Glossary - S
A variation of the spot gouging technique which is used to remove surface defects from the surface of steel billets before rolling. Constitution Diagram used for the estimation of ferrite and other metallurgical phases present in stainless steel weld metal derived from Chromium and Nickel contents and their equivalents. A joint which comprises two pieces of metal which fit together to form a gas tight seal. As distinct from metal components that are screwed together using a thread. Arc welding with equipment that controls only the filler metal feed. The advantage of the welding is manually controlled. Shielding gases are the gases and mixtures used to protect the weld pool from contamination from the atmosphere. They play a significant role by affecting the physical and metallurgical characteristics of the weld, the arc characteristics and the speed and ease of welding. Sigma is an iron-chromium (roughly 50-50) phase, which can form from ferrite in austenitic stainless steel weld metal at elevated temperatures ( approximately between 450 and 850oC). It, therefore, forms during high temperature service and its presence in the stainless steel is only apparent at room temperature, during plant shutdown, when the sigmatised material becomes extremely brittle and will crack readily with low toughness. In arc and gas welding, any joint welded from one side only. A vitreous or glass like material containing oxides of materials such as manganese, silicon and aluminium. The slag produced solidifies on the surface of the weld protecting it from atmospheric contamination as it cools and is removed later. SMAW stands for Shielded Metal Arc Welding (another name for MMA welding), an electric arc welding process in which the arc is struck between a covered metal electrode and the workpiece. Shielding of the weld pool is provided by the decomposition of the electrode covering and the electrode is consumed to provide filler metal. The practice of momentarily opening a cylinder valve to remove moisture and dirt. There must be no possible source of ignition in the vicinity and the operator should wear eye protection and stand clear of the gas stream. Snifting must never be carried out on a hydrogen cylinder because spontaneous ignition can occur. A non-fusion joining process which uses capillary action to draw a filler material into the joint to form a bond. The properties of the joint are not the same as the parent metal. Soldering uses a filler material which melts below 450 degrees Celsius, and often as low as 300 degrees Celsius. The phase of a substance in which the constituent molecules, atoms or ions have no translational motion but vibrate about fixed positions Solid solutions are solid phases containing more than one component and are the basis of the ability of metals to form alloys. There are two general classes of solid solution, 'substitutional' and 'interstitial'. Substitutional solid solutions are those in which the solute atoms are substituted for solvent atoms in the crystal structure. Interstitial solid solutions are those in which the solute atoms occupy interstices in the crystal structure of the solvent. Also known as hot cracking it is a discontinuity produced by tearing of the metal while it is at an elevated temperature. The maximum temperature at which a metal or an alloy is completely solid. The small particles of weld metal ejected from the weld pool which can adhere to the surface of the metal. A compound containing a mixture of one or more metal oxides. A type of MIG welding torch where the welding wire is carried on a small spool located on the torch itself. This type of torch is used to feed soft wires such as aluminium that could suffer from wire feed problems if fed through the length of the torch liner. The mode of transfer in which small droplets of consumable wire are thrown across the arc by means of the forces generated by the arc. Also known as 'free flight transfer'. A corrosion resisting steel which contains a minimum of 13% Chromium. The corrosion resisting characteristics are caused by the formation of a thin layer of chrome oxide which adheres very strongly to the surface of the material. A range of stainless steels with different compositions and metallurgical structures are produced to deliver different mechanical properties. Plain Cr-Ni stainless steel may be susceptible to weld decay due to formation of chromium carbides in the HAZ during welding. Weld decay can be avoided in several ways, one being to add 'stabilising' elements, such as niobium or titanium to the steel. These elements form carbides preferentially to chromium over a wide temperature range, freeing the chromium to provide a corrosion-resistant passive film. Stainless steels containing niobium or titanium are said to be 'stabilised'. A relative term used to describe the arc stability characteristics of a process or product. Lower the Stability Index the more stable the process. In MIG welding, products with high Stability Indexes normally produce high levels of spatter. A technique used to increase the productivity of a machine cutting operation. Several plates are laid on top of each other and cut at the same time. For the process to work efficiently there must be no gap between the plates. Plates are often clamped together to prevent this from happening. A technique used to increase the productivity of a machine cutting operation. Several plates are laid on top of each other and cut at the same time. For the process to work efficiently there must be no gap between the plates. Plates are often clamped together to prevent this from happening. The distance between the end of the contact tip or electrode and the workpiece. The amount of a substance which is consumed when a chemical reaction proceeds to completion. A post-weld heat-treatment designed to relieve residual stresses and restore mechanical properties, particularly toughness and ductility, in a welded structure. It normally involves holding at a specified elevated temperature for a set time, followed by slow cooling. The process whereby a solid becomes a gas under a change in temperature or pressure without going through a liquid phase.
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