JP2023530420A - hot work tool steel - Google Patents

Abstract

The present invention relates to matrix type hot work tool steels with improved wear resistance during use in demanding applications. It is particularly suitable for hot forging, die casting, and hot extrusion applications. In addition, it is suitable for hot pressing, particularly for hot pressing of advanced high strength steel (AHSS), and has high hot wear resistance. The hot work tool steel according to the invention has a composition as defined by the independent claims.

Description

The present invention relates to matrix type hot work tool steel.

Vanadium alloy matrix tool steels have been commercially available for decades and have attracted considerable interest due to their combination of high wear resistance, excellent dimensional stability and good toughness.

Matrix tool steels are steels which contain no primary carbides or only a very low content of primary carbides and which have a matrix consisting of tempered martensite.

US Pat. No. 5,300,000 is probably the first patent directed to matrix steel. The basic idea in WO 2005/030201 was to make a steel with the composition of the known high speed steel (HSS) matrix. This type of steel structure was developed to refine the microstructure to improve toughness and fatigue strength.

The Applicant's US Pat. No. 5,300,000 discloses a hot work matrix steel having good hot strength and wear resistance together with excellent toughness and ductility. The material is known under the name UNIMAX® which is commercially available.

WO 2005/010002 describes another matrix steel that has high hardness and wear resistance combined with very high toughness and is therefore particularly suitable for tools that are stressed at high temperatures, such as tools for hot and warm forming. disclosed. This steel is commercially known under the name W360 ISOBLOC® and has a nominal composition of 0.50% C, 0.20% Si, 0.25% Mn, 4.5% Cr, 3.00% Mo and 0.60%V.

Matrix steels are usually produced by vacuum arc remelting (VAR) or electroslag remelting (ESR) to improve chemical homogeneity and microcleanliness.
Further examples of hot work tool matrix steels are described in US Pat.

Modern matrix steels are developed using software that calculates phase diagrams and equilibrium phase balances as a function of temperature.
Themo-Calc® (TC) is easy to use to find compositions that lead to large austenitic single-phase domains at soaking temperatures, since the dissolution of MC carbides formed by segregation during casting is important. It is a frequently used software.

Hot work tool matrix steel has a wide range of applications such as die casting and forging. This steel is generally produced by conventional metallurgical methods followed by electroslag remelting (ESR). A disadvantage of known steels, however, is their limited wear resistance. Especially in demanding hot work operations such as hot forging, extrusion and hot pressing, wear resistance can limit the life of known steels. These tools are expensive and often require welding for repair. Therefore, weldability is important.
However, tool steels with high carbon content usually have poor weldability and require special measures such as high preheat temperatures.
Therefore, it would be useful if the steel could be welded with standard welding consumables, preferably without preheating.

US3117863 WO03/106727A1 EP1300482A1 JP2003226939A, EP3050986A1 US2004/0187972A1 US2005/0161125A1

Invention disclosure:
It is an object of the present invention to provide a matrix hot work tool steel with improved wear resistance during use in demanding applications. In particular, the steel should be suitable for hot forging, die casting or hot extrusion applications.
It should also be suitable for press hardening, especially hot pressing of Advanced High Strength Steel (AHSS). These applications require high thermal wear resistance.

Tempering resistance is an important property because steel can be exposed to high temperatures for long periods of time during use. Therefore, it is preferable that not only the hardness after quenching is high, but also the decrease in hardness is small.
Further important properties are high ductility and toughness, which means that the steel should have a uniform hardness for thicknesses up to 300 mm and a high degree of cleanliness for fine slag and be completely free of intergranular carbides. means that
To optimize the steel for its intended use, it should be possible to adjust the hardness over a large interval. In addition, it should be possible to obtain high tensile strength and yield strength combined with sufficient ductility.

The aforementioned objects, together with further advantages, are achieved to a large extent by providing a hot work tool steel having a composition as defined in the claims.

The invention is defined in the claims.

Detailed explanation:
The importance of the separate elements and their interactions with each other, as well as the chemical composition limits of the claimed alloys, are briefly described below. All percentages for the chemical composition of steel are given in weight percent (wt%) throughout the specification. The amount of hard phase is given in volume percent (vol%). The upper and lower limits of individual elements can be freely combined within the limits defined in the claims. Numerical ranges can be calculated with an order of magnitude or two. Thus, for example, a value given as 0.1% can also be expressed as 0.10% or 0.100%.

