High-strength steel sheet and method for producing same
A technology of high-strength steel plate and manufacturing method, which is applied in the direction of manufacturing tools, furnaces, heat treatment equipment, etc., can solve the problems of reduced ductility and stretch flangeability, the inability to simply realize thin-walled steel plates, and reduced formability of steel plates, etc. Achieve high utilization value, excellent ductility and hole expandability, and improved fuel efficiency
Active Publication Date: 2019-07-02
JFE STEEL CORP
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Problems solved by technology
[0003] However, in general, increasing the strength of the steel sheet leads to a decrease in ductility and stretch flangeability (hole expandability). Therefore, when the strength is increased, the formability of the steel sheet decreases, and problems such as cracks during forming occur.
Therefore, thinning of the steel plate cannot be easily achieved
Method used
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[0164] Steel having the composition shown in Table 1, with the balance consisting of Fe and unavoidable impurities was melted in a converter and cast into billets by continuous casting. The obtained slabs were hot-rolled under the conditions shown in Table 2, pickled, then annealed for hot-rolled sheets, then cold-rolled, and then annealed for cold-rolled sheets to obtain cold-rolled sheets (CR). In addition, some cold-rolled sheets are further subjected to hot-dip galvanizing treatment (including alloying treatment after hot-dip galvanizing treatment), hot-dip aluminum treatment or electro-galvanizing treatment to make hot-dip galvanized steel sheets (GI), Alloyed galvanized steel sheet (GA), hot-dip aluminized steel sheet (Al), and electro-galvanized steel sheet (EG).
[0165] In addition, the hot-dip galvanizing bath used the zinc bath containing 0.19 mass % of Al for GI, and used the zinc bath containing 0.14 mass % of Al for GA, and both bath temperatures were set to 465 ...
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Abstract
After adopting a predetermined constituent composition, this steel microstructure is set to have, in terms of surface area ratio, 35% to 80% ferrite, 5% to 25% martensite, and in terms of volume ratio, at least 8% retained austenite, the average crystal grain sizes of the ferrite, martensite and retained austenite are set to 6.0 [mu]m or less, 3.0 [mu]m or less, and 3.0 [mu]m or less, respectively, the average aspect ratios of the ferrite, martensite, and retained austenite crystal grains are set to each exceed 2.0 but not exceed 15.0, and the value obtained by dividing the Mn content (% mass)in the retained austenite by the Mn content (% mass) in the ferrite is set to at least 2.0. As a result, a high-strength steel sheet having excellent ductility and pore expandability, having a yieldratio (YR) of less than 68% and a tensile strength (TS) of at least 590 MPa is provided.
Description
technical field [0001] The present invention relates to a high-strength steel sheet that is excellent in ductility and stretch-flangeability (hole expandability) and has a low yield ratio, and a method for manufacturing the same, suitable as a member used in the automotive, electric, and other industrial fields. Background technique [0002] In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of protecting the global environment. Therefore, there is an active trend toward reducing the thickness of the vehicle body itself by increasing the strength of the vehicle body material and reducing the weight of the vehicle body itself. [0003] However, generally, increasing the strength of a steel sheet leads to a decrease in ductility and stretch-flangeability (hole expandability). Therefore, when increasing the strength, the formability of the steel sheet decreases, causing problems such as cracks during forming. Therefor...
Claims
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IPC IPC(8): C22C38/00C21D9/46C22C38/14C22C38/58C22C38/60C23C2/06C23C2/12C23C2/40
CPCC21D9/46C22C38/14C23C2/06C23C2/40C22C38/001C22C38/02C22C38/04C22C38/06C21D6/005C21D8/0226C21D8/0236C21D8/0263C21D8/0273C21D2211/001C21D2211/005C21D2211/008C23C2/12C23C2/024C23C2/02C23C2/0224C22C38/58C22C38/60C21D8/0205C21D8/0247C22C38/002C22C38/005C22C38/008C22C38/08C22C38/12C22C38/16C22C38/38
Inventor 川崎由康山下孝子植野雅康田路勇树小林崇船川义正
Owner JFE STEEL CORP