KR20130091351A - Die steel having superior rusting resistance and thermal conductivity, and method for producing same - Google Patents

Abstract

After satisfying the basic characteristics as the steel for a mold, there is provided a steel for a mold and a method for producing the same, which have both excellent rust resistance and heat conductivity. In mass%, C: 0.07 to 0.15%, Si: greater than 0 to less than 0.8%, Mn: greater than 0 to less than 1.5%, P: less than 0.05%, S: less than 0.06%, Ni: greater than 0 to less than 0.9%, Cr: 2.9 to 4.9%, Mo and W alone or in combination (Mo + 1 / 2W): more than 0 to less than 0.8%, more than V: 0 to less than 0.15%, Cu: 0.25 to 1.8%, the remainder being Fe And steel having a composition composed of unavoidable impurities, and having a hardness of 30 to 42 HRC. It is preferable to regulate Al as an unavoidable impurity to less than 0.1%, N to less than 0.06%, and O to less than 0.005%. Said hardness can be obtained by hardening and tempering of 530 degreeC or more.

Description

DIE STEEL HAVING SUPERIOR RUSTING RESISTANCE AND THERMAL CONDUCTIVITY, AND METHOD FOR PRODUCING SAME}

The present invention relates to a steel for a mold which has excellent rust resistance and heat conductivity, and is mainly optimized for plastic molding applications, and a method for producing the same.

Conventionally, in particular for steel for metal molds used for plastic molding,

(1) Good mirror finish and small tendency of pinholes and other fine pits,

(2) the time signal workability is good,

(3) good strength, wear resistance, toughness,

(4) good machinability;

(5) good corrosion resistance and corrosion resistance;

(6) good thermal conductivity

Etc. are required.

In particular, the improvement of the rust resistance and the thermal conductivity is an important required characteristic in recent years for die steel. In other words, when the mold is not used, such as production or maintenance, there is a problem that rust occurs on the surface of the mold due to condensation. If rust occurs on the surface of the mold, a step of dropping rust such as polishing is essential when starting to use again, which causes a decrease in productivity. Therefore, much improvement of the rust resistance is calculated | required by the steel for metal mold | die. Moreover, the improvement of the thermal conductivity of the steel for metal mold | die is an important improvement characteristic for shortening the heat cycle and raising productivity in the plastic molding which repeats heating and cooling.

As a steel for a metal mold | die used for plastic shaping | molding, it is C: 0.075-0.15%, Si: 1.0% or less, Mn: 1-3%, Cr: 2-5%, Ni: 1 in mass% (it is expressed in% below). To 4% (but Mn + Cr + Ni ≧ 6), Mo and W are used alone or in combination (Mo + 1 / 2W): 0.1 to 1.0%, P: 0.015% or less, S: 0.02% or less, alloy consisting of the remaining portions Fe and impurities Steel is proposed (patent document 1).

In addition, C: 0.10 to 0.25%, Si: 1.00% or less, Mn: 2.00% or less, Ni: 0.60 to 1.50%, Cr: 1.00 to 2.50%, Mo and W, alone or in combination (Mo + 1 / 2W): 1.00% or less, V: 0.03 to 0.15%, Cu: 0.50 to 2.00%, S: 0.05% or less, Al is 0.10% or less, N is 0.06% or less, O is 0.005% or less, and the remainder is There is proposed a steel for a mold having a composition of Fe and unavoidable impurities (Patent Document 2).

Japanese Patent Application Publication No. 2001-505617 Japanese Patent Application Publication No. 2007-146278

The steel for metal mold | die of patent document 1 containing 2 to 5% of Cr is excellent in rust resistance. However, since the thermal conductivity is low, the heat cycle time increases depending on the molding conditions, which may lower the productivity. On the other hand, the steel for metal molds of patent document 2 whose Cr is 2.5% or less has high thermal conductivity, and can shorten heat cycle time. However, compared with the steel for metal mold | die of patent document 1, there exists a room for improvement of rust resistance. As described above, since the thermal conductivity and the rust resistance are opposite characteristics, it has been desired to provide a steel for a mold having these characteristics at a high level.

