Analisis del procedimiento de ensayo de la fragilización por hidrógeno mediante el uso del SPT

Résumé

Three structural steels were used to evaluate the influence of hydrogen in their mechanical properties. A testing procedure based on the Small Punch Test (SPT) was proposed to determinate hydrogen embrittlement and the results obtained in these tests were compared with the ones obtained using standard fracture toughness tests. Two pre-charging methods were also applied to introduce hydrogen in the samples. The first method was using gaseous hydrogen in a high-pressure reactor at 19.5 MPa and 450ºC for 21 hours. The second one was carried out by means of cathodic charging from 2M H2SO4 + As2O3 electrolyte under a current density of 2 mA/cm2 . Under these conditions, the effect of the steel’s chemical composition and microstructure on the corresponding embrittlement indexes was determined from results obtained on notched small punch and standard fracture toughness tests using energy and crack tip opening displacement (CTOD) criteria. Furthermore, hydrogen diffusivity was also determined by means of permeation tests, as to explain and justify the results. The low thickness and lower stress triaxiality of the SPT samples may also be taken into account to justify the lower embrittlement indexes detected when this miniature test was used.