Insert chip of oil-drilling tricone bit, manufacturing method thereof and oil-drilling tricone bit

An insert chip of an oil-drilling tricone bit comprising:

• an insert-chip substrate made of a cemented carbide of a first composition, said substrate including a cylindrical body and a cutting edge for drilling;
• and
• a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from said first composition, said cemented carbide coating layer covering at least 80% of a surface area of said cutting edge of said insert-chip substrate;
• wherein
• said coating layers each have a thickness, at a tip portion of said cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of said cemented carbide coating layer is in a range from 1 mm to 5 mm,
• said coating layers include an outermost cemented carbide layer and at least one coating layer besides said outermost cemented carbide layer, and said outermost cemented carbide layer has a hardness higher than that of said at least one coating layer and of said insert-chip substrate, and
• said outermost cemented carbide layer contains WC particles of an average particle size of at most 1 μm.

An insert chip of an oil-drilling tricone bit comprising:

• an insert-chip substrate made of a cemented carbide of a first composition, said substrate including a cylindrical body and a cutting edge for drilling;
• and
• a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from said first composition, said cemented carbide coating layer covering at least 80% of a surface area of said cutting edge of said insert-chip substrate;
• wherein
• said coating layers each have a thickness, at a tip portion of said cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of said cemented carbide coating layer is in a range from 1 mm to 5 mm,
• said coating layers include an outermost cemented carbide layer and at least one coating layer besides said outermost cemented carbide layer, and said outermost cemented carbide layer has a hardness higher than that of said at least one coating layer and of said insert-chip substrate, and
• only said outermost cemented carbide layer among said coating layers contains diamond particles of a particle size in a range from 10 μm to 100 μm and said diamond particles constitute 5% to 40% by volume of said outermost cemented carbide layer.

An insert chip of an oil-drilling tricone bit comprising:

• an insert-chip substrate made of a cemented carbide of a first composition, said substrate including a cylindrical body and a cutting edge for drilling;
• and
• a cemented carbide coating layer formed of at least two stacked coating layers made of a cemented carbide of a composition different from said first composition, said cemented carbide coating layer covering at least 80% of a surface area of said cutting edge of said insert-chip substrate;
• wherein
• said coating layers each have a thickness, at a tip portion of said cutting edge, in a range from 0.1 mm to 2.5 mm, and the total thickness of said cemented carbide coating layer is in a range from 1 mm to 5 mm,
• said coating layers include an outermost cemented carbide layer and at least one coating layer besides said outermost cemented carbide layer, and said outermost cemented carbide layer has a hardness higher than that of said at least one coating layer and of said insert-chip substrate, and
• said outermost cemented carbide layer has a micro Vickers hardness of at least 15 GPa.