NOVELTY - A drill pipe tool joint (1) comprises: a pin (2) including a male threaded portion (23) at an outer surface (21); and a box (3) including a female threaded portion (33) at an inner surface (31), the female threaded portion to be screwed and fastened to the male threaded portion in a contacting zone consisting of a male threaded contacting surface and a female threaded contacting surface; where at least a portion of the male threaded contacting surface or a portion of the female threaded contacting surface is a surface layer consisting of a hard metal.    USE - The drill pipe tool joint is useful in well drilling for oil, natural gas, shale gas, geothermal and the like.    ADVANTAGE - The drill pipe tool joint has optimized surface hardness for repeating make-up/break-out operation without the use of a screw grease when drill pipes used in well drilling for oil, natural gas, shale gas, geothermal and the like are screwed together, thus being environment-friendly, as well as improving operating efficiency.    DETAILED DESCRIPTION - A drill pipe tool joint (1) comprises: a pin (2) including a male threaded portion (23) at an outer surface (21); and a box (3) including a female threaded portion (33) at an inner surface (31), the female threaded portion to be screwed and fastened to the male threaded portion in a contacting zone consisting of a male threaded contacting surface and a female threaded contacting surface; where at least a portion of the male threaded contacting surface or a portion of the female threaded contacting surface is a surface layer consisting of a hard metal and respectively at least a portion of the female threaded contacting surface or a portion of the male threaded contacting surface is a surface layer consisting of a soft material and where the both surface portions are contacting surfaces after screwing. INDEPENDENT CLAIMS are included for:    (1) a drill pipe (4) which comprises: a pipe body (50); and a pin (2) including a male threaded portion (23) at an outer surface (21); and a box (3) including a female threaded portion (33) at an inner surface (31), the female threaded portion to be screwed and fastened to a male threaded portion of another drill pipe of the same kind, in a contacting zone consisting of a male threaded contacting surface and a female threaded contacting surface; where at least a portion of the male threaded contacting surface or a portion of the female threaded contacting surface is a surface layer consisting of a hard metal and respectively at least a portion of the female threaded contacting surface or a portion of the male threaded contacting surface is a surface layer consisting of a soft material and where the both surface portions are contacting surfaces after screwing; and    (2) a method of assembling drill pipes, where the pins including the male threaded portion and the boxes including the female threaded portion are devoid of dope or of lubricant grease when being screwed and fastened for assembling.    DESCRIPTION OF DRAWING(S) - The drawing shows a whole structure of a drill pipe tool joint.    Drill pipe tool joint (1)    Pin (2)    Box (3)    Drill pipe (4)    Male threaded portion (23)    Pipe body (50)