Method of manufacturing multi phase microstructured steel piece

A technology of microstructure and parts, applied in the direction of manufacturing tools, heat treatment equipment, coatings, etc., can solve problems such as difficult to control springback of formed parts, limited shape range, unpredictable part behavior, etc.

Active Publication Date: 2008-10-22
ARCELORMITTAL INVESTIGACION Y DESARROLLO SL
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Problems solved by technology

[0005] However, the development of parts made of dual-phase or TRIP steels has been limited due to the difficulty in controlling the springback of formed parts, the greater the springback, the greater the steel's tensile strength R m higher
This is because in order to reduce the effects of springback, automakers have to introduce this parameter i

Method used

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  • Method of manufacturing multi phase microstructured steel piece
  • Method of manufacturing multi phase microstructured steel piece

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Embodiment Construction

[0036] The method according to the invention consists in hot forming a blank previously cut from a steel strip, in a specific temperature range, to form a steel part, the composition of which is typically that of a steel with a multiphase microstructure, but which in It is not necessary to start with a multiphase structure, the steel part acquires a multiphase microstructure when it cools between the forming tools. The inventors have also demonstrated that a homogeneous multiphase microstructure can be obtained independent of the billet cooling rate between tools as long as the cooling rate is sufficient.

[0037] The advantage of the invention is that it is not necessary that the multiphase microstructure is formed already during the stage of manufacturing the hot-rolled sheet or its coating, but rather at the stage of manufacturing the part by hot forming, which makes it possible to ensure the final A multiphase microstructure is uniform in every region of the part. This is...

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Abstract

The invention concerns a method for making a steel part of multiphase microstructure, said microstructure comprising ferrite and being homogeneous in each of the zones of said part, including the following steps: cutting a blank in a steel strip whereof the composition is typical of that of multiphase microstructure steel; heating said blank until a holding temperature T1 higher than Ac1 but lower than Ac3 is reached, and maintaining said holding temperature T1 for a dwell time M adjusted so that the steel after the blank has been heated includes an austenite proportion not less than 25 % of the surface; transferring said heated blank into a shaping equipment so as to shape by heat process said part; and cooling the part inside the equipment at a cooling speed V such that the steel microstructure after the part has been cooled is a multiphase microstructure, said microstructure comprising ferrite and being homogeneous in each of the zones of said part.

Description

technical field [0001] The present invention relates to a method for producing parts made of steel having a homogeneous multiphase microstructure in every area of ​​the part and having high mechanical properties. Background technique [0002] In order to meet the requirements of lightening automotive structures, it is known to use TRIP steels (the term TRIP means Transformation Induced Plasticity) and dual phase steels which combine very high mechanical strength with very high deformability. TRIP steels have a microstructure consisting of ferrite, retained austenite and optionally bainite and martensite, which allows these TRIP steels to achieve tensile strengths of 600-1000 MPa. Dual phase steels have a microstructure consisting of ferrite and martensite which allows these dual phase steels to achieve tensile strengths ranging from 400 MPa to greater than 1200 MPa. [0003] These types of steels are widely used in the production of energy absorbing parts such as structural...

Claims

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Application Information

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IPC IPC(8): C21D1/18C21D1/673C21D7/13C23C2/26
CPCC21D9/48C21D1/673C21D7/13C21D2211/005C22C38/22C21D2211/001C21D9/46C21D2211/002C23C2/26C21D2211/008C22C38/06C22C38/02C21D1/185C22C38/28C22C38/38C22C38/34
Inventor J·科基耶J·德夫罗克J-L·奥沙尔J-P·洛朗A·穆兰N·罗曼诺夫斯基
Owner ARCELORMITTAL INVESTIGACION Y DESARROLLO SL
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