Extending the life of cast excavator parts in northern climates

Abstract

The cold brittleness of steel is of particular importance in Siberia and the Far North. More than half of the territory of Russia—including the Siberian, Zapolyarnii, Yakutsk, and Far East regions and the continental shelf of the Arctic Ocean—is north of the ‐20 ° C isotherm in January. These regions are also characterized by large mineral reserves and are promising for industrial development. In Siberia, the failure rate of drilling equipment in winter is more than twice that in summer. Below − 35 ° C, to avoid major fractures, powerful excavators, drilling equipment, and some construction-industry machinery must be shut down, although the operating regulations of northern mining enterprises call for their year-round use. Cast-steel parts account for most of the failures due to wear; they are most often in contact with rock. According to data from the Institute of Physical and Engineering Problems in Northern Climates, Yakutsk Branch, Siberian Division, Russian Academy of Sciences, the actual working life of components of the EKG-8I excavator is as follows: for the caterpillar tracks, 2 years; for the bucket, 1.5 years. The excavator teeth are most frequently replaced, however. Depending on the type of ground and the climatic conditions, the bucket teeth last from three weeks to six months. Traditionally, the bucket teeth are made from 110E13a steel (Hadfield steel), of the following chemical composition, wt % (according to State Standard GOST 2176-77): 0.9‐1.4 C; 0.8‐1.0 Si; 11.5‐15.0 Mn; Cr 1.0; Ni 1.0; Cu 0.3; S 0.05; P 0.12. Manganese is the basic alloying element in 110E13a steel. Alloying with manganese may be based on ferromanganese or on metallic manganese. Economic considerations favor the use of high-carbon FMn70 ferromanganese (State Standard GOST 475591), containing 7% carbon and 0.30‐0.70% phosphorus. However, when using high carbon ferromanganese, carbophosphide deposits appear in the structure, with corresponding decline in its cold strength; as a result, brittle failure of steel with an austenitic structure is seen. By reducing the phosphorus content, the life of the steel may be extended by 40% [1].