| Half hard |
A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength about mid-way between that of dead soft and full hard tempers. |
| Half nut |
A mechanism attached to the apron of a lathe and operated by a lever. The lever opens and closes a nut that has been split lengthwise so that the two halves of the nut can be closed upon the lead screw when threads are being cut. Also called Split Nut. |
| Hard temper |
Same as full hard temper. |
| Hardenability |
The relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surface where the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure. |
| Hardenability |
Defined as the ability of a ferrous material to acquire hardness after austenitization and quenching. |
| Hardening |
Increasing hardness by suitable treatment, usually involving heating and cooling. When applicable, the following more specific terms should be used: age hardening, flame hardening, induction hardening, laser hardening, precipitation hardening, and quench hardening. |
| Hardness |
A measure of the resistance of a material to surface indentation or abrasion; may be thought of as a function of the stress required to produce some specified type of surface deformation. There is no absolute scale for hardness; therefore, to express hardness quantitatively, each type of test has its own scale of arbitrarily defined hardness. Indentation hardness can be measured by Brinell hardness test, Rockwell hardness test, Vickers hardness test, Knoop hardness test, and the Scleroscope hardness test. |
| Hardness |
The ability of a ductile material to resist permanent deformation. It is a measure of plastic flow properties determined principally by indentation testing, but scratch hardness and rebound hardness are also employed. |
| Hardness |
hardness scales The different measures of hardness given by different tests, such as indentation pressure in the Brinell and in the Vickers hardness tests, and the different Rockwell hardness numbers. |
| Hardness profile |
Hardness as a function of distance from a fixed reference point (usually from the surface). |
| Hardness test |
1. Any of various tests in which different hard indenters are forced into the surface of a solid under different loads to give permanent impressions, the pressure to cause which being called the hardness. The Brinell test employs a spherical indenter; the Vickers test a square-based pyramid. The relation between indentation hardness H and uniaxial yield stress Y is approximately H = (2.5 ~ 3.0)Y. Originally hardnesses were given in kg/mm2 but now are often given in Pa. 2. The tests for scratch and file hardness relate either to one material being able to mark another (Mohs hardness scale for minerals), or to the size of groove produced by a rigid indenter slid under load across a surface. 3. Rebound hardness concerns the height of rebound of a dropped indenter, or an indenter at the end of a pivoted arm, having struck a surface. |
| Head height |
The head height shall be that overall distance measured parallel to the axis of the product from the top of the head to the bearing surface and shall include the thickness of the washer face. Raised grade and manufacturer’s identification are excluded from head height. |
| Heat (q, Q) (Unit J) |
A form of energy that is transferred across the boundary of a system at one temperature to another system (or the surroundings) at a different temperature by virtue of the temperature difference between them. Heat can be identified only as it crosses the boundary. A body can never be said to contain heat which is thus a transient phenomenon. |
| Heat balance (heat budget) |
An energy balance involving only heat transfer across the system boundary and the stored energy. |
| Heat capacity (C) (Unit J/K) |
The energy required to raise the temperature of a body by 1K without change of phase. Heat capacity is an extensive thermodynamic property dependent on temperature and pressure. |
| Heat tinting |
Coloration of a metal surface through oxidation by heating to reveal details of the microstructure. |
| Heat treatment |
(heat treating) Alteration of the mechanical properties of materials, particularly metals, by different sequences of heating, holding at temperature, and cooling at different rates. |
| 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. |
| Heat-capacity rate (c) (Unit W/K) |
For fluid flow in a duct with mass flow rate ṁ, the product ṁC where C is the specific-heat capacity, at constant pressure (CP) in the case of a gas. |
| Heat-capacity ratio (c*) |
A non-dimensional parameter that arises in the analysis of heat exchangers, defined as the ratio cMIN/cMAX where cMIN is the heat-capacity rate c for the fluid with the smaller value of c and cMAX the value for the fluid with the larger value of c. Different flow rates and specific-heat values give rise to different values for c. |
| Heat-treatable alloy |
An alloy that can be hardened by heat treatment. |
| Helical spring |
A spring manufactured by forming elastic wire into a helix which may be cylindrical, conical, barrel-shaped, or hourglass in overall form. Closed-coiled springs are used in tension; open-coiled in both tension and compression. |
| Hexagon nut |
A nut having six sides and shaped like a hexagon. |
| High strength low alloy steels |
(HSLA steels) Steels with various micro-alloying elements such as copper, nickel, chromium, molybdenum, niobium, titanium, and vanadium in small quantities that give improved strength (as high as 900 MPa) and corrosion properties compared with plain carbon steels. Improvements are due to grain refinement and precipitation hardening, better control of the chemistry during steel making, and accurate rolling temperatures. |
| High-tensile bolt |
(high-tension bolt) A bolt manufactured from an alloy steel that has a high tensile strength of about 1 GPa. |
| Homogeneous carburizing |
Use of a carburizing process to convert a low-carbon ferrous alloy to one of uniform and higher carbon content throughout the section. |
| Homogenizing |
Holding at high temperature to eliminate or decrease chemical segregation by diffusion. |
| Honing |
Honing is a controlled, low-speed sizing and surface-finishing process in which stock is removed by the shearing action to the bonded abrasive grains of a honing stone, or stick. |
| Honing |
Finish polishing of surfaces and cutting edges in which very fine abrasive powders, such as rouge, are employed. Honing is usually applied to cylindrical surfaces and lapping to flat, but the usage is not consistent. |
