JP5515442B2 - Hot tool steel and steel products using the same - Google Patents

Description

  The present invention relates to a hot work tool steel and a steel product using the hot work tool steel. More specifically, while maintaining machinability equal to or higher than that of a general-purpose mold steel (JIS SKD61), the thermal conductivity is improved from that of a general-purpose mold steel. The present invention also relates to a hot work tool steel having an impact value higher than that of general-purpose mold steel and a steel product using the hot tool steel.

  As a die material used for die casting, hot forging, and hot forging, JIS SKD61 having excellent machinability is used for general purposes. However, since JIS SKD61 has low thermal conductivity, there is a problem that the mold temperature tends to be high, seizure and heat check occur frequently, and the mold life is shortened. Moreover, since JIS SKD61 is not high in hardenability, with the increase in size of the mold, it becomes difficult to harden and the toughness is significantly reduced. Therefore, JIS SKD61 has a problem that the heat check is promoted and the mold life is further shortened. For this reason, there is a demand from the industry for hot work tool steel that has better thermal conductivity and impact value than JIS SKD61.

Therefore, various steels suitable for this type of application have been proposed.
For example, in Patent Document 1, as hot tool steel having excellent hardenability and creep characteristics that can be substituted for JIS SKD61, C: 0.30 to 0.38 wt%, Si: 0.10 to 0.40 wt% %, Mn: 0.60 to 0.80 wt%, Cr: 5.40 to 5.70 wt%, Mo: 1.50 to 1.70 wt%, V: 0.70 to 0.85 wt% A steel is disclosed that contains it as an essential component, the balance being Fe and inevitable impurities.

  In Patent Document 2, as a mold for sizing the width of a hot slab in which a thermal shock coefficient K is introduced to improve wear resistance and heat crack resistance, C: 0.1 to 0.5% in weight% Si: 0.1 to 1.5%, Mn: 0.2 to 1.5%, Ni: 5.0% or less, Cr: 0.5 to 5.0%, Mo: 1.5% or less, Steel having V: 1.0% or less, Cu: 0.2% or less, the balance being Fe and inevitable impurities is disclosed.

  In Patent Document 3, as hot tool steel excellent in low cycle fatigue characteristics formed by remelting electroslag, by weight%, C: 0.32 to 0.42%, Si: 0.10 to 1.20. %, Mn: 0.10 to 0.50%, Cr: 4.50 to 5.50%, Mo: 1.00 to 1.50%, V: 0.30 to 0.80%, P: 0.00. A steel made of 010% or less, S: 0.003% or less, Ni: 1.00% or less, Co: 1.00% or less, W: 1.00% or less, the balance Fe and impurities is disclosed.

  In Patent Document 4, as hot tool steel in which the wear resistance and crack resistance and chipping resistance of a practical mold are simultaneously improved, by weight%, C: 0.15% or more and 0.80% or less, Si: Less than 0.10%, Mn: 3.0% or less, Ni: 4.0% or less, Cr: 10.0% or less, Cu: 3.0% or less Furthermore, Mo: 5.0% or less, W: 5.0% or less, V: 3.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, Zr: 1.0% or less Co: One or more of 5.0% or less, S: 0.005% or less, P: 0.015% or less, O: 0.0030% or less, balance Fe and impurities Steel is disclosed.

  In Patent Document 5, as an alloy tool steel excellent in hot workability and fatigue characteristics, C: 0.35 to 1.50%, Si: 0.1 to 2.0%, Mn: 0 0.1-1.5%, Cr: 2.0-10.0%, and 2Mo + W: 1.5-30.0%, V: 0.5 or 5.0% As described above, REM: 0.001 to 0.60%, Co: 1.0 to 20.0%, Ni: 0.01 to 2.0%, Cu: 0.25 to 1.0%, B: One or more of 0.001 to 0.050% is included, S: 0.0020% or less, O: 0.0030% or less, N: 0.020% or less, Al: 0.020% Hereinafter, steel is disclosed which is restricted to P: 0.020% or less and the balance is substantially made of Fe.

  In Patent Document 6, as a mold steel that can suppress heat check and water-cooled hole cracking by increasing thermal fatigue characteristics and softening resistance, and can increase the life of the mold, mass%, C: 0.1 0.6, Si: 0.01 to 0.8, Mn: 0.1 to 2.5, Cu: 0.01 to 2.0, Ni: 0.01 to 2.0, Cr: 0.1 2.0, Mo: 0.01 to 2.0, one or more of V, W, Nb and Ta in total: 0.01 to 2.0, Al: 0.002 to 0.04 , N: 0.002 to 0.04, O: 0.005 or less, and steel composed of the balance Fe and inevitable impurities is disclosed.

  In Patent Document 7, as an inexpensive steel for plastic molds that achieves both machinability and thermal conductivity, C: 0.25 to 0.45%, Si: less than 0.3%, Mn: 0 .5 to 2%, S: 0.01 to 0.05%, sol. A steel is disclosed that contains Al: 0.02% or less, the balance being Fe and impurities, which may contain up to 0.5% Cr and less than 0.2% V.

  In Patent Document 8, as a pre-hardened steel for die casting molds that can extend the life of die casting molds, the mass content is 0.15% or more and 0.35% or less C, and 0.05% or more and 0%. Less than 20% Si, 0.05% or more and 1.50% or less Mn, 0.020% or less P, 0.013% or less S, 0.10% or less Cu, 0% .20% or less of Ni, 0.20% or more and 2.50% or less of Cr, 0.50% or more and 3.00% or less of Mo, and a total of 0.05% or more and 0.30% or less of V Nb, 0.020% or more and 0.040% or less of Al, 0.003% or less of O, and 0.010% or more and 0.020% or less of N, with the balance being substantially Fe. A steel consisting of is disclosed.

  In Patent Document 9, C: 0.10 to 0.45 wt%, Si: 0.10 to 2.0 wt%, Mn: 0.10 to 2.0 wt% as a steel for press dies having high thermal fatigue characteristics. Mo: 0.50 to 3.0 wt% and V: 0.50 to 0.80 wt%, Cr: 3.0 to 8.0 wt%, Ni: 0.05 to 1.2 wt% %, And the balance Fe and unavoidable impurities are disclosed.

