Abstract
Room temperature creep behavior has been investigated for nitrogen-strengthened austenitic stainless steels (SUS304N2, SUS317J2), cold-rolled SUS304 and precipitation-hardened austenitic alloy (N280 : 35%Ni-20%Cr-2%Ti-0.5%Al). The relationship between the creep behavior and the 0.2% proof stress (0.2% P.S.) is discussed. At a higher stress above 0.2% P.S., all specimens brought about creep strain decreasing strain rate with time. At a lower stress below 0.2% P.S., creep took place in nitrogen-strengthened steels and cold-rolled ones, but not in N280 alloy. The creep strain depends strongly on the normalized stress (applied stress/0.2% P.S.). Increasing the 0.2% P.S. by any strengthening methods raises the stress at which creep strain can be observed. The creep strain can not be determined only by the normalized stress, and affected by the characteristics of the strengthening methods. Comparing the creep strain at the same normalized stress, the creep strain decreases as a following order : nitrogen-strengthened steels, cold-rolled SUS304 and precipitation-hardened alloy.
The strain rate dependence of 0.2% P.S. decreases in the same order, It is concluded, therefore, that the less strain rate dependence of 0.2% P.S. can lead to the less creep strain at the same normarized stress.
