Investigations into mechanical properties of 50 and 70 mm thick high strength S690 butt-welded sections

Abstract

A comprehensive investigation into the mechanical properties of 50 and 70 mm thick high strength S690 steel plates and their butt-welded sections under tension was presented in this paper, and a total of 40 tensile tests were conducted. Firstly, a total of 18 proportional coupons with circular cross-sections were extracted at three different layers within the plate thicknesses. Tensile tests on all of these coupons were carried out to obtain their mechanical properties, and their variations across the plate thicknesses were also examined. Secondly, submerged arc welding was adopted to prepare butt-welded sections between these thick steel plates with various heat input energy. Micrographic examinations on typical heat-affected zones of the welded sections were also performed. Standard tensile tests on a total of 22 proportional coupons with rectangular cross-sections were carried out to obtain their mechanical properties, and the full range deformation characteristics of these coupons were assessed and compared, in particular, their tensile strengths and elongations at fracture. This paper presents important experimental evidence on the mechanical properties of these high strength steel plates of practical thicknesses in construction, and also of their butt-welded sections. It is demonstrated that there is little or even no reduction in their mechanical properties of these butt-welded sections, provided that the welding processes are properly controlled according to established welding practice. Hence, full strength butt-welded sections between these thick high strength S690 steel are readily achieved in practice, similar to those of the commonly adopted S355 steel. These important findings are contrary to general understanding as many researchers and engineers consider that the mechanical properties of these high strength S690 steel are reduced significantly after welding, irrespective of their plate thicknesses.