JP5273952B2 - Hot forging die and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot forging mold which secures basic properties such as toughness and has superior abrasion resistance at the same time, and to provide a manufacturing method therefor. <P>SOLUTION: The hot forging mold comprises, by mass%, 0.32 to 0.42% of C, 0.3% or less of Si, 0.3 to 1.5% of Mn, 0.5% or less of Ni, 4.0 to 6.0% of Cr, 0.2 to 1.0% of V, 0.8 to 2.0% of Mo+1/2W, 0.005 to 0.04% of N, and the balance Fe with unavoidable impurities. In this case, the hot forging mold can further include, by mass%, 0.1 to 1.0% of Co, and further 0.1 to 1.0% of Cu. The hot forging mold preferably has an oxide film formed on its surface. This oxide film may be formed through heat treatment. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a hot forging die and a manufacturing method thereof, and more particularly, to a hot forging die having excellent wear resistance and crack resistance and a manufacturing method thereof.

  A common form of damage in hot forging dies is a combination of cracking and wear. Therefore, improvement of crack resistance (fracture toughness value, fatigue strength) and hot wear resistance (high temperature strength) are indispensable for extending the life of the mold. Conventionally, 5Cr type hot die steel represented by JIS SKD61 is inexpensive as a material for various tool steels such as hot forging die, hot press die, die casting die, aluminum extrusion die, etc. It has been used for many reasons.

However, JIS SKD61 has a slightly excessive amount of V, resulting in problems such as stripe segregation and anisotropy of toughness (Patent Document 1), and coarse VC (primary carbide) in the manufacturing process. ) Is easy to crystallize, and the problem that fatigue fracture is promoted (Patent Document 2) has been pointed out.
Therefore, Patent Document 1 discloses a hot work tool steel in which stripe segregation is eliminated and toughness anisotropy is reduced by reducing the amount of V. Further, Patent Document 2 discloses an alloy tool steel having excellent characteristics in strength, toughness, etc., by preventing the amount of Si from being reduced to 0.05% or less so that a huge primary carbide does not remain in the steel. Yes. Non-Patent Document 1 proposes a steel with low Si and high Mo for the purpose of extending the mold life.

JP 5-148589 JP 7-017986 Mold technology, Vol. 19, no. 1 (2004), p. 100

However, in the case of a hot forging die made of the above-mentioned conventional steel, softening of the forged surface by contact with a high temperature work material reduces heat crack resistance, wear resistance, etc., and increases the degree of plastic flow. There was a problem. And the heat_generation | fever by plastic flow caused the further softening, and there existed a problem of accelerating wear and reducing a mold life.
In addition, the steel of Non-Patent Document 1 has a problem that the fracture toughness value is lowered as an adverse effect of increasing Mo while the wear resistance is improved.
Furthermore, Mo and V are rare metals, and it is desired to improve the characteristics by using alternative materials.

  This invention is made | formed in view of the said situation, The objective is to provide the hot forging die excellent in abrasion resistance, and its manufacturing method, ensuring basic characteristics, such as toughness. .

In order to solve the above-mentioned problem, the hot forging die according to the present invention is in mass%, C: 0.32 to 0.42%, Si: 0.05 to 0.15 % , Mn: 0.3 -1.5%, Ni: 0.2% or less , Cr: 4.0-6.0%, V: 0.2-1.0%, Mo + 1 / 2W: 0.8-2.0%, and , N: 0.005 to 0.04%, with the balance being Fe and inevitable impurities. In this case, it may further contain Co: 0.1 to 1.0% by mass and Cu: 0.1 to 1.0%. An oxide film is desirably formed on the surface of these hot forging dies.

In order to solve the above-mentioned problems, the method for producing a hot forging die according to the present invention is mass%, C: 0.32 to 0.42%, Si: 0.05 to 0.15 % , Mn: 0.3-1.5%, Ni: 0.2% or less , Cr: 4.0-6.0%, V: 0.2-1.0%, Mo + 1 / 2W: 0.8-2.0 %, And N: 0.005 to 0.04%, and the steel obtained by roughing the steel consisting of Fe and unavoidable impurities, quenching and tempering, and then finishing. The gist is that the forging die is subjected to additional heat treatment at 150 ° C to 700 ° C. The steel used in this case may further contain, by mass%, Co: 0.1 to 1.0%, and may further contain Cu: 0.1 to 1.0%.

