EP3966354A1

EP3966354A1 - Bainitic hot work tool steel

Info

Publication number: EP3966354A1
Application number: EP19730566.7A
Authority: EP
Inventors: Peter KIRBIS; Andrej VRECIC; Tatjana VECKO PIRTOVSEK; Borut URNAUT
Original assignee: Sij Metal Ravne DD
Current assignee: Sij Metal Ravne DD
Priority date: 2019-05-10
Filing date: 2019-05-10
Publication date: 2022-03-16
Also published as: WO2020231346A1

Abstract

A novel group of hot work tool steels which exhibit exceptionally high values of thermal conductivity, typically above 45W/mK at the commonly used range work hardness (44-51HRC) has been developed. These steels are characterized by their tendency of largely retaining or even increasing their thermal conductivity at elevated temperatures, with a peak of thermal conductivity typically in the range between 400°C and 500°C. The impact toughness and other mechanical properties remain in compliance with the most common toughness requirements and standard specifications, for hot work tool steels (i.e. H13), while retaining sufficient hardenability to ensure homogenous properties within thick sections. This steel exhibits high tempering stability, low distortion during heat treatment and a very high resistance to heat checking.

Description

Bainitic hot work tool steel

These characteristics make the newly developed steel especially suitable for production of die casting dies which operate between 400°C and 650°C, and tools for hot stamping of high strength steel and aluminum sheets. Generally, this steel is also suitable for applications of die forging and extrusion as well as other tools for hot working and plastic molding which operate at temperatures above 200°C.

Description

The present invention refers to a novel low-chromium high thermal conductivity hot-work tool steel that is suitable for production of die casting dies and hot stamping tools and to a method of producing said steel. The new type of hot-work tool steel retains very high values of thermal conductivity at elevated temperatures.

A novel hot-work tool steel was developed having the following chemical composition (all percentages being in weight percent): C 0.25-0.45% Si max 0.15% Cr max 0.20% Mn 0.05- 0.25% Mo 1.5-4.0% W 0.0-2.0% Co 0.2-1.0% as well as optional elements such as Ni 0.0-2.5% or Cu 0.0-1.0% and the intentional micro additions of Ti, Nb, B, Ta, Ce, the remainder being essentially iron except for unavoidable impurities. Said hot-work tool steel is of predominantly bainitic microstructure. The current invention is feasible without any special manufacturing requirements using the conventional equipment. However, as with all hot-work tool steels used in demanding applications such as die casting/forging, a secondary refining process such as ESR or VAR re melting is highly recommended.

State of the art

Hot-work tool steels are a group of ferrous alloys used for production of tools which operate at elevated temperatures in applications of die forging, squeezing and extrusion of light metals (Al, Mg), die casting of light metals (Al, Mg), hot stamping as well as plastic molding and continuous casting of Al and its alloys. The most common critical temperature range of operation in the above mentioned applications is generally considered to be between SOOT and 650°C, the requirements are significantly different though, depending on process. The proposed steel of the invention is suitable for all fields of applications, particularly for the production of die casting and hot stamping tools.

Die casting

In die casting applications, tools are exposed to temperatures of liquid aluminum, whereby the contact layer can heat up to 650°C and the bulk temperature of tools is about 200-300°C. Within this temperature range, steel is subjected to cyclic thermal and mechanical loading, due to the heating via injection of liquid aluminum and forced cooling after ejection of the solidified part. This leads to the occurrence of small surface cracks known as thermal fatigue damage.

It is a well-known fact that thermal fatigue is the most common failure mode of dies for die casting of non-ferrous metals and alloys, predominantly based on aluminum and magnesium. The resistance of materials to the occurrence of thermal fatigue is proportional to the surface stress induced due to thermal loading which can be expressed with equation (1) as follows [1]: Where:

T_up= the highest temperature within the cycle Tiow⁼ the lowest temperature within the cycle E= elastic module v= poisons ratio cr=thermal diffusivity defined with equation (2) as ratio:

K=coefficient of heat transfer/thermal conductivity k= specific heat capacity

From equations 1, 2 it can be concluded that stress amplitude and consequently material's resistance to thermal fatigue damage is directly proportional to the steel's thermal conductivity. Steel with a significantly higher thermal conductivity can therefore be expected to perform better and tool to last much longer.

