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Induction Hardening

Induction hardening is based on the generation of magnetic fields by an alternating current. When a metal component is placed inside the coil, eddy currents are induced in surface regions of the object, which in turn generate heat because of the resistance of the metal. The depth of heating depends on the strength of the magnetic field, the magnetic properties of the material, and the proximity of coils to the object. Cooling may be carried out in air or by quenching in oil or water if a deep hardened zone is required. Hardened regions up to about 5mm can be produced by the two processes ;the shallower, darker regions were produced by laser hardening. Induction hardening is easily incorporated into a production environment, has a relatively low cost, and is particularly suitable for rotationally symmetric components such as gear wheels and shafts, especially when high volumes of identical components are to be treated. Codes of practice have been written that specify the required hardness and geometry of the treated region, enabling the process be automated by using preset values.

(John C. Ion, Laser Processing of Engineering Materials, p. 224)

Low carbon steels

Low carbon steels, steels that contain less than 0.25% C, make up the highest tonnage of all steels produced in a given year. Structural shapes and beams for building and bridges, plate for line pipe, and automotive sheet applications are just a few major applications for low carbon steels.  These applications are driven by manufacturing requirements for good formability and weldability, and performance requirements of good combinations of strengths and fracture resistance for given applications. While early approaches to design of steel structures involved increasing section size of low-strength, low-carbon steels to increase load carrying capacity, recent approaches have been based on developing low carbon steel microstructures of higher strength in order to reduce section size and weight. Higher strengths are increasingly produced in steels with lower and lower carbon contents, an approach that improves formability, weldability, and toughness or fracture resistance. As a result, the last two decades of the twentieth century have seen dramatic changes in the compositions of low carbon steels, theri strength, ductility, and toughness, and the processing approaches for their manufacture.

(George Krauss, Steels: Processing, Structure, and Performance, p.217)

Medium Carbon Steels

There are two groups of medium carbon steels:

1.      From 0.3% to 0.5% carbon. These can be heat treated to make them taough and strong.

2.      From 0.5% to 0.8% carbon. These can be heat treated to make them fairlyhard yet remain a degree of toughness(impact resistance)
Medium carbon steels are harder, stronger and tougher than low carbon steels. They are also more
expensive. They cannot be bent or formed in the cold condition to the same extend as low carbon
steels without cracking. However, medium carbon steels hot forge well, but close temperature
control is required to prevent:

·         ‘Burning’  at high tempratures over 1150⁰C, as this leads to embrittlement. The metal cannot be reclaimed and the forging has to be scrapped.

·         Cracking when forging is in the ‘cold’ condition from a forging point o f view.

Medium carbon steels with a carbon content in the 0.5% to 0.8% range are used for such products as wood saws, cold chisels, forged blanks for connecting rods, cranckshafts, gears and other stressed components such as high-tensile pipes and tubes.

(Roger Timings, Fabrication and Welding Engineering, p. 79)

Gray Cast Iron

Gray cast iron is the most widely used of all cast irons. Pieces of gray cast iron are usually cast ins and molds and then allowed to cool inthe mold. As a rule, if you come across somecast iron, chances are you’re looking at gray cast iron. Why it is called gray cast iron? You guessed it: the fractured metal looks gray.

All gray cast irons contains graphite in the form of flakes. For the most part, gray cast irons aren’t ductile, which means they break instead of bending and elongating. The tensile strength of a gray cast iron can range from 20,000 pounds per square inch to as much as 55,000. (Tensile strength is the amount of force you can apply to something before it tears apart or break) You can weld gray cast iron, and it still retains all its properties.

You can findd gray cast ironin all kinds of common everyday items, from internal combustion engines( especially diesel engines) to pump housings to teh cast iron cookware that, in this welder’s humble opinion, is an absolute must if you are trying to make the perfect batch of cornbread.

(Steven Robert Farnsworth, Welding for Dummies, p. 218)