Materials Science Chapter 9 Engineering Alloys
Martempering (marquenching)
A quenching process whereby a steel in the austenitic condition is hot-quenched in a liquid (salt) bath at above the Ms temperature, held for a time interval short enough to prevent the austenite from transforming, and then allowed to cool slowly to room temperature. After this treatment, the steel will be in the martensitic condition, but the interrupted quench allows stresses in the steel to be relieved
Mf
The temperature at which the austenite in a steel finishes transforming to martensite
White cast irons
Iron-carbon-silicon alloys , contain large amounts of iron carbide that make them hard and brittle
Gray cast irons
Iron-carbon-silicon alloys, contain large amounts of carbon in the form of graphite flakes. They are easy to machine and have good wear resistance
Ductile cast irons
Iron-carbon-silicon alloys, contain large amounts of carbon in the form of graphite nodules instead of flakes as in the case of gray cast iron. More ductile that gray cast irons
Malleable cast irons
Iron-carbon-silicon alloys. First cast as white cast irons and then are heat-treated.
Intermetallics
Stoichiometric compounds of metallic elements with high hardness and high temperature strength, but brittle
Hardenability
The ease of forming martensite in a steel upon quenching from the austenitic condition. A highly hardenable steel is one that will form martensite throughout in thick sections. Hardenability should not be confused with hardness. Hardness is the resistance of a material to penetration. The hardenability of a steel is mainly a function of its composition and grain size
Shape-memory alloys
Metal alloys that recover a previously defined shape when subjected to an appropriate heat treatment process
Amorphous Metal
Metals with a noncrystalline structure also called glassy metal. These alloys have high elastic strain threshold
Martensite
A supersaturated interstitial solid solution of carbon in body-centered tetragonal iron
Jominy hardenability test
A test in which a 1 in. diameter bar 4 in. long is austenitized and then water-quenched at one end. Hardness is measured along the side of the bar up to about 2.5 in from the quenched end. A plot called the Jominy hardenability curve is made by plotting the hardness of the bar against the distance from the quenched end
Continuous-cooling transformation (CCT) diagram
A time-temperature-transformation diagram that indicates the time for a phase to decompose into other phases continuously at different rates of cooling
Isothermal transformation (IT) diagram
A time-temperature-transformation diagram that indicates the time for a phase to decompose into other phases isothermally at different temperatures
α ferrite
(α phase in the Fe-Fe3C phase diagram): an interstitial solid solution of carbon in BCC iron: maximum solid solubility of carbon in BCC iron is 0.02 percent
Austenite
(γ phase in Fe-Fe3C phase diagram): an interstitial solid solution of carbon in FCC iron; the maximum solubility of carbon in austenite is 2.0 %
Spheroidite
A mixture of particles of cementite (Fe3C) in an α ferrite matrix
Pearlite
A mixture of α ferrite and cememtite (Fe3C) phases in parallel plates (lamellar structure) produced by eutectoid decomposition of austenite
Bainite
A mixture of α ferrite and very small particles of Fe3C particles produced by the decomposition of austenite; a nonlamellar eutectoid decomposition product of austenite
Austempering
A quenching process whereby a steel in the austenitic condition is quenched in a hot liquid (salt) bath at a temperature just above the Ms of the steel, held in the bath until the austenite of the steel is fully transformed, and then cooled to room temperature. With this process, a plain-carbon eutectoid steel can be produced in the fully bainitic condition
Plain-carbon steel
An iron-carbon alloy with 0.02 to 2 % C. All commercial plain-carbon steels contain about 0.3 to 0.9 percent manganese along with sulfur, phosphorous, and silicon impurities
Proeutectoid cementite (Fe3C)
Cementite that forms by the decomposition of austenite at temperatures above the eutectoid temperature
Eutectoid cementite (Fe3C)
Cementite that forms during the eutectoid decomposition of austenite; the cementite in pearlite
Austenizing
Heating a steel into the austenite temperature range so that its structure becomes austenite. The temp for this vary depending on the composition of steel
Cementite
The intermetallic compound Fe3C; a hard and brittle substance
Tempering (of a steel)
The process of reheating a quenched steel to increase its toughness and ductility. In this process martensite is transformed into tempered martensite
Ms
The temperature at which the austenite in a steel starts to transform to martensite
Proeutectoid α ferrite
α ferrite that forms by decomposition of austenite at temperatures above the eutectoid temperature
Eutectoid α ferrite
α ferrite that forms during the eutectoid decomposition of austenite; the α ferrite in pearlite