Steel material for brake disc of motor vehicle having excellent wear resistance and high temperature strength and method of manufacturing the same
The present invention provides a steel material, and a method of manufacturing the same. The steel material comprises, by weight %, 0.02 to 0.07% of carbon, 0.1 to 0.5% of silicon, 0.2 to 0.7% of manganese, 0.05% or less of phosphorus, 0.02% or less of sulfur, 0.07% or less of aluminum, 0.1 to 0.5% of chromium, 0.3 to 1.0% of molybdenum, 0.05% or less of vanadium, 50 ppm or less of boron, 0.01 to 0.5% of nickel, 0.5% or less of copper, 0.02% or less of titanium, 0.05% or less of niobium, and 2 to 100 ppm of calcium, and the balance of Fe and other unavoidable impurities, and satisfies relational expressions 1 and 2 mentioned below, wherein the microstructure thereof contains, by area %, 90% or more of martensite and 10% or less of bainite. 260≤1589×[C]+228≤340 [Relational Expression 1] [C]/[Mo]≤0.250 [Relational Expression 2]
1. A steel material for a brake disc of a motor vehicle, the steel material comprising, by weight: 0.02 to 0.07% of carbon (C), 0.1 to 0.5% of silicon (Si), 0.2 to 0.7% of manganese (Mn), 0.05% or less (excluding 0) of phosphorus (P), 0.02% or less (excluding 0) of sulfur(S), 0.07% or less (excluding 0) of aluminum (Al), 0.1 to 0.5% of chromium (Cr), 0.3 to 1.0% of molybdenum (Mo), 0.05% or less (excluding 0) of vanadium (V), 50 ppm or less (excluding 0) of boron (B), 0.01 to 0.5% of nickel (Ni), 0.5% or less (excluding 0) of copper (Cu), 0.02% or less (excluding 0) of titanium (Ti), 0.05% or less (excluding 0) of niobium (Nb), and 2 to 100 ppm of calcium (Ca), with a balance of Fe and unavoidable impurities,
wherein the steel material has a Brinell hardness of 260 to 340 HB, the steel material satisfies the following Relational Expressions 1 and 2, and a microstructure includes, by area, 90% or more martensite and 10% or less of bainite:
260≤1589×[C]+228≤340 [Relational Expression 1]
[C]/[Mo]≤0.250 [Relational Expression 2]
wherein [C] and [Mo] are in % by weight.
2. The steel material of claim 1 , wherein the steel material has a yield strength at 600° C. of 300 MPa or more.
3. A method of manufacturing the steel material of claim 1 , the method comprising:
heating a steel slab in a temperature range of 1050 to 1250° C., the steel slab including, by weight: 0.02 to 0.07% of carbon (C), 0.1 to 0.5% of silicon (Si), 0.2 to 0.7% of manganese (Mn), 0.05% or less (excluding 0) of phosphorus (P), 0.02% or less (excluding 0) of sulfur(S), 0.07% or less (excluding 0) of aluminum (Al), 0.1 to 0.5% of chromium (Cr), 0.3 to 1.0% of molybdenum (Mo), 0.05% or less (excluding 0) of vanadium (V), 50 ppm or less (excluding 0) of boron (B), 0.01 to 0.5% of nickel (Ni), 0.5% or less (excluding 0) of copper (Cu), 0.02% or less (excluding 0) of titanium (Ti), 0.05% or less (excluding 0) of niobium (Nb), and 2 to 100 ppm of calcium (Ca), with a balance of Fe and other unavoidable impurities and satisfying the following Relational Expressions 1 and 2;
roughly rolling the heated steel slab in a temperature range of 950 to 1050° C. to obtain a roughly rolled bar;
subjecting the roughly rolled bar to finish hot rolling in a temperature range of 850 to 950° C. to obtain a hot rolled steel plate;
air-cooling the hot rolled steel plate to room temperature, and reheating the steel plate in a temperature range of 880 to 930° C. for a residual time 1.3t+10 minutes (t: plate thickness (mm)) or more; and
cooling the reheated hot rolled steel plate to 150° C. or lower at a cooling rate of 10° C./s or more:
260≤1589×[C]+228≤340 [Relational Expression 1]
[C]/[Mo]≤0.250 [Relational Expression 2]
wherein [C] and [Mo] are in % by weight.