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

Inactive Publication Date: 2017-12-28
KOBE STEEL LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The present invention provides a hot-dip galvanized and galvannealed steel sheet that has a strength of 980 MPa or higher, excellent formability in bendability and balance between strength and ductility, as well as delayed fracture resistance. The steel sheet has a unique structure that includes an internal oxide layer, a soft layer, and a hard layer, which works as a hydrogen trap site to effectively suppress hydrogen embrittlement. The average depth of the internal oxide layer and the relationship between it and the soft layer are controlled, which further enhances bendability and delayed fracture resistance. Overall, the invention provides a high-quality plated steel sheet that meets various demands.

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

[0122]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.

[0123]Some of the examples, i.e. Nos. 26 to 28, 37 to 39 and 41, 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.

[0124]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.

[0125]The pickling solution was 10% hydrochloric acid, the temperature was 82° C. and the pickling time as given in Table 2.

[0126]Next, annealing (oxidation, reduction) and cooling ...

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Abstract

A high-strength plated steel sheet 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 and 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 platability, excellent formability in terms of both bendability 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 both bendability and balance between strength and ductility, and to exhibit moreover excellent delayed fracture resistance.[0003]Adding a substantial amount of strengthening elements such as Si or Mn into steel is effectiv...

Claims

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Application Information

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IPC IPC(8): C21D9/46C21D8/02C23C2/06C23C2/02C22C38/32C22C38/28C22C38/22C22C38/18C22C38/16C22C38/14C22C38/12C22C38/08C22C38/06C22C38/04C22C38/02C22C38/00C23C2/40C23F17/00
CPCC21D9/46C23F17/00C21D8/0226C21D8/0236C21D8/0278C23C2/02C23C2/06C23C2/40C22C38/32C22C38/28C22C38/22C22C38/18C22C38/14C22C38/12C22C38/16C22C38/08C22C38/06C22C38/04C22C38/02C22C38/002C22C38/001C21D8/0205C23G1/06C23G1/08C23C2/0222C23C2/024C23C2/0224C23C2/28C23C2/29C21D1/76C21D8/0257C22C38/58C21D2211/005C21D2211/001C21D2211/009
Inventor IKEDA, MUNEAKIFUTAMURA, YUICHINAKAYA, MICHIHARU
Owner KOBE STEEL LTD
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