Effect of heat treatment on the stress corrosion resistance of a microalloyed pipeline steel

In this work, the effect of heat treating on a pipeline steel exposed to a sulfide stress cracking (SSC) environment was investigated using LEFM compact specimens. In the as-received condition, specimens with crack orientations parallel and normal to the rolling direction were exposed to H(2)S saturated synthetic sea water at an applied stress intensity (K(I)) of 30 MPa.m(1/2). In both cases, crack propagation rates were very close to each other (da/dt = 8.77 x 10(-9) m/s), As the microstructure was modified by heal treating, the rates of crack growth exhibited appreciable differences under similar applied stress intensities. In the martensitic (as-quenched) condition, crack growth was relatively fast (da/dt = 4.72 x 10(-7) m/s) indicating severe hydrogen embrittlement. In the water sprayed, and in the quenched and tempered conditions, the LEFM specimens exhibited crack arrest events. This, in turn, enabled the determination of threshold stress intensity values (K(ISSC)) for the water sprayed, and for the quenched and tempered conditions of 26 and 32 MPa.m(1/2), respectively. In addition, favorable paths for microcrack growth were found to be provided by globular inclusions and grain boundary precipitates. (C) 1999 Elsevier Science Ltd. All rights reserved.