Fenómeno de fragilización asistido por el medio en acero de alto silicio

R.A. MARTÍNEZ

Concepción

Congreso; CONAMET/SAM 2015; 2015

Facultad de Ingeniería-Universidad de concepción

Prevoius works developed by the author relative to the embrittlement of austempered ductile iron (ADI) when its surface is in contact with water, lead to the evaluation of steel under the same environmental conditions. The mentioned phenomenon produce falls in elongation and ultimate tensile strength of about 75% and 10% respectively meanwhile the 0,2% offset strain stress is unaffected.In the case of the ADI the investigations have proved that the process of embrittlement starts in a surface crack generated at the early stages of plastic deformation allowing the water penetrating and weakening the material strength, making the crack grows very fast and producing the instantaneous fail of the samples.The microstructure of ADI is composed by graphite nodules and a metallic matrix known as ?ausferrite? which is product of the austempering heat treatment applied to the ductile iron. This metallic matrix gives a very good combination of tensile strength and elongation turning ADI in an attractive material for metal mechanic designers. Also present in the ADI microstructure are the LTF zones (or cell boundaries) which are the product of the solidification process, where pores, inclusions and unreacted austenite are present.An ausferritic matrix with similar characteristics of the ADI can be obtained by heat treatment of high Si steel avoiding nodules and LTF zones, which allow the evaluation of the metallic matrix when its surface is in contact with water.A steel of this kind (SAE 5260) was heat treated obtaining an ausferritic matrix and tested in dry and wet conditions, in this manner was possible to conclude about the influence of the metallic matrix in the process of embrittlement of ADI.