| Hooke’s law |
Within the limit of proportionality, the extension of a material is proportional to the applied force. Approximately, it is the relationship between stress and strain in an elastic material when it is stretched. The law states that the stress (force per unit area) is proportional to the strain (a change in dimensions). The law, which holds only approximately and over a limited range, was discovered in 1676 by Robert Hooke. |
| Horizontal batch furnace |
A versatile batch-type furnace that can give light or deep case depths, and because the parts are not exposed to air, horizontal batch furnaces can give surfaces almost entirely free of oxides. |
| Horsepower |
Unit indicating the rate at which work is done. The electrical equivalent of one horsepower is 746 watts. |
| Hoseclip |
(hose clamp) A circular metal band, one end of which has a screw mechanism through which passes the other end such that the screw engages with indentations in the band, allowing the clip to be tightened or loosened. Used to hold a hose on to a pipe such as a water outlet. |
| Hot dipping |
(hot-dip galvanizing) A process of coating an iron, steel, or aluminium object with a thin layer of zinc by passing it through a bath of molten zinc at a temperature of about 460°C. |
| Hot hardness |
The hardness of materials at high temperatures, often used to rank the performance of cutting tools. |
| Hot isostatic pressing |
Sintering of powdered materials at high temperature and high hydrostatic pressure in order to minimize porosity. |
| Hot pressing |
1. Sintering of metal or ceramic powder at high temperature. 2. Formation of components from fibre-reinforced composite material in which bonding is ensured through application of pressure and temperature, often against a mould to give the required shape. |
| Hot quenching |
An imprecise term used to cover a variety of quenching procedures in which a quenching medium is maintained at a prescribed temperature above 70 °C (160 °F) |
| Hot shortness |
The reduction of ductility in steels at high temperatures caused by melting of sulfides that wet grain boundaries and spread along them. |
| Hot stamping |
Hot forging of brass and bronze alloys. |
| Hot strength (Unit Pa) |
The yield stress (or sometimes fracture stress) of a material at temperatures above about half its melting point in kelvins. |
| Hot working |
Plastic deformation of a metal, by rolling, drawing, forging, etc., at a temperature above its recrystallization temperature (in commercial alloys above about 40% of their melting points in kelvins) which results in permanent shape change but no increase in strength or loss of ductility. |
| Hot-wire analyzer |
An electrical atmosphere analysis device that is based on the fact that the electrical resistivity of steel is a linear function of carbon content over a range from 0.05% C to saturation. The device measures the carbon potential of furnace atmospheres (typically). This term is not to be confused with the hot-wire test which measures heat extraction rates. |
| Hot-wire test |
Method used to test heat extraction rates of various quenchants. Faster heat-extracting quenchants will permit more electric current to pass through a standard wire because it is cooled more quickly. Compare with hot-wire analyzer. |
| Humidify |
To add water vapour to air or another gas to increase its humidity. |
| Hydraulic air compressor |
1. A compressor powered by a hydraulic motor. 2. A device in which air is compressed as a result of being entrained in water flowing in a downcomer pipe. The compressed air is released in a chamber at the bottom of the pipe. |
| Hydraulics |
The study of water flow in open channels (including canals, rivers, etc.), water-supply, drainage, and irrigation systems. |
| Hydrodynamics |
A term sometimes used to mean fluid dynamics, even when the fluid is a gas or a liquid other than water. |
| Hydrogen damage |
A general term for the embrittlement, cracking, blistering, and hydride formation that can occur when hydrogen is present in some metals. |
| Hydrogen embrittlement |
A common and troublesome form of Stress cracking. Several theories have been proposed to explain hydrogen embrittlement, but, at present, the exact mechanism is still unknown. What is known, however, is the fact that if hydrogen is trapped in a bolt by poor electroplating practices, it can encourage stress cracking. Bolts can fail, suddenly and unexpectedly, under normal loads. |
| Hydrogen embrittlement |
A condition of low toughness, low ductility or cracking in metals resulting from the absorption of hydrogen. |
| Hydrogen embrittlement |
Premature crack growth over time under tensile stress leading to unexpected failure in certain metals, caused by small amounts of hydrogen in the microstructure. Hydrogen may enter steels during melting or heat treating, or during processes such as electroplating. |
| Hydrogen-induced delayed cracking |
A term sometimes used to identify a form of hydrogen embrittlement in which a metal appears to fracture spontaneously under a steady stress less than the yield stress. There is usually a delay between the application of stress (or exposure of the stressed metal to hydrogen) and the onset of cracking. Also referred to as static fatigue. |
| Hypereutectic alloy |
In an alloy system exhibiting a eutectic, any alloy whose composition has an excess of alloying element compared with the eutectic composition, and whose equilibrium microstructure contains some eutectic structure. |
| Hypereutectoid alloy |
In an alloy system exhibiting a eutectoid, any alloy whose composition has an excess of alloying element compared with the eutectoid composition, and whose equilibrium microstructure contains some eutectoid structure. |
| Hypoeutectic alloy |
In an alloy system exhibiting a eutectic, any alloy whose composition has an excess of base metal compared with the eutectic composition, and whose equilibrium microstructure contains some eutectic structure. |
| Hypoeutectoid alloy |
In an alloy system exhibiting a eutectoid, any alloy whose composition has an excess of base metal compared with the eutectoid composition, and whose equilibrium microstructure contains some eutectoid structure. |
| Hysteresis |
The phenomenon of permanently absorbed or lost energy that occurs during any cycle of loading or unloading when a material is subjected to repeated loading. |
