High-strength cold-rolled steel sheet, high-strength plated steel sheet, and their manufacturing methods
A technology of cold-rolled steel sheets and manufacturing methods, applied in the field of high-strength plated steel sheets, which can solve problems such as unavailability of raw materials and formability deviations, and achieve excellent in-plane stability, improved fuel costs, and great utility value
Active Publication Date: 2021-12-31
JFE STEEL CORP
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Problems solved by technology
However, as a result of increasing the content of alloying elements for high strength, in-plane variations in formability, especially stretch flangeability, occurred, and there was a problem that it was not possible to provide a raw material with sufficient properties.
Method used
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[0159] Steel having the composition shown in Table 1 (remainder: Fe and unavoidable impurities) was melted, and a billet was produced by a continuous casting method. After heating the slabs under the conditions shown in Tables 2 to 4, they were rough rolled, finished rolled and cooled, and coiled by strictly controlling the coiling temperature in the width direction to obtain hot-rolled steel sheets. The obtained hot-rolled steel sheet was subjected to descaling treatment, and then cold-rolled to obtain a cold-rolled steel sheet. Here, the thickness of each cold-rolled steel sheet is within a range of 1.2 to 1.6 mm. Then, heat the cold-rolled steel sheet, anneal at the soaking temperature (first soaking temperature) shown in Tables 2 to 4, and then cool to 500°C at the average cooling rate shown in Tables 2 to 4 under strict control of the cooling rate. , strictly control the cooling stop temperature distribution in the width direction, after stopping cooling at the cooling s...
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Abstract
The object of the present invention is to provide a high-strength cold-rolled steel sheet and a high-strength Galvanized steel sheets, and their efficient method of manufacture. The high-strength cold-rolled steel sheet of the present invention has a specific composition, and has a steel structure that includes 50 to 80% of ferrite by area ratio and 8% or less of martensite by area ratio, and the The average grain size of martensite is 2.5 μm or less, 6 to 15% of retained austenite is included in the area ratio, and 3 to 40% of tempered martensite is included in the area ratio, and the martensite Area ratio f M and the total area ratio f of martensite and tempered martensite M+TM Ratio f M / f M+TM The value is 50% or less, and in the width central portion which is the center in the width direction of the plate, both end portions 50 mm from both ends in the width direction of the plate to the center in the width direction of the plate, between the central width portion and the two end portions The standard deviation of the crystal grain size of martensite at a total of 5 locations in the center between them is 0.7 μm or less.
Description
technical field [0001] The present invention relates to a high-strength cold-rolled steel sheet, a high-strength plated steel sheet, and a method for producing them, which are excellent in formability and are mainly suitable for structural members of automobiles. In particular, it relates to a high-strength cold-rolled steel sheet having a tensile strength (TS) of 780 MPa or more, excellent in ductility, stretch-flangeability, and in-plane stability of stretch-flangeability, a high-strength plated steel sheet, and their Manufacturing method. Background technique [0002] In recent years, high-strength steels have been widely used due to increasing demands for crash safety and fuel costs of automobiles. In addition, since thin steel sheets for automobiles are formed into automobile parts by press working, flanging, etc., excellent formability is required. Therefore, steel sheets for automobiles need to maintain high strength, and also need to have excellent ductility and st...
Claims
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IPC IPC(8): C22C38/00C21D9/46C22C38/06C22C38/60
CPCC22C38/00C21D9/46C22C38/06C22C38/60C22C38/02C22C38/04C22C38/001C22C38/12C22C38/14C22C38/002C22C38/38C22C38/08C22C38/16C22C38/008C22C38/10C22C38/005C21D8/02C21D8/0226C21D8/0236C21D6/00C21D6/008C21D6/005C21D2211/005C21D2211/008C22C38/18C21D8/0273C21D2211/001C22C38/105C22C38/20C22C38/32C23C2/06
Inventor 土桥诚悟小峰慎介中垣内达也南秀和
Owner JFE STEEL CORP