Influence of Melting Atmosphere on Heat-Resisting Property of 316 L Type Steels.

On the function of nitrogen as an alloying element in heat-resisting materials-V

Abstract

Interest has existed among high-temperature alloy producers in utilizing leaner alloys than are currently used. Nitrogen-bearing austenitic alloys offer possibilities in this respect.
An investigation has been made of the hot-strength potentialities of 316L type alloys melted in vacuum, in air or in nitrogen of two atmospheric pressure using an induction furnace.
It was presumed that the relation between the partial pressure of nitrogen in the melting atmosphere and the nitrogen content of these ingots deviates markedly from Sieverts' law.
Comparing with air-melted and vacuum-melted steels, the nitrogen-melted steel showed higher hardness and strength at room temperature in any states such as solution-quenched, solution-quenched followed by cold-working, or solution-quenched followed by hot-cold working. For the nitrogen-melted steel, significant resistance to recrystallization-softening and excellent properties in both the high-temperature bending creep and tensile creep-rupture tests were also found. On the other hand, vacuum-melted steel showed in a tensile creep-rupture test longer life and larger elongation than those melted in air, although it had less hardness and resistance to recrystallization-softening than air-melted one.
It was also investigated how the sort of raw chromium used in melting influenced on the steel properties, and the bending creep property was found to be improved in the case of the steel prepared from Thermit-process chromium than in the case of that from electrolytic chromium.