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H-band steel

Alloy steel produced to specified limits of hardenability. The chemical-composition range may be slightly different from that of the corresponding grade of ordinary alloy steel.

hacksaw blade

Serrated blade for a manual or power hacksaw that cuts on the forward or return stroke. See sawing.

hard chromium

Chromium electrodeposited for engineering purposes (such as to increase the wear resistance of sliding metal surfaces) rather than as a decorative coating. It is usually applied directly to basis metal and is customarily thicker than a decorative deposit, but not necessarily harder.

hard tooling

Tooling made for a specific part. Also called dedicated tooling.

hard turning

Single-point cutting of a workpiece that has a hardness value higher than 45 HRC.


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 at which the metal exhibits a specific hardness (50 HRC, for example) or a specific percentage of martensite in the microstructure.


Process of increasing the surface hardness of a part. It is accomplished by heating a piece of steel to a temperature within or above its critical range and then cooling (or quenching) it rapidly. In any heat-treatment operation, the rate of heating is important. Heat flows from the exterior to the interior of steel at a definite rate. If the steel is heated too quickly, the outside becomes hotter than the inside and the desired uniform structure cannot be obtained. If a piece is irregular in shape, a slow heating rate is essential to prevent warping and cracking. The heavier the section, the longer the heating time must be to achieve uniform results. Even after the correct temperature has been reached, the piece should be held at the temperature for a sufficient period of time to permit its thickest section to attain a uniform temperature. See workhardening.


Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.

headchanging machine

Multifunction, NC machine tool. It differs from machining centers in that single- or multiple-spindle heads, rather than tools, are transferred to a single workstation in proper sequence to perform the required series of operations. The single workstation is equipped with a spindle drive and slide feed unit; the workpiece remains in a fixed or indexable position. Additional workstations can be added on some machines if required.

heat-affected zone

That portion of the base metal that was not melted during brazing, cutting or welding, but whose microstructure and mechanical properties were altered by the heat.


Process that combines controlled heating and cooling of metals or alloys in their solid state to derive desired properties. Heat-treatment can be applied to a variety of commercially used metals, including iron, steel, aluminum and copper.

heeling (heel drag)

Rubbing that occurs on the cutter’s heel, the area just behind the tooth’s cutting edge.

helical cutter

Endmill or other cutter with spiral or helical flutes. May be right- or left-hand.

helix angle

Angle that the tool’s leading edge makes with the plane of its centerline.

high-speed steels (HSS)

Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.

hydrodynamic machining

General term for various forms of waterjet and abrasive waterjet machining. In all cases, a fine, highly pressurized jet of water cuts and removes the material. See AWJ, abrasive waterjet; waterjet cutting.