A piercing plug includes a plug main body, and a sprayed coating which is formed on a surface of the plug main body and includes iron and iron oxide. A chemical composition of the sprayed coating includes, in addition to the iron and the iron oxide, by mass %, C: 0.015% to 0.6%, Si: 0.05% to 0.5%, Mn: 0.1% to 1.0%, and Cu: 0 to 0.3%.

A piercing plug includes a plug main body, and a sprayed coating which is formed on a surface of the plug main body and includes iron and iron oxide. A chemical composition of the sprayed coating includes, in addition to the iron and the iron oxide, by mass %, C: 0.015% to 0.6%, Si: 0.05% to 0.5%, Mn: 0.1% to 1.0%, and Cu: 0 to 0.3%.

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 rolling rod configured as an inner tool in the production of seamless hollow bodies, such as seamless pipes. The rolling rod has a nitrided surface layer and may consist of a heat-resistant steel material having a chromium equivalent calculated by a formula, as well as has a minimum hardness, yield point and tensile strength. A seamlessly hot-rolled, metallic hollow body is produced by a stretch-forming procedure in a multiple-stand rolling mill via the rolling rod which is threaded into the hollow block. Prior to threading the rolling rod into the hollow block, the rolling rod is provided with a liquid lubricant and is subsequently dried. The rolling rod is threaded in with a clearance with respect to the inner diameter of the hollow block. Prior to threading-in the rod, the hollow block may have an average temperature of at least 1000 C., with the rod having a determined speed.

A rolling rod configured as an inner tool in the production of seamless hollow bodies, such as seamless pipes. The rolling rod has a nitrided surface layer and may consist of a heat-resistant steel material having a chromium equivalent calculated by a formula, as well as has a minimum hardness, yield point and tensile strength. A seamlessly hot-rolled, metallic hollow body is produced by a stretch-forming procedure in a multiple-stand rolling mill via the rolling rod which is threaded into the hollow block. Prior to threading the rolling rod into the hollow block, the rolling rod is provided with a liquid lubricant and is subsequently dried. The rolling rod is threaded in with a clearance with respect to the inner diameter of the hollow block. Prior to threading-in the rod, the hollow block may have an average temperature of at least 1000 C., with the rod having a determined speed.

A piercer plug with increased life and a method of manufacturing it are provided. The piercer plug 1 includes a tip portion 2 and a trunk portion 3 made of the same material as the tip portion 2 and continuous to the tip portion 2. The trunk portion 3 includes a cylindrical portion 5 having a hole used for attaching a bar. The tip portion 2 is harder than the cylindrical portion 5.

A piercer plug with increased life and a method of manufacturing it are provided. The piercer plug 1 includes a tip portion 2 and a trunk portion 3 made of the same material as the tip portion 2 and continuous to the tip portion 2. The trunk portion 3 includes a cylindrical portion 5 having a hole used for attaching a bar. The tip portion 2 is harder than the cylindrical portion 5.

A piercing plug of the present invention includes: a plug body; a NiCr layer formed on a surface of the plug body; and a sprayed coating formed on a surface of the NiCr layer. The plug body contains, by mass %, 20 to 30% of Cr, 30 to 55% of Ni, 0.005 to 0.5% of C, 0.1 to 1.0% of Si, 0.2 to 1.5% of Mn, and at least one of Mo and W which satisfy a following conditional expression (A), and remainder including Fe and impurities.
1.5%Mo+0.5W8.5%(A)

A piercing plug of the present invention includes: a plug body; a NiCr layer formed on a surface of the plug body; and a sprayed coating formed on a surface of the NiCr layer. The plug body contains, by mass %, 20 to 30% of Cr, 30 to 55% of Ni, 0.005 to 0.5% of C, 0.1 to 1.0% of Si, 0.2 to 1.5% of Mn, and at least one of Mo and W which satisfy a following conditional expression (A), and remainder including Fe and impurities.
1.5%Mo+0.5W8.5%(A)