An object of the present invention is to provide a steel for a mold having excellent heat conductivity and rust resistance, and a manufacturing method suitable for obtaining the steel for a mold.

This inventor reviewed the component composition of the steel for metal mold | die. As a result, it was confirmed that even in the case of many elemental species constituting conventional die steels, they are mutually and complexly acting on the rust resistance and the thermal conductivity. The present invention has been achieved by extracting a factor having a particularly high influence among many elemental species for the purpose of having both of the above characteristics, and revealing that there is an optimum relationship between these contents.

That is, the present invention, in mass%, C: 0.07 to 0.15%, Si: more than 0 to less than 0.8%, Mn: more than 0 to less than 1.5%, P: less than 0.05%, S: less than 0.06%, Ni: 0 More than less than 0.9%, Cr: 2.9 to 4.9%, Mo and W alone or in combination (Mo + 1 / 2W): more than 0 to less than 0.8%, V: more than 0 to less than 0.15%, Cu: 0.25 to 1.8% It is contained, and remainder is steel of the composition which consists of Fe and an unavoidable impurity, and is a steel for metal mold | die excellent in the rust resistance and heat conductivity characterized by the hardness of 30-42 HRC. It is preferable to regulate Al as an unavoidable impurity to less than 0.1%, N to less than 0.06%, and O to less than 0.005%.

In addition, the present invention is, in mass%, C: 0.07 to 0.15%, Si: more than 0 to less than 0.8%, Mn: more than 0 to less than 1.5%, P: less than 0.05%, S: less than 0.06%, Ni: 0 More than less than 0.9%, Cr: 2.9 to 4.9%, Mo and W alone or in combination (Mo + 1 / 2W): more than 0 to less than 0.8%, V: more than 0 to less than 0.15%, Cu: 0.25 to 1.8% The remaining portion is for a mold having excellent corrosion resistance and thermal conductivity, characterized in that the hardness of the composition consisting of Fe and unavoidable impurities is adjusted to 30 to 42 HRC by quenching and tempering by a temperature of 530 ° C. or higher. It is a manufacturing method of steel. It is preferable to regulate Al as an unavoidable impurity to less than 0.1%, N to less than 0.06%, and O to less than 0.005%.

And preferably, the composition of said steel is steel for metal mold | die which satisfy | fills 100 or more by the value by following formula (1) and (2) by mass%, respectively, and its manufacturing method.

[Equation 1]

&Quot; (2) "

Here, in parentheses of [] shows content (mass%) of each element.

According to the present invention, excellent rust resistance and heat conductivity, which can only be achieved with individual die steels, can be simultaneously realized with high reproducibility. Therefore, it becomes an effective technique in the technical improvement of a metal mold | die.

The characteristic of this invention is that the element type which has a big influence on rust resistance and heat conductivity as a structural element of the steel for metal mold | die can be specified. That is, C, S, Ni, Cr, Mo, and W have a great influence on the rust resistance, and C, Si, Mn, Ni, Cr, Mo, W, and Cu are elemental species having a great influence on the thermal conductivity. By this specification, about the metal for metal mold | die described in patent document 1 which has the outstanding rust resistance, the improvement of thermal conductivity can be achieved by reviewing the amount of C, Si, Mn, Ni, Cr, Mo, W, Cu. Moreover, about the steel for metal molds of patent document 2 which has the outstanding thermal conductivity, improvement of rust resistance can be achieved by reviewing content of C, S, Ni, Cr, Mo, and W. FIG.

In addition, another feature of the present invention lies in that the influence degree given to each of the rust resistant and thermal conductivity of the above-described specified element species can also be quantified. By quantifying this influence degree, since the optimum component composition of the steel for metal mold which should be aimed at adjustment becomes clearer, further improvement of rust resistance and heat conductivity can be achieved. Hereinafter, it demonstrates for every structural requirement.