Hot stamping

Hot stamping is the technology of choice in development of sheet metal parts from martensitic high strength steels and aluminum alloys. The process includes the forming of hot metal sheet in the desired shape during stamping and subsequent heat treatment - quenching, within the closed cavity of the forming tool. Mechanical properties of the final part and tools performance are therefore largely dependent on the cooling rate of sheet metal.

Limitations of currently available hot-work tool steels

The steels currently in use for die casting applications vary significantly in terms of achievable work hardness and toughness, whereby thermal conductivities are severely limited due to their alloy design which commonly includes additions of Cr (3.0-6.0 wt. %), V (0.5-1.6 wt. %), Si (0.25-2.0 wt. %) and Mn (0.4- 0.6 wt. %); the values in brackets serve as orientation for the most commonly used standardized grades of Wr. Nr 1.2343, 1.2344, 1.2367 and so forth. The additions of afore mentioned elements are known to be beneficial for the obtainment of desired mechanical properties of hardness, toughness, hot strength and tempering resistance. However, the presence of these elements is unfavorable in terms of achievable thermal conductivity, as even very small concentrations introduce lattice distortions that hinder the movement of electrons and phonons which are the conductors of heat flow and determine material's thermal conductivity.

Known methods of improving thermal conductivity of hot-work tool steels

In order to obtain a tool steel with high thermal conductivity, several commonly used alloying elements such as Cr and V need to be excluded, whereby the attention is directed predominantly towards Mo and W, as described in EP 2492366 [2], in combination with suitable amounts of C (typically 0.3-0.5 wt. %).

Such alloying principles are sufficient to reach adequate work hardness (45-50HRC) however they do not provide all the necessary properties such as hardenability. The latter is solved via addition of Ni in varying amounts between 1.0-3.0 wt. %, typically around 2 wt. %, which is used to increase hardenability, while being the least detrimental element to the steel's thermal conductivity.

Such alloy design led to the development of tool steels with high thermal conductivity as described in EP 2492366 [2]

The currently available materials being sold as high thermal conductivity hot-work tool steels exhibit significantly higher values of thermal conduction at room temperature which gradually decreases with the increasing temperature. This is a common phenomenon which originates from the physics of thermal conductivity whereby every material exhibits a peak of thermal conductivity at a given temperature. This peak is determined by the intersection of different mechanisms of thermal conduction. After a certain temperature is reached, the Umklap processes or U-processes occur which hinder the movement of phonons which are essential for the propagation of heat within steel microstructures. For many materials with high thermal conductivity (such as for instance pure metals), this peak temperature is close to, or below, room temperature. Such example is seen with some of known hot-work tool steels with improved thermal conductivity. This is due to the fact that those steels put a high emphasis on the carbide structure favoring MeO type carbides promoting a large number of free electrons which act favorably in promoting high thermal conductivity at low temperatures. Additional increases in free electron density are also achievable by a partial substitution of C with N or B within carbides. As temperatures increase, free electrons will be interacting with the movement of phonons as part of the U-processes, thereby it is reasonable to assume that this will make their contribution negligible or even negative.

Proposed solution

The invention is described in details below and presented in figures which present:

Figure 1: Comparison of thermal conductivity of standard tool steel grades and the steel of the invention, quenched in oil and tempered to a hardness range of 44-46HRC.

Figure 2: The influence of Co additions on the microhomogeneity of hot-work tool steel of the invention - steel R (conventionally cast)

Figure 3: Influence of 0.5% Cr additions on hot-work tool steel of the invention - steel S

Figure 4: Influence of Co additions on thermal conductivity of hot-work tool steels of the invention in relation to testing temperature

Figure 5: A continuous cooling transformation (CCT) curve of hot-work tool steel of the invention - steel S, with recommended cooling rates.

