미량의 Cr 첨가량과 열처리 조건이 회주철 GC250 기지의 브레이크 디스크 로터용 소재에 미치는 영향에 관한 연구

Abstract

In this study, Fe-Cr alloy was added to the gray cast iron GC250, which is a disc rotor material of a brake system that is directly related to automobile safety, braking, and energy reuse to observe changes in the properties of the material according to the Cr content, In addition, through heat treatment, changes in material properties of alloying elements were observed according to micro-structure control. In order to design the material alloy composition, the brake disc materials from advanced companies were analyzed, and with reference to the result, a designed alloys with Cr contents of 0.1%, 0.2%, and 0.3% were cast using a high-frequency induction furnace to determine the change in physical properties according to the amount of Cr added in the ferro-alloys. Normalizing was conducted with a box furnace to remove the internal stress and control the structure of the ferro-alloy, as a result, it was confirmed that the ferrite structure was transformed into a pearlite structure in which cementite and ferrite were laminated and nitriding heat-treatment was conducted using atmosphere box furnace to improve the surface hardness of the designed alloy. It was confirmed that the optimal conditions for normalizing are the temperature of 930℃, time of 8hrs, and air atmosphere, and the optimal conditions for nitriding heat treatment are temperature of 560℃, time of 5hrs, atmosphere of N2 1.5m3/h, NH3 15m3/h, CO2 0.3m3/h. As a result of comparing the physical properties of ferro-alloy according to the Cr content through the above optimal conditions, the designed alloy with a Cr content of 0.1% achieved a tensile strength of 268 MPa and a surface hardness of 251 HBW 10/3 000, which were higher in hardness and strength than other conditions. Compared to gray cast iron GC250, the existing brake disc material, the tensile strength increased by about 58% and the surface hardness by about 21%.