  In Patent Document 10, the hardenability is good, the required impact value is obtained, the die life can be increased, the spheroidizing annealing property is good, and the steel for the die is easy to cut. C: 0.2-0.6%, Si: 0.01-1.5%, Mn: 0.1-2.0%, Cu: 0.01-2.0%, Ni: 0.01 -2.0%, Cr: 0.1-8.0%, Mo: 0.01-5.0%, one of V, W, Nb and Ta or a total of two or more: 0.01- A steel having a composition of 2.0%, Al: 0.002-0.04%, N: 0.002-0.04%, the balance Fe and inevitable impurities is disclosed.

Japanese Patent Laid-Open No. 06-322483 JP 03-0000402 A JP 07-062494 JP 60-059053 A JP 08-1003009 JP2008-056882 JP 2004-183008 A JP-A-2005-307242 JP-A-64-062444 JP2008-121032

However, generally, when the heat conductivity is increased by increasing the heat conductivity, the machinability is deteriorated, and there is a possibility that the processing efficiency is lowered and the cost is increased. Therefore, the effect is often offset when viewed as a whole.
Further, the steels disclosed in Patent Documents 1 to 10 do not have all of the machinability, thermal conductivity, and impact value that the present invention intends to achieve.
For example, in Patent Document 1, there is no suggestion or disclosure about thermal conductivity, and there is a concern about impact value deterioration due to excessive V. Further, in Patent Document 1, there is a concern that machinability deterioration due to too little Si is remarkably difficult to process into a mold shape.
In Patent Document 2, there is concern about a decrease in thermal conductivity due to excess Si and machinability deterioration due to too little Si. Further, in Patent Document 2, there is a concern that the impact value may be lowered due to too little Mn and too little Cr.
Patent Documents 3 to 5 also do not suggest or disclose thermal conductivity. In Patent Document 3, there are concerns about insufficient hardenability and a decrease in impact value due to the insufficient Mn. In Patent Document 4, there is a concern about machinability deterioration due to excessive Si. Further, in Patent Document 4, there is a concern that the impact value may be reduced due to too little Cr or too little or too much V. In Patent Document 5, there are concerns about insufficient hardenability due to insufficient Mn, a decrease in impact value, a decrease in high-temperature strength due to excessive Mo, and a decrease in impact value due to excessive or excessive V.
In Patent Documents 6 to 8, there are concerns about a decrease in hardenability due to too little Cr, and a decrease in hardness and impact value.
In Patent Documents 9 and 10, there is a concern that machinability deterioration due to excessive Si, thermal conductivity decrease due to excessive Si, or impact value decrease due to excessive Cr.

  The present invention has been made in view of the above circumstances, and has better thermal conductivity than general-purpose mold steel while maintaining machinability equivalent to or higher than general-purpose mold steel (JIS SKD61), and moreover than general-purpose mold steel. Another object of the present invention is to provide a hot tool steel having a high impact value and a steel product using the hot tool steel.

General-purpose mold steel (JIS SKD61) is excellent in machinability but has low thermal conductivity and impact value. Therefore, steels with increased machinability, thermal conductivity, and impact value are required in the industry. Generally, improving machinability lowers thermal conductivity, and increasing thermal conductivity increases steel coverage. There is a relationship that the machinability deteriorates. Therefore, no steel has been proposed that satisfies the characteristics required by the present invention in all of machinability, thermal conductivity, and impact value.
Therefore, the present inventor conducted earnest research to improve the thermal conductivity of the general-purpose mold steel while maintaining the machinability at the same level as or higher than that of the general-purpose mold steel, and to further increase the impact value of the general-purpose mold steel. It was. As a result, the present inventor
(A) By adjusting the amount of Si, while improving the thermal conductivity while preventing deterioration of machinability,
(B) By adjusting the amount of Mn, the amount of Cr, the amount of Mo, and the amount of V, it is found that the impact value can be increased more than that of general-purpose mold steel while maintaining higher thermal conductivity than that of general-purpose mold steel. It came to do.
The present invention has been made based on such knowledge.

In order to solve the above problems, the hot work tool steel according to the present invention is:
0.20 ≦ C ≦ 0.42 % by mass,
0.40 <Si <0.75% by mass,
0.65 ≦ Mn ≦ 1.50 mass%,
5.24 ≦ Cr ≦ 9.00 mass%,
1.08 <Mo ≦ 2.50 % by mass, and
Including 0.30 <V <0.70 mass%,
The gist is that the balance consists of Fe and inevitable impurities.
Here, as inevitable impurities, for example, W <0.30 mass%, Co <0.30 mass%, Nb <0.004 mass%, Ta <0.004 mass%, Ti <0.004 mass%. Zr <0.004 mass%, Al <0.004 mass%, N <0.004 mass%, Cu <0.15 mass%, Ni <0.15 mass%, B <0.0010 mass%, S <0.010% by mass, Ca <0.0005% by mass, Se <0.03% by mass, Te <0.005% by mass, Bi <0.01% by mass, Pb <0.03% by mass, Mg <0 0.005% by mass, O <0.0080% by mass, and the like.

The hot work tool steel according to the present invention further comprises:
It may contain 0.30 ≦ W ≦ 4.00 mass%.

The hot work tool steel according to the present invention further comprises:
It may contain 0.30 ≦ Co ≦ 3.00 mass%.

The hot work tool steel according to the present invention further comprises:
0.004 ≦ Nb ≦ 0.100 mass%,
0.004 ≦ Ta ≦ 0.100 mass%,
0.004 ≦ Ti ≦ 0.100 mass%,
0.004 ≦ Zr ≦ 0.100 mass%,
0.004 ≦ Al ≦ 0.050 mass%, and
It may contain at least one selected from the group consisting of 0.004 ≦ N ≦ 0.024 mass%.

The hot work tool steel according to the present invention further comprises:
0.15 ≦ Cu ≦ 1.50 mass%,
0.15 ≦ Ni ≦ 0.96 % by mass, and
It may contain at least one selected from the group consisting of 0.0010 ≦ B ≦ 0.0100 mass%.

The hot work tool steel according to the present invention further comprises:
0.010 ≦ S ≦ 0.500 mass%,
0.0005 ≦ Ca ≦ 0.2000 mass%,
0.03 ≦ Se ≦ 0.50 mass%,
0.005 ≦ Te ≦ 0.100 mass%,
0.01 ≦ Bi ≦ 0.30 mass%, and
It may contain at least one selected from the group consisting of 0.03 ≦ Pb ≦ 0.50 mass%.

The gist of the steel product according to the present invention is the use of the hot tool steel according to the present invention.
Here, the “steel product” refers to, for example, a die casting mold, a hot forging mold, and a hot forging mold, but is not limited thereto.

