Metalsreactwithoxygenintheatmosphereandformoxidefilmsonthesurface.Ironoxideformedonordinarycarbonsteelcontinuestooxidize,causingcorrosiontoexpandandeventuallyformholes.
Paintoroxidationresistantmetalssuchaszinc,nickelandchromiumcanbeusedtoensurethesurfaceofcarbonsteel,butthisprotectionisonlyathinfilm.Iftheprotectivelayerisdamaged,thesteelbelowwillrust.
Thecorrosionresistanceofthemetalhosejointdependsonthechromiumcontent.Whentheamountofchromiumisaddedto10.5%,thecorrosionresistanceofthesteelincreasessignificantly,butthecorrosionresistancecanstillbeimproved,butitisnotobvious,thoughthechromiumcontentishigher.Thereasonisthatwhenchromiumisusedforalloyingsteel,thetypeofsurfaceoxideischangedintoasurfaceoxidesimilartothatformedonpurechromiummetal.Thistightlyadheredchromiumrichoxideprotectsthesurfacefromfurtheroxidation.
Thisoxidelayerisverythin,throughwhichitcanseethenaturallusterofthestainlesssteelsurface,sothatthestainlesssteelhasauniquesurface.Moreover,ifthesurfaceisdamaged,theexposedsteelsurfacewillrepairitselfwiththeatmosphericreaction,reformedthe"passivationfilm"andcontinuetoplayaprotectiverole.
