| 摘要 |
PURPOSE:To improve the low-temp. toughness of a weld heat affected zone by decreasing the content of Al as far as possible, adding Ti to a molten steel after the deoxidation treatment thereof to disperse the precipitate uniform and fine nitride, oxide, etc. of Ti in the stage of producing a steel for welding. CONSTITUTION:The molten steel consisting, by wt%, of <0.19% C, <0.80% Si, 0.40-2.0% Mn, <0.020% P, <0.020% S, <0.0050% N, <0.0050% O or <0.020% Al as basic components, or further contg. a specific ratio of 1 or >=2 kinds among Ni, Cr, Mo, Nb, Cu, V, B, REM, Ca, Mg, and Zr is subjected to the deoxidation treatment and thereafter an adequate ratio of Ti is added thereto. The content of Al having the high affinity to N is not so low and therefore, the N in the molten steel does not form AlN and the pulverized particles of TiO, TiN and TiON series having 100-500Angstrom particle size and 5X10<7>-10<9>/mm<3> number of particles are uniformly deposited to provide the ferrite precipitation nuclei of the weld heat affected zone. The low temp. toughness of the weld heat affected zone is thus improved.
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