Influence of the 475°C hardening of MA 956 on its corrosion behaviour at room temperature

The corrosion behaviour of MA 956 in the Hank's solution has been investigated after three different thermal cycles, which lead to hardness values of 250, 289, and 330 HV. The electrochemical tests have shown that the uniform corrosion resistance is independent of the material state. The alloy develops a passive layer on the surface, which provides it with low corrosion rates. The pitting corrosion resistance, however, was seriously affected by the degree of precipitation. Specimens with the lowest and intermediate hardness were able to withstand polarization above 1000 mV, whereas specimens with the higher hardness had a value of 250 mV. We believe that the local differences in Cr concentration associated with the spinodal decomposition, which increase with increasing annealing time at 475°C, could have influenced the characteristics of the passive layer. © 2001 Elsevier Science Ltd. All rights reserved.