Hydrogen embrittlement testing procedure for the analysis of structural steels with Small Punch Tests using notched specimens

Abstract

The influence of hydrogen on the mechanical properties of three structural steels has been evaluated. A testing procedure based on the Small Punch Test with notched specimens was used to measure hydrogen embrittlement. Two pre-charging methods were applied to introduce hydrogen in the samples. The first method used gaseous hydrogen in a high-pressure reactor at 19.5 MPa and 450 °C for 21 h. The second involved cathodic charging from 2 M H2SO4 + As2O3 electrolyte with a current density of 2 mA/cm2. The results obtained in the Small Punch Tests were compared with those obtained using standard fracture tests. The hydrogen embrittlement behaviour of the different steels, with special attention to the effect of their chemical compositions and microstructures, were compared. The embrittlement indexes obtained with Small Punch Tests are lower than those obtained with standard tests. The low thickness and lower stress triaxiality of the Small Punch Test specimens explains this result. Regardless of the test method used, hydrogen embrittlement grows with the strength of the analysed steel.