Evaluation of hydrogen content in the surface layer of austenitic stainless steel by means of micro-indentation test with a spherical indenter

Abstract

In order to investigate the relationship between hydrogen-induced hardening of austenitic stainless steel and the hydrogen content, the spherical micro-indentation tests and thermal desorption analysis have been conducted on hydrogen charged austenitic stainless steel JIS SUS316L. Due to the relatively low hydrogen embrittlement susceptibility, this material has been widely used in a hydrogen environment. Hydrogen has been charged by using a cathodic method. In order to change the hydrogen content, charging current density and charging time were changed from 0.01 to 1.0 mA/mm², from 0 to 48 h, respectively. The obtained results show the hardness increases along with charging current density and charging time. The maximum change in the hardness is 28 %. Hydrogen content also depends on the charging current density and charging time. These relationships result in the strong linear correlation between hydrogen-induced hardening rate and the hydrogen content. Their correlation factor is 0.98 and the probability that these are uncorrelated is less than 0.001 %. The depth of hydrogen absorption was investigated by using secondary ion mass spectroscopy (SIMS). Hydrogen-induced hardening might be due to dislocation-pinning effect of hydrogen during indentation process. This phenomenon is dependent on not so much hydrogen absorption depth as hydrogen content. By using this phenomenon, there is a possibility to apply micro-indentation tests for evaluation of local hydrogen content.