EFFECTS OF SULFUR AND PHOSPHORUS ON HYDROGEN EMBRITTLEMENT OF CARBON STEEL MODIFIED WITH RARE-EARTH METALS.

Hydrogen embrittlement studies during hydrogen charging, as well as in saturated H//2S solution, on a normalized 20 YuCh steel modified with rare-earth metals, and with various S and P contents (0. 003 - 0. 007% and 0. 010 - 0. 028%, respectively), showed that the negative S effect in hydrogen-rich environments is much stronger than that of P. The individual contributions of each impurity to the deterioration of delayed fracture resistance depends on their concentration, mode and size of external loads during charging with hydrogen. The stronger negative effect of S in comparison with P in normalized steels is caused by its higher catalytic activity as a hydrogen absorption stimulator, by the increased surface electrolytic heterogeneity due to sulfide formation, by the increased deformation intensity and hydrogen concentration which they bring about, as well as by the higher tendency of S to segregate at normalization temperatures in comparison with P.