Since the hot forging die according to the present invention is provided with the above component composition, it is possible to obtain wear resistance superior to that of conventional tool steel while ensuring basic properties such as toughness equivalent to JIS SKD61. effective. And the oxide film formed by heat treatment and the oxide film formed by heat application during forging have good adhesion and good lubricity, so it functions as a protective film and alleviates the plastic flow of the mold during forging However, in order to suppress softening due to the processing heat generation, there is an effect of improving wear resistance.
The method of manufacturing a hot forging die according to the present invention is a hot forging die obtained by roughing steel having the above component composition, tempering to the required hardness, and then finishing. Since an additional heat treatment is performed at 150 to 700 ° C., an oxide film such as FeO is formed on the surface. Therefore, according to the method for producing a hot forging die according to the present invention, a die having the above component composition can be obtained. Therefore, the basic properties such as toughness are ensured to be equivalent to JIS SKD61 and superior to the conventional method. There is an effect that high wear resistance is obtained. Since the formed oxide film such as FeO has good adhesion and good lubricity, it functions as a protective film, relaxes the plastic flow of the mold during forging, and suppresses softening due to its processing heat generation. There is an effect of improving wear resistance.

  Since the hot forging die and the manufacturing method thereof according to the present invention do not increase the amount of use of rare metals such as Mo and V, there is also an effect that an environmental load can be reduced.

Hereinafter, an embodiment of the present invention will be described in detail. In the following description, “%” means “mass%” unless otherwise specified.
(Ingredient composition and reasons for limitation)
The hot forging die steel according to an embodiment of the present invention includes the following elements (1) to (8) as essential elements.

(1) C: 0.32 to 0.42%.
C is contained in order to obtain martensite hardness by quenching and tempering and necessary strength and hardness by precipitation hardening of the alloy carbide. Therefore, the lower limit of the amount of C is set to 0.32% or more. On the other hand, as the amount of C increases, the amount of supersaturated solid solution in martensite becomes excessive and the toughness decreases. Therefore, the upper limit of the C amount is set to 0.42% or less.

(2) Si: 0.30% or less.
Si is an element having the most important role in the steel for hot forging die according to one embodiment of the present invention, in order to form an oxide film such as FeO having a high effect as a protective film against wear by heat treatment. Contain. Specifically, the oxide film such as FeO is an additional heat treatment not conventionally performed on a hot forging die obtained by finishing, that is, 150 ° C. to 700 ° C. using an atmospheric furnace. It can be formed by performing an additional heat treatment. An oxide film such as FeO has good adhesion to a mold base material and has a higher effect as a protective film against wear than conventional tool steel. Therefore, a hot forging die on which an oxide film such as FeO is formed is excellent in wear resistance. When the amount of Si is excessive, it is considered that FeSiO ₄ that is an oxide layer containing Si is formed between the mold base material and the FeO oxide film. Since FeSiO ₄ inhibits the adhesion of FeO as a protective film, the effect as a protective film cannot be obtained with FeSiO ₄ .
Therefore, the amount of Si needs to be reduced as much as possible. Therefore, the upper limit of Si content is set to 0.30% or less. Considering the balance between machinability and wear resistance, the amount of Si is more preferably 0.05 to 0.15%, still more preferably 0.08 to 0.12%. Further, in order to suppress the formation of FeSiO ₄ that is a harmful layer, the upper limit of the Si content is more preferably 0.10% or less.

(3) Mn: 0.3 to 1.5%.
Mn is an element to be included for improving hardenability. In order to obtain this effect, the lower limit of the amount of Mn is set to 0.3% or more. However, excessive addition of Mn deteriorates the softening resistance, and in addition, it takes a long time for the spheroidizing annealing treatment and decreases the productivity. Therefore, the upper limit of the amount of Mn is set to 1.5% or less.

(4) Ni: 0.5% or less.
Ni improves hardenability and impact resistance, but if added in a large amount, it takes a long time for annealing. Therefore, the upper limit of Ni content is set to 0.5% or less. In addition, if Ni is added in an amount of more than 0.5%, it is difficult to form an oxide film due to the Ni concentration phenomenon. In order to form a uniform oxide film on the surface of the mold, the Ni content is preferably 0.2% or less.