Carbon (0.5-0.9%)
Carbon is present in a minimum content of 0.5%, preferably at least 0.55, 0.60, 0.66, 0.67 or 0.68%. The upper limit for carbon is 0.9% and may be set at 0.85, 0.80, 0.75, 0.74, 0.73 or 0.72%. Preferred ranges are 0.6-0.8% and 0.65-0.75%. In either case, the amount of carbon is preferably such that the steel contains primary carbides of the _M23C6 , _M7C3 and _M6C types so that _the amount of such primary carbides in _the steel is limited. It should be controlled so that it does not occur.

Silicon (0.03-0.8%)
Silicon is used for deoxidation. Si is present in steel in dissolved form. Si is a strong ferrite former, increasing carbon activity and thus increasing the risk of formation of undesirable carbides that adversely affect impact strength. Silicon is also prone to interfacial segregation, which can result in reduced toughness and thermal fatigue resistance. Si is therefore limited to 0.8%. Upper limits are 0.7, 0.6, 0.5, 0.40, 0.35, 0.30, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23 and 0.22%. The lower limit may be 0.05, 0.10, 0.11, 0.12, 0.13, 0.14 or 0.15%.

Manganese (0.1-1.8%)
Manganese contributes to the improvement of the hardenability of steel and contributes to the improvement of machinability by forming manganese sulfide with sulfur.
Manganese shall therefore be present in a minimum content of 0.1%, preferably in a content of at least 0.2, 0.3, 0.35 or 0.4%.
On the high sulfur content side, manganese prevents red shortness in steel.
The steel shall contain max 1.8%, preferably max 0.8, 0.75, 0.7, 0.6, 0.55 or 0.5% manganese.

Chromium (4.0-6.6%)
Chromium should be present in a content of at least 4% to provide good hardenability in wider cross sections during heat treatment.
Too high a chromium content can lead to the formation of high temperature ferrite, which reduces hot workability.
The lower limit may be 4.5, 4.6, 4.7, 4.8 or 4.9%.
The upper limit may be 6.0, 5.9, 5.8, 5.7, 5.6, 5.5, 5.4, 5.3, 5.2 or 5.1%.

Molybdenum (1.8-3.5%)
Mo is known to have a very favorable effect on hardenability. Molybdenum is essential for obtaining a good secondary cure reaction. The minimum content is 1.8% and may be set at 1.9, 2.0, 2.1, 2.15 or 2.2%. Molybdenum is a strong carbide former and also a strong ferrite former. The maximum content of molybdenum is therefore 3.5%. Mo may be limited to 2.9, 2.7, 2.6, 2.5, 2.4 or 2.3%.

Tungsten (≦0.5%)
Tungsten is not an essential element in the present invention. The upper limit is 0.5%, but may be set at 0.4, 0.3, 0.2 or 0.1%.

Nickel (≤1%)
Nickel is not an essential element in the present invention. The upper limit may be set at 0.5, 0.4, 0.3 or 0.25%.

Vanadium (1.3-2.3%)
Vanadium forms uniformly distributed VC and V(C,N) type primary precipitated carbides and carbonitrides in the matrix of the steel. Further, these carbides and carbonitrides are MX (where M is mainly V, but Cr and Mo may be present, and X is one or more of C, N, and B). is sometimes represented.
However, hereinafter only VC is used with the same meaning as MX. Vanadium is used to form relatively large VCs in controlled amounts and should be present in an amount of 1.3-2.3%. The lower limit may be set at 1.35, 1.4, 1.45, 1.5 or 1.55%. The upper limit may be set at 2.2, 2.1, 2.0, 1.9, 1.8, 1.7 or 1.65%.

Aluminum (≦0.1%)
Aluminum may be used for deoxidation in combination with Si and Mn. The lower limit is set at 0.001, 0.003, 0.005 or 0.007% to ensure good deoxidation. The upper limit is limited to 0.1% to avoid precipitation of undesirable phases such as AlN. The upper limit may be 0.05, 0.04 or 0.3%.

Nitrogen (≦0.12%)
Nitrogen is an optional element. N is limited to 0.12% so that the amount of hard phases, especially V(C,N), is not too high.
However, the nitrogen and vanadium contents can be balanced to form predominantly precipitated vanadium-rich carbonitrides.
These will partially dissolve during the austenitizing process and then precipitate out as nanometer-sized particles during the tempering process. The thermal stability of vanadium carbonitrides is believed to be superior to that of vanadium carbides, and thus can improve the tempering resistance of tool steels and improve their resistance to grain growth at high austenitizing temperatures. .
If the nitrogen content is intentionally controlled for the above reasons, the lower limit should be 0.006, 0.007, 0.08, 0.09, 0.01, 0.012, 0.013, 0.014 or It may be set to 0.015%. The upper limit may be 0.11, 0.10, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04 or 0.03%.

