METHOD OF MAKING DRILLING MACHINE DRILL STEMS Russian patent published in 2012 - IPC C21D8/10 E21B17/00 C23C8/24 

FIELD: machine building.

SUBSTANCE: tubular billet from alloyed steel is divided into measured sections. Said sections are subjected to tempering at optimum temperature of their heating to ensure equality of preset core and billet outer surface hardness values and, at a time, maximum hardness of bar surface of up to 80 HRA in nitrogen hardening, as well as fourfold reduction in nitrogen hardening time. After tempering, curvature of tube sections is driven to process-oriented value of <1 mm per 1000 mm of length. Section end faces, iner and outer surfaces are machined and formed. Formed section is subjected to treatment by hitrogen hardening.

EFFECT: stable transfer of percussion power, higher reliability and longer life.