Since the hot tool steel and the steel product using the same according to the present invention have the above-described composition, they are more thermally conductive than general-purpose mold steel while maintaining machinability equivalent to or higher than that of general-purpose mold steel (JIS SKD61). It has the effect of being excellent in rate and having a high impact value. That is, it has an unprecedented effect of being excellent in the balance of machinability, thermal conductivity, and impact value.
Specifically, the hot work tool steel according to the present invention has an optimized amount of Si so that a thermal conductivity superior to that of general-purpose mold steel can be obtained and machinability equivalent to or higher than that of general-purpose mold steel can be secured. Furthermore, the amount of Mn, the amount of Cr, the amount of Mo, and the amount of V are optimized. Therefore, the hot work tool steel according to the present invention has not only excellent machinability and high thermal conductivity, but also has an effect of providing high hardenability and a high impact value. Therefore, the hot tool steel according to the present invention does not have a higher cost for die machining than general-purpose die steel. Moreover, the hot work tool steel according to the present invention hardly causes seizure or heat check. As a result, a long die life can be obtained, and the manufacturing cost reduction and productivity improvement of die casting and hot forging can be achieved.

Below, the hot tool steel which concerns on one Embodiment of this invention, and the steel products using this are demonstrated.
(Component composition of hot tool steel and reasons for limitation)
The hot tool steel according to the present embodiment contains C, Si, Mn, Cr, Mo, and V as essential elements, and the balance is made of Fe and inevitable impurities. The hot tool steel according to the present embodiment includes, for example, W, Co, Nb, Ta, Ti, Zr, Al, N, Cu, Ni, B, S, Ca, Se, Te, Bi, as unavoidable impurities. Pb, Mg, O and the like are included.

(1) 0.20 ≦ C ≦ 0.50 mass%
C is an essential element necessary for adjusting the strength of steel. If the amount of C is less than 0.20% by mass, it is difficult to obtain the required hardness of 36 HRC or more. When the amount of C exceeds 0.50% by mass, the hardness tends to be saturated and the amount of carbide becomes excessive, and the fatigue strength and impact value are deteriorated. Therefore, the C amount is set to 0.20 ≦ C ≦ 0.50 mass%. The amount of C is more preferably 0.24 ≦ C ≦ 0.46% by mass, and more preferably 0.28 <C ≦ 0.42% by mass, which is excellent in the balance of hardness, fatigue strength, and impact value.

(2) 0.40 <Si <0.75 mass%
Si is an essential element necessary for adjusting the machinability of steel. When the Si amount is 0.40 mass% or less, it becomes difficult to ensure machinability equivalent to or higher than that of general-purpose mold steel. When the Si amount is 0.75% by mass or more, the thermal conductivity is greatly reduced. Therefore, the Si amount is set to 0.40 <Si <0.75 mass%. The amount of Si is more preferably 0.44 ≦ Si ≦ 0.70% by mass with a good balance between machinability and thermal conductivity, and further preferably 0.48 ≦ Si ≦ 0.65% by mass.

(3) 0.50 <Mn ≦ 1.50 mass%
Mn is an essential element for improving hardenability. When the amount of Mn is 0.50% by mass or less, hardenability is insufficient, and it is difficult to ensure hardness and impact value. When the amount of Mn exceeds 1.50 mass%, not only the impact value is lowered, but it is difficult to maintain high thermal conductivity. Therefore, the amount of Mn is set to 0.50 <Mn ≦ 1.50 mass%. Further, the amount of Mn is more preferably 0.55 ≦ Mn ≦ 1.35% by mass, which can ensure hardness and impact value and high thermal conductivity, and further 0.65 ≦ Mn ≦ 1.20% by mass. preferable.

(4) 5.24 ≦ Cr ≦ 9.00 mass%
Cr is an essential element not only for improving hardenability but also for forming a carbide to increase the strength of the steel. If the amount of Cr is less than 5.24% by mass, the hardenability is insufficient and the hardness and impact value cannot be sufficiently obtained. Further, the corrosion resistance required for the die casting mold exposed to the corrosive environment is higher when the amount of Cr is larger. On the other hand, if the Cr content exceeds 9.00 mass%, it is difficult to maintain high thermal conductivity. Therefore, the Cr amount is set to 5.24 ≦ Cr ≦ 9.00 mass%. The amount of Cr is more preferably 5.40 <Cr ≦ 8.40% by mass, which can ensure hardness, impact value and corrosion resistance and obtain high thermal conductivity, and 5.55 ≦ Cr ≦ 7.80% by mass. Is more preferable.

(5) 1.08 <Mo <2.99% by mass
Mo is an essential element not only for improving hardenability, but also for increasing the strength of the steel by forming carbides, and in particular for increasing the high-temperature strength. If the Mo amount is 1.08% by mass or less, sufficient high-temperature strength cannot be obtained. On the other hand, when the amount of Mo is 2.99% by mass or more, the high temperature strength tends to be saturated, and at the same time, the cost is significantly increased and the economy is hindered. Therefore, the Mo amount is set to 1.08 <Mo <2.99% by mass. The amount of Mo is more preferably 1.15 <Mo ≦ 2.80 mass%, and further preferably 1.20 ≦ Mo ≦ 2.50 mass%.

(6) 0.30 <V <0.70 mass%
V is an essential element not only for improving hardenability but also for increasing the strength of the steel by forming carbides, and in particular for increasing the high-temperature strength. When the amount of V is 0.30% by mass or less, crystal grains at the time of quenching tend to be coarsened, and the impact value is lowered. On the other hand, if the amount of V is 0.70% by mass or more, the amount of coarse carbide becomes excessive and the impact value is deteriorated. Therefore, the V amount is set to 0.30 <V <0.70 mass%. Further, the amount of V is more preferably 0.40 ≦ V ≦ 0.67% by mass, which can ensure softening resistance and sufficient fatigue strength and impact value, and 0.50 ≦ V ≦ 0.64% by mass. Further preferred.

(7) Inevitable impurities: W <0.30 mass%, Co <0.30 mass%, Nb <0.004 mass%, Ta <0.004 mass%, Ti <0.004 mass%, Zr <0. .004 mass%, Al <0.004 mass%, N <0.004 mass%, Cu <0.15 mass%, Ni <0.15 mass%, B <0.0010 mass%, S <0.010. Mass%, Ca <0.0005 mass%, Se <0.03 mass%, Te <0.005 mass%, Bi <0.01 mass%, Pb <0.03 mass%, Mg <0.005 mass%. , O <0.0080 mass%, etc.
When W, Co, Nb, Ta, Ti, Zr, Al, N, Cu, Ni, B, S, Ca, Se, Te, Bi, Pb, Mg, O, etc. are within the above ranges. These elements are included as inevitable impurities.

