Ductile-brittle transition temperatures and dynamic fracture toughness of 9Cr-1 Mo steel

The ductile-brittle transition temperature (DBTT) of 9Cr-lMo steel was characterized by an RTNDT-based K-IR curve approach and a reference temperature (T-0)-based master curve (MC) approach. The MC was developed at a dynamic loading condition (loading rate of 5.12 m/s), using precracked Charpy V-notch (PCVN) specimens, and the reference temperature was termed T-0(dy). The RTNDT and T-0(dy) were determined to be -25 degrees C and -52 degrees C, respectively. The T-0(dy) was also estimated from instrumented CVN tests, using a modified Schindler procedure to evaluate K-Jd; the result shows close agreement with that obtained from the PCVN tests. The ASME K-IR-curve approach proves to be too conservative compared to the obtained trend of the fracture toughness with temperature. The cleavage fracture stress, sigma(f)*, estimated from the critical length, l*, shows good agreement with that estimated from the load-temperature diagram (2400 to 2450 MPa), which was constructed from the CVN test results. The crack initiation mechanism has been identified as decohesion of the particle-matrix interface, rather than as the fracture of the particles.