A piercer plug with increased wear resistance is provided. A piercer plug includes: a plug body; and a sprayed coating formed on the surface of the plug body. The sprayed coating contains an iron-based alloy and oxides thereof. The chromium concentration determined by analyzing the sprayed coating with X-ray fluorescence analysis is 3 to 20 mass %.

A piercer plug with increased wear resistance is provided. A piercer plug includes: a plug body; and a sprayed coating formed on the surface of the plug body. The sprayed coating contains an iron-based alloy and oxides thereof. The chromium concentration determined by analyzing the sprayed coating with X-ray fluorescence analysis is 3 to 20 mass %.

A method for preparing a multilayer metal composite pipe includes steps of: internally and externally grinding blank pipes; cleaning oil stains; assembling a multilayer metal pipe; drawing to reduce a diameter; performing high-speed friction welding at the pipe ends; performing heat treatment; performing four-roller cross-rolling; straightening; performing two-roller cold-rolling; performing cold-drawing to reduce the diameter; performing cold-expansion to reduce the diameter; performing precise cold-rolling; degreasing; brightening; performing surface grinding; cleaning dust; detecting multilayer metal interface bonding; detecting flaws; testing metal structure performance; and sizing and packaging. By cycling the cold-drawing, the cold-expansion, and the precision cold-rolling, key indicators such as product dimensional accuracy, surface quality, material properties, and crystal grain size can be collaboratively controlled, so as to achieve higher accuracy, better performance, and more outstanding extreme specifications. The present invention solves the problem of inconsistent extension due to differences in metal properties.

A method for preparing a multilayer metal composite pipe includes steps of: internally and externally grinding blank pipes; cleaning oil stains; assembling a multilayer metal pipe; drawing to reduce a diameter; performing high-speed friction welding at the pipe ends; performing heat treatment; performing four-roller cross-rolling; straightening; performing two-roller cold-rolling; performing cold-drawing to reduce the diameter; performing cold-expansion to reduce the diameter; performing precise cold-rolling; degreasing; brightening; performing surface grinding; cleaning dust; detecting multilayer metal interface bonding; detecting flaws; testing metal structure performance; and sizing and packaging. By cycling the cold-drawing, the cold-expansion, and the precision cold-rolling, key indicators such as product dimensional accuracy, surface quality, material properties, and crystal grain size can be collaboratively controlled, so as to achieve higher accuracy, better performance, and more outstanding extreme specifications. The present invention solves the problem of inconsistent extension due to differences in metal properties.

Provided is a round billet capable of reducing damage on a piercing plug in a method of producing a seamless metal tube with a Mannesmann process. The round billet (5), for use in a seamless metal tube, to be produced into a seamless metal tube with a Mannesmann process includes a body having a hole (6) formed in an axial direction of the body. The hole (6) includes an aperture (6a) opening at least at one end face of the round billet (5), and a tapered portion (61) continued to the aperture (6a) and having a diameter gradually increasing toward the aperture (6a).

Provided is a round billet capable of reducing damage on a piercing plug in a method of producing a seamless metal tube with a Mannesmann process. The round billet (5), for use in a seamless metal tube, to be produced into a seamless metal tube with a Mannesmann process includes a body having a hole (6) formed in an axial direction of the body. The hole (6) includes an aperture (6a) opening at least at one end face of the round billet (5), and a tapered portion (61) continued to the aperture (6a) and having a diameter gradually increasing toward the aperture (6a).

A piercer plug having good base-material deformation resistance is provided. A method of manufacturing a piercer plug (10) includes the steps of; preparing a plug body (1) including a tip portion (11) and a cylindrical portion (12) having a hole (121) usable to attach a bar and located rearward of the tip portion (11); forming a build-up layer (2) on the surface of the tip portion (11); and heating the plug body (1) such that the temperature of the tip portion (11) with the build-up layer (2) formed thereon is not lower than the austenite transformation temperature and the temperature of the cylindrical portion (12) is lower than the austenite transformation temperature.

A piercer plug having good base-material deformation resistance is provided. A method of manufacturing a piercer plug (10) includes the steps of; preparing a plug body (1) including a tip portion (11) and a cylindrical portion (12) having a hole (121) usable to attach a bar and located rearward of the tip portion (11); forming a build-up layer (2) on the surface of the tip portion (11); and heating the plug body (1) such that the temperature of the tip portion (11) with the build-up layer (2) formed thereon is not lower than the austenite transformation temperature and the temperature of the cylindrical portion (12) is lower than the austenite transformation temperature.

A high-temperature forming tool is formed at least partly of a molybdenum-based alloy having a fraction of molybdenum of 90 wt. %. The molybdenum-based alloy is in a pressed-and-sintered state and in the pressed-and-sintered state has a thermal shock resistance of at least 250 K. The thermal shock resistance is defined as the quotient of R.sub.eH/(.Math.E), where R.sub.eH is the yield point at room temperature in MPa, a is the thermal expansion coefficient in 1/K and E is the elasticity modulus in MPa.

A high-temperature forming tool is formed at least partly of a molybdenum-based alloy having a fraction of molybdenum of 90 wt. %. The molybdenum-based alloy is in a pressed-and-sintered state and in the pressed-and-sintered state has a thermal shock resistance of at least 250 K. The thermal shock resistance is defined as the quotient of R.sub.eH/(.Math.E), where R.sub.eH is the yield point at room temperature in MPa, a is the thermal expansion coefficient in 1/K and E is the elasticity modulus in MPa.