Hot work tool steel with outstanding toughness and thermal conductivity

1. A steel, for a hot work tool steel, having the following composition, all percentages being in weight percent:

% Ceq = 0.26-0.55

% C = 0.20-0.55

% N = 0-0.6

% B = 0-0.45

% Cr < 1.5

% Ni = 1.0-9

% Si < 0.4

% Mn = 0-3

% Al = 0-2.5

% Mo = 0-10

% W = 0-15

% Ti = 0-3

% Ta = 0-3

% Zr = 0-3

% Hf = 0-3,

% V = 0-4

% Nb = 0-3

% Cu = 0-4

% Co = 0-6,

% S = 0-1

% Se = 0-1

% Te = 0-1

% Bi = 0-1

% As = 0-1

% Sb = 0-1

% Ca = 0-1,

the rest consisting of iron and unavoidable impurities, wherein

% C eq =% C+0.86*% N+1.2*% B,

% Ni+9*% Mn+5*% Si<8,

and

% Mo+½% W>1.2,

said steel having a low scattering structure permitting a thermal diffusivity higher than 8 mm 2 /s

and wherein:

x C eq *( x Mo+0.5* x W)/( x Cr+ x V+ x Nb)>8

where:

xCeq—weight percent Carbon;

xMo—weight percent Molybdenum:

xW—weight percent Tungsten;

xV—weight percent Vanadium;

xNb—weight percent Niobium;

where xCr, xV and xNb are the real weight percents even if present at concentrations lower than 0.05%.

2. A steel according to claim 1 , wherein at least 80% weight of the carbides are carbides of primarily Fe, Mo or W, alone or in combination.

3. A steel according to claim 2 , wherein no other single metallic element is present in solid solution within the Fe, Mo and/or W carbides in a concentration higher than 10% weight.

4. A steel according to claim 2 , wherein the % C in the carbides is at least partly replaced by % N and/or % B.

5. A steel according to claim 1 , wherein no single element is present in solid solution within the Fe metallic matrix embedding the carbides in a concentration higher than 0.5% except % Ni and/or % Mn.

6. A steel according to claim 1 , wherein no single element is present in solid solution within the Fe metallic matrix embedding the carbides in a concentration higher than 0.1% except % Ni.

7. A steel according to claim 1 , wherein:

0.03 <x C eq −A C[ x Mo/(3 A Mo)+ x W/(3 A W)+ x V/ A V]<0.165

where:

xCeq—weight percent Carbon;

xMo—weight percent Molybdenum;

xW—weight percent Tungsten;

xV—weight percent Vanadium;

AC—carbon atomic mass (12.0107 u);

AMo—molybdenum atomic mass (95.94 u);

AW—tungsten atomic mass (183.84 u);

AV—vanadium atomic mass (50.9415 u).

8. A steel according to claim 1 , wherein:

% Cr<0.2, % Si<0.2 and % Ni>2.99.

9. A steel according to claim 1 , wherein % Cr<0.1.

10. A steel according to claim 1 , wherein % Si<0.1.

11. A steel according to claim 1 , wherein % Cr<0.05 and % Si<0.05.

12. A steel according to claim 1 , wherein % Mo=2-10, and 3<% Mo+½·% W<11.

13. A steel according to claim 1 , wherein:

% C eq = 0.26-0.4

% C = 0.26-0.4

% N = 0-0.45

% B = 0-0.3

% Cr < 0.5

% Ni = 2.99-6

% Si < 0.3

% Mo = 2.5-8

% W = 0-5.

14. A steel according to claim 1 , wherein:

% C eq = 0.28-0.36

% C = 0.28-0.36

% N = 0-0.4

% B = 0-0.25

% Cr < 0.3

% Ni = 2.99-5

% Si < 0.25

% Mo = 3-6.5

% W = 1-4.

