Project nominated in the Excellence in innovation Steelie 2022
As the noise generation of the electric vehicle reducer parts is lower than that of the existing internal combustion engine, it is necessary to improve the quietness, so high dimensional precision is required after heat treatment.
In addition, as the RPM of a motor increases by 2.7 times compared to the engine (600 million cycles of internal combustion engine transmission / 1.6 billion cycles of electric vehicle reducer (based on a guaranteed distance of 300,000 km), and oil temperature rises, it is essential to develop materials that ensure durability and high-temperature stability.
The development of the materials for the reducer and transmission gear parts has been carried out in a way that increases the hardenability after the carburising heat treatment.
However, even though the durability can be secured due to the improvement of the hardenability, it can reduce quietness because the heat deformation increases after the carburising heat treatment.
Therefore, HYUNDAI Steel Company’s goal was to develop a steel grade that satisfies the conflicting properties, which is reducing thermal deformation while improving durability.
The content of Cr (chromium) and Mo (molybdenum), which are hardening elements, was reduced to decrease the carburising thermal deformation. Instead, the content of precipitated V (vanadium) element and Si (silicon), a high-temperature softening resistance element, was increased to improve durability.
As a result of the mechanical property evaluation of the material development, the carburising thermal deformation was reduced by 48% compared to the original steel, and the contact fatigue life was improved by 105% in the gear simulation test due to the increase in the precipitate by 15% and the high temperature softening resistance by 82%.
As a result of this development, Hyundai Motor/Kia Materials Specification Registration and domestic patent application (KR1020210133564) have been completed, and overseas patent applications are in progress. The company acquired NET (New Excellent Technology) by the Ministry of Trade, Industry and Energy.