Copper (≤1%)
Cu is an optional element and may contribute to improving the hardness and corrosion resistance of the steel. However, once copper is added, it is impossible to extract it from the steel. This makes scrap handling significantly more difficult. For this reason copper is usually not intentionally added. The upper limit may be limited to 0.5, 0.4, 0.3, 0.2 or 0.15%.

Cobalt (≤5%)
Co is an optional element. Co increases the solidus temperature, thereby providing an opportunity to increase the quenching temperature. Therefore, it is possible to dissolve a greater proportion of carbides during austenitization, thereby increasing hardenability. However, Co is expensive and high amounts of Co can lead to decreased toughness and wear resistance. The maximum amount is therefore 5%. However, Co is generally not intentionally added. The maximum content may be set at 2%, 1%, 0.5% or 0.2%.

Niobium (≦0.1%)
Niobium is similar to vanadium in that it forms M(N,C) type carbonitrides. However, Nb leads to a more angular shape of M(N,C) and at high contents can reduce hardenability. The maximum amount is therefore 0.1%, preferably 0.05%.
The fine dispersion of NbC plays a role of pinning grain boundaries, which leads to improvement in softening resistance at high temperatures, refinement of crystal grains, and improvement in toughness. It is stable and can be used for grain refinement. may be available. For this reason, Nb is an optional element and can be present in amounts ≦0.1%. The upper limit can be set at 0.06, 0.05, 0.04, 0.03, 0.01 or 0.005%. The lower limit can be set at 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01%.

Ti, Zr and Ta
These elements are carbide formers and may be present in the alloy to the extent defined in the claims to alter the composition of the hard phase. However, these elements are usually not added. The amount of each element is preferably ≤0.5%, 0.1% or ≤0.05%, more preferably ≤0.01% or 0.005%.

Boron (≦0.01%)
B may be used to further increase the hardness of the steel. Its amount is limited to 0.01%, preferably ≤0.006%, more preferably ≤0.005%.

Ca, Mg and REM (rare earth metals)
These elements are included in the claims for various reasons for the purpose of modifying non-metallic inclusions and/or for the purpose of further improving the machinability, hot workability and/or weldability of steel. It may optionally be added to the steel in the stated amounts.
The amount of Ca and Mg is preferably ≤0.01%, more preferably ≤0.005%. The amount of REM is preferably ≤0.2%, more preferably ≤0.1%, or even ≤0.05%.

Impurity Elements Impurity elements cannot be avoided when manufacturing steel. Impurity elements are therefore included in the balance and the level of such elements is not essential to the definition of the present invention. These elements are unavoidable elements and may be present in steel at common impurity contents. However, since these elements can adversely affect the properties of the steel, the impurity content can be further limited. Preferred limits are set as follows. P can be limited to 0.1, 0.05 or 0.03%. S may be limited to 0.5, 0.1, 0.05, 0.0015, 0.0010, 0.0008, 0.0005, or even 0.0001%. O can be limited to 0.01, 0.003, 0.0015, 0.0012, 0.0010, 0.0008, 0.0006, or 0.0005%.

Steel Production Tool steels having the claimed chemistries can be manufactured by conventional metallurgical processes including melting in an electric arc furnace (EAF), further refining in ladles and optionally vacuum treatment prior to casting. can be manufactured by The ingot may also undergo Electro Slag Remelting (ESR) to further improve cleanliness and microstructural homogeneity of the ingot. Additionally, the steel can be subjected to vacuum induction melting (VIM) and vacuum arc remelting (VAR).
An alternative manufacturing process for the steels covered by the patent ball is gas atomization followed by hot isostatic pressing (HIP) to form a HIPed ingot, in which the HIPed condition is may be used in The ingot may be further hot worked to final dimensions and soft annealed to a Brinell hardness of ≤360 HBW, preferably ≤300 HBW. Brinell hardness is measured with a load of 3000 kgf (29400 N) using a tungsten carbide ball with a diameter of 10 mm, and is sometimes expressed as HBW _10/3000 .
This steel may undergo hardening and tempering prior to use.

