Comparison of constant load, SSRT and CSRT methods for hydrogen embrittlement evaluation using round bar specimens of high strength steels

Abstract

Resistance to hydrogen embrittlement of low alloy steels was evaluated based on their critical hydrogen content and critical stress. Constant load test, Slow Strain Rate Technique (SSRT) and Conventional Strain Rate Technique (CSRT) were carried out using JIS-SCM435 and Vadded steels in six laboratories. It was confirmed that the same test results were obtained in different laboratories under the same test conditions. Furthermore, the relationships between the diffusible hydrogen content and nominal fracture stress obtained by means of CLT and by SSRT were similar to each other. In SSRT and CSRT, fracture surfaces showed Quasi-cleavage mode under small hydrogen content, while they showed Inter-granular fracture under large hydrogen content. In order to compare the three methods considering the concentration of hydrogen in stress field, locally accumulated hydrogen content under the same fracture stress was calculated. The order of the locally accumulated hydrogen content at a given fracture stress is as follows; SSRT 〈 CLT 〈 CSRT in JIS-SCM435, and CSRT 〈 CLT ≒ SSRT in V-added steels. The difference of the evaluation results for JIS-SCM435 is presumably attributed to the dependence of the interaction between hydrogen and dislocations on the strain rate.