Steel wide flats (SM50A) produced by electric furnaces are gradually used as plate elements of the main members in steel building structures, as well as ones by blast furnaces. In Japan, 6 makers produce this kind of flats, which range of the sectional sizes is from 19mm×200mm to 36mm×300mm. These are inclined to include so-called "tramp elements", for example, Cu, Cr, Sn, so on, because the main raw material is supplied from scrap iron. Therefore, it is necessary to clarify the fracture behavior and mechanical characteristics on the base metals and the weld zones, when these are adopted to the flange plate of columns, especially at the portion of the beam-column connections, where the stress state is very complicated. The present report describes the controlled temperatures at tapping teeming, preheating and finishing of rolling. It also summarises the chemical components, grain size and non-metallic inclusions. Tension tests and V notch Gharpy tests are carried out to clarify the anisotropy of mechanical properties and impact toughness of base metals. Maximum hardness is measured along a line at the section of the weld zone. The impact toughness at the welded joints are investigated by use of the V notch Charpy specimens sampled from the weld interfaces and heat affected zones. Finally tension tests are executed by cruciform welded joints. The all test results obtained from the steel by electric furnaces, are compared with those from the steel by blast furnaces.
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