The steel is usually delivered to the customer in a soft annealed condition with a ferritic matrix with uniform carbide distribution inside.
The soft annealed steel has uniform properties even over large dimensions and according to a preferred embodiment the hardness uniformity is an average hardness of ≤360 HBW and a thickness of at least 100 mm. and having a maximum deviation of less than 10%, preferably less than 5%, from the average Brinell hardness value in the thickness direction measured according to ASTM E10-01, wherein from the edge of the specimen or the edge of another indentation The minimum distance between the centers of the indentations shall be at least 2.5 times the diameter of the indentation, and the maximum distance shall be no more than 4 times the diameter of the indentation.

Atomized powders can also be used for additive manufacturing.

The present invention will be described in more detail below.

The hot work tool steel according to the present invention is
in percent by weight (wt%),
C 0.5-0.9
Si 0.03-0.8
Mn 0.1-1.8
Cr 4.0-6.6
Mo 1.8-3.5
V 1.3-2.3
Al≤0.1
N≤0.12
Ni≤1
W≤1
Co≤5
Cu≤1
Nb ≤ 0.1
Ti≦0.05
Zr≤0.05
Ta≤0.05
B ≤ 0.01
Ca ≤ 0.01
Mg≤0.01
REM≤0.2
Balance iron and impurities

Preferably, the hot work tool steel fulfills at least one of the following requirements.
C 0.6-0.8
Si 0.05-0.6
Mn 0.2-0.8
Cr 4.4-5.6
Mo 2.0-2.5
V 1.5-1.9
Al≤0.05
N≤0.08
Ni≤0.5
W≤0.5
Co≤2
Cu≤0.5
Nb≤0.05
Ti≤0.01
Zr≤0.01
Ta≤0.01
B ≤ 0.006
Ca ≤ 0.005
Mg≤0.005
REM≤0.1

More preferably, the composition of the steel meets one or more of the following requirements.
C 0.65-0.75
Si 0.15-0.5
Mn 0.4-0.5
Cr 4.9-5.1
Mo2.2-2.3
V 1.5-1.7
Al≤0.03
N≤0.05
Ni 0.25
W≤0.2
Co≤1
Cu≤0.2
Nb ≤ 0.005
Ti≤0.005
Zr≤0.005
Ta≤0.005
REM≤0.05

Preferably, the steel fulfills at least one of the following requirements.
C 0.66-0.75
Si 0.15-0.25
V 1.52-1.68
Al 0.001-0.03
N≤0.05
W≤0.1
Cu≤0.15

All of these requirements are met in certain preferred embodiments.

To enhance wear resistance, the composition can be adjusted so that the steel in the quenched and tempered condition contains small and controlled amounts of vanadium carbides with a size of 1 μm or more.

The size is given as the equivalent circular diameter (ECD) calculated from the image area (A) obtained by image analysis. The ECD has the same projected area as the grain and corresponds to 2√(A/π).

The steel desirably contains 0.2-4% by volume of VC, preferably 0.5-3% by volume, more preferably 1.5-2.3% by volume.

The amount of M ₆ C and M ₇ C ₃ should be limited to 2% by volume, preferably 0.5% by volume, more preferably 0.1% by volume each.

The hardness of the steel can be adjusted by choosing the appropriate combination of austenitizing time and temperature, the cooling rate as well as the tempering temperature cooling in the temperature interval from 800°C to 500°C (t5/8). Expressed as hours.

Generally, the steel is tempered twice for 2 hours (2x2h) to reduce the amount of retained austenite below 2% by volume.

The steel after quenching and tempering with a hardness of 55-57 HRC preferably fulfills at least one of the following requirements.
The yield strength (Rp0.2) is ≧1700 MPa, preferably ≧1725 MPa, more preferably ≧1750 MPa.
The tensile strength (Rm) is ≧1950 MPa, preferably ≧2050 MPa, more preferably ≧2050 MPa, most preferably ≧2100 MPa.
Elongation (A5) is ≧3%, preferably ≧4, more preferably ≧5%, most preferably ≧6%.
The area reduction (Z) is ≧5%, preferably ≧10, more preferably ≧15%, most preferably ≧20%.

Example 1
Table 1 discloses the hardness of Rockwell C (HRC) as a function of the hardening parameters austenitizing time and temperature.
It can be seen that the hardness can be easily adjusted within the range of 49 to 61 HRC.
The composition of the ESR ingot was C 0.71%, Si 0.22%, Mn 0.46%, Cr 5.01%, Mo 2.24%, V 1.62%, Al 0.007%. .

