Case hardening steel, carburized component, and manufacturing method of case hardening steel
View Patent ↗This case hardening steel has a chemical composition including, by mass %: C: 0.1 to 0.6%; Si: 0.02 to 1.5%; Mn: 0.3 to 1.8%; P: 0.025% or less; S: 0.001 to 0.15%; Al: over 0.05 to 1.0%; Ti: 0.05 to 0.2%; N: 0.01% or less; and O: 0.0025% or less, and further including, by mass %, one or more of Cr: 0.4 to 2.0%, Mo: 0.02 to 1.5%, Ni: 0.1 to 3.5%, V: 0.02 to 0.5%, and B: 0.0002 to 0.005%, and the balance consisting of iron and unavoidable impurities.
1. A case hardening steel wherein a chemical composition of the case hardening steel consists of, by mass %:
C: 0.1 to 0.6%;
Si: 0.02 to 1.5%;
Mn: 0.3 to 1.8%;
P: 0.025% or less;
S: 0.001 to 0.15%;
Al: over 0.05 to 1.0%;
Ti: 0.059 to 0.2%;
N: 0.01% or less;
O: 0.0025% or less, and
one or more of Cr: 0.4 to 2.0%, Mo: 0.02 to 1.5%, Ni: 0.1 to 3.5%, V: 0.02 to 0.5%, and B: 0.0002 to 0.005%, and
the balance consisting of iron and unavoidable impurities,
wherein a structure of the case hardening steel is a hot-rolled structure,
wherein in the hot-rolled structure,
a structural fraction of a bainite is 30% or less,
a ferrite grain size index is any of Nos. 8 to 11 defined in JIS G0552 dated 1998, and
a maximum diameter of Ti-based precipitates in a cross-section along longitudinal direction in a matrix of the steel is 40 μm or less.
2. A carburized component including the case hardening steel according to claim 1 , which is worked into a component shape.
3. A manufacturing method of a case hardening steel, comprising:
preparing a steel whose chemical composition consists of, by mass %:
C: 0.1 to 0.6%;
Si: 0.02 to 1.5%;
Mn: 0.3 to 1.8%;
P: 0.025% or less;
S: 0.001 to 0.15%;
Al: over 0.05 to 1.0%;
Ti: 0.05 to 0.2%;
N: 0.01% or less;
O: 0.0025% or less, and
one or more of Cr: 0.4 to 2.0%, Mo: 0.02 to 1.5%, Ni: 0.1 to 3.5%, V: 0.02 to 0.5%, and B: 0.0002 to 0.005%, and
the balance consisting of iron and unavoidable impurities; and
heating the steel at a temperature of 1150° C. or higher for 10 minutes or longer and hot-rolling the steel into a wire rod or a steel bar,
gradually cooling the steel in a temperature range of 800 to 500° C. at a cooling rate of 1° C./second or less,
hot-rolling the steel at a finishing temperature of hot rolling is 840 to 1000° C.,
wherein a structural fraction of a bainite of the steel after hot rolling is 30% or less, and
a ferrite grain size index of the steel is any of No. 8 to 11 defined in JIS G0552 dated 1998 and a maximum diameter of Ti-based precipitates in a cross-section along longitudinal direction in a matrix of the steel is 40 μm or less.