Hard metal or cermet body and method for producing the same

Details Hard metal or cermet body and method for producing the same Hard metal or cermet body and method for producing the same

2000-11-03

2003-01-14

Mai, Ngoclan (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Consolidated metal powder compositions

C428S548000, C419S013000, C419S014000, C419S016000, C419S025000, C419S038000, C419S053000, C419S057000

Reexamination Certificate

active

06506226

ABSTRACT:

SPECIFICATION
FIELD OF THE INVENTION
The invention relates to a hard metal or cermet body with a hard material phase of WC and/or at least one carbide, nitride, carbonitride and/or oxycarbonitride of at least one of the elements of Group IVa, Va or VIa of the classification of elements and a metal binder phase of Fe, Co and/or Ni, whose proportion amounts to 3 to 25% by mass.
The invention relates further to a method for producing such a hard metal or cermet body through mixing, grinding, granulation and pressing of an initial mixture containing the corresponding components and subsequent sintering thereof.
BACKGROUND OF THE INVENTION
In EP 0 344 421 A1 a cermet is proposed which should have either an average grain size of the hard material phase in the surface layer as compared to a core with a penetration depth of 0.05 mm, ranging between 0.8-1.2 times of the average grain size of the hard material phase in the cermet body core, or at the same penetration depth has a binder phase which ranges between 0.7 to 1.2 times of the corresponding average binder content of the cermet core, or wherein the hardness in the aforementioned penetration depth ranges between 0.95 and 1.1 times the average hardness of the cermet core. For the production of this cermet, the initial mixture is sintered after grinding, mixing and preliminary pressing. In a first step it is sintered under vacuum or in an inert gas atmosphere at up to 1300° C. or below, while in a second step it is sintered at over 1330° C. at a nitrogen pressure of 0.1 to 20 Torr (13.3 Pa to 2.66 Pa×10
3
Pa). The nitrogen pressure is increased with increasing temperature.
The EP 0 368 336 B1 describes a cermet substrate with a hard surface layer, wherein the region with the maximal hardness lies at a depth between 5 &mgr;m and 50 &mgr;m from the substrate surface and the substrate surface has a hardness of 20 to 90% of the maximal hardness. For the production of this cermet the prepressed mixture is subjected to an initial temperature increase up to 1100° C. in vacuum and to a subsequent temperature increase from 1100° to a temperature range between 1400° C. and 1500° C. in a nitrogen atmosphere. It is subsequently sintered in vacuum.
The EP 0 374 358 B1 describes a method for producing a cermet with 7 to 30% by weight of a binder phase and a hard phase of titanium carbide, titanium nitride and/or titanium carbonitride with 35 to 59% by weight Ti, 9 to 29% by weight W, 0.4 to 3.5% by weight Mo, 4 to 24% by weight of at least one metal from the group of Ta, Nb, V and Zr, 5.5 to 9.5% by weight N and 4.5 to 12% by weight C. The formulated, mixed, dried and prepressed mass is sintered in such a manner that the temperature is increased in vacuum to 1350° C., whereby the nitrogen atmosphere is set at 1 Torr (133 Pa) at 1350° C., the partial nitrogen pressure together with the temperature of 1350° C. are gradually increased up to the sintering temperature, whereby the nitrogen atmosphere is set at 5 Torr (665 Pa) at the sintering temperature.
The EP 0 492 059 A2 describes a cermet body, whose hardness at a penetration depth of no less than 1 mm is higher than in the cermet interior, whereby the binder content can be reduced in a layer thickness of 0.5 to 3 &mgr;m with respect to the core substrate. The cermet should have a hard material coating whose thickness ranges between 0.5 to 20 &mgr;m of carbides, nitrides, oxides and borides of titanium and Al
2
O
3
. For the production of this body a green compact is at first heated under vacuum to a temperature between 1100° C. and 1400° C., then nitrogen gas is introduced up to a pressure level at which the partial nitrogen pressure ranges between 5 and 10 Torr (665 and 1330 Pa), so that the nitrogen is removed from the substrate surface. The sintering and the subsequent cooling are performed in a non-oxidizing atmosphere, such as a vacuum or an inert gas atmosphere. After that the body is coated by CVD or PVD.
