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| Decarburisation |
| A loss of carbon from the surface layers of steel caused by the steel having been held at high temperatures in an oxidising atmosphere. |
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| Decoiling and Cutting to Length |
| The uncoiling, flattening if necessary and cutting to required length of strip originally in coil form. |
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| Deep Drawing Steel |
| A steel, produced usually in the form of sheet, in which the composition and microstructure have been carefully controlled such that it has excellent cold forming properties when shaped by drawing or by pressing. In the case of carbon steel sheet a deep drawing quality grade would contain <0.06%C, <0.25%Mn and would have limitation on the sulphur and phosphorous contents. It will be aluminium killed. |
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| Delta Iron |
| The form of pure iron that exists between 1392C and its melting point in which the iron atoms are arranged in a body centred cubic (bcc) crystalline pattern. |
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| Deoxidation |
| The practice of adding elements to liquid steel before it is cast to reduce and control the level of dissolved oxygen in the liquid and therefore to control the amount of carbon monoxide evolved during solidification. Elements added for this purpose are Mn, Si and Al. Modern casting practice requires the complete removal of gaseous oxygen before casting commences; this steel is 'fully killed'. |
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| Descaling |
| A process in which oxide (scale), formed on steel when it is at high temperature in an oxidising environment, is removed from the steel surface. Primary scale is usually removed in the first stage of a hot working operation using high pressure water jets whereas secondary scale is usually removed by hot acid pickling or by shot blasting. |
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| Deseaming |
| The removal of surface imperfections on steel by the controlled use of an oxy-acetylene gas burner. When used on-line in a rolling mill the process is often called 'scarfing'. |
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| Die |
| A tool, usually containing a cavity, which is used to impart shape, or to change the shape of metal in liquid, solid or powder form. Examples are die-casting dies, forging dies, draw dies. |
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| Dislocation |
| A discontinuity in the regular arrangement (crystallinity) of atoms in a metal grain (crystal). |
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| Drawing |
| A process in which steel in the form for example of bar, rod, tube, section or wire is drawn (pulled) through a die in order to reduce its cross-sectional area, or in which a steel sheet blank is formed into a cup-shape by being deep drawn into a die. |
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| Dress |
| To clean or prepare an edge for the next process or despatch. |
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| Drop Forging |
| A process in which hot steel blanks are shaped by forging into an impression formed within two dies. One die is attached to a stationary anvil and the other to a drop hammer. When the latter is dropped, either freely or under a power drive, the forging is formed by the closing together of the two dies. |
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| Dry Film |
| Thickness of paint film (dry). |
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| Ductility |
| The ability of a metal to deform plastically without fracturing. From a tensile test, two simple measures of ductility obtained are elongation % and reduction in cross-sectional area %. |
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| Dye Penetrant Inspection |
| A method of Non-Destructive Testing for determining whether or not surface porosity or cracks are present in a metal. The metal is coated with a penetrating liquid dye. The surface liquid is then removed and the metal coated with a white absorbent powder. The powder absorbs the dye held in the defects, so indicating their location. |
