Aluminum coated steel sheet and process for producing the same

• US 4,546,051 A
• Filed: 06/12/1984
• Issued: 10/08/1985
• Est. Priority Date: 07/08/1982
• Status: Expired due to Term

• Current Assignee: Nisshin Steel Company Limited (Nippon Steel Corporation)
• Original Assignee: Nisshin Steel Company Limited (Nippon Steel Corporation)
• Inventors: Katayama, Kiichiro, Uchida, Yukio, Takagi, Kazuhiro, Kawase, Hisao
• Primary Examiner(s): Rutledge, L. Dewayne
• Assistant Examiner(s): Yee, Deborah
• Application Number:
  US06/619,804
• Time in Patent Office: 483 Days
• Field of Search: 428/653, 148/11.5 Q, 148/127
• US Class Current: 428/653
• CPC Class Codes: C23C 2/12 Aluminium or alloys based thereon
• CPC Class Codes: C23C 2/26 After-treatment C23C2/14 takes precedence
• CPC Class Codes: C23C 2/28 Thermal after-treatment, e.g. treatment in oil bath
• CPC Class Codes: Y10T 428/12757 Fe

Abstract

An aluminum coated steel sheet having excellent formability and corrosion resistance comprising a steel substrate of a recrystallized structure, an Al--Si coating layer of a recrystallized structure on at least one surface of the substrate, and a discontinuous intermediate layer of Al--Fe--Si intermetallic compounds. The product may be conveniently produced by rolling an Al--Si hot dipped steel sheet and annealing the rolled sheet under suitably selected conditions.

Claims

1. An aluminum hot dip coated steel sheet consisting essentially of

(1) a steel substrate containing 0.002 to 0.02% by weight of solute N and not more than √

5/3N-1/300% by weight of total C, wherein N represents the percentage of the solute N, and having a recrystallized structure;

(2) an aluminum coating layer on at least one surface of said steel substrate comprising essentially Al and 1 to 15% by weight of spheroidal Si and having a recrystallized structure, and;

(3) a discontinuous intermediate layer at the interface between said steel substrate and aluminum coating layer and comprising essentially Al--Fe--Si intermetallic compounds.

2. An aluminum hot dip coated steel sheet according to claim 1 wherein, when observed on a longitudinal cross-section, said discontinuous intermediate layer comprises successive discrete islands comprising essentially Al--Fe--Si intermetallic compounds, the individual islands having an average size of not larger than 10 μ

m with the sum of gaps between adjacent islands being 10 to 50% of the total length of said islands and said gaps.

3. A process for the production of an aluminum coated steel sheet comprising the steps of

(a) rolling an aluminum hot dip coated steel sheet, which comprises a steel substrate containing 0.002 to 0.02% by weight of solute N and not more than √

5/3N-1/300% by weight of total C, wherein N represents the percentage by weight of the solute N;

an aluminum coating layer on at least one surface of said steel substrate comprising essentially Al and 1 to 15% by weight of Si, and;

a continuous intermediate layer between said steel substrate and aluminum coating layer and comprising essentially Al--Fe--Si intermediate compounds, at a rolling rate sufficient to cause division of said continuous intermediate layer into sections, and

(b) annealing the rolled aluminum coated steel sheet at a temperature sufficient for the recrystallization of said steel substrate but insufficient for Al--Fe mutual diffusion between said steel substrate and aluminum coating layer.

4. A process according to claim 3 wherein the rolling step is carried out at a rolling rate sufficient to divide said continuous intermediate layer into successive discrete islands when observed on a cross-section taken along the direction of rolling, the individual islands having an average size of not larger than 10 μ

m with the sum of gaps between adjacent islands being 10 to 50% of the total length of said islands and gaps.

5. A process according to claim 3 wherein the rolling step is carried out at a rolling rate of 30 to 70% and the annealing step is carried out at a temperature of from 500°

to 600°

C.