High carbon thin steel sheet and method for producing same
Inactive Publication Date: 2014-03-20
JFE STEEL CORP
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Benefits of technology
The present patent aims to provide a method for producing a mild high carbon steel sheet with uniform properties in the sheet thickness direction and excellent formability. The method involves a two-step process of light reduction cold rolling followed by annealing. By controlling the reduction ratio and annealing temperature, the method ensures that nonuniform strain distribution and complex temperature control during annealing are minimized, resulting in a more uniform microstructure and better formability of the final product. Overall, this method improves the mildness of the high carbon steel sheet while maintaining its strength.
Problems solved by technology
In addition, the annealing after the cold rolling is composed of three steps including the combination of heating in specific temperature ranges just below and just above the Ac1 transformation point, so that the temperature control during annealing is complicated and, from this point of view as well, nonuniformity occurs in the steel sheet characteristics easily.
Therefore, so-called hydrogen annealing is necessary and practical annealing equipment is limited.
Therefore, execution is not possible unless equipment having very high cooling capacity is available and, in addition, characteristics of the resulting steel sheet also become nonuniform easily because cooling variations exert an influence easily.
Method used
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[0087]Steel slabs A to K having chemical compositions shown in Table 1, where the remainder was composed of Fe and incidental impurities, were made into hot rolled steel sheets having a sheet thickness of 4.0 mm under the hot rolling condition shown in Table 2. Thereafter, scale on the steel sheet surface layer was removed by pickling. Subsequently, the resulting hot rolled steel sheets were cold-rolled under the cold rolling condition shown in Table 2, and were annealed under the annealing condition also shown in Table 2, so as to obtain Steel sheets 1 to 25. In this regard, the Ar3 transformation point and the Ac1 transformation point shown in Table 1 were determined by rough calculation from the chemical compositions of the steel on the basis of the following formulae.
Ar3 transformation point (° C.)=910−203[C]1 / 2+44.7[Si]−30.0[Mn]−11.0[Cr]+31.5[Mo]−15.2[Ni]
Ac1 transformation point (° C.)=727−29.1[Si]−10.7[Mn]+16.9[Cr]−16.9[Ni]
Here, [C], [Si], [Mn], [Cr], [Mo], and [Ni] represent ...
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Abstract
A steel sheet having a composition containing C: 0.20% to 0.50%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.02% or less, sol.Al: 0.08% or less, N: 0.02% or less, and Fe and incidental impurities, and a microstructure composed of ferrite and cementite, wherein each of the average grain size ds of the ferrite in the region from the surface of the steel sheet to the position at one-quarter of the sheet thickness and the average grain size dc of the ferrite in the region from the position at one-quarter of the sheet thickness of the steel sheet to the sheet thickness center is 20 to 40 μm, 0.80≦ds / dc≦1.20 is satisfied, the average grain size of the cementite is 1.0 μm or more, the spheroidizing ratio is 90% or more, and 90% or more of cementite is present inside ferrite grains.
Description
CROSS REFERENCE TO RELATED APPLICATIONS[0001]This is the U.S. National Phase application of PCT / JP2012 / 003194, filed May 16, 2012, which claims priority to Japanese Patent Application No. 2011-110918, filed May 18, 2011, the disclosure of these applications being incorporated herein by reference in their entirety for all purposes.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates to a high carbon steel sheet, in particular a mild high carbon steel sheet containing 0.20 to 0.50 percent by mass of C, and a method for manufacturing the same.BACKGROUND OF THE INVENTION[0003]In general, high carbon steel sheets are formed into various shapes and, thereafter, are subjected to a heat treatment for enhancing hardness, so as to be used for machine structural parts and the like. Among them, a high carbon steel sheet having a C content of 0.2 to 0.5 percent by mass can have enhanced mildness by being subjected to spheroidizing of cementite and is suitable for a raw material of...
Claims
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Login to View More IPC IPC(8): C22C38/44C22C38/18C22C38/00C22C38/06C22C38/04C22C38/02C21D8/02C22C38/14
CPCC22C38/44C21D8/0263C22C38/18C22C38/001C22C38/06C22C38/04C22C38/02C22C38/14C21D6/00C21D9/46C21D1/42C21D1/667C22C38/002C21D2211/003C21D2211/005C21D8/0226C21D8/0236C21D1/32Y02P10/25B21B3/00C22C38/58
InventorKOBAYASHI, TAKASHINAKAMURA, NOBUYUKIFUNAKAWA, YOSHIMASA
OwnerJFE STEEL CORP