Influence of the 475 degrees 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 investiga ted 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 devel ops a passive layer on the surface, which provides it with low corrosion ra tes. The pitting corrosion resistance, however, was seriously affected by t he degree of precipitation. Specimens with the lowest and intermediate hard ness were able to withstand polarization above 1000 mV, whereas specimens w ith the higher hardness had a value of 750 mV. We believe that the local di fferences in Cr concentration associated with the spinodal decomposition, w hich increase with increasing annealing time at 475 degreesC, could have in fluenced the characteristics: of the passive layer. (C) 2001 Elsevier Scien ce Ltd. All rights: reserved.