The abrasion and abrasion-corrosion properties of a 9% chromium steel

Abstract

A 9Cr2Ni0.7Mo steel was assessed for its dry abrasion and abrasion-corrosion performance using a laboratory test which simulates the conditions experienced by rock conveyors in South African gold mines. The alloy is found to exhibit abrasion and abrasion-corrosion properties comparable with most and better than several higher chromium containing alloys designed for mining applications. The good dry abrasion performance of the alloy is attributed to the good combination of high hardness, strength and toughness imparted to the alloy by its duplex microstructure of lath martensite and thin film of interlath retained austenite. The good abrasion-corrosion results are a product of the good dry abrasion performance coupled with the excellent corrosion properties in the simulated mine water. The favourable corrosion properties are linked to the effect of the Ni and Mo additions on suppressing pitting tendencies thereby imparting corrosion resistance equivalent to higher chromium containing steels. Experimental evidence however shows that the alloy is operating at the limit of its passivity for the 46 h corrosion period employed in the corrosion-abrasion test. Exposure for periods much in excess of this figure will lead to breakdown and poor corrosion-abrasion performance relative to higher chromium containing steels. The production variables of prior cold working and plate thickness are found to exert negligible influence on dry abrasion and abrasion-corrosion properties.