(5) Cr: 4.0 to 6.0%.
Cr improves hardenability and fracture toughness. Therefore, the lower limit of the Cr content is 4.0% or more. On the other hand, when a large amount of Cr is contained, the high temperature strength is extremely lowered, so the upper limit of the Cr amount is 6.0% or less.

(6) V: 0.2 to 1.0%
V is an element that greatly affects the toughness, and suppresses the coarsening of crystal grains during quenching to prevent a decrease in impact resistance. Therefore, the lower limit of the V amount is 0.2% or more. On the other hand, when a large amount of V is contained, coarse crystallized VC that cannot be completely dissolved by soaking remains, and the fatigue strength and impact resistance are greatly reduced. Therefore, the upper limit of the V amount is 1.0% or less.

(7) Mo + 1 / 2W: 0.8-2.0%.
Of these, Mo is an essential element, but W may be contained as necessary. Since Mo is an element effective for improving the high-temperature strength, the lower limit is set to 0.8% or more in the amount of (Mo + 1/2 W). However, since the fracture toughness is lowered when a large amount is contained, the upper limit of the amount of (Mo + 1 / 2W) is set to 2.0% or less.

(8) N: 0.005 to 0.04%.
N becomes a constituent element forming VCN, and thereby, a pinning effect for suppressing coarsening of crystal grains is obtained. Therefore, the lower limit of N content is set to 0.005% or more. On the other hand, when N is contained in a large amount, VCN crystallizes in a coarse state. Therefore, the upper limit of the N amount is set to 0.04% or less.

The hot forging die steel according to an embodiment of the present invention may further include the following component elements (9) to (10) as optional elements.
(9) Co: 0.1 to 1.0%.
Co is an element effective for improving the high-temperature strength. Therefore, the lower limit of the amount of Co is set to 0.1% or more. On the other hand, when it is contained in a large amount, the toughness is lowered. Therefore, the upper limit of the amount of Co is set to 1.0% or less.

(10) Cu: 0.1 to 1.0%.
Cu contributes to toughness. Therefore, the lower limit of the amount of Cu is set to 0.1% or more. On the other hand, when it is contained in a large amount, hot workability is lowered. Therefore, the upper limit of the amount of Cu is set to 1.0% or less.

The hot forging die steel according to an embodiment of the present invention further includes the following component elements (11) to (14) as inevitable impurities.
(11) P: 0.015% or less.
P precipitates at the grain boundary as inclusions and lowers the impact resistance, and also increases the concentration gradient of segregation and deteriorates anisotropy. Therefore, the upper limit of the amount of P is set to 0.015% or less .

(12) S: 0.01% or less.
S improves the machinability at the time of molding, but generates a large amount of inclusions as a starting point of fatigue fracture. Therefore, the upper limit of the amount of S is set to 0.01% or less.

(13) Al: 0.025% or less.
Al is an effective element as a deoxidizing element . When the amount of Al becomes large, Al oxide remains in the steel to reduce the fatigue strength. Therefore, the upper limit of the Al amount is set to 0.025% or less.

(14) O: 0.005% or less.
O combines with Mn and Al to leave a large amount of oxide in the steel and lower the fatigue strength. Therefore, the upper limit of the amount of O is set to 0.005% or less.

(Production method)
Next, the manufacturing method of the hot forging die which concerns on one Embodiment of this invention is demonstrated.
A hot forging die according to an embodiment of the present invention is obtained by melting steel having the above component composition into a steel ingot (melting → soaking), and then hot working into a predetermined shape (forging → firing). Tempering → tempering → spheroidizing annealing → roughing), tempering to the required hardness (quenching / tempering), and finishing (mirror finishing, mold completion by conventional methods) It is obtained by performing an additional heat treatment at 150 ° C. to 700 ° C. (mold completion). Here, the lower limit is set to 150 ° C. because an effective oxide film is not formed when the temperature is lower than 150 ° C., and the upper limit is set to 700 ° C. If the temperature exceeds 700 ° C., sufficient hardness cannot be obtained due to softening. Because. By this heat treatment, an oxide film such as FeO is formed on the surface of the hot forging die, and the resulting hot forging die has high wear resistance. Moreover, this heat treatment is preferably performed at 500 to 700 ° C. for 1 to 2 hours in order to uniformly form an oxide film on the surface of the hot forging die. This is because the oxide film formed in this temperature range is excellent in lubricity and wear resistance. In order to perform the heat treatment at 500 to 700 ° C., it is preferably carried out in an atmospheric furnace.

