I am surprised to see that my beloved Poäng armchair (mine has served me well for 20 years now, with a new upholstery every 6 years) is already present on the cover of the 1977 catalogue: https://ikeacatalogues.ikea.com/77436/1102677/pages/4a7b75dd...
The part for sitting seems to have been made out of metal back then, in my version, it is the same plywood material as the frame.