C: 0.07 to 0.15%

C is an element that enhances the hardenability, and in tempering, is an element that causes the strengthening of the structure by precipitation of Cr, Mo (W), and V carbide, and is necessary for maintaining the hardening tempering hardness of 30 to 42 HRC described later. It is an additional element. And in order to suppress the processing deformation which arises at the time of cutting, etc., it is preferable to reduce the residual stress in steel, and for this purpose, it is necessary to be able to make said tempering temperature high. Therefore, in the present invention steel, it is important to add a sufficient amount of C such that, for example, even when tempered at 530 ° C or higher, the hardness of 30 HRC or higher can be stably achieved.

However, with increase of the addition amount, when solid solution Cr in a matrix decreases by formation of Cr carbide, since rust resistance falls, it is made into 0.15% or less in this invention. On the other hand, since the solid solution Cr is a great factor for lowering the thermal conductivity of the steel for dies, if too little C forms Cr carbide, the thermal conductivity of the steel for dies is degraded. And since the required hardness is no longer obtained, it is made into 0.07% or more. Preferably it is 0.08% or more and / or 0.13% or less. More preferably, it is 0.1% or more and / or 0.12% or less. 0.1% or less is more preferable.

Si: greater than 0 to less than 0.8%

Si is an element which improves the corrosion resistance with respect to the atmosphere at the time of using a metal mold | die, such as the gas which arises from the to-be-molded material at the time of plastic molding, for example. However, when too large, the thermal conductivity which the steel for metal mold | die has will fall remarkably, and thermal conductivity will deteriorate. In addition, when Si is reduced, the anisotropy of the mechanical properties is reduced, the stripe segregation is also reduced, and excellent mirror workability is obtained. Therefore, in this invention, you may be less than 0.8%. Preferably it is 0.1% or more and / or 0.6% or less. More preferably, it is 0.15% or more and / or 0.5% or less. More preferably, it is 0.2% or more. 0.25% or more is especially preferable.

Mn: greater than 0 to less than 1.5%

Mn is an element which improves hardenability, suppresses the formation of ferrite, and imparts an appropriate hardening tempering hardness. However, excessively high not only impairs thermal conductivity significantly, but also forms a non-metallic inclusion MnS in combination with S described later, which may cause rust and pinholes. Moreover, since a known viscosity is raised and machinability falls, it is made into less than 1.5%. Preferably it is 0.1% or more and / or 1.0% or less. More preferably, it is 0.2% or more and / or 0.8% or less. 0.3% or more is more preferable.

P: less than 0.05%

P is an element which reduces hot workability and toughness when too much. Therefore, in this invention, you may be less than 0.05%. It is preferably 0.03% or less.

S: less than 0.06%

S exists as MnS of a nonmetallic interference | inclusion, and has a big effect on the improvement of machinability. However, the presence of a large amount of MnS is a factor that lowers the performance of the mold itself, such as promoting mechanical properties, particularly toughness anisotropy. MnS may also be a starting point for rust and pinhole generation, which greatly deteriorate the rust resistance and polishing finish, which are important characteristics in the present invention steel. Therefore, S is limited to less than 0.06% even when added. 0.035% or less is preferable. Moreover, a preferable minimum is 0.005% or more.

Ni: greater than 0 to less than 0.9%

Ni also improves the hardenability of the present invention steel and suppresses the formation of ferrite. And it is an element which improves the rust resistance of this invention steel. However, when too large, not only will a thermal conductivity be lowered, but a known viscosity will also be raised and a machinability will also fall. Therefore, Ni is made into less than 0.9%. Preferably it is 0.1% or more and / or 0.6% or less. More preferably, it is 0.15% or more, More preferably, it is 0.2% or more.

