FWM 1058

General Information



FWM 1058, Conichrome®, Phynox® and Elgiloy® are trademark names for the cobalt-chromium-nickel-molybdenum-iron alloy specified by ASTM F 1058 and ISO 5832-7. Batelle Laboratories originally developed the alloy for making watch springs, and it was patented in 1950.

As demonstrated in the table below, the current FWM 1058 melt specification is equivalent to Conichrome, Phynox and Elgiloy. The alloy is first melted using Vacuum Induction Melting (VIM) techniques. A secondary melt operation, Electro Slag Remelt (ESR), is then employed to further remove impurities and improve overall homogeneity.

FWM 1058 derives its maximum properties from a combination of cold work and thermal processing, and is not a true precipitation-hardening alloy since the response to heat treatment is a function of the degree of cold work.

Thermal Treatment

After cold working, the mechanical strength of this cobalt based super alloy can be increased by heat treating. In wire form, cold worked FWM 1058 will gain tensile strength at temperatures from 480-540°C when exposed for
approximately 2-5 hours. Reducing or inert atmospheres are typically used for protection during thermal treatment. After annealing with a rapid quench, the alloy has a face-centered cubic structure.



Although there is no universally accepted definition for biocompatibility of biomaterials, a medical device should be safe for its intended use. ASTM F1058 has been employed successfully in human implant applications in contact with soft tissue and bone for over a decade. Long-term clinical experience of the use of this material has shown that an acceptable level of biological response can be expected if the alloy is used in appropriate applications.


Because of its excellent corrosion resistance, mechanical strength and fatigue resistance combined with high elastic modulus, FWM 1058 wire and rod is an attractive candidate for surgical implants. It is one of the preferred materials for the fabrication of various stents, pacemaker lead conductors, surgical clips, vena cava filters, orthopaedic cables, and orthodontic appliances. The alloy is also commonly used in the watchmaking industry as a precision spring material.

Surface Conditions

Cobalt based alloys develop a highly polished appearance as they are drawn to fine diameters. Surface roughness can be less than 5 microinches RMS when processed using single crystal natural diamond dies and measured with a profilometer. Diameters over 0.040" are finished with polycrystalline dies and therefore exhibit a rougher surface. Wire measuring over 0.100" will have an even rougher surface because it is drawn through carbide dies. However, the surface of the wire can be enhanced with additional finish treatments.

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