Thesis Topic

Study of post-casting metallurgical transformations in grey cast irons to improve machinability in turning operations

Abstract

This PhD research topic addresses an industrial issue encountered at the Renault Le Mans plant concerning the machining of cast iron brake discs produced through the green sand-casting process. More specifically, when brake discs are machined immediately after casting during the finishing operation of the braking surfaces, cutting tool wear occurs at an abnormally high rate. To date, the only effective countermeasure has been to machine the discs between one week and one month after casting. Existing studies on the subject report a slight structural hardening after casting, characterized by an initial phase of rapid evolution during the first seven days followed by near-complete stabilization after approximately fourteen days. The primary parameter governing the occurrence of the maturation phenomenon is the presence of free nitrogen, that is, nitrogen not trapped by nitride-forming elements such as titanium. Furthermore, manganese content has also been shown to influence the phenomenon, acting as an inhibitor in some cases while promoting it in others. These observations have led to the hypothesis that the precipitation of iron nitrides within the cast iron matrix may explain the maturation phenomenon.
Accordingly, the main outcomes of this research are organized around three key objectives:

• Development of a maturation behavior model coupling the effects of nitrogen and manganese;
• Identification and characterization of the precipitates involved in the maturation phenomenon using Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM);
• Proposal of a preliminary explanation for the relationship between cast iron maturation and machinability.

Doctoral advisors

• Philippe JACQUET - Director
• Alexis VAUCHERET
• Frédéric ROSSI
• Frédéric TRITZ (Renault)

Partner

• Renault Le Mans

Project

N/A

Funding

• CIFRE

Start

01/10/2023

Expected end

08/10/2026