| P | Chemical symbol for Phosphorus. |
| Parkerizing | 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. |
| Partial Annealing | An imprecise term used to denote a treatment given cold worked material to reduce its strength to a controlled level or to affect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated. |
| 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 distinctive two-phase lamellar structure in steel consisting of thin platelets of iron carbide (Fe3C) in a ferrite (essentially, Fe) matrix. The fine pearlitic structure (small grain size) allows maximum drawability and strengthening in steel wire, 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%. |
| Physical Properties | Properties of a metal or alloy that are relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of thermal expansion, magnetic permeability and lattice parameter. Does not include chemical reactivity. Compare with mechanical properties. |
| 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 sulfuric 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 neutralize 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. |
| Plasma Spraying | A thermal spraying process in which the coating material is melted with heat from a plasma torch that generates a non-transferred arc (defined in plasma-arc welding); molten coating material is propelled against the basis metal by the hot, ionized gas issuing from the torch. |
| 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 carburized parts directly from the carburizing 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. Heating before some further thermal or mechanical treatment. For tool steel, heating to an intermediate temperature immediately before final austenitizing. For some nonferrous alloys, heating to a high temperature for a long time, to homogenize the structure before working. In welding and related processes, heating to an intermediate temperature for a short time immediately before welding, brazing, soldering, cutting, or thermal spraying. Pre-heating reduces the time of exposure to the hardening temperature and helps to minimize scaling and decarburization. |
| Precipitation Hardening | Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging. |
| Precipitation Heat Treatment | Artificial Aging in which a constituent precipitates from a supersaturated solid solution. |
| Projection Welding | A welding process that uses small projections on one or both components of the weld to localize 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. |
| Proportional Limit | The stress (load divided by original area of cross section of the test piece) at which the strain (elongation per unit of gauge length) ceases to be proportional to the corresponding stress. If the load is removed for any stress up to this point, the material will spring back, or assume its original dimensions. The limit is usually determined from a load-elongation diagram, obtained by plotting extensometer readings and is the stress at which the load-elongation line ceases to be straight.
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| Pusher Furnace | A type of continuous furnace in which parts to be heated are periodically charged into the furnace in containers, which are pushed along the hearth against a line of previously charged containers thus advancing the containers toward the discharge end of the furnace, where they are used. |
