JP2003293083A5 - - Google Patents

Description

First group: B: 0.0002 to 0.01%
Second group: Ti, Nb, V and Zr: 0.005 to 1.0% in total of one or more types,
Third group: Cr, Mo, Cu and Ni: 0.005 to 3.0% in total of one or more kinds,
Group 4: Ca: 0.0001 to 0.005% and REM (rare earth element): 0. One or more of 0001 to 0.20% (3) When continuously casting the steel having the chemical composition described in (1) or (2) above, at a position of 10 mm from the solidification shell surface from the start of solidification of the molten steel. Until the solidified part reaches 1300 ° C., the solidified layer within 10 mm from the surface of the solidified shell is cooled to a cooling rate of 10 ° C./second or more to form a slab, and then the slab is 950 to 1280 ° C. after rough rolling in the temperature range, (Ae ₃ point + 100 ℃) ~Ae total reduction ratio in the temperature range of ₃ points 70%, at finishing temperatures Ae ₃ point or more, and the following formula (1) and (2) Or finish-rolling under conditions satisfying the following formula (3), within 2 seconds after finishing rolling, water-cooled to a temperature range of 600 to 800 ° C. at an average cooling rate of 30 ° C./second or more, and then 3 After air cooling for ~ 15 seconds, further average cooling rate Method for manufacturing a hot-rolled steel sheet, characterized in that wound water cooled at 0 ° C. / sec or more.
△ FT ≦ 0.8 × △ RT (1)
50 ℃ <△ FT ≦ 100 ℃ (2)
ΔFT ≦ 50 ° C (3)
Here, ΔFT is the fluctuation range (° C.) of the hot finish rolling completion temperature, and ΔRT is the fluctuation range (° C.) of the hot rough rolling completion temperature.
(4) A method of producing a hot-rolled steel sheet by finish rolling after rough rolling in the same manner as (3) above, when continuously casting steel having the chemical composition described in (1) or (2) above. after rough rolling the cast slab, (Ae ₃ point + 100 ℃) ~Ae total reduction ratio in the temperature range of ₃ points 70%, at finishing temperatures Ae ₃ point or more, and the following formula (4) and (5) After finishing finish rolling, water cooling to an average cooling rate of 30 ° C./second or more to a temperature range of 600 to 800 ° C. within 2 seconds, and then air cooling for 3 to 15 seconds, Furthermore, the manufacturing method of the hot-rolled steel sheet characterized by winding with water cooling at an average cooling rate of 30 degrees C / sec or more.
ΔFT {Σ (0.8 ⁿⁱ × εi)} ≦ 300 (4)
△ FT ≦ 100 ℃ (5)
Here, ΔFT is the fluctuation range (° C.) of the hot finish rolling end temperature, n is an integer, and the exit temperature of the finish rolling stand of the material to be rolled is a finish at Ae ₃ points to Ae ₃ points + 100 ° C. The number of rolling stands is indicated, and ε i indicates the true strain at the time of reduction in the i-th stand from the upstream among the n rolling stands.
(5) The hot-rolled steel sheet wound by the production method according to the above (3) or (4) is cold-rolled at a reduction rate of 50% or more, and then annealed within a temperature range of 600 to 950 ° C. A method for producing a cold-rolled steel sheet.

From the results shown in FIG. 7, the TS × EL balance and the TS × λ balance of the hot-rolled steel sheet can be increased by making the relationship between ΔFT and ε _i satisfy the following formulas (4) and (5). . This is because strain can be effectively accumulated in the austenite region relatively easily by hot rolling to satisfy this condition.
ΔFT {Σ (0.8 ⁿⁱ × εi)} ≦ 300 (4)
△ FT ≦ 100 ℃ (5)
Furthermore, it has been confirmed that a cold-rolled steel sheet with good TS × EL balance and TS × r balance can be obtained by pickling the hot-rolled steel sheet under appropriate conditions, annealing after cold rolling.

[0122]
【Example】
In order to confirm the effect of the steel plate of the present invention, steel types AA to CD having chemical compositions shown in Tables 2 and 3 were cast using a vacuum melting furnace, and a slab having a thickness of 70 mm was produced by hot forging. Hot rolled steel sheets were manufactured using these slabs. In Tables 2 and 3 , the liquidus temperature (TL) and the temperature at _three points Ae are shown as reference values.

Claims (2)

The hot-rolled steel sheet according to any one of claims 1 to 3 , which contains 0.005 to 1% in total of at least one of Ti, Nb, V and Zr instead of a part of Fe. When continuously casting the steel having the chemical composition according to any one of claims 1 to 6, from the start of solidification of the molten steel until the solidified part at a position 10 mm from the solidified shell surface reaches 1300 ° C, A solidified shell within 10 mm from the surface is cooled to a cooling rate of 10 ° C./second or more to form a slab, and then the slab is roughly rolled in a temperature range of 950 to 1280 ° C., then (Ae ₃ point + 100 ° C. ) To Ae ₃ points, the total rolling reduction is 70% or more, the finishing temperature Ae is ₃ points or more, and hot finish rolling is performed under the conditions satisfying the following formulas (4) and (5). Within 2 seconds, the water is cooled to a temperature range of 600 to 800 ° C. at an average cooling rate of 30 ° C./second or more, then air-cooled for 3 to 15 seconds, and further cooled with water at an average cooling rate of 30 ° C./second or more. A method for producing a hot-rolled steel sheet.
ΔFT {Σ (0.8 ⁿⁱ × ε i )} ≦ 300 (4)
△ FT ≦ 100 ℃ (5)
here,
ΔFT: Fluctuation width of hot finish rolling end temperature
n: Number of finish rolling stands, which is an integer, and the exit temperature of the finish rolling stand of the material to be rolled is Ae ₃ points to Ae ₃ points + 100 ° C.
εi: True strain at the time of rolling down at the i-th stand from the upstream among the n rolling stands