Cr: 2.9 to 4.9%

Cr is an element that precipitates and agglomerates fine carbide by tempering to increase the strength of the present invention steel. On the other hand, it is an element which improves the rust resistance of this invention steel by solid-solution to a base. Moreover, when performing nitriding process, it also has an effect which raises the hardness of a nitride layer. However, if it is too large, the amount of solid solution Cr described above increases, not only lowers the thermal conductivity significantly but also lowers the softening resistance. Therefore, Cr of this invention is 2.9 to 4.9%. Preferably it is 3.5% or more and / or 4.8% or less. 3.8% or more is more preferable.

Mo and W alone or in combination (Mo + 1/2 W): greater than 0 to less than 0.8%

Mo and W precipitate and aggregate fine carbide at the time of tempering, and improve the strength of the present invention steel. In addition, the softening resistance during tempering is increased. And like Cr, since it is an element which improves the rust resistance of this invention steel by solid solution to a base, it is an element contained individually or in combination. In addition, a part of Mo or W is partially dissolved in an oxide film on the surface of the mold, and thus has an effect of improving the corrosion resistance against corrosive gas generated from, for example, plastic during use of the mold. However, too much results in a decrease in machinability. In addition, when the above-mentioned solid solution amount increases, the thermal conductivity significantly decreases. Therefore, in this invention, Mo and W were made into less than 0.8% by the single or compound amount defined by the relationship of (Mo + 1 / 2W). Preferably it is 0.1% or more and / or 0.6% or less. More preferably, it is 0.3% or more and / or 0.5% or less.

V: greater than 0 to less than 0.15%

V increases the temper softening resistance, suppresses coarsening of crystal grains, and contributes to improvement of toughness. In addition, there is an effect of forming a hard carbide fine, improving the wear resistance. However, too much would cause a decrease in machinability, so it was less than 0.15%. Preferably it is 0.03% or more and / or 0.10% or less. More preferably, it is 0.05% or more, More preferably, it is 0.07% or more.

Cu: 0.25-1.8%

Cu is an element which precipitates and aggregates Fe-Cu solid solution at the time of a tempering process, and improves the intensity | strength of this invention steel. However, when too much, hot workability will fall remarkably. And thermal conductivity is also reduced and the thermal conductivity of this invention steel deteriorates. Therefore, Cu of this invention shall be 0.25 to 1.8%. Preferably it is 0.4% or more and / or 1.5% or less. More preferably, it is 0.7% or more, More preferably, it is 1.0% or more.

Al: less than 0.1%

Al which is an unavoidable impurity is normally used as a deoxidation element in a solvent. In the present invention steel in which the hardness is obtained after refining, when a large amount of Al ₂ O ₃ exists in the steel, specular workability deteriorates. Therefore, it is preferable to regulate Al of this invention to less than 0.1%. More preferably, it is less than 0.05%.

N (nitrogen): less than 0.06%

N which is an unavoidable impurity is an element which forms nitride in steel. If the nitride is formed excessively, the toughness, machinability and abrasiveness of the mold are significantly degraded. Therefore, it is preferable to restrict N in steel. Therefore, in this invention, it is preferable to define N to less than 0.06%. More preferably, it is less than 0.03%.

O (oxygen): less than 0.005%

O, which is an unavoidable impurity, is an element which forms an oxide in steel. Excessive oxide becomes a factor which remarkably deteriorates the plastic workability and polishing property in cold. In the present invention, it is important to suppress especially the formation of the above-described Al ₂ O _3. Therefore, it is preferable that O of this invention regulates an upper limit to 0.005%. More preferably, it is less than 0.003%.

Preferably, the value of following formula (1) and (2) satisfies 100 or more, respectively. {[] The parenthesis shows content (mass%) of each element}.

[Equation 1]

&Quot; (2) "

After satisfying basic characteristics such as strength, softening resistance, and machinability, and in order to achieve excellent rust resistance and thermal conductivity, which are the characteristics of the present invention, the content of many elemental species constituting the present invention steel is in the above-described component range. Need to be adjusted. However, the degree of influence on the rust resistance and thermal conductivity is different for these individual elements. Therefore, it is effective to mutually manage the content of the constituent element species in order to maintain the basic characteristics and to achieve more excellent rust resistance and thermal conductivity.

