And some common terms that get used quite often:
A brief look at some of the common tool steel terminology used.
Abrasive Wear The loss of material due to hard particles moving against and reducing softer particles.
Adhesive Wear The displacement of material resulting from two materials sliding against one another while under pressure then being redeposited on the other surface leaving pits and surface projections. Also known as galling.
Alloy A material that is dissolved into another metal in a solid solution. Also, a material that results when two or more elements combine in a solid solution.
Annealing Refers to the heating and controlled cooling of steel for the purpose of removing stresses, softening, refining its structure or changing its ductility.
Austenite The metallic non-magnetic solid solution of steel. This phase is achieved by heating the steel to above its critical transformation temperature to dissolve the alloying elements into the iron matrix.
Billet A solid semi-finished round or square ingot that has been hot-worked by forging or rolling.
Breakage Refers to the premature failure of a tool by cracking, complete failure of the tool, unrepairable.
Carbide A chemical compound combining carbon and another metallic element, normally produced for the purpose of providing wear resistance in steels, such as vanadium carbide or chromium carbide.
Charpy V-notch test A Pendulum-type swing impact test in which the specimen with a V-notch is supported at both ends as a simple beam and broken by the swinging pendulum. The energy absorbed, as determined by the subsequent rise of the pendulum, is a measure of impact toughness strength or notch strength.
Chipping The fracture and subsequent breakage of steel due to a lack of toughness.
Cold-work Plastic deformation of steel at a temperature low enough to insure strain hardening. Also, a group of tool steel grades chemically enhanced to perform at temperatures below 800 degrees F.
Compressive strength - the ability for a tool steel to resist permanent deformation when a load is applied axially. When a load is applied in compression on a tool steel, the tool will compress in the longitudnal direction and expand outward. When the load is removed the tool will return to its original shape and size. If the tool doesn't return to its original dimensions, then the load has exceeded the tool's compressive strength.
Corrosion The gradual chemical or electrochemical attack on steel by atmospheric moisture or other agents resulting in rusting or tarnishing.
Critical Temperature - The temperature at which austenite transforms to martensite. This is the stage of the heat treating process when hardening of the steel actually takes place.
Decarburization The loss of carbon from the surface of steel. It is a common surface condition of hot rolled steel and is produced during the heating and rolling operations when atmospheric oxygen reacts with the heated surface removing the carbon.
Dimensional stability Normally refers to the steels ability to hold its size during the heat treating processes.
Ductility The ability of a steel to deform plastically without fracturing, being measured by elongation or reduction of area in a tensile test or by height of cupping in an Erichsen test.
Elastic Limit The greatest amount of stress that a steel can withstand without a permanent deformation remaining upon complete removal of the stress.
Elements a pure chemical substance consisting of one type of atom. Steels are comprised of iron, carbon and other elements such as silicon, manganese,chromium and vanadium.
Elongation The amount of permanent extension in the vicinity of the fracture in the tensile or tension test, usually expressed as a percentage of the original gauge length, such as 20% in 3.
Fatigue The progressive fracture of a steel by means of a crack which spreads under repeated cycles of stress.
Galling See adhesive wear.
Grade Designates divisions within different groups of steel based on carbon content and mechanical properties.
Grain Size The physical size of the austenite grains during austenizing. The actual size can vary due to thermal treatment, time and forging operations.
Grindability Refers to the steel ability to readily be ground to a smooth finish, measured by the amount of material removed from the steel in comparison to the amount of grinding wheel removed.
Hardenability Relates to the steels ability to harden upon quenching. The depth of the hardening is determined by the chemical analysis and grain size of the steel, the size of the part and the method of quenching. Carbon steels are generally considered to be shallow hardening while tool and high-speed steels are considered to be deep hardening or through hardening.
Hardening The process of heating and cooling a steel to increase the hardness, also known as heat treating. Depending on the grade of steel, hardening can include age hardening, case hardening, flame hardening, induction hardening, precipitation hardening and quench hardening.
Hardness The steels ability to resist indentation or penetration. Hardness is measured and reported bases on test results from Rockwell, Brinell or Vickers hardness tests.
Heat Treatment - The series of processes through which a steel in a solid state is repeatedly heated and cooled to achieve its desirable properties and hardness. The series of processes can include austenizing, quenching and tempering.
High-Speed Indicates a class of tool steels that can withstand elevated temperatures for extended periods of time without softening after repeated use. Normally they are found to be used in high-speed cutting tools.
