Metallurgical analysis is widely used in the field of heat treatment of metals to ensure the quality of the treatments carried out on a wide variety of industrial parts and treatments carried out. It is therefore a valuable tool for subcontractors of the heat treatment industry to monitor their production and treatment response on various parts. Through different examples, we will present actual cases that involve in particular automotive parts. We show that there is a strong interdependence between material and heat treatment, one being related to each other, a successful treatment depends both on the metallurgical quality of the material and the production quality of the heat treatment process. We will discuss the type of treatments like: vacuum hardening or under protective atmosphere, surface induction hardening, carburizing, nitriding and brazing.