Test method for threshold of hydrogen-induced crack growth KI,H of SCM435 in 115 MPa hydrogen gas

Abstract

In order to investigate the suitable test methods for determining threshold of hydrogen-induced crack growth, KI,H, JIc, none-unloading JIc, constant-load and constant-displacement tests were conducted in 115 MPa hydrogen gas at room temperature, using SCM435 low alloy steels whose tensile strengths were between 824 and 1127 MPa. Constant-load and constant-displacement tests have been standardized by ASME KD-10 for determining KI,H in hydrogen gas. JIc test has been standardized by ASTM E1820 for determining fracture toughness JIc or KIc in air. Recently, JIc test was done in hydrogen gas to obtain KI,H. In this study, there were many cases when JIc tests were not conducted in hydrogen gas, because CT specimens broke before the first unloading. Then, none-unloading JIc test, where unloading processes were eliminated in JIc test, was employed in hydrogen gas. All four tests were done under small scale yielding in 115 MPa hydrogen gas. KI,H obtained by four tests was almost the same. KD-10 demands that constant-load and constant-displacement tests of ferritic steels such as SCM435 are done for 1000 hours. Contrary to this, none-unloading test at displacement rate of 2×10-3 mm/s was finished within one hour. It was concluded from these results that none-unloading JIc test was the best test for determining KI,H in 115 MPa hydrogen gas. On the other hand, JIc test was the only test for determining KIc in air, because KIc was obtained under large scale yielding.

Keywords

• scm435
• 115 mpa hydrogen gas
• threshold of hydrogen-induced crack growth
• ki,h
• test method