Impact Test The test used to measure the steels ability to resist energy from impact. The test involves impact from a hammer on the sample material and is usually measured in foot pounds of energy. Two common test methods are Charpy and Izod.
Inclusions Undesirable non-metallic elements occurring in metals such as oxides, sulphides and silicates.
Ingot A steel casting that was formed when molten steel solidifies in a mold. The ingot is then reheated and rolled into slabs, plates, blooms or billets for further processing into bars and sheets.
Machinability Refers to the steels ability to be turned, milled or shaped by mechanical means. Machinability ratings for tool steels are based on the ease of machining of W-1, usually indicated as a percentage of W-1's machinabilty.
Martensite The resulting maximum hardness microstructure acquired from the transformation of the softer austenite microstructure. Steel must undergo this fully hardened stage before it can be tempered into a usable tool.
Mechanical Properties The properties of steel that include modulus of elasticity, tensile strength, elongation, hardness and fatigue limit. These properties indicate the steels suitability for mechanical applications.
Metallurgy The class of science dealing with the extraction of metals from their ores and the adaption and application of those raw elements for their intended use. Metallurgists formulate the chemical composition of the steel grades to fit a particular application.
Microstructure - The arrangement of atoms in steel. A ground, highly polished and etched picture of a sample which reveals the microstruure is referred to as a photomicrograph..
Modulus of Elasticity The ratio within the limit of elasticity of the stress to the corresponding strain. The stress in pounds per square inch is divided by the elongation in fractions of an inch for each inch of the orginal length of the test specimen.
Nitriding The process of adding nitrogen to an steel alloy by heating the metal in contact with ammonia gas or other suitable nitrogenous material. The purpose of the process if to produce a surface hardness. Nitriding is performed at temperatures between 935 and 1000 degrees F.
Oxidation Exposure of steel to oxygen. Staining and discoloration can result from atmospheric exposure. Scaling and decarburization can result from exposure to oxygen at high temperatures.
Plastic Deformation Deformation of a material that will remain after removal of the load which caused it.
Quenching The process of rapidly cooling steel in order to obtain the fully hardened martensite microstructure by immersing or quickly cooling the steel in a quenching media. Quenching mediums can include salt brine, water, oil or air. The intensity of the quench is determined by the temperature, volume and velocity of the media.
Red Hardness A steels ability to resist softening at elevated temperatures over extended periods of time.
Reduction of Area The percentage difference between the original cross sectional area and that of the smallest area at the point of rupture.
Residual Stress - Stresses resulting from nonuniform plastic deformation or thermal gradients. Excessive coldworking or drastic temperature differences from quenching or welding may cause residual stress.
Rockwell Hardness A measure of a hardened tool or high speed steel. A number based on the steels resistance to indentation.
Segregation Referring to the chemical separation that can occur during the cooling of the molten metal into the ingot form.
Stainless Designates the class of steels with the ability to resist corrosion from exposure to acids. High levels of Chromium or Nickel are added to the alloy to provide the necessary corrosion resistance.
Strain Deformation of a material produced by an outside force.
Stress Releiving The heating of steel to a temperature below its transformation temperature and then slowly cooling to minimize the development of new residual stresses.
Tempering The process of reheating quenched steel to a suitable temperature below the transformation temperature for an appropriate amount of time. The steel is then allowed to cool to room temperature. This process changes the hardness, increases the toughness and reduces the stress in the steel.
Tensile Strength The maximum amount of pressure in pounds per square inch that a material will carry before breaking under a slowly applied, gradually increasing load during a tensile test.
Tool Steel A class of steel melted in electric furnaces to assure cleanliness and homogeneity that includes high carbon and alloy content. These steels are characterized by high hardness and resistance to abrasion and may include the resistance to softening at elevated temperatures. The intended purpose of the special steels are to be used as tools used to form other materials.
Toughness The ability of a metal to absorb energy and plastically deform before fracturing. It is usually measured by the energy absorbed in a notched impact test.
Transverse Toughness This is the steel's ability to flex in a sideways direction while maintaining the ability to return to its original shape without breaking or cracking.
Wear Resistance A steels ability to resist erosion from contact with another material. Two types exist, see abrasive wear and adhesive wear.
Yield Strength Stress corresponding to the fixed permanent deformation such as .1 or .2% offset from the modulus or elastic slope.
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