Cold-rolled steel sheet with high yield ratio and excellent weather resistance and its manufacture method
A technology of cold-rolled steel sheet and high yield-strength ratio, applied in the field of high-strength cold-rolled steel sheet and its manufacturing, can solve problems such as damage to workability, center segregation of cold-rolled steel products, etc., and achieve energy saving, high yield-strength ratio, The effect of improving annealing efficiency
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[0045] The cold-rolled steel sheet of the invention has both high strength and high yield ratio. According to an exemplary embodiment of the present invention, the steel plate has a tensile strength of at least 80 kg / mm 2 , such as 80-110kg / mm 2 . The steel plate has a yield strength of at least 80%, such as 85% to 94%. In addition, the steel plate has a ductility of at least 10%.
[0046] These characteristics meet the requirements of the above-mentioned composition system and can be obtained by the low temperature annealing of the present invention. The low temperature annealing may partially retain the deformed grains in the microstructure, rather than fully recovering them. The microstructure of the present invention may be ferrite or a mixture of ferrite and pearlite, but is not limited thereto.
[0047] Hereinafter, a method of manufacturing a cold-rolled steel sheet will be described.
[0048] A method of manufacturing a steel material having the above composition...
Embodiment 1
[0060] The normalized corrosion index (CI) and weather resistance of steel materials having the compositions shown in Table 1 were measured. The results are shown in Table 2.
[0061] In the weather resistance test, the steel material was subjected to a salt spray test (SST) at 30° C. for 480 hours with 5% salt water (NaCl solution). Here, the corrosion resistance index (CI) is an index for estimating weather resistance according to ASTM G101. The higher the corrosion resistance index, the stronger the weather resistance.
[0062] The corrosion resistance index is mainly obtained based on alloying elements, and satisfies the following formula.
[0063] Corrosion resistance index (CI)≤26.01(%Cu)+3.88(%Ni)+1.2(%Cr)+1.49(%Si)+17.28(%P)-7.29(%Cu)(%Ni)-9.10(% Ni)(%P)-33.39(%Cu) 2
[0064] Table 1
[0065]
[0066] Table 2
[0067]
[0068] As shown in Table 2, comparative steel 2 has a low corrosion resistance index and a high corrosion weight loss, so it is difficult ...
Embodiment 2
[0071] Each of the steel materials, that is, the inventive steel materials 1 and 2 and the comparative steel materials 1-4 in Table 1 of Example 1, was used to manufacture cold-rolled steel sheets under the conditions described in Table 3. The mechanical properties and workability properties of each steel sheet were measured, and the results are shown in Table 4.
[0072] table 3
[0073]
[0074] Table 4
[0075]
[0076] As shown in table 4, the embodiment 1-4 of the present invention whose chemical composition and production conditions meet the conditions of the present invention obtains respectively at least 80kgf / mm 2 Tensile strength, yield ratio of at least 80% and ductility of at least 10%. The embodiment of the present invention does not crack during the bending process, so it can be made into a steel plate with high strength and high yield ratio.
[0077] Meanwhile, Comparative Examples 1-5, whose chemical composition satisfies the conditions of the steel ma...
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Abstract
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