The Effect of Processing Conditions and Cooling Rate on the Microstructure and Properties of API X-70 and API X-100 Steels

摘要

The final microstructure and subsequent properties of pipeline steel have been shown to be highly dependent of both the controlled rolling conditions and accelerated cooling conditions. This research utilized a novel physical deformation simulator to evaluate the evolution of microstructure in an X-70 and an X-100 grade pipeline steel during finish hot deformation and cooling. A series of plane strain compression (PSC) tests have been designed to simulate the processes of plate rolling and strip rolling, with the influence of finishing temperature and cooling rate being of particular interest. Single and multi-pass reductions at a constant strain rate of 70 s~(-1), together with constant delay times were used in this work. A total of three different deformation temperatures, namely, 950°C, 900°C, and 850°C were used for the present experiments, in which multipass isothermal deformation took place. Additionally, multipass deformation took place under non-isothermal conditions (i.e., descending temperature processing). Microstructures were characterized optically, and micro-hardness were obtained from the as-deformed PSC specimens. Analyses from the microstructural characterization together with the results from mechanical testing will reveal the optimal processing-microstructure-properties window for this important engineering alloy.