Steel for carburizing, carburized steel component, and method of producing the same
View Patent ↗A steel for a carburizing and a carburized steel component having a steel portion and a carburized layer with a thickness of more than 0.4 mm to less than 2 mm which is formed on an outside of the steel portion. A chemical composition of the steel for the carburizing and the steel portion of the carburized steel component satisfies simultaneously equations of a hardness parameter, a hardenability parameter, and a TiC precipitation parameter.
1. A steel for a carburizing comprising as a chemical composition, by mass %,
C: 0.07% to 0.13%,
Si: 0.0001% to 0.50%,
Mn: 0.0001% to 0.80%,
S: 0.0001% to 0.100%,
Cr: more than 1.30% to 5.00%,
B: 0.0005% to 0.0100%,
Al: 0.0001% to 1.0%,
Ti: 0.010% to 0.10%,
N: limited to 0.0080% or less,
P: limited to 0.050% or less,
O: limited to 0.0030% or less, and
a balance consisting of iron and unavoidable impurities,
wherein amounts expressed in mass % of each element in the chemical composition satisfy simultaneously
a following Equation 1 as a hardness parameter,
a following Equation 2 as a hardenability parameter, and
a following Equation 3 as a TiC precipitation parameter,
0.10<C+0.194×Si+0.065×Mn+0.012×Cr+0.078×Al<0.235 (Equation 1),
7.5<(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)<44 (Equation 2),
and
0.004<Ti—N×(48/14)<0.030 (Equation 3),
wherein a metallographic structure includes, by area %, a ferrite and a pearlite of 85% to 100% in total, and the hardness of the steel is HV 125 or less.
2. The steel for the carburizing according to claim 1 , further comprising as the chemical composition, by mass %, at least one of
Nb: 0.002% to 0.100%,
V: 0.002% to 0.20%,
Mo: 0.005% to 0.50%,
Ni: 0.005% to 1.00%,
Cu: 0.005% to 0.50%,
Ca: 0.0002% to 0.0030%,
Mg: 0.0002% to 0.0030%,
Te: 0.0002% to 0.0030%,
Zr: 0.0002% to 0.0050%,
Rare Earth Metal: 0.0002% to 0.0050%, and
Sb: 0.002% to 0.050%,
wherein the hardness parameter is defined as a following Equation 4 on behalf of the Equation 1 and the hardenability parameter is defined as a following Equation 5 on behalf of the Equation 2,
0.10<C+0.194×Si+0.065×Mn+0.012×Cr+0.033×Mo+0.067×Ni+0.097×Cu+0.078×Al<0.235 (Equation 4),
and
7.5<(0.7×Si+1)×(5.1×Mn+1)×(2.16×Cr+1)×(3×Mo+1)×(0.3633×Ni+1)<44 (Equation 5),
wherein a metallographic structure includes, by area %, a ferrite and a pearlite of 85% to 100% in total, and the hardness of the steel is HV 125 or less.
3. A method of producing the steel for the carburizing according to claim 1 , the method comprising,
a casting process to obtain a bloom,
a hot working process of hot-working the bloom to obtain a hot worked steel material, and
a slow cooling process of slow-cooling by a cooling rate of more than 0° C./s to 1° C./s in a temperature range where a surface temperature of the hot worked steel material is 800° C. to 500° C. after the hot working process.
4. The method of producing the steel for the carburizing according to claim 3 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-worked steel material after the slow cooling process.
5. A method of producing the steel for the carburizing according to claim 1 , the method comprising,
a casting process to obtain a bloom,
a hot controlled rolling process of hot-rolling the bloom by controlling conditions so that a surface temperature at an exit side of a final finish rolling becomes 700° C. to 1000° C. to obtain a hot-controlled-rolled steel material,
a rapid cooling process of rapid-cooling so that the surface temperature of the hot-controlled-rolled steel material is more than 0° C. to 500° C. after the hot controlled rolling process, and
a heating process of heating the hot-controlled-rolled steel material after the rapid cooling process at least one time or more.
6. The method of producing the steel for the carburizing according to claim 5 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-controlled-rolled steel material after the heating process.
7. A method of producing the steel for the carburizing according to claim 2 , the method comprising,
a casting process to obtain a bloom,
a hot working process of hot-working the bloom to obtain a hot worked steel material, and
a slow cooling process of slow-cooling by a cooling rate of more than 0° C./s to 1° C./s in a temperature range where a surface temperature of the hot worked steel material is 800° C. to 500° C. after the hot working process.
8. The method of producing the steel for the carburizing according to claim 7 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-worked steel material after the slow cooling process.
9. A method of producing the steel for the carburizing according to claim 2 , the method comprising,
a casting process to obtain a bloom,
a hot controlled rolling process of hot-rolling the bloom by controlling conditions so that a surface temperature at an exit side of a final finish rolling becomes 700° C. to 1000° C. to obtain a hot-controlled-rolled steel material,
a rapid cooling process of rapid-cooling so that the surface temperature of the hot-controlled-rolled steel material is more than 0° C. to 500° C. after the hot controlled rolling process, and
a heating process of heating the hot-controlled-rolled steel material after the rapid cooling process at least one time or more.
10. The method of producing the steel for the carburizing according to claim 9 , the method further comprising,
a spheroidizing annealing process of spheroidizing-annealing the hot-controlled-rolled steel material after the heating process.