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Heat Treatment of Steel 230

Materials Training

Class Information

Tooling U classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and typically requires at least two hours of instruction time.

Class Name:	Heat Treatment of Steel 230
Description:	This class describes the different steel phases as well as common heat treatment methods for steel. Includes an Interactive Lab.
Prerequisites:	500110 500210
Difficulty:	Intermediate
Number of Lessons:	18

Class Outline
Objectives What Is Heat Treatment? The Phases of Steel Effects of Carbon Content Hypoeutectoid and Hypereutectoid Steels Formation of Pearlite Bainite Martensite Annealing Types of Annealing Normalizing Quenching Tempering Combination of Heat Treatment Steps Hardenability Types of Furnaces Surface Hardening Summary

Class Objectives

Describe heat treatment.
Describe the phases of steel.
Describe the formation of cementite.
Define hypoeutectoid and hypereutectoid steels.
Describe the formation of pearlite.
Describe the formation of bainite.
Describe the formation of martensite.
Define annealing.
Distinguish among different types of annealing.
Define normalizing.
Define quenching.
Define tempering.
Describe the combination of heat treatment steps.
Define hardenability.
Distinguish between the types of furnaces used in heat treatment.
Distinguish among surface hardening methods.

Class Vocabulary
annealing	The steady heating of a metal at a certain temperature above the recrystallization phase followed by a gradual cooling process.
austenite phase	The phase at which solid steel recrystallizes and has a face-centered cubic crystal structure. Austenite steel holds a greater amount of dissolved carbon and exhibits increased formability.
bainite	A combination of ferrite and cementite in ferrous metals that is harder than pearlite. Bainite contains needlelike grain structures, and it requires an initial rapid cooling followed by gradual cooling.
batch furnace	A heat-treatment furnace that soaks a stationary workpiece.
body-centered cubic	The crystal structure that contains an atom in the center and one atom in each corner of a cube. Ferrite has a BCC crystal structure.
body-centered tetragonal	A body-centered cubic crystal structure that has been distorted by the presence of extra atoms of carbon. Martensite has a BCT crystal structure.
carburizing	A surface hardening method that heats metal within a carbon-rich environment to increase carbon levels on the metal surface for added hardness.
cementite	A compound of iron and carbon that is very hard and brittle. The presence of cementite hardens steel.
chromium	A shiny, hard, steel-gray metal that increases the hardenability of steel. Stainless steels also contain large amounts of chromium.
cold working	The shaping of metal at temperatures substantially below the point of recrystallization. Cold working adds strength and hardness.
continuous furnace	A heat-treatment furnace that soaks a workpiece as it moves along a conveyor or rotating hearth.
crystal structure	The formation of a consistent, repeating pattern of atoms. A crystal structure develops as a liquid metal cools and changes into a solid.
ductility	The ability of a metal to be drawn, stretched, or formed without breaking.
electric furnace	A heat-treatment furnace that uses electric current to control the temperature of a metal.
eutectoid temperature	The lowest temperature at which austenite transforms into ferrite and cementite. Steel with 0.77 percent carbon transforms at this temperature.
face-centered cubic	The crystal structure that contains one atom in the center of the six sides of a cube and one atom in each corner of the cube. Austenite has an FCC crystal structure.
ferrite phase	The phase at which solid steel has a body-centered cubic crystal structure. Ferrite steel can hold only a minimal amount of carbon, and it is relatively soft.
flame hardening	A surface hardening method that heats a metal with a high-temperature flame, followed by quenching.
full annealing	An annealing process that soaks the metal above the austenite phase, followed by gradual cooling. A full anneal may take a day or longer.
hardenability	The ability of a metal to be hardened by normal heat treatment processes.
heat treatment	The controlled heating and cooling processes used to change the structure of a material and alter its physical and mechanical properties.
hypereutectoid steel	Steel that contains more than 0.77 percent carbon. Hypereutectoid steel consists of pearlite and cementite at room temperature.
hypoeutectoid steel	Steel that contains less than 0.77 percent carbon. Hypoeutectoid steel consists of ferrite and pearlite at room temperature.
induction hardening	A surface hardening method that heats a metal with an electrical current.
manganese	A hard, brittle, gray-white metal that increases the hardenability of steel. Manganese also increases strength and hardness.
martensite	A steel that consists of a distorted, body-centered tetragonal crystal structure. Martensite is very hard and brittle.
mechanical properties	A property that describes a material's ability to compress, stretch, bend, scratch, dent, or break.
molybdenum	A hard, silvery white metal that increases the hardenability of steel. Molybdenum is also an effective substitute for tungsten in many high-speed tool steels.
nitriding	A surface hardening method that heats a metal within a nitrogen-rich environment. Metals that are nitrided typically contain aluminum or chromium.
normalizing	The steady heating of a metal above the recrystallization phase, followed by a cooling process at a moderate pace. Normalized metals are often cooled in open air at room temperature.
pearlite	A combination of ferrite and cementite. Pearlite grain structures resemble human fingerprints. Steel with exactly 0.77 percent carbon consists of uniform pearlite at room temperature.
phase	A portion of material with a uniform crystal structure, consistent properties, and recognizable boundaries. At room temperature, steel consists of two or more phases.
precipitation	The separation of a substance that was previously dissolved in another substance.
process annealing	An annealing process that heats the metal below the austenite phase to restore ductility after cold working.
quenching	The soaking of a metal at a high temperature above the recystallization phase, followed by a rapid cooling process. The quenching of steel creates martensite.
quenching medium	The liquid or air substance used to cool a metal during quenching. Water, saltwater, air, and oil are common quenching mediums.
recovery annealing	An annealing process that attempts to partially restore the original grain structure of the metal and still preserve the strain hardening that has developed.
scaling	The development of an unwanted rough coating on the surface of the metal.
soaking	The heating of a metal at a constant temperature for a suitable duration of time.
strain hardening	The increase of hardness and strength in steel caused by the cold working of the metal.
stress relieving	An annealing process that heats the metal below the austenite phase to reduce distortions or changes in dimensions that might occur after shaping.
surface hardening	Any heat-treatment method used to alter the properties within the surface or localized area of a metal.
tempered martensite	Martensite steel that has been tempered to improve ductility and toughness.
tempering	The steady heating of martensite steel at a temperature below the recrystallization phase, followed by a gradual cooling process.
toughness	The amount of energy a material can absorb before it breaks.