(Function)
Since the hot forging die according to an embodiment of the present invention has the above component composition, the basic characteristics such as toughness are ensured to be equivalent to JIS SKD61, and heat treatment at 150 ° C. to 700 ° C. or an actual machine. When heat is applied, an oxide film such as FeO is formed, and excellent wear resistance is obtained.
The manufacturing method of the hot forging die concerning one embodiment of the present invention melts the steel provided with the above-mentioned ingredient composition, makes it a steel ingot, then hot-works it into a predetermined shape, and has the required hardness. Since the mold obtained by tempering and finishing is subjected to an additional heat treatment at 150 ° C. to 700 ° C., an oxide film such as FeO is formed. Since the hot forging die according to one embodiment of the present invention thus obtained has the above-described component composition, it is superior to the conventional one while ensuring basic properties such as toughness equivalent to JIS SKD61. High wear resistance.
An oxide film such as FeO has good adhesion and good lubricity, so it functions as a protective film, relaxes plastic flow of the mold during forging, and suppresses softening due to heat generated by the process. Improve the wear resistance of the mold. Since the Si amount is reduced as much as possible, the oxide layer FeSiO ₄ that inhibits the adhesion of FeO as a protective film is not formed.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
(Production of test materials)
Steel having each component composition shown in Table 1 is melted in an arc melting furnace, and after ingot forming, it is processed into a cylinder having a diameter of 260 mm by forging, normalizing, tempering, spheroidizing annealing, and a test A material was used.

(Friction and wear test)
The friction coefficient was measured by a friction wear test by the pin-on-disk method, and this will be described.
The disk test piece was produced by the following procedure. First, for each example and each comparative example, a disk having a diameter of 25 mm and a thickness of 6 mm was cut out from the above-described test material, and this was processed and tempered to 53 HRC (quenched (1030 ° C.) and tempered (550) The test surface was finished (mirror polishing). And about each Example and each comparative example, (a) what carried out the additional heat processing which hold | maintains this in the atmosphere of 600 degreeC for 1 hour, and (b) what carried out mirror polishing again to this were produced, these Was used as a disk test piece (see FIG. 1).

The outline of the friction and wear test by the pin-on-disk method is briefly shown in FIG. 1, but the disk was conditioned using SUJ2 (10R) conditioned as a pin, a load of 10 gf, a relative sliding speed of 100 mm / sec and a measurement time of 1500 sec. This was done by rotating the specimen.
The results are shown in Table 2 and FIGS. Table 2 summarizes the tempered hardness and the friction coefficient (average value), and FIG. 2 is a graph showing the friction coefficient for the total friction distance for Example 1 and Comparative Example 2 (SKD61). FIG. 3 shows an external view photograph of the disk test piece after the frictional wear test for Example 1 and Comparative Example 2 (SKD61).

(Punch wear test)
A punch wear test was performed under sub-hot forging conditions, which will be described.
The punch test piece was produced by the following procedure. First, for each example and each comparative example, a cylinder having a diameter of 22 mm and a length of 114 mm was cut out from the above-described test material, and this was processed and tempered to 53 HRC (quenched (1030 ° C.) and tempered (550). C. to 620.degree. C.) and then finished (wrapped). And about each Example and each comparative example, (a) what carried out the additional heat processing which hold | maintains this in the atmosphere of 600 degreeC for 1 hour, and (b) what was wrapped again in this were produced, and these were made. A punch specimen was obtained. The external appearance is shown in FIG.

The punch wear test was performed by two-step forging shown in FIG. 4B using an NS5-10PL part former (140t) manufactured by Daido Machine.
In this test, the workpiece material was S53C, forging was performed at a forging temperature of 800 ° C., a forging speed of 85 spm, and 5000 shots, and the amount of punch wear after forging (see FIG. 5) was measured. The results are shown in Table 2.
Further, forging was performed under the same conditions as in the punch wear test except that the forging temperature was set to 820 ° C., and the amount of punch wear after this forging was measured. The result is shown in FIG.

(Actual wear test)
Example 1 and Comparative Example 2 were applied to hot forging in actual production (however, the tempered hardness of Example 1 and Comparative Example 2 was HRC45). Then, the amount of wear of the hatched part mold shown in FIG. 7A was measured. The amount of wear was measured using a three-dimensional shape measuring machine. The shape before and after forging was measured, and the difference was defined as the amount of wear. The amount of wear was plotted using the measured value of the portion with the largest amount of wear in the hatched portion. The result is shown in FIG.

