STUDY OF THE ENVIRONMENTAL EMBRITTLEMENT OF ADI

ROBERTO BOERI, RICARDO MARTÍNEZ

Montpellier

Congreso; European congress on advanced materials and processes; 2011

Federation of european materilas science

In this article the authors revise the advances in the understanding and characterization of the unusual embrittlement phenomenon, discovered several years ago by Shibutani, Komatsu and co-workers. The phenomenon affects the behavior of austempered ductile iron (ADI) while stressed in contact with water and other liquids, reducing its strength, elongation and fracture toughness. The revision includes different studies carried out by the authors, leading with ·       Characterization by means of tensile, hardness and fracture toughness tests. ·       Influence of selected liquids, on the mechanical properties. ·       Test carried out under controlled electrochemical potential evaluating the role of Hydrogen. ·       Influence of the microstructure and its relationship with the degradation process. ·       Surface protection by different coatings is also included. ·       Particular characteristics of fracture surfaces.           The results show that there have been significant advances in the characterization of the embrittlement phenomenon, but its fundamentals are still unexplained. However, latest investigations show that the fracture of ADI involves progressive cracking of the matrix, mostly located at the last to freeze portions. This cracking develops earlier during stressing when ADI is in contact with water. A model based on fracture surfaces examination is proposed, the mechanism has been called “Localized slip process induced by adsorption in aqueous environments”. The last section is devoted to the review of the studies dealing with the embrittlement of dual phase ADI. Results show that DPADI is also affected, but the extent appears to be controlled by the amount of free ferrite present in the matrix microstructure, the larger the amount of ferrite, the smaller the embrittlement.