Mill Terms: Thermal Treatment
Heat Treatment—Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties. Heating for the sole purpose of hot working is excluded from the meaning of this definition.
Austenitizing—Forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing).
Annealing—Heating to and holding at a suitable temperature and then cooling at a suitable rate, for such purposes as reducing hardness, Improving machinability, facilitating cold working, producing a desired microstructure, or obtaining desired mechanical, physical, or other properties. When applicable, the following more specific terms should be used: Black Annealing, Blue Annealing, Box Annealing, Bright Annealing, Flame Annealing, Full Annealing, Graphitizing, Intermediate Annealing, Isothermal Annealing, Malleablizing, Process Annealing, Quench Annealing. Recrystallization Annealing, and Spheroidizing.
When applied to ferrous alloys, the term “annealing,” without qualification, implies full annealing.
When applied to nonferrous alloys, the term “annealing” implies a heat treatment designed to soften a cold worked structure by recrystallization or subsequent grain growth or to soften an age hardened alloy by causing a nearly complete precipitation of the second phase in relatively coarse form.
Full Annealing—Annealing a ferrous alloy by austenitizing and then cooling slowly through the transformation range. The austenitizing temperature for hypoeutectoid steel is usually above Ac3 and for hypereutectoid steel usually between Ac1 and Ac cm.
Spheroidizing—Heating and cooling to produce a spheroidal or globular form of carbide in steel. Spheroidizing methods frequently used are:
1. Prolonged holding at a temperature just below Ae1.
2. Heating and cooling alternately between temperatures that are Just above and just below Ae1.
3. Heating to a temperature above Ae1 or Ae3 and then cooling very slowly in the furnace or holding at a temperature just below Ae1.
4. Cooling at a suitable rate from the minimum temperature at which all carbide is dissolved, to prevent the reformation of a carbide network, and then reheating in accordance with Method 1 or 2 above.
Isothermal Annealing—Austenitizing a ferrous alloy and then cooling to and holding at a temperature at which austenite transforms to a relatively soft ferric carbide aggregate.
Normalizing—Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range.
Quenching—Rapid cooling. When applicable, the following more specific terms should be used: Direct Quenching. Fog Quenching. Hot Quenching, Interrupted Quenching, Selective Quenching, Spray Quenching, and Time Quenching.
Tempering—(1) Reheating a quench hardened or normalized ferrous alloy to a temperature below the transformation range (Ac) and then cooling at any desired rate. (2) A term used in conjunction with a qualifying adjective to designate the relative properties of a particular metal or alloy induced by cold work or heat treatment, or both.
Stress Relieving—Heating to a suitable temperature, holding long enough to reduce residual stresses and then cooling slowly enough to minimize the development of new residual stresses.
Recrystallization—(1) The change from one crystal structure to another, as occurs on heating or cooling through a critical temperature (2) The formation of a new, strain-free grain structure from that existing in cold worked metal, usually accomplished by heating.
Maraging—A precipitation hardening treatment applied to a special group of iron base alloys to precipitate one or more intermetallic compounds in a matrix of essentially carbon-free martensite.
Hardenability—In a ferrous alloy, the property that determines the depth and distribution of hardness induced by quenching.
Case Hardening—Hardening a ferrous alloy so that the outer portion or case is made substantially harder than the inner portion or core.
Core—In a ferrous alloy, the inner portion that is softer than the outer portion or Case.
Carburizing—Introducing carbon into a solid ferrous alloy by holding above Ac’ in contact with a suitable carbonaceous material. The carburized alloy is usually quench hardened.
Grain Size—In killed steels, grain size is specified as either coarse (grain size 1 to 5 inclusive) or fine (grain size 5 to 8 inclusive), determined in accordance with ASTM Designation El 12. Standard Methods for Estimating the Average Grain Size of Metals (by the comparison procedure).
Segregation—A phenomenon associated with solidification, which causes nonuniformity in chemical composition.
Internal Soundness—Relative freedom from segregation and porosity, as evaluated by means of a macroetch test which is performed on representative samples.