US 9,540,720 B2 · High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having excellent formability and small material anisotropy with ultimate tensile strength of 980 MPa or more

Abstract

Disclosed is a high-strength hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more. The hot-dip galvanized steel sheet includes a hot-dip galvanized layer formed on a surface of a base steel plate. The base steel plate contains C, Si, Mn, O, P, S, Al and N within predetermined ranges and a balance including Fe and inevitable impurities. The hot-dip galvanized layer contains Fe at less than 7 mass % or 7 to 15 mass % and a balance including Zn, Al, and inevitable impurities.

Drawings

Drawings are temporarily unavailable. Open the PDF at USPTO

Drawings

Claims6

Dependent claims

A high-strength hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the hot-dip galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet,

wherein the base steel sheet contains:
by mass %,
C:
0.1 to less than 0.40%;
Si:
0.5 to 3.0%;
Mn:
1.5 to 3.0%;
O:
0.0001 to 0.006%;
P:
0.0001 to 0.04%;
S:
0.0001 to 0.01%;
Al:
0.0005 to 2.0%;
N:
0.0005 to 0.01%;
and
a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, contains residual austenite of 8 to 27%, by volume fraction, and contains bainite and a balance being martensite or less than 10% of pearlite,
an average value of pole densities of orientation groups {100} <011> to {223} <110> represented by each of crystal orientations {100} <011>, {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> in a sheet thickness range of ⅝ to ⅜ from the surface of the base steel sheet is 6.5 or less and a pole density of a crystal orientation {332} <113> is 5.0 or less, and
the hot-dip galvanized layer contains Fe:
less than 7 mass % and a balance including Zn, Al, and inevitable impurities.

21 more elements

A high-strength alloyed hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the alloyed hot-dip galvanized steel sheet comprising an alloyed hot-dip galvanized layer formed on a surface of a base steel sheet,

wherein the base steel sheet contains:
by mass %,
C:
0.10 to less than 0.4%;
Si:
0.5 to 3.0%;
Mn:
1.5 to 3.0%;
O:
0.0001 to 0.006%;
P:
0.0001 to 0.04%;
S:
0.0001 to 0.01%;
Al:
0.0005 to 2.0%;
N:
0.0005 to 0.01%;
and
a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, contains residual austenite of 8 to 27%, by volume fraction, and contains bainite and a balance being martensite or less than 10% of pearlite,
an average value of pole densities of orientation groups {100} <011> to {223} <110> represented by each of crystal orientations {100} <011>, {116} <110>, {114} <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> in a sheet thickness range of ⅝ to ⅜ from the surface of the base steel sheet is 6.5 or less and a pole density of a crystal orientation {332} <113> is 5.0 or less, and
the alloyed hot-dip galvanized layer contains Fe:
7 to 15 mass % and a balance including Zn, Al, and inevitable impurities.

21 more elements

Dependencies are inferred from the claim text.

Description22,384 words

Summary4,216 words

#The present invention relates to a high-strength plated steel sheet and a high-strength alloyed hot-dip galvanized steel sheet having excellent plating adhesion and formability with an ultimate tensile strength (TS) of 980 MPa or more which is particularly suitable for a structural member, a reinforcing member, and a suspension member of automobiles.

#This application is a national stage application of International Application No. PCT/JP2012/075214, filed Sep. 28, 2012, which claims priority to Japanese Patent Application No. 2011-218040, filed on Sep. 30, 2011, the content of which is incorporated herein by reference.

#Reduction of weight of members such as cross members and side members of automobiles has been considered so as to support trends for reduction of fuel consumption in recent years. In terms of materials, from the viewpoint of securing strength and impact safety even when being thinned, a steel sheet has been made higher in strength. However, the formability of materials deteriorates along with the rise of strength thereof. In order to implement lighter weight of the members, a steel sheet which satisfies both of the press formability and the high strength has to be produced. In particular, excellent ductility is required in the case of forming the structural member or the reinforcing member of automobiles that has a complicated shape.

Brief description of the drawings3 figures

#FIG. 1 is a diagram illustrating a relation between ΔEl and an average value of pole densities of orientation groups {100} <011> to {223} <110>.

#FIG. 2 is a diagram illustrating a relation between ΔEl and a pole density of an orientation {332} <113>.

#FIG. 3 is an explanatory diagram of a continuous hot rolling line.

Detailed description18,112 words

#From the result obtained by an earnest examination on the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet to solve the above problems, the present inventors have found to exhibit the ultimate tensile strength of 980 MPa or more and the excellent formability when the primary phase of a microstructure of the base steel sheet is ferrite and the residual austenite is contained. In addition, the inventors have found that even in the steel sheet containing a large amount of Si and Mn, it is possible to manufacture the cold-rolled steel sheet having the small material anisotropy by controlling the hot-rolled conditions within a specific range. Further, even in the steel sheet containing a large amount of Si, the plating wettability and the alloying are ensured by allowing the molten zinc to flow in the galvanizing bath.

#Hereinafter, the present invention will be described in detail.

#(Crystal Orientation of Base Steel Sheet)

Facts

Application

14/347,269Filed 28 Sep 2012

Priority

JP 2011-21804030 Sep 2011

Published

US 2014/0242415 A128 Aug 2014

Granted

10 Jan 2017

Term ends

5 Aug 2033

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment, including 311 days of adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification47 codes

C23C 2/28
After-treatment: thermal after-treatment, e.g. treatment in oil bath
B32B 15/013
All layers being exclusively metallic: one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or…
C21D 8/0226
Characterised by the working steps: hot rolling
C21D 8/0236
Characterised by the working steps: cold rolling

Timeline

30 Sep 2011Priority claimedJP 2011-218040
28 Sep 2012Application filedUS 14/347,269
24 Jun 2014Assigned to Nippon Steel & Sumitomo Metal Corporationassignment of assignor's interest
28 Aug 2014PublishedUS 2014/0242415 A1
10 Jan 2017GrantedUS 9,540,720 B2
14 May 2019Assigned to Nippon Steel Corporationchange of name
12 Oct 2026TodayWithin its term
5 Aug 2033Term endsEstimated, includes 311 days of adjustment

High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having excellent formability and small material anisotropy with ultimate tensile strength of 980 MPa or more

Life of this patent

High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having excellent formability and small material anisotropy with ultimate tensile strength of 980 MPa or more

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims6

Description22,384 words

Drawings

Classification47 codes

Life of this patent

Description22,384 words