0.60%.

However, if the amount of C + N is too low, the hardness will decrease, so the lower limit is set to 0.20%. Desirably, it should be 0.30 to 0.45%.

C / N: ≤ 6

In order to improve A1 erosion resistance, it is effective to reduce C while adding N. That is, by controlling C / N to 6 or less, AI erosion resistance is improved. Was found to be significantly improved. One possible reason for this is that the amount of fine nitrides and carbonitrides is increasing.

0: ≤ 0.0100%

0 is an element that is preferably reduced in order to reduce toughness and heat check resistance, but is an element that is unavoidably contained, and is regulated to 0.0100% or less in the present invention. Preferably, the content is 0.0030% or less.

P: ≤ 0.050%

P is an element that is preferably reduced in order to reduce toughness and heat check resistance, but is an element that is inevitably contained, and is set to 0.050% or less in the present invention. It is desirable to reduce it to 0.015% or less.

A1: ≤ 0.050%

A1 is an element effective as a strong deoxidizing material, and is also effective for preventing crystal grain coarsening and improving nitriding properties, and is desirably added at 0.001% or more.

However, if added excessively, the cleanliness of the material is reduced and the machinability is reduced, so the content is limited to 0.050% or less.

V: 0.01 to less than 0.5%

V forms carbides and is effective in strengthening the matrix and improving wear resistance.In addition, the formation of fine carbides is also effective in refining crystal grains and thus improving toughness. Therefore, add 0.01% or more as necessary can do.

However, if added excessively, coarse eutectic carbides and carbonitrides are generated during smelting, and the amount of carbides and carbonitrides remaining without solid solution during quenching increases, resulting in increased toughness and heat resistance. The content is set to less than 0.5% in order to reduce the performance. Preferably it is 0.4% or less, and more preferably 0.3% or less.

Ni: ≤ 2.0%

Ni is effective in improving hardenability and strengthening the base, and can be added as necessary. In this case, the desirable amount is 0.01% or more, more preferably 0.03% or more, and further preferably 0.05% or more. However, if added excessively, the workability is reduced, so the upper limit must be set to 2.0%. Preferably it is 1.5% or less, more preferably 1.0% or less.

Co: ≤ 5.0%

Co is effective for strengthening the matrix and improving the wear resistance, and can be added as needed. In this case, the preferable amount is 0.01% or more, more preferably 0.03% or more, and further preferably 0.05% or more.

However, excessive addition lowers the workability, so the upper limit must be set to 5.0%. Preferably it is 4.0% or less, more preferably 3.0% or less.

Ti: ≤ 1.0%

T i has the effect of forming carbonitrides to prevent crystal grain coarsening during quenching, and can be added as necessary. The desirable amount at that time is 0.01% or more, more preferably 0.03% or more, and further preferably 0.05% or more.

However, if added excessively, coarse carbonitrides are formed, and the upper limit must be set to 1.0% in order to reduce toughness and heat check resistance. Preferably it is 0.7% or less, more preferably 0.5% or less.

Ta: ≤ 1.0% Ta has the effect of forming carbonitrides to prevent crystal grain coarsening during quenching, and can be added as necessary. In this case, the preferable amount is 0.01% or more, more preferably 0.03% or more, and further preferably 0.05% or more.

B: ≤ 0.010%

B is an element effective for improving hardenability and can be added as needed. The desirable amount at that time is 0.0001% or more, more preferably 0.0003% or more, and still more preferably 0.0005% or more.

However, if added excessively, the hot workability and toughness decrease, so the upper limit must be made 0.010%. Preferably it is 0.007% or less, more preferably 0.005% or less.

Cu: ≤ 1.0%

Cu is effective in strengthening the matrix and can be added as needed. In this case, the desirable amount is 0.01% or more, more preferably 0.03% or more, and still more preferably 0.05% or more.

However, if added excessively, the toughness decreases, so the upper limit must be set to 1.0%. Preferably it is 0.7% or less, more preferably 0.5% or less.

S: ≤ 0.050%

S is an element that is inevitably contained, but is effective in improving machinability and can be added as necessary. However, if added excessively, the toughness decreases, so the upper limit is made 0.050%.

Ca: ≤ 0.0100%

Ca is an element effective for improving machinability, and can be added as necessary. However, if added excessively, the toughness will decrease.

