JPWO2023008003A5 - - Google Patents

Claims (10)

in % by mass,
C: 0.15% or more and 0.45% or less,
Si: 1.5% or less,
Mn: more than 1.7%,
P: 0.03% or less,
S: less than 0.0040%,
sol. Al: 0.20% or less,
N: 0.005% or less,
B: 0.0015% or more and 0.0100% or less,
Containing 0.005% or more and 0.080% or less in total of one or more of Nb and Ti,
Having a component composition in which the balance is Fe and unavoidable impurities,
Having a structure in which the area ratio of martensite to the entire structure is 95% or more and 100% or less,
The average grain size of the prior austenite grains is less than 11.2 μm,
A steel sheet in which the number density A of precipitates having an equivalent circle diameter of 500 nm or more satisfies the following formula (1).
A (pieces/mm ² )≦8.5×10 ⁵ ×[B] Expression (1)
Here, [B] represents the content of B (% by mass). The steel sheet according to claim 1, containing one or more selected from the following (A) to (D) as the component composition.
(A) in mass%, one or two selected from Cu: 1.0% or less and Ni: 1.0% or less,
(B) in mass%, selected from Cr: 1.0% or less, Mo: less than 0.3%, V: 0.5% or less, Zr: 0.2% or less, and W: 0.2% or less 1 or 2 or more
(C) By mass %, Ca: 0.0030% or less, Ce: 0.0030% or less, La: 0.0030% or less, REM (excluding Ce and La): 0.0030% or less, and Mg: 0.0030% or less. 1 or 2 or more selected from 0030% or less,
(D) In mass%, one or two selected from Sb: 0.1% or less and Sn: 0.1% or less The steel sheet according to claim 1 or 2 , having a plating layer on the surface of the steel sheet. A member using the steel plate according to claim 1 or 2 . A member using the steel plate according to claim 3. A steel slab having the chemical composition according to claim 1 or 2 is heated at a slab surface temperature from 1000 ° C. to a heating and holding temperature of 1250 ° C. or higher at an average heating rate of 10 ° C./min or less, and at the heating and holding temperature After holding for more than 30 minutes,
Hot finish rolling is performed under the conditions of a residence time of 20 seconds or more and 150 seconds or less at 900 to 1000 ° C. and a finish rolling temperature of 850 ° C. or more,
Cooling is performed at an average cooling rate of 40 ° C./sec or more in the range from the finish rolling temperature to 650 ° C.,
After that, it is coiled at a coiling temperature of 650 ° C. or less to form a hot rolled steel sheet,
A cold-rolled steel sheet is obtained by cold-rolling the hot-rolled steel sheet at a rolling reduction of 40% or more,
The annealing temperature is 800 to 950° C., and the cold-rolled steel sheet is heated from 400° C. to the annealing temperature at an average heating rate of 1.0° C./second or more,
Hold at the annealing temperature for 600 seconds or less,
Cooling from the annealing temperature to 420 ° C. at a first average cooling rate of 2 ° C./sec or more,
Cooling from 420 ° C. to a cooling stop temperature of 260 ° C. or less at a second average cooling rate of 10 ° C./sec or more,
A method for manufacturing a steel sheet, followed by continuous annealing at a holding temperature of 150 to 260° C. for 20 to 1500 seconds. immersing the cold-rolled steel sheet in a plating bath when cooling at the first average cooling rate in the continuous annealing,
The method for manufacturing a steel sheet according to claim 6, wherein the alloying treatment is performed by heating to 480 to 600°C after immersion in the plating bath. The method for manufacturing a steel sheet according to claim 6 , wherein the surface of the steel sheet is plated after the continuous annealing. A method for manufacturing a member, comprising the step of subjecting the steel plate according to claim 1 or 2 to at least one of forming and joining to form a member. A method for manufacturing a member, comprising the step of subjecting the steel plate according to claim 3 to at least one of forming and joining to form a member.