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The effect of Co additions on tensile properties in the secondary hardening Co-Ni alloy steels has been studied in as-quenched and aged conditions. Three kinds of (5-13)Co-11Ni steels, containing Mo and Cr, were severely multipass-rolled in unrecrystallized region and followed by accelerated cooling. In as-quenched condition, an increase in yield strength and a decrease in uniform elongation with an increase in Co content are closely related with a decrease in the amount of retained austenite. In peak-aged condition, yield and tensile strengths and peak hardness increased with the increase of Co content, but peak time remained around 5 hours. Thus, Co additions would enhance the nucleation of fine M2C carbides rather than their growth.


The effect of Co additions on tensile properties in the secondary hardening Co-Ni alloy steels has been studied in as-quenched and aged conditions. Three kinds of (5-13)Co-11Ni steels, containing Mo and Cr, were severely multipass-rolled in unrecrystallized region and followed by accelerated cooling. In as-quenched condition, an increase in yield strength and a decrease in uniform elongation with an increase in Co content are closely related with a decrease in the amount of retained austenite. In peak-aged condition, yield and tensile strengths and peak hardness increased with the increase of Co content, but peak time remained around 5 hours. Thus, Co additions would enhance the nucleation of fine M2C carbides rather than their growth.