Abstract
The influence of boriding on hydrogen embrittlement was studied by means of delayed failure tests performed on borided UNI 30NiCrMo12 steel. The samples were borided at 900°C for 8 hours with powders ( B 4 C=30%, KBF 4=5%, SiC=65% and quenched at the end of the thermochemical treatment. Hydrogen was introduced into the samples under galvanostatic conditions (d.c. 10 mA/cm 2) by means of cathodic charge in a 0.1 N sulphuric acid solution kept at a constant temperature of 22° C±1. The tests carried out on borided specimens showed an appreciable increase in both the threshold load value and the crack incubation times with respect to the untreated steel. This behaviour is due to the barrier effect of the borided layer. With this coating, hydrogen entry into the base metal was delayed. As a consequence the critical hydrogen concentration in a potential fault was reached later and the crack nucleation and the fracture propagation were delayed. Furthermore the load needed to cause failure within a fixed time was higher for borided samples than for untreated ones.
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