Abstract
The effect of the cooling rate from the preoxidation temperature on the room temperature tensile behaviour of the alloy MA 956 is analysed for scale free specimens and specimens with scale. It is shown that an increase in the cooling rate causes a decrease in yield stress and tensile strength. For scale free specimens, this effect is caused by less extensive precipitation of the Cr rich α′ phase at about 475°C and higher constraint of the tensile residual stresses associated with the difference in the thermal expansion coefficients of the dispersoids and the matrix. For specimens with scale, yield stress and tensile strength were even lower than those of scale free specimens because of the additional scale induced residual stresses. Moreover, a ductile to brittle transition was observed at the lowest cooling rate as a consequence of the highest precipitation of the Cr rich α′ phase.
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