Vehicle collision energy absorbing member excellent in energy absorbing performance and manufacturing method therefor

Patent metadata

Field	Value
Publication number	US-9452792-B2
Application number	US-201214116847-A
Country	US
Kind code	B2
Filing date	Apr 23, 2012
Priority date	May 12, 2011
Publication date	Sep 27, 2016
Grant date	Sep 27, 2016

Abstract

A vehicle collision energy absorbing member is excellent in collision energy absorbing performance in the axial direction upon collision. The vehicle collision energy absorbing member is formed of a high strength thin steel sheet having TS of at least 980 MPa and having an n-value and a limit bending radius Rc satisfying the following Formula: Rc/t≦1.31×ln(n)+5.21.

First claim

The invention claimed is:

1. A vehicle collision energy absorbing member formed by shaping a high strength thin steel sheet,
wherein the high strength thin steel sheet has a tensile strength TS of at least 980 MPa, and has an n-value and a limit bending radius Rc satisfying Formula (1) below:
Rc/t≦ 1.31×ln( n )+5.21  (1);

where
Rc: limit bending radius (mm),
t: sheet thickness (mm), and
n: n-value obtained for a true strain is 5% to 10%,

the high strength thin steel sheet includes a chemical composition containing, by mass %:
C: 0.14% to 0.30%;
Si: 0.01% to 1.6%;
Mn: 3.5% to 10%;
P: 0.060% or less;
S: 0.0050% or less;
Al: 0.01% to 1.5%;
N: 0.0060% or less;
Nb: 0.01% to 0.10%; and
the balance being Fe and incidental impurities, and

the high strength thin steel sheet has a microstructure including a ferrite phase by 30% to 70% in volume fraction with respect to the entire microstructure and a secondary phase other than the ferrite phase, the ferrite phase having an average grain size of 1.0 μm or smaller, the secondary phase at least containing a retained austenite phase by at least 10% in volume fraction to the entire microstructure, the retained austenite phase having an average spacing of 1.5 μm or less.

2. A vehicle collision energy absorbing member formed by shaping a high strength thin steel sheet,
wherein the high strength thin steel sheet has a tensile strength TS of at least 980 MPa, and has an n-value and a limit bending radius Rc satisfying Formula (2) below:
Rc/t≦ 1.31×ln( n )+4.21  (2);

where
Rc: limit bending radius (mm),
t: sheet thickness (mm), and
n: n-value obtained for a true strain is 5% to 10%,

the high strength thin steel sheet includes a chemical composition containing, by mass %:
C: 0.14% to 0.30%;
Si: 0.01% to 1.6%;
Mn: 3.5% to 10%;
P: 0.060% or less;
S: 0.0050% or less;
Al: 0.01% to 1.5%;
N: 0.0060% or less;
Nb: 0.01% to 0.10%; and
the balance being Fe and incidental impurities, and

the high strength thin steel sheet has a microstructure including a ferrite phase by 30% to 70% in volume fraction with respect to the entire microstructure and a secondary phase other than the ferrite phase, the ferrite phase having an average grain size of 1.0 μm or smaller, the secondary phase at least containing a retained austenite phase by at least 10% in volume fraction to the entire microstructure, the retained austenite phase having an average spacing of 1.5 μm or less.

3. The vehicle collision energy absorbing member according to claim 1 , wherein the chemical composition contains Si and Al such that total content of Si and Al (Si+Al) by mass % is at least 0.5%.

4. The vehicle collision energy absorbing member according to claim 2 , wherein the chemical composition contains Si and Al such that total content of Si and Al (Si+Al) by mass % is at least 0.5%.

5. A method of manufacturing a vehicle collision energy absorbing member comprising:
hot-rolling a steel slab to obtain a hot-rolled steel sheet;
cooling the hot-rolled steel sheet at an average cooling rate of 5° C./s to 200° C./s in a temperature range to 750° C.;
cold-rolling the cooled steel sheet at a reduction rate of 30% to 60% to obtain a cold-rolled steel sheet;
annealing the cold-rolled steel sheet at an annealing temperature to obtain a high strength thin steel sheet; and
forming the high strength thin steel sheet into a predetermined shape to obtain the vehicle collision energy absorbing member,
wherein
the annealing temperature is 650° C. to 750° C.,
an average heating rate from 300° C. to 600° C. is 1° C./s to 50° C./s, and
an average heating rate from 600° C. to the annealing temperature is 0.1° C./s to 10° C./s in the annealing,
the high strength thin steel sheet has a tensile strength TS of at least 980 MPa and an n-value and a limit bending radius Rc satisfying Formula (1) below;
Rc/t≦ 1.31×ln( n )+5.21  (1);

