High-strength steel sheet and method for manufacturing same
A technology of high-strength steel plate and manufacturing method, which is applied in the direction of manufacturing tools, metal material coating process, heat treatment furnace, etc. Efficiency improvement and the effect of high utilization value
Active Publication Date: 2021-09-28
JFE STEEL CORP
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Problems solved by technology
However, the above-mentioned documents only studied the improvement of the ductility and hole expandability of high-strength steel sheets, and the improvement of hole expandability and bending properties brought about by the control of the dispersion state of the second phase composed of retained austenite and martensite Sex was not studied
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[0123] Steel having the composition shown in Table 1, with the balance consisting of Fe and unavoidable impurities was smelted in a converter and cast into billets by continuous casting. After reheating the obtained slab to 1250°C, hot rolling is carried out under the conditions shown in Tables 2 and 3, optionally at Ac 1 Heat treatment and cold rolling below the transformation point, at Ac 3 Cooling after heating and holding above the phase transition point, at Ac 1 Above the phase transition point and Ac 1 After annealing below the transformation point +150°C, a high-strength cold-rolled steel sheet (CR) is obtained. Furthermore, a galvanizing treatment is performed to obtain a galvanized steel sheet (GI) and a galvannealed steel sheet (GA). It should be noted that two Ac 1 Above the phase transition point and Ac 1 In the case of annealing at a transformation point of +150°C or lower, after the first annealing, it is cooled to room temperature once, and then the second ...
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Abstract
The purpose of the present invention is to provide a high-strength steel sheet having 980 MPa or greater tensile strength and excellent formability, and a manufacturing method thereof. This high-strength steel sheet with excellent formability has a prescribed component composition and optimized manufacturing conditions, and has a steel composition which, by area ratio, has 35-80% ferrite, 5-35% quenched martensite, and at least 0.1% and less than 3.0% tempered martensite, has, by area ratio, greater than or equal to 8% retained austenite, and wherein the average crystal grain size of the ferrite is less than or equal to 6 [mu]m, the average crystal grain size of said retained austenite is less than or equal to 3 [mu]m, and the value obtained by dividing the average amount of Mn in the retained austenite by the average amount of Mn in the ferrite is greater than or equal to 1.5; the value obtained by dividing the sum of the area ratio of quenched martensite with a particle size greater than or equal to 3 [mu]m by equivalent circle diameter and retained austenite with an equivalent circle diameter greater than or equal to 3 [mu]m by the sum of the area ratio of the total quenched martensite and the total retained austenite is less than 0.4; and the value obtained by dividing the area ratio of the retained austenite contacting 3 or more ferrites having different crystal orientations by the area ratio of the total retained austenite is less than 0.6.
Description
technical field [0001] The present invention relates to a high-strength steel sheet with excellent formability and a manufacturing method suitable for use as members in the automotive, electric, and other industrial fields. High-strength steel sheet with excellent porosity and bendability. 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 towards reducing the weight of the vehicle body itself by increasing the strength of the vehicle body material to achieve thinner walls. and high formability materials. [0003] A high-strength steel sheet using a process-induced transformation of retained austenite has been proposed as a high-strength and high-ductility steel sheet. Such a steel sheet exhibits a structure having retained austenite, and is easily formed due to the retained austenite during forming of the stee...
Claims
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IPC IPC(8): C21D9/46C22C18/04C22C38/00C22C38/06C22C38/60
CPCC22C18/04C22C38/06C21D9/48C21D6/005C21D8/005C21D8/0426C21D8/0436C21D2211/005C21D2211/008C21D2211/001C21D1/26C21D1/185C21D8/0463C21D1/22C21D1/19C22C38/02C22C38/04C22C38/14C21D8/0447C23C2/02C23C2/06C23C2/28C23C2/40C23C30/00C22C38/38C22C38/001C23C2/024C23C2/0224C22C38/58C22C38/50C22C38/48C22C38/46C22C38/54C22C38/44C22C38/42C21D8/0226B21C47/02C21D8/0236C21D9/46C22C38/002
Inventor 远藤一辉川崎由康田路勇树船川义正青山麻衣
Owner JFE STEEL CORP