Electric motors are required to deliver high instantaneous power and power density. Due to the need for variable speed operation, they must also maintain high efficiency across a wide range of speeds. In addition, electric motors must possess strong overload capacity, high starting torque, and rapid torque response. These performance demands place stringent requirements on the motor shaft material, which must exhibit excellent strength, toughness, and structural stability under challenging operating conditions.
To meet the operational demands of motor shafts, specific technical requirements have been established for the mechanical properties and microstructure of forged round bars. One critical aspect is the enhanced longitudinal impact toughness. These bars must perform well in impact tests at -40°C, with absorbed energy values exceeding the standard room-temperature requirements outlined in EN 10083-3:2006 (Delivery technical conditions for alloy steels – Part 3).
After heat treatment, 42CrMo4 forged bars must meet defined standards for tensile strength and impact toughness. In the hardening process, when water quenched at 850°C, the grain size reaches grades 6–8, with the maximum allowable non-uniform grain size not exceeding grade 5. When subjected to austenitizing at 850°C for 1.5 hours followed by water quenching, grain size analysis per ASTM E112 indicates a result of grade 6–7, fully compliant with the required grade 6–8 range. Due to the elongation-only forging process, a certain degree of banded structure is present in the material.
Through systematic testing using both small and large samples, the optimal heat treatment process for these forged bars has been identified as quenching at 850°C followed by tempering at 640°C. This treatment results in a uniform and fine-tempered sorbite microstructure. The refined microstructure significantly enhances the bar’s overall mechanical performance, ensuring that it meets all technical criteria related to strength, toughness, and microstructural uniformity required for motor shaft applications.
In conclusion, 42CrMo4 forged round bars—when processed using carefully controlled heat treatment procedures—can fully meet the high-performance standards demanded by modern electric motors. This makes them a reliable and preferred material choice for motor shaft manufacturing in industries that value both efficiency and durability under extreme conditions.
Post time: May-16-2025
