secondary hardening

secondary hardening

[′sek·ən‚der·ē ′härd·ən·iŋ]
(metallurgy)
The hardening of certain alloy steels at moderate temperatures (250-650°C) by the precipitation of carbides; the resultant hardness is greater than that obtained by tempering the steel at some lower temperature for the same time.
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These steels are usually tempered above 572F (300C), which lowers the soluble carbon in ferrite to that being in equilibrium with cementite (Stage III tempering) or with the alloy carbide formed during secondary hardening. These elevated tempering temperatures also promote tramp element segregation to grain boundaries.
The initial hardening of material is depending upon the generation of dislocations and their mutual interaction within self and secondary hardening is due to DSA effect [6].
[10] on martensitic steel Ni-Mo to find out effect of tempering temperature on hardness, revealed the effect of secondary hardening in temperatures 500-560[degrees]C.
Increasing hardness during tempering in the range of 400-500[degrees]C can be attributed to the secondary hardening phenomenon.
[3] on martensitic stainless steel 16Cr-2Ni shows the secondary hardening in the temperature range of 300-450[degrees]C.
By means of growth of volume share of a rather tough complex brazing alloy and the gap width from 225 to 400 | m heterogeneous structure of the seam with different kinds of secondary hardening phases was formed.
In tempering of hardened high speed steel secondary hardening takes place in the metal due to precipitation from solid solution of disperse excessive carbides, and in subsequent cooling transformation of residual austenite into martensite occurs.
The layer containing manganese in course of cooling after welding hardened up to 49 HRC, and it's tempering at 550[degrees]C temperature resulted 57 HRC hardness (secondary hardening).