chromium is hard,shiny metal,suggest two reasons why chromium is used to electroplate steel
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Chromium is a lustrous, hard, steel-gray metallic element, resistant to tarnish and corrosion and found primarily in chromite. It is used in the hardening of steel alloys and the production of stainless steels, in corrosion-resistant decorative platings, and as a pigment in glass. Chromium has a high melting point, stable crystalline structure, and moderate thermal expansion. The metal is commonly used for plating to produce a shiny, hard surface that is resistant to corrosion.All chromium compounds are colored. Chromium compounds are toxic. The most common uses of Chromium are in Dyes and paints, Stainless steel, Metallurgy, Chrome plating, Green rouge metal polish and Magnetic tape.
There are two different general applications for chrome plating: "hard chrome plating" (sometimes called 'engineering chrome plating') and "decorative chrome plating".
Hard chrome plating is chrome plating that has been applied as a fairly heavy coating (usually measured in thousandths of an inch) for wear resistance, lubricity, oil retention, and other 'wear' purposes. Some examples would be hydraulic cylinder rods, rollers, piston rings, mold surfaces, thread guides, gun bores, etc. 'Hard chrome' is not really harder than other chrome plating, it is called hard chromium because it is thick enough that a hardness measurement can be performed on it, whereas decorative chrome plating is only millionths of an inch thick and will break like an eggshell if a hardness test is conducted, so its hardness can't really be measured directly. Most people would not be very familiar with hard chrome plating.
Hard chrome plating is almost always applied to items that are made of steel, usually hardened steel. It is metallic in appearance but is not particularly reflective or decorative. Hard chrome plating is not a finish that you would want on a wheel or bumper.
Decorative chrome plating is sometimes called nickel-chrome plating because it always involves electroplating nickel onto the object before plating the chrome (it sometimes also involves electroplating copper onto the object before the nickel, too). The nickel plating provides the smoothness, much of the corrosion resistance, and most of the reflectivity. The chrome plating is exceptionally thin, measured in millionths of an inch rather than in thousandths.
When you look at a decorative chrome plated surface, such as a chrome plated wheel or truck bumper, most of what you are seeing is actually the effects of the nickel plating. The chrome adds a bluish cast (compared to the somewhat yellowish cast of nickel), protects the nickel against tarnish, minimizes scratching, and symbiotically contributes to corrosion resistance. But the point is, without the brilliant leveled nickel undercoating, you would not have a reflective, decorative surface.