Influence of carbide on intergranular creep rupture of type 304 stainless steel

The creep rupture behaviours of type 304L stainless steel and 304 stainless steel were investigated in argon at 823 K. The creep ductility of the 304L and solution annealed 304 steels decreases with increasing creep rupture t ime, while the ductility of sensitised 304 steel increases slightly with ru pture time. The extent of necking of solution annealed 304 steel depends on creep rupture time and necking always occurs in sensitised 304 steel. Solu tion annealed 304 maintains a nearly equiaxed grain structure on a longitud inal section of specimens fractured after long creep rupture times, while s ensitised 304 has elongated grains that are clear evidence of high plastici ty within the grains. Intergranular fracture surfaces of solution annealed 304 steel are primarily observed with increasing creep rupture time, and cr eep rupture of sensitised 304 is characterised by transgranular fracture su rfaces with carbide walls at grain boundaries. It is suggested that continu ous plate shaped carbides at grain boundaries completely inhibit grain boun dary sliding, thus causing large total creep str ain and high creep ductili ty in sensitised 304 steel.