Fracture toughness tests at 77 K and 4 K on 316L stainless steel welded plates

Abstract

In the framework of a collaborative project between ASME, NASA, and NIST, quasi-static fracture toughness tests have been performed at liquid nitrogen temperature (77 K, or -196 C) and liquid helium temperature (4 K, or -269 C) on weld specimens extracted from the centers of four 316L welded stainless steel plates, each produced by a different vendor. Although the plates were produced in accordance with the same specifications from the same material (316L), large differences in fracture toughness have been observed, with the best weld (W2) exhibiting twice the critical toughness of the worst (W1) at 77 K, and more than seven times the critical toughness of W1 at 4 K. The Charpy absorbed energies recorded at 77 K for three of the welds within the same project were found to be strongly linearly correlated with fracture toughness at both test temperatures. The exception was weld W4, which provided the highest impact toughness and the second lowest quasi-static fracture toughness (stable crack initiation and resistance to crack propagation).

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“…The U.S. National Institute of Standards and Technology (NIST) performed a fracture toughness test at quasi-static strain rates instead of the Charpy impact test at 4 K on a 316 L stainless steel plate after welding, and they found a sevenfold reduction compared to the vaporization temperature of liquid nitrogen, 77 K [38]. The reason for not performing the Charpy impact test is that it is difficult to maintain the target temperature due to factors in the external environment and the material itself.…”