Abstract
Metastable austenitic stainless steels, SUS 302, SUS 304 and SUS 304L, were cold-rolled with 20% to 80% reduction. Hydrogen evolution from these steels after electrolytical hydrogen-charging was investigated. The main results are as follows:
(1) The amount of evolved hydrogen at room temperature increased with working degree and martensite content in SUS 302, but decreased in SUS 304 and SUS 304L.
(2) During continuous heating of the specimens after aging at room temperature, hydrogen evolution began at about 373K (100°C) and had almost finished at about 623K (350°C). In SUS 304 and SUS 304L, the temperature of maximum hydrogen evolution was about 533K (260°C), but SUS 302 had the maximum at a lower temperature. The peaks of SUS 302 decreased as the working degree increased.
(3) The amount of hydrogen evolved due to continuous heating fluctuated with working degree. At the same working degree, the order of the amounts was SUS 302<SUS 304<SUS 304L.
(4) In 20% cold-rolled SUS 302, hydrogen charging caused lattice expansion, so the peaks of X-ray diffraction shifted to a lower angle. The peaks returned to the angles of uncharged specimens after aging at room temperature since hydrogen was released. In 20% cold-rolled SUS 304 and SUS 304L, a hydride was formed by hydrogen charging, in addition to lattice expansion. This caused a transformation due to aging at room temperature while hydrogen was released. The strain-induced martensite phase decreased hydrogen-induced transformation.
(5) In SUS 302, blisters caused by hydrogen charging became more noticeable with increasing working degree. In SUS 304 and SUS 304L, surface cracks caused by hydrogen charging became pronounced as working degree decreased.
