Abstract
From among welded joints produced by high-heat-input process in TMCP-manufactured 50kgf/mm^2 high tensile steel plate of relatively low carbon equivalent the authors selected those whose minimum Vickers hardness readings at HAZ have gone down to about 120Hv attesting to the significant HAZ softening and studied the characteristics of fatigue crack propagation along the weld HAZ in an artificially created seawater (natural-corrosive) environment, with the following results. (1) The fatigue crack propagation along the weld HAZ as determined in the artificially created seawater environment using welded test specimens fabricated from TMCP-manufactured 50kgf/mm^2 high tensile steel plate may be said to exhibit nearly same characteristics as the fatigue crack behavior in the base metal or weld HAZ of conventionally rolled steel plates already in use in huge quantities. (2) The fatigue crack propagation taking place along HAZs of the abovementioned welded test specimens in the artificially created seawater environment was found to accelerate to about three times the rate of crack propagation in the atmosphere. This "approx. ×3 acceleration" phenomenon holds true, as well, for the fatigue crack propagation in the mild steel plate base metal reported previously and also for the fatigue crack propagating along the HAZ of high-heat-input welded joint produced in TMCP-manufactured 50kgf/mm^2 high tensile steel plate of not so low carbon equivalent.
