Cobalt-base alloys microstructures

Most of the low-carbon, cobalt-base alloys are available in the form of wrought products (plates, sheets, bars, etc.), from which industrial components can be fabricated. Some of these alloys are common in cast and weld overlay form also. The high-carbon alloys are not easily produced in wrought product form they are therefore used mostly in cast or weld overlay form. From a microstructural standpoint, not only is there a large difference between the wrought and cast versions of certain cobalt-base alloys, but there is also an enormous microstructural difference... 

FIG. 1—Microstructures of cobalt-base alloys, (a) UNS R31233 wrought plate (b) UNS R30006 wrought plate (c) UNS R30006 weld overlay (d) UNS R30012 weld overlay (e) UNS R30001 weld overlay. 

Microstructures of severtil cobalt-based alloys are presented in Fig. 1. From these, the influence of carbon content on the nature and volume fraction of carbide precipitates is evident. 

The chief industrial attribute of the cobalt-base alloys is their resistance to wear. They hold a unique position in that they are also corrosion-resistant (when the carbon content is low), and maintain their strengths and wear resistance at high temperatures, by virtue of reasonable microstructural stability (relative to, say, the austenitic manganese steels, the tool steels, and the high-silicon stainless steels). 

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