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High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same

a technology of high-strength plated steel and workability, which is applied in the direction of metal layered products, metal coating processes, thin material processing, etc., can solve the problems of significant impairment of hot-dip galvanizing wettability and poor wettability, and achieve the effects of reducing hydrogen embrittlement effectively, reducing bendability and delay fracture resistance in particular, and reducing the number of welded parts

Inactive Publication Date: 2018-01-11
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

This patent describes a new type of plated steel sheet that has high strength, good ductility, and resistance to delayed fracture. The steel sheet includes an internal oxide layer, a soft layer, and a hard layer. The internal oxide layer acts as a hydrogen trap site, which helps to prevent embrittlement and obtain a high-strength sheet. The soft layer enhances bendability and delayed fracture resistance, while the hard layer ensures strength and ductility. By controlling the depth of the internal oxide layer and the relationship with the soft layer, the overall formability and resistance to delayed fracture are improved.

Problems solved by technology

However, Si and Mn are readily oxidizable elements, and hot-dip galvanizing wettability is significantly impaired by Si oxides, Mn oxides, and complex oxides of Si and Mn, that are formed on the surface.
This poor wettability gives rise to problems such as bare spots and the like.

Method used

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  • High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same
  • High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same
  • High-strength plated steel sheet having excellent plating properties, workability, and delayed fracture resistance, and method for producing same

Examples

Experimental program
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examples

[0121]Slabs having the component composition given in Table 1, the balance being iron and inevitable impurities, were heated to 1250° C., and were hot-rolled down to 2.4 mm at a finish rolling temperature of 900° C., followed by coiling at the temperature given in Table 2.

[0122]Some of the examples, i.e. Nos. 27 to 29, 38 to 40 and 42, were placed thereafter in a ceramic fiber heat-insulating apparatus, where the temperature was kept under the conditions given in Table 2. The keeping time at a temperature of 500° C. or higher was measured using a thermocouple attached to the outer periphery of the coil.

[0123]Each hot-rolled steel sheet thus obtained was then pickled under the conditions below, and was thereafter cold-rolled at a cold rolling ratio of 50%. The sheet thickness after cold rolling was 1.2 mm.

[0124]The pickling solution was 10% hydrochloric acid, the temperature was 82° C. and the pickling time as given in Table 2.

[0125]Next, annealing (oxidation, reduction) and cooling ...

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Abstract

The high-strength plated steel sheet of the present invention has a plated layer on the surface of a base steel sheet and contains predetermined steel components. The steel sheet includes, in the order from the interface of the base steel sheet and the plated layer towards the base steel sheet: a soft layer having a Vickers hardness that is 90% or less of the Vickers hardness at a portion t / 4 of the base steel sheet, where t is a sheet thickness of the base steel sheet: and a hard layer containing martensite, bainite, and ferrite in predetermined ranges. The average depth D of the soft layer is 20 μm or greater, and the average depth d of an internal oxide layer is 4 μm or greater and smaller than D.

Description

TECHNICAL FIELD[0001]The present invention relates to a high-strength plated steel sheet having a tensile strength of 980 MPa or higher and having excellent plalability; excellent formability in terms or bendability, hole expandability, and balance between strength and ductility; and excellent delayed fracture resistance, and also relates to a method for producing the steel sheet. The term plated steel sheet of the present invention denotes both of a hot-dip galvanized steel sheet and a hot-dip galvannealed steel sheet.BACKGROUND ART[0002]Hot-dip galvanized steel sheets and hot-dip galvannealed steel sheets that are widely used in the fields of automobiles, transport aircrafts and the like, are required to have, in addition to high strength, also excellent formability in terms of bendability, hole expandability (stretch flangeability), and balance between strength and ductility, and to exhibit moreover excellent delayed fracture resistance.[0003]Adding a substantial amount of streng...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C23C2/40C23C2/06C22C38/06C22C38/04C22C38/02C22C38/00C21D9/46C23C2/28C21D8/02
CPCC23C2/40C23C2/28C23C2/06C21D8/0278C22C38/04C22C38/02C22C38/06C22C38/001C21D9/46C21D8/0226C21D1/74C21D8/0205C21D8/0247C21D8/0236C21D8/0263B32B15/013Y10T428/24967Y10T428/12667Y10T428/12799Y10T428/2495Y10T428/12611Y10T428/12583Y10T428/12792Y10T428/12972Y10T428/1259Y10T428/1266Y10T428/263Y10T428/265Y10T428/264C22C38/18C22C38/002C22C38/22C22C38/28C22C38/14C22C38/12C22C38/08C22C38/32C22C38/16C22C38/60C22C38/48C22C38/26C22C38/24C22C38/42C22C38/44C22C38/50C22C38/20C22C38/46C22C38/54C22C38/40C23C2/0222C23C2/024C23C2/29C21D1/76C21D8/0257C22C38/38C21D2211/008C22C38/34C23C2/0224C21D2211/002C21D2211/005C23G1/06B32B15/04B32B15/043C23C30/005C23G1/08C23F17/00C23C30/00B32B15/18
Inventor IKEDA, MUNEAKIFUTAMURA, YUICHINAKAYA, MICHIHARU
Owner KOBE STEEL LTD
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