Some Aspects of Nitrogen Addition and Removal During Special Melting and Processing of Iron and Nickel Base-Alloys

Abstract

In this work we review the published information on the exchange of nitrogen across the gas/metal interface in the case of liquid iron-and nickel-base alloys.Although the thermochemistry of these systems is reasonably well-established, it is clear that the kinetics of the reactions involved are rather complex and hence not as well defined. The role of precipitated nitrides is also considered, since this feature is an integral part of the use of filters as well as being a core facet of the nitride removal reaction in several of the processes surveyed. We also review the present position in respect of the production of high-nitrogen alloys, including the role of systems relying on the presence of N + ions to establish concentrations greater than those predicted by Sieverts' Law. We conclude that the basic information needed to establish a rational production route for any given alloy affected by nitrogen content is available, but that a very careful consideration of all the factors involved is required before defining such a route.

Influence of Microsegregation on the TiN Inclusions Formation Behavior in a K418 Superalloy during the Continuous Unidirectional Solidification Process

“…19) Subsequently, Brody and Flemings, 20) Clyne and Kurz, 21) Ohnaka, 22) and Voller and Beckermann 23) proposed back-diffusion models with different back-diffusion coefficients, which assumed incomplete back diffusion in the solid phase. Young and Mitchell 24) discussed the influence of strong microsegregation of solute elements on the precipitation behavior of TiN inclusions according to the Scheil equation. Wang et al 25) conducted thermodynamic and kinetic calculations of the formation behavior of Al 2 O 3 and TiN inclusions by applying the Ohnaka equation.…”

Nitrogen-Bearing Carbides in K417G Alloy Doped with Different Nitrogen Contents

“…K417G alloy developed from K417 (IN100) alloy is a Ni-based investment casting superalloy characterized with high contents of Al and Ti, and can be used to fabricate turbine blades and gas guide vanes under 950 ℃. And nitrogen as a strong austenitic stabilizer in steels has already been used in high-nitrogen stainless steels not only as structural materials but also as biomaterials [1,2], but little benefits was found in nickel base alloys [3]. However superalloys hold high amount of strong nitride-forming elements such as Ti and Hf, and the forming of N-bearing inclusions would cause negative influence during the recycling process.…”

Primary Carbides in Alloy 718

“…It has been noted that in alloys with very low nitrogen content, the precipitation of primary carbide is delayed until close to the solidus temperature when the segregation has driven the C and Nb contents to a level enabling nucleation on particles other than TiN. In such alloy composition the extent of eutectic precipitation is enhanced and there is also a higher level of eutectic Laves phase present at the end of solidification (16). The nitrogen levels required to produce this effect are less than 5ppm (the solubility product of TiN at the solidus temperature) and are hence not encountered in commercial production of 718.…”