Annealing is a heat treatment that alters the microstructure of a material, causing changes in its properties such as strength and hardness. It is a process that produces equilibrium conditions by heating a material and maintaining it at a suitable temperature, and then cooling it very slowly. The process is used to induce softness, relieve internal stresses, refine the structure and improve cold working properties.
Bonding is structurally joining parts by adhesive cured under elevated temperature.
Brazing or "hard soldering" is a joining process whereby a nonferrous filler metal or alloy is heated to melting temperature above 450°C (800°F) and distributed between two or more close-fitting parts by capillary action.
Curie point (also called Curie temperature) is the temperature at which certain magnetic materials undergo a sharp change in their magnetic properties. Specification: the temperature at which there is a transition between the ferromagnetic and paramagnetic phases. Above the Curie point, the ferromagnetic material is purely paramagnetic.
Eddy current (also known as Foucault current) is caused by a timevarying magnetic field intersecting a conductor or vice versa.
Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux.
Flux is used in brazing to remove oxides, prevent oxidation and wet the joining areas. Excess flux should be removed when the joint is completed. Flux left in the joint can lead to corrosion.
Frequency converter is the power source supplying the highfrequency alternating current. Modern frequency converters for induction are based on semi-conductor technology.
An induction coil is a coil carrying high- or medium- frequency alternating current and intended to induce eddy currents to heat objects placed in the interior of the coil. The induced current also generates its own magnetic field, in opposition to the field generated by the coil, thus preventing the latter field from penetrating to the center of the heated object.
Induction heating is a process of heating electrically conductive material by electromagnetic induction, where eddy currents are generated within the material and its resistance leads to the heating.
Induction surface hardening is the process of hardening the surface of steel or cast iron objects by heating only the surface to produce martensitic microstructure in the heated zone after quenching.
Magnetic flux is the integral of the magnetic field times the perpendicular area that it penetrates.
Normalizing means to heat ferrous alloy to a suitable temperature above the transformation range and then cool it in air to a temperature substantially below the transformation range. Steel is normalized to refine grain size, make its structure more uniform, or to improve machinability.
Penetration depth is the distance from the surface to the depth where current density has dropped to 37%. The depth of penetration increases as the frequency decreases. It is essential that the frequency is chosen with respect to the dimensions and electrical properties of the object to be heated.
Post heating of weldments occurs immediately after welding, for tempering, for stress relieving, or for providing a controlled rate of cooling to prevent formation of a hard or brittle structure.
Preheating occurs before a heating or mechanical process is applied to the material.
Quenching generally means rapid cooling of metals and alloys to below the critical temperature range to harden them.
Soft soldering is a process of low temperature soldering using a solder with a melting point below 450 °C (800 °F).
Stainless steel is a common name for steel alloys that are resistive to corrosion and oxidation (rust). These normally include:
- Austenitic steel—the largest category of stainless steel, accounting for about 70% of all production. The austenitic class offers the most resistance to corrosion in the stainless group, due to its substantial nickel (Ni) content and higher levels of chromium (Cr). The steel is nonmagnetic and has no Curie point.
- Ferritic steel—the second-largest class of stainless steel, constituting approximately 25% of stainless production. Ferritic stainless steels are plain chromium (Cr) steels with no significant nickel (Ni) content; the lack of nickel results in lower corrosion resistance than the austenitic (chromium-nickel stainless steels). The steel is magnetic and has a Curie point.
- Martensitic steel—a small category of stainless steel characterized by the use of heat treatment for hardening and strengthening. Martensitic stainless steels are plain chromium (Cr) steels with no significant nickel (Ni) content. The steel is magnetic and has a Curie point.
Tempering is a reheating process that increases the ductility and impact strength of a hardened structure (martensite). The microstructure of quenched and tempered steel is referred to as tempered martensite.
Tube welding is in this connection a method of longitudinally welding steel and aluminum tubes, pipes and profiles by using induction coils or electrical contacts. The raw material is coiled and sheared in strips in a width and thickness that correspond to the dimensions of the final product. The strip is fed into a forming and welding line, and formed by rollers before the edges are welded together. The welding process is done without using filler metal or alloy as the edges are heated up to the forging temperature and pressed together.