The best method to activate the surface of stainless steel is cathodic polarization in a solution of sulfuric acid. In this case, the metals entering into the oxides are reduced and the surface is freed from the passive layer.

The removing of passive film present on the surface of the stainless steel and preventing the re-formation of this passive film during the steps between the activating treatment and the plating stage is an art process that highly depend on the activation solution compounds and their compositions. Therefore it is useful to go through the patent US4422906A as it contain a bundle of knowledge on stainless steel activation solutions compositions and the operation process design.

https://patents.google.com/patent/US4422906A/en

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Woods Ni strike

Since the stainless steel consists of passive coating(Primarily due to the chromium content of the metal), you might consider a mechanism to breakdown of passivity before electroplating on the alloy. This passive coating can develop simultaneously when exposed to air. Thus the method should include a mechanism to prevent re-passivation. There are a few ways to do this task. Wood's nickel strike (Strike was originally developed by Donald Wood, who published the article, “A Simple Method of Plating Nickel on Stainless Steel,” in Metal Industry, July, 1938.) is considered a proper method among all the solutions for passivity breakdown and to prevent the re-passivation of the metal.

Refer to these articles for more information.

https://www.researchgate.net/publication/335495008_Lead_Free_Solder_Compatibility_Improvement_on_Nichrome_Alloy_Through_Contact_Angle_Modification

https://www.researchgate.net/publication/344174136_Surface_Wettability_Analysis_of_Nichrome_Alloy_Based_on_the_Measurements_of_Sessile_Droplet_Contact_Angles

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