High-strength galvanized steel sheet having excellent formability and crashworthiness and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-9617630-B2
Application number	US-201113640851-A
Country	US
Kind code	B2
Filing date	Apr 11, 2011
Priority date	Apr 16, 2010
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

A high-strength galvanized steel sheet having excellent formability and crashworthiness, including a component composition containing 0.03% to 0.13% C, 1.0% to 2.0% Si, 2.4% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 0.0003% to 0.01% B on a mass basis, the remainder being Fe and unavoidable impurities, and a microstructure containing a tempered martensitic phase and a bainitic phase such that the sum of an area fraction of the tempered martensitic phase and an area fraction of the bainitic phase is 30% or more (the area fraction of the martensitic phase is 30% or more in the absence of the bainitic phase), wherein a distance of closest approach of the tempered martensitic phase is 10 μm or less and the contents of C, Mn, and B satisfy (1):

(% Mn)+1000×(% B)≧35×(% C)  (1).

First claim

The invention claimed is:

1. A method of manufacturing a galvanized steel sheet having formability and crashworthiness, comprising:
heating a steel sheet consisting of 0.03% to 0.13% C, 1.0% to 2.0% Si, 2.4% to 3.5% Mn, 0.001% to 0.05% P, 0.0001% to 0.01% S, 0.001% to 0.1% Al, 0.0005% to 0.01% N, and 0.0003% to 0.01% B on a mass basis; and optionally containing at least one selected from the following A-C: A: at least one selected from the group consisting of 0.0005% to 0.1% Ti and 0.0005% to 0.05% Nb on a mass basis;
B: at least one selected from the group consisting of 0.01% to 1.0% Mo, 0.01% to 2.0% Ni, and 0.01% to 2.0% Cu on a mass basis; and
C: 0.001% to 0.005% Ca on a mass basis;
the remainder being Fe and unavoidable impurities to a temperature not lower than the Aci transformation temperature at an average heating rate of 5° C./s or more, followed by;
heating the steel sheet to Ac 3 −50° C. or higher at an average heating rate of less than 5° C./s, soaking the steel sheet at a temperature of Ac 3 −50° C. to Ac 3 +50° C. for 30 s to 500 s, primarily cooling the steel sheet to a temperature of 600° C. or lower at an average cooling rate of 3° C./s to 30° C./s,
galvanizing the steel sheet; and
secondarily cooling the galvanized steel sheet to a temperature of 200° C. to 400° C. at an average cooling rate of 15° C./s or less such that the galvanized steel sheet has a microstructure containing a tempered martensitic phase and a bainitic phase such that the sum of an area fraction of the tempered martensitic phase and an area fraction of the bainitic phase is 30% or more, the area fraction of the tempered martensitic phase is 30% or more in the absence of the bainitic phase, wherein a distance of closest approach of the tempered martensitic phase is 10 pm or less and contents of C n Mn, and B satisfy (1):
(% Mn)+1000×(% B)>35×(% C)  (1).

2. The method according to claim 1 , further comprising holding the primarily cooled steel sheet at a temperature of 300° C. to 550° C. for 20 s to 150 s prior to galvanizing.

3. The method according to claim 1 , further comprising alloying a zinc coating of the galvanized steel sheet at a temperature of 450° C. to 600° C. prior to secondary cooling.

4. The method according to claim 2 , further comprising alloying a zinc coating of the galvanized steel sheet at a temperature of 450° C. to 600° C. prior to secondary cooling.

Assignees

• Kaneko Shinjiro
• Nakagaito Tatsuya
• Hasegawa Hiroshi
• Nagataki Yasunobu
• Jfe Steel Corp

Inventors

• Kaneko Shinjiro
• Nakagaito Tatsuya
• Hasegawa Hiroshi
• Nagataki Yasunobu

Classifications

• C21D2211/008

  Martensite · CPC title

• C21D8/0236

  Cold rolling · CPC title

• Y02P10/212

  Cross-Sectional Technologies · mapped topic

• C21D2211/002

  Bainite · CPC title

• C22C38/32

  with boron · CPC title