(Basic characteristics)
Since the axial force fatigue characteristics, the plane fracture toughness value, and the temper softening resistance were investigated for Example 1 and Comparative Example 2 (SKD61), the results are shown in FIGS. 8A, 8B, and 8C, respectively. Show.

(Evaluation)
(Friction and wear test-evaluation)
According to Table 2, the friction coefficient of Examples 1-14 which performed additional heat processing was smaller than the friction coefficient of Examples 1-14 which mirror-polished again. From this, it was found that in Examples 1 to 14, an oxide film with good lubricity was formed.
Moreover, the friction coefficient of Examples 1-14 was small compared with the friction coefficient of Comparative Examples 1 and 2. In Examples 1 to 14, the amount of Si is reduced particularly in relation to Comparative Examples 1 and 2. From this, it has been confirmed that the friction coefficient depends on the Si amount and decreases as the Si amount decreases.

  The same thing was found in FIG. In Example 1 in which the oxide film was formed by the additional heat treatment, the friction coefficient was remarkably reduced as compared with the case where the oxide film was removed by mirror polishing again. From this, it was found that when the hot forging die is subjected to heat treatment, the friction coefficient can be reduced and the lubricity is improved. Further, Example 1 and Comparative Example 2 in which an oxide film was formed by additional heat treatment had a smaller coefficient of friction than that obtained by mirror polishing again. In particular, Example 1 was significantly more than Comparative Example 2. The coefficient of friction has decreased. From this, it was confirmed that when the hot forging die composed of the component composition of Example 1 was subjected to additional heat treatment, the effect of improving lubricity was particularly high.

According to FIG. 3, the surface of the disk test piece of Example 1 in which the oxide film was formed by additional heat treatment did not peel off, but the disk test piece of Example 1 in which the oxide film was removed by mirror polishing again. The surface is sharpened by the pin material. From this, it was found that the effect of lubrication can be obtained by applying heat treatment to the hot forging die.
Further, in Comparative Example 2 in which the oxide film is formed by additional heat treatment, the surface of the disk specimen is scraped less than Comparative Example 2 in which the oxide film is removed by mirror polishing again. From this, it was found that the effect of improving the adhesion is particularly high when an additional heat treatment is applied to the hot forging die having the component composition of Example 1. When the oxide film was removed by mirror polishing again, there was almost no difference between Example 1 and Comparative Example 2 in terms of the coefficient of friction and the degree of wear.

(Punch wear test-evaluation)
According to Table 2, in Examples 1 to 14, the amount of wear decreased by 5 to 10% in the case where the oxide film was formed by additional heat treatment, compared with the case where the oxide film was removed by mirror polishing again. From this, it was found that the oxide film formed by heat treatment has high wear resistance. In Comparative Examples 1 and 2, even when an oxide film was formed by additional heat treatment, the reduction rate of the amount of wear was 2-3%, and the effect was small. From this, it was found that the effect of increasing the wear resistance was particularly high when an additional heat treatment was applied to the hot forging die having the composition of Examples 1 to 14.
Moreover, since Examples 1-14 reduced Si amount, it turned out that wear amount decreases by reducing Si amount. The reason is that, according to Table 1, the Si amounts of Example 1 and Comparative Examples 1 and 2 are 0.1% and 1%, respectively, while the other components are almost the same amount.
Moreover, according to Examples 1-14 of Table 2, it turned out that there is a tendency for the amount of wear to decrease with the increase in the amount of addition of C and Mo and the amount of addition of Si, Mn, and Cr.
Further, according to Table 2, there is no difference in the tempering hardness in any of the examples and the comparative examples, but according to FIG. 6, there is a difference in the wear resistance under the actual forging conditions. Also from this, in Examples 1-14, it turned out that the oxide film produced | generated on a forge surface has an effect which improves abrasion resistance and a lubrication effect | action.

(Actual wear test-evaluation)
Further, according to FIG. 7, the forging number of Example 1 was 1.3 times that of Comparative Example 2, but the wear amount of Example 1 was reduced by 35%. From this, it was confirmed even in actual production that Example 1 was superior in wear resistance as compared with Comparative Example 2.