Figure 6: Heat treatment diagram

Figure 7: Influence of cooling rate on the thermal conductivity of steel S

Figure 8: Tempering diagram for hot-work tool steel of the invention - steel S (SITHERM

S140R), on cube samples 20mm, double tempered

Figure 9: Annealed microstructure of hot-work tool steel of the invention - steel S. While a lot of attention was put on the type, amount and distribution of carbides, the microstructure of tempered martensite is predominantly considered as being the most suitable. As previously mentioned, heat within steels is transferred both via electrons and lattice vibrations; and as the content of alloying elements increases - the latter become increasingly influential, whereby the contribution of electrons in highly alloyed cast iron can be essentially neglected [3]. However, cast iron exhibits thermal conductivity which is comparable or even higher than that of steels. This indicates that neither the purity of the lattice nor the character of imbedded carbides but rather the microstructure itself should be the main focus in designing steels with high thermal conductivity. The phononic thermal conductivity is expressed by equation 3 as [4]:

K_R = ± C_vvl (3) where;

(^Specific heat capacity

i?=Speed of sound in the metal

l=mean free phonon path

It is known from thermoelectrics that the microstructure which inhibits the phonon movement the most, is the one that consists of mesoscale grains with nanoscale precipitates, i.e. with a high dislocation density and a high content of solid solution elements in the matrix [5]. This is a typical description of a martensitic microstructure as the first blocks will grow essentially throughout the entire grain. In comparison, the microstructure of bainite is much more uniform in scale, as the width of the individual subunits is mostly influenced by the strength of austenite matrix. Bainite is also much less supersaturated with respect to carbon which is also a major factor that determines thermal conductivity of steel, as illustrated from tempering data [6]

As hot-work tool steel rarely operates at room temperature, it was the goal for the newly developed steel to obtain the peak of thermal conductivity within the common critical range of working temperatures, which is between 300°C and 650°C. This was accomplished with a special alloy design wherein the steel contains Mo, W and C according to the following relation expressed with equation (4):

M:C = %Cp_ar_t (9%Mo + 20% W) (4) where:

M: C= the ratio between carbide forming alloying elements and carbon, whereby it is noted that the major alloying elements are Mo and W. This ratio is determined as to minimize the amount of alloying elements present in a solid solution.

Further the steel of the invention is alloyed with Co in concentrations between 0.2 and 1.0 wt. % preferably between 0.75 and 0.85 wt. %.

The influence of Co in physical metallurgy of steel exerts the favorable effect to obtain the desired microstructure and thereby retain or even increase thermal conductivity at elevated temperatures. At least 0.2 wt. % Co should be added to the steel whereas the amount close to 0.8 wt. % is deemed ideal, as can be seen from Fig. 2.

Small additions of Cu are added to the steel in the range of 0.1% to 0.15 wt. % for improvement of corrosion resistance.

Elements detrimental to thermal conductivity of steels such as Cr, Si, Mn and V are preferably kept at a minimum concentration, below 0.2 wt. %, preferably below 0.1 wt. %. Amongst these elements, V is the least detrimental; therefore V content up to 1.6 wt. % may be acceptable in order to improve abrasive wear resistance. To improve abrasive wear resistance Ti may also be added in the amount up to 0.2 wt. % .

Alloying with Mo may be used independently or in combination with W.

A novel hot work tool steel alloy with bainitic microstructure denoted as 1A (basic composition), with the following nominal composition is thereby proposed, all percentages being in weight percent:

C: 0. B0-0.40 % Si: 0.05°/o-0.15%

Mn: 0.05-0.25%

Cr: max 0.2%

Mo: 3.1-3.6%

W: 0.7-1.2%

Ni: max 0.1%

Cu: 0.1- 0.15%

Co: 0.2-1.0%

V: max. 0.15% the rest consisting of Fe and unavoidable impurities.

The amount of Mn is dependent upon the S content in a ratio of 15 : 1. Within said ratio the whole sulfur present in the steel binds in Mn and forms deformable MnS excrements which are substantially more favorable as if the sulfur does not form inclusions, but stays at the boundaries of crystalline grains of steel where it causes fragility.

Thermal conductivity of steel was measured at different temperatures within the hardness range 44-46 HRC. The results are presented in Table 1.

Table 1: Thermal conductivity of steel 1A [W/mK]

As the basic composition of the hot work tool steel alloy 1A exerts a low hardenability due to the lack of austenite stabilizing elements, a modification of the basic composition has been developed with the additions of Ni. In order to obtain sufficient hardenability, additions of Ni may be added to the composition in amounts between 1.0 and 2.4 wt. %. Alternatively, if steel does not contain Ni, hardenability may be increased through a combined use of Cu+B, preferably in combination with other micro-additions, such as Ti and Nb.

If Ni is added to steel, Cu additions are to be limited to max. 0.15 wt. % preferably around 0.1 wt. %, as the co-alloying of these elements results in a higher amount of Cu remaining in a solid solution which is in turn detrimental to thermal conductivity.