Therefore, the degree of the influence on the rust resistance and thermal conductivity was examined for each of the constituent elements of the present invention steel. As a result, about the rust resistance, the improvement effect was large in order of Cr, Mo, W, and Ni, On the contrary, it turned out that S and C reduce the said characteristic in this order. Moreover, about thermal conductivity, the improvement effect by containing C is large, and it discovered that Si, Ni, Mn, Cr, Cu, Mo, and W reduced the said characteristic in this order. Furthermore, by performing the regression analysis when the content of these elements was used as a variable, the above degree of influence could be expressed as an accurate mutual coefficient.

That is, the influence of the constituent elements on the rust resistance of the present invention steel can be expressed mutually by the following equation (1). At this time, the coefficient of the improvement element of the said characteristic is positive and the coefficient of the degradation element of the said characteristic is represented by minus, The larger the absolute value of each, the greater the influence degree. And in the case of this invention steel, it is preferable for the value of Formula (1) to be 100 or more for further improvement of rust resistance. More preferably, the value is 105 or more.

The influence of the constituent elements on the thermal conductivity of the present invention steel can be expressed mutually by the following expression (2). At this time, the coefficient of the element which acts on the improvement of the said characteristic is positive, and the coefficient of the element which acts on the fall of the said characteristic is represented by minus, The larger the absolute value of each, the greater the influence. In the case of the present invention steel, the value of the expression (2) is preferably 100 or more for further improvement of the thermal conductivity. More preferably, the value is 105 or more.

The hardness of the mold steel is 30 to 42 HRC.

If the hardness of the raw material is too low, the mirror workability at the time of mold production is lowered. And the wear resistance as a mold product also falls. On the other hand, when the hardness of a raw material is too high, the machinability at the time of metal mold | die manufacture falls. And the toughness as a mold product also falls. Therefore, the hardness of the die steel of this invention shall be 30-42 HRC. Preferably it is 35 HRC or more and / or 40 HRC or less. The steel for metal mold | die of this invention can be used as what is called early hardened steel which is refined to said hardness by quenching and tempering heat processing, and is cut into die shape.

And the present invention steel can stably achieve the hardness of 30HRC or more, more preferably 35HRC or more, even at high tempering of 530 ° C or higher. Achievement is possible even at tempering above 540 ℃. In order to suppress the processing deformation which arises at the time of cutting etc., it is as mentioned above that tempering at high temperature which can reduce the residual stress in steel is advantageous. The steel for metal mold | die of this invention is adjusted to the optimal component composition which has the said tempering characteristic as well as the outstanding rust resistance and heat conductivity. In addition, about the hardening temperature at this time, a special setting is not necessary. For example, quenching from temperatures of 900 ° C. or higher can be applied.

First Embodiment

A 10 kg steel ingot was adjusted to a predetermined component composition in a vacuum melting furnace. The component composition is shown in Table 1. In Table 1, the value of Formula (1) and (2) by this invention was also written together. Conventional steels 1 and 2 correspond to Patent Literatures 1 and 2, respectively.

Next, these steel ingots were forged at 1150 ° C to be steel materials having a thickness of 30 mm × width of 30 mm, which were then annealed at 860 ° C. And from each annealing treatment material, three pieces for the hardness evaluation of 10 mm x 10 mm x 10 mm, the rust resistance evaluation of 5 mm x 8 mm x 15 mm, and the thermal conductivity evaluation of diameter 10 mm x thickness 1 mm The steel slab of the dimension shape was processed. And the following tests were done about having given predetermined hardening tempering process to these steel slabs.

(Evaluation of hardness)

Using a steel piece of 10 mm x 10 mm x 10 mm, the quenching process by gas cooling from 950 degreeC was performed to this. And tempering process was the high temperature tempering which is favorable for reducing residual stress in steel, and made it the conditions of 2 hours at 550 degreeC. The results of hardness are shown in Table 2. The present invention steel attained a hardness of 30 HRC or more even at a tempering of 550 ° C., and preferably achieved a hardness of 35 HRC or more.

