Variation of microstructures and mechanical properties in the post-weld heat-treated HAZ of Cu containing HSLA steel welds

Abstract

The present study focuses on the effect of Cu and post-weld heat treatment (PWHT) on the microstructure and mechanical properties in the coarse grained heat affected zone (CGHAZ) of Cu containing high strength low alloy (HSLA) steel welds. For this study, HSLA steels with and without Cu were prepared in laboratory. Mechanical properties were estimated by Vickers hardness and Charpy impact tests. As a result, despite PWHT, the Vickers hardness did not change noticeably; however, the impact toughness deteriorated significantly with increasing PWHT time. In case of Cu added steel, intergranular brittle fractures occurred after PWHT, due to the strengthening of the grain interior by precipitation of Cu particles. Additionally, the formation of a soft denuded grain boundary zone also played a significant role in lowering the fracture toughness during PWHT.

Effects of B on microstructure and hardenability of resistance seam welded HSLA linepipe steel

“…4b and c were (Ti,Nb)(C,N) carbonitrides precipitated during the TMCP for hot coils as well as seam heat treatment of pipes. 4,5 Therefore, in the as welded 16B steel pipe, because most of the solute B atoms were already consumed to form the B precipitates near the grain or phase boundaries, the effect of B on the improvement of hardenability was negligible, giving rise to little differences in microstructure (Fig. 1) and hardness (Fig.…”

“…[1][2][3][4][5] However, recently, higher graded linepipe steels have been required because of demands for high pressure gas transportation and reduction in thickness of linepipes.…”

“…High strength low alloy (HSLA) steels have been widely used as oil and gas transportation linepipes due to the excellent combination of high strength and ductility. [1][2][3][4][5] However, recently, higher graded linepipe steels have been required because of demands for high pressure gas transportation and reduction in thickness of linepipes.…”

“…One way to enhance the mechanical properties of HSLA linepipe steels is the addition of alloying elements, such as Mn, Nb, Ti, V, Cu and B. [3][4][5][6][7][8][9][10][11][12] Especially, B has been often added to linepipe steels because even a tiny amount of B effectively increases the hardenability of steels. [6][7][8][9][10][11][12] Therefore, many investigators have studied the segregation and precipitation behaviours of B in austenite [6][7][8] and their effects on the microstructure and mechanical properties of steels.…”