Cold-rolled steel sheet and manufacturing method thereof
A technology of cold-rolled steel sheets and manufacturing methods, applied in the field of cold-rolled steel sheets and their manufacturing, capable of solving problems such as high local yield strength, uneven alloying speed, and residual unrecrystallized grains
Active Publication Date: 2014-10-08
JFE STEEL CORP
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- Description
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- Application Information
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Problems solved by technology
However, Ti forms not only carbonitrides but also fine sulfides and carbon sulfides, and these fine precipitates sometimes hinder recrystallization and grain growth after recrystallization, so there is a problem that unrecrystallized grains remain locally
When non-recrystallized grains remain locally, there is a region with a local high yield strength, which may cause uneven shape after stamping, so it is not preferable.
In addition, when hot-dip galvanizing is performed, if there are residual parts of unrecrystallized grains on the surface of the steel sheet, the alloying rate will be uneven, and the appearance will also be uneven.
Method used
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Embodiment 1
[0088] Hereinafter, the effect of this invention is demonstrated concretely. First, molten steel having the composition shown in Table 1 was subjected to vacuum degassing treatment, and then cast into billets by continuous casting. Next, the steel slab was heated to remove scale, and then rough rolled to a thickness of 40 mm. Next, the surface layer of the steel sheet was cooled using a descaling device, then finish rolled to a thickness of 3.5 mm, and coiled at a coiling temperature of 700°C. In this case, the heating conditions of the slab, the surface temperature of the steel sheet after cooling before finish rolling, and the finish rolling temperature are shown in Table 2.
[0089]
[0090]
[0091] Next, the coiled steel sheet is pickled, then cold-rolled (cold rolling rate: 80%) to 0.70mm, as a test material, after degreasing and pickling as a pretreatment, it is carried out on a hot-dip galvanizing line. Annealing, hot-dip galvanizing, alloying, and skin pass ro...
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Abstract
Disclosed is a cold-rolled steel sheet that is an IF steel sheet containing Ti and has superior deep drawing characteristics in which a uniform appearance and shape uniformity after pressing can be obtained without carrying out special processing, and a method for producing the same. The IF steel sheet has Ti added. The steel sheet contains 0.02 - 0.1% Ti, 0.03% or less Sb, more than 0.005% and not more than 0.03% Cu, and Ti*, such that Ti* = (Ti%)-3.4 × (N%)-1.5 × (S%)-4 × (C%), in a range that satisfies 0 < Ti* 0.02. The steel sheet content is also in a range that satisfies (Sb%) = (Cu%) / 5. Furthermore the elemental Ti content (mass%) contained in deposits sized less than 20 nm in a sheet thickness surface layer part from each of the surfaces on both sides of the steel sheet to 10 µm is 9% or less of the total Ti content (mass%) in the steel sheet.
Description
technical field [0001] The present invention relates to a cold-rolled steel sheet that is soft and excellent in shape uniformity after processing and is used for outer panels of automobiles, and a method for producing the same. Background technique [0002] Conventionally, as exterior panels of automobiles, soft cold-rolled steel sheets and galvanized steel sheets having a tensile strength of less than 350 MPa and excellent workability have been widely used. For example, as a cold-rolled steel sheet that is soft and excellent in workability, a cold-rolled steel sheet manufactured by the following method, a so-called IF (Interstitial Free) steel sheet, is known: Hot rolling is performed to form carbonitrides at the stage of hot rolling the steel sheet to reduce solid solution C and solid solution N in the steel, and then cold rolling and recrystallization annealing are performed. [0003] Among such IF steel sheets, the IF steel sheet containing Ti as a carbonitride-forming ...
Claims
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IPC IPC(8): C22C38/00C21D9/46C22C38/60
CPCC22C38/14C21D9/48C22C38/12C21D2211/004C22C38/04C22C38/60C21D8/0405C22C38/06C21D8/04C22C38/004C22C38/02C22C38/16C22C38/001
Inventor 山下孝子杉原玲子长泷康伸饭塚俊治渡边恭二妻鹿哲也
Owner JFE STEEL CORP