| Budget Amount *help |
¥29,700,000 (Direct Cost: ¥29,700,000)
Fiscal Year 1985: ¥9,400,000 (Direct Cost: ¥9,400,000)
Fiscal Year 1984: ¥20,300,000 (Direct Cost: ¥20,300,000)
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| Research Abstract |
50kgf/ <mm^2> -calss high-tensile steel plate produced by newly TMCP (thermo-mechanical controll process) is superior to cenventional rolled steel plate in weldability (resistance to cold cracking) as well as in toughness of HAZ of the high heat-input welded joint. If the applicability of this kind of TMCP steel is made clear, this must contribute to the practical merit from the engineering sense for fabricating the large scale ships and the other welded structures. However, in the HAZ of high heat-input welded joint of the TMCP steel of which carbon equivalent is low, softening behavior occurs inevitably. In the present study, considerations have been carried out on the acceptable range of the softening level of HAZ of the new TMCP steel welds from the structural integrity point of view. The various kinds of tests, such as weldability tests, tensile tests of HAZ specimen and welded joint specimens, fatigue tests, bending tests, and buckling test, have been conducted for determining th
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e allowable range of the selection of the TMCP HT50 steels to satisfy the requirement in the practical ship-structural design.
The degree of softening in HAZ of high heat-input welds depends upon the carbon equivalent Ceq. of steel used. The simplified equation for evaluating strength of the HAZ zone was given as a function of Ceq. The static strength of welded joints with the softening HAZ becomes lower than that of conventional welded joints if the degree of softening is remarkable. In the present research, the simplified evaluation method was proposed in order to calculate static tensile strength of welded joint with lower strength region. As a result, it was found that even with the maximum heat-input welding process prevalently in use in most of the domestic ship-yards, the tensile strength of the welded joint thereby produced in wide plate would be 50kgf/ <mm^2> or more and appoximate that of the base metal when Ceq. <>!=> 0.25%. Moreover, if we use the TMCP steel of which carbon equivalent is in the above range, fatigue strength and final load carrying capacity, e.g. buckling strength, are sufficient values in the practical use as ship structures.
According to the present research, the applicability of the new TMCP HT50 steel and its applicable range were clarified. Less
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