Influence of Manganese Content on the Dissolution of the Iron Carbide Phase (Cementite) during a Graphitization Anneal of Spheroidal Graphite Cast Iron

The transformation of iron carbide cementite was investigated on spheroidal graphite containing different contents of manganese. The isothermal maintain were carried out at 600, 650, 700, and 750°C for periods of up to one hour. It was observed that the kinetics of graphitization is slowed even more than cast iron rich in manganese. 1. Introduction Graphitization heat treatment aims mainly at softening the structure by transforming the ferrite matrix. The corresponding treatment in the case of cast iron is usually time consuming and costly. This explains the number of studies devoted to the influence of the addition of alloying elements on the processes involved in the graphitization [1]. Copper, nickel, and silicon are commonly considered part graphitization. The effect of the molybdenum and/or manganese differs because of their power stabilizing against the carbides [2–4]. Thus, these elements cause a slowing of the kinetics of graphitization. The influence of manganese after the graphitization process of spheroidal graphite cast iron will be specifically studied. 2. Materials In Table 1 are collected the composition of the studied spheroidal graphite cast iron and hardness in the state of reception. Values of carbon content—measured using a LECO CS 244 type dosing—show that it is a hypoeutectic cast iron (1.7 < C < 4.3). Table 1: Composition in weight percent of the spheroidal graphite cast iron studied. In their “as received state” the samples under study have a ferrito-perlitic structure. Thus, the perlitic cementite leads to the formation of graphite, according to the following decomposition reaction (R): F e 3 C ？ 3 F e + C . ( R ) This graphitization—similar to the bainitic or martensitic structure—is called secondary (as opposed to primary graphitization developed, either in the liquid metal or in the austenite supersaturated in carbon). The results obtained confirm the retarding effect exerted by manganese on the kinetics of graphitization of spheroidal graphite cast iron? In fact, we have the following.(i)As shown in Figures 1(a) and 1(b), the magnitude of the dilatometric expansion corresponding to the reaction (R) decreases as the manganese content increases from 0.9 to 2.15？wt%.(ii)The dilatometric curves recorded during isothermal heat treatment applied to the cast iron containing 2.15？wt% (Figure 1(a)) show the importance of the temperature parameter (θg) on the process of graphitization. Indeed, we note that cementite graphitized even faster than θg is close to Ac1. In addition, early maintenance develops a contraction whose amplitude