The Influence Of Cobalt And Molybdenum On The Microstructure And Mechanical Properties Of High Cobalt-Chromium-Molybdenum Bearing Steel

Cobalt-chromium-molybdenum alloy (CoCrMo) is one of the cobalt-based alloys, and is also a kind of Stellite alloy, which is a kind of cobalt-based alloy that is resistant to wear and corrosion. The first cobalt-based alloy was a binary cobalt-chromium alloy, which was later developed into a ternary composition of cobalt-chromium-tungsten, and only later did cobalt-chromium-molybdenum alloys.

Cobalt-chromium-molybdenum alloy is a kind of alloy with cobalt as the main component, containing a considerable amount of chromium, molybdenum and a small amount of nickel, carbon and other alloying elements, and occasionally also containing iron. According to the different composition of the alloy, they can be made into welding wire, powder used for hard surface welding, thermal spraying, spray welding and other processes, and can also be made into castings and forgings and powder metallurgy parts.

Through performance testing and microstructure observation, the influence of cobalt and molybdenum on the microstructure and mechanical properties of high cobalt-chromium-molybdenum bearing steel was studied. The results show that the decrease of the mass fraction of cobalt and molybdenum and the matching change will reduce the comprehensive mechanical properties of the test steel. The quenched and tempered structure of the test steel is lath martensite + retained austenite. Under the influence of cobalt and molybdenum elements, the difference between Cr_(eq) and Ni_(eq) becomes larger, resulting in residual austenite in the test steel structure. Decrease of stellite produces δ-ferrite. In addition, the carbide changes from granular M6C with a mass fraction of 1.17% to acicular M_2C with a mass fraction of less than 0.15%.

The strength of the test steel is mainly affected by carbides, and when the carbide mass fraction is less than 0.15%, the smaller the value of w(Co)/w(Mo) and the higher the dislocation density, the higher the strength of the test steel. The toughness of the test steel is mainly affected by δ-ferrite. If the area fraction of δ-ferrite is greater than 6.3%, the test steel will be brittle, and the area fraction is less than 1.1%, the toughness of the test steel is better.