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High-strength alloyed aluminum-system plated steel sheet and high-strength automotive part excellent in heat resistance and after-painting corrosion resistance

A corrosion-resistant, high-strength technology that is applied in the field of steel plates coated with an aluminum alloy system, which can solve problems such as delays in plating, increased stress, and scarring, and achieve excellent heat resistance

Inactive Publication Date: 2004-09-22
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0010] Also, there is the potential for spalled plating to build up on the die and cause scarring during pressing
This is due to the fact that, although the plating layer can withstand the processing of thermoforming, it is actually difficult to heat-work the entire part, and there is a problem that the plating layer tends to peel off at a part where the processing is delayed and the temperature is lowered
Another problem here is that as the temperature is lowered, quenching causes the base steel to form a hard structure consisting mainly of martensite, so the stress tends to gradually rise

Method used

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  • High-strength alloyed aluminum-system plated steel sheet and high-strength automotive part excellent in heat resistance and after-painting corrosion resistance
  • High-strength alloyed aluminum-system plated steel sheet and high-strength automotive part excellent in heat resistance and after-painting corrosion resistance
  • High-strength alloyed aluminum-system plated steel sheet and high-strength automotive part excellent in heat resistance and after-painting corrosion resistance

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Experimental program
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Effect test

Embodiment approach 1

[0049] The chemical composition of the steel sheet used in the present invention is explained below.

[0050] C: The steel sheet of the present invention has a high strength of not less than 1,000 MPa after forming, which is obtained by rapid cooling after high-temperature pressing and thereby transforming its structure into a structure mainly composed of martensite. In this sense, it is desirable that the C content is not less than 0.05%, and in order to stably obtain high strength, it is more desirable that the content is not less than 0.1%. On the other hand, even if the C content is increased to not less than 0.7%, its strength is saturated and weld cracks tend to occur, so it is limited to 0.7%.

[0051] Si: Since the Si content is too low to impair the fatigue properties, it is desirable to add it in an amount of not less than 0.05%. However, Si forms a stable oxide film on the steel sheet surface during recrystallization annealing and hinders the aluminum plating perfo...

Embodiment approach 2

[0065] The reason for adjusting the steel composition in Embodiment 2 of the present invention will be described below.

[0066] N is an element that is inevitably included and is specifically added when B is not added, however, when B is added and its amount is too large, it is necessary to increase the amount of Ti added. As a result, there are problems in that the amount of TiN finally produced increases and thermal cracks occur, and the cost also increases. Therefore, its upper limit is 0.1%.

[0067] B is added to improve the hardenability upon cooling during or after press molding, and in order to obtain this effect, its addition must be not less than 0.0002%. However, when its added amount is too large, there is a problem of thermal cracking and the effect is saturated. Therefore, its upper limit is 0.03%.

[0068] Ni, Cu, and Sn have an effect of changing the state of surface cracks during press-forming after high-temperature heating by changing the state of alloyed a...

Embodiment approach 3

[0080] First, the reason for adjusting the steel composition according to the present invention in Embodiment 3 will be explained below.

[0081] The addition of C element makes the structure after cooling consist of martensite, and ensures the quality of the material, and its addition amount is required to be not less than 0.15% to ensure that the strength is not lower than 1,200MPa. On the other hand, if the added amount is too large, the strength against impact deformation can hardly be ensured, so it is limited to 0.55%.

[0082] Si is a solute strengthening element and can increase the strength of steel sheets at relatively low cost. However, if it is added in excess, the plating performance will be impaired, so it is limited to 0.5% at its upper limit.

[0083] Mn is added to ensure post-cooling strength over a wide range of cooling rates.

[0084] When the amount of C is large but the amount of Mn added is small, the martensitic structure cannot be obtained within the...

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Abstract

The present invention provides a hot press method used for producing a high-strength member for an automobile and, in particular, a part which requires high-strength, such as an undercarriage component of an automobile. More specifically, the present invention provides an aluminum plated steel sheet or an aluminum-zinc plated steel sheet suitable for high temperature forming (hot forming) wherein high strength is obtained after high temperature forming, and a method of producing the same. Also, the present invention provides a hot dip aluminum plated steel sheet which suppresses the alloying reaction of a plated layer during press forming and has beautiful appearance, and an aluminum-system plated steel sheet for hot press having excellent after-painting corrosion resistance. Concretely, the present invention is a high-strength aluminum-system plated steel sheet excellent in heat resistance and after-painting corrosion resistance, characterized by having an Fe-Al-system coating containing, in mass, Mn and Cr of more than 0.1% in total on the surface of the steel containing, in mass, C: 0.05 to 0.7%, Si: 0.05 to 1%, Mn: 0.5 to 3%, P: not more than 0.1%, S: not more than 0.1% and Al: not more than 0.2%, and, in addition, one or more element(s) selected from among Ti: 0.01 to 0.8%, Cr: not more than 3% and Mo: not more than 1%, so as to satisfy the following expression (1): Ti + 0.5xMn + Cr + 0.5xMo > 0.4 ... 1

Description

technical field [0001] The present invention relates to a steel plate coated with an aluminum alloy system, which is suitable for parts requiring strength (such as structural parts of automobile parts) produced by high-temperature pressing and a method for preparing the steel plate. Specifically, the present invention relates to a Components that require high strength (such as chassis components of automobiles, etc.) and the steels used to make such components. Background technique [0002] In order to reduce the weight of automobiles (derived from global environmental concerns), steel sheets used for automobiles are required to have as high a strength as possible. However, in general, while increasing the strength of a steel sheet, the elongation and r-value decrease, and thus the formability is impaired. Therefore, there is a need for a steel plate having high strength, high formability and shape fixity at the same time. [0003] One method of solvi...

Claims

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Application Information

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IPC IPC(8): C23C2/12C23C28/00
CPCC23C2/12C23C2/29C23C2/40C21D1/673C22C38/28C22C38/22C22C38/04
Inventor 末广正芳真木纯布田雅裕宫腰寿拓高田良久江口晴彦伊崎辉明楠见和久
Owner NIPPON STEEL CORP
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