Strength and thougness of AISI 304 and 316 at 4 K

Structural design of superconducting magnets in fusion energy devices requires reliable poperty data at 4 K. Nitrogen strengthened AISI 304 and 316 stainless stels are considered to be the best currently available low temperature structural alloys on the basis of their fabricability and their potential to meet the US fusion research goals of combined 1000 MPa yield strength and 200 MPa m1/2 fracture toughness at 4 K. This paper presents provisional equations for the yield strength of 304- and 316-type alloys at 4 K as a function of N content and grain size. Provisional equations for the 4 K fracture toughness KIc(J), of these alloys are presented, in which the effects of yield stength, Ni and Mn content, and inclusion spacing are expressed quantitatively. The equations result from regression analyses of a matrix of NBS measurements that includes more extensive numerical data on alloying, refining, and processing parameters than have previously been available. (orig.)