found 14 matching terms.
| Term |
Definition |
| Decalescence |
A term used in reference to the absorption of heat without a corresponding increase in temperature, when steel is heated through the critical points (phase changes). |
| Decarburisation |
The loss of carbon from the surface of steel as a result of heating in a carbon weak atmosphere. During the rolling of steel hot surfaces are exposed to the decarburising effects of oxygen in the atmosphere and as a result the surface is depleted of carbon. In steels where the components are to be subsequently heat treated it is necessary to remove the decarburised surface by machining. |
| Delta Iron |
When pure or practically carbon-free iron is cooled from above its melting point it solidifies at about 1535oC as delta iron having a body-centred cubic lattice structure, which persists down to about 1400oC. On further cooling it undergoes an allotropic change to gamma iron which has a face-centred cubic lattice and is non-magnetic. |
| Deoxidation |
Elements such as silicon and aluminium when added to molten steel react to form stable oxides and reduce the amount of dissolved oxygen. The solubility of oxygen in steel is reduced as temperature is lowered during solidification and the excess oxygen combines to form carbon monoxide. If the molten metal is not deoxidised the effervescence produced by the evolution of carbon monoxide during solidification would result in blow holes and porosity. Steel treated in this way is termed, "Killed Steel". |
| Descaling |
It is necessary to remove the scale from hot rolled bars or coil before bright drawing. This is normally carried out by shot blasting or pickling in acid. Other methods of descaling steel products include sand blasting, flame descaling and tumbling. |
| Deseaming |
A process of burning out defective areas on the surface of ingots, blooms or billets. The condition of the surface is such that it can then be rolled or forged into a satisfactory product. |
| Diamond Pyramid Hardness Test |
This test, more commonly known as the Vickers test, finds greater use in the laboratory than the workshop. It employs a pyramid shaped diamond with an included angle of 136o which is impressed into the specimen using loads of 5 to 120 kg making a small square impression. This test is used for finished or polished components because the impression can be very small. The diamond pyramid hardness number is obtained from a calculation based on measuring the diagonals of the impressions in the steel. |
| Die |
The term die is most commonly used in tooling, i.e. press tools "punch and die" but there are many other types of die, e.g. thread cutting dies, forming dies, forging dies, die-casting dies, etc. The term when applied to steel often refers to drawing dies through which hot rolled wire and bar are drawn to produce the finish and dimensional accuracy that is required for bright steel. |
| Dislocation |
A discontinuity in the crystal lattice of a metal. The movement of dislocations under stress may be used to explain slip, creep, plastic yielding, etc. |
| Dolomite |
A natural carbonate of calcium and magnesium generally used as a flux in blast furnaces. |
| Drawing |
The process of pulling metal wire, rods, or bars through a die with the effect of altering the size, finish and mechanical properties. In the USA, it is a term used for tempering. |
| Drop Forging |
An operation in which a metal shape is formed by forcing hot metal into impressions formed in solid blocks of hardened alloy steel, the forging dies. The dies are made in halves, one attached to the rising and falling block of the drop forge and the other to the stationary anvil. Drop forgings are widely used in the automotive industry for crankshafts, stub-axles, gears, etc. |
| Ductility |
The property of metal which permits it to be reduced in cross sectional area without fracture. In a tensile test, ductile metals show considerable elongation eventually failing by necking, with consequent rapid increase in local stresses. |
| Dye Penetrant Inspection |
A method for detecting surface porosity or cracks in metal. The part to be inspected is cleaned and coated with a dye which penetrates any flaws that may be present. The surface is wiped clean and coated with a white powder. The powder absorbs the dye held in the defects indicating their location. |
