Abstract
Results of a study on influence of Cr, Mo and Al on the microstructure, abrasive wear and corrosion resistance of Ni-Mn-Cu cast iron in the as-cast and heat-treated conditions are presented. Because of the chilling effect of first two elements (tendency to create hard spots), graphitising Al was added to the alloys, with the highest concentration of Cr and Mo. All castings in the as-cast condition showed an austenitic matrix, guaranteeing good machinability. Heat treatment of raw castings, consisting in annealing at 500 °C for 4 h, resulted in partial transformation of austenite. As a result the carbon-supersaturated acicular ferrite, morphologically similar to bainitic ferrite was formed. The degree of this transformation increased with increasing concentrations of Cr and Mo, which successively decreased the thermodynamic stability of austenite. A change of matrix structure made it possible to significantly increase hardness and abrasive-wear resistance of castings. The largest increment of hardness and abrasion resistance was demonstrated by the castings with the highest total concentration of Cr and Mo with an addition of 0.4% Al. Introduction of Cr and Mo also resulted in an increase of corrosion resistance. In the heat-treated specimens, increasing the concentration of Cr and Mo resulted in a successive decrease of the depth of corrosion pits, with an increase in their number at the same time. This is very favourable from the viewpoint of corrosion resistance.
Highlights
A typical example of cast iron with relatively good machinability and corrosion resistance isNi-Resist austenitic cast iron [1,2]
The alternative is Ni-Mn-Cu cast iron with a radically reduced Ni content compared to Ni-Resist cast iron, wherain the reduced Ni content is compensated by the addition of austenitizing elements, such as Mn and Cu [2]
Examinations were carried-out on cast iron coming from nine melts (Table 1)
Summary
A typical example of cast iron with relatively good machinability and corrosion resistance isNi-Resist austenitic cast iron [1,2]. Proper selection of heat treatment parameters, provoking radical changes on the casting matrix, which makes it possible to obtain good mechanical properties and high abrasive-wear resistance while maintaining increased corrosion resistance (high electrochemical potential of the alloying elements) [3,4,5,6,7,8]. This makes it Materials 2019, 12, 3500; doi:10.3390/ma12213500 www.mdpi.com/journal/materials. Thisofwas due accompanied to significant by differences of of austenitic matrix) resulted in successive decrease of depth of the pits accompanied by an increase of their number.potentials
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