Big cavity will allow oxygen and other gasses to enter and make it brittle. Close grain Good quality and no stress good quality 100% strength.
Close grain or close packed grain is formed due to heat treatment of metal and metal grain become soft.
Open grain: Poor quality high stress, poor ductility and highly brittle.
Over heating and very low temperature makes grain of metal brittle and loss of ductility and strength and boundry between two grains is far apart and cavity size become large.
Posted by: Adnan
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