Seamless steel tube which is intended to be used as a guide pipe and production method thereof

A process for manufacturing a seamless steel, the process comprising:

• manufacturing a steel;
• obtaining a solid cylindrical piece from the steel;
• perforating said solid cylindrical piece to form a steel pipe;
• rolling said steel pipe to form a rolled pipe;
• subjecting the rolled pipe to a heat treatment comprising re-heating to a austenitic temperature followed by water quenching and a tempering treatment that results in the seamless steel pipe having a microstructure having austenite grains with an average size from ASTM 10 to 20 microns,
• wherein said process is characterized by the addition of certain amounts of elements during the manufacturing and the elimination of other elements so as to produce a final composition in % by weight that contains, besides iron and inevitable impurities, the following:
• C 0.06 to 0.13
• Mn 1.00 to 1.30
• Si 0.35 Max.
• P 0.015 Max.
• S 0.003 Max.
• Mo 0.1 to 0.2
• Cr 0.10 to 0.30
• V 0.050 to 0.10
• Nb 0.020 to 0.035
• Ni 0.30 to 0.45
• Al 0.015 to 0.040
• Ti 0.020 Max.
• N 0.010 Max.
• Cu 0.2 Max.
• and also the chemical composition complying with the relationship among the alloying elements:
• 0.5≦(Mo+Cr+Ni)<1
• (Mo+Cr+V)/5+(Ni+Cu)/15≦0.14.