Steel for carbonitrided bearing
View Patent ↗Provided is a steel for carbonitrided bearing which excels in hardenability and also excels in toughness, wear resistance, and surface-originated flaking life after quenching and tempering. A steel for carbonitrided bearing of the present embodiment has a chemical composition containing, in mass %, C: 0.22 to 0.45%, Si: not more than 0.50%, Mn: 0.40 to 1.50%, P: not more than 0.015%, S: not more than 0.005%, Cr: 0.30 to 2.0%, Mo: 0.10 to 0.35%, V: 0.20 to 0.40%, Al: 0.005 to 0.10%, N: not more than 0.030%, and O: not more than 0.0015%, with the balance being Fe and impurities, and satisfying Formulae (1) and (2). 1.20<0.4Cr+0.4Mo+4.5V<2.60 (1) 2.7C+0.4Si+Mn+0.8Cr+Mo+V>2.20 (2)
1. A steel for carbonitrided bearing, comprising
a chemical composition consisting of, in mass %,
C: 0.25 to 0.45%,
Si: not more than 0.50%,
Mn: 0.40 to 1.50%,
P: not more than 0.015%,
S: not more than 0.005%,
Cr: 0.30 to 2.0%,
Mo: 0.10 to 0.35%,
V: 0.20 to 0.40%,
Al: 0.005 to 0.10%,
N: not more than 0.030%,
O: not more than 0.0015%,
B: 0 to 0.0050%,
Nb: 0 to 0.10%, and
Ti: 0 to 0.10%, with the balance being Fe and impurities, and satisfies Formulae (1) and (2):
1.20<0.4Cr+0.4Mo+4.5V<2.60 (1)
2.7C+0.4Si+Mn+0.8Cr+Mo+V>2.20 (2)
where each symbol of element in Formulae (1) and (2) is substituted by a content (mass %) of a corresponding element.
2. The steel for carbonitrided bearing according to claim 1 , wherein the chemical composition further contains one or more kinds selected from the group consisting of:
B: 0.0003 to 0.0050%,
Nb: 0,005 to 0.10%, and
Ti: 0.005 to 0.10%.
3. The steel for carbonitrided bearing according to claim 1 , wherein L 10 life is not less than 7.0×10 5 , where the L10 life indicates 10% failure probability, when a rolling fatigue test is performed by using a thrust-type rolling fatigue test machine, and a maximum contact interfacial pressure at a time of test is 5.0 GPa, and a repetition rate is 1800 cycle per minute, and a lubrication oil used at the time of test is admixed with gas atomized powder of high speed steel, which is classified into Vickers hardness of 750 (Hv) and a particle size of 100 to 180 μm.
4. The steel for carbonitrided bearing according to claim 1 , wherein
an evaluation index Index of toughness is not less than 950, wherein
the evaluation index Index of toughness is determined by Formula (3):
Index=σ y ×( vE 20 ) 0.1 (3)
where σy is 0.2% proof stress determined by a tensile test conforming to JIS Z2241 (2011) at room temperature, and vE 20 is an impact value determined by dividing an absorbed energy by an original sectional area of a notched part of a Charpy test specimen, where the absorbed energy is obtained by a Charpy test conforming to JIS Z2242 (2009) at room temperature.