Bearing steel and manufacturing method therefor
A bearing steel according to an embodiment of the present disclosure includes, as a chemical composition: 0.51 to 0.56 wt % of carbon (C); 0.30 to 0.55 wt % of silicon (Si); 0.60 to 0.90 wt % of manganese (Mn); 0.025 wt % or less (excluding 0 wt %) of phosphorus (P); 0.008 wt % or less (excluding 0 wt %) of sulfur (S); 0.01 to 0.20 wt % of chromium (Cr); 0.08 wt % or less (excluding 0 wt %) of molybdenum (Mo); 0.25 wt % or less (excluding 0 wt %) of nickel (Ni); 0.01 to 0.20 wt % of vanadium (V); 0.20 wt % or less (excluding 0 wt %) of copper (Cu); 0.003 wt % or less (excluding 0 wt %) of titanium (Ti); 0.01 to 0.05 wt % of aluminum (Al); 0.0015 wt % or less (excluding 0 wt %) of oxygen (O); 0.001 wt % or less (excluding 0 wt %) of calcium (Ca); and iron (Fe) and unavoidable impurities as a remainder.
1. A bearing steel having a composition comprising:
0.51 to 0.56 wt % of carbon (C);
0.30 to 0.55 wt % of silicon (Si);
0.60 to 0.90 wt % of manganese (Mn);
0.025 wt % or less (excluding 0 wt %) of phosphorus (P);
0.008 wt % or less (excluding 0 wt %) of sulfur (S);
0.01 to 0.20 wt % of chromium (Cr);
0.08 wt % or less (excluding 0 wt %) of molybdenum (Mo);
0.04 wt % or less (excluding 0 wt %) of nickel (Ni);
0.01 to 0.20 wt % of vanadium (V);
0.20 wt % or less (excluding 0 wt %) of copper (Cu);
0.003 wt % or less (excluding 0 wt %) of titanium (Ti);
0.01 to 0.05 wt % of aluminum (Al);
0.0015 wt % or less (excluding 0 wt %) of oxygen (O);
0.001 wt % or less (excluding 0 wt %) of calcium (Ca); and
iron (Fe) and unavoidable impurities as a remainder,
wherein the bearing steel comprises:
a substrate, and
a hardened layer formed on a surface of the substrate,
wherein the substrate comprises:
a ferrite structure, and
a pearlite structure,
the hardened layer comprises a martensite structure,
austenite crystal grains having an average diameter of 22.5 to 31.8 μm are formed on the substrate, and
austenite crystal grains having an average diameter of 5 μm or less are formed on the hardened layer.
2. A method of manufacturing the bearing steel of claim 1 , the method comprising:
continuous casting and rolling a steel; hot-forging the rolled steel; and
high-frequency quenching and tempering the hot-forged steel.
3. The method of claim 2 , wherein, in the step of hot-forging, the temperature of the hot-forging is 1,150 to 1,250 degrees C.
4. The method of claim 2 , further comprising normalizing or refining after the hot-forging.
5. The method of claim 4 , wherein, in the step of normalizing, the temperature of the normalizing is 880 to 910 degrees C.
6. The method of claim 4 , wherein the refining comprises: quenching at 850 to 880 degrees C.; and tempering at 500 to 600 degrees C.
7. The method of claim 2 , wherein, in the step of high-frequency quenching and tempering, the temperature of the high-frequency quenching is 750 to 1,000 degrees C.
8. The method of claim 2 , wherein, in the step of high-frequency quenching and tempering, the temperature of the high-frequency quenching is 780 to 850 degrees C.
9. The method of claim 2 , wherein, in the step of high-frequency quenching and tempering, the temperature of the tempering is 150 to 200 degrees C.
10. An automotive wheel bearing comprising the bearing steel of claim 1 .