PEC EPE Metallurgical key terms

The ratio of basic oxides to acidic oxides in a slag, usually expressed as CaO/SiO2 by mass. It controls slag fluidity, sulphur and phosphorus capacity, and refractory wear in iron and steelmaking furnaces.

The concentration of an element in slag divided by its concentration in metal at equilibrium, denoted L. A high value means the slag removes that element efficiently, which guides sulphur and phosphorus removal practice.

Removal of sulphur from hot metal or steel by transferring it to a slag or flux as sulphide. It needs low oxygen potential, high slag basicity and good slag-metal mixing, and is often done in ladles or by injection.

Removal of phosphorus from steel by oxidising it into a basic oxidising slag. It requires low temperature, high slag basicity and high oxygen potential, so it is favoured in primary steelmaking rather than reducing ladle treatments.

Secondary steelmaking operations performed in or with a ladle after tapping, such as deoxidation, alloying, degassing, desulphurisation and inclusion flotation. It gives tighter composition and cleanliness control than furnace treatment alone.

Removal of dissolved oxygen from liquid steel by adding elements with high oxygen affinity, such as aluminium or silicon, so that oxides form and float out. It prevents gas porosity and controls inclusion type.

A non-metallic particle such as an oxide, sulphide or nitride suspended in or trapped by solidified metal. Inclusions act as stress raisers and fatigue initiation sites, so their size, type and distribution are controlled.

The charged raw materials in an ironmaking blast furnace, typically iron ore sinter or pellets, coke and fluxes such as limestone. Burden composition and size distribution govern permeability, gas flow and hot metal chemistry.

Metallic iron produced below the melting point of iron by reducing iron ore with a reducing gas or coal, often called sponge iron. It is used as a scrap substitute and must be handled carefully because it can reoxidise and self-heat.

A test measure of how well coke resists degradation after reaction with carbon dioxide at high temperature. Higher values indicate coke that keeps its size and permeability in the blast furnace, supporting stable gas flow.

The reversible reaction of carbon with carbon dioxide to form carbon monoxide, strongly temperature dependent. It governs coke consumption and gas composition in the blast furnace and in direct reduction processes.

A measure of the tendency of a chemical species to gain electrons and be reduced, expressed as an electrode potential in volts. In metallurgy it predicts whether a reductant can convert an oxide or solution species to metal.

A plot of the standard Gibbs energy of formation of oxides or other compounds per mole of oxygen against temperature. It shows which metal can reduce another's oxide and where carbothermic or electrolytic routes become viable.

A thermodynamic function whose change at constant temperature and pressure determines whether a reaction is spontaneous. A negative change means the reaction proceeds as written; zero means equilibrium.

A factor relating the effective concentration (activity) of a species to its measured concentration, correcting for non-ideal behaviour. In liquid metal and slag it quantifies how strongly a solute deviates from ideal mixing.

Agglomeration of fine ore or concentrate into porous lumps by heating below the melting point, with partial fusion bonding the particles. In ironmaking, sinter plants prepare blast furnace burden from fines; in powder metallurgy the term means particle bonding.

A mineral separation method in which hydrophobic particles attach to air bubbles and rise into a froth, while hydrophilic particles stay in the pulp. Reagents called collectors, frothers and depressants tune selectivity.

The degree to which valuable minerals are physically freed from gangue by comminution, expressed as a particle size. Overgrinding wastes energy and loses fines, while undergrinding prevents clean separation in downstream processes.

Recovery of a metal from a purified solution by electrolysis, depositing metal at the cathode. It is used for zinc, copper and nickel, and its current efficiency and cell voltage determine energy consumption.

The fraction of the theoretical metal deposition or dissolution predicted by Faraday's law that is actually achieved. Losses come from side reactions such as hydrogen evolution, short circuits or re-dissolution of product.

The relationship stating that the mass of substance electrolysed is proportional to the charge passed, with the constant of proportionality being molar mass divided by electrons transferred. It underpins sizing of electrorefining and electrowinning cells.

Selective dissolution of a valuable constituent from an ore or concentrate into an aqueous solution using an acid, alkali or complexing agent. Leach conditions such as temperature, reagent and particle size determine recovery and selectivity.

Purification and concentration of a metal from leach liquor by contacting it with an immiscible organic phase containing an extractant. The metal transfers selectively and is then stripped back into an aqueous solution.

