Mechanical characteristics and microstructure of weld joint of high-temperature martensitic steel containing 9% Cr

The structure and mechanical characteristics of a weld joint of 10Kh9K3V2MFBR steel (0.097 C, 0.17.Si, 0.54 Mn, 8.75 Cr, 0.21 Ni, 0.51 Mo, 0.07 Nb, 0.23 V, 0.004 N, 0.003 B, 1.6 W, 0.15 Cu, and Fe for balance, wt %) have been studied; the joint was produced by hand welding in an argon atmosphere using 03Kh20N45M7G6B welding wire (0.3 C, 20 Cr, 45 Ni, 7 Mo, 6 Mn, and 1 Nb, wt %). The weld joint is divided into the zone of the base metal, a thermal effect zone, which consists of zones that contain fine and coarse original austenitic grains, and the zone of seam metal. It has been shown that the weld joint of 10Kh9K3V2MFBR steel possesses high strength characteristics at the room temperature under static loading and a satisfactorily impact toughness, which has the minimum value of 30 J/cm 2 in the zone of the seam metal and does not depend on the temperature. With a decrease in the temperature from the room temperature to 253 K, a ductile–brittle transition occurs in the thermal effect zone. Creep tests carried out at the temperature of 923 K have shown that the long-term strength of the weld seam is lower than that of the base material in the entire stress range being tested. At stresses of 140 MPa or higher, the acceleration of creep in the weld seam is observed, while at low stresses of about 120 MPa, the rates of creep in the weld seam and in the base metal remain similar until the transition to the stage of accelerated fracture occurs. The difference in the values of the long-term strength is due to premature fracture, which occurs in the thermal effect zone with the finegrained structure.