The hot tool steel according to the present embodiment is further selected as a selection element,
(A) W,
(B) Co,
(C) at least one selected from the group consisting of Nb, Ta, Ti, Zr, Al, and N,
(D) at least one selected from the group consisting of Cu, Ni, and B, and / or
(E) It may contain at least one selected from the group consisting of S, Ca, Se, Te, Bi, and Pb.

(8) 0.30 ≦ W ≦ 4.00 mass%
W is a selective element that can be added to increase strength by precipitation of carbide (precipitation hardening). If the amount of W is less than 0.30% by mass, the effect of increasing the strength is small. On the other hand, if the amount of W exceeds 4.00% by mass, the effect is saturated and the cost is significantly increased. Therefore, the W amount is set to 0.30 ≦ W ≦ 4.00 mass%.

(9) 0.30 ≦ Co ≦ 3.00 mass%
Co is a selective element that can be added to increase the strength by solid solution in the base material (solid solution hardening). If the amount of Co is less than 0.30% by mass, the effect of increasing the strength is small. On the other hand, if the amount of Co exceeds 3.00 mass%, saturation of effects and a significant increase in cost are caused. Therefore, the amount of Co is set to 0.30 ≦ Co ≦ 3.00 mass%.

(10) 0.004 ≦ Nb ≦ 0.100 mass%,
0.004 ≦ Ta ≦ 0.100 mass%,
0.004 ≦ Ti ≦ 0.100 mass%,
0.004 ≦ Zr ≦ 0.100 mass%,
0.004 ≦ Al ≦ 0.050 mass%, and
At least one or more selected from the group consisting of 0.004 ≦ N ≦ 0.050 mass% Nb, Ta, Ti, Zr, Al, and N are strengths obtained by refining crystal grains (refining crystal grains). It is a selective element that can be added to increase toughness. If any element is less than a predetermined amount, the effect of improving strength and toughness is small. On the other hand, when the amount exceeds a predetermined amount, carbides, nitrides, and oxides are excessively generated, which leads to a decrease in toughness.

(11) 0.15 ≦ Cu ≦ 1.50 mass%,
0.15 ≦ Ni ≦ 1.50 mass%, and
At least one selected from the group consisting of 0.0010 ≦ B ≦ 0.0100% by mass Cu, Ni, and B are selections that can be added to improve hardenability (improving hardenability) It is an element. If any element is less than the predetermined amount, the effect of improving the hardenability is small. Moreover, if it exceeds a predetermined amount, the effect is saturated and the actual profit is poor. In particular, excessive addition of Cu and Ni lowers the thermal conductivity.

(12) 0.010 ≦ S ≦ 0.500 mass%,
0.0005 ≦ Ca ≦ 0.2000 mass%,
0.03 ≦ Se ≦ 0.50 mass%,
0.005 ≦ Te ≦ 0.100 mass%,
0.01 ≦ Bi ≦ 0.30 mass%, and
At least one selected from the group consisting of 0.03 ≦ Pb ≦ 0.50 mass% S, Ca, Se, Te, Bi, and Pb are for improving machinability (improving machinability), It is a selective element that can be added. If any element is less than a predetermined amount, the machinability improving effect is small. Moreover, since hot workability will deteriorate remarkably when it exceeds predetermined amount, the crack in plastic processing will occur frequently and productivity and a yield will be reduced.

(Production method)
Although the steel which concerns on this embodiment can be obtained with the following procedures, for example, it is not limited to this.

(1) Casting The raw materials blended so as to have the predetermined components are melted, and the molten metal is cast into a mold to obtain an ingot.

(2) Homogenizing heat treatment / hot working Homogenizing heat treatment and hot working are performed to homogenize the components of the obtained ingot and destroy the cast structure. As the conditions for the homogenization heat treatment and the hot working, it is preferable to select optimum conditions according to the components.
Homogenization heat processing is normally performed by hold | maintaining an ingot at 1100-1500 degreeC for about 10 to 30 hours.
Hot working is usually performed at 1000 to 1300 ° C., and air cooling is performed after the end of the working.

(3) Tempering, spheroidizing annealing and roughing Since the steel according to this embodiment has relatively good hardenability, bainite transformation and martensitic transformation occur during air cooling after hot working, and harden. There are many cases. For this reason, after hot working, tempering and spheroidizing annealing are performed to soften the material, followed by roughing.
As the tempering conditions, it is preferable to select optimum conditions according to the components. Tempering is usually performed by holding at 600 to 750 ° C. for about 1 to 10 hours.
The spheroidizing annealing is preferably performed so that the steel has a hardness of about 90 to 97 HRB. Spheroidizing annealing is usually performed by holding at 800 to 950 ° C. for about 1 to 10 hours and then cooling at a rate of 5 to 30 ° C. per hour.
The roughing is performed by machining the softened material into a predetermined shape.

(4) Conditioning (quenching / tempering)
Conditioning (quenching and tempering) is performed in order to make the rough-processed material a desired hardness. As for quenching conditions and tempering conditions, it is preferable to select optimum conditions according to the components and required characteristics, respectively.
Quenching is usually performed by holding at 1000 to 1050 ° C. for 0.5 to 5 hours and then rapidly cooling. The rapid cooling method is not particularly limited, and it is preferable to select an optimum method according to the purpose. Examples of the rapid cooling method include water cooling, oil cooling, and blast cooling.
Tempering is usually performed by holding at 500 to 650 ° C. for 1 to 10 hours.
Through the above steps (1) to (4), the machinability is maintained to be equal to or higher than that of general-purpose mold steel (JIS SKD61), and the thermal conductivity is superior to that of general-purpose mold steel, and the general-purpose mold steel. Steel with a higher impact value is obtained.

(5) Finishing process The finishing process is performed on a material tempered to a desired hardness.
By passing through the step (5), a steel product using the hot work tool steel according to the present embodiment is obtained.

