Mechanical Engineering Dictionary-Heat and Surface Treatment

Important Terms and their Meaning of Mechanical Engineering-Heat and Surface Treatment:



AGING – The process of holding metals at room temperature or at a predetermined temperature for the purpose of increasing their hardness or strength by precipitation. Aging is also used to increase dimensional stability in metals such as castings.

AGE HARDENING – Change in the physical properties, e.g., hardness and strength that occurs in certain light metals after heat treatment.

ALLOYING OF METAL – The addition of varying proportions of other elements to a basic metal in order to produce an alloy having specific properties.

ANODIC TREATMENT – Formation of a protective layer of oxide on the surface of aluminium and its alloys by electrolytic action, in order to resist corrosion.

ANNEALING – A heat treatment in which metals are heated and then cooled very slowly for the purpose of decreasing hardness. Annealing is used to improve machinability and to remove stresses from weldments, forgings and castings. Also used to remove stresses resulting from cold working and to refine and make uniform the microscopic internal structures of metals.

ANODIZING – To subject a metal to electrolytic action, as takes place at the anode of a cell, in order to coat it with a protective or decorative film, used for nonferrous metals.

AUSTEMPERING – A heat treating process consisting of quenching a ferrous alloy at a temperature above the transformation range in a medium such as molten lead, the temperature of the quenching medium is maintained below that of pearlite and above that of martensite formation to produce a tough, hard microstructure.

AUSTENITIZING – The process of forming austenite (a solid solution of iron and carbon and sometimes other elements).

BLACK OXIDE COATING – Coating produced by converting the surface of iron or steel to black iron oxide having a thickness of about 0.0025 mm.

CADMIUM PLATING – Electroplating process for the application of cadmium to steel and iron parts to prevent rust.

CALORIZING – Rust proofing process for ferrous metals in which an aluminium film is formed on the surface of the metal. Means of protecting iron from oxidation at elevated temperatures.

CARBURIZING – A process that introduces carbon into a heated solid ferrous alloy by having it in contact with a carbonaceous material. The metal is held at a temperature above the transformation range for a period of time. This is generally followed by quenching to produce a hardened case.

CASE HARDENING – Heating a steel in the presence of a solid, liquid or gas, rich in carbon, in order to enable the surface to be hardened, while retaining a tough, ductile core.

CHROMIUM PLATING – Electrolytic deposition of chromium on a metal surface, as a protection against corrosion, to provide improved wearing properties, or to build up an undersized part.

CHROMIZING – Similar to carburizing. Low carbon steel parts are packed with a mixture of alumina and chromium powder and heated in a hydrogen atmosphere, forming a surface layer of chromized material of 10 to 20% chromium, according to time and temperature of heating.

COLOURING METAL – Production of a coloured surface on a metal or alloy by the use of heat or chemical action, or by a combination of the two.

COSLETTIZING – Rust proofing process in which an iron phosphate skin is formed on the surfaces of ferrous parts, the skin follows even the microscopic irregularities, yet is remarkably tough and corrosion resistant.

DECARBONIZATION – The loss of carbon from the surface of a ferrous alloy as a result of heating it in the presence of a medium such as oxygen that reacts with the carbon.

ELECTROLYTIC POLISHING – Method of polishing metals in which the work forms the anode of an electrical circuit, and is suspended in a suitable bath of acid.

ELECTROPLATING – Deposition of a metal on a surface by electrolytic action.

FLAME HARDENING – Process of hardening by which steel or cast iron is raised to a high temperature by a gas torch flame and then almost immediately quenched.

GALVANIZING – Rust prevention treatment which consists of coating the metal (iron or steel) with a fairly thick film of zinc.

HARDENING – Process of increasing the hardness of a ferrous alloy by austenitizing and quenching, also the process of increasing the hardness of some stainless steels and non-ferrous alloys by solution heat treatment and precipitation.

HARD SURFACING – Arc welding a surface layer usually at strategic spots on a part, using an electrode having a suitable alloy content for the purpose. Also known as SURFACING and FACING.

HEAT TREATMENT – Operation or combination of operations, involving the heating and cooling of a metal or alloy in its solid state with the object of changing the characteristics of the material.

HOT ROLLING – Surface layers of noble metals are often hot rolled (or inlayed) on less noble metals.

