AEB-L Multiple Tempering Cycles

[redsquid2]

Just curious, what does it do for the qualities of the steel, when you give AEBL multiple tempering cycles?

Thanks.

 

[samuraistuart]

All steels benefit from multiple tempering cycles. From Verhoeven.....

"Several things are going on in the steel during the tempering
process that result in the loss of strength and the gain in ductility
and toughness. The first thing that happens is the relief of the
high degree of volume strain in the steel produced by the
formation of the higher volume per atom martensite phase. Then a series of internal
structure changes occurs which is generally partitioned into the 3 stages of tempering.
Stage 1: This first stage consists of the formation of very small carbides in the martensite,
so small (around 10 nm) they can only be seen in an electron microscope. These first
formed carbides are metastable carbides (do not appear on the equilibrium phase
diagram), epsilon carbide (Fe2.4C) in hypoeutectoid steels and Hagg (Fe2.2C) and eta
(Fe2C) carbides in hypereutectoid steels. Stage 2: This stage is simply the
decomposition of any retained austenite into carbides and ferrite. It is only important in
high carbon steels where % retained austenite is significant. Stage 3: This stage occurs at
the highest tempering temperatures and here the metastable carbides are replaced with
small particle of cementite, the stable carbide of steels.*"