Component with a component (1) made of steel, wherein the component is at least partially coated with a nickel diffusion layer (10), and the layer thickness of the nickel diffusion layer (10) is 1-500 m and the nickel diffusion layer (10) has a nickel content, based on the total weight of the nickel diffusion layer, of 2 wt. % above the nickel content of the steel up to a maximum concentration, the nickel content in the nickel diffusion layer (10) increasing continuously in the direction of the surface (12) of the nickel diffusion layer (10) from 2% by weight up to the maximum concentration and the maximum concentration being 20-100% by weight.

Provided is a plating solution for a threaded connection for pipe or tube used for forming a plating film excellent in galling resistance, crevice corrosion resistance, and exposure corrosion resistance. The plating solution for a threaded connection for pipe or tube of the present embodiment contains no cyanide, but contains: a water-soluble copper salt; a water-soluble tin salt; a water-soluble bismuth salt; a free acid; and a thiourea-based compound of 10 g/L or less (excluding 0) that is represented by Chemical Formula (1):

X.sup.1X.sup.2NC(S)NX.sup.3X.sup.4(1),

where each of X.sup.1, X.sup.2, X.sup.3, and X.sup.4 is any one of hydrogen, an alkyl group, an allyl group, a tolyl group, or a group represented by Chemical Formula (2), but excluding that X.sup.1, X.sup.2, X.sup.3, and X.sup.4 are all hydrogen:

CH.sub.2CH.sub.2SCH.sub.2CH.sub.2X.sup.5(2),

where X.sup.5 is OH or NH.sub.2.

Provided is a plating solution for a threaded connection used for forming a plating film excellent in galling resistance, crevice corrosion resistance, and exposure corrosion resistance. The plating solution contains no cyanide, but contains copper pyrophosphate, tin pyrophosphate, zinc pyrophosphate, pyrophosphate as a metal complexing agent, and a sulfur-containing compound of 40 g/L or less (excluding 0). The sulfur-containing compound includes: a mercapto compound and a sulfide compound defined by Chemical Formula (1); a dimer formed through a disulfide bond of the mercapto compounds; and one or more types of salts thereof:

RS(CHX.sup.1).sub.m(CHX.sup.2).sub.nCHX.sup.3X.sup.4(1), where each of m and n is an integer of 1 or 0; each of X.sup.1, X.sup.2, X.sup.3 and X.sup.4 is any one of hydrogen, OH, NH.sub.2, SO.sub.3H, and CO.sub.2H, but excluding that X.sup.1, X.sup.2, X.sup.3, and X.sup.4 are all hydrogen; and R is any one of hydrogen, a methyl group, and an ethyl group.

The present invention is related to an aqueous post treatment composition for providing a post treatment layer on at least a part of a passivation layer, which is covering at least a part of a zinc layer being on at least a part of an iron containing substrate, characterized in that the aqueous post treatment composition comprises at least one chromium (III) ion source and at least one compound containing the chemical element silicon; wherein a molar ratio of silicon versus chromium is given in said composition, with the proviso that said molar ratio is ranging from 2600:1 to 1:1 for the zinc layer obtained by an electrolytic acid zinc deposition process; or that said molar ratio is ranging from 5200:1 to 1:1 for the zinc layer obtained by an electrolytic alkaline zinc deposition process.