(Evaluation of rust resistance)

Using the steel piece of 5 mm x 8 mm x 15 mm, the hardening process similar to the above was performed to this. Tempering process was made into the conditions for 2 hours at the appropriate temperature of 540 degreeC-580 degreeC so that hardness might be 34-36 HRC (target hardness 35HRC). Then, the test piece after the tempering treatment was subjected to a 24 hour exposure test in an atmosphere at a temperature of 80 ° C. and a humidity of 90%. Surface area (mm 2)] was calculated. The results are shown in Table 3.

(Evaluation of thermal conductivity)

The same hardening process as above-mentioned was performed using the steel piece of diameter 10mm x thickness 1mm. The tempering treatment was performed under conditions of 2 hours at an appropriate temperature of 540 ° C to 580 ° C such that the hardness was 34 to 36 HRC (target hardness 35HRC) as described above, and was treated together with the test piece for evaluation of rust resistance. And thermal conductivity was measured with the laser flash method about the test piece after a tempering process. The results are shown in Table 3.

From the results of Table 3, the present invention steels 1 to 6, in which the component composition is optimally adjusted, achieve both excellent rust resistance and thermal conductivity as compared with the conventional steels 1 and 2. And in the present invention steels 3-6 whose value of Formula (1) is 100 or more, the generation | occurrence | production of rust was not confirmed. On the other hand, in the comparative steel 1 with high Si and the comparative steel 3 with high Ni, the thermal conductivity is greatly reduced. Even Comparative Steel 2 having a component composition close to the present invention steel has high Ni and low thermal conductivity. Comparative steel 3 having a low Cr has a low rust resistance.

Second Embodiment

A 10 kg steel ingot was solvented in the same manner as in the first example except that the component composition was changed. The component composition is shown in Table 4. In Table 4, similarly to Table 1, the values of the equations (1) and (2) according to the present invention were also written.

Next, these ingots were forged under the same conditions as those of the first embodiment described above, and annealing treatment was performed. And from each annealing treatment material, three pieces for the hardness evaluation of 10 mm x 10 mm x 10 mm, the rust resistance evaluation of 5 mm x 8 mm x 15 mm, and the thermal conductivity evaluation of diameter 10 mm x thickness 1 mm The steel slab of the dimension shape was processed. And the following tests were done about having given predetermined hardening tempering process to these steel slabs.

(Evaluation of hardness)

Using the steel strip of 10 mm x 10 mm x 10 mm, the quenching process on the same conditions as 1st Example was performed to this. And tempering process performed 2 conditions of the conditions of 2 hours at 550 degreeC of the 1st Example, and the conditions of 2 hours at 580 degreeC. The results of hardness are shown in Table 5. In addition, in Table 5, the result of this invention steel 2, 3, 5, 6 evaluated by the 1st Example, the comparative steels 1-3, and the conventional steels 1 and 2 is also shown. In addition to tempering at 550 ° C, the present invention achieves a hardness of 30 HRC or more even at 580 ° C tempering, and preferably at least 35HRC. In addition, the present invention steel 22 with a slightly lower V had a hardness of less than 30 HRC at 580 ° C tempering. On the other hand, Comparative Steel 4 having a small amount of C did not achieve 30 HRC in both tempering at 550 ° C and 580 ° C.

(Evaluation of rust resistance)

Using a 5 mm x 8 mm x 15-mm steel piece, the quenching and tempering process of the same conditions as the evaluation of the rust resistance of 1st Example, and the exposure test were done to this. And the mass of the test piece before the test and the mass of the test piece which dropped the rust after the test were measured, and the reduction rate of mass (the amount of reduction of the 100x test piece (g) / mass of the test piece before the test) was calculated. The results are shown in Table 6. In addition, in Table 6, the result of the conventional steel 2 evaluated by the 1st Example is also written together.