0.0100%.

Se: ≤ 0.0100% Se is an element effective for improving machinability and can be added as necessary. However, if added excessively, the toughness will decrease.

0.0100%.

Te: ≤ 0.0100%

Te is an element effective in improving machinability and can be added as needed. However, if added excessively, the toughness and hot workability deteriorate, so the upper limit is made 0.0100%.

Zr: ≤ 0.0100%

Zr is an element effective in improving machinability and can be added as needed. However, if added excessively, the toughness will decrease.

0.00%.

Mg: ≤ 0.0100%

Mg acts as a deoxidizing and desulfurizing element during melting. It is also effective in improving strength and ductility at high temperatures. ,

It can be added as needed, but if added excessively, the hot workability decreases, so the upper limit is made 0.0100%.

Y: ≤ 0. 100%

Y forms an oxide film on the mold surface, has the effect of improving wear resistance, seizure resistance and heat check resistance, and can be added as necessary. However, if added excessively, the toughness will decrease.

0. 100%.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, examples of the present invention will be described in detail below.

In order to increase the nitrogen concentration in the steel ingot, 50 kg of steel with the composition shown in Table 1 was melted and manufactured in a pressure melting furnace that can pressurize the entire melting and mixing equipment to 10 atm. However, 50 kg of the conventional steel in Table 1 was melted in a vacuum melting furnace and manufactured. ,

Subsequently, soaking was performed at 1230 ° C x 10 hr, then forged into a 60 mm square bar, annealed at 870 ° C for 3 hr and then slowly cooled, and A1 erosion test was performed. Specimens Hardness P test h, Charpy test specimen, heat check type test specimen, and 咼 ί 曰曰大大越大各荒荒荒荒荒荒荒.

Then, quenching and tempering were performed under the conditions shown in Table 2 below (however, the hardness test pieces were quenched and tempered under the conditions of (B) below). Specimen, Heat Check Specimen, Taka

ism.Each Ogoshi abrasion test specimen

Here, A1 erosion test piece is 10 mm x 60 mmL, hardness test piece is 1 Omm square x 1 Omm, Charbie test piece is JIS No.3 test piece, heat check test piece is Φ15nunX5 mm, high temperature overpass wear The test piece was 1 Omm x 17 mm x 30 mm. table

The A1 erosion test, hardness test, Charpy test, and heat check test were performed on each specimen under the following test conditions.

The results are shown in Table 3.

(A) A1 erosion test

3 Omm of the test piece was immersed in the A1 molten metal, and the center of the test piece was rotated so as to draw a circle with a diameter of 3 Omm, and the state of melting by A1 was investigated.

Climbing A1 alloy: B390 (Al-17Si-4.5Cu)

• Melt temperature: 750 ° C

• Speed: 200rpm

• Immersion time: 30 minutes

The Pit specimen after the it test was immersed in a saturated NaOH aqueous solution to remove the attached A1 alloy, and the weight was measured to evaluate the erosion resistance by the erosion rate according to the following equation. Melting rate () = (weight before test-weight after test) ÷ (Φ 1 Omm before test) X30mmL part weight) xlOO

(B) Hardening and tempering hardness

After heat treatment in a salt furnace under the following conditions, the Rockwell hardness was measured.

• Quenching: 1030 ° C for 30 minutes, oil cooled

• Tempering: 650 ^D CX for 1 hour, air cooling X 2 times

(C) Charpy test

Specimens were sampled from the width direction of the steel material (T direction), and the Charpy impact value was evaluated in accordance with JIS Z 2242.

(D) Heat check test

Evaluation was performed using a high-frequency heating and water-cooled heat check tester. Specifically, after repeating the heating of the surface layer at 700 ° C »water cooling 1000 times, the depth and number of cracks generated on the sample surface are measured, and the heat check resistance is evaluated based on the average crack length. did.

(E) High temperature Ogoshi abrasion test

Based on the results of the Ogoshi-type wear test at 700 ° C, the wear resistance of conventional steel No. 27 was set to 100, and the wear resistance of other steel types was indicated by an index.