A modified steel alloy denoted R, yielding increased hardenability due to Ni with the following composition is proposed, all percentages being in weight percent:

C: 0.30-0.40%

Si: 0.05%-0.15%

Mn: 0.05-0.25%

Cr: max 0.2%

Mo: 3.1-3.6%

W: 0.7-1.2%

Ni: 2.0-2.4%

Cu: 0.1-0.15%

Co: 0.2-1.0%

V: max 0.15% the remainder being Fe except for unavoidable impurities.

Additions of Co are the most critical to obtain the desired thermal conductivity characteristics. The effect of Co on physical metallurgy is appreciative from dilatometry measurements. When Co is added to these steels, the Ms temperature slightly increases but, more importantly, a transformation finish temperature can be obtained (denoted Mf), indicating that the retained austenite content becomes negligible. Co is often added to hot-work tool steels in similar amounts in order to improve tempering stability [7], however, in the context of the steels of the invention this is regarded as merely a secondary effect and is not the main reason for alloying with Co, as tempering stability is ensured by the high Mo and/or W content.

The main reason for alloying with Co is that the addition of Co increases the overall micro homogeneity of steel and results in predominantly bainitic microstructures. A homogenous microstructure is essential to obtain high thermal conductivity values however, all hot-work tool steels have a certain tendency for the formation of micro-segregations which are commonly referred to as microstructural bands. The formation of micro-banding is in practice very difficult to prevent even if secondary refining (re-melting) processes such as ESR and VAR are applied - which are nevertheless, the preferred technological route for production of hot- work tool steels. In the present invention, the formation of banding is mitigated by additions of Co, which affects the microstructure as seen in Fig. 2.

The effect of Co has been studied in detail whereby the Co content was altered in the R steel and thermal conductivity was measured at temperatures 200°C, 400°C and 500°C, as summarized in the following graph in Fig. 4.

Based on the results shown in Fig. 4, it is recommended that the steel contains at least 0.2% wt. Co, preferably from 0.6-0.9 wt. % Co, more preferably from 0.75-0.85 wt. %, and it has been henceforth named S for the sake or distinction, which is presented in greater detail. The most recommended amount is 0.8 wt. % Co (designated as SITHERM S140R). A higher amount of Co additions must be balanced with Ni content as Co is known to increase the thermodynamic driving force for ferrite formation whereby, the presence of grain boundary ferrite deteriorates the toughness.

The influence of Co addition on the retained austenite content are summarized in Table 2: Table 2: Influence of Co addition on the retained austenite content of novel hot-work tool steel

As can be seen from results the addition of Co has influence on thermal conductivity and on the increase the overall microhomogeneity of the steel.

Further it should be noted that steels of the invention contain very low amounts of Cr due to the detrimental effect that Cr exerts on thermal conductivity. There are, however, sound arguments to minimize the Cr content also from the microstructural point of view. It has been argued that Cr is detrimental for the properties of hot-work tool steels, as Cr rich carbides tend to coarsen more rapidly compared to other (Mo, W) carbides [8] In steels of the invention, the effect of Cr additions is very pronounced and it results in an appreciative grain growth under identical heat treatment conditions, as shown in Fig. 3. If the amount of Cr is higher the microhomogeneity of the steel decreases.

Different steel compositions of the invention were prepared and thermal conductivity coefficients were measured at different temperatures. The results are shown in Table 3.

Table 3: Chemical composition and thermal conductivity of novel steels

Samples were quenched in oil and double tempered to a hardness of 44-46 HRC.

The results shows that steels of the invention retain thermal conductivity at elevated temperatures.

In table 4 and on Fig. 1 the comparison of thermal conductivity of known hot work tool steels and steal of the invention (S steel) is shown, which further demonstrates that steels of the invention exhibits at least 40% higher thermal conductivity compared to standardized Cr-Mo- V grades of steel and whereby the coefficient of thermal conductivity remains the same or is increasing with the temperature to no less that min 45 W/mK at 400°C.

Table 4

*Values for standard grades were taken as average values of the standard interval of chemical compositions. Steels of the invention can be prepared by conventional heat treatment. However as already mentioned the homogeneous, predominantly bainitic microstructures are obtained by additions of Co, but in the case of steels with high hardenability (additions of Ni), a wider range of cooling rates are available, whereby the most recommended are shown on the example of the CCT diagram of steel S as depicted in Fig. 5.

