Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1995-11-22
1997-07-15
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148541, 148530, 148534, C21D 713
Patent
active
056479220
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a high manganese steel and a process for manufacturing a high manganese steel sheet for use in manufacturing automobiles in which a superior formability and a high strength are required. In particular, the present invention relates to an austenitic high manganese steel having superior hot workability in which the reduction of area at high temperature is 40% or more, and also relates to a process for manufacturing a high manganese hot rolled steel sheet, in which cracks are not generated.
DESCRIPTION OF THE PRIOR ART
In accordance with the reinforcement of regulations for the discharges of carbon dioxide which aggravates the air pollution, the automobile manufacturing field requires a steel which is high in the formability and strength, and which can reduce the weight of the automobile and can improve the fuel combustion efficiency.
By considering the formability, the conventional automobile steel sheet is an extremely low carbon steel in which the matrix structure is ferritic. However, in the case where an extremely low carbon steel is used as the automobile steel sheet, the formability is superior, but the tensile strength is low, down to 28-38 kg/mm.sup.2. Therefore, not only can the automobile weight not be reduced, but in addition the safety of automobile is aggravated, with the result that human life is jeopardized in the case of an accident.
In an attempt to overcome the above described disadvantages, the present inventors invented a high manganese austenitic steel having superior formability and strength, and filed a patent application under Korean Patent Application No. 25112 (title of the invention: Austenitic High Manganese Steel Having Superior Formability And Strength, filed on Dec. 30, 1991); Korean Patent Application No. 13309 (title of the invention: Method for Manufacturing High Manganese Steel Having Superior Formability, Strength And Weldability, filed on Jul. 24, 1992); and PCT Application No. PCT/KR92/00082 (title of the invention: Austenitic High Manganese Steel Having Superior Formability, Strength and Weldability, And Manufacturing Process thereof, filed on Dec. 30, 1992).
The above mentioned high manganese steel having superior formability and strengths is of Fe-Mn-Al-C system. This steel has the problem that, when it is hot rolled in the usual hot rolling method, cracks are formed on the sides and faces of the steel sheet in a severe degree. If cracks are formed during a hot rolling, not only there is the possibility that the hot rolling mill can be damaged, but also the side portions of the hot rolled steel sheet have to be cut off, and therefore, the intended dimension of the steel sheet cannot be attained. Further, the face of the steel sheet has to be ground off, and therefore, the actual yield of the product is greatly lowered.
Further, this high manganese steel contains large amounts of aluminum and manganese which are alloy elements having a high oxidation trend. Therefore, when the high manganese steel ingot or continuous casting slab is heated to a high temperature, a thick oxide scale layer is formed on the surface by the selective oxidation of the highly oxidizable elements. Further, the alloy elements are depleted in the surface layer, and the selective oxidation also occurs along grain boundaries. The thick oxide scales become a surface defect by being retained after a high temperature processing such as hot rolling. The depletion of the alloy elements and the selective oxidation along grain boundaries cause tiny cracks during a hot rolling. Therefore, the face of the steel sheet has to be ground, with the result that the product yield is decreased.
SUMMARY OF THE INVENTION
The present invention is intended to improve the above described high manganese steel, and to overcome the above described disadvantages of the above described steel.
Therefore it is an object of the present invention to provide a high manganese steel having superior hot workability, in which tiny amounts of alloy elements are added into
REFERENCES:
patent: 5431753 (1995-07-01), Kim et al.
Kim Tai Woung
Kim Young Gil
Park Shin Hwa
Pohang Iron & Steel Co. Ltd.
Research Institute of Industrial Science & Technology
Yee Deborah
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