High-strength steel sheet and method for producing same
A technology of high-strength steel plates and manufacturing methods, applied in the direction of manufacturing tools, chemical instruments and methods, furnace types, etc.
Active Publication Date: 2021-09-07
JFE STEEL CORP
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- Claims
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Problems solved by technology
Various techniques have been proposed so far, but the fatigue strength of the welded part is not directly aimed at
Method used
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[0106] Steel slabs having the composition shown in Table 1 were subjected to hot rolling, cold rolling, and annealing under the conditions shown in Table 2 to manufacture steel sheets. In addition, the roll diameter used for the bending back in an annealing process was set to radius 425mm. In addition, the steel sheet produced under the conditions shown in Table 2 was immersed in a coating bath to form a coating with a coating weight of 20 to 80 g / m 2 hot-dip galvanized layer. In addition, alloying treatment was performed on a part after the formation of the galvanized layer to obtain a galvannealed steel sheet. The material division is shown in Table 2 together. After the plating treatment, cooling is performed. The survey method is as follows.
[0107] [Table 1]
[0108]
[0109] ※Underlined means outside the scope of the present invention.
[0110] [Table 2]
[0111]
[0112] ※1: Average heating rate from 600°C to 700°C
[0113] ※2: Average cooling rate from a...
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Abstract
The purpose of the present invention is to provide a high-strength steel sheet which can exhibit excellent fatigue strength at a resistance spot-welded part thereof. A high-strength steel sheet having a specified component composition and such a steel structure that the area ratio of a ferrite is 5 to 50% and the total area ratio of fresh martensite and residual gamma is 2 to 30% in a thickness cross section taken in a rolling direction, the average grain diameter of each of the fresh martensite and the residual gamma is 5 [mu]m or less, and the total area ratio of a portion of the fresh martensite and a portion of the residual gamma which are adjacent to only the ferrite is 30% by area or less in a region between the surface and a depth of 200 [mu]m as observed in the thickness direction, and also having yield strength of 550 MPa or more.
Description
technical field [0001] The present invention relates to a high-strength steel sheet suitable for members used in transportation machines such as automobiles, having high workability and excellent fatigue properties even under repeated loads, and a method for producing the same. Background technique [0002] In recent years, in the mobile body, such as the automobile industry, from the viewpoint of protecting the global environment, in order to reduce carbon dioxide (CO 2 ) emissions, improving the fuel efficiency of automobiles has always been an important issue. In order to improve the fuel efficiency of automobiles, it is effective to reduce the weight of the automobile body, and it is necessary to reduce the weight of the automobile body while maintaining the strength of the automobile body. Weight reduction can be achieved by increasing the strength of steel sheets used as raw materials for automobile parts, simplifying the structure, and reducing the number of parts. ...
Claims
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IPC IPC(8): C22C38/00C21D9/46C22C38/14C22C38/60C23C2/06C23C2/28C23C2/40
CPCC23C2/28C22C38/14C21D9/46C23C2/40C22C38/60C23C2/02C23C2/04C22C38/02C22C38/04C22C38/06C22C38/12C22C38/008C22C38/16C22C38/32C22C38/002C22C38/005B32B15/013C21D1/19C21D1/185C21D1/25C21D8/021C21D8/0226C21D8/0236C21D8/0252C21D8/0273C21D8/0263C21D8/041C21D8/0426C21D8/0436C21D8/0463C21D8/0473C21D8/0452C21D9/48C21D2211/005C21D2211/008C21D2211/001C21D2211/002C21D2211/009C23C2/0224C22C38/001C22C38/38C23C2/06B21C47/02C21D6/001C21D6/002C21D6/005C21D6/007C21D6/008C21D8/0205C22C38/08C22C38/10C22C38/26C22C38/28
Inventor 杨灵玲中垣内达也竹田裕紀
Owner JFE STEEL CORP