1. Normalizing
The heat treatment method most frequently used for it is normalizing, and the most suited is medium frequency induction normalizing. The Tapered Drill Rods is thin and long, and if quenched as a whole, it is easily to distort. After forging the collar and polishing the molding, the Tapered Drill Rods are normalized. The major goals of normalizing are to refine the grains, get high fatigue strength, strong damping performance, and reasonably homogeneous structure, as well as create a solid base for the quenching of the shank adapter. It is clear that one of the most crucial heat treatment steps for tapered drill rods is normalizing.
2. Quenching
The process of quenching involves heating the steel to the critical temperature (or above), maintaining the heat for a predetermined amount of time, austenitizing the steel, and then rapidly cooling the steel at a cooling rate greater than the critical cooling rate to produce martensite. The shank adapter must be quenched because the tapered drill rod shank must withstand the high-frequency impact of the rock drill piston, which is typically between HRC59 and HRC62 in hardness.
3. Tempering
The Tapered Drill Rods has to be tempered before it can be utilized after quenching. In order to reduce internal stress, the Tapered Drill Rods is heated to a temperature below Ac1, kept there for a certain period of time, and then cooled to room temperature. After quenching, we may then achieve the necessary structure and characteristics.
In conclusion, the drill rod will perform better and have a longer service life after being heat treated. To ensure the quality of the drill rods and increase their service life, drill rod makers must choose an appropriate heat treatment procedure.
