This lecture on Metal Casting explains defects arising from unfavorable metallurgical transformations during and after solidification. Key issues include gaseous defects (porosity, blowholes), shrinkage porosity, misruns, cold shuts, inclusions, hard spot formation, martensitic embrittlement, hydrogen-induced cracking, and hot tearing. It highlights how cooling rate, molten metal temperature, impurities, alloy composition, and gating/feeding design strongly influence defect formation and casting quality .