  From the above, in Examples 1 to 14, an oxide film having good adhesion and lubricity is formed by additional heat treatment, and this oxide film relaxes the plastic flow of the mold in forging and softens due to its processing heat generation. It was found that by suppressing it, the wear resistance was improved. Therefore, it was found that this oxide film is effective as a protective film.

(Basic characteristics-evaluation)
According to the axial force fatigue characteristics shown in FIG. 8A, the number of repeated fractures in Example 1 was two to three times that in Comparative Example 2 with the same load stress. On the fatigue fracture surface of Comparative Example 2, coarse VC was confirmed, while VC starting from the fracture surface of Example 1 was not recognized. The reason for this is considered that, in Example 1, since Si and V were reduced as compared with Comparative Example 2, the crystallization VC during solidification was reduced and reduced in diameter, and was completely dissolved by subsequent soaking.

  Since early rupture of the mold, so-called large initial crack, is more likely to occur in a mold material having a lower fracture toughness value, ensuring a high fracture toughness value is an essential issue in extending the life of the mold material. According to the fracture toughness value shown in FIG. 8 (b), the fracture toughness value of Example 1 was almost equal to the fracture toughness value of Comparative Example 2. Therefore, as in Example 1, it was confirmed that large cracks did not increase even if Si and V were reduced as compared with Comparative Example 2.

  FIG.8 (c) shows the hardness after heating the tempered material of Example 1 and Comparative Example 2 to the temperature range of 500 to 700 degreeC. According to this, there was no difference between Example 1 and Comparative Example 2. In Example 1, although the amount of V was reduced, an amount sufficient to suppress the coarsening of crystal grains during quenching was contained, so that no coarsening of crystal grains in the quenched structure was observed. Moreover, although Si content contributes greatly to solid solution hardening and secondary hardening, it has confirmed that softening resistance did not deteriorate in Example 1 even if Si was reduced.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The hot forging die and the manufacturing method thereof according to the present invention are particularly useful as a material for hot forging dies because they are excellent in wear resistance and crack resistance, and in addition to hot press dies and die castings. It is also suitable for materials such as molds and dies for aluminum extrusion. Therefore, it is extremely useful industrially for many steel manufacturers and mold manufacturers.

It is a figure which shows the outline | summary of the pin-on-disk method. It is a graph which shows the result of the friction abrasion test of Example 1 and Comparative Example 2. It is an external appearance photograph which shows the state of the disk test piece of Example 1 and the comparative example 2 after the friction abrasion test by a pin on disk method. (A) It is a figure which shows a part of external appearance of a punch test piece, (b) It is a figure which shows the process of two process forging. It is a figure which shows the measuring method of punch wear amount. It is a graph which shows the amount of punch wear of Examples 1-14 and comparative examples 1 and 2. It is a graph which shows the amount of wear of the real type of Example 1 and Comparative Example 2. It is a graph which shows the various basic characteristics of Example 1 and Comparative Example 2, (a) SN curve, (b) Relationship between hardness and fracture toughness value, (c) Graph showing temper softening resistance.

Claims (6)

  In mass%, C: 0.32 to 0.42%, Si: 0.05 to 0.15%, Mn: 0.3 to 1.5%, Ni: 0.2% or less, Cr: 4.0 -6.0%, V: 0.2-1.0%, Mo + 1 / 2W: 0.8-2.0%, and N: 0.005-0.04%, the balance being Fe and A hot forging die characterized by comprising inevitable impurities.   The hot forging die according to claim 1, further comprising Co: 0.1 to 1.0% by mass. A hot forging die, wherein an oxide film is formed on a surface of the hot forging die according to claim 1 or 2 . In mass%, C: 0.32 to 0.42%, Si: 0.05 to 0.15%, Mn: 0.3 to 1.5%, Ni: 0.2% or less, Cr: 4.0 -6.0%, V: 0.2-1.0%, Mo + 1 / 2W: 0.8-2.0%, and N: 0.005-0.04%, the balance being Fe and After roughly processing steel consisting of inevitable impurities, quenching and tempering, hot forging die obtained by finishing processing,
A method for producing a hot forging die, wherein an additional heat treatment is performed at 150 ° C to 700 ° C. The steel further contains, by mass%, Co: hot forging dies The method according to claim 4 you, characterized in that it contains 0.1 to 1.0%. The steel further contains, by mass%, Cu: hot forging dies The method according to claim 4 or 5, characterized in that it contains 0.1 to 1.0%.

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