INDUCTION HARDENING – Heating the surface of cast iron or tool steel by means of electromagnetic currents followed by a quench.

LACQUERING – A protective coat given to an article to prevent the polished surface from tarnishing, to prevent oxidation or to improve the general appearance and make the article more pleasing to the eye, and hence more saleable.

MARTEMPERING – The process of quenching an austenitized ferrous alloy to a temperature just above or near the M’s point and maintaining until the temperature throughout the part is uniform. The alloy is then allowed to cool slowly in air through the range of martenistic formation.

METALLIZING – Metal spraying process in which the coating metal is melted (either in a gas flame or in a separate melting pot), then atomized by an air blast and deposited in atomized form on the surface to be coated.

NEGRADIZING – Rust proofing process in which a ferrosoferric oxide surface is produced on steel or iron.

NICKEL PLATING – Deposition of nickel on a metal by electrolytic action to provide a protective surface or to build up the surface of a worn or undersize part.

NITRIDING – A process of case hardening in which a special ferrous alloy is heated in an atmosphere of ammonia or is in contact with any other nitrogenous material. By this, surface hardening is achieved by the absorption of nitrogen without quenching.

NORMALIZING – Process applied to iron base alloys, such as steel, to refine the grain structure and remove the effects of previous processing for example hot rolling.

ORGANIC FINISHING – Coating a surface with a continuous film of an organic material for protecting the surface from corrosive influences, for enhancing the appearance or a combination of both.

PARKERIZING – A coslettizing process in which a patented mixture of iron and manganese phosphates is used in solution to provide a rust proof surface on iron and steel parts.

PHOSPHATE COATING – Coating produced by converting the surface of iron or steel parts to insoluble phosphate, such as iron phosphate or zinc iron phosphate.

PICKLING – Treatment of objects with an acid solution to remove all oxide, scale or dirt. Usually done to clean and brighten the surface, although sometimes used for etching.

POWDER COATING – Surface coating of almost any metal or alloy applied to another by powder method.

PRECIPITATION HARDENING – A process of hardening an alloy by heat treatment in which a constituent precipitates from a supersaturated solid solution while at room temperature or at some slightly elevated temperature.

QUENCHING – Rapid cooling of a metal in a bath of fluid during heat treatment after it has been heated to a given temperature, thus trapping the molecules of the metal in the desired structure.

RECRYSTALLIZATION – A process in which the distorted grain structure of metals that are subjected to mechanical deformation is replaced by a new strain free grain structure during annealing.

RUST PROOFING – Treatment of iron and steel parts to render them resistant to rust, implies a more permanent form of protection.

SHERADIZING – Heat treatment process in which zinc dust is used for producing a rust proof surface on ferrous metals. It derives its title from the name of the inventor SHERARD OSBORN COWPER COLES.

SILICONIZING – Process in which iron and steel parts are impregnated with silicon for improving the surface resistance to corrosion, heat and wear.

SOAKING – A prolonged heating of a metal at a predetermined temperature to create a uniform temperature throughout its mass.

SOLUTION HEAT TREATMENT – A process in which an alloy is heated to a predetermined temperature far a length of time that is suitable to allow a certain constituent to enter into solid solution. The alloy is then cooled quickly to hold the constituent in solution, causing the metal to be in an unstable supersaturated condition. This condition is often followed by age hardening.

STRAIN HARDENING – An increase in hardness and strength of a metal that has been deformed by cold working or at temperatures lower than the recrystallization range.

SUBZERO HEAT TREATMENT – Method of heat treatment of steel, introducing a cooling period or periods at a temperature well below freezing point, the object being to ensure complete transformation of austenite to martensite.

TEMPERING STEEL – Heat treatment designed to relieve the stresses and brittleness set up in carbon or alloy steel tools and other parts after hardening and to restore the required degree of toughness and ductility to hardened steel.

TINNING – Application of a layer of tin to the surface of another metal, either as a protection against corrosion or as a preliminary to soldering.

WORK HARDENING – Phenomena in which the grains become distorted and elongated in the direction of working (rolling). This process, also called STRAIN HARDENING, hardens and strengthens metals but reduces their ductility.

ZINC PLATING – Electroplating process for the deposition of zinc on metallic surfaces.



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