High strength cold rolled steel sheet and method for manufacturing the same
a cold rolled steel and high strength technology, applied in the direction of manufacturing tools, furnaces, heat treatment equipment, etc., can solve the problems of cracking at press forming, non-uniform microstructure, and tendency to crack at the parts where deep drawing is performed, and achieve high strength, high strength, and high strength
Inactive Publication Date: 2006-02-23
JFE STEEL CORP
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- Description
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- Application Information
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Benefits of technology
The present invention provides a high strength cold rolled steel sheet with a TS of 340 to 440 MPa and a r value of 1.8 or more, preferably 1.7 or more. The steel sheet has a chemical composition of 0.015% or less of C, 1.5% or less of Si, 0.4 to 3% of Mn, 0.15% or less of P, 0.02% or less of S, 0.1 to 1% of sol.Al, 0.01% or less of N, 0.2% or less of Ti, by mass%. The method for manufacturing the steel sheet involves heating a slab, hot rolling, coiling, cold rolling, and annealing steps. The technical effect of the invention is to provide a high strength cold rolled steel sheet without any special manufacturing steps.
Problems solved by technology
However, when those parts are press formed by using the high strength cold rolled steel sheets, such as a steel sheet having the TS of 340 to 390 MPa and the r value of approximately 1.7, a steel sheet having the TS of approximately 440 MPa and the r value of approximately 1.5, or a steel sheet having the TS of approximately 590 MPa and the r value of approximately 1.0, cracking tends to occur at the parts where the deep drawing is performed.
However, it is believed that the cracking at press forming is caused by the non-uniform microstructure resulting from the segregation of P at casting.
However, the above-mentioned methods need the special manufacturing step, resulting in the increase in the manufacturing cost and the decrease in the productivity.
Method used
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[0062] Various types of steel Nos. A to X shown in Table 1 were smelt and continuously cast into slabs having a thickness of 230 mm. After heating these slabs at the heating temperature SRT shown in Table 2, they were hot rolled to 3.2 mm thick at the finishing temperature FDT shown in Table 2, followed by the coiling at the coiling temperature CT shown in Table 2. The hot bands were cold to 0.8 mm thick and subsequently annealed at the annealing temperature AT shown in Table 2 in CAL, CGL, or BAF, followed by skin pass rolling with the elongation of 0.8%, thereby producing steel sheet Nos. 1 to 34. In CGL, the annealed steel sheets were immersed in the molten zinc bath at the temperature of 460° C., and heated at the temperature of 500° C. in the in-line alloying furnace. The amount of zinc on one side surface was 45 g / m2.
[0063] The r value and the TS were measured by the methods described above. In addition, the surface defects were measured by eye inspection so as to evaluate th...
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Abstract
The present invention relates to a high strength cold rolled steel sheet consisting of 0.015% or less of C, 1.5% or less of Si, 0.4 to 3% of Mn, 0.15% or less of P, 0.02% or less of S, 0.1 to 1% of sol.Al, 0.01% or less of N, 0.2% or less of Ti, by mass %, and the balance of Fe and inevitable impurities. In this steel sheet, 1≦([Ti] / 48) / ([C] / 12+[N] / 14) is satisfied, in which [M] represents the content of the element M. Since having the superior deep drawability and the TS of 340 to 590 MPa, the high strength cold rolled steel sheet of the present invention is preferably used for automobiles parts difficult to be press formed, such as a side outer panel and a door inner panel.
Description
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a high strength cold rolled steel sheet used for automobiles, home appliances, and the like, more particularly to a high strength cold rolled steel sheet having the superior deep drawability and the tensile strength TS of 340 to 590 MPa, and to a manufacturing method thereof. [0003] 2. Description of Related Arts [0004] Heretofore, for automobile parts having a complicated shape such as a side outer panel or a door inner panel, which are difficult to be press formed, the interstitial free (IF) mild cold rolled steel sheets (SPC270E,F) having the TS of approximately 270 MPa and the r value of 1.8 to 2.0, namely the superior deep drawability have been used. In recent years, due to the further increasing needs of the lighter automobile bodies, the high strength cold rolled steel sheets having the TS of 340 to 590 MPa have been progressively applied to those parts difficult to be press f...
Claims
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IPC IPC(8): C21D8/00C21D8/04C21D9/46C21D9/48C22C38/00C22C38/04C22C38/06C22C38/12
CPCC21D8/0426C21D8/0436C21D8/0473C22C38/06C22C38/02C22C38/04C21D8/0478C22C38/008C22C38/14C22C38/60
Inventor ONO, YOSHIHIKOKITANO, FUSATONAGATAKI, YASUNOBUTANAKA, YASUSHIANDO, HISANORI
Owner JFE STEEL CORP