Non-Metallic Inclusions
Non-metallic inclusions such as oxides and sulfides in steel can reduce its mechanical properties and worsen the processability of gear steel, thereby affecting the service life of automotive carburized gears. Non-metallic inclusion levels are rated according to ASTM E45. The optimization of LF and RH refining processes facilitates the removal and flotation of inclusions. The steel has high purity, with non-metallic inclusions well-controlled.
Banded Structure
Severe banded structures can affect carburization uniformity, increase quenching deformation, and reduce the dimensional accuracy of carburized gears. During production, the content of harmful elements, gases, and inclusions in the steel is minimized, the pouring temperature is lowered, the cooling rate is increased, and electromagnetic stirring is applied. A high-rigidity and large-deformation process is adopted, along with an increased rolling (or forging) ratio, to strictly control the degree of banded structure. The banded structure is rated according to relevant standards, with the technical requirement specifying a grade not exceeding 2.0. Cross-sectional metallographic examination confirmed that the steel’s microstructure consists of ferrite and pearlite, with no significant network ferrite or acicular ferrite defects detected, indicating a desirable microstructure.
Grain Size
Grain size is tested using relevant methods, with the technical requirement specifying an austenite grain size grade no coarser than 6.0. A reasonable hot-working process is adopted, and the steelmaking process ensures an appropriate residual aluminum content in the steel, resulting in fine and uniform grains that meet technical requirements. Being an inherently fine-grained steel, it provides good support for subsequent heat treatments.
End Quench Hardenability
This steel is subjected to mutual friction under high-speed operation. If the material hardness is low, it will wear quickly. If the hardenability is poor, the wear rate of the gear accelerates once a thin hardened layer is worn, leading to material failure and potential danger. Therefore, the J6, J9, and J15 end quench performance must be controlled. Here, J6, J9, and J15 refer to the hardness values measured at 6 mm, 9 mm, and 15 mm from the quenched end during end-quench testing, expressed as Rockwell Hardness C (HRC) values. The steel exhibits stable hardenability with low dispersion, meeting technical requirements, indicating a reasonable compositional design.
Post time: Jan-24-2025