表１：焼入れ及び焼戻し状態の硬さ（ＨＲＣ）。すべてのサンプルについて、ｔ８／５＝３００ｓの真空中で冷却し、２ｘ２ｈの焼き戻しを行った。

Table 1: Hardness (HRC) in quenched and tempered condition. All samples were cooled in vacuum at t8/5=300s and tempered for 2x2h.

The tempering resistance of steels austenitized at 1130°C and tempered at 580°C and 600°C was investigated. The steel samples were heated at 600°C for 10 hours. In the first case the hardness decreased from 58.4 HRC to 53.6 HRC and in the second sample the hardness decreased from 55.9 HRC to 52.8 HRC. Therefore, the loss in hardness was 4.8 HRC and 3.1 HRC respectively.

These values can be compared with the corresponding values of the UNIMAX® steel mentioned at the outset.
Samples of said steel were prepared having a nominal composition of 0.5% C, 0.2% Si, 0.5% Mn, 5.0% Cr, 2.3% Mo and 0.5% V.
The steel was austenitized at 1050° C. for 30 min, t8/5=300 s, tempered at 540° C. for 2×2 h and hardened to 57.8 HRC.
The initial hardness was 57.8 HRC and the hardness after 10 hours at 600° C. was 49.4 HRC. The decrease in hardness was therefore 8.4 HRC for the known steel. Therefore, the steel of the present invention is judged to be superior in tempering resistance as compared with known steels.

The cleanliness of the steels of the present invention with respect to fine slag according to ASTM E45-97, Method A, Plate Ir, is shown in Table 2.

表２、ＡＳＴＭ Ｅ４５－９７、方法Ａ、プレートＩ－ｒに準拠した清浄度

Cleanliness per Table 2, ASTM E45-97, Method A, Plate Ir

Example 2
The ESR ingot of Example 1 was hot rolled to a diameter of 196 mm, from which three samples were taken in the LC2 direction to examine mechanical properties.
This steel sample was austenitized at 1050° C. for 30 minutes, cooled in vacuum at t8/5=300 seconds, and then tempered twice at 560° C. for 2 hours to harden to a hardness of 56 HRC.
The average values of the test are shown below.
Yield strength (Rp0.2): 1761 MPa
Tensile strength (Rm): 2117 MPa
Elongation (A5): 7%
Area reduction rate (Z): 26%

Example 3
In this example, the steel of the invention was compared with a standard matrix steel used for forging tools.
The alloy had the following composition (% by weight)
Steel of the invention Comparative steel C 0.7 0.5
Si 0.2 0.2
Mn 0.5 0.5
Cr 5.0 4.2
Mo 2.3 2.0
V 1.6 1.2
W 0.01 1.6
Remaining amount Fe and impurities

The alloy was subjected to standard heat treatment, forging and softening annealing to a hardness of approximately 300 HBW.
Both steels were quenched and tempered by heating to 1100°C for 30 minutes and performing quenching and tempering twice at 540°C for 2 hours (2 x 2 hours).
The hardness of the steel of the invention was 57 HRC and the hardness of the comparative steel was 56 HRC.
Abrasion resistance was investigated by the Pin on Disk method using 800 mesh aluminum oxide paper taken from the same batch.
The wear loss of the steel of the invention was found to be 178 mg/min and the wear loss of the comparative steel to be 219 mg/min.
Further samples of the steel according to the invention were produced in order to obtain the same hardness as the comparative steel. This was achieved by heating at 1100°C for 30 minutes and tempering at 540°C for 2x2 hours. Hardness was 56 HRC.
As expected, the wear loss of this sample was slightly higher (189 mg/min) compared to the 57 HRC hardness steel, but substantially lower than the comparative steel with the same hardness.

Example 4
A sample of steel of the same composition as in Example 1 was prepared for welding testing.
A solid block of steel was ground to have a sharp 90° internal angle and the samples were subjected to two different hardening treatments.
The first heat treatment consisted of austenitizing at 1050° C. for 30 minutes, cooling in vacuum at t8/5=300 seconds, and then tempering at 560° C. for 2 hours twice.
The second heat treatment differs in that it austenitizes at 1130° C. for 10 minutes.
The samples were then TIG welded at room temperature (RT), 80°C, 225°C and 325°C using a 1.6mm diameter rod with three different standard welding consumables.
The Applicant owns the Caldie TIG and the QRO 90 TIG as well as the UTP A 696 TIG from UTP Schweissmaterial GmbH.
Caldie TIG consumables cracked at all temperatures. Surprisingly, however, it was found that using the other two consumables allows crack-free welding even at room temperature.
The steel of the invention therefore has surprisingly good weldability.

