Glad to see other MEs here.
Allow me to make one clarification about the heat treatment process described.

The three steps you described are more specifically termed:
1. solution treatment - in which the metal alloy is heated to above the solvus temperature, the effect of which you correctly described.
2. Quenching - as you decribed.
3. Age hardening - the metal alloy is heated to below the solvus temp and allowed to cool slowly. This process is repeated several times till the desired properties are reached. The end goal is typically for enough pearlite and other softer phases to be transformed into a matrix around pockets of hard martensite. This reduces the brittleness while retaining the strength of the quenched metal.

If all the martensite is allowed to be transform back to pearlite and such, the alloy is in effect annealed, not tempered.

Not all metal alloys are age hardenable. Many Al-Si alloys aren't. And solution treatment and quenching alone (cryogenic or not) may not produce the desired properties for engine components. One needs to know the exact metal alloy content in order to determine the eutectic and solvus temperatures and subsequently prescribe an appropriate heat treatment schedule. A blow torch and a bucket of ice does not tempered metal make.

Also, the cyclic heating and cooling of automobile engines do not get anywhere hot enough to enter the age hardening regime. Tempering engine blocks this way is a common misconception. At most what it will do is relieve some of the localized work hardening and residual stresses from the manufacturering processes.