Abstract
Wear resistant, high chromium white cast irons contain high volume fractions of M 7C 3 type carbides, which grow as rods and blades during solidification to produce a highly anisotropic microstructure. In this study, the effect of carbide orientation on the wear properties of these alloys is examined using both a high-stress pin-on-drum abrasion test and a single scratch test. It is found that when the carbides are oriented with their long axes perpendicular to the wear surface, abrasion resistance is considerably reduced. When the long axes of the carbides are parallel to the wear surface, the cast irons are more wear resistant, and the alloys show the least wear when the long axes of the carbides are parallel to the wear surface and oriented perpendicular to the wear direction. Scanning electron microscopy reveals that fracture of the carbides depends upon the orientation of the carbides with respect to the wear surface and the wear direction.
Highlights
The High Chromium White Cast Iron (HCWCI) is a material highly used in the mining and oil industry, to manufacture crushing hammers and drilling rigs, due to the presence of a significant proportion quantity of chromium rich carbide phase in their microstructures
It was determined that the matrix structure is predominantly austenite (austenite dendrites, with an approximate 1.41.5% C and secondary austenite), while the precipitated chromium carbides are found along the dendrite boundaries
The as-cast microstructure is made of dendrites, which remain fully austenitic at room temperature, while the eutectic micro-constituent is a continuous network of chromium-rich carbides and eutectic austenite, similar to the investigation realized by Hann et al [3]
Summary
The High Chromium White Cast Iron (HCWCI) is a material highly used in the mining and oil industry, to manufacture crushing hammers and drilling rigs, due to the presence of a significant proportion quantity of chromium rich carbide phase in their microstructures. The high demand of these materials led to the increment of imports in Colombia, while the local companies, that produce these materials, became a second option for the buyers. This increase in imports is caused by the better performance of the tools, as the duration of the materials is about 4-four times higher, than the tools manufactured locally. The microstructure of the high-chromium white cast irons, influences the wear behavior. In order to obtain a better wear performance, the high chromium white cast irons should present a martensitic structure, because the martensitic formation, compared to the austenitic, minimizes cracking and removal during wear. An additional influence on the wear behavior is given by the secondary carbides [7], which improves the mechanical strength [8], through increasing the matrix strength
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