| The fracture toughness of a series of Fe-26Cr, Fe-26Cr-3Mo and Fe-29Cr-4Mo alloys, in strip gages, has been investigated. The materials were used in the annealed, as-welded (GTAW) and 540(DEGREES)C aged conditions. Aging at 540(DEGREES)C produced rapid precipitation of small, plate-like Cr(,2)N nitrides and was studied in detail. General characterization included tensile testing, optical and electron microscopy and extensive sub-size (1.5 mm) Charpy impact testing. R-Curve fracture toughness testing, using a standard tensile testing machine and a large compact tension specimen, was employed to measure the fracture toughness stress intensity factor values for 1.5, 3.0 and 4.5 mm strip. Load versus crack length data were used to calculate K values. The effects of temperatures down to -45(DEGREES)C and thickness were determined. Studies of TIG welded material included tensile testing, penetration studies, examination of hot-cracking susceptibility and sub-size Charpy testing with notches in the fusion zone and HAZ. Principal conclusions include the observation that fracture toughness stress intensity factors were in the range of 150 MPaSQRT.(m) throughout the range of conditions studied. A ductile tearing mechanism, with necking and microvoid coalescence occurring ahead of the crack tip prior to crack extension, was found to occur, and is analyzed. The alloying effects of Mo, Ni, Ti, Nb and (C('+)N) content on properties are focussed upon throughout this work. |
