Automobile chassis part excellent in low cycle fatigue characteristics and method of production of same
View Patent ↗An automobile chassis part which is excellent in low cycle fatigue characteristics, characterized by being formed by steel which contains, by mass %, C: 0.02 to 0.10%, Si: 0.05 to 1.0%, Mn: 0.3 to 2.5%, P: 0.03% or less, S: 0.01% or less, Ti: 0.005 to 0.1%, Al: 0.005 to 0.1%, N: 0.0005 to 0.006%, and B: 0.0001 to 0.01 and has a balance of Fe and unavoidable impurities, in which 80% or more of the part structure comprises a bainite structure and in which a portion where a ratio R/t of the thickness “t” and external surface curvature radius R is 5 or less has an X-ray half width of an (211) plane of 5 (deg) or less.
1. An automobile chassis part which is excellent in low cycle fatigue characteristics comprising a steel which contains, by mass %,
C: 0.02 to 0.10%,
Si: 0.05 to 1.0%,
Mn: 0.3 to 2.5%,
P: 0.03% or less,
S: 0.01% or less,
Ti: 0.005 to 0.1%,
Al: 0.005 to 0.1%,
N: 0.0005 to 0.006%, and
B: 0.0001 to 0.01 and
has a balance of Fe and unavoidable impurities,
wherein the automobile chassis part has a portion having a ratio of external surface curvature radius R/thickness t of 5 or less,
wherein the automobile chassis part which is excellent in low cycle fatigue characteristics has 80% or more of the part structure being a bainite structure, and
wherein the portion has an X-ray half width of an (211) plane of 5 (deg) or less.
2. The automobile chassis part which is excellent in low cycle fatigue characteristics as set forth in claim 1 , wherein the steel which forms said automobile chassis part further contains, by mass %, one or more elements which are selected from
Cu: 0.005 to 1.0%,
Ni: 0.005 to 1.0%,
Cr: 0.03 to 1.0%,
Mo: 0.1 to 0.5%,
Nb: 0.003 to 0.2%,
V: 0.001 to 0.2%,
W: 0.001 to 0.1%,
Ca: 0.0001 to 0.02%,
Mg: 0.0001 to 0.02%,
Zr: 0.0001 to 0.02%, and
REM: 0.0001 to 0.02%.
3. A method of production of the automobile chassis part which is excellent in low cycle fatigue characteristics according to claim 1 , the method comprising heating a steel slab which contains, by mass %,
C: 0.02 to 0.10%,
Si: 0.05 to 1.0%,
Mn: 0.3 to 2.5%,
P: 0.03% or less,
S: 0.01% or less,
Ti: 0.005 to 0.1%,
Al: 0.005 to 0.1%,
N: 0.0005 to 0.006%, and
B: 0.0001 to 0.01%
and has a balance of Fe and unavoidable impurities,
to 1070° C. to 1300° C., then
hot rolling by a finish rolling end temperature of 850° C. to 1070° C., then
cooling by a cooling speed V (° C./sec) which satisfies formula (A) down to 500° C. or less, then
forming a pipe so that a pipemaking strain Δε of an outermost surface of the steel material in a breakdown process becomes a range of the following formula (B) at the time of an outside diameter D and a thickness “t”, then
press-forming the pipe:
300 /M≦V≦ 3000 /M (A)
0.7 t /( D−t )≦Δε≦1.2 t /( D−t ) (B)
where, M =exp{6.2(C+0.27Mn+0.2Cr+0.05Cu+0.11Ni+0.25Mo)+0.74} (C)
the values of C, Mn, Cr, Cu, Ni, and Mo of formula (C) are mass %.
4. A method of production of the automobile chassis part which is excellent in low cycle fatigue characteristics according to claim 2 , the method comprising heating a steel slab which contains, by mass %,
C: 0.02-0.10%,
Si: 0.05 to 1.0%,
Mn: 0.3 to 2.5%,
P: 0.03% or less,
S: 0.01 or less,
Ti: 0.005 to 0.1%,
Al: 0.005 to 0.1%,
N: 0.0005 to 0.006%,
B: 0.0001 to 0.01%, and
one or more elements which are selected from
Cu: 0.005 to 1.0%
Ni: 0.005 to 1.0%
Cr: 0.03 to 1.0%
Mo: 0.1 to 0.5%
Nb: 0.003 to 0.2%,
V: 0.001 to 0.2%,
W: 0.001 to 0.1%,
Ca: 0.0001-0.02%,
Mg: 0.0001-0.02%,
Zr: 0.0001 to 0.02%,
REM: 0.0001 to 0.02%,
and has a balance of Fe and unavoidable impurities,
to 1070° C. to 1300° C., then
hot rolling by a finish rolling end temperature of 850° C. to 1070° C., then
cooling by a cooling speed V (° C./sec) which satisfies formula (A) down to 500° C. less,
forming a pipe so that a pipemaking strain Δε of an outermost surface of the steel material in a breakdown process becomes a range of the following formula (B) at the time of an outside diameter D and a thickness “t”, then
press-forming the pipe:
300 /M≦V≦ 3000 /M (A)
0.7 t /( D−t )≦Δε≦1.2 t /( D−t ) (B)
where, M =exp{6.2(C+0.27Mn+0.2Cr+0.05Cu+0.11Ni+0.25Mo)+0.74} (C)
the values of C, Mn, Cr, Cu, Ni, and Mo of formula (C) are mass %.