(Function)
Since the hot work tool steel according to the present embodiment has an optimized amount of Si, machinability equivalent to or higher than that of general-purpose mold steel can be secured, and thermal conductivity superior to that of general-purpose mold steel can be obtained. . In addition, since the hot work tool steel according to the present embodiment is optimized in terms of Mn amount, Cr amount, Mo amount, and V amount, the general-purpose mold steel while ensuring machinability equivalent to or higher than that of the general-purpose mold steel. Better thermal conductivity and higher impact value. Therefore, the hot tool steel according to the present invention does not have a higher cost for die machining than general-purpose die steel. Moreover, the hot work tool steel according to the present invention hardly causes seizure or heat check. As a result, a long die life can be obtained, and the manufacturing cost reduction and productivity improvement of die casting and hot forging can be achieved.

(Example A)
In order to manufacture each invention steel of the following Example B, Examples 1-5 were performed in order to investigate preferable Si amount, Mn amount, Cr amount, Mo amount, and V amount.

(Example 1: Si amount investigation)
A preferred amount of Si has been investigated and will be described with reference to FIGS.
FIG. 1 shows a case where 0.35 mass% C-0.82 mass% Mn-5.73 mass% Cr-1.21 mass% Mo-0.62 mass% Vx mass% Si steel is cut. The distance shaved until the cutting tool reaches the end of its life is shown relative to the amount of Si. Here, as for the numerical value of each plot point in FIG. 1 and FIG. 2, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the shaved distance (mm). The test piece for machinability evaluation is a 55 mm × 55 mm × 200 mm square bar (prepared in the same procedure as in Example B below and softened to 90 to 97 HRB by spheroidizing annealing), and a cutting tool The point at which the maximum lateral flank wear amount was 300 μm was determined as the life. The larger the cutting distance, the better the cutting.
According to FIG. 1, the cutting distance increases with an increase in the Si amount. Therefore, the larger the Si amount, the better from the viewpoint of improving machinability. According to FIG. 1, when the Si amount is 0.40% by mass or less, the cutting distance is noticeably reduced. Therefore, the amount of Si is preferably more than 0.40% by mass, more preferably 0.44% by mass or more, and still more preferably 0.48% by mass or more from the viewpoint of improving machinability. On the other hand, when the Si amount is 0.75% by mass or more, the improvement effect is not remarkable.

A round bar of φ11 mm × 50 mm made of the same material as in FIG. 1 was heated to 1030 ° C., rapidly cooled, tempered and tempered to 49 HRC. Furthermore, a test piece for measuring thermal conductivity of φ10 mm × 2 mm was produced from this round bar. FIG. 2 shows the thermal conductivity measured at room temperature by the laser flash method with respect to the amount of Si. As for the numerical value of each plot point in FIG. 2, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the thermal conductivity (W / m / K). Higher thermal conductivity is preferable because of excellent cooling ability when it becomes a mold.
According to FIG. 2, the thermal conductivity decreases as the Si amount increases, and when the Si amount exceeds 0.80% by mass, the thermal conductivity is a general-purpose mold steel (JIS SKD61 (thermal conductivity 24 W / m / K )) To a level that is not so different. For this reason, from the viewpoint of obtaining a thermal conductivity equal to or higher than that of general-purpose mold steel (JIS SKD61 (thermal conductivity 24 W / m / K)), less than 0.75 mass% was selected as the upper limit of the Si amount.
In addition, according to FIG. 2, a high thermal conductivity of 28.3 W / m / K or more can be obtained when the Si amount is in the range of 0.10 to 0.40 mass%, and the Si amount is 0.10 to 0.70. In the mass% range, a good thermal conductivity of 26 W / m / K or more can be obtained.
From the above, the thermal conductivity decreases as the amount of Si increases, but from the viewpoint of comparison with general-purpose mold steel, the upper limit of the amount of Si may be less than 0.75% by mass. From the viewpoint of increasing the thermal conductivity, the amount of Si is more preferably 0.70% by mass or less, and further preferably 0.65% by mass or less.

(Example 2: Mn content investigation)
Since the preferable amount of Mn was investigated, it demonstrates with reference to FIG.3 and FIG.4.
FIG. 3 shows the impact value at room temperature of 0.32 mass% C-0.42 mass% Si-5.03 mass% Cr-1.22 mass% Mo-0.60 mass% Vx mass% Mn steel. It is plotted against the amount of Mn. Here, as for the numerical value of each plot point in FIG. 3, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the impact value (J / cm ² ). The test material for impact value measurement was prepared by heating a square bar of 11 mm × 11 mm × 55 mm (produced in the same procedure as in Example B below and softened to 90 to 97 HRB by spheroidizing annealing) to 1030 ° C. Then, it was rapidly cooled and tempered and tempered to 49HRC. A 10 mm × 10 mm × 55 mm JIS No. 3 impact test piece was produced from this square bar, and the impact value was measured at room temperature. A larger impact value is preferable because it is less likely to break when it becomes a mold.
According to FIG. 3, it can be seen that the impact value is relatively low when the amount of Mn is 0.50 mass% or less. Moreover, according to FIG. 3, although an impact value improves as the amount of Mn increases, it turns out that it will fall when it exceeds 1.50 mass%.
According to FIG. 3, when the amount of Mn was 0.45 mass% and 0.55 mass%, it was found that an impact value of 30 J / cm ² or more was obtained. Therefore, the Mn amount is 0.50% by mass, which is between 0.45 and 0.55, as the lower limit of the Mn amount. Moreover, according to FIG. 3, when the amount of Mn is 0.65 mass% or more, an impact value of 31 J / cm ² or more is obtained. However, according to FIG. 3, when the amount of Mn exceeds 1.50 mass%, the impact value is good but decreases.

FIG. 4 is a plot of the thermal conductivity at room temperature of the same material as in FIG. 3 against the amount of Mn. Here, as for the numerical value of each plot point in FIG. 4, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the thermal conductivity (W / m / K).
The thermal conductivity was measured by the laser flash method as in Example 1.
According to FIG. 4, the thermal conductivity decreases as the amount of Mn increases. According to FIG. 4, the amount of Mn is 1.50 in order to obtain a thermal conductivity of 26 W / m / K or more where the cooling ability is improved as compared with JIS SKD61 (thermal conductivity 24 W / m / K). What is necessary is just to set it as mass% or less, and in order to obtain 26.4 W / m / K or more which further improves cooling capacity, it should just be 1.35 mass% or less, and it further improves cooling capacity 26.8 W / m / K. In order to obtain K, the content may be 1.20% by mass or less.

