High strength thin steel sheet having high hydrogen embrittlement resisting property and high workability

Inactive Publication Date: 2006-06-29
KOBE STEEL LTD
View PDF13 Cites 25 Cited by
  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0024] According to the present invention, it is made possible to manufacture, with a high level of productivity, a high strength thin steel sheet having tensile strength of 1180 MPa or higher that neutralizes hydrogen that infiltrates from the outside after the steel sheet has been formed into a part thereby to maintain satisfactory hydrogen em

Problems solved by technology

In the realm of high strength of 1180 MPa upward, however, the TRIP steel sheet is known to suffer a newly emerging problem of delayed fracture caused by hydrogen embrittlement, similarly to the conventional high strength steel.
Delayed fracture refers to the failure of high-strength steel under stress, that occurs as hydrogen originating in corrosive environment or the atmosphere infiltrates and diffuses in microstructural defects such as dislocation, void and grain boundary, and makes the steel brittle.
This results in decreases in ductility and toughness of the metallic material.
Also hydrogen embrittlement has rarely been regarded as a problem for thin steel sheets where hydrogen that has infiltrated therein is immediately released due to the small thickness.
For these reasons, much efforts have not been dedicated to counter the hydrogen embrittlement.
However, in the case of “New Development in Elucidation of Delayed Fracture” (published by The Iron and Steel Institute of Japan in January, 1997), for example, 0.4% or higher of C content and much alloy elements are contained, and therefore application of this technology to a thin steel sheet compromises the workability required of the thin steel sheet.
The technology also has a drawback related to the manufacturing process, since it takes several hours or longer period of heat treatment to cause the alloy carbide to precipitate.
However, improvement of the workability without variability essentially requires it to provide a tempering process which makes it necessary to strictly control the temperature and duration of the process.
This also sometimes increases the possibility of tempering embrittlement and makes it difficult to reliably improve workability.
Although there is a steel of composite struc

Method used

the structure of the environmentally friendly knitted fabric provided by the present invention; figure 2 Flow chart of the yarn wrapping machine for environmentally friendly knitted fabrics and storage devices; image 3 Is the parameter map of the yarn covering machine
View more

Image

Smart Image Click on the blue labels to locate them in the text.
Viewing Examples
Smart Image
  • High strength thin steel sheet having high hydrogen embrittlement resisting property and high workability
  • High strength thin steel sheet having high hydrogen embrittlement resisting property and high workability
  • High strength thin steel sheet having high hydrogen embrittlement resisting property and high workability

Examples

Experimental program
Comparison scheme
Effect test

first embodiment

[0039] The first high strength thin steel sheet according to the present invention is constituted from higher than 0.25 and up to 0.60% of C (contents of components given in terms of percentage in this patent application all refer to percentage by weight), 1.0 to 3.0% of Si, 1.0 to 3.5% of Mn, 0.15% or less P, 0.02% or less S, 1.5% or less (higher than 0%) of Al, 1.0% or less (higher than 0%) of Mo and 0.1% or less (higher than 0%) of Nb, while iron and inevitable impurities making up the rest, and is characterized in that:

(i) the metal structure after the forming process contains: 1% or more residual austenite;

80% or more in total of bainitic ferrite and martensite; and

9% or less (may be 0%) in total of ferrite and pearlite in terms of the proportion of area to the entire structure, and

the mean axis ratio (major axis / minor axis) of the residual austenite grains is 5 or higher; and

(ii) the steel contains a specified amount of Mo and / or Nb.

[0040] The requirements described...

second embodiment

[0081] The second high strength thin steel sheet according to the present invention is constituted from higher than 0.25% and up to 0.60% of C (contents of components given in terms of percentage in this patent application all refer to percentage by weight), 1.0 to 3.0% of Si, 1.0 to 3.5% of Mn, 0.15% or less of P, 0.02% or less of S, 1.5% or less (higher than 0%) of Al while iron and inevitable impurities constitute the rest, wherein: (i) the structure after the forming process comprises:

1% or more residual austenite;

mean axis ratio (major axis / minor axis) of the residual austenite grains is 5 or higher;

80% or more in total of bainitic ferrite and martensite; and

9% or less (may be 0%) in total of ferrite and pearlite in the proportion of area to the entire structure, and

(ii) the steel contains specified amount of Cu and / or Ni.

