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Definition
| A special dispersion-strengthening heat treatment. By solution treatment, quenching, and aging, a coherent precipitate forms that provides a substantial strengthening effect. (also known as precipitation hardening) |
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Definition
| A heat treatment used to produce a soft, coarse pearlite in steel by austenitizing, then furnace cooling. |
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Definition
| When the amount of the transformation depends only on the temperature, not on the time. |
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Definition
| When the amount of the transformation depends only on the temperature, not on the time. |
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Definition
| Heating a steel or cast iron to a temperature where homogeneous austenite can form. austenitizing is the first step in most of the heat treatments for steel and cast iron. |
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Definition
| A two-phase microconstituent, containing ferrite and cementite, that forms in steels that are isothermally transformed at relatively low temperatures |
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Definition
| A phase diagram for a system with two components |
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Definition
| the hard, brittle, ceramic-like compound Fe3C that, when properly dispersed, provides the strengthening in steels |
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Definition
| A precipitate whose crystal structure and atomic arrangement have a continuous relationship with the matrix from which the precipitate is formed. the coherent precipitate provides excellent disruption of the atomic arrangement in the matrix and provides excellent strengthening |
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Term
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Definition
| Strengthening, typically used in metallic materials, by the formation of ultra-fine dispersions of a second phase. The interface between the newly formed phase and the parent phase provides additional resistance to dislocation motion, thereby causing strengthening of metallic materials. |
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Definition
| A three-phase invariant reaction in which one liquid phase solidifies to produce two solid phases. |
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Term
| eutectic microconstituent |
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Definition
| A characteristic mixture of two phases formed as a result of the eutectic reaction |
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Term
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Definition
| a three-phase invariant reaction in which one solid phase transforms to two different solid phases |
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Term
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Definition
| The name given to the BCC crystal structure of iron that can occur as (alpha) or (delta). this is not to be confused with ceramic ferrites which are magnetic materials |
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Term
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Definition
| The temperature difference between the liquidus and solidus temperatures |
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Term
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Definition
| Describes the number of degrees of freedom, or the number of variables that must be fixed to specify the temperature and composition of a phase (2+C=F+P, where pressure and temperature can change, 1+C=F+P, where pressure or temperature is constant). |
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Term
| Guinier-Preston (GP) zones |
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Definition
| Tiny clusters of atoms that precipitate from the matrix in the early stages of the age-hardening process. Although the GP zones are coherent with the matrix, they are too small to provide optimum strengthening. |
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Term
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Definition
| The ease with which a steel can be quenched to form martensite. steels with high hardenability form martensite even on slow cooling |
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Definition
| Graphs showing the effect of the cooling rate on the hardness of the asquenched steel |
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Term
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Definition
| The conditions that an alloy or ceramic system must meet if the system is to display unlimited solid solubility. Hume-Rothery's rules are necessary but are not sufficient for materials to show unlimited solid solubility. |
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Term
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Definition
| A prefix indicating that the composition of an alloy is more than the composition at which a three-phase reaction occurs |
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Term
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Definition
| An alloy composition between that of the right-hand-side end of the tie line defining the eutectic reaction and the eutectic composition |
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Term
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Definition
| The addition of an agent to the molten cast iron that provides nucleation sites at which graphite precipitates during solidification |
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Definition
| The distance between the center of a lamella or plate of one phase and the center of the adjoining lamella or plate of the same phase |
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Term
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Definition
| A compound formed of two or more metals that has its own unique composition, structure, and properties |
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Term
| Isomorphous phase diagram |
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Definition
| A phase diagram in which components display unlimited solid solubility. |
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Term
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Definition
| A line on a phase diagram that shows constant chemical composition |
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Definition
| The distance from the quenched end of a Jominy bar. The Jominy distance is related to the cooling rate |
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Term
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Definition
| The test used to evaluate hardenability. an austenitized steel bar is quenched at one end only, thus producing a range of cooling rates along the bar |
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Term
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Definition
| A thin plate of a phase that forms during certain three-phase reactions, such as the eutectic or eutectoid |
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Term
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Definition
| A technique for determining the amount of each phase in a two-phase system |
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Term
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Definition
| When only a maximum amount of a solute material can be dissolved in a solvent material |
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Definition
| Curves on phase diagram that describe the liquidus temperatures of all possible alloys |
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Definition
| The temperature at which the first solid begins to form during solidification |
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Term
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Definition
| A metastable phase formed in steel and other materials by a diffusionless, athermal transformation |
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Term
| martensite transformation |
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Definition
| A phase transformation that occurs without diffusion. |
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Definition
