High manganese high strength steel sheets with excellent crashworthiness and method for manufacturing of it

a high-strength, high-carbon steel technology, applied in the direction of metal rolling arrangement, etc., can solve the problems of affecting the welding process, difficult to manufacture parts with complicated structures, deterioration in elongation of steel, etc., and achieve excellent impact absorption ability, high strength, and high elongation

Inactive Publication Date: 2009-03-19
POHANG IRON & STEEL CO LTD
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  • Abstract
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  • Claims
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Benefits of technology

[0011]According to the present invention, an aspect of the present invention is to provide a steel sheet that is suitable for elaborate internal sheets as well as structural members of a car body since it has high elongation and high strength. The steel sheet can be useful to be used for parts such as a front side member of an automobile since, among its characteristics, the steel sheet has an excellent impact absorbing ability.

Problems solved by technology

However, the increased strength of the materials results in deterioration in elongation of steel, and therefore a dual-phase steel, a transformation induced plasticity steel and the like, all of which have excellent formability, have been increasingly used to solve the above problems.
However, high strength steel for processing, used as structural parts and internal sheets for automobiles developed thus far, does not satisfy workability that automobile parts require, and therefore it is difficult to manufacture parts with complicated structure.
The welding process is hampered by a variety of restrictions, for example, difficulty in designing a car body since strength of a welded portion is different from that of the parent metal, and parts characteristics are deteriorated due to the increased strength in the welded portion, and the manufacturing cost is extremely high since the parts are molded separately.
However, when the high strength steel such as low carbon steel is used as the automotive steel sheet, it is impossible to ensure up to 30% elongation in high strength steels whose tensile strength is greater than 800 MPa.
Accordingly, it is difficult to design parts easily, for example, make simple structures of parts, since it is difficult to apply the high strength steel of greater than 800 MPa to complicated and elaborate parts.
In the case of the Japanese patent, the high manganese steel sheet has a high ductility by the addition of high manganese, but may be easily broken after its processing since strain hardening is serious in its transformed region.
Also, in the case of the international patent, the high manganese steel sheet has high ductility, but its electroplating and hot plating properties are low due to the addition of a large amount of silicon.
Also, the steel sheets have excellent workability but deteriorated crashworthiness due to the low yield strength.
However, the high manganese steel sheet has low yield strength due to its austenite structure, and therefore the problems regarding the high manganese steel sheet remains to be solved.

Method used

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  • High manganese high strength steel sheets with excellent crashworthiness and method for manufacturing of it
  • High manganese high strength steel sheets with excellent crashworthiness and method for manufacturing of it
  • High manganese high strength steel sheets with excellent crashworthiness and method for manufacturing of it

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example

[0048]The inventive steels and the comparative steels are listed in the following Table 1, and molten steel ingots were kept in a 1200° C. heating furnace for one hour, and then hot-rolled. At this time, a hot rolling finish temperature was 900° C., and a coiling temperature was 650° C. Some of the hot-rolled steel sheets were processed into tensile test samples according to the JIS5 standard, and the tensile test samples were tested for tensile strength using a conventional universal testing machine. And, the hot-rolled steel sheets were pickled and cold-rolled at a cold reduction ratio of 50%. The cold-rolled test samples were continuously annealed, simulated and heat-treated at an annealing temperature of 800° C. and an over-aging temperature of 400° C. After the continuous annealing, simulation and heat-treatment processes, the cold-rolled test samples were tested for tensile strength using a conventional universal testing machine. Meanwhile, the cold-rolled test samples were co...

example 2

[0053]The high strength steel sheets with high workability and high manganese having an austenite single phase, prepared in Example 1, were cold-rolled again, and measured for mechanical properties. The results are listed in the following Table 3.

TABLE 3RollingYSTST-ElamountNote19471.3939.960.40Comparative Steel19-1750.51047.244.610Inventive Steel19-2930.51209.722.220Inventive Steel19-31088.31371.312.530Inventive Steel19-41247.71554.28.640Inventive Steel19-51388.21704.16.850Inventive Steel19-61503.61808.64.660Inventive Steel19-71612.81924.52.870Inventive Steel

[0054]As shown in Table 3, it was revealed that the yield strengths of the high strength steel sheets are enhanced. It was usually seen that the yield strengths are increased to 750 MPa or more in the 10% phase transformation, and the elongation is excellent at 44%, indicating that the high strength steel sheets have excellent formability and crash-worthiness as the structural members.

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Abstract

There are provided a high-workability high strength steel sheet with excellent workability due to the high elongation and excellent crashworthiness due to the high yield strength, and a method for manufacturing of it. The high manganese steel sheet includes, by weight: carbon (C): 0.2 to 1.5%, manganese (Mn): 10 to 25%, aluminum (Al): 0.01 to 3.0%, phosphorus (P) 0.03% or less, sulfur (S): 0.03% or less, nitrogen (N): 0.040% or less, at least one selected from the group consisting of silicon (Si): 0.02 to 2.5%, titanium (Ti): 0.01 to 0.10% and niobium (Nb): 0.01 to 0.10%, and the balance of Fe and other inevitable impurities. The high manganese steel sheet may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a plated steel sheet, and is suitable for elaborate internal sheets as well as structural members of a car body since it has press workability due to the high elongation and high strain hardening index. Also, the high manganese steel sheet may be used for parts such as a front side member of an automobile since, among its characteristics, the steel sheet has an excellent impact absorbing ability.

Description

TECHNICAL FIELD[0001]The present invention relates to a high manganese steel sheet used for a automobile steel sheet and a method for manufacturing of it, and more particularly, to a high-workability high strength steel sheet whose workability is excellent due to the high elongation and crashworthiness is excellent due to the high yield strength, and a method for manufacturing of it.BACKGROUND ART[0002]Motor companies have increasingly used lightweight and high-strength materials for the purpose of preventing environmental pollutions and improving fuel efficiency and stability, which is one of important characteristics that materials used for structural members should have in addition to the automobile parts. However, the increased strength of the materials results in deterioration in elongation of steel, and therefore a dual-phase steel, a transformation induced plasticity steel and the like, all of which have excellent formability, have been increasingly used to solve the above pr...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C38/04C21D8/02B21B1/00
CPCC22C38/06C22C38/04C21D8/02
Inventor KIM, SUNG KYUCHIN, KWANG GEUNSOHN, IL-RYOUNG
Owner POHANG IRON & STEEL CO LTD
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