Reduction of Area - The percentage difference between the original cross sectional area and that of the smallest area at the point of rupture. The percentage figure can be considered a measurement of ductility.

Reflectivity (Reflectance) - A term to indicate the percentage of reflected light from a painted surface. Considered a function of color rather than specular gloss. Reflectance percentages usually range from 80% to 90% for white colors to 5% to 15% for dark colors. Reflectivity standards vary for each industry and specific application.

Registry Printing - Printing successive colors or figures in a precise pattern and with exact superposition.

Residual Stress - Macroscopic stresses that are set up within a metal as the result of non-uniform plastic deformation or thermal gradients. Stresses of this nature are caused by cold working or by drastic gradients of temperature from quenching or welding.

Residuals - Elements present in an alloy in small quantities, but not added intentionally.

Resilience - The tendency of a material to return to its original shape after the removal of a stress that has produced elastic strain.

Rimmed Steel - Low-carbon steel in which incomplete deoxidation permits the metal to remain liquid at the top of the ingot, resulting in the formation of a bottom and side rim of relatively pure iron of considerable thickness. Steel products such as sheets produced from this type of ingot will have a very good surface quality free of surface defects.

Rockwell Hardness Test - See hardness tests.

Roll Forming - A fabrication process whereby the metal sheet is deformed continuously in a linear manner by passing it through a consecutive series of rolls which produce a predetermined profile in it.

Rolled Edges - Finished edges, the final contours of which are produced by side or edging rolls. The edge contours meet commonly used are square corners, rounded corners and a rounded edge.

Rolling Direction - The direction in which the steel product is rolled perpendicular to the axes of the rolls during rolling.

Rolling Mills - Equipment used for rolling down metal to a smaller size or to a given shape employing sets of rolls the contours of which determine or fashion the product into                   numerous intermediate and final shapes, e.g., blooms, slabs, rails, bars, rods, sections, plates, sheets and strip.        

Rollinq - A term applied to the operation of shaping and reducing metal in thickness by pressing it between rolls that compress, shape and lengthen it following the roll pattern.                   Steel is either hot rolled or cold rolled depending upon the product being manufactured,

Rust - A corrosion product consisting of hydrated oxides of iron. This term is only applied to ferrous alloys.