where
Rc: limit bending radius (mm),
t: sheet thickness (mm), and
n: n-value obtained for a true strain is 5% to 10%,

the high strength thin steel sheet includes a chemical composition containing, by mass %:
C: 0.14% to 0.30%;
Si: 0.01% to 1.6%;
Mn: 3.5% to 10%;
P: 0.060% or less;
S: 0.0050% or less;
Al: 0.01% to 1.5%;
N: 0.0060% or less;
Nb: 0.01% to 0.10%; and
the balance being Fe and incidental impurities, and

the high strength thin steel sheet has a microstructure including a ferrite phase by 30% to 70% in volume fraction with respect to the entire microstructure and a secondary phase other than the ferrite phase, the ferrite phase having an average grain size of 1.0 μm or smaller, the secondary phase at least containing a retained austenite phase by at least 10% in volume fraction to the entire microstructure, the retained austenite phase having an average spacing of 1.5 μm or less.

6. A method of manufacturing a vehicle collision energy absorbing member comprising:
hot-rolling a steel slab to obtain a hot-rolled steel sheet;
cooling the hot-rolled steel sheet at an average cooling rate of 5° C./s to 200° C./s in a temperature range to 750° C.;
cold-rolling the cooled steel sheet at a reduction rate of 30% to 60% to obtain a cold-rolled steel sheet;
annealing the cold-rolled steel sheet at an annealing temperature to obtain a high strength thin steel sheet; and
forming the high strength thin steel sheet into a predetermined shape to obtain the vehicle collision energy absorbing member;
wherein
the annealing temperature is 650° C. to 750° C.,
an average heating rate from 300° C. to 600° C. is 1° C./s to 50° C./s, and
an average heating rate from 600° C. to the annealing temperature is 0.1° C./s to 10° C./s in the annealing,
the high strength thin steel sheet has a tensile strength TS of at least 980 MPa and an n-value and a limit bending radius Rc satisfying Formula (2) below;
Rc/t≦ 1.31×ln( n )+4.21  (2);

where
Rc: limit bending radius (mm),
t: sheet thickness (mm), and
n: n-value obtained for a true strain is 5% to 10%,

the high strength thin steel sheet includes a chemical composition containing, by mass %:
C: 0.14% to 0.30%;
Si: 0.01% to 1.6%;
Mn: 3.5% to 10%;
P: 0.060% or less;
S: 0.0050% or less;
Al: 0.01% to 1.5%;
N: 0.0060% or less;
Nb: 0.01% to 0.10%; and
the balance being Fe and incidental impurities, and

the high strength thin steel sheet has a microstructure including a ferrite phase by 30% to 70% in volume fraction with respect to the entire microstructure and a secondary phase other than the ferrite phase, the ferrite phase having an average grain size of 1.0 μm or smaller, the secondary phase at least containing a retained austenite phase by at least 10% in volume fraction to the entire microstructure, the retained austenite phase having an average spacing of 1.5 μm or less.

7. The method according to claim 5 , wherein the chemical composition contains Si and Al such that total content of Si and Al (Si+Al) by mass % is at least 0.5%.

8. The method according to claim 6 , wherein the chemical composition contains Si and Al such that total content of Si and Al (Si+Al) by mass % is at least 0.5%.

Assignees

• Takagi Shusaku
• Okuda Kaneharu
• Tamai Yoshikiyo
• Fujita Takeshi
• Okitsu Yoshitaka
• Naito Tadashi
• Takaki Naoki
• Sugiura Tomoaki
• Jfe Steel Corp
• Honda Motor Co Ltd

Inventors

• Takagi Shusaku
• Okuda Kaneharu
• Tamai Yoshikiyo
• Fujita Takeshi
• Okitsu Yoshitaka
• Naito Tadashi
• Takaki Naoki
• Sugiura Tomoaki

Classifications

• C22C38/12

  containing tungsten, tantalum, molybdenum, vanadium, or niobium · CPC title

• C21D9/46

  for sheet metals · CPC title

• C21D2211/005

  Ferrite · CPC title

• C21D9/0068 Primary

  for particular articles not mentioned below · CPC title

• C22C38/06

  containing aluminium · CPC title