| The continuous solid phase in a complex microstructure. solid dispersed phase particles may form within the matrix |
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Term
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Definition
| A phase or mixture of phases in an alloy that has a distinct appearance. frequently, we describe a microstructure in terms of the microconstituents rather than the actual phases. |
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Term
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Definition
| A region in a phase diagram in which two phases, with essentially the same structure, do not mix, or have no solubility in one another |
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Term
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Definition
| A three-phase reaction in which one liquid transforms to a solid state and a second liquid on cooling |
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Term
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Definition
| When a coherent precipitate forms from a solution-treated and quenched age hardenable alloy at room temperature, providing optimum strengthening |
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Term
| nonstoichiometric intermetallic compound |
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Definition
| A phase formed by the combination of two components into a compound having a structure and properties different from either component. the nonstoichiometric compound has a variable ratio of the components present in the compound (see also intermediate solid solution) |
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Term
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Definition
| A two-phase lamellar microstituent, containing ferrite and cementite, that forms in steels cooled in a normal fashion or isothermally transformed at relatively high temperatures |
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Term
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Definition
| A three-phase reaction in which a solid and a liquid combine to produce a second solid on cooling |
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Term
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Definition
| A three-phase reaction in which two solids combine to form a third solid on cooling |
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Term
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Definition
| Any portion, including the whole of a system, which is physically homogeneous within it and bounded by a surface so that it is mechanically separable from any other portions |
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Term
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Definition
| Diagrams showing phases present under equilibrium conditions and the phase compositions at each combination of temperature and overall composition. sometimes phase diagrams also indicate metastable phases. |
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Term
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Definition
| A solid phase that forms from the original matrix phase when the solubility limit is exceeded. We often use the term precipitate, as opposed to dispersed phase particles, for alloys formed by precipitation or age hardening. In most cases we try to control the formation of the precipitate second phase particles to produce the optimum dispersion strengthening or age hardening (also called the dispersed phase). |
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Term
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Definition
| A strengthening mechanism that relies on a sequence of solid-state phase transformations in generating a dispersion of ultrafine precipitates of a second phase (ch 12). this is same as age hardening. It is a form of dispersion strengthening. |
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Term
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Definition
| The microconstituent that forms before the start of a three-phase reaction |
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Term
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Definition
| An alloy consisting of one phase |
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Term
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Definition
| A solid phase formed by combining multiple elements or compounds such that overall phase has uniform composition and properties that are different from those of the elements or compounds forming it |
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Term
| solid solution strengthening |
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Definition
| Increasing the strength of a metallic material via the formation of a solid solution |
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Term
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Definition
| The temperature below which all liquid has completely solidified. Curves on phase diagrams that trace the solidus temperatures for all possible alloys. |
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Term
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Definition
| The amount of one material that will completely dissolve in a second material without creating a second phase |
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Term
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Definition
| The first step in the age-hardening heat treatment. The alloy is heated above the solvus temperature to dissolve any second phase and to produce a homogeneous single-phase structure. |
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Term
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Definition
| A solubility curve that separates a single-solid phase region from a two-solid phase region in the phase diagram |
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Term
| stoichiometric intermetallic compound |
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Definition
| A phase formed by the combination of two components into a compound having a structure and properties different from either component. the stoichiometric intermetallic compound has a fixed ratio of the components present in the compound |
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Term
| supersaturated solid solution |
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Definition
| The solid solution formed when a material is rapidly cooled from a high-temperature single-phase region to a low temperature two-phase region without the second phase precipitating. because the quenched phase contains more alloying element than the solubility limit, it is supersaturated in that element |
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Term
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Definition
| The microconstituent of ferrite and cementite formed when martensite is tempered |
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Term
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Definition
| A low-temperature heat treatment used to reduce the hardness of martensite by permitting the martensite to begin to decompose to the equilibrium phases. This leads to increased toughness. |
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Term
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Definition
| A horizontal line drawn in a two-phase region of a phase diagram to assist in determining the compositions of the two phases |
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Term
| time-temperature-transformation (TTT) diagram |
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Definition
| The TTT diagram describes the time required at any temperature for a phase transformation to begin and end. the TTT diagram assumes that the temperature is constant during the transformation |
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Term
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Definition
| A phase diagram in which there is only one component |
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Term
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Definition
| When the amount of one material that will dissolve in a second material without creating a second phase is unlimited |
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