Rolling rod as an inner tool in the production of seamless metal hollow bodies and method for producing a metal hollow body

A method for producing a seamless, hot-rolled, metallic hollow steel pipe comprising:

• producing a hollow block that is subject to a stretch-forming procedure in a multiple-stand rolling mill;
• applying a liquid lubricant to a rolling rod for the multiple-stand rolling mill, with the rolling rod having a surface comprising a nitriding layer, wherein the rolling rod comprises a heat-resistant steel material having a chromium equivalent Creq. of more than 6.5, calculated according to Creq.=% Cr+% Mo+1.5×% Si+0.5×% Nb+2×% Ti, having a minimum hardness of 200 HV 0.5, measured 0.5 mm below the surface of the rolling rod, having a yield point of at least 450 MPa at 500° C. and having a tensile strength of at least 600 MPa at 500° C., and that starting from the surface, the nitriding layer has a depth of more than 0.15 mm and a nitriding hardness of more than 950 HV 0.5;
• drying the rolling rod after said applying said liquid lubricant to the rolling rod;
• performing said stretch-forming procedure on the hollow block in the multiple-stand rolling mill using the rolling rod after said drying the rolling rod, wherein said stretch-forming comprises threading the rolling rod into the hollow block
• with a clearance with respect to an inner diameter of the hollow block of at least 10 mm, and immediately prior to commencement of threading-in of the rod, the hollow block has an average temperature of at least 1000° C. and a speed of the rod VST during rolling in the rolling mill satisfies at least a plurality of conditions such that:
• VSTmax=0.9×rod length/rolling time of last stand and VSTmax=0.9×VMmin, wherein VMmin is a minimum speed of the hollow block during rolling in the rolling mill;
• and forming the pipe.