Close relations between metallic materials, heat treatment and thermochemical treatment on the microstructure: contribution of metallographic examinations performed on industrial parts through several case studies

摘要

Metallurgical analysis is widely used in the field of heat treatment of metals to ensure that the quality of the treatments carried out on a wide variety of industrial parts and treatments is properly done. 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 parts of treated areas of mechanical engineering, automotive, machinery, aerospace. We show that there is a strong interdependence between material and heat treatment, one being related to each other, with successful treatment depending both on the metallurgical quality of the material and the production quality of the heat treatment process. We will discuss some types of treatment: vacuum core-hardening, gas and low pressure carburizing, gas and plasma nitriding and vacuum brazing. This paper shows current applications of metallurgical investigations carried out on several types of mechanical parts which have been heat treated and exhibit after heat treatment some defects, damages, cracks, failures, anomalies, discolored surface, and others problems. The goal of such investigations is to determine, the precise origin of the defects with more or less certainty. This is done in order to: avoid reoccurrence of the problem; improve the overall level of heat treatment quality; decrease the scrap rates; or improve general knowledge and know-how. Furthermore, we show that there is strong interaction between: the material to be treated, its structure, machining or forming mode, design of the shapes, surface quality, heat treatment parameters, and finally how it is use in service.