Non-Magnetic Drill Collars For well drilling NMDC The drill collars are made of modified AISI 4145H chromium molybdenum alloy steel. These drill collar bars are full-length heat treated and water quenched to obtain ASTM A-370 mechanical properties. Full mechanical and chemical mill test certifications are supplied with all drill collars. These mill test certifications guarantee a hardness range of 285 to 341 BHN and an impact value of 40 ft.-lbs. at room temperature one inch below the surface. To ensure close tolerance bores, all drill collar bars are trepanned then drifted to API specifications. Bar surface finish is â??as rolledâ?? which is original mill finish.
