Metal powder

#This application is a national stage application (under 35 U.S.C. §371) of PCT/EP2007/060060, filed Sep. 21, 2007, which claims benefit of German application 10 2006 045339.5, filed Sep. 22, 2006.

#Cemented hard materials as sintered and composite material consist of at least two phases, namely a metallic binder phase and one or more hard material phases. Their various properties can be weighted by means of the respective proportion of the metallic and hard phases and the desired properties of the cemented hard material, e.g. strength, hardness, modulus of elasticity, etc., can be set in this way. The hard material phase usually consists of tungsten carbide but can, depending on the application of the cemented hard material tool, also comprise cubic carbides such as vanadium carbide, zirconium carbide, tantalum carbide or niobium carbide, their mixed carbides with one another or with tungsten carbide and also chromium carbide or molybdenum carbide. It is also possible to use nitrogen-containing cubic carbides (“carbonitrides”), for example in order to influence the phase ratios of the boundary zones during sintering. Typical binder contents in the case of cemented hard materials are in the range from 5 to 15% by weight, but in the case of specific applications they can also be lower at down to 3% and higher at up to 40% by weight.

#In the case of classical cemented hard material, the metallic binder phase comprises predominantly cobalt. Due to the liquid-phase sintering and the dissolution and precipitation processes of the carbidic phase occurring during this, the metallic phase after sintering contains proportions of dissolved tungsten and carbon, often also Cr if, for example, chromium carbide is used as additive, and in the case of corrosion-resistant cemented hard materials also molybdenum. Very rarely, rhenium or ruthenium are also used as additive. The proportions of such metals which form cubic carbides are considerably lower in the binder because of the very low solubility.

#FIG. 1 illustrates the binary phase diagrams FeNi.

#FIG. 2 illustrates the binary phase diagram of FeCo.

#FIG. 3 illustrates the two boundary systems of the ternary system, FeCoNi.

#An advantageous embodiment of the invention is a process for producing a cemented hard material mixture as claimed in claim 1, wherein the overall composition of the binder comprises not more than 90% by weight of Co, not more than 70% by weight of Ni and at least 10% by weight of Fe, wherein the iron content satisfies the inequality

#Fe ≥ 100 ⁢ % - % ⁢ ⁢ Co · 90 ⁢ % ( % ⁢ ⁢ Co + % ⁢ ⁢ Ni ) - % ⁢ ⁢ Ni · 70 ⁢ % ( % ⁢ ⁢ Co + % ⁢ ⁢ Ni ) (where Fe: iron content in % by weight, % Co: cobalt content in % by weight, % Ni: nickel content in % by weight), and at least two binder powders a) and b) are used, one binder powder is lower in iron than the overall composition of the binder and the other binder powder is richer in iron than the overall composition of the binder and at least one binder powder is prealloyed from at least two elements selected from the group consisting of iron, nickel and cobalt.

#It has surprisingly been found that it is not the actual proportion of the bcc phase of the metallic binder powder which is responsible for the poor densification behavior when using prealloyed powders, but instead the bcc proportion which is to be expected from theoretical considerations and is stable at room temperature, since phase transformations of prealloyed binder powders which are mechanically induced during mix-milling of these powders which have proportions of phases which are still metastable at room temperature (and lead to transformation hardening) are clearly responsible for the poor densification behavior. The stable fcc proportion which is to be expected at room temperature from theoretical considerations is therefore critical for favorable pressing and shrinkage behavior.