Localized variations in chemistry can cause slight changes in ultimate tensile strength when drawing to fine wire. The pdf file at the bottom of the page (Typical Chemistry) will elaborate on this further.
Physical Properties
Density..............................0.285 lbs/in3
Modulus of Elasticity.......28.0 psi x 106
Electrical Resistivity........720 µohms-mm
Thermal Conductivity......16.3 W/m K (100°C)
Thermal Treatment
In wire form, cold worked 302 will gain tensile strength when stress relieved at 350 - 427°C for 4 - 6 hours. A reducing atmosphere is preferred, but inert gas can be used. 302 will fully anneal at 1010 - 1121°C in just a few minutes. There is a carbide precipitation phenomenon that occurs between 427 and 899°C that reduces the corrosion resistance of the alloy. American Society for Testing Materials (ASTM) has described a test method to ensure the alloy has not been damaged.
Applications
302 alloy is the same as 304 alloy except for the .12% carbon maximum. In 304 the maximum carbon is .08%. Technically, all 304 alloy meets the requirements of 302 alloy, but not all 302 can meet 304 chemistry. Practically, this means in general 302 is harder than 304 with the same amount of cold work. End uses for 302 include: stylets, catheters, guide wires, spring and needles.
Surface Conditions
Stainless steels develop a highly polished appearance as they are drawn to fine diameters. Surface roughness can be less than 5 RMS when processed using SCND* dies and measured with a profilometer. Diameters over .040" will not have as smooth a finish because of polycrystaline dies. Diameters over .100" have an even rougher surface because they are drawn with carbide dies. Additional finish treatments can enhance the surface of the wire.
