| Ra | Chemical symbol for Radium. |
| Racking | A term used to describe the placing of parts to be heat treated on a rack or tray. This is done to keep parts in a proper position to avoid heat-related distortions and to keep the parts separated. See fixturing. |
| Radiography | A method of non-destructive testing. Internal examination of a metallic structure or component is carried out by exposing it to a beam of X-Ray or gamma radiation. Internal defects can be seen on a screen or recorded on film. |
| Rb | Chemical symbol for Rubidium. |
| Re | Chemical symbol for Rhenium. |
| Re-crystallization | The re-arrangement of crystals in cold worked metal brought about by heating so that the deformed crystals are absorbed by newly-formed crystals and the effects of work hardening are removed. Also occurs when steel is heated through the transformation range and when steel is hot worked. |
| Recarburize | (1) To increase the carbon content of molten cast iron or steel by adding carbonaceous material, high-carbon pig iron, or a high-carbon alloy. (2) To carburize a metal part to return surface carbon lost in processing; also known as carbon restoration. |
| Recuperator | Equipment for transferring heat from gaseous products of combustion to incoming air or fuel. The incoming material passes through pipes surrounded by a chamber through which the outgoing gasses pass. |
| Red Hardness | A term sometimes associated with high speed steel because it has the property of retaining sufficient hardness for cutting metals even when heated to a temperature high enough to cause a dull redness. The tungsten content has a significant influence on this property. |
| Reduction of Area | (1) Commonly, the difference, expressed as a percentage of original area, between the cross-sectional area of a tensile test specimen and the minimum cross-sectional area measured after complete separation. (2) The difference, expressed as a percentage of original area, between original cross-sectional area and that after straining of the specimen. |
| Refining | (a) The removal of impurities and metallic oxides from the molten bath by the reaction of the slag and other additions. (b) A heat treatment process with the object of refining or making the grain size of the steel uniform. |
| Refractory | (1) A material of very high melting point with properties that make it suitable for such uses as furnace linings and kiln construction. 2) The quality of resisting heat. |
| Residual Stress | The stress which exists in an elastic solid body in the absence of, or in addition to, the stresses caused by an external load. Such stresses can arise from deformation during cold working such as cold drawing or stamping, in welding from weld metal shrinkage, and in changes in volume due to thermal expansion. |
| Retort | A vessel used for distillation of volatile materials, as in separation of some metals and in destructive distillation of coal. |
| Rh | Chemical symbol for Rhodium. |
| Rockwell Hardness Testing | A method for testing the hardness of metals by determining the depth of penetration of a steel ball or a diamond sphero-conical indentor. The value is read from a dial and is an arbitrary number related to the depth of penetration. For testing hard steels, a sphero-conical diamond is used with a 150 kg load, the result is read from the black scale on the dial and is prefixed with the letter C. A hardened tool steel would typically give a reading of 62Rc. For softer metals Scale B is used with a 1/16" diameter steel ball and a standard load of 100 kgs. |
| Rolling | The process of shaping metal by passing it between rolls revolving at the same peripheral speed and in opposite directions. In steel there are a number of different types of rolling mill for processing the ingot to its finished shape. These are variously known as Cogging mills, Slabbing mills, Billet mills, Bar mills and Strip mills, which produce plate, sections, bars, sheet and strip. Cold rolling of previously hot rolled strip is carried out to produce strip that is accurate to size and with a smooth bright polished surface. |
| Rolling Lap | A fault arising from the overfilling or mis-alignment of rolls, the result is a bulge on the bar which is rolled into the metal and is lapped over. It remains throughout subsequent working and appears as a longitudinal crack. |
| Rotary Retort Furnace | A continuous-type furnace in which the work advances by means of an internal spiral, which gives good control of the retention time within the heated chamber. |
| Ru | Chemical symbol for Ruthenium. |
| Ruling Section | More accurately termed limiting ruling section. One of the most important factors associated with the choice of steel for a given purpose is to ensure that the desired mechanical properties are obtained throughout the section when the material has been heat treated. The limiting ruling section determines the maximum diameter or cross-section of a bar or component in which the specified properties can be achieved by a given heat treatment. The analysis of the steel also has an important bearing on this. |
