Steel material for CVT sheave, CVT sheave, and method for manufacturing CVT sheave
Steel materials for continuously variable transmissions sheaves, and methods for manufacturing a continuously variable transmission sheaves, are provided. In the disclosed steel materials for continuously variable transmission sheaves, the steel materials satisfy the following expressions: 13.9≤Fn1≤15.5, and 1.20≤Fn2≤4.35 (in which Fn1=7×Cr−6×Si+4×Mn; and Fn2=Al×N×10 4 ).
1. A steel material for a CVT sheave, the steel material consisting of the following components, in terms of mass percent (mass %):
carbon (C): 0.15 mass % or more and 0.20 mass % or less,
silicon (Si): 0.21 mass % or more and 0.30 mass % or less,
manganese (Mn): 0.70 mass % or more and 0.90 mass % or less,
sulfur (S): 0.010 mass % or more and 0.025 mass % or less,
chromium (Cr): 1.80 mass % or more and 1.90 mass % or less,
aluminum (Al): 0.015 mass % or more and 0.035 mass % or less,
nitrogen (N): 0.008 mass % or more and 0.017 mass % or less, and
optionally at least one member selected from the group consisting of copper (Cu) and nickel (Ni);
where
a remainder of the steel material is iron (Fe) and incidental impurities, and of the incidental impurities, phosphorus (P) and oxygen (O) contents are as follows:
phosphorus (P): 0.030 mass % or less, and
oxygen (O): 0.0020 mass % or less; wherein
the contents of the Si, Mn, and Cr components satisfy:
the above mass % ranges, and
the following expression (1):
Fn1=7×Cr−6×Si+4×Mn (1)
where
Fn1 satisfies: 13.9≤Fn1≤15.5, and
“Cr,” “Si,” and “Mn” represent the Cr, Si, and Mn contents in mass %; and
the contents of the Al and N components satisfy:
the above mass % ranges, and
the following expression (2):
Fn2=Al×N×10 4 (2)
where
Fn2 satisfies: 1.20≤Fn2≤4.35, and
“Al” and “N” represent the Al and N contents in mass %.
2. The steel material for a CVT sheave according to claim 1 , wherein
the Cu is present at a content of no more than 0.30 mass %, and/or
the Ni is present at a content of no more than 0.25 mass %.
3. A CVT sheave formed by using a steel material for a CVT sheave as raw steel, wherein
Vickers hardness in a surface region from a sliding surface on which a CVT belt slides to 100 μm in a depth direction is 680 HV or more and 800 HV or less,
a volume fraction of retained austenite in the surface region is 13% or more and 28% or less, and
the steel material consists of the following components, in terms of mass percent (mass %):
carbon (C): 0.15 mass % or more and 0.20 mass % or less,
silicon (Si): 0.21 mass % or more and 0.30 mass % or less,
manganese (Mn): 0.70 mass % or more and 0.90 mass % or less,
sulfur (S): 0.010 mass % or more and 0.025 mass % or less,
chromium (Cr): 1.80 mass % or more and 1.90 mass % or less,
aluminum (Al): 0.015 mass % or more and 0.035 mass % or less, and
nitrogen (N): 0.008 mass % or more and 0.017 mass % or less, where
a remainder of the steel material is iron (Fe) and incidental impurities, and of the incidental impurities, phosphorus (P) and oxygen (O) contents are as follows:
phosphorus (P): 0.030 mass % or less, and
oxygen (O): 0.0020 mass % or less; wherein
the contents of the Si, Mn, and Cr components satisfy:
the above mass % ranges, and
the following expression (1):
Fn1=7×Cr−6×Si+4×Mn (1)
where
Fn1 satisfies: 13.9≤Fn1≤15.5, and
“Cr,” “Si,” and “Mn” represent the Cr, Si, and Mn contents in mass %; and
the contents of the Al and N components satisfy:
the above mass % ranges, and
the following expression (2):
Fn2=Al×N×10 4 (2)
where
Fn2 satisfies: 1.20≤Fn2≤4.35, and
“Al” and “N” represent the Al and N contents in mass %.
4. A CVT sheave formed by using a steel material for a CVT sheave as raw steel, wherein
Vickers hardness in a surface region from a sliding surface on which a CVT belt slides to 100 μm in a depth direction is 680 HV or more and 800 HV or less,
a volume fraction of retained austenite in the surface region is 13% or more and 28% or less, and
the steel material consists of the following components, in terms of mass percent (mass %):
carbon (C): 0.15 mass % or more and 0.20 mass % or less,
silicon (Si): 0.21 mass % or more and 0.30 mass % or less,
manganese (Mn): 0.70 mass % or more and 0.90 mass % or less,
sulfur (S): 0.010 mass % or more and 0.025 mass % or less,
chromium (Cr): 1.80 mass % or more and 1.90 mass % or less,
aluminum (Al): 0.015 mass % or more and 0.035 mass % or less,
nitrogen (N): 0.008 mass % or more and 0.017 mass % or less, and
at least one member selected from the group consisting of copper (Cu) and nickel (Ni), where, when present, the Cu is present at a content of no more than 0.30 mass %, and, when present, the Ni is present at a content of no more than 0.25 mass %, where
a remainder of the steel material is iron (Fe) and incidental impurities, and of the incidental impurities, phosphorus (P) and oxygen (O) contents are as follows:
phosphorus (P): 0.030 mass % or less, and
oxygen (O): 0.0020 mass % or less; wherein
the contents of the Si, Mn, and Cr components satisfy:
the above mass % ranges, and
the following expression (1):
Fn1=7×Cr−6×Si+4×Mn (1)
where
Fn1 satisfies: 13.9≤Fn1≤15.5, and
“Cr,” “Si,” and “Mn” represent the Cr, Si, and Mn contents in mass %; and
the contents of the Al and N components satisfy:
the above mass % ranges, and
the following expression (2):
Fn2=Al×N×10 4 (2)
where
Fn2 satisfies: 1.20≤Fn2≤4.35, and
“Al” and “N” represent the Al and N contents in mass %.
5. A method for manufacturing a CVT sheave, comprising:
processing the steel material for a CVT sheave according to claim 1 into a predetermined shape; and
gas carburizing a processed workpiece with a carbon potential (CP) of 0.70 mass % or more and 1.10 mass % or less.
6. A method for manufacturing a CVT sheave, comprising:
processing the steel material for a CVT sheave according to claim 2 into a predetermined shape; and
gas carburizing a processed workpiece with a carbon potential (CP) of 0.70 mass % or more and 1.10 mass % or less.
7. The CVT sheave formed according to claim 3 , wherein the silicon (Si) mass percent is 0.25 mass % or more and 0.30 mass % or less.
8. The CVT sheave formed according to claim 4 , wherein the silicon (Si) mass percent is 0.25 mass % or more and 0.30 mass % or less.
9. The CVT sheave formed according to claim 3 , wherein the Vickers hardness is 720 HV or more and 800 HV or less.
10. The CVT sheave formed according to claim 3 , wherein the Vickers hardness is 720 HV or more and 800 HV or less.