chapter 29

nitriding

A case hardening method that uses heated gaseous ammonia to form a very hard shell on the metal.

cyaniding

A case hardening technique used to create a high nitrogen low carbon case.

induction hardening

A fast-acting hardening process that uses electromagnetic currents to generate that necessary heat in the part.

austempering

A form of tempering in which metal is cooled in a salt bath to increase ductility and toughness.

phase diagram

A graphic representation of the phase changes that takes place in a metal at various temperatures.

artificial aging

A hardening process for aluminium alloys conducted at heat levels above room temperature.

pure metals

A metal that contains only one kind of atoms, such as iron or copper.

overaging

A problem that can occur when too high a heat level is used in artificially aging aluminum alloys.

annealing

A process for softening metal and relieving stresses by holding it at high temperature for an extended length of time, then slowly cooling it.

carbonitriding

A process similar to nitriding that is used for hardening low-carbon steel parts.

fluidized bed furnaces

A type of furnace that suspends heated aluminum oxide particles in a chamber with hot gases.

batch furnaces

A type of furnace used to heat-treats small quantities of parts carried on a rack or flat car that is loaded into the furnace.

continuous furnaces

A type of reheating furnace in which the charge introduced at one end moves continuously through the furnace and is discharged at the other end.

eutectoid

An alloy that changes immediately from solid to liquid at a specific temperature.

full annealing

Annealing a ferrous alloy by austenitizing and then cooling slowly through the transformation range.

blue annealing

Annealing process in which the exterior of a ferrous part is exposed to the atmosphere, forming a bluish oxide on its surface.

normalizing

Annealing process that involves cooling the heated metal to room temperature in still air to produce a more uniform and fine-grained structure.

bright annealing

Annealing taking place in a controlled atmosphere furnace or in a vacuum, nearly eleminating oxidation and leaving the surface relatively bright.

nonferrous metals

Any metal other than iron and its alloy.

cryogenic conditioning

Conditioning process for the metals that occurs at a temperature od around and is able to improve certain properties beyond the capability of cold treatment.

isothermal annealing

Heating a ferrous alloy part near the critical temperature( upper transformation temperature) to produce a structure that is partly or wholly.

intermediate annealing

Heating a part to a temperature close to or just below the lower limit of the critical temperature then allowing the part to cool.

soft annealing

Heating metal to a temperature above its critical range and then cooling it appropriately to achieve the greatest softness or ductility possible.

precipitates

In precipitation hardening of nonferrous metals, small particles of a different phase that are added to the original matrix to achieve hardening.

flame-hardened

Metallic workpieces that have been heated and quenched.

upper transformation temperature

On a equilibrium chart, the temperature where the changing of a material from one phase to another is complete.

solidus line

On a temperature graph, the point at which a molten alloy changes from a mushy solid to a hardened solid.

liquidus line

On a temperature, the point at which a molten alloy begins to change from a liquid to a mushy liquid.

lower transformation temperature

On an equilbrium chart, the temperature where a material begins to change from one phase to another.

Kasenit

One type of carbon-hardening powder used in carburizing

equilibrium diagram

Phase diagram

case hardening

Process that is used to produce a hard shell or case on a workpiece.

heat-treating

Processes that use controlled heating and cooling of materials in their solid state to change mechanical or physical properties without altering their chemical composition.

quenching

Rapid cooling of metal, usually by plunging into a liquid such as water or oil.

tempered

Reheating a part to just below the lower transformation point, then cooling it.

toughness

Resistance to breaking; a physical property used to describe a material.

solution treating

The first step in precipitation hardening, which involves heating the alloy, which exists as a two-phase solid solution at room temperature, to a temperature that causes it to become a single-phased solid solution.

martensite

The metallic structure that is created when steel is rapidly quenched or cooled, usually by plunging it into a liquid bath.

autenite

The most dense form of low carbon steel.

cementite

The phase that is reached when steel is slowly cooled after being heated to above 1341F

natural aging

The process by which some aluminum alloys harden and become stronger over a period of time at room temperature.

precipitation hardening

The process in which small particles of a different phase are added into the original matrix to harden a nonferrous metal.

pearlite

The soft and relatively ductile state that occurs when steel reached 0.8 percent carbon.

ferrite

The softest and most ductile form of low carbon steel found on an equilibrium diagram.

carburizing

a method of casehardening in which the heated workpiece is covered with a carbon hardening powder that melts and forms a thin coating.