STEEL PLATE EXHIBITING EXCELLENT BENDABILITY BY LINE HEATING AND PROCESS FOR PRODUCTION OF THE PLATE

摘要

For the purpose of improving the operating efficiency in the plate bending by line heating, the invention provides a steel plate which exhibits large bending deformation even under the conditions of enhanced heating rate and shortened heating time and a process for production of the plate. The steel plate has both a chemical composition which contains by mass C:0.01 to 0.08%, P: =0.05%, S: =0.05%, Al: 0.002 to 0.1%, and N: 0.001 to 0.008% with the balance being iron and unavoidable impurities and a microstructure which comprises a non-deformed ferrite phase at an area fraction of 90% or above and in which the mean grain diameter of theferrite phase is 15 to 45µm and cementite particles having circle-equivalent diameters of 0.5µm or below are present in the ferrite grains at a number density of 100000 particles/mm2 or above. Further, the plate exhibits a yield strength of 235MPa or above at room temperature, a yield strength of 180MPa or below at 400°C, and an average Charpy absorbed energy of 100J or above at 0°C.