TEMPERATURE-DEPENDENCE OF TENSILE PROPERTIES OF 2.25 CR-1MO STEEL BASE, WELDMENTS AND SIMULATED HEAT-AFFECTED ZONE STRUCTURES

The heat affected zones (HAZ) of 2.25 Cr-1Mo steel weldments prepared by the shielded metal arc welding process using basic coated 2.25 Cr-1Mo electrodes consisted of coarse-grained bainite, fine-grained bainite and intercritical structure. The three zones of HAZ have been successfully simulated with respect to microstructure, hardness and grain size by controlled heat treatment cycles in the temperature range 1023 - 1623 K. Tensile tests at a strain rate of 3 x 10(-4)s-1 over the range 298-873 K showed that 0.2% yield strength and ultimate tensile strength values for the various microstructural conditions were in the descending order of coarse grained bainite, fine grained bainite, base metal, weldments and intercritical structure. Intercritical structure and coarse grained bainite showed respectively the maximum and minimum ductility. Fine grained bainite exhibited an ideal combination of strength and ductility in the HAZ. Dynamic strain ageing occurred in the temperature interval 423 - 673 K in all the material conditions except coarse grained bainite.