(Example 3: Investigation of Cr content)
Since the preferable Cr amount was investigated, it demonstrates with reference to FIG.5 and FIG.6.
FIG. 5 shows room temperature of 0.35 mass% C-0.51 mass% Si-0.84 mass% Mn-1.22 mass% Mo-0.61 mass% V-xCr mass% steel tempered to 49 HRC. The impact value at is plotted against the Cr content. Here, as for the numerical value of each plot point in FIG. 5, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the impact value (J / cm ² ). Moreover, the production of the test piece and the measurement of the impact value were performed in the same manner as in Example 2.
According to FIG. 5, the impact value increases as the Cr content increases, and the effect is particularly remarkable when the Cr content exceeds 5 mass%. According to FIG. 5, it was found that the Cr amount should be 5.24% by mass or more in order to obtain 27.2 J / cm ² or more as an impact value. Therefore, the lower limit of the Cr amount is set to 5.24% by mass or more from the viewpoint of securing the impact value. Further, according to FIG. 5, when the Cr content is less than 5% by mass, the impact value is significantly reduced.

FIG. 6 shows room temperature thermal conductivity of 0.21 mass% C-0.41 mass% Si-0.52 mass% Mn-1.22 mass% Mo-0.61 mass% Vx mass% Cr steel. Is plotted against the Cr content. Here, as for the numerical value of each plot point in FIG. 6, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the thermal conductivity (W / m / K). The thermal conductivity was measured by the laser flash method as in Example 1.
According to FIG. 6, thermal conductivity falls with the increase in Cr amount. According to FIG. 6, the Cr amount is 9.00 mass for obtaining a thermal conductivity of 25 W / m / K or more where the cooling ability is improved as compared with JIS SKD61 (thermal conductivity 24 W / m / K). %, And in order to obtain 25.6 W / m / K or more which improves the cooling capacity, it may be 8.40% by mass or less, and 26.3 W / m / K or more which further improves the cooling capacity. In order to obtain, it should just be 7.80 mass% or less. Further, according to FIG. 6, the Cr amount should be 6.70% by mass or less in order to obtain 28 W / m / K or more in which the cooling performance is dramatically improved as compared with JIS SKD61. Good.

(Example 4: Mo amount investigation)
Since the preferable amount of Mo was investigated, it demonstrates with reference to FIG.
FIG. 7 shows the high temperature strength (600 ° C.) of 0.35% by mass C-0.47% by mass Si-0.83% by mass Mn-5.74% by mass Cr-0.59% by mass Vx% by mass Mo steel. (Deformation resistance) is shown with respect to the Mo amount. Here, as for the numerical value of each plot point in FIG. 7, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the high temperature strength (MPa). The test material for measuring deformation resistance was a φ15 mm × 50 mm round bar (produced in the same procedure as in Example B below and softened to 90 to 97 HRB by spheroidizing annealing) to 1030 ° C. Quenched, tempered and tempered to 45HRC. A test piece for measuring deformation resistance of φ14 mm × 21 mm was prepared from this round bar, and the test piece was heated to 600 ° C. at 5 ° C./s, held for 100 s, and then processed at a strain rate of 10 s ⁻¹ to measure the deformation resistance. did.

Here, “deformation resistance” is a force per unit area required to deform a material. Specifically, "deformation resistance", the force _{p w} during working at strain rate ^{10s -1,} the _{K f} was determined from the vertical contact area _{a w} to that force as _K f ₌ p _w / _a w (Hereinafter referred to as “deformation resistance” in the same meaning).

The deformation resistance thus measured was defined as the strength at 600 ° C. (high temperature strength), and this was plotted against the Mo amount (see FIG. 7). The higher the deformation resistance, the higher the strength.
According to FIG. 7, the high-temperature strength increases with an increase in the Mo amount, and is relatively high due to the increase in the high-temperature strength, particularly in the range where the Mo amount exceeds 1.08 mass% (corresponding to the content of JIS SKD61). High temperature strength (> 930 MPa) is obtained. According to FIG. 7, the increase in high temperature strength is moderate when the Mo amount is 1.25% by mass or more and 3% by mass or less, and the increase in high temperature strength is saturated when the Mo amount is 3% by mass or more. Therefore, in the Mo amount of 1.25% by mass or less where the increasing tendency of the high-temperature strength is moderate, for example, the Mo amount is more preferably more than 1.15% by mass, and further preferably 1.20% by mass or more.
Moreover, according to FIG. 7, Mo amount should just be 1.23 mass% or more in order to obtain 950 Mpa or more and 2.5 mass% or more to obtain 970 Mpa or more as high temperature strength. However, when the amount of Mo is in the range of 3% by mass or more, a significant cost increase is caused. Therefore, the Mo amount is preferably less than 2.99% by mass from the viewpoint of cost reduction, more preferably 2.80% by mass or less, and further preferably 2.50% by mass or less.

(Example 5: V amount investigation)
A preferred V amount has been investigated and will be described with reference to FIG.
FIG. 8 shows a 0.34 mass% C-0.49 mass% Si-0.82 mass% Mn-5.75 mass% Cr-1.23 mass% Mo-x mass% V steel tempered to 48 HRC. The impact value is shown with respect to the V amount. Here, as for the numerical value of each plot point in FIG. 8, the upper numerical value indicates the x value (mass%), and the lower numerical value indicates the impact value (J / cm ² ). Here, the preparation of the test piece and the measurement of the impact value were performed in the same manner as in Example 2.
According to FIG. 8, when the amount of V is changed in the range of 0.1 to 1% by mass, a good impact value (20 J / cm ² or more) can be obtained at any value. According to FIG. 8, the inflection point is in the vicinity of 0.30% by mass of V and 0.70% by mass of V. Therefore, if the V content is more than 0.30% by mass and less than 0.70% by mass, it is considered that it contributes to improving the hardenability and increasing the strength of the steel by forming carbides. On the other hand, according to FIG. 8, when the V amount is 0.30% by mass or less, the impact value is remarkably reduced. When the V amount is 0.70% by mass or more, the impact value is decreased and the material cost is increased. Is a big industrial problem. Therefore, the V amount is preferably 0.30 <V <0.70% by mass. According to FIG. 8, the amount of V is 0.40% by mass or more for obtaining an impact value of 31 J / cm ² or more, and 0.50% by mass or more for obtaining 34 J / cm ² or more. You can see that

(Example B)
Each inventive steel and each comparative steel was prepared and evaluated based on the investigation results of Example A, which will be described.

