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Ra
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Chemical symbol for Radium. |
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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. |
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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. |
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Rb
|
Chemical symbol for Rubidium. |
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Re
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Chemical symbol for Rhenium. |
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Recarburize
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(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. |
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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. |
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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. |
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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. |
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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. |
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Refining
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(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. |
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Refractory
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(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. |
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Refractory Metal
|
The refractory metals include niobium (formerly known as columbium),
tantalum, molybdenum, tungsten and rhenium. With the exception of
two of the platinum-group metals, osmium and iridium, the refractory
metals have the highest melting temperatures (greater than 2000 °C,
or 3630 °F) and the lowest vapor pressures of all metals. They are
readily degraded by oxidizing environments at moderately low
temperatures, a property that has restricted their use as
high-temperature materials. Protective coating systems have been
developed, mostly for niobium alloys, to permit their use in
high-temperature oxidizing aerospace applications. |
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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. |
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Retort
|
A vessel used for distillation of volatile materials, as in
separation of some metals and in destructive distillation of coal. |
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Rh
|
Chemical symbol for Rhodium. |
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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. |
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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. |
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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. |
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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. |
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Ru
|
Chemical symbol for Ruthenium. |
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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. |