The face-centred cubic solid solution of carbon in iron, stable above about 727 degrees Celsius in plain carbon steel. Its high solubility for carbon and its transformation behaviour underpin heat treatment of steel.

A hard, supersaturated and strained phase formed when austenite cools too fast for diffusion, so carbon is trapped in a body-centred tetragonal lattice. Its hardness rises with carbon content but so does brittleness.

A time-temperature-transformation diagram showing when austenite begins and finishes transforming to pearlite, bainite or martensite during isothermal holding. It guides selection of cooling rates and quench media.

The depth to which a steel can be hardened by quenching, determined mainly by alloy content and prior austenite grain size. It is measured by the Jominy end-quench test and differs from hardness itself.

The stress amplitude below which a material survives an indefinitely large number of cycles without failure, shown as a horizontal line on an S-N curve. Ferrous alloys often show one; most non-ferrous alloys do not.

A material property measuring resistance to propagation of a pre-existing crack, usually expressed as critical stress intensity factor. It links flaw size and applied stress to the likelihood of sudden brittle failure.

Loss of ductility and premature cracking caused by absorbed hydrogen in a metal, often after pickling, plating or welding. High-strength steels are especially susceptible, and baking or process control is used to mitigate it.

Corrosion control by making a metal the cathode of an electrochemical cell, either with a sacrificial anode or an impressed current. It works only in an electrolyte and must be designed to avoid overprotection.

A ranking of metals and alloys by their measured corrosion potential in a specific electrolyte such as seawater. When two are coupled, the more active one corrodes preferentially, so dissimilar metal joints need care.

Formation of a thin, adherent and self-repairing oxide film that greatly reduces corrosion rate, as on stainless steel or aluminium. Breakdown of this film by chlorides or mechanical damage leads to localised attack.

Localised breakdown of a passive film producing small deep cavities, typically in chloride-containing environments. Pits can penetrate through-wall while most of the surface remains unaffected, making inspection difficult.

Internal stress locked into a component without external load, arising from non-uniform heating, cooling, forming or phase change. It can be beneficial by design, as in shot peening, or harmful by promoting cracking and distortion.

The region of base metal adjacent to a weld that is altered by welding heat but not melted. Its microstructure and properties can degrade, causing hardening, softening or toughness loss depending on the alloy.

A written document specifying the variables for a production weld, including joint design, filler, current, preheat and post-weld heat treatment. It is supported by a qualified procedure qualification record and governs shop-floor practice.

A reservoir of liquid metal in a casting mould that feeds the solidifying casting to compensate for shrinkage. Its size and placement must ensure it freezes after the casting, which is the basis of directional solidification.

An empirical relationship stating that solidification time is proportional to the square of the volume-to-surface-area ratio of a casting. It is used to size risers and compare freezing order of sections.

A decision rule holding that where serious harm is plausible but scientific certainty is lacking, protective action should be taken rather than postponed. Engineers invoke it when designing safeguards for uncertain hazards.

A ranked order of risk reduction measures, from elimination and substitution through engineering controls and administrative measures to personal protective equipment. Higher-ranked controls are preferred because they do not rely on individual behaviour.

Reporting an employer's unlawful or dangerous practice to an internal or external authority after normal channels fail. Professional codes generally support it when public safety outweighs confidentiality obligations.

The time required for cumulative cash inflows to recover an initial investment, ignoring cash flows after that point. It is simple but ignores the time value of money and project value beyond breakeven.

The sum of a project's future cash flows discounted to today at a chosen rate, minus the initial investment. A positive value indicates the project adds value at that discount rate.

The rate used to convert future cash flows to present value, reflecting the cost of capital and project risk. A higher rate penalises distant cash flows more heavily and reduces apparent project value.

The total expenditure to acquire, build and commission a plant or asset before operation begins, including equipment, civil works and contingency. It is distinct from operating cost, which recurs during production.

A scheduling technique that identifies the longest sequence of dependent activities, which sets the minimum project duration. Delaying any activity on the critical path delays the whole project unless it is compressed.

A project control method comparing planned value, earned value and actual cost to measure schedule and cost performance objectively. Indexes derived from these reveal whether a project is ahead or behind and over or under budget.

Use of control charts and statistical limits to distinguish normal random variation from special-cause variation in a process. It supports decisions about when to adjust a process and when to leave it alone.