V-notch Impact Energy Research Articles

Friction taper plug welding for S355 steel in underwater wet conditions: Welding performance, microstructures and mechanical properties

The present work reports new results regarding developing the friction taper plug welding (FTPW) process in wet conditions for underwater welding and repairing solutions. In this study, the FTPW process, microstructures and mechanical properties of the weld are investigated. The main findings are as follows: defect-free FTP welds can be obtained with a 7000rpm rotational speed and an axial force of 30–50kN. In the heat-affected zone (HAZ) and the lower region of the weld metal (WM), a large volume of lath bainite and small amounts of acicular ferrite, polygonal ferrite, and martensite are observed. However, in the upper region of the WM, the microstructure mainly consists of lath martensite. The best results of ultimate tensile strength and V-notch impact energy are 500MPa and 39.5J, respectively, on the joint that was welded with a 45kN axial force. The impact failure is characterised by brittle fracture with a large area of cleavage and notably little quasi-cleavage and ductile.

Effect of modified heat treatment on mechanical properties of 300M steel

AbstractThe effects of modified heat treatment (MHT) on the mechanical properties of 300M steel have been studied to assess MHT steel for possible ultrahigh strength applications. The microstructure of MHT steel has variable amounts of martensite, carbide free upper bainite, and retained austenite. This is produced by partial isothermal transformation at 593, 623, or 673 Kfor the required times, followed by oil quenching and subsequent tempering at 473 K after 1173 K austenitisation. The optimum combination of plane strain fracture toughness with other relevant mechanical properties was obtained when 50 vol.-% bainite was associated with tempered martensite and retained austenite for MHT at 593 and 623 K. The MHT steel transformed at 593 K showed improved plane strain fracture toughness over conventional quenched and tempered steel at a similar tensile strength level, with little change of percentage elongation and Charpy 2 mm V-notch impact energy. Compared with conventional quenched and tempered steel, ...

Effect of bainitic transformation on mechanical properties of 0.6C-Si-Mn steel

The mechanical properties of 0.6C-Si-Mn steel transformed isothermally in the bainitic temperature region (593 and 648 K) were investigated. The mechanical properties of the steels were improved with increasing bainite and retained austenite and the corresponding decrease in martensite. Marked benefits of the mechanical properties were obtained for the steels containing the maximum content of retained austenite in the bainite matrix, independent of transformation temperature. For isothermal transformation at 593 K, the 0.2% yield stress, σy, ultimate tensile stress, σu, and notch tensile stress (NTS) were improved significantly, while the advantage of the per cent elongation and Charpy 2 mm V-notch (CVN) impact energy was relatively small. As a result of isothermal transformation at 648 K, the per cent elongation and CVN impact energy were dramatically improved, while the superiority of σy, σu and NTS was not much greater than isothermal transformation at 593 K. Compared to 0.6C steels transformed isothermally at the same temperatures, in which little appreciable retained austenite was found, the isothermally transformed steels having a microstructure consisting of bainite and retained austenite improved the mechanical properties remarkably. These results are described and discussed.