TH2401005385A - Steel plates, components, and methods for manufacturing them. - Google Patents

Abstract

DEPCT67 provides steel plates and components exhibiting excellent material uniformity and high strength, and methods for their production. The steel plates have a chemical composition with the following percentages by mass: C: 0.10% or more and 0.30% or less; Si: 0.01% or more and 3.0% or less; Mn: 1.0% or more and 3.5% or less; P: 0.002% or more and 0.100% or less; S: 0.0002% or more and 0.0200% or less; sol. Al: 0.20% or less (excluding 0%); N: 0.010% or less; and Ti: 0.008% or more and 0.10% or less. Balanced are Fe and unavoidable impurities, which influence the microstructure of the steel plates. In terms of area fraction, ferrite: 5% or more and 50% or less, and martensite and bainite combined: 50% or more and 95% or less. Non-recrystallizing ferrite in ferrite is 0% or more and 10% or less in terms of area fraction. Based on the overall microstructure, the difference between the maximum and minimum values of the area fraction of non-recrystallizing ferrite in the width direction of the steel sheet is 5% or less.

Claims (13)

DEPCT67 1. Steel plates with the following chemical composition, expressed in percentages by mass: C: 0.10% or more and 0.30% or less; Si: 0.01% or more and 3.0% or less; Mn: 1.0% or more and 3.5% or less; P: 0.002% or more and 0.100% or less; S: 0.0002% or more and 0.0200% or less; Al: 0.20% or less (excluding 0%); N: 0.010% or less; and Ti: 0.008% or more and 0.10% or less. Balanced is Fe and unavoidable impurities, which influence the steel plate's microstructure in terms of space fraction. Ferrite: 5% or more and 50% or less. And martensite and bainite in total: 50% or more and 95% or less. Non-recrystallizing ferrite in ferrite is 0% or more and 10% or less in terms of area fraction, based on the overall microstructure, and the difference between the maximum and minimum values of the area fraction of non-recrystallizing ferrite in the direction along the width of the steel sheet is 5% or less. 2. Steel plate pursuant to claim 1 where the difference between the maximum and minimum values of the area fraction of non-recrystallized ferrite in the longitudinal direction of the steel plate is 5% or less. 3. Steel plates according to claim 1 or 2, whereby the chemical composition continues, by % by mass, one or more selected elements from: Nb: 0.2% or less, B: 0.0050% or less, Cu: 1% or less, Ni: 0.5% or less, Cr: 1.0% or less, Mo: 0.3% or less, V: 0.45% or less, Zr: 0.2% or less, and W: 0.2% or less. 4. Steel plates pursuant to any one of Reservations 1 through 3, whereby the chemical composition continues, by % by mass, one or more selected elements from: Sb: 0.1% or less, Sn: 0.1% or less, Ca: 0.0050% or less, Mg: 0.01% or less, and REM: 0.01% or less. 5. Steel plates as per any of the claims 1 through 4, where the steel plates have a coating on the surface of the object. 6. Components obtained by subjecting any one of the steel plates under claims 1 through 5 to at least one forming and welding process. 7. Methods for the production of steel plates under any of the claims 1 through 4. The methods are comprised of: a hot rolling step of heating the steel slab to 1,220 °C or higher for 1.0 hour or more; hot rolling of the steel slab and coiling operation at coiling temperature of 650 °C or lower with a coiling temperature difference of 50 °C or lower in the temperature distribution in the width direction to obtain hot-rolled steel plates; a cold rolling step of cold rolling the steel plate after the hot rolling step to obtain cold-rolled steel plates; and an annealing step of heating the cold-rolled steel plate to an annealing temperature above point Ac1 and equal to or lower than (point Ac3 + 50 °C), the annealing temperature is consistent with Equation (1) in the range of 600 °C to 700 °C and with a temperature difference of 50 °C or lower in the temperature distribution in the width direction. [Mathematical Formula 1] (Equation) ••• Equation (1) in which t is the time (seconds) obtained by dividing the time taken from 600°C to 700°C into n equal parts (n: an integer equal to 10 or more). Ti = (Si+1 + Si) / 2 i: a natural number n or less. S1 = 600°C Sn+1 = 700°C and Si is the temperature (°C) at time t x (i - 1) seconds after the time when the temperature reached 600°C. 8. Method for the production of steel sheets under claim 7, whereby in the hot rolling step the steel slab is heated to 1,220 °C or higher for 1.0 hour or more, hot rolled and coiled at a coiling temperature of 650 °C or lower with a coiling temperature difference of 50 °C or lower in the width distribution and a coiling temperature difference of 70 °C or lower in the length distribution of the steel sheet to obtain hot-rolled steel sheets. 9. Methods for the production of steel plates in accordance with claims 7 or 8, including the coating procedure after the annealing step. 10. Method for the production of steel sheets in accordance with claim 9, in which the coating process shall involve hot-dip galvanizing. 11. Method for the production of steel sheets according to claim No. 10, where alloying operations are carried out after hot-dip galvanizing operations in the coating step. 12. A method for the production of steel plates under any one of the claims 9 through 11, which, after the coating step, involves reheating the steel plate to a freeze-cooling temperature equal to or above room temperature and equal to or below 250°C. The steel plate is then reheated to a freeze-cooling temperature of 440°C and the temperature of the steel plate is maintained for 20 seconds or more. 13. A method for manufacturing components that includes steps for making steel sheets produced by any one of the steel sheet manufacturing methods under claims 7 through 12 subject to at least one forming and welding process.