Abstract
Abstract Modified 9Cr-1Mo steel (9Cr-1Mo-0.2V-0.06Nb-0.1C-0.05N) was micro alloyed with boron (≈100 ppm) and cerium (≈80 ppm) to investigate its effect on creep rupture strength of the base steel and its weld joint. The microalloying was with the understanding that boron will increase the microstructural stability to increase the creep rupture strength and cerium will suppress the creep cavitation through its control over the soluble sulphur. Creep tests were carried out on the steels of T91, T91 micro-alloyed with boron, and T91 micro-alloyed with boron and cerium and its weld joints at 923 K over a stress range of 50 – 140 MPa. It was observed that the difference in creep rupture strength of the above base metals and its weld joints is marginally appreciable. Further, the steels were subjected to annealing at temperatures in and around the intercritical temperature range (1023 – 1273 K). Intercritical annealing reduced the hardness and tensile strength of the steels. Boron and cerium additions in the steel also resulted in marginal improvement on the hardness and tensile strength of the steels on intercritical annealing. It has been concluded that within the ASTM specification of the T/P 91 steel, the amount of nitrogen present concerned that the additions of 100 ppm boron and of 80 ppm cerium, and have no appreciable effect on creep rupture strength of the steel and its weld joint.
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