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The term hardened steel is often used for a medium or high carbon steel that has been given heat treatment and then quenching followed by tempering. The quenching results in the formation of metastable martensite , the fraction of which is reduced to the desired amount during tempering.
Martensitic transformation, more commonly known as quenching and tempering, is a hardening mechanism specific for steel. The steel must be heated to a temperature where the iron phase changes from ferrite into austenite, i.e. changes crystal structure from BCC (body-centered cubic) to FCC (face-centered cubic). In austenitic form, steel can ...
Diagram of a cross section of a katana, showing the typical arrangement of the harder and softer zones. Differential hardening (also called differential quenching, selective quenching, selective hardening, or local hardening) is most commonly used in bladesmithing to increase the toughness of a blade while keeping very high hardness and strength at the edge.
Steel can be softened to a very malleable state through annealing, or it can be hardened to a state as hard and brittle as glass by quenching. However, in its hardened state, steel is usually far too brittle, lacking the fracture toughness to be useful for most applications. Tempering is a method used to decrease the hardness, thereby ...
To harden by quenching, a metal (usually steel or cast iron) must be heated above the upper critical temperature (Steel: above 815~900 degrees Celsius [23]) and then quickly cooled. Depending on the alloy and other considerations (such as concern for maximum hardness vs. cracking and distortion), cooling may be done with forced air or other ...
Case-hardening or carburization is the process of introducing carbon to the surface of a low-carbon iron, or more commonly a low-carbon steel object, in order to harden the surface. Iron which has a carbon content greater than ~0.02% is known as steel .
In diffusion hardening, diffusion occurs between a steel with a low carbon content and a carbon-rich environment to increase the carbon content of the steel and ultimately harden the workpiece. [ 1 ] [ 2 ] Diffusion only happens through a small thickness of a piece of steel (about 2.5 μm to 1.5 mm), so only the surface is hardened while the ...
The steel is then quenched so that the austenite is transformed into martensite, and the ferrite remains on cooling. The steel is then subjected to a temper cycle to allow some level of marten-site decomposition. By controlling the amount of martensite in the steel, as well as the degree of temper, the strength level can be controlled.