>In reference to bluing metal by heat: > >I would use it [Bluing by heating] for cosmetic effect on a part under stress >(like pressure bar screws)only with due regard for its potential effect on the >strength of the parts. For a eutectoid plain-carbon steel the microstructure of the material will vary according to the cooling rate. A water quench will produce a microstructure of martensite and an oil quench will produce a microstructure of martensite and pearlite. If the material is allowed to cool in still air ( to minimize heat transfer by forced convection ) the microstructure will consist of proeutectiod ferrite and fine pearlite. Dan Squire -Claiming Lumped Thermal Capacity-
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