Time optimization of the step loading technique in hydrogen embrittlement small punch tests

Abstract

The small punch tests consists of punching a plane small specimen until it breaks. This technique is very interesting in situations where there is a shortage of material. In recent works, it has been used with steel employed in aggressive environments, to estimate the threshold stress under which subcritical cracking will never occur. It has been presented in previous papers in combination with standard ASTM 1624, applying gradually increasing constant loads until the sample fails, to reduce the duration of the test and the results dispersión.In the present paper, a further optimization is performed on the steps durations for SPT, simplifying the test and therefore helping to reduce the lab workload while at the same time saving costs and resources and increasing productivity. The present work is carried out on an X80 medium-strength rolled steel in hydrogen embrittlement environments under three different levels of cathodic polarization in an acid electrolyte; the chosen steel belongs to the lowest hardness range (33 ≤ HRC < 45) according to the ASTM 1624 standard. Different steps duration from 10 to 60 mintures had been analyzied, cocluding that 20–40 min for 1st to 10th and 11th to 20th steps respectivley are proposed as the minimum ones to reach accurate results. The proposed optimization allows to reduce the total test duration, being for sure of great interest for the metal industry as well as for the scientific comunity.