7. Effect of Line-Heating on Notch Toughness of 50 kg/mm^2-Class High-Tensile Steel Plates

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It is inevitable that high-strength steels of the 50 kg/mm^2-class suffer from some embrittlement when they are subjected to bending by the line-heating process. The embrittlement, however, is localized in some limited zone of the plate thickness. Therefore, it is a problem to estimate the notch toughness of the line-heated zone by the Charpy V-notch impact test as generally performed. In this study, an investigation was made to find the behaviour of the full thickness of the plates to the characteristics of brittle fracture initiation (by the deep-notch test) and brittle fracture propagation arrest (by the double-tension and ESSO tests) at the line-heated zone, using large-sized test specimens including full thickness plate. The results of the above-mentioned tests are examined about criterions of _vT_<rs>, _<16>T_<ic=10>, _<16>T_<akc=220> and _<16>T_<akc=439>. Consequently, having control of cooling condition, the more efficient conditions of line-heating than the actually suggested ones are obtained without the much embrittlement of plate. The line-heating conditions are outlined as follows; 1) In air-cooling after heating, there is no unfavourable effect observed even if the heating temperature is as high as 800℃〜900℃. 2) In water-cooling immediately after heating, there is no unfavourable effect observed when the heating temperature is as high as 6OO℃〜650℃. 3) In water-cooling during air-cooling after heating, there is comparatively little unfavourable effect observed when the heating temperature is 800℃〜900℃, as long as the temperature at the start of water-cooling is below 500℃.
社団法人日本船舶海洋工学会の論文

7. Effect of Line-Heating on Notch Toughness of 50 kg/mm^2-Class High-Tensile Steel Plates

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