Steel sheet having high young's modulus, hot-dip galvanized steel sheet using the same, alloyed hot-dip galvanized steel sheet, steel pipe having high young's modulus, and methods for manufacturing the same
View Patent ↗In an embodiment of a steel sheet having high Young's modulus, the steel can include in terms of mass %, e.g., C: 0.0005 to 0.30%, Si: 2.3% or less, Mn: 2.7 to 5.0%, P: 0.15% or less, 0.015% or less, Mo: 0.15 to 1.5%, B: 0.0006 to 0.01%, and Al: 0.15% or less, with the remainder being Fe and unavoidable impurities. One or both of {110}<223> pole density and {110}<111> pole density in the ⅛ sheet thickness layer can be 10 or more, and a Young's modulus in a rolling direction can be more than 230 GPa. Other embodiments can include, e.g., Mn: 0.1 to 5.0%, N: 0.01% or less, and one or more of Mo: 0.005 to 1.5%, Nb: 0.005 to 0.20%, Ti: at least 48/14×N (mass %) and 0.2% or less, and B: 0.0001 to 0.01%, at a total content of 0.015 to 1.91 mass %.
1. A steel sheet having high Young's modulus, which has a composition comprising, in terms of mass %, C: 0.0005 to 0.30%, Si: 2.5% or less, Mn: 0.1 to 5.0%, P: 0.15% or less, S: 0.015% or less, Al: 0.15% or less, N: 0.0005 to 0.01%; and
further comprising all of Mo: 0.005 to 1.5%, Nb: 0.005 to 0.20%, Ti: at least 48/14×N (mass %) and 0.2% or less, and B: 0.0001 to 0.01%, at a total content of 0.015 to 1.91 mass %,
with the remainder being Fe and unavoidable impurities,
wherein the {110}<223> pole density and/or the {110}<111> pole density in the ⅛ sheet thickness layer is 10 or more,
the {211}<011> pole density in the ½ sheet thickness layer is 6 or more, and
a Young's modulus in a rolling direction is more than 230 GPa.
2. The steel sheet having high Young's modulus according to claim 1 ,
wherein the respective contents of Mo, Nb, Ti, and B are Mo: 0.15 to 1.5%, Nb: 0.01 to 0.20%, Ti: at least 48/14×N (mass %) and 0.2% or less, and B: 0.0006 to 0.01%; and
the {110}<001> pole density in the ⅛ sheet thickness layer is 3 or less.
3. The steel sheet having high Young's modulus according to claim 1 ,
wherein the {110}<001> pole density in the ⅛ sheet thickness layer is 6 or less.
4. The steel sheet having high Young's modulus according to claim 1 ,
wherein the Young's modulus in the rolling direction is 240 GPa or more in at least a range from the surface layer to the ⅛ sheet thickness layer.
5. The steel sheet having high Young's modulus according to claim 1 ,
wherein the {332}<113> pole density in the ½ sheet thickness layer is 6 or more.
6. The steel sheet having high Young's modulus according to claim 1 ,
wherein the {100}<011> pole density in the ½ sheet thickness layer is 6 or less.
7. The steel sheet having high Young's modulus according to claim 1 ,
wherein a BH amount (MPa) is in a range from 5 MPa or more to 200 MPa or less, and the BH amount is expressed by the following formula, BH=σ 1 −σ 2 (MPa), wherein σ 2 (MPa) is the flow stress when the steel sheet has been stretched 2%, and σ 1 (MPa) is an upper yield point when, after the steel sheet has been stretched 2%, it is treated with heat at 170° C. for 20 minutes and then stretched again.
8. The steel sheet having high Young's modulus according to claim 1 , which further comprises Ca: 0.0005 to 0.01 mass %.
9. The steel sheet having high Young's modulus according to claim 1 , which further comprises one or two or more of Sn, Co, Zn, W, Zr, V, Mg, and REM at a total content of 0.001 to 1.0 mass %.
10. The steel sheet having high Young's modulus according to claim 1 , which further comprises one or two or more of Ni, Cu, and Cr at a total content of 0.001 to 4.0 mass %.
11. A hot-dip galvanized steel sheet comprising:
the steel sheet having high Young's modulus according to claim 1 , and
hot-dip zinc plating that is applied to the steel sheet having high Young's modulus.
12. An alloyed hot-dip galvanized steel sheet comprising:
the steel sheet having high Young's modulus according to claim 1 ; and
alloyed hot-dip zinc plating that is applied to the steel sheet having high Young's modulus.
13. A steel pipe having high Young's modulus comprising the steel sheet having high Young's modulus according to claim 1 ,
wherein the steel sheet having high Young's modulus is curled in any direction.
14. The steel sheet having high Young's modulus according to claim 1 ,
wherein the steel sheet is manufactured by a method which comprises heating a slab having the composition at a temperature of 1000° C. or more and subjecting the slab to hot rolling so as to obtain a hot rolled steel sheet, and
in the hot rolling, the rolling is carried out in such a manner that a coefficient of friction between the pressure rollers and the steel sheet is greater than 0.2, an effective strain amount ε* calculated by the following formula [1] is 0.4 or more, and the total of the reduction rates is 50% or more, and the hot rolling is finished at a temperature in a range from the Ar 3 transformation temperature or more to 900° C. or less,
ɛ
*
=
∑
j
=
1
n
-
1
ɛ
j
exp
[
-
∑
i
=
j
n
-
1
(
t
i
τ
i
)
2
/
3
]
+
ɛ
n
[
1
]
in which n is the number of rolling stands of the finishing hot rolling, ε j is the strain added at the j-th stand, ε n is the strain added at the n-th stand, t i is the travel time (seconds) between the i-th and the i+1-th stands, and τ i can be calculated by the following Formula [2] using the gas constant R (=1.987) and the rolling temperature T i (K) of the i-th stand,
τ i =8.46×10 −9 ×exp{43800 /R/T i } [2].