A Steel Material For Drill Bits (Part 2)

3.3 High Magnification Examination

Samples are taken from the R/2 position of the rolled steel bars. These samples are subjected to tests for non-metallic inclusions, austenite grain size, and banded structure. Furthermore, the microstructure of the samples is analyzed in detail under a microscope to ensure compliance with the required specifications.

3.4 Mechanical Properties

For mechanical performance evaluation, samples are selected from any rolling heat batch of steel bars. These are subjected to a heat treatment process, including quenching at 870–950°C followed by tempering at 200°C. The tensile properties at room temperature (20°C) and Charpy impact energy absorption values are tested in accordance with relevant standards. To ensure comprehensive comparative analysis, Charpy impact tests are conducted using both “U”-shaped and “V”-shaped notched specimens.

4. Conclusions

4.1 By carefully selecting raw materials and employing advanced processes such as electric furnace smelting, LF external refining, vacuum degassing, vertical continuous casting of round billets, and subsequent annealing, it is possible to produce high-quality continuous casting billets.

4.2 Using continuous casting billets directly for rolling, coupled with scientifically designed rolling deformation parameters and post-rolling annealing processes, ensures excellent surface and internal quality. Adequate allowance for peeling also contributes to achieving superior product standards.

4.3 By adopting well-planned production routes and carefully designed process parameters, steel bars for drill bits that meet stringent technical requirements can be manufactured. These steel bars exhibit outstanding indicators and excellent overall performance.

4.4 The carbon (C) element distribution in vertically cast round billets exhibits a symmetrical inverted “N” trend from the billet edge to the center. Further studies and control measures are required in future production to better understand and manage the billet solidification mechanism and composition distribution.