As can be seen from the results in Table 3, the conventional steels of Nos. 27, 28 and 29 all have poor erosion resistance (melt loss rate), and have toughness (Charpy impact value) and heat check resistance. Properties (average crack length) are all inadequate values. On the other hand, in the comparative steels, Nos. 21, 23 and 24 have poor erosion resistance (melting rate), and Nos. 22, 25 and 26 have low toughness (Charpy impact value). Has insufficient heat check resistance (average crack length), but in the case of Examples, all of the erosion resistance, hardness, toughness, heat check resistance, and wear resistance are good. Characteristics are obtained. In particular, No. 3, 12, 14, and 17, which have a large N content, have particularly excellent erosion resistance.

In addition, high toughness (Charpy impact value) was obtained for Nos. 3, 5, and 13 with no V added.

Example 2>

For a steel having the composition shown in Table 4 (Example and conventional steel), a 50 kg ingot was melted in the same pressure melting furnace (Example) and vacuum induction furnace (Conventional steel) as in Example 1, and It was forged into Φ20mni round material and then annealed at 870 ° C.

Subsequently, after cutting three pieces each of the Example and the conventional steel to a length of 20 Omm, rough-cut to 15 mm x 200 mm by turning, then quenched at 1030 ° C x lhr, and then 580 590 ^ Tempering was performed twice under the conditions, and the hardness was adjusted to HRC38, 45, and 52, respectively.

Then, they were finished into punched pin shapes, and surface treatment for surface layer modification was performed. Here, in the surface treatment, gas nitrocarburizing treatment was performed on the HRC 38 material for both the working example and conventional steel at 525 ° C X 2.51ir, and for the HRC 52 material, a CrN coating was formed by PVD treatment. Formed.

No surface treatment was applied to HRC45 material.

A1 A die-casting die (cylinder head type) was assembled with the above-mentioned punching pin, and a forging test was performed. At that time, 5000 shots were used for unpinned pins without surface treatment, and up to 20000 shots for unpinned pins after surface treatment.

Then, the weight of the punched pin before and after the fabrication was measured.

At this time, the punched pin after fabrication was immersed in a saturated NaOH aqueous solution to remove the attached A 1 alloy, and then weighed.

The weight loss due to erosion was determined from (weight before test) and (weight after test), and the erosion resistance was evaluated.

The results are shown in Table 5. Table 5

From the results shown in Table 5, it can be seen that, in the examples, the surface loss for the surface layer reforming can be reduced more effectively.

Although the embodiment of the present invention has been described in detail, this is merely an example, and the present invention can be implemented in various modified forms without departing from the spirit thereof.

Claims

8

The scope of the claims

In a rice bowl,

C: 0.10 to 0.35%

Si: <0.80%

Mn: ≤ 3.0%

Cr: 2.0 to less than 7.0%

1 / 2W + M0: 0.3-5.0%

N: Over 0.05 to 0.50%

C + N: 0.20 to 0.60% (however, C / N: 6)

0: ≤ 0.0100%

P: ≤ 0.050%

A1: ≤ 0.050%

A hot work tool steel excellent in erosion resistance, characterized by satisfying the above condition and having a composition substantially consisting of Fe.

2. In claim 1, in weight percent,

V: 0.01 to less than 0.5%

Hot work tool steel with excellent erosion resistance, characterized by further containing

3. In any of Claims 1 and 2,

Ni: ≤ 2.0%

Co: ≤ 5.0%

A hot work tool steel excellent in erosion resistance, characterized by further containing one or two of the following.

4. In any one of claims 1 to 3,

• Ti · ≤ 1.0%

Ta: ≤ 1.0%

B: ≤ 0.010%

Cu: ≤ 1.0%

Dissolution resistance characterized by further containing one or more of the following: Hot tool steel with excellent heat resistance

In any one of claims 1 to 4,

S ≤ 0.050%

Ca '≤ 0.0100%

Se: ≤ 0.0100%

Te: ≤ 0.0100%

Zr: ≤ 0.0100%

Mg: ≤ 0.0100%

Y: ≤ 0. 100%

A hot work tool steel excellent in erosion resistance, characterized by further containing one or more of the following.

A mold member having excellent erosion resistance, comprising the hot work tool steel according to any one of claims 1 to 5.

The hot-work tool steel according to any one of claims 1 to 5, characterized in that the surface layer is modified by a surface treatment into a layer with higher A1 erosion resistance than the base metal. Mold member with excellent erosion resistance.