Influence of Manufacturing Process and Resulting Microstructure on HISC Susceptibility of 25Cr Duplex Stainless Steel Pipe

摘要

In this paper, the hydrogen induced stress cracking (HISC) susceptibility of 25Cr duplex stainless-steel tubulars produced through hot extrusion with- and without subsequent cold drawing, forging and centrifugal casting have been examined. Two different test methods have been used; i) Stepwise (slow) Load Increase, and ⅱ) Slow Strain Rate Testing. Samples pre-charged with hydrogen and samples without hydrogen were included in the test program. Pre-charged samples were also polarized cathodically during testing under stress. The microstructure was characterised, including measurements of austenite spacing. After testing, the samples were examined in an optical microscope for secondary cracks. In addition, the fracture surfaces were examined in a scanning electron microscope for characterization of fracture morphology. Reduction in area was calculated for all samples. Finally, hydrogen content was measured with a melt extraction technique. The outcome from a similar test with HIP and forged material were compared with the results from this test. The ranking of production methods regarding resistance against HISC from this test was as follows: Hot extruded pipes > hot extruded pipes with subsequent cold drawing > forged pipes > centrifugal cast pipes. The two test methods - Stepwise Load Increase and Slow Strain Rate Testing - gave consistent test results.