(Production of test pieces and die cast molds)
About each Example and each comparative example (Comparative steel A11 is JIS SKD61) shown in Table 1 and Table 2, each steel type was melt | dissolved in the vacuum and the molten metal was cast into the casting_mold | template, and it was set as 6 ton ingot.
The ingot was homogenized at 1240 ° C. Thereafter, a rectangular block having a cross section of 310 mm × 660 mm was manufactured by hot forging.
Next, the rectangular block was tempered at 700 ° C., and further heated to 900 ° C. and gradually cooled. This softened the rectangular block to 90-97 HRB. Then, a die cast mold of about 700 kg was cut out from the rectangular block.
This die casting mold was heated to 1030 ° C. in a vacuum, and after holding for 1 hour, nitrogen gas was injected and quenched. Subsequently, it was tempered at 580 to 610 ° C. and tempered to about 42 HRC.
After tempering, various test pieces were cut out from the die cast mold. Further, the die casting mold was subjected to finishing machining to produce a die casting mold of about 650 kg.

(Measurement and investigation of basic characteristics)
Basic characteristics (high temperature strength, thermal conductivity, impact value, corrosion resistance, cost) were measured and investigated using each test piece cut out from the die cast mold.
The high temperature strength was measured as follows. A test piece of φ14 mm × 21 mm was cut out from the die cast mold. The test piece was heated to 600 ° C. at 5 ° C./s and held for 100 s, and then processed at a strain rate of 10 s ⁻¹ to measure deformation resistance. The results are as shown in Table 3.
The thermal conductivity was measured as follows. A test piece of φ10 mm × 2 mm was cut out from the die cast mold. The thermal conductivity of the specimen was measured at room temperature by the laser flash method. The results are as shown in Table 3.
The impact value was measured as follows. A 10 mm × 10 mm × 55 mm JIS No. 3 impact test piece was cut out from the die cast mold. The impact value of the specimen was measured at room temperature. The results are as shown in Table 3.
Corrosion resistance was measured as follows. A test piece was cut out from the die cast mold, and a hole was provided in the test piece. Then, industrial water at 30 ° C. was passed through the hole at a rate of 5.0 liter / min for 24 hours. The state of occurrence of rust on the inner surface of the hole after passing water was visually evaluated. The results are as shown in Table 3.

(Evaluation of basic characteristics)
The high-temperature strength was evaluated as good (indicated by “◯” in Table 3) at 920 MPa or more and defective (indicated by “x” in Table 3) otherwise. The thermal conductivity was determined to be 26 W / m / K or more as good (indicated by “◯” in Table 3), and otherwise defective (indicated by “X” in Table 3). The impact value was evaluated as good (indicated by “◯” in Table 3) exceeding 20 J / cm ² and defective (indicated by “x” in Table 3) other than that. Corrosion resistance is based on JIS SKD61 (Comparative Steel A11) as a standard when rust is not generated (shown by “◯” in Table 3), and when rust is generated, it is somewhat poor (Table 3 was indicated as “△”), and those having rusted more than that were evaluated as defective (indicated by “x” in Table 3).
Invented steel showed good properties in all items. Moreover, the machinability of the inventive steel was never worse than that of general-purpose mold steel (JIS SKD61). The evaluation of machinability is judged from the work efficiency when the die casting die is actually cut and the wear state of the cutting tool. Cutting steel with poor machinability tends to cause local abnormal wear and chipping in the cutting tool, resulting in lower work efficiency due to frequent replacement of the cutting tool and increased cost due to the use of a large number of cutting tools. Will be forced. The working efficiency when cutting the invention steel and the wear state of the cutting tool were the same as in the case of the general-purpose steel, and it was confirmed in actual die machining that the machinability of the invention steel was the same as that of the general-purpose steel.
Invented steel having a thermal conductivity of more than 27 W / m / K has an Si content of 0.55% by mass or less (excluding Invention Steel A12, the Si content is 0.52% by mass or less), and an Mn content of 0.81 to 1.04% by mass (0.81 to 0.95% by mass excluding the invention steel A12, 0.81 to 0.84% by mass excluding the invention steel A11), and the amount of Cr is 5.55 to 5.74. It was mass% (5.63-5.74 mass% excluding invention steel A12, 5.71-5.74 mass% excluding invention steel A11).
The invention steel having an impact value of 34 J / cm ² or more has a Mn content of 0.51 to 1.42 mass% (excluding invention steel A05, 0.51 to 0.83 mass%), and a Cr content of 5. It was 25 to 8.61% by mass (excluding Example A01, 5.25 to 8.08% by mass), and the V amount was 0.57 to 0.69% by mass.

On the other hand, in the case of the comparative steel A11, all the evaluation items other than the high temperature strength and the cost were “x”. The test piece used was a test piece cut out from a large die-cast mold with a low quenching speed. Therefore, in particular, the comparative steel A11 has a large amount of V carbonitride and has a low impact value.
Other comparative steels were better than comparative steel A11 (JIS SKD61) in some evaluation items, but there were no steel types in which all items were “◯”.

For example, the comparative steel A01 has a low C strength due to a low C content. Moreover, because of the excessive V, the crystal grains became coarse during quenching and the impact value decreased. Further, the comparative steel 01 had poor corrosion resistance because Cr and Mo were relatively small.
In comparative steel A02, the amount of carbides was excessive due to excess C and excess V, and the impact value decreased. Moreover, since comparative steel A02 had comparatively much Si and Mn, thermal conductivity fell. Further, the comparative steel A02 had relatively little Cr and Mo, so the corrosion resistance was poor, and the cost was high due to excessive V.
In comparison steel A03, the thermal conductivity decreased due to excess Si.
In comparison steel A04, although the amount of Si was too small, Mn and Cr were relatively large, so that the thermal conductivity was lowered.

Since comparative steel A05 had insufficient Mn, the hardenability was insufficient and the impact value was lowered. Moreover, since comparative steel A05 had a slightly low Cr content, the corrosion resistance was poor.
In comparison steel A06, the thermal conductivity decreased due to excess Mn. Moreover, although the comparative steel A06 was judged to have a good impact value, the value barely met the judgment criteria. Furthermore, since comparative steel A06 had a large amount of C, a large amount of Cr carbide was formed, and as a result, the amount of solid solution Cr decreased, and thus the corrosion resistance was poor.
Since comparative steel A07 had insufficient Cr, its hardenability was insufficient and the impact value was lowered. Further, the comparative steel A07 was poor in corrosion resistance because of too little Cr.
In comparison steel A08, thermal conductivity decreased due to excess Cr.
In comparison steel A09, the high-temperature strength decreased due to the insufficient Mo.
The comparative steel A10 was extremely expensive due to excess Mo.
In Comparative Steel A11, the thermal conductivity decreased due to excessive Si, and the impact value decreased due to excessive Mn and excessive V.

