Cemented carbide and cutting tool
A cemented carbide includes a hard phase and a binder phase, wherein the hard phase has first hard phase grains each composed of tungsten carbide, second hard phase grains including a core portion and a rim portion, a composition of the core portion is represented by M1 x1 W 1-x1 C 1-y1 N y1 , a composition of the rim portion is represented by M2 x2 W 1-x2 C 1-y2 N y2 , each of the M1 and M2 is at least one metal element selected from a group consisting of a group 4 element, a group 5 element in a periodic table, chromium and molybdenum, and the binder phase includes at least one iron group element selected from a group consisting of iron, cobalt and nickel, and a 50% cumulative number grain size of the second hard phase grains is 0.01 μm or more and 1.0 μm or less.
1 . A cemented carbide comprising a hard phase and a binder phase, wherein
the hard phase has first hard phase grains and second hard phase grains,
each of the first hard phase grains is composed of tungsten carbide,
a second hard phase grain includes a core portion and a rim portion that covers at least a portion of the core portion,
a composition of the core portion is represented by M1 x1 W 1-x1 C 1-y N y1 ,
the M1 is at least one metal element selected from a group consisting of a group 4 element, a group 5 element in a periodic table, chromium and molybdenum,
the x1 is 0.70 or more and 1.00 or less,
the y1 is 0 or more and 0.90 or less,
a composition of the rim portion is represented by M2 x2 W 1-x2 C 1-y2 N y2 ,
the M2 is at least one metal element selected from a group consisting of a group 4 element, a group 5 element in the periodic table, chromium and molybdenum,
the x2 is 0.20 or more and less than 0.70,
the y2 is 0 or more and 0.90 or less,
the binder phase includes at least one iron group element selected from a group consisting of iron, cobalt, and nickel,
a 50% cumulative number grain size of the second hard phase grains is 0.01 μm or more and 1.0 μm or less,
in the cemented carbide, the number of unit regions R in each of which a percentage of the number of the second hard phase grains with respect to a total number of the second hard phase grains in a total of 48 unit regions R is less than 0.5% or is more than 5% is 14 or less among the total of 48 unit regions R, and
the total of 48 unit regions R are provided by arranging six unit regions R in a longitudinal direction and eight unit regions R in a lateral direction in an electron microscope image of the cemented carbide at an observation magnification of 10000×, each of the unit regions R being in a form of a square having each side of 1.5 μm.
2 . The cemented carbide according to claim 1 , wherein
the x1 is 0.80 or more and 1.00 or less, and
the x2 is 0.40 or more and less than 0.70, and
the 50% cumulative number grain size of the second hard phase grains is 0.01 μm or more and 0.5 μm or less.
3 . The cemented carbide according to claim 1 , wherein a 50% cumulative number grain size of the first hard phase grains is 0.1 μm or more and 1.5 μm or less.
4 . The cemented carbide according to claim 1 , wherein the cemented carbide does not include one or both of chromium and vanadium.
5 . The cemented carbide according to claim 1 , wherein the second hard phase grains exist dispersedly.
6 . The cemented carbide according to claim 1 , wherein
a content ratio of the first hard phase grains of the cemented carbide is 80 volume % or more and 99 volume % or less,
a content ratio of the second hard phase grains of the cemented carbide is 0.2 volume % or more and 3.0 volume % or less, and
a content ratio of the binder phase of the cemented carbide is 0.5 volume % or more and 19.8 volume % or less.
7 . The cemented carbide according to claim 1 , wherein
the cemented carbide consists of the hard phase, the binder phase, and an inevitable impurity,
a content ratio of the first hard phase grains of the cemented carbide is 80 volume % or more and 99 volume % or less, and
a content ratio of the second hard phase grains of the cemented carbide is 0.2 volume % or more and 3.0 volume % or less.
8 . A cutting tool comprising the cemented carbide according to claim 1 .
9 . The cemented carbide according to claim 1 , wherein the cemented carbide is prepared by:
preparing source material powders, the source material powders including tungsten carbide powder, a metal hydride powder of the at least one metal element selected from a group consisting of a group 4 element in the periodic table, a group 5 element in the periodic table, chromium, and molybdenum, a graphite powder, and an iron group element powder,
mixing the source material powders to prepare a mixed powder,
molding the mixed powder to prepare a molded powder,
sintering the molded powder to prepare a sintered powder, and
cooling the sintered powder.
10 . The cemented carbide according to claim 9 , wherein an average particle size of the metal hydride powder is 0.1 μm or more and 1.0 μm or less.
11 . The cemented carbide according to claim 9 , wherein sintering the molded powder includes:
heating at a temperature of 1350° C. to 1500° C. for 60 to 120 minutes under a mixed gas atmosphere including nitrogen gas and carbon monoxide gas, and
heating at a temperature of 1350° C. to 1500° C. and being fed with a pressure of more than 10 kPa and 30 kPa or less for 60 to 120 minutes under nitrogen gas.