Featured Posts
Hardening, Quenching (Part 2)
February 7, 2012 By gNT
Jominy test
Standardized test which consists of austenitizing a steel test piece and then cooling it by means of a jet of water applied to one end. The variation in hardness with distance from the quenched end (jominy curve) characterizes the hardenability of the metal.
Critical cooling rate
Cooling rate corresponding to the critical variation of temperature as a function of time during cooling.
Kritischer Abkuhlverlauf
Successive variations of temperature corresponding to the least severe cooling condition which will never thelese permit the full development of a given transformation. This term should be completed by an indication of the transformation considered (for martensite formation , for bainite formation).
Quenching hardening
Hardening of a ferrous product obtained, after austenitizing, by cooling under conditions such that the austenite transform more or less completely into martensite and possibly into bainite.
Maximum achievable hardness
Maximum value of hardness that can be obtained by quench hardening, under ideal conditions only.
Dept of transformation
Development of transformation
Development of quench hardening of a piece from its surface. The depth of transformation is generally measured in term of the depth of hardening.
Quench hardening layer
Surface layer of a ferrous product, hardened by quenching, the thickness of which is generally defined by the depth of quenching hardening.
Depth of hardening
Distance between the surface of a ferrous product and a limit characterizing the penetration of quench hardening. This limit may be defined starting from a structural state or a level of hardness.
Through-hardening
Quench hardening such that the depth of hardening is not less than the distance between the core and the surface of the ferrous product.
Local hardening
Quench hardening limited to part of a ferrous product.
Surface hardening
Quench hardening treatment after surface heating.
Effective case depth after surface hardening
Distance between the surface and the point the Vickers hardness of which, measured under a load of 9.81N, is equal to 80% of the minimum surface hardness required for the ferrous product considered.
Sub-zero treating (deep freezing)
Treatment carried out after quenching to transform the retained austenite into martensite and consisting of cooling and soaking at a temperature below ambient.
Hardening, Quenching
January 18, 2012 By gNT
Austenitizing
Operation during which the ferrous product is brought to a temperature (above Ac1) such that the structure becomes austenitic. If this
transformation is incomplete, the austenitization is termed partial.
Austenitizing temperature
Highest temperature at which the ferrous product is held during austenitization.
Quench hardening
Heat treatment comprising austenitizing followed by cooling under such condition that a hardness increase will occur on account of more or
less complete transformation of austenite to martensite and possibly to bainite.
Quenching
Operation which consist of cooling a ferrous product more rapidly than in still air. The use of a term specifying the cooling condition is recommended for example air-blast quenching, water quenching, step quenching, etc.
Interrupted quenching
Quenching carried out in a medium giving rapid cooling and interrupted before the ferrous product can reach thermal equilibrium with the
quenching medium. This expression is not to be used to designate “step quenching”.
Step quenching
Quenching during which the cooling is temporary interrupted by soaking in a mediu at a suitable temperature.
Martempering
Heat treatment involving austenitization followed by step quenching, at a rate fast enough to avoid the formation of ferrite, pearlite or bainite, to a temperature slightly above Ms and soaking for long enough to ensure that the temperature is uniform but short enough to avoid the formation of bainite. Final cooling during which martensite forms, is generally carried out in air.
Austempering
Heat treatment involving austenitization followed by quenching, at a rate fast enough to avoid the formation of ferrite or pearlite, to a temperature above Ms and soaking to ensure partial or total transformation of the austenite to bainite. The final coolong to ambient temperature is not at any specific rate.
Patenting
Heat treatment applied to wire or strip consisting of austenitizing followed by cooling under condition suitable for producing the
appropriate structures for subsequent wire-drawing or rolling. A distinction is drawn between :
Continuous patenting, when the operation of heating and cooling of the unwound product are carried on continuously
Batch patenting, when the product remains in the form of a coil or bundle during this heat treatment
It is necessary to distinguish between air, lead bath, salt bath and fluidized bed patenting, according to the cooling medium used.
Quenching temperature
The temperature from which quenching is carried out. When quenching is done from austenitizing temperature, the term “hardening
temperature” is also used.
Solution annealing
Heat treatment intended to dissolve and retain in solution previously precipitated constituents.
Solution annealing
Heat treatment applied to austenitic steels. It consist of heating to a high temperature followed by cooling sufficiently rapidly to
preserve a homogeneous austenitic structure on return to ambient temperature .
Hardenability
Capacity of a ferrous product to give rise to martensitic and/or bainite transformation. Hardenability is often characterized under
define experimental condition by the development of hardeness as a function of the distance from a quenched surface.