The steels of the present invention are useful in hot working applications where tools are subject to wear. In particular, the steel of the present invention is suitable as tools for hot forging, hot pressing, die casting, high pressure die casting or hot extrusion.

Claims (11)

in percent by weight (wt%),
C 0.65-0.85
Si 0.03-0.8
Mn 0.1-1.8
Cr 4.5-6.6
Mo 1.8-3.5
V 1.3-2.3
Al≤0.1
N≤0.12
Ni≤1
W≤0.5
Co≤2
Cu≤1
Nb ≤ 0.1
Ti≦0.05
Zr≤0.05
Ta≤0.05
B ≤ 0.01
Ca ≤ 0.01
Mg≤0.01
REM≤0.2
Hot work tool steel for hot forging, hot pressing, die casting or hot extrusion, consisting of iron and impurities. 2. Hot work tool steel according to claim 1, wherein the steel fulfills at least one of the following requirements.
C 0.65-0.8
Si 0.05-0.6
Mn 0.2-0.8
Cr 4.5-5.6
Mo 2.0-2.5
V 1.5-1.9
Al≤0.05
N≤0.08
Ni≤0.5
W≤0.5
Co≤2
Cu≤0.5
Nb≤0.05
Ti≤0.01
Zr≤0.01
Ta≤0.01
B ≤ 0.006
Ca ≤ 0.005
Mg≤0.005
REM≤0.1 3. Hot work tool steel according to claim 1 or 2, wherein the steel fulfills at least one of the following requirements.
C 0.65-0.75
Si 0.15-0.5
Mn 0.4-0.5
Cr 4.9-5.1
Mo2.2-2.3
V 1.5-1.7
Al≤0.03
N≤0.05
Ni 0.25
W≤0.2
Co≤1
Cu≤0.2
Nb ≤ 0.005
Ti≤0.005
Zr≤0.005
Ta≤0.005
REM≤0.05 Hot work tool steel according to any one of the preceding claims, wherein the steel comprises carbides with a size of ≧1 μm and fulfills at least one of the following requirements regarding the amount of said carbides in volume %: .
VC 0.2-4
_{M6C≤2
M7C3≤2 _} 5. The hot work tool steel according to claim 4, wherein said steel comprises carbides with a size of ≧1 μm and fulfills at least one of the following requirements regarding the amount of said carbides in volume %.
VC 0.5-3
_{M6C≤0.5
M7C3≤0.5 _} 6. The hot work tool steel according to claim 5, wherein said steel comprises carbides with a size of ≧1 μm and fulfills at least one of the following requirements regarding the amount of said carbides in volume %.
VC 1.5-2.3
_{M6C≤0.1
M7C3≤0.1 _} Hot work tool steel according to any one of the preceding claims, wherein the steel after quenching and tempering has a hardness of 55-57 HRC, said steel fulfilling at least one of the following requirements:
Rp0.2≧1750MPa,
Rm≧2100MPa,
A5≧6%,
Z≧20%,
The following maximum requirements for fine slag according to ASTM E45-97, Method A, Plate Ir

Cleanliness that satisfies Hot work tool steel according to any one of the preceding claims, wherein the steel satisfies at least one of the following requirements:
C 0.66-0.75
Si 0.15-0.25
Mo2.2-2.3
V 1.52-1.68
Al 0.001-0.03
N≤0.05
W≤0.1
Co≤1
Cu≤0.15
Nb≤0.005
Ti≤0.005
Zr≤0.005 Hot work tool steel according to any one of the preceding claims, wherein the steel satisfies at least one of the following requirements:
C 0.66-0.75
Si 0.15-0.25
Mo2.2-2.3
V 1.52-1.68
Al 0.005-0.03
N≤0.05
W≤0.1
Co ≤ 0.5
Cu≤0.15
Nb ≤ 0.005
Ti≤0.005
Zr≤0.005 The steel is soft annealed and has an average hardness ≦360 HBW, the steel has a thickness of at least 100 mm and a maximum deviation from the average Brinell hardness value through the thickness measured according to ASTM E10-01. less than 10%, preferably less than 5% (where the minimum distance of the center of the indentation from the edge of the specimen or the edge of another indentation shall be at least 2.5 times the diameter of the indentation and the maximum the distance being less than or equal to four times the diameter of the indentation), the steel of any one of claims 1-6. Use of the steel according to any one of claims 1 to 10 as tools for hot forging, hot pressing, die casting, high pressure die casting or hot extrusion.