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(11) | EP 0 687 744 A3 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Nitrogen-containing sintered hard alloy |
| (57) A nitrogen-containing sintered hard alloy includes at least 75 percent by weight
and not more than 95 percent by weight of a hard phase containing Ti, a group 6A metal
and WC in a prescribed composition, and at least 5 percent by weight and not more
than 25 percent by weight of a binder phase containing Ni, Co and unavoidable impurities,
and contains at least 5 percent by weight and not more than 60 percent by weight of
Ti in terms of a carbide or the like, and at least 30 percent by weight and not more
than 70 percent by weight of a metal belonging to the group 6A of the periodic table
in terms of a carbide, while the atomic ratio of nitrogen/(carbon + nitrogen) in the
hard phase is at least 0.2 and less than 0.5, and the nitrogen-containing sintered
hard alloy is provided with a soft layer containing a binder phase metal and WC in
its outermost surface, and has a layer which is hardly provided with the hard phase
containing WC in a portion immediately under the soft layer in a thickness of at least
3 µm and not more than 30 µm. According to this composition, it is possible to provide
a nitrogen-containing sintered hard alloy which can be employed as a cutting tool
having high reliability with no surface coating also in working under conditions bringing
a strong thermal shock. |