(Evaluation of thermal conductivity)

Using a steel piece having a diameter of 10 mm and a thickness of 1 mm, the quenching and tempering treatment under the same conditions as those at the time of evaluation of the thermal conductivity of the first example and measurement of the thermal conductivity were performed. The results are shown in Table 6. In addition, in Table 6, the result of the conventional steel 2 evaluated by the 1st Example is also written together.

From the result of Table 6, this invention steels 7-22 have the outstanding rust resistance and heat conductivity, and are achieving these compatibility. Although the amount of C is high in this invention steel 10, the value of Formula (1) is high and rust resistance is favorable. On the other hand, Comparative steels 5 and 6 with high Si have low thermal conductivity. Comparative steel 7 having a low Cr has a large amount of decrease in mass due to the occurrence of rust, and has low rust resistance.

Third Embodiment

In the arc melting furnace, 10 t of steel ingot adjusted to the component composition of Table 7 was dissolved. In Table 7, similarly to Table 1, the values of Equations 1 and 2 according to the present invention were also written together.

Next, these steel ingots were cogged to obtain a square material having a cross section of 6500 cm 2. And from this angle material, the steel piece of two dimension shapes for the evaluation of the corrosion resistance of 5 mm x 8 mm x 15 mm, and the thermal conductivity evaluation of diameter 10 mm x thickness 1 mm was extract | collected, and on the conditions similar to 2nd Example Was evaluated for the rust resistance and thermal conductivity. The results are shown in Table 8.

From the result of Table 8, it turns out that this invention steel 23 has achieved the outstanding compatibility of both rust-resistance and thermal conductivity.

Since the present invention also satisfies the basic characteristics of the mold, the present invention can be applied to molds such as rubber molding, hot work used for small lot production, die casting, and the like, in addition to plastic molding molds.

Claims (6)

In mass%, C: 0.07 to 0.15%, Si: greater than 0 to less than 0.8%, Mn: greater than 0 to less than 1.5%, P: less than 0.05%, S: less than 0.06%, Ni: greater than 0 to less than 0.9%, Cr: 2.9 to 4.9%, Mo and W alone or in combination (Mo + 1 / 2W): more than 0 to less than 0.8%, more than V: 0 to less than 0.15%, Cu: 0.25 to 1.8%, the remainder being Fe And a steel having a composition composed of unavoidable impurities, and having a hardness of 30 to 42 HRC. The steel for a mold according to claim 1, wherein the composition of the steel satisfies 100 or more in terms of the following formulas (1) and (2) by mass%.
[Equation 1]

&Quot; (2) "

Here, in parentheses of [] shows content (mass%) of each element. The mold steel according to claim 1 or 2, wherein Al, which is an unavoidable impurity, is regulated to less than 0.1%, N to less than 0.06%, and O to less than 0.005%. In mass%, C: 0.07 to 0.15%, Si: greater than 0 to less than 0.8%, Mn: greater than 0 to less than 1.5%, P: less than 0.05%, S: less than 0.06%, Ni: greater than 0 to less than 0.9%, Cr: 2.9 to 4.9%, Mo and W alone or in combination (Mo + 1 / 2W): more than 0 to less than 0.8%, more than V: 0 to less than 0.15%, Cu: 0.25 to 1.8%, the remainder being Fe And the hardness of 30-42 HRC by hardening and tempering by the temperature of 530 degreeC or more, the steel of the composition which consists of an unavoidable impurity, The manufacturing method of the steel for metal mold | die excellent in the rust resistance and heat conductivity characterized by the above-mentioned. The method of manufacturing a steel for a mold according to claim 4, wherein the composition of the steel satisfies 100 or more in terms of the following formulas (1) and (2) in terms of mass%.
[Equation 1]

&Quot; (2) "

Here, in parentheses of [] shows content (mass%) of each element. The method for producing a mold steel having excellent rust resistance and thermal conductivity according to claim 4 or 5, wherein Al, which is an unavoidable impurity, is regulated to less than 0.1%, N to less than 0.06%, and O to less than 0.005%. .