15. A die, tool or part comprising at least one steel according to claim 1 .

16. A steel, for a hot work tool steel, having the following composition, all percentages being in weight percent:

% Ceq = 0.20 − 1.2

% C = 0.20 − 1.2

% N = 0 − 0 − 1

% B = 0 − 1

% Cr < 0.05

% Ni = 1.0 − 9

% Si < 0.05

% Mn = 0 − 3

% Al = 0 − 2.5

% Mo = 0 − 10

% W = 0 − 15

% Ti = 0 − 3

% Ta = 0 − 3

% Zr = 0 − 3

% Hf = 0 − 3,

% V = 0 − 4

% Nb = 0 − 3

% Cu = 0 − 4

% Co = 0 − 6,

% S = 0 − 1

% Se = 0 − 1

% Te = 0 − 1

% Bi = 0 − 1

% As = 0 − 1

% Sb = 0 − 1

% Ca = 0 − 1,

the rest consisting of iron and unavoidable impurities, wherein

% C eq % C+0.86*% N+1.2*% B,

and

% Mo+½% W>1.2

and wherein:

x C eq *( x Mo+0.5* x W)/( x Cr+ x V+ x Nb)>8

where:

xCeq—weight percent Carbon;

xMo—weight percent Molybdenum:

xW—weight percent Tungsten;

xV—weight percent Vanadium;

xNb—weight percent Niobium;

where xCr, xV and xNb are the real weight percents even if present at concentrations lower than 0.05%.

17. A steel, for a hot work tool steel, having the following composition, all percentages being in weight percent:

% C eq = 0.26 − 0.4

% C = 0.26 − 0.4

% N = 0 − 0.45

% B = 0 − 0.3

% Cr < 0.5

% Ni = 2.99 − 6

% Si < 0.3

% Mn = 0 − 3

% Al = 0 − 2.5

% Mo = 2.5 − 8

% W = 0 − 5

% Ti = 0 − 3

% Ta = 0 − 3

% Zr = 0 − 3

% Hf = 0 − 3,

% V = 0 − 4

% Nb = 0 − 3

% Cu = 0 − 4

% Co = 0 − 6,

% S = 0 − 1

% Se = 0 − 1

% Te = 0 − 1

% Bi = 0 − 1

% As = 0 − 1

% Sb = 0 − 1

% Ca = 0 −1,

the rest consisting of iron and unavoidable impurities, wherein

% C eq =% C+0.86*% N+1.2*% B,

and

% Mo+½·% W>1.2

and wherein:

x C eq *( x Mo+0.5* x W)/( x Cr+ x V+ x Nb)>8

where:

xCeq—weight percent Carbon;

xMo—weight percent Molybdenum:

xW—weight percent Tungsten;

xV—weight percent Vanadium;

xNb—weight percent Niobium;

where xCr, xV and xNb are the real weight percents even if present at concentrations lower than 0.05%.

18. A steel, for a hot work tool steel, having the following composition, all percentages being in weight percent:

% C eq = 0.28 − 0.36

% C = 0.28 − 0.36

% N = 0 − 0.4

% B = 0 − 0.25

% Cr < 0.3

% Ni = 2.99 − 5

% Si < 0.25

% Mn = 0 − 3

% Al = 0 − 2.5

% Mo = 3 − 6.5

% W = 0 − 4

% Ti = 0 − 3

% Ta = 0 − 3

% Zr = 0 − 3

% Hf = 0 − 3,

% V = 0 − 4

% Nb = 0 − 3

% Cu = 0 − 4

% Co = 0 − 6,

% S = 0 − 1

% Se = 0 − 1

% Te = 0 − 1

% Bi = 0 − 1

% As = 0 − 1

% Sb = 0 − 1

% Ca = 0 − 1,

the rest consisting of iron and unavoidable impurities, wherein

% C eq =% C+0.86*% N+1.2*% B,

and

% Mo+½·% W>1.2

and wherein:

x C eq *( x Mo+0.5* x W)/( x Cr+ x V+ x Nb)>8

where:

xCeq—weight percent Carbon;

xMo—weight percent Molybdenum:

xW—weight percent Tungsten;

xV—weight percent Vanadium;

xNb—weight percent Niobium;

where xCr, xV and xNb are the real weight percents even if present at concentrations lower than 0.05%.