The minimal interval of continuous cooling rates lies between 120 and 10°K/min, preferably 120 and 30°K/min, and is as such compatible with the current industry practice, as most heat treatments of hot work tools are performed in vacuum furnaces at slower cooling rates compared to oil quenching. The importance of cooling rate is best illustrated on the example where steel S is cooled at two different cooling rates corresponding to 120°K/min and water quenching in order to ensure a fully bainitic and martensitic microstructure respectively. The corresponding thermal conductivities are shown in the graph in Fig. 6. The newly developed steels are characterized by the fact that they form negligible retained austenite contents within predominantly bainitic microstructures, which is in a sharp contrast to conventional high chromium hot-work tool steels. These form more retained austenite when cooled through the bainitic region of the CCT diagram.

Optimal heat treatment involves rapid cooling into the bainite region and a short isothermal holding at 400°C.This serves to fully complete the bainite formation and to equalize the temperatures of surface and central region of tool. Quenching rates can be high as bainite produces distortions which are up to an order of magnitude smaller compared to martensite. The volume change from the initial spheroidized pearlite is considered to be negligible [9] After the equalization step at 400°C, steel is further cooled to 200°C or lower as shown in Fig. 7. The Bf temperature as indicated in the CCT diagram is at approx. 350°C, however one should keep in mind that all such data are essentially dependent on the resolution of the measurement equipment. Accordingly, a higher undercooling is recommended to achieve a retained austenite content below 1% which is common for this steel, after which we proceed with tempering.

The first temper is to be performed at temperatures 580°C and 590°C for small and large tools respectively, for duration of 5h adjusted by common additions accounting for the tool cross sections of l/2h per inch. A prolonged first temper is due to the initially sluggish tempering kinetics. After the first temper, steel achieves hardness between 47-51HRC depending on quenching rate, whereby a slower cooling rate results in a lower obtainable hardness. After the first temper, steel is suitable for applications where high toughness is not required, such as for instance die inserts prone to washout or hot stamping tools with simple geometries, exposed primarily to abrasive and adhesive wear.

Example:

In accordance with above criteria, a 2t heat of S steel was conventionally cast and forged into round electrodes -0200 mm diameter. The electrodes were then ESR re-melted into the shape of 0330 mm ingot which was open die forged (upsetting and longitudinal forging) with a reduction ratio of 4.5 into the square shape forging of dimensions 220x145mm. The steel exhibits the tempering response presented in Figure 8.

The achieved hardness is higher compared to H13, when tempering above 590°C.

Thermal conductivity in relation to austenitization temperature QT was measured at different temperatures within the hardness range 44-46 HRC.

Table 1: Coefficient of thermal conductivity [W/mK]

The acclaimed tendency of retaining/increasing thermal conductivity with temperature is clearly visible.

For this heat, its mechanical properties and microstructure were evaluated in accordance with standard NADCA #229 2016, and the following results obtained:

Impact toughness KV2: avg. 19J, min 15J

Annealed microstructure: AS3

The annealed microstructure of steel S is presented in Figure 9.

When comparing the steels of the present invention to other high thermal conductivity steels such as for example disclosed in JP application No. JP2017061712 [10], the B parameter is generally below 0.74.

(AC:-0.300 to 0.300% and B value: 0.74 to 0.94, where C eq is 0.20% or more and AC=C-C eq, B value=(0.063x%Mo+0.033x%W+0.2x%V+0.1x%Nb)/Ceq)

Newly developed steels as proposed in the present invention show such behavior that, in conventional heat treatment, a bainite microstructure is formed instead of the conventional martensite. This microstructure is further characterized as being structurally homogeneous, that is, other microstructural constituents, such as martensite, ferrite are not present within the segregation bands. Under the conditions when other known hot tool steels form martensite, steels of the invention develop a predominantly bainite microstructure.

Cited literature:

[1] J. H. HATTEL and P. N. HANSEN, "a 1-D Analytical Model for the Thermally-Induced Stresses in the Mold Surface During Die-Casting," Appl. Math. Model., vol. 18, no. 10, pp. 550-559, 1994.

[2] I. Vails Angles, "Hot work tool steel with outstanding toughness and thermal conductivity," EP 2 492 366 Al, 2008.

