1962 Volume 48 Issue 6 Pages 770-776
Influence of melting atmosphere of 18%Cr-8%Ni stainless steels on austenite stability, hardness change due to subzero-treatment, ageing after cold rolling and mechanical properties at room-and high temperatures was studied. Main results obtained were as follows:
(1) The steels NM (0·158%N) and NNM (0·177%N) both melted in nitrogen atmosphere at 600 mm Hg had greater stability of austenite to martensite transformation due to high content of nitrogen compared with the steels melted in vacuum (VM) or in air (AM).
(2) In the steels VM and AM, isothermal martensite transformation was found to occur at temperatures below their Ms point, and in AM even at temperatures above the Ms point.
(3) Remarkable work-hardening caused by rolling at room-and subzero-temperatures, and further hardening caused by subsequent ageing at 300°C were observed with all of the steels except with the steel VM, which consisted largely of martensite in a solution-quenched state.
(4) High-nitrogen steels NM and NNM exhibited lower strength and higher ductility at room temperature than VM and AM in solution-quenched state due to greater austenite stability, while the strength of the former was increased remarkably and the ductility was decreased somewhat by 30%cold-rolling.
(5) Tensile creep-rupture strength of the steels at 700°C was improved considerably with increasing content of nitrogen.
