Beitrag zur kenntnis des verschleisswiderstandes von gusseisen mit zwischenstufengefüge

Abstract

The structure and properties of two grades of cast iron with flake graphite have been investigated after isothermal transformation in the “tempering” range of bainitic hardening. They were compared as regards structure and properties with the same grades of cast iron after a normal hardening and tempering, i.e. oil quenching resulting in a martensitic structure, followed by tempering until the same Brinell hardness is reached as with the bainitic hardening. Comparison was also made with the martensitic, untempered condition. It was found that isothermal transformation, but only in the lower bainitic hardening range (350°C), gives a favourable ratio between toughness and hardness. Particularly when comparing the wear-resistance, the superiority of this bainitic-hardened cast iron over the normally hardened and tempered cast iron was established. These comparative experiments were carried out with a specially constructed wear-testing machine, designed to take into account the influence of the cold-working of the surface zone as an important component of the wear process. Our data confirm in principle the results reported in the literature and emphasize once more the importance of residual austenite present in the Bainite and its subsequent transformation into martensite by cold-working during the wear process. This structure, together with the comparatively high value of toughness of this grade of cast iron, is responsible for the superior wear-resistance of bainitic iron. However, this superiority becomes apparent only over a comparatively small range of the bainitic hardening process.