The wear of metallic materials by soil—Practical phenomena

Abstract

The wear rates of metallic materials in cutting soil, as in ploughing, have been compared in the field, using simplified tools. The field test method is described. The field results show that the wear is of the general type investigated by Khrushchov and Babichev 1 and that in many soils most of the wear is caused by stones. The principal abrasives were quartz and other forms of silica such as flint. Very hard steels and particularly materials containing massive carbides, wear differently in different soils relative to steels at Hv 500 kg/mm. 2 Relative wear results on bonded abrasive discs using flint papers of different grit size show similarities with results in the field. The coarse grit condition, in which grit fracture is prevalent, compares quite closely with results in a soil containing ironstone, grains of which also fracture. Results in a stone-free soil approach those on fine grit. The maximum hardness Hu of a selection of metals and alloys has been estimated by measurements taken in surfaces severely strained by ‘trepanning’. The relative wear resistance β on abrasive of a hardness Ha that greatly exceeds Hu , is not fully determined by Hu as hitherto accepted. A soft abrasive wear regime commences when Hu exceeds about 0·8 Ha and ceases, under some conditions, when the yield stress of the material approximates that of the abrasive. Increases in the relative wear resistance b when Hu > 0·8 Ha , compared with β , suggest that local regions reach Hu , but other evidence shows that the complete surface does not reach this hardness. A lower relative wear resistance b on coarse grit compared with that on fine grit abrasive, is attributed to fracture of the coarse grit when plastic zones in the grit exceed a critical size. For heterogeneous materials this effect is augmented due to hard particles becoming less effective when they are small compared with the scale of deformation. Various practical considerations are discussed.