| 摘要 |
PURPOSE: A method of manufacturing a steel plate for welding fabric is provided to give superior toughness in weld heat-affected zone of the steel plate when welded by promoting transformation of acicular structure ferrite. CONSTITUTION: The steel plate is manufactured by the following step: (i) heat treatment of a steel slab that is composed of C 0.03-0.17wt.%, Si 0.01-0.5wt.%, Mn 0.4-2.0wt.%, Ti 0.005-0.2wt.%, Al 0.03-0.3wt.%, N 0.008-0.030wt.%, B 0.0003-0.01wt.%, W 0.001-0.2wt.%, P 0.03wt.% or less, O 0.00-0.03wt.%, the balance of Fe and inevitable impurities and that further satisfies below constituents ratio: 1.2<=Ti/N<=2.5, 10<=N/B<=40, 2.5<=Al/N<=7, 6.5<=(Ti+2Al+4B)/N<=14, 8<=Al/O<=22, 250<=Mn/O<=530 in the temperature range 1100 to 1250deg.C for 60-180min; (ii) hot rolling the steel slab at a reduction ratio higher than 40% during austenitic recrystallization; (iii) cooling the hot rolled steel slab at a cooling rate higher than 1deg.C/min until temperature of the steel slab reach a temperature of ferrite transformation temperature±10deg.C. In addition, the steel slab is manufactured by casting molten steel at 0.9-1.1m/min and then slowly cooling in 2nd cooling zone by spraying water 0.3-0.35L/kg. When the steel plate is welded, prior austenite smaller than 80μm is formed in heat affected zone, and acicular/polygonal structure ferrite smaller than 20μm occupies at least 70% in the heat affected zone when quenched.
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