Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2002-04-09
2004-08-10
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S244000, C075S246000, C419S011000, C419S014000, C419S028000, C419S049000
Reexamination Certificate
active
06773482
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 of Austrian Patent Application No. 587/2001, filed Apr. 11, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cold work steel alloy for the manufacture of parts by powder metallurgy, particularly tools, with a high degree of toughness and hardness as well as resistance to wear and material fatigue.
2. Discussion of Background Information
As a rule, tools and tool parts are stressed in many different ways, which necessitates a corresponding property profile of the same. However, creating a particularly good suitability for one type of stress of the material is naturally associated with a deterioration of the resistance of the same to other stresses, so that in many cases several property features should be present at a high level for a high functional quality of a tool, in other words, the functional properties of a tool represent a compromise regarding the respective individual material values. However, for economic reasons there is a general desire to have tools or parts available with overall improved material properties.
Heavy-duty tool steel components consistently have a hard phase component of carbides and a matrix phase part accepting these, which phases depend on the chemical composition of the alloy, particularly regarding their proportions in the material.
With a conventional production with a solidification of the alloy in casting molds, its respective content of carbon and carbide-forming elements is limited due to the solidification kinetics because, with high contents, the carbides primarily precipitated from the melt result in a coarse, inhomogeneous material structure, thus creating poor mechanical properties and adversely affecting, or ultimately precluding, the material's workability.
In order on the one hand to make it possible to increase the concentrations of the carbide-forming elements and the carbon proportion with regard to an increased carbide proportion and thus an improved wear resistance of the material, while on the other hand still ensuring adequate workability, homogeneity and toughness of the parts or tools made therefrom, a manufacture of the same by powder metallurgy is to be provided.
A manufacture of materials by powder metallurgy (PM) essentially includes gas or nitrogen atomization or fragmentation of a steel melt into fine droplets which are solidified into metal powder at a high solidification rate, placing and compressing the metal powder into or in a capsule, sealing the capsule and heating and hot isostatic pressing (HIP) of the powder in the capsule to produce a dense, homogeneous material. A PM material produced in this way can be used directly as-HIPed for manufacturing parts or tools, or subjected beforehand to a hot working, e.g., by forging and/or rolling.
In terms of stress, highly stressed tools or parts, e.g., knives, punches, dies and the like simultaneously require the material to have resistance to abrasive wear, a high degree of toughness and resistance to fatigue. A high proportion of hard, optionally coarse carbides, preferably monocarbides, should be aimed for to reduce wear, although the toughness of the material is reduced with an increasing proportion of carbides. On the other hand, high matrix hardness and low crack initiation by carbide grains and nonmetallic inclusions promote resistance to fatigue, i.e., essentially the absence of cracking at very high pulsating or changing mechanical straining of the material.
As mentioned above, the functional quality of parts or tools represents a compromise between wear resistance, toughness and resistance to fatigue of the material in a thermally treated state. In terms of a general improvement in the quality of cold work steels, attempts have long been made in the technical field to improve the steel property profile as a whole.
SUMMARY OF THE INVENTION
Taking into account the requirements, the object of the present invention is to simultaneously increase the mechanical characteristics in a thermally treated state, i.e., the bend fracture strength, impact bending work and wear resistance of the tool steel material in a quality assured way.
This object is attained according to the invention with a cold work steel alloy containing in percent by weight:
Carbon (C)
2.05 to 2.65
Silicon (Si)
up to 2.0
Manganese (Mn)
up to 2.0
Chromium (Cr)
6.10 to 9.80
Tungsten (W)
0.50 to 2.40
Molybdenum (Mo)
2.15 to 4.70
Vanadium (V)
7.05 to 9.0
Niobium (Nb)
0.25 to 2.45
Cobalt (Co)
up to 10.0
Sulfur (S)
up to 0.3
Nitrogen (N)
0.04 to 0.22
Nickel (Ni)
up to 1.50
and accompanying elements up to 2.6 and production-related impurities with the balance being iron (Fe) for the powder metallurgical manufacture of parts with a high degree of toughness and hardness as well as resistance to wear and material fatigue, in particular tools, which parts have an oxygen (O) content of less than 100 ppm and a content and configuration of nonmetallic inclusions corresponding to a K0 value of a maximum of 3 according to testing according to DIN 50 602.
Accordingly, the present invention provides a cold work steel alloy comprising, in percent by weight:
C
2.05 to 2.65
Si
up to 2.0
Mn
up to 2.0
Cr
6.10 to 9.80
W
0.5 to 2.4
Mo
2.15 to 4.70
V
7.05 to 9.0
Nb
0.25 to 2.45
Co
up to 10.0
S
up to 0.3
N
0.04 to 0.32
Ni
up to 1.50
accompanying elements
up to 2.6
as well as production-related impurities, with the balance being iron. The alloy has an oxygen content of less than 100 ppm and a content of nonmetallic inclusions corresponding to a K0 value of a maximum of 3 when tested according to DIN 50 602.
In one aspect, the nitrogen content of the alloy is up to 0.22 percent by weight. In another aspect, the alloy comprises one or more element(s) in the following weight percentages: C 2.30 to 2.59; Si 0.80 to 1.50; Mn 0.30 to 1.40; Cr 6.12 to 7.50; Ni up to 1.0; W 0.60 to 1.45; Mo 2.40 to 4.40; V 7.40 to 8.70; Nb 0.50 to 1.95; N 0.06 to 0.25; and the value (Mn-S) is at least 0.19. In yet another aspect, the alloy comprises one or more element(s) in the following weight percentages: Si 0.85 to 1.30; Mn 0.40 to 0.80; Cr 6.15 to 6.95; Ni up to 0.90; Mo 3.55 to 4.40; V 7.80 to 8.59; Nb 0.75 to 1.45; and N 0.06 to 0.15.
In another aspect, the cold work steel alloy is in the form of a part, e.g., in the form of a tool. In a still further aspect, the alloy is in the form of a metal powder. Said metal powder may have a grain size distribution wherein at least 60% of the grains have a grain size of not more than 100 &mgr;m and/or may have been produced by gas (e.g., nitrogen) atomization of a liquid alloy.
In yet another aspect, the alloy in the form of a part comprises monocarbides having a diameter of less than 10 &mgr;m, e.g., less than 4 &mgr;m. In a further aspect, the part has been produced by a process comprising hot isostatic pressing of a metal powder. The metal powder may have a grain size distribution wherein at least 60% of the grains have a grain size of not more than 100 &mgr;m.
The present invention also provides a method for making a part of a cold work steel alloy, said method comprising conditioning and atomizing with a gas a liquid alloy which comprises, in percent by weight:
C
2.05 to 2.65
Si
up to 2.0
Mn
up to 2.0
Cr
6.10 to 9.80
W
0.50 to 2.40
Mo
2.15 to 4.70
V
7.05 to 9.0
Nb
0.25 to 2.45
Co
up to 10.0
S
up to 0.3
N
0.04 to 0.32
Ni
up to 1.50
accompanying elements
up to 2.6
as well as production-related impurities, with the balance being iron. The gas is nitrogen having a purity of at least 99.999%. Thereby a metal powder with a grain size distribution wherein at least 60% of the grains have a grain size of not more than 100 &mgr;m is produced. Thereafter, while maintaining the nitrogen atmosphere and avoiding a physisorption of oxygen at the grain surfaces, th
Liebfahrt Werner
Rabitsch Roland
Bohler Edelstahl GmbH
Greenblum & Bernstein P.L.C.
Mai Ngoclan
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