The production of a super tough cermet is proposed in EP 0 499 223, wherein the relative binder concentration in a 10 &mgr;m thick layer close to the surface is 5 to 50% of the average medium content of binder in the cermet core, and in the underlying layer of 10 &mgr;m to 100 &mgr;m penetration depth the binder content at 70 to 100% in relation to the cermet core. In the method used therefore the sintering is performed under nitrogen gas with a constant pressure of 5 to 30 Torr (665 to 3.99×10
3
Pa) and the cooling is performed under vacuum with a cooling rate of 10 to 20° C./min.
The EP 0 519 895 A1 discloses a cermet with a triple-layer border zone, wherein a first layer reaches to a depth of 50 &mgr;m TiN, the next layer to a depth of 50 to 150 &mgr;m penetration depth with a binder enrichment and the next layer of 150 &mgr;m to 400 &mgr;m is conceived with a binder reduction relative to the inner cermet core. For this purpose the sinter body is treated in an atmosphere of N
2
and or NH
3
, optionally in combination with CH
4
, CO, CO
2
at 1100° to 1350° C., for 1 to 25 hours at atmospheric pressure or at a pressure above 1.1 bar (1.1×10
5
Pa).
The cermets known to the state of the art have at their surface either different binder contents, which can be recognized by their spotted appearance, or tend to adherence of the binder to the sinter substrate, which due to the thereto related reaction, leads to changes in the composition of the contact zone. A further disadvantage of the cermets known to the state of the art is that, at increased contents of metal binder in the surface, the adhesion of thereto applied wear-resistant layers is poor. To the extent that the nickel proportion increases in the surface, CVD coating becomes impossible. Therefore the DE 44 23 451 A1 proposes a cermet which has a hard material content of 95 to 75% mass and 5 to 25% by mass Co and/or Ni binder, whereby the hard material phase consists of carbonitrides with cubic B1 crystal structure and 30 to 60% by mass Ti, 5 to 25% by mass W, 5 to 15% by mass Ta, up to 70% by mass of which can be replaced by Nb, 0 to 12% by mass Mo, 0 to 5% by mass V, 0 to 2% by mass Cr, and 0 to 1% by mass Hf and/or Zr. The (C+N) content in the carbonitride phase should be >80% by mol, whereby the nitrogen content ratio N/(C+N) ranges between 0.15 and 0.7. In a certain surface depth of 0.01 to 3 &mgr;m, the proportion of the binder phase with respect to the underlying cermet core area is lower than 30% by mass. In this zone the titanium content is 1.1 to 1.3 times higher than in the underlying cermet core area, while the contents of tungsten, tantalum, as well as any content of molybdenum, niobium, vanadium and/or chromium are present only in an amount of 0.7 to 1 times in relation to the underlying cermet core areas. In an alternative embodiment of this cermet in the same surface border zone the relative content of binder phase is 90% by mass, the relative Ti content 100% to 120% and the sum of contents of tungsten, tantalum and optionally molybdenum, niobium, vanadium, chromium ranges between 80% by mass and 110% by mass, each in relation to the inner cermet core.
This border structure according to the aforementioned reference is produced through a process of cermet manufacturing, according to which the green compact produced through mixing, grinding, granulation and pressing is at first heated under vacuum up to the melting point of the binder phase at a pressure of 10
−1
mbar (10 Pa). During the further heating from the melting temperature of the binder phase to the sintering temperature, which is maintained from 0.2 to 2 hours, and a subsequent cooling to 1200° C. a gas mixture of N
2
and Co is introduced into the oven atmosphere, with a N
2
/(N
2
+CO) ratio between 0.1 and 0.9 which fluctuates within a period of time between 40 to 240 sec around a pressure on the average of 10% to 80% of an average pressure. The average pressure as well as the aforementioned ratio are selected depending on the binder content.
The EP 0 687 744 A2 also describes a nitrogen-containing sintered ha

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