Mill trial for application of accelerated cooling combined with controlled rolling to X70 linepipe steel plates.

概要

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Application of accelerated cooling combined with controlled rolling (ACC) to X70 linepipe steel plates was tried using conventional Nb- and V-containing steels. Firstly, stability of the properties of ACC plates to possible rolling and cooling condition changes in commercial mass-production, uniformity of the properties along, across, and through a plate, weldability, and changes in the properties due to roller bending as a simulation of pipe forming were examined. Then, mill trial for UOE pipe forming was carried out. As a result, ACC plates had enough stability for mass-production and sufficient uniformity as pipe plates. Accelerated cooling increased tensile strength by 3 to 5kg f/mm2 at the finish-rolling temperature of 740 to 780°C, the cooling rate of approximately 9 deg C/sec, and the finish-cooling temperature of about 550°C. In the mill trial, no difference was found in UOE pipe formability between the ACC plates and the controlled rolled one. Dimensions of the ACC pipes satisfied the API specification. Mechanical properties of the base metal in the ACC pipe also met the API specification. A combination of Mn-Ni-Mo-Ti type and low Mn type wires with SiO2-CaO-CaF2 Al2O3 MgO type flux provided the SAW seam weld of the ACC pipe with sufficient strength and toughness for an X70 linepipe. It is concluded that there are no problems in applying ACC to X70 linepipe steel plates.
The Iron and Steel Institute of Japanの論文