During the solution treating of steel materials, which of the following statements are true: (a) the rapid cooling aims to create a hard shell of the parts; (b) the quenching could potentially result in metastable martensitic microstructure; (c) the quenching should be carried out in water; (d) the purpose of initially heating up the material to high temperature is to relieve stress sufficiently; (e) the subsequent aging procedure promotes microstructural evolution from metastable phases to more stable phases.