[0082] The requirements (i) have the reasons as described above.

[0083] The requirement (ii) described above has the reason as follows.

[0084] Spec...

third embodiment

[0100] A third high strength thin steel sheet according to the present invention is constituted from higher than 0.25 and up to 0.60% of C (contents of components given in terms of percentage in this patent application all refer to percentage by weight), 1.0 to 3.0% of Si, 1.0 to 3.5% of Mn, 0.15% or less of P, 0.02% or less of S, 1.5% or less (higher than 0%) of Al, while iron and inevitable impurities making up the rest,

wherein: (iii) the structure satisfies the following requirements after forming:

1% or more residual austenite; the mean axis ratio (major axis / minor axis) of the residual austenite grains is 5 or higher;

mean length of minor axes of the residual austenite grains is 1 μm or less; and

minimum distance between residual austenite grains is 1 μm or less.

[0101] When the metal structure is controlled as described above, hydrogen embrittlement resisting property of the high strength thin steel sheet can be sufficiently improved without adding much alloy elements.

[0...

the structure of the environmentally friendly knitted fabric provided by the present invention; figure 2 Flow chart of the yarn wrapping machine for environmentally friendly knitted fabrics and storage devices; image 3 Is the parameter map of the yarn covering machine
Login to view more

PUM

PropertyMeasurementUnit
Lengthaaaaaaaaaa
Fractionaaaaaaaaaa
Fractionaaaaaaaaaa
Login to view more

Abstract

The present invention provides a high strength thin steel sheet that has high hydrogen embrittlement resisting property and high workability. The high strength thin steel sheet having high hydrogen embrittlement resisting property has a metallurgical structure after stretch forming process to elongate 3% comprises: (i) 1% or more residual austenite; 80% or more in total of bainitic ferrite and martensite; and 9% or less (may be 0%) in total of ferrite and pearlite in terms of proportion of area to the entire structure, wherein the mean axis ratio (major axis/minor axis) of the residual austenite grains is 5 or higher, or (ii) 1% or more residual austenite in terms of proportion of area to the entire structure; mean axis ratio (major axis/minor axis) of the residual austenite grains is 5 or higher; mean length of minor axes of the residual austenite grains is 1 μm or less; minimum distance between the residual austenite grains is 1 μm or less; and the steel has tensile strength of 1180 MPa or higher.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a high strength thin steel sheet that has high hydrogen embrittlement resisting property (particularly the hydrogen embrittlement resisting property after being subjected to forming process) and high workability, especially to a high strength thin steel sheet that has high resistance against fractures due to hydrogen embrittlement such as season crack and delayed fracture that pose serious problems for steel sheets having tensile strength of 1180 MPa or higher, and has high workability. [0003] 2. Description of the Related Art [0004] There are increasing demands for the steel sheet, that is pressed or bent into a form of a high-strength component of automobile or industrial machine, to have both high strength and high ductility at the same time. In recent years, there are increasing needs for high strength steel sheets having strength of 1180 MPa or higher, as the automobiles are bei...

Claims

the structure of the environmentally friendly knitted fabric provided by the present invention; figure 2 Flow chart of the yarn wrapping machine for environmentally friendly knitted fabrics and storage devices; image 3 Is the parameter map of the yarn covering machine
Login to view more

Application Information

Patent Timeline
no application Login to view more
IPC IPC(8): C22C38/06
CPCC21D2211/002C22C38/02C22C38/04C22C38/06C22C38/08C22C38/12C22C38/14C22C38/16
Inventor YUSE, FUMIOIKEDA, SHUSHIMUKAI, YOICHIAKAMIZU, HIROSHIKINUGASA, JUNICHIROSAITO, KENJISUGIMOTO, KOICHIHOJO, TOMOHIKO
Owner KOBE STEEL LTD
Who we serve
  • R&D Engineer
  • R&D Manager
  • IP Professional
Why Eureka
  • Industry Leading Data Capabilities
  • Powerful AI technology
  • Patent DNA Extraction
Social media
Try Eureka
PatSnap group products

Browse by: Latest US Patents, China's latest patents, Technical Efficacy Thesaurus, Application Domain, Technology Topic.

© 2024 PatSnap. All rights reserved.Legal|Privacy policy|Modern Slavery Act Transparency Statement|Sitemap