Steel and aluminum refer to the material or metal the factory original wheel is made with. There are also chrome stock wheels but they are in another category. To understand the difference between the rims, you can examine a few different factors.
Weight is one of the main differences between alloy rims, another name for aluminum, and steel wheels. Steel wheels are much heavier than their aluminum counterparts. This characteristic allows for cars with stock alloy wheels to maneuver better since the vehicle is lighter. Steel wheels on the other hand weigh the car down. However having used steel rims on your vehicle may lead to some advantages such as during snow season. The extra weight of steel wheels allows your tires to have better traction with the snow. This weight difference also leads to strength differences.
Although this detail may not be recognizable in distinguishing whether you have steel or alloy used rims, steel wheels are less likely to be damaged by an impact of some sort. Because of this difference in material strength, factory original steel rims often have very plain and simple designs. On the other hand, aluminum stock wheels are much more malleable. This allows for the intricate designs on many aluminum wheels. So another way to tell the difference between your OEM used wheels is to determine whether the design is as simple as five flat spokes or a bunch of holes around the rim or as intricate as 12 Y shaped spokes or 10 double spokes.
However, original equipment steel rims may also come equipped with hub caps or wheel covers. These are plastic covers that give the look of aluminum wheels but don’t be fooled. Underneath this alloy rim designed like cap is still the plain and simple steel wheel.
OEM aluminum rims also come in various finishes ranging from painted to chrome to polished to machine finished. Factory original steel wheels are most likely a painted finish, unless a hub cap is placed onto the used rim.