Hot-forged section material and common rail
View Patent ↗A rolled steel bar for hot forging consisting, by mass percent, of C: 0.25-0.50%, Si: 0.40-1.0%, Mn: 1.0-1.6%, S: 0.005-0.035%, Al: 0.005-0.050%, V: 0.10-0.30%, and N: 0.005-0.030%, and the balance of Fe and impurities, i.e., P: 0.035% or less and O: 0.0030% or less, wherein Fn1=C+Si/10+Mn/5+5Cr/22+1.65V−5S/7 is 0.90 to 1.20. The predicted maximum width of nonmetallic inclusions at the time when a cumulative distribution function obtained by extreme value statistical processing by taking the width of nonmetallic inclusion in an R 1 /2 part of a longitudinal cross section of the steel bar as W (μm) is 99.99% is 100 μm or narrower. The number density of sulfides each having a circle-equivalent diameter of 0.3 to 1.0 μm observed per unit area of the R 1 /2 part of a transverse cross section of the steel bar is 500 pieces/mm 2 or higher.
1. A hot-forged section material consisting of, in mass percent,
C: 0.25 to 0.50%,
Si: 0.40 to 1.0%,
Mn: 1.0 to 1.6%,
S: 0.005 to 0.035%,
Al: 0.005 to 0.050%,
V: 0.10 to 0.30%,
N: 0.005 to 0.030%, and
the balance being Fe and impurities,
wherein
contents of P and O in the impurities being P: 0.035% or less and O: 0.0030% or less, and
Fn1 represented by Formula (i) being 0.90 to 1.20,
wherein the hot-forged section material has
a predicted maximum width of nonmetallic inclusions, W, of 100 μm or narrower, wherein the predicted maximum width of nonmetallic inclusions is determined at a time when a cumulative distribution function obtained by extreme value statistical processing by taking a width of nonmetallic inclusion in an R 2 /2 part or a T/4 part of a longitudinal cross section of the hot-forged section material is 99.99%;
an internal structure consisting of a ferrite/pearlite structure;
an average pearlite grain size in an R 2 /2 part or a T/4 part of a transverse cross section of the section material of 150 μm or smaller; and
an area fraction of pearlite accounting for a micro-structure of a center part of the hot-forged section material of 75% or less;
wherein
R 2 =radius of the hot-forged section material;
T=thickness of the hot-forged section material;
Fn1=C+Si/10+Mn/5+5Cr/22+1.65V−5S/7 Formula (i)
wherein the symbol of an element in Formula (i) represents its content in mass %.
2. A hot-forged section material consisting of, in mass percent,
C: 0.25 to 0.50%,
Si: 0.40 to 1.0%,
Mn: 1.0 to 1.6%,
S: 0.005 to 0.035%,
Al: 0.005 to 0.050%,
V: 0.10 to 0.30%,
N: 0.005 to 0.030%,
one or more elements selected from the group consisting of Ti: 0.030 or less, Cu: 0.30% or less, Ni: 0.20% or less, Cr: 0.50% or less and Mo: 0.10% or less, and
the balance being Fe and impurities,
wherein
contents of P and O in the impurities being P: 0.035% or less and O: 0.0030% or less, and
Fn1 represented by Formula (i) being 0.90 to 1.20,
wherein the hot-forged section material has
a predicted maximum width of nonmetallic inclusions, W, of 100 μm or narrower, wherein the predicted maximum width of nonmetallic inclusions is determined at a time when a cumulative distribution function obtained by extreme value statistical processing by taking a width of nonmetallic inclusion in an R 2 /2 part or a T/4 part of a longitudinal cross section of the hot-forged section material is 99.99%;
an internal structure consisting of a ferrite/pearlite structure;
an average pearlite grain size in an R 2 /2 part or a T/4 part of a transverse cross section of the section material of 150 μm or smaller; and
an area fraction of pearlite accounting for a micro-structure of a center part of the hot-forged section material of 75% or less;
wherein
R 2 =radius of the hot-forged section material;
T=thickness of the hot-forged section material;
Fn1=C+Si/10+Mn/5+5Cr/22+1.65V−5S/7 Formula (i)
wherein the symbol of an element in Formula (i) represents its content in mass %.
3. A common rail comprising the hot-forged section material of claim 1 .
4. A common rail comprising the hot-forged section material of claim 2 .