Hot forged product
There is provided a hot forged product having excellent wear resistance and fatigue strength even when the hot forged product is produced with a thermal refining treatment and a case hardening thermal treatment after hot forging omitted, and having a chemical composition consisting of, in mass %, C: 0.45 to 0.70%, Si: 0.01 to 0.70%, Mn: 1.0 to 1.7%, S: 0.01 to 0.1%, Cr: 0.05 to 0.25%, Al: 0.003 to 0.050%, N: 0.003 to 0.02% with the balance being Fe and impurities. The matrix at the depth of 500 μm to 5 mm from an unmachined surface of the forged product is a ferrite-pearlite structure, in which a pro-eutectoid ferrite area fraction is 3% or less or a pearlite structure, and the average diameter of pearlite colonies in the pearlite structure at the depth of 500 μm to 5 mm from the unmachined surface is 5.0 μm or less.
1. A hot forged product having a chemical composition consisting of, in mass %,
C: 0.45 to 0.70%,
Si: 0.01 to 0.70%,
Mn: 1.0 to 1.7%,
S: 0.01 to 0.1%,
Cr: 0.05 to 0.25%,
Al: 0.003 to 0.050%,
N: 0.003 to 0.02%,
Ca: 0 to 0.01%,
Cu: 0 to 0.15%, and
Ni: 0 to 0.15% with the balance being Fe and impurities,
wherein a matrix at a depth of 500 μm to 5 mm from an unmachined surface of the forged product is a ferrite-pearlite structure, in which a pro-eutectoid ferrite area fraction is 3% or less or a pearlite structure,
an average diameter of pearlite colonies in the pearlite structure at the depth of 500 μm to 5 mm from the unmachined surface is 5.0 μm or less, and
the hot forged product exhibits a wear resistance,
wherein an amount of wear is less than or equal to 0.0080 g when a specimen having a size of 1.5 mm by 2.0 mm by 3.7 mm is subjected to a pin-on-disk wear test.
2. The hot forged product according to claim 1 ,
wherein the chemical composition contains, in mass %, Ca: 0.0005 to 0.01%.
3. The hot forged product according to claim 2 ,
wherein the chemical composition contains, in mass %, at least one selected from a group consisting of
Cu: 0.02 to 0.15%, and
Ni: 0.02 to 0.15%.
4. The hot forged product according to claim 3 ,
wherein the hot forged product is a crankshaft.
5. The hot forged product according to claim 2 ,
wherein the hot forged product is a crankshaft.
6. The hot forged product according to claim 1 ,
wherein the chemical composition contains, in mass %, at least one selected from a group consisting of
Cu: 0.02 to 0.15%, and
Ni: 0.02 to 0.15%.
7. The hot forged product according to claim 6 ,
wherein the hot forged product is a crankshaft.
8. The hot forged product according to claim 1 ,
wherein the hot forged product is a crankshaft.
9. The hot forged product according to claim 1 ,
wherein the hot forged product exhibits a fatigue strength of greater than 400 MPa
wherein a test bar of the hot forged product having a round cross-section formed from a parallel section of the hot forged alloy has a diameter of 8 mm and opposing grip sections each having a diameter of 12 mm.