Yoke iron seat (cobalt-based alloy casting)

Cobalt-chromium-molybdenum (CoCrMo) alloy is a type of cobalt-based alloy, also known as Stellite alloy, a cobalt-based alloy with wear and corrosion resistance.

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Cobalt-chromium-molybdenum (CoCrMo) alloy is a type of cobalt-based alloy, also known as Stellite alloy, a cobalt-based alloy with wear and corrosion resistance. The initial cobalt-based alloy was a binary cobalt-chromium alloy, which later developed into a ternary cobalt-chromium-tungsten composition, and then into a cobalt-chromium-molybdenum alloy. Cobalt-chromium-molybdenum alloys are alloys with cobalt as the main component, containing a considerable amount of chromium, molybdenum, and a small amount of nickel, carbon, and other alloying elements, occasionally also containing iron. Depending on the composition of the alloy, they can be made into welding wires, powders used for hardfacing, thermal spraying, and other processes, or cast and forged parts and powder metallurgy parts.

CoNiCrMo alloy is one of the promising forged cobalt-based alloys, originally known as MP35N. It exhibits high corrosion resistance in seawater (containing chloride ions) under stress. Cold working can increase the strength of this alloy, but cold working is quite difficult, especially for manufacturing large devices such as hip stems. Hot forging is more suitable.

The wear resistance of forged CoNiCrMo alloy is similar to that of cast CoCrMo alloy. It has the advantages of good fatigue resistance and high tensile strength, making it suitable for applications requiring long life and resistance to fracture or stress fatigue, such as artificial joints in the hip joint. This advantage is important for the difficult and expensive surgery of deeply implanting the implant into the femoral medullary canal.

The elastic modulus of cobalt-based alloys does not change with the change in maximum tensile strength, ranging from 220 to 234 GPa, higher than other materials such as stainless steel.

CoCrMo alloys are particularly susceptible to work hardening, so they cannot use the same manufacturing processes as other metals and require vacuum precision casting. Controlling the mold temperature can control the grain size of the casting. Higher temperatures form coarser grains, which reduce strength but also precipitate larger and more widely spaced carbides, reducing the brittleness of the material.

Currently, the main domestic units producing and researching and promoting cobalt-chromium-molybdenum alloys include the Iron and Steel Research Institute and Beijing Rongdian Metal Co., Ltd.