[3] R. P. POWELL, R. W. TYE, "THERMAL CONDUCTIVITIES OF SOME IRON ALLOYS HAVING UNUSUALLY HIGH LATTICE COMPONENTS," Int. J. Heat Mass Transf., vol. 9, pp. 845-852, 1966.

[4] N. G. Backlund, "An experimental investigation of the electrical and thermal conductivity of iron and some dilute iron alloys at temperatures above 100XK," J. Phys. Chem. Solids, vol. 20, no. 12, pp. 1-16, 1961.

[5] J. He, M. G. Kanatzidis, and V. P. Dravid, "High performance bulk thermoelectrics via a panoscopic approach," Mater. Today, vol. 16, no. 5, pp. 166-176, 2013.

[6] J. Wilzer, F. Ludtke, S. Weber, and W. Theisen, "The influence of heat treatment and resulting microstructures on the thermophysical properties of martensitic steels," J. Mater. Sci., vol. 48, no. 24, pp. 8483-8492, 2013.

[7] D. A. C. G.G. Liversidge, K.C. Cundy, J.F. Bishop, "United States Patent (19) 54," vol.

96, no. 19, pp. 62-66, 1980. [8] A. Grellier and M. Siaut, "A New Hot Work Tool Steel for High Temperature and High Stress Service Conditions," 6th Int. Tool. Conf., pp. 39-48, 2002.

[9] K.-E. Thelning, "Dimensional changes during hardening and tempering," Steel its heat tratment, pp. 581-641, 1984.

[10] S. Yuta, "JP2017061712 ( A ) - 2017-03-30 Hot work tool steel having excellent thermal conductivity and tougthness," JP20150186625 20150924, 2017.

Claims

1. A steel, in particular a hot-work tool steel having the following chemical composition in weight percent:

C: 0.25-0.45%

Si: 0.05-0.15%

Mn: 0.05-0.25%

Cr: 0.05-0.2%

Mo: 1.5-4.0%

W: 0.0-2.0%

Ni: 0.0-2.5%

Cu: 0.0- 0.15%

Co: 0.2-1.0%

V: below 0.2% the rest consisting of Fe and unavoidable impurities and wherein said hot-work tool steel is of predominantly bainitic microstructure.

2. The steel according to claim 1 having the following chemical composition in weight percent:

C: 0.30-0.40 %

Si: 0.05%-0.15%

Mn: 0.05-0.25%

Cr: max 0.2%

Mo: 3.1-3.6% W: 0.7-1.2%

Ni: max 0.1%

Cu: 0.1- 0.15%

Co: 0.2-1.0%

3. The steel according to claim 1 having the following chemical composition in weight percent:

C: 0.30-0.40 %

Si: 0.05%-0.15%

Mn: 0.05-0.25%

Cr: max 0.2%

Mo: 3.1-3.6%

W: 0.7-1.2%

Ni: 2.0-2.4%

Cu: 0.1- 0.15%

Co: 0.2-1.0%

V: max 0.15% the rest consisting of Fe and unavoidable impurities and wherein said hot-work tool steel is of predominantly bainitic microstructure.

4. The steel according to claim 3, wherein the steel comprises from 0.75-0.85 wt. % Co.

5. The steel according to claims 1 to 4, wherein the steel comprises Mo, W and C according to the following criteria:

M:C = %Cp_ar_t (9%Mo + 20% W) where:

M: C= the ratio between carbide forming alloying elements and carbon.

6. The steel according to claims 3 to 5, wherein the bainite microstructure is formed in a clear bainitic region in the CCT diagram at cooling rates in interval between 120°K/min and 10°K/min, preferably in interval 120°K/min and 30°K/min.

7. The steel according to previous claims, wherein it exhibits at least 40% higher thermal conductivity compared to standardized Cr-Mo-V grades of steel and whereby the coefficient of thermal conductivity remains the same or is increasing with the temperature to no less that min 45 W/mK at 400°C.

8. The steel according to previous claims, wherein a retained austenite content is below 1% after quenching.

9. The steel according to previous claims, wherein when subjected to prolonged exposure to temperatures of 610 °C or more, hardness of more than 45 HRC is obtained with thermal conductivity above 45 W/mK at 400°C.

10. The steel according to previous claims with a very low tendency for the formation of microstructural banding.

11. The steel according to previous claims for use in the production of die casting dies, forging dies, extrusion dies, tools for hot stamping, plastic molding and continuous casting.