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Your search for "p" found 17 matching terms. Click here to search again.

Term	Definition
P	Chemical symbol for Phosphorus.
Parkerising	A chemical treatment applied to ferrous metals to improve their corrosion resistance. The process is based on a manganese phosphate solution which produces a fairly thick coating. This can subsequently be painted or impregnated with oil. Patenting A heat treatment process often applied to high carbon wire. The steel is heated to a suitable temperature well above the transformation range, followed by cooling in air or a bath of molten lead or salt. A structure is produced suitable for subsequent cold drawing and which will give the desired mechanical properties in the finished state.
Pd	Chemical symbol for Palladium.
Pearlite	A lamellar constituent of steel consisting of alternate layers of ferrite (alpha-iron) and cementite (iron Carbide Fe3C) and is formed on cooling austenite at 723oC. This produces a tough structure and is responsible for the mechanical properties of unhardened steel.
Ph	Chemical symbol for Lead.
pH Value	A method of expressing differences in the acidity or alkalinity of a solution. A figure of 7 is regarded as neutral, figures below this indicate the decree of acidity and above alkalinity.
Phosphorus	An element that forms 0.12% of the earth's crust, chiefly in the form of phosphates. Its presence in steel is usually regarded as an undesirable impurity due to its embrittling effect, for this reason its content in most steels is limited to a maximum of 0.050%.
Pickling	A process to chemically remove scale or oxide from steel to obtain a clean surface. When applied to bars or coils prior to bright drawing, the steel is immersed in a bath of dilute sulphuric acid heated to a temperature of around 80oC. An inhibitor is added to prevent attack and pitting of the cleaned metal. After pickling, a washing process takes place followed by immersion in a lime-water bath to neutralise any remaining acid. For environmental reasons shot blasting has largely replaced pickling.
Pig Iron	The product of the blast furnace. The term was derived from the method of casting the bars of the pig iron in depressions or moulds formed in the sand floor adjacent to the furnace. These were connected to a runner (known as a sow) and when filled with metal the runner and the numerous smaller moulds were supposed to resemble a litter of suckling pigs, hence the term pig iron.
Pinch Pass	A term applied when, after annealing, sheet or strip is lightly rolled with the object of preventing stretcher lines or kinks on subsequent cold working.
Pipe	A defect that arises during the solidification of steel in the ingot mould. As steel contracts on solidification a central cavity forms in the upper portion of the ingot, if this is not completely removed before rolling into bars a central defect known as "pipe" results. The risk of piping is considerably reduced on continuously cast steel due to molten steel being available to fill any shrinkage cavity.
Poisson's Ratio	If a square bar is stressed in a testing machine in the direction of its length so that the length increases, there is a contraction in each opposite direction, which produces a decrease in the thickness of the bar. The ratio between the contraction at right angles to a stress and the direct extension is called the Poisson's ratio. Its value in steel is in the order of 0.28.
Pot Quenching	Quenching carburised parts directly from the carburising pot or box.
Powder Metallurgy	A method of producing components by pressing or moulding metal powders which may be simultaneously or subsequently heated to produce a coherent mass.
Pre-Heating	Used in the hardening process. Tools are pre- heated before heating to the final temperature, this is particularly important in tools of complex shape to prevent distortion or cracking. Pre-heating reduces the time of exposure to the hardening temperature and helps to minimise scaling and decarburisation.
Projection Welding	A welding process that uses small projections on one or both components of the weld to localise the heat and pressure, the projections collapse when the weld is made.
Proof Stress	The stress that will cause a specified small, permanent extension of a tensile test piece. Commonly the stress to produce 0.2% extension is quoted in N/mm2 for steel. This value approximates to the yield stress in materials not exhibiting a definite yield point.

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