(Actual machine test using a die-casting mold)
An actual machine test using a die-cast mold was performed as follows. The produced die casting mold was assembled in a machine, and an aluminum alloy was cast. ADC12 was used for the aluminum alloy, and the temperature of the melting and holding furnace was 680 ° C. The weight of the die-cast product is about 5 kg, and one cycle is 60 s. After casting 10,000 shots, a heat check on the mold surface and corrosion cracks in the internal cooling circuit were evaluated. In addition, it was also evaluated whether remarkable seizure occurred until the completion of the 10,000 shot casting, or whether there was water leakage due to cracks in the internal cooling circuit. Table 4 shows the results of the actual machine test. The thermal conductivity and impact value shown in Table 4 are the same as those shown in Table 3.

(Evaluation of actual machine test)
Heat check, seizure, abrasion, and water hole cracking were judged visually, and those that did not occur were good (indicated by “◯” in Table 4), and those that occurred slightly were slightly bad (in Table 4). The occurrence was evaluated as defective (indicated by “x” in Table 4).
Invented steels showed good properties in all items, while some of the comparative steels did not satisfy the evaluation criteria in any item. The reason is that the steel according to the invention has the above component composition and has high thermal conductivity and impact value, but the comparative steel does not have the above component composition and has low thermal conductivity and / or impact value.

  In other words, the inventive steel has a high thermal conductivity, so the thermal stress is small and heat check is difficult to occur. Inventive steel has high thermal conductivity, so that overheating of the mold is suppressed, and seizure between the aluminum alloy and the mold is drastically reduced. Furthermore, the wear caused by the aluminum alloy injected at a high speed is very slight, corresponding to the high temperature strength. Invented steel was not so noticeable in corrosion of the internal cooling circuit, and water leakage due to crack penetration starting from the corroded portion did not occur.

In contrast, the comparative steels A01 to A10 (excluding the comparative steel A02) tend to be improved compared to JIS SKD61 (comparative steel A11), but are inferior to the inventive steel. Moreover, it turns out that comparative steel A02 is still worse than JIS SKD61 (comparative steel A11).
Steel types with low thermal conductivity and low impact values (comparative steels A02 and A11) are susceptible to heat check. Further, seizure frequently occurred in the steel types having low thermal conductivity (comparative steels A02, A03, A04, A06, A08, A11). In the steel types having low corrosion resistance (comparative steels A01, A02, A05, A06, A07), the corrosion of the internal cooling circuit was quite serious, and the cracks based on the corroded part were also sporadically scattered. In steel types with low internal high-temperature strength (comparative steels A01 and A09), wear is conspicuous. Since the comparative steel A10 has a high Mo content, it is not a material that can be recommended from the viewpoint of cost and resource saving.

  In particular, as for the comparative steel A11 (JIS SKD61), the items other than wear and cost were all “x” or “Δ” as in the case of the basic characteristics. In Comparative Steel A11, since the thermal conductivity was low, the mold was overheated, and the aluminum alloy and the mold were frequently baked. The reason why many heat checks are generated is that the thermal stress is high because the thermal conductivity is low.

  Furthermore, the mold used in the actual machine test is a large mold. According to this test result, it was found that even when the mold using the inventive steel is large in size, a high impact value is obtained, the thermal conductivity is high, and the high-temperature strength is high.

  Although the present invention has been described above, the present invention is not limited to the above embodiment.

  The hot work tool steel according to the present invention and the steel product using the hot tool steel improve the thermal conductivity compared to the general-purpose mold steel while maintaining the machinability equivalent to or higher than that of the general-purpose mold steel (JIS SKD61). Since the impact value is higher than that of mold steel, it is extremely useful industrially for mold manufacturers and mold users.

It is a graph which shows the relationship between machinability and Si content. It is a graph which shows the relationship between thermal conductivity and Si content. It is a graph which shows the relationship between an impact value and Mn content. It is a graph which shows the relationship between heat conductivity and Mn content. It is a graph which shows the relationship between an impact value and Cr content. It is a graph which shows the relationship between heat conductivity and Cr content. It is a graph which shows the relationship between the intensity | strength (high temperature intensity) in 600 degreeC, and Mo content. It is a graph which shows the relationship between an impact value and V content.

Claims (7)

0.20 ≦ C ≦ 0.42 % by mass,
0.40 <Si <0.75% by mass,
0.65 ≦ Mn ≦ 1.50 mass%,
5.24 ≦ Cr ≦ 9.00 mass%,
1.08 <Mo ≦ 2.50 mass%, and
Including 0.30 <V <0.70 mass%,
A hot work tool steel characterized in that the balance consists of Fe and inevitable impurities. Furthermore,
The hot work tool steel according to claim 1, comprising 0.30 ≦ W ≦ 4.00 mass%. Furthermore,
The hot work tool steel according to claim 1, wherein the hot work tool steel contains 0.30 ≦ Co ≦ 3.00 mass%. Furthermore,
0.004 ≦ Nb ≦ 0.100 mass%,
0.004 ≦ Ta ≦ 0.100 mass%,
0.004 ≦ Ti ≦ 0.100 mass%,
0.004 ≦ Zr ≦ 0.100 mass%,
0.004 ≦ Al ≦ 0.050 mass%, and
The hot work tool steel according to any one of claims 1 to 3, comprising at least one selected from the group consisting of 0.004≤N≤0.024 mass%. Furthermore,
0.15 ≦ Cu ≦ 1.50 mass%,
0.15 ≦ Ni ≦ 0.96 % by mass, and
The hot tool steel according to claim 1, comprising at least one selected from the group consisting of 0.0010 ≦ B ≦ 0.0100 mass%. Furthermore,
0.010 ≦ S ≦ 0.500 mass%,
0.0005 ≦ Ca ≦ 0.2000 mass%,
0.03 ≦ Se ≦ 0.50 mass%,
0.005 ≦ Te ≦ 0.100 mass%,
0.01 ≦ Bi ≦ 0.30 mass%, and
The hot work tool steel according to claim 1, comprising at least one selected from the group consisting of 0.03 ≦ Pb ≦ 0.50 mass%.   A steel product using the hot tool steel according to any one of claims 1 to 6.

Images