Embrittlement of ADI by contact with liquids: influence of alloy content and preventive methods

Abstract

In view of its excellent mechanical properties and low cost when compared to high strength steels, austempered ductile iron (ADI) is being applied to replace mechanical components in different applications. However, ADI is known to suffer noticeable embrittlement when its surface is in contact with liquids during quasi-static tensile testing. Although the embrittlement phenomena has been characterised in detail, the acting mechanism is not well understood at the present time. Water has shown to cause the greatest degree of embrittlement, while other liquids, such as alcohol and other organic reagents, cause milder though noticeable effects, too. An apparently obvious protection of ADI against the embrittlement caused by liquid environments would be through ADI surface isolation from the environment. The present article examines the efficiency of several paints and coatings by means of tensile tests carried out under dry and wet conditions. From a good number of protective coatings applied on the tensile samples, only one was able to protect the sample under stress from water contact, thus preventing the embrittlement phenomena. The protection method is effective when the layer integrity is not affected by the deformation undergone by the substrate. Another aspect dealt with in the present paper is the assessment of the influence of the chemical composition on the susceptibility of ADI to embrittlement. The results show that the presence of alloy elements in the melt does not influence the degree of embrittlement in the samples.