Are you going to combine this with another metal or use for cable damascus?

I took a class recently on cable Damascus taught by a skilled blacksmith.  Our cable was the size of yours and relatively clean...  I asked about using rusty cable, and he said to heat it up, as in a yellow white welding heat and begin to forge weld.  A lot of the rusty and oxidation may melt or flake off.  -- DO NOT overheat, so that your steel looks like a sparkler !

I believe that other smiths have tried using solvents IE: Diesel soak and then a wire brush to clean rust.  This might be worth a try too.

Being that you have 75' I would first heat to welding temp, and twist one end as much as possible, place the cable in a 90 degree swage or V block ( IRON MOUNTAIN FORGE $45), and start the welding process.  Repeat this until the end appears solid.  Let it cool and inspect.  Perhaps cut into your weld and inspect for cold shuts or issues. 

Sometimes the fun is learning how to fix or do something new or adapting to make use.  Please post before and after pictures documenting success or failure. 

NOTE:  We were using coal forges which allowed very high localized heat on the cable, if your using gas, make certain it can achieve heat necessary for welding.  Also, use plenty of flux, your going to need it.  20 Mule Team borax or Iron Mountain Flux (Premium).  I would use Iron Mountain for a higher end project due to its cost, while you can get borax as Walmart for about $5.

i don't plan on combining with other steels. i will send some pictures. Thank you for the great advice. It helps alot.

Thanks for the great advice, i appreciate it.