EFFECT OF HYDROGEN ON TENSILE PROPERTIES OF A DUCTILE CAST IRON

摘要

Effect of hydrogen-charging and strain rate was investigated on the tensile properties of a ductile cast iron having the microstructure comprised of ferrite/pearlite matrix and spheroidal graphites. Hydrogen-charging accelerated the process of crack growth from graphite. The crack growth acceleration resulted in a marked decrease in reduction of area at final fracture (RA). In the uncharged specimens RA was nearly constant with strain rate, whereas in the hydrogen-charged specimens RA was gradually decreased with a decrease in strain rate. Thermal desorption spectroscopy and hydrogen microprint technique revealed that in the hydrogen-charged specimen most of solute hydrogen was diffusive and mainly segregated at graphite, graphite/matrix interface zone and pearlite. Considering all the obtained results together, the hydrogen-induced degradation was attributed to a combination of the following three factors: (i) hydrogen supply to the crack tip from the graphite/matrix interface zone, (ii) hydrogen-enhanced pearlite cracking and